explanation blue bibcodes open ADS page with paths to full text
Author name code: soon
ADS astronomy entries on 2022-09-14
author:"Soon, Willie Wei-Hock"
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Title: The interplanetary origins of geomagnetic storm with
Dst<SUB>min</SUB> ≤ - 50 nT during solar cycle 24 (2009-2019)
Authors: Qiu, Shican; Zhang, Zhiyong; Yousof, Hamad; Soon, Willie;
Jia, Mingjiao; Tang, Weiwei; Dou, Xiankang
2022AdSpR..70.2047Q Altcode:
In this study, we analyzed 149 geomagnetic storms of moderate and
intensity (i.e., Dst<SUB>min</SUB> ≤ - 50 nT) occurred during the
solar cycle 24 from 2009 to 2019, and identified their interplanetary
sources. Among them, there are 20 strong storms with <SUB>- 200 nT
≤ Dst min</SUB> ≤ - 100 nT , and 2 super-strong storms with
Dst<SUB>min</SUB> ≤ - 200 nT . We have found that corotating
interaction regions (CIRs) account for 37% (55/149) of geomagnetic
storms, interplanetary coronal mass ejections (ICMEs) result in 30%
(45/149) of geomagnetic storms and sheath regions (SH) are responsible
for 15% (23/149) of geomagnetic storms. Meanwhile, 18/20 of the strong
storms are caused by the structures associated with interplanetary
coronal mass ejections (ICME, SH, and SH + ICME), while the CIR
constitutes only to 2/20 of the strong storms. It is found that the
two super-strong geomagnetic storms are caused by the SH + ICME. Our
findings also suggest that geomagnetic storms in different periods
of solar activity are caused by different interplanetary structures,
which is consistent with previous research. In comparison to solar
cycle 23, there is no substantial geomagnetic storm induced by CIR
during the dwindling and subsiding phases of solar cycle 24. In the
descending stage, the proportion of moderate events caused by ICME
decreases, and ICMEs cause no super-strong event. In ascending stage,
neither strong nor super strong events occur.
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Title: The New Composite Solar Flare Index from Solar Cycle 17 to
Cycle 24 (1937 - 2020)
Authors: Velasco Herrera, Victor Manuel; Soon, Willie; Knoška,
Štefan; Perez-Peraza, Jorge Alberto; Cionco, Rodolfo G.; Kudryavtsev,
Sergey M.; Qiu, Shican; Connolly, Ronan; Connolly, Michael; Švanda,
Michal; Acosta Jara, José; Gregori, Giovanni Pietro
2022SoPh..297..108V Altcode:
The chromosphere is a highly dynamic outer plasma layer of the
Sun. Its physical processes accounting for the variability are poorly
understood. We reconstructed the solar chromospheric flare index (SFI)
to study the solar chromospheric variability from 1937 to 2020. The
new SFI database is a composite record of the Astronomical Institute
Ondřejov Observatory of the Czech Academy of Sciences from 1937 -
1976 and the records of the Kandilli Observatory of Istanbul, Turkey
from 1977 - 2020. The SFI records are available in daily, monthly, and
yearly resolutions. We carried out the time-frequency analyses of the
new 84-year long SFI records using the wavelet transform. We report
the periodicities of 21.88 (Hale cycle), 10.94 (Schwabe cycle), 5.2
(quasi-quinquennial cycle), 3.5, 1.7, 1, 0.41 (or 149.7 days, Rieger
cycle), 0.17 (62.1 days), 0.07 (25.9 days, solar rotational modulation)
years. All these periodicities seem always present and persistent
throughout the observational interval. Thus, we suggest that there is
no reason to assume these solar periodicities are absent from other
solar cycles. Time variations of the amplitude of each oscillation or
periodicity were also studied using the inverse wavelet transform. We
found that for the SFI the most active flare cycles over the record were
Cycles 17, 19, and 21, while Cycles 20, 22, 23, and 24 were the weakest
ones with Cycle 18 was intermediate in flare activity. This shows
several differences to the equivalent relationships for solar activity
implied by sunspot number records. Furthermore, this confirms that
solar activity trends and variability in the chromosphere as captured
by SFI are not necessarily the same as those of the Sun's photosphere,
as implied by the sunspot number activity records, for instance. We
have also introduced a new signal/noise wavelet coherence metric
to analyze two different chromospheric indices available (i.e. the
SFI and the disk-integrated chromospheric Ca II K activity indices)
and to quantify the differences and similarities of the oscillations
within the solar chromosphere. Our findings suggest the importance of
carrying out additional co-analyses with other solar activity records
to find physical inter-relations and connections between the different
solar layers from the photosphere, the chromosphere to the corona.
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Title: Group Sunspot Numbers: A New Reconstruction of Sunspot Activity
Variations from Historical Sunspot Records Using Algorithms from
Machine Learning
Authors: Velasco Herrera, Víctor Manuel; Soon, Willie; Hoyt, Douglas
V.; Muraközy, Judit
2022SoPh..297....8V Altcode:
Historical sunspot records and the construction of a comprehensive
database are among the most sought after research activities in
solar physics. Here, we revisit the issues and remaining questions
on the reconstruction of the so-called group sunspot numbers (GSN)
that was pioneered by D. Hoyt and colleagues. We use the modern tools
of artificial intelligence (AI) by applying various algorithms based
on machine learning (ML) to GSN records. The goal is to offer a new
vision in the reconstruction of sunspot activity variations, i.e. a
Bayesian reconstruction, in order to obtain a complete probabilistic
GSN record from 1610 to 2020. This new GSN reconstruction is consistent
with the historical GSN records. In addition, we perform a comparison
between our new probabilistic GSN record and the most recent GSN
reconstructions produced by several solar researchers under various
assumptions and constraints. Our AI algorithms are able to reveal
various new underlying patterns and channels of variations that
can fully account for the complete GSN time variability, including
intervals with extremely low or weak sunspot activity like the
Maunder Minimum from 1645 - 1715. Our results show that the GSN
records are not strictly represented by the 11-year cycles alone,
but that other important timescales for a fuller reconstruction of
GSN activity history are the 5.5-year, 22-year, 30-year, 60-year,
and 120-year oscillations. The comprehensive GSN reconstruction by
AI/ML is able to shed new insights on the nature and characteristics
of not only the underlying 11-year-like sunspot cycles but also on the
22-year Hale's polarity cycles during the Maunder Minimum, among other
results previously hidden so far. In the early 1850s, Wolf multiplied
his original sunspot number reconstruction by a factor of 1.25 to
arrive at the canonical Wolf sunspot numbers (WSN). Removing this
multiplicative factor, we find that the GSN and WSN differ by only
a few percent for the period 1700 to 1879. In a comparison to the
international sunspot number (ISN) recently recommended by Clette et
al. (Space Sci. Rev. 186, 35, 2014), several differences are found and
discussed. More sunspot observations are still required. Our article
points to observers that are not yet included in the GSN database.
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Title: Magnetic and Rotational Evolution of ρ CrB from
Asteroseismology with TESS
Authors: Metcalfe, Travis S.; van Saders, Jennifer L.; Basu, Sarbani;
Buzasi, Derek; Drake, Jeremy J.; Egeland, Ricky; Huber, Daniel; Saar,
Steven H.; Stassun, Keivan G.; Ball, Warrick H.; Campante, Tiago L.;
Finley, Adam J.; Kochukhov, Oleg; Mathur, Savita; Reinhold, Timo;
See, Victor; Baliunas, Sallie; Soon, Willie
2021ApJ...921..122M Altcode: 2021arXiv210801088M
During the first half of main-sequence lifetimes, the evolution
of rotation and magnetic activity in solar-type stars appears to be
strongly coupled. Recent observations suggest that rotation rates evolve
much more slowly beyond middle age, while stellar activity continues to
decline. We aim to characterize this midlife transition by combining
archival stellar activity data from the Mount Wilson Observatory
with asteroseismology from the Transiting Exoplanet Survey Satellite
(TESS). For two stars on opposite sides of the transition (88 Leo and
ρ CrB), we independently assess the mean activity levels and rotation
periods previously reported in the literature. For the less active star
(ρ CrB), we detect solar-like oscillations from TESS photometry, and
we obtain precise stellar properties from asteroseismic modeling. We
derive updated X-ray luminosities for both stars to estimate their
mass-loss rates, and we use previously published constraints on magnetic
morphology to model the evolutionary change in magnetic braking
torque. We then attempt to match the observations with rotational
evolution models, assuming either standard spin-down or weakened
magnetic braking. We conclude that the asteroseismic age of ρ CrB is
consistent with the expected evolution of its mean activity level and
that weakened braking models can more readily explain its relatively
fast rotation rate. Future spectropolarimetric observations across a
range of spectral types promise to further characterize the shift in
magnetic morphology that apparently drives this midlife transition in
solar-type stars.
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Title: Does Machine Learning reconstruct missing sunspots and forecast
a new solar minimum?
Authors: Velasco Herrera, V. M.; Soon, W.; Legates, D. R.
2021AdSpR..68.1485V Altcode:
The retrodiction and prediction of solar activity are two
closely-related problems in dynamo theory. We applied Machine
Learning (ML) algorithms and analyses to the World Data Center's newly
constructed annual sunspot time series (1700-2019; Version 2.0). This
provides a unique model that gives insights into the various patterns
of the Sun's magnetic dynamo that drives solar activity maxima and
minima. We found that the variability in the ~ 11 -year Sunspot Cycle
is closely connected with 120-year oscillatory magnetic activity
variations. We also identified a previously under-reported 5.5 year
periodicity in the sunspot record. This 5.5-year pattern is co-modulated
by the 120-year oscillation and appears to influence the shape and
energy/power content of individual 11-year cycles. Our ML algorithm
was trained to recognize such underlying patterns and provides a
convincing hindcast of the full sunspot record from 1700 to 2019. It
also suggests the possibility of missing sunspots during Sunspot Cycles
-1, 0, and 1 (ca. 1730s-1760s). In addition, our ML model forecasts a
new phase of extended solar minima that began prior to Sunspot Cycle
24 (ca. 2008-2019) and will persist until Sunspot Cycle 27 (ca. 2050
or so). Our ML Bayesian model forecasts a peak annual sunspot number
(SSN) of 95 with a probable range of 80-115 for Cycle 25 between 2023
and 2025.
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Title: Possible Origin of Some Periodicities Detected in
Solar-Terrestrial Studies: Earth's Orbital Movements
Authors: Cionco, R. G.; Kudryavtsev, S. M.; Soon, W. W. -H.
2021E&SS....801805C Altcode:
Periodicities matching planetary cycles have been argued to be detected
in key geophysical time series. In general, these periodicities were
indirectly attributed to a planetary influence on solar activity. This
supposes that planetary gravity affects the internal functioning
of the Sun's dynamo, that is, the planetary hypothesis (PH) of the
solar cycles. The Earth's heliocentric dynamics already includes the
planetary gravitational effects on the Sun. Taking into account this
fact, these periodicities, ultimately attributed to possible planetary
modulations of the solar activity, could have a more direct origin in
cyclical changes in the relative Sun-Earth geometry, but then, wrongly
or partially explained invoking internal solar changes. We present
an original decomposition analysis of the high-precision ephemeris
DE431 from NASA/JPL in order to obtain and classify the most important
planetary/lunar purely periodic changes of the Earth's orbital movement
at sub-Milanković scales. A comprehensive list of cyclic changes of the
Earth's orbital parameters involved in the relative Sun-Earth position
and the Earth's speed around the Sun is given. We show that these
particular geophysical quasi-periods are identifiable in the cyclic
oscillations of these orbital parameters. Since the Earth's movement
in space physically affects the manner in which the solar radiant
flux reaches the planet, these oscillations provide, unlike the PH,
a clear, causal, and testable link for their possible attribution.
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Title: How much has the Sun influenced Northern Hemisphere temperature
trends? An ongoing debate
Authors: Connolly, Ronan; Soon, Willie; Connolly, Michael; Baliunas,
Sallie; Berglund, Johan; Butler, C. John; Cionco, Rodolfo Gustavo;
Elias, Ana G.; Fedorov, Valery M.; Harde, Hermann; Henry, Gregory W.;
Hoyt, Douglas V.; Humlum, Ole; Legates, David R.; Lüning, Sebastian;
Scafetta, Nicola; Solheim, Jan-Erik; Szarka, László; van Loon,
Harry; Velasco Herrera, Víctor M.; Willson, Richard C.; Yan, Hong;
Zhang, Weijia
2021RAA....21..131C Altcode: 2021arXiv210512126C
In order to evaluate how much Total Solar Irradiance (TSI)
has influenced Northern Hemisphere surface air temperature
trends, it is important to have reliable estimates of both
quantities. Sixteen different estimates of the changes in TSI
since at least the 19<SUP>th</SUP> century were compiled from the
literature. Half of these estimates are "low variability" and half are
"high variability". Meanwhile, five largely-independent methods for
estimating Northern Hemisphere temperature trends were evaluated using:
1) only rural weather stations; 2) all available stations whether urban
or rural (the standard approach); 3) only sea surface temperatures; 4)
tree-ring widths as temperature proxies; 5) glacier length records as
temperature proxies. The standard estimates which use urban as well as
rural stations were somewhat anomalous as they implied a much greater
warming in recent decades than the other estimates, suggesting that
urbanization bias might still be a problem in current global temperature
datasets - despite the conclusions of some earlier studies. Nonetheless,
all five estimates confirm that it is currently warmer than the late
19<SUP>th</SUP> century, i.e., there has been some "global warming"
since the 19<SUP>th</SUP> century. For each of the five estimates
of Northern Hemisphere temperatures, the contribution from direct
solar forcing for all sixteen estimates of TSI was evaluated using
simple linear least-squares fitting. The role of human activity on
recent warming was then calculated by fitting the residuals to the UN
IPCC's recommended "anthropogenic forcings" time series. For all five
Northern Hemisphere temperature series, different TSI estimates suggest
everything from no role for the Sun in recent decades (implying that
recent global warming is mostly human-caused) to most of the recent
global warming being due to changes in solar activity (that is, that
recent global warming is mostly natural). It appears that previous
studies (including the most recent IPCC reports) which had prematurely
concluded the former, had done so because they failed to adequately
consider all the relevant estimates of TSI and/or to satisfactorily
address the uncertainties still associated with Northern Hemisphere
temperature trend estimates. Therefore, several recommendations on how
the scientific community can more satisfactorily resolve these issues
are provided.
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Title: Holocene Millennial-Scale Solar Variability and the Climatic
Responses on Earth
Authors: Zhao, Xinhua; Soon, Willie; Velasco Herrera, Victor M.
2021Univ....7...36Z Altcode:
No abstract at ADS
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Title: How the astronomical aspects of climate science were
settled? On the Milankovitch and Bacsák anniversaries, with lessons
for today
Authors: Szarka, László; Soon, Willie W. -H.; Cionco, Rodolfo G.
2021AdSpR..67..700S Altcode:
It was 100 years ago (on August 7, 1920), that the comprehensive
mathematical foundations of climate change research, written by a
Serbian researcher, Milutin Milankovitch, were published. A later
interpreter and developer of his results, Georg (in Hungarian: György)
Bacsák (Pozsony/Pressburg/Bratislava, June 5, 1870 - Fonyód, March
4, 1970) was born 150 years ago and died at the age of one hundred,
half a century ago. In this commemorative paper we look back to
special circumstances in revealing the secrets of ice ages that had
puzzled scientists for at least several centuries. Recently, after 100
years, the Milankovitch theory, including related short-term forcings
(ranging from interannual, multidecadal to millennial timescales) has
not only been confirmed, but its climate forcing mechanism has also
been identified and proposed. Owing to the uniqueness of the problem,
the science of the orbital forcing of climate change can be proclaimed
to be essentially settled.
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Title: Latitudinal insolation gradients throughout the Holocene II -
High frequency variations
Authors: Cionco, Rodolfo G.; Soon, Willie W. -H.; Elias, Ana G.;
Quaranta, Nancy E.
2020AdSpR..66.1992C Altcode:
In a first paper, we presented an in-depth discussion and a
computational method (free of the calendar problem) to reckon any kind
of latitudinal insolation gradients, LIGs, throughout the Holocene and
up to CE 3000. One of the main insights from this exact definition
of LIGs is that, unlike what is argued in prior works, during the
Holocene, a general classification of LIGs in terms of obliquity
signal or climatic precession variations is much more complex, even in
summertime. It is especially evident in the Southern Hemisphere, where
summer half-year LIGs evolve under the relatively stronger modulation
by climatic precession. In this work, the short-term periodicities
(high frequency variations in time domain) of all these LIGs are
studied by means of the multitaper spectral analysis. The goal is
to get more insights on the competing effects between obliquity and
climatic precession during the Holocene, and to know how the relative
intensity of the obliquity's periodicities is when compared to the main
spectral peaks produced by the climatic precession effects at short
time scales (e.g., from annual to decadal bands). Our main result is
the clarification of the role of the 18.63 yr periodicity originated in
the well known retrograding cycle of the Moons' orbit. We found that
this lunar cycle is always present at a 99 % significance level in
all the analysed LIGs, even in winter with solar cycle included. The
conceptual explanation of this persistence is based on the fact that
all accurate short-term orbital forcing calculation must include the
lunar nodal cycle even in climatic precession variations. We propose
to use more specific definitions when short-term orbital variations
are taken into account in describing Milanković forcing.
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Title: Evidence for Solar Modulation on the Millennial-Scale Climate
Change of Earth
Authors: Zhao, Xinhua; Soon, Willie; Velasco Herrera, Victor M.
2020Univ....6..153Z Altcode:
No abstract at ADS
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Title: The Evolution of Rotation and Magnetic Activity in 94 Aqr Aa
from Asteroseismology with TESS
Authors: Metcalfe, Travis S.; van Saders, Jennifer L.; Basu, Sarbani;
Buzasi, Derek; Chaplin, William J.; Egeland, Ricky; Garcia, Rafael
A.; Gaulme, Patrick; Huber, Daniel; Reinhold, Timo; Schunker, Hannah;
Stassun, Keivan G.; Appourchaux, Thierry; Ball, Warrick H.; Bedding,
Timothy R.; Deheuvels, Sébastien; González-Cuesta, Lucía; Handberg,
Rasmus; Jiménez, Antonio; Kjeldsen, Hans; Li, Tanda; Lund, Mikkel N.;
Mathur, Savita; Mosser, Benoit; Nielsen, Martin B.; Noll, Anthony;
Çelik Orhan, Zeynep; Örtel, Sibel; Santos, Ângela R. G.; Yildiz,
Mutlu; Baliunas, Sallie; Soon, Willie
2020ApJ...900..154M Altcode: 2020arXiv200712755M
Most previous efforts to calibrate how rotation and magnetic activity
depend on stellar age and mass have relied on observations of clusters,
where isochrones from stellar evolution models are used to determine the
properties of the ensemble. Asteroseismology employs similar models to
measure the properties of an individual star by matching its normal
modes of oscillation, yielding the stellar age and mass with high
precision. We use 27 days of photometry from the Transiting Exoplanet
Survey Satellite to characterize solar-like oscillations in the G8
subgiant of the 94 Aqr triple system. The resulting stellar properties,
when combined with a reanalysis of 35 yr of activity measurements
from the Mount Wilson HK project, allow us to probe the evolution of
rotation and magnetic activity in the system. The asteroseismic age
of the subgiant agrees with a stellar isochrone fit, but the rotation
period is much shorter than expected from standard models of angular
momentum evolution. We conclude that weakened magnetic braking may be
needed to reproduce the stellar properties, and that evolved subgiants
in the hydrogen shell-burning phase can reinvigorate large-scale dynamo
action and briefly sustain magnetic activity cycles before ascending
the red giant branch.
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Title: On the calculation of latitudinal insolation gradients
throughout the Holocene
Authors: Cionco, Rodolfo G.; Soon, Willie W. -H.; Quaranta, Nancy E.
2020AdSpR..66..720C Altcode:
In paleoclimatology, the concept of latitudinal insolation
gradients (LIGs), reckoned in various ways, has received increasing
attention regarding glacial/inter-glacial climatic transitions
and oscillations. In particular, the Holocene, which permits the
reconstruction of past climatic proxies with an increasingly
finer spatial and temporal resolutions, has provided evidence
that suggests that LIGs are a key forcing on climate at different
timescales. Nevertheless, LIGs' own dynamics (chiefly their variations
in relation to astronomical parameters and geographical zones) and
even basic definitions, have not been properly investigated, especially
during the last part of the present geological epoch. The main reason
is the lack of broadly accessible, theoretical insolation data that
account for short-term orbital variations (i.e., for describing
sub-Milanković-orbital forcing during the Holocene). Based on
our latest astronomical-orbital solutions, we present an in-depth
discussion on the calculation of LIGs and their variations all
through the Holocene and 1 kyr into the future. Our results show
a much more complex variety and behaviour of LIGs than those that
were shown previously. We report that during the studied period,
daily LIGs in summer, around the solstitial days (both hemispheres),
are strongly modulated by obliquity only at mid-latitude band, whereas
at tropical and polar bands LIGs are modulated by "precession". Summer
half-year LIGs for the Northern Hemisphere show a marked modulation
in out-of-phase sense with obliquity, just for the mid-latitude and
polar bands. Surprisingly, this competing effect between "precession"
and obliquity also produces the fact that the southern counterpart of
these LIGs are more modulated by "precession" than obliquity. In cases
involving inter-band latitudes or different intra-annual lapses, they
need to be examined separately and carefully and the results could
be very different from traditional presumptions. Our novel results
and study are based on the precise estimation of the duration of the
orbital interval considered in the definition of LIGs. Our new study
also avoids the difficulties of insolation calculations regarding the
relationship between orbital longitudes and time.
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Title: Waldmeier Effect in Stellar Cycles
Authors: Garg, Suyog; Karak, Bidya Binay; Egeland, Ricky; Soon,
Willie; Baliunas, Sallie
2019ApJ...886..132G Altcode: 2019arXiv190912148G
One of the most robust features of the solar magnetic cycle is that
the stronger cycles rise faster than the weaker ones. This is popularly
known as the Waldmeier Effect, which has been known for more than 100
yr. This fundamental feature of the solar cycle has not only practical
implications, e.g., in predicting the solar cycle, but also implications
in understanding the solar dynamo. Here we ask whether the Waldmeier
Effect exists in other Sun-like stars. To answer this question, we
analyze the Ca II H and K S-index from Mount Wilson Observatory for
21 Sun-like G-K stars. We specifically check two aspects of Waldmeier
Effect, namely, (1) WE1: the anticorrelation between the rise times
and the peaks and (2) WE2: the positive correlation between rise rates
and amplitudes. We show that, except for HD 16160, HD 81809, HD 155886,
and HD 161239, all stars considered in the analysis show WE2, while WE1
is found to be present only in some of the stars studied. Furthermore,
the WE1 correlation is weaker than the WE2. Both WE1 and WE2 exist in
the solar S-index as well. Similar to the solar cycles, the magnetic
cycles of many stars are asymmetric about their maxima. The existence of
the Waldmeier Effect and asymmetric cycles in Sun-like stars suggests
that the dynamo mechanism which operates in the Sun is also operating
in other stars.
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Title: Reply to Li & Yang's comments on "Comparing the current
and early 20th century warm periods in China"
Authors: Soon, Willie Wei-Hock; Connolly, Ronan; Connolly, Michael;
O'Neill, Peter; Zheng, Jingyun; Ge, Quansheng; Hao, Zhixin; Yan, Hong
2019ESRv..19802950S Altcode:
From a cursory reading of Li & Yang's comments [Li and Yang, 2019,
henceforth LY2019] on our recent review article, Soon et al. (2018)
[henceforth S2018], some readers might think that LY2019 is somehow
disputing our analysis and conclusions. Specifically, they claim to
offer "some comments on the arbitrary or deductive conclusions ofSoon
et al. (2018)as [sic.] the following five aspects…"
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Title: Searching for solar-like interannual to bidecadal effects on
temperature and precipitation over a Southern Hemisphere location
Authors: Heredia, Teresita; Bazzano, Flavia M.; Cionco, Rodolfo G.;
Soon, Willie; Medina, Franco D.; Elias, Ana G.
2019JASTP.19305094H Altcode:
Precipitation and temperature over Tucuman (26.8°S, 65.2°W), a
province located in the Northwestern region of Argentina, is analyzed
for the interval 1889-2018 in search of any plausible statistical
associations with impacts and responses from solar variability. The
aim of the study was to contribute data to the controversial issue
of climate variations in response to both anthropogenic and natural
forcings. The long-term behavior of Tucuman climatic series involves
overall warming and augmented precipitation tendencies, possibly
linked to the increasing greenhouse gases concentration or even other
local man-made factors like increasing urbanization. In addition,
we identified sporadic ~4 and ~8-year periodicities, and a ~20-year
oscillation after the 1950-1960's. Based on the physical hint that
bidecadal periodicities detected in climate parameters are probably
not linked to the solar 11-year-like irradiance cycles, we expand
our scope of investigations to include another effect which has been
recently considered in the dynamics of large rivers as "the planetary
hypothesis of the solar cycles". This new hypothesis supposes that the
barycentric dynamics of the Sun could be involved in modulations of the
intrinsic solar magnetic and radiative output cycles and therefore
Earth-bound climatic responses. Thus, we present a wide-ranging
statistical analysis of correlation, cross spectrum, and coherence
between Tucuman's climatic series and solar orbital parameters,
including also the analysis of hemispheric mean temperatures. Our
results show significant coherence at the ~20-year cycle, which is
clearly present in the Sun's barycentric dynamic that could in turn be
linked to some features of the quasi-decadal solar activity variations.
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Title: Covariations of chromospheric and photometric variability of
the young Sun analogue HD 30495: evidence for and interpretation of
mid-term periodicities
Authors: Soon, W.; Velasco Herrera, V. M.; Cionco, R. G.; Qiu, S.;
Baliunas, S.; Egeland, R.; Henry, G. W.; Charvátová, I.
2019MNRAS.483.2748S Altcode: 2018MNRAS.tmp.3133S
This study reports the synchronization between the chromospheric and
photometric variability at time-scale of about 1.6-1.8 yr as observed
for the young, rapidly rotating solar analogue HD 30495. In addition,
HD 30495 may be presenting evidence of surface differential rotation
at time-scales of about 11 d and 21 d, as well as the sunspot-like
decadal cycles at 11-12 yr or so. We apply a new gapped wavelet method
of time-frequency analysis for studying the variability in a new
composite of the chromospheric S-index (1967-2018) and the longest
photometric Δ(b + y)/2 index (1993-2018). We discuss and interpret
our results in relation to other observed mid-term periodicities
roughly of the same time-scales that had been found recently from not
only chromospheric and photospheric activity indices but also from
coronal X-ray emissions as observed in a considerably large set of
stellar samples including those young Sun analogues from the Kepler
satellite project. Thus, there is an apparent universality of such
mid-term activity modulation time-scales as this solar-stellar magnetic
phenomenon is well observed directly for a host of solar activity
related indices covering the photopsheric, chromospheric, coronal,
and even the heliospheric (utilizing the measures of incoming galactic
cosmic rays as a probe of activity variations) activity records. This
is why we made a further attempt to interpret the results in search of
a realistic generation mechanism as well as spatio-temporal persistency
of the phenomenon under a wide scenario of dynamo simulations.
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Title: Comparing the current and early 20th century warm periods
in China
Authors: Soon, Willie Wei-Hock; Connolly, Ronan; Connolly, Michael;
O'Neill, Peter; Zheng, Jingyun; Ge, Quansheng; Hao, Zhixin; Yan, Hong
2018ESRv..185...80S Altcode:
Most estimates of Chinese regional Surface Air Temperatures since
the late-19th century have identified two relatively warm periods -
1920s-40s and 1990s-present. However, there is considerable debate over
how the two periods compare to each other. Some argue the current
warm period is much warmer than the earlier warm period. Others
argue the earlier warm period was comparable to the present. In this
collaborative paper, including authors from both camps, the reasons
for this ongoing debate are discussed. Several different estimates
of Chinese temperature trends, both new and previously published,
are considered. A study of the effects of urbanization bias on Chinese
temperature trends was carried out using the new updated version of the
Global Historical Climatology Network (GHCN) - version 4 (currently
in beta production). It is shown that there are relatively few rural
stations with long records, but urbanization bias artificially makes
the early warm period seem colder and the recent warm period seem
warmer. However, current homogenization approaches (which attempt
to reduce non-climatic biases) also tend to have similar effects,
making it unclear whether reducing or increasing the relative warmth
of each period is most appropriate. A sample of 17 Chinese temperature
proxy series (12 regional and 5 national) is compared and contrasted
specifically for the period since the 19th century. Most proxy series
imply a warm early-20th century period and a warm recent period, but
the relative warmth of these two periods differs between proxies. Also,
with some proxies, one or other of the warm periods is absent.
---------------------------------------------------------
Title: Sudden Sodium Layers: Their Appearance and Disappearance
Authors: Qiu, Shican; Soon, Willie; Xue, Xianghui; Li, Tao; Wang,
Wanyin; Jia, Mingjiao; Ban, Chao; Fang, Xin; Tang, Yihuan; Dou,
Xiankang
2018JGRA..123.5102Q Altcode:
Temperature variation has been proposed to play an important role in
the formation of the sporadic sodium layers (SSLs or Na<SUB>S</SUB>)
in subtropic area, based on the observed significant correlation
between SSLs and high temperatures. The icy-dust particle, which
could form in the extremely cold conditions and act as absorbers
of sodium species, was proposed to be a possible candidate for
the sodium reservoir of the SSLs. In this study, the University of
Science and Technology of China temperature/wind lidar and the sodium
fluorescence lidar at a subtropic station Hefei (31°N, 117°E), China,
were used to observe sodium density, temperature, and wind profiles
simultaneously throughout the SSL events. Based on the observations
of two SSLs occurring on 12 and 13 May 2013, the possibility of an
icy-dust layer existing and acting as the sodium reservoir is tested
for the first time in details. Both events experienced an extremely
cold temperature (<150 K) several hours before the onset of SSLs,
followed by a subsequently fast production of sodium atoms during a
large temperature enhancement (>40 K). An empirical model including
two main steps is then proposed: first, sodium species are collected
by an icy-dust reservoir and stored during the extremely cold phase;
second, free sodium atoms could be released from the reservoir by
a possible trigger. As a result, this kind of SSLs could possibly
be regarded as a quasi-continuous phenomenon caused and modulated
by temperature variations with an icy-dust model that can exhibit
intermittent time variations related to the water vapor concentration.
---------------------------------------------------------
Title: The quasi-biennial oscillation of 1.7 years in ground level
enhancement events
Authors: Velasco Herrera, V. M.; Pérez-Peraza, J.; Soon, W.;
Márquez-Adame, J. C.
2018NewA...60....7V Altcode:
The so-called Ground Level Enhancement events are sporadic relativistic
solar particles measured at ground level by a network of cosmic ray
detectors worldwide. These sporadic events are typically assumed to
occur by random chance. However, we find that by studying the last 56
ground level enhancement events reported from 1966 through 2014, these
events occur preferentially in the positive phase of the quasi-biennial
oscillation of 1.7 year periodicity. These discrete ground level
enhancement events show that there is another type of solar emission
(i.e., wavelike packets) that occurs only in a specific phase of a
very particular oscillation. We interpret this empirical result to
support that ground level enhancement events are not a result of purely
stochastic processes. We used the Morlet wavelet to analyze the phase
of each of the periodicities found by the wavelet analyses and local
variations of power spectral density in these sporadic events. We found
quasi-regular periodicities of 10.4, 6.55, 4.12, 2.9, 1.73, 0.86, 0.61,
0.4 and 0.24 years in ground level enhancements. Although some of these
quasi-biennial oscillation periodicities (i.e., oscillations operating
between 0.6 and 4 years) may be interpreted as simply harmonics and
overtones of the fundamental solar cycle from the underlying sun-spot
magnetism phenomenon. The sources of these periodicities are still
unclear. Also there is no clear mechanism for the variability of the
quasi-biennial oscillation periodicities itself. The quasi-biennial
oscillation periodicities are broadly considered to be a variation of
solar activity, associated with the solar dynamo process. Also, the
intensity of these periodicities is more important around the years
of maximum solar activity because the quasi-biennial oscillation
periodicities are modulated by the solar cycle where the Sun is
more energetically enhanced during activity maxima. To identify the
relationships among ground level enhancement, solar, and cosmic rays
indices in time-frequency framework, we apply the wavelet coherence
analysis. The fingerprints of solar activity and galactic cosmic rays
on these phenomena can also be discerned in terms of the prominent
quasi-biennial oscillation of about 1.7 years.
---------------------------------------------------------
Title: Lunar fingerprints in the modulated incoming solar radiation:
In situ insolation and latitudinal insolation gradients as two
important interpretative metrics for paleoclimatic data records and
theoretical climate modeling
Authors: Cionco, Rodolfo Gustavo; Valentini, José Ernesto; Quaranta,
Nancy Esther; Soon, Willie W. -H.
2018NewA...58...96C Altcode:
We present a new set of solar radiation forcing that now incorporated
not only the gravitational perturbation of the Sun-Earth-Moon
geometrical orbits but also the intrinsic solar magnetic modulation of
the total solar irradiance (TSI). This new dataset, covering the past
2000 years as well as a forward projection for about 100 years based
on recent result by Velasco-Herrera et al. (2015), should provide a
realistic basis to examine and evaluate the role of external solar
forcing on Earth climate on decadal, multidecadal to multicentennial
timescales. A second goal of this paper is to propose both in situ
insolation forcing variable and the latitudinal insolation gradients
(LIG) as two key metrics that are subjected to a deterministic
modulation by lunar nodal cycle which are often confused with tidal
forcing impacts as assumed and interpreted in previous studies of
instrumental and paleoclimatic records. Our new results and datasets
are made publicly available for all at PANGAEA site.
---------------------------------------------------------
Title: Evolution of Long Term Variability in Solar Analogs
Authors: Egeland, Ricky; Soon, Willie; Baliunas, Sallie; Hall,
Jeffrey C.; Henry, Gregory W.
2017IAUS..328..329E Altcode: 2017arXiv170402388E
Earth is the only planet known to harbor life, therefore we may
speculate on how the nature of the Sun-Earth interaction is relevant
to life on Earth, and how the behavior of other stars may influence the
development of life on their planetary systems. We study the long-term
variability of a sample of five solar analog stars using composite
chromospheric activity records up to 50 years in length and synoptic
visible-band photometry about 20 years long. This sample covers a
large range of stellar ages which we use to represent the evolution in
activity for solar mass stars. We find that young, fast rotators have an
amplitude of variability many times that of the solar cycle, while old,
slow rotators have very little variability. We discuss the possible
impacts of this variability on young Earth and exoplanet climates.
---------------------------------------------------------
Title: Generalization of the cross-wavelet function
Authors: Velasco Herrera, V. M.; Soon, W.; Velasco Herrera, G.;
Traversi, R.; Horiuchi, K.
2017NewA...56...86V Altcode:
We introduce the method of multiple cross-wavelet algorithm, hereafter
also as Einstein's cross functions, for the time-frequency study
of solar activity records or any astronomical and geophysical time
series in general. The main purpose of this algorithm is to allow the
simultaneous examination of the time-frequency information contents in
n > 2 time series available. Previous cross-wavelet algorithm only
permit the study of two time series at a time and was not extended
to the generalized n > 2 problems until now. Furthermore, our new
work lifted the restriction from the original formulation that are
valid only for stationary processes. We applied our new algorithm to
several of the solar activity proxies available in order to demonstrate
the broad and powerful utility of this technique. We have used solar
activity proxy records that are obtained under different geophysical
archives and time periods which are, in turn, suitable for studying both
the statistical and physical properties for solar variations valid on
timescales of multi-century, millennium to several millennia. We focus
on documenting the methodology in this paper rather than any elaborate
interpretation of the results.
---------------------------------------------------------
Title: VizieR Online Data Catalog: Calibrated solar S-index time
series (Egeland+, 2017)
Authors: Egeland, R.; Soon, W.; Baliunas, S.; Hall, J. C.; Pevtsov,
A. A.; Bertello, L.
2017yCat..18350025E Altcode:
The Mount Wilson HK Program observed the Moon with both the HKP-1
and HKP-2 instruments. After removing 11 obvious outliers, there
are 162 HKP-1 observations taken from 1966 September 2 to 1977 June
4 with the Mount Wilson 100 inch reflector, covering the maximum
of cycle 20 and the cycle 20-21 minimum. As mentioned in Baliunas+
(1995ApJ...438..269B), observations of the Moon resumed in 1993 with
the HKP-2 instrument. After removing 10 obvious outliers, there are 75
HKP-2 observations taken from 1994 March 27 to 2002 November 23 with
the Mount Wilson 60 inch reflector, covering the end of cycle 22 and
the cycle 23 minimum, extending just past the cycle 23 maximum. The
end of observations coincides with the unfortunate termination of
the HK Project in 2003. <P />We seek to extend our time series of
solar variability beyond cycle 23 by establishing a proxy to the
NSO Sacramento Peak (NSO/SP) observations taken from 1976 to 2016,
covering cycles 21 to 24. The spectral intensity scale is set by
integrating a 0.53Å band centered at 3934.869Å in the K-line wing
and setting it to the fixed value of 0.162. <P />We extend the S-index
record back to cycle 20 using the composite K time series of Bertello+
(2016SoPh..291.2967B). See section 3 for further explanations. <P />(1
data file).
---------------------------------------------------------
Title: Short-term orbital forcing: A quasi-review and a reappraisal
of realistic boundary conditions for climate modeling
Authors: Cionco, Rodolfo G.; Soon, Willie W. -H.
2017ESRv..166..206C Altcode: 2016arXiv161208380C
The aim of this paper is to provide geoscientists with the most accurate
set of the Earth's astro-climatic parameters and daily insolation
quantities, able to describe the Short-Term Orbital Forcing (STOF)
as represented by the ever-changing incoming solar radiation. We
provide an updated review and a pragmatic tool/database using the
latest astronomical models and orbital ephemeris, for the entire
Holocene and 1 kyr into the future. Our results are compared with
the most important database produced for studying long-term orbital
forcing showing no systematic discrepancies over the full thirteen
thousand years period studied. Our detailed analysis of the periods
present in STOF, as perturbed by Solar System bodies, yields a very
rich dynamical modulation on annual-to-decadal timescales when compared
to previous results. In addition, we addressed, for the first time,
the error committed considering daily insolation as a continuous
function of orbital longitudes with respect to the nominal values,
i.e., calculating the corresponding daily insolation with orbital
longitudes tabulated at noon. We found important relative differences
up to ± 5%, which correspond to errors of 2.5 W m<SUP>-2</SUP> in
the daily mean insolation, for exactly the same calendar day and set
of astro-climatic parameters. This previously unrecognized error could
have a significant impact in both the initial and boundary conditions
for any climate modeling experiment.
---------------------------------------------------------
Title: The Mount Wilson Observatory S-index of the Sun
Authors: Egeland, Ricky; Soon, Willie; Baliunas, Sallie; Hall,
Jeffrey C.; Pevtsov, Alexei A.; Bertello, Luca
2017ApJ...835...25E Altcode: 2016arXiv161104540E
The most commonly used index of stellar magnetic activity is the
instrumental flux scale of singly ionized calcium H & K line
core emission, S, developed by the Mount Wilson Observatory (MWO)
HK Project, or the derivative index {R}<SUB>{HK</SUB>}<SUP>\prime
</SUP>. Accurately placing the Sun on the S scale is important for
comparing solar activity to that of the Sun-like stars. We present
previously unpublished measurements of the reflected sunlight from
the Moon using the second-generation MWO HK photometer during solar
cycle 23 and determine cycle minimum {S}<SUB>23,\min </SUB>=0.1634+/-
0.0008, amplitude {{Δ }}{S}<SUB>23</SUB>=0.0143+/- 0.0012, and mean
< {S}<SUB>23</SUB>> =0.1701+/- 0.0005. By establishing a proxy
relationship with the closely related National Solar Observatory
Sacramento Peak calcium K emission index, itself well correlated with
the Kodaikanal Observatory plage index, we extend the MWO S time series
to cover cycles 15-24 and find on average < {S}<SUB>\min </SUB>>
=0.1621+/- 0.0008, < {{Δ }}{S}<SUB>{cyc</SUB>}> =0.0145+/-
0.0012, < {S}<SUB>{cyc</SUB>}> =0.1694+/- 0.0005. Our measurements
represent an improvement over previous estimates that relied on stellar
measurements or solar proxies with non-overlapping time series. We
find good agreement from these results with measurements by the
Solar-Stellar Spectrograph at Lowell Observatory, an independently
calibrated instrument, which gives us additional confidence that we
have accurately placed the Sun on the S-index flux scale.
---------------------------------------------------------
Title: Dynamo Sensitivity In Solar Analogs With 50 Years Of Ca II
H & K Activity
Authors: Egeland, Ricky; Soon, Willie; Baliunas, Sallie; Hall,
Jeffrey C.; Pevtsov, Alexei A.; Henry, Gregory W.
2016csss.confE...6E Altcode: 2016csss.confE..73E; 2016arXiv160904756E
The Sun has a steady 11-year cycle in magnetic activity most well-known
by the rising and falling in the occurrence of dark sunspots on the
solar disk in visible bandpasses. The 11-year cycle is also manifest
in the variations of emission in the Ca II H & K line cores, due to
non-thermal (i.e. magnetic) heating in the lower chromosphere. The large
variation in Ca II H & K emission allows for study of the patterns
of long-term variability in other stars thanks to synoptic monitoring
with the Mount Wilson Observatory HK photometers (1966-2003) and Lowell
Observatory Solar-Stellar Spectrograph (1994-present). Overlapping
measurements for a set of 27 nearby solar-analog (spectral types G0-G5)
stars were used to calibrate the two instruments and construct time
series of magnetic activity up to 50 years in length. Precise properties
of fundamental importance to the dynamo are available from Hipparcos,
the Geneva-Copenhagen Survey, and CHARA interferometry. Using these
long time series and measurements of fundamental properties, we do
a comparative study of stellar "twins" to explore the sensitivity
of the stellar dynamo to small changes to structure, rotation, and
composition. We also compare this sample to the Sun and find hints
that the regular periodic variability of the solar cycle may be rare
among its nearest neighbors in parameter space.
---------------------------------------------------------
Title: Corrigendum to 'A review of Holocene solar-linked climatic
variation on centennial to millennial timescales: Physical processes,
interpretative frameworks and a new multiple cross-wavelet transform
algorithm' Earth Sci. Rev. 134 [1-15]
Authors: Soon, Willie; Velasco Herrera, Victor M.; Selvaraj, Kandasamy;
Traversi, Rita; Usoskin, Ilya; Arthur Chen, Chen-Tung; Lou, Jiann-Yuh;
Kao, Shuh-Ji; Carter, Robert M.; Pipin, Valery; Severi, Mirko;
Becagli, Silvia
2016ESRv..159..462S Altcode:
In the article "A review of Holocene solar-linked climatic variation on
centennial to millennial timescales: Physical processes, interpretative
frameworks and a new multiple cross-wavelet transform algorithm",
published in Earth-Science Reviews 134 (2014) 1, it was omitted to
state that at the time this article was submitted the corresponding
author Dr. Soon received funding from the Southern Company Services and
Donors Trust. We have no indication that this funding has influenced
the results presented in the article.
---------------------------------------------------------
Title: The Solar Dynamo Zoo
Authors: Egeland, Ricky; Soon, Willie; Baliunas, Sallie; Hall,
Jeffrey C.; Pevtsov, Alexei A.; Henry, Gregory W.
2016csss.confE..72E Altcode:
We present composite time series of Ca II H & K line core emission
indices of up to 50 years in length for a set of 27 solar-analog stars
(spectral types G0-G5; within 10% of the solar mass) and the Sun. These
unique data are available thanks to the long-term dedicated efforts
of the Mount Wilson Observatory HK project, the Lowell Observatory
Solar-Stellar Spectrograph, and the National Solar Observatory/Air Force
Research Laboratory/Sacramento Peak K-line monitoring program. The Ca II
H & K emission originates in the lower chromosphere and is strongly
correlated with the presence of magnetic plage regions in the Sun. These
synoptic observations allow us to trace the patterns long-term magnetic
variability and explore dynamo behavior over a wide range of rotation
regimes and stellar evolution timescales.In this poster, the Ca HK
observations are expressed using the Mount Wilson S-index. Each time
series is accompanied by a Lomb-Scargle periodogram, fundemental stellar
parameters derived from the Geneva-Copenhagen Survey, and statistics
derived from the time series including the median S-index value and
seasonal and long-term amplitudes. Statistically significant periodogram
peaks are ranked according to a new cycle quality metric. We find that
clear, simple, Sun-like cycles are the minority in this sample.
---------------------------------------------------------
Title: Magnetic cycles at different ages of stars
Authors: Oláh, K.; Kővári, Zs.; Petrovay, K.; Soon, W.; Baliunas,
S.; Kolláth, Z.; Vida, K.
2016A&A...590A.133O Altcode: 2016arXiv160406701O
<BR /> Aims: We study the different patterns of interannual magnetic
variability in stars on or near the lower main sequence, approximately
solar-type (G-K dwarf) stars in time series of 36 yr from the Mount
Wilson Observatory Ca II H&K survey. Our main aim is to search
for correlations between cycles, activity measures, and ages. <BR
/> Methods: Time-frequency analysis has been used to discern and
reveal patterns and morphology of stellar activity cycles, including
multiple and changing cycles, in the datasets. Both the results from
short-term Fourier transform and its refinement using the Choi-Williams
distribution, with better frequency resolution, are presented in this
study. Rotational periods of the stars were derived using multifrequency
Fourier analysis. <BR /> Results: We found at least one activity cycle
on 28 of the 29 stars we studied. Twelve stars, with longer rotational
periods (39.7 ± 6.0 days), have simple smooth cycles, and the remaining
stars, with much faster rotation (18.1 ± 12.2 days) on average, show
complex and sometimes vigorously changing multiple cycles. The cycles
are longer and quite uniform in the first group (9.7 ± 1.9 yr), while
they are generally shorter and vary more strongly in the second group
(7.6 ± 4.9). The clear age division between stars with smooth and
complex cycles follows the known separation between the older and
younger stars at around 2 to 3 Gyr of age.
---------------------------------------------------------
Title: Re-evaluating the role of solar variability on Northern
Hemisphere temperature trends since the 19th century
Authors: Soon, Willie; Connolly, Ronan; Connolly, Michael
2015ESRv..150..409S Altcode:
Debate over what influence (if any) solar variability has had on surface
air temperature trends since the 19th century has been controversial. In
this paper, we consider two factors which may have contributed to
this controversy: <P />Several different solar variability datasets
exist. While each of these datasets is constructed on plausible
grounds, they often imply contradictory estimates for the trends in
solar activity since the 19th century. <P />Although attempts have
been made to account for non-climatic biases in previous estimates
of surface air temperature trends, recent research by two of the
authors has shown that current estimates are likely still affected by
non-climatic biases, particularly urbanization bias. <P />With these
points in mind, we first review the debate over solar variability. We
summarise the points of general agreement between most groups and the
aspects which still remain controversial. We discuss possible future
research which may help resolve the controversy of these aspects. Then,
in order to account for the problem of urbanization bias, we compile a
new estimate of Northern Hemisphere surface air temperature trends since
1881, using records from predominantly rural stations in the monthly
Global Historical Climatology Network dataset. Like previous weather
station-based estimates, our new estimate suggests that surface air
temperatures warmed during the 1880s-1940s and 1980s-2000s. However,
this new estimate suggests these two warming periods were separated by
a pronounced cooling period during the 1950s-1970s and that the relative
warmth of the mid-20th century warm period was comparable to the recent
warm period. <P />We then compare our weather station-based temperature
trend estimate to several other independent estimates. This new record
is found to be consistent with estimates of Northern Hemisphere Sea
Surface Temperature (SST) trends, as well as temperature proxy-based
estimates derived from glacier length records and from tree ring
widths. However, the multi-model means of the recent Coupled Model
Intercomparison Project Phase 5 (CMIP5) climate model hindcasts
were unable to adequately reproduce the new estimate - although the
modelling of certain volcanic eruptions did seem to be reasonably well
reproduced. <P />Finally, we compare our new composite to one of the
solar variability datasets not considered by the CMIP5 climate models,
i.e., Scafetta and Willson, 2014's update to the Hoyt and Schatten,
1993 dataset. A strong correlation is found between these two datasets,
implying that solar variability has been the dominant influence on
Northern Hemisphere temperature trends since at least 1881. We discuss
the significance of this apparent correlation, and its implications
for previous studies which have instead suggested that increasing
atmospheric carbon dioxide has been the dominant influence.
---------------------------------------------------------
Title: The Maunder minimum (1645-1715) was indeed a grand minimum:
A reassessment of multiple datasets
Authors: Usoskin, Ilya G.; Arlt, Rainer; Asvestari, Eleanna; Hawkins,
Ed; Käpylä, Maarit; Kovaltsov, Gennady A.; Krivova, Natalie;
Lockwood, Michael; Mursula, Kalevi; O'Reilly, Jezebel; Owens, Matthew;
Scott, Chris J.; Sokoloff, Dmitry D.; Solanki, Sami K.; Soon, Willie;
Vaquero, José M.
2015A&A...581A..95U Altcode: 2015arXiv150705191U
<BR /> Aims: Although the time of the Maunder minimum (1645-1715) is
widely known as a period of extremely low solar activity, it is still
being debated whether solar activity during that period might have
been moderate or even higher than the current solar cycle #24. We have
revisited all existing evidence and datasets, both direct and indirect,
to assess the level of solar activity during the Maunder minimum. <BR />
Methods: We discuss the East Asian naked-eye sunspot observations, the
telescopic solar observations, the fraction of sunspot active days,
the latitudinal extent of sunspot positions, auroral sightings at
high latitudes, cosmogenic radionuclide data as well as solar eclipse
observations for that period. We also consider peculiar features of
the Sun (very strong hemispheric asymmetry of the sunspot location,
unusual differential rotation and the lack of the K-corona) that imply
a special mode of solar activity during the Maunder minimum. <BR />
Results: The level of solar activity during the Maunder minimum is
reassessed on the basis of all available datasets. <BR /> Conclusions:
We conclude that solar activity was indeed at an exceptionally low
level during the Maunder minimum. Although the exact level is still
unclear, it was definitely lower than during the Dalton minimum of
around 1800 and significantly below that of the current solar cycle
#24. Claims of a moderate-to-high level of solar activity during the
Maunder minimum are rejected with a high confidence level.
---------------------------------------------------------
Title: The Maunder minimum: A reassessment from multiple dataset
Authors: Usoskin, Ilya; Arlt, Rainer; Asvestari, Eleanna; Kovaltsov,
Gennady; Krivova, Natalie; Lockwood, Michael; Käpylä, Maarit; Owens,
Matthew; Sokoloff, Dmitry D.; Solanki, Sami; Soon, Willie; Vaquero,
Jose; Scott, Chris
2015IAUGA..2253036U Altcode:
The Maunder minimum (MM) in 1645-1715 was a period of the lowest ever
known solar activity recorded via sunspot numbers since 1610. Since
it is the only Grand minimum of solar activity directly observed,
it forms a benchmark for the solar variability studies. Therefore,
it is crucially important to assess the level and other features
of temporal and spatial solar magnetic variability during that
time. However, because of uncertainties related mostly to ambiguity
of some historical sunspot observation records, the exact level of
solar activity during the MM is somewhat unclear, leaving room for
continuous discussions and speculations. Many of these issues have been
addressed by Jack Eddy in his cornerstone papers of 1976 and 1983,
but since then numerous new pieces of evidence and datasets have
appeared, making it possible to verify the paradigm of the Maunder
minimum with far greater certainty than before.Here we provide a full
reassessment of the Maunder minimum using all the available datasets:
augmented sunspot counts and drawings; revisited historical archives;
both well-known and newly revealed records of auroral observations;
cosmic ray variability via cosmogenic isotope records of <SUP>14</SUP>C
in tree trunks, <SUP>10</SUP>Be in ice cores and<SUP> 44</SUP>Ti in
fallen meteorites. We show that, while the exact level of the activity
is not easy to determine, the Sun indeed exhibited exceptionally low
magnetic activity during the MM, in comparison to other periods of
moderate or decreased activity, such as the Dalton minimum (ca. 1800),
the Gleissberg minimum (ca. 1900) and the present weak solar cycle #
24. We show that a scenario of moderate or strong activity during the
MM contradicts all the available datasets.Thus, we confirm, using
all the presently available datasets of different nature, that the
period of the Maunder minimum in 1645-1715 was indeed a Grand minimum,
with very low solar surface magnetic activity, low intensity of the
interplanetary magnetic field, as well as lower frequency and higher
geographical latitude of auroral occurrence. Meanwhile some indications
of the continuation, but at a very low level, of the 11-year solar
cycle can be found in the data.
---------------------------------------------------------
Title: Response to the comment on: “Soon, W., and Legates, D.R.,
solar irradiance modulation of equator-to-pole (Arctic) temperature
gradients: empirical evidence for climate variation on multi-decadal
timescales. Journal of Atmospheric and solar-terrestrial physics, 93,
(2013) 45-56” by F. Meunier and A. H. Reis
Authors: Soon, Willie; Legates, David R.
2015JASTP.128...92S Altcode:
We thank Meunier and Reis (hereafter as MR) for their comments on
our paper. We, however, do not see the relevance of their alternative
interpretation to our original results and believe this reflects their
confusion regarding our conclusions rather than a discussion on physical
mechanisms. <P /></ce:displayed-quote></ce:para>In the
context of this quote, note that even Pallé et al. (2009:3)admitted
that “while the deseasonalized CERES data has a small year to year
variability (Fig. 2 of Pallé et al., 2009), the Earthshine data
seem to present overly large interannual anomalies, along with a
large size of the error bars associated to the yearly means [which]
is mostly due to sampling issues, as Earthshine measurements are taken
from a single station.”</ce:para>To put this in a different
way, the relatively short duration of Earthshine or satellite-borne
measurements of global albedo is unable to provide the necessary
information on how this important quantity may vary on multi-decadal
timescales as studies by Soon and Legates (2013). We note that efforts
to 'reconstruct' Earth albedo over a 120-to-130 year period have
been discussed by Zavalishin (2014) but we stress that such research
requires non-independent information regarding surface temperatures
and some unproven assumptions about the thermal inertia of the
hydrosphere.</ce:para></ce:sections></ja:body><ja:simple-tail
view="all"><ce:bibliography
---------------------------------------------------------
Title: Indian summer monsoon rainfall: Dancing with the tunes of
the sun
Authors: Hiremath, K. M.; Manjunath, Hegde; Soon, Willie
2015NewA...35....8H Altcode:
There is strong statistical evidence that solar activity influences
the Indian summer monsoon rainfall. To search for a physical link
between the two, we consider the coupled cloud hydrodynamic equations,
and derive an equation for the rate of precipitation that is similar to
the equation of a forced harmonic oscillator, with cloud and rain water
mixing ratios as forcing variables. Those internal forcing variables
are parameterized in terms of the combined effect of external forcing
as measured by sunspot and coronal hole activities with several well
known solar periods (9, 13 and 27 days; 1.3, 5, 11 and 22 years). The
equation is then numerically solved and the results show that the
variability of the simulated rate of precipitation captures very
well the actual variability of the Indian monsoon rainfall, yielding
vital clues for a physical understanding that has so far eluded
analyses based on statistical correlations alone. We also solved
the precipitation equation by allowing for the effects of long-term
variation of aerosols. We tentatively conclude that the net effects
of aerosols variation are small, when compared to the solar factors,
in terms of explaining the observed rainfall variability covering the
full Indian monsoonal geographical domains.
---------------------------------------------------------
Title: A composite sea surface temperature record of the northern
South China Sea for the past 2500 years: A unique look into
seasonality and seasonal climate changes during warm and cold periods
Authors: Yan, Hong; Soon, Willie; Wang, Yuhong
2015ESRv..141..122Y Altcode:
High-resolution late Holocene climate records that can resolve
seasonality are essential for confirming past climatic dynamics,
understanding the late 20th century global warming and predicting future
climate. Here a new composite record of the sea surface temperature,
SST, variation in the northern South China Sea (SCS) during the late
Holocene is constructed by combining seven seasonally-resolved coral
and Tridacna gigas Sr/Ca-based SST time-windows with the instrumental
SST record from modern interval between 1990 and 2000. This composite
multi-proxy marine record, together with the reconstructions from
mainland China and tropical Western Pacific, indicates that the
late Holocene warm periods, the Roman Warm Period (RWP) and Medieval
Warm Period (MWP), were prominently imprinted and documented in the
climatic and environmental history of the East Asia-Western Pacific
region. Meanwhile, substantial and significant SST seasonality
variations during the late Holocene were observed in the composite
record. The observed increase in seasonality (or amplitude of seasonal
cycles) during the cold periods around our study area was probably
caused by the different amplitudes between winter versus summer SST
variations in northern SCS, with much larger SST variation during
winters than during summers for the late Holocene. In addition,
the distinctive warm, cold and neutral climatic episodes identified
in our northern SCS composite SST record correspond well with other
paleo reconstructions from mainland China and especially well with
the Northern Hemisphere-wide composites by Moberg et al. (2005) and
Ljungqvist (2010). The overall agreement however also calls for more
information and insights on how seasonal temperatures and their ranges
vary on decadal-centennial timescales.
---------------------------------------------------------
Title: A phenomenological study of the timing of solar activity
minima of the last millennium through a physical modeling of the
Sun-Planets Interaction
Authors: Cionco, Rodolfo Gustavo; Soon, Willie
2015NewA...34..164C Altcode:
We numerically integrate the Sun’s orbital movement around the
barycenter of the solar system under the persistent perturbation of
the planets from the epoch J2000.0, backward for about one millennium,
and forward for another millennium to 3000 AD. Under the Sun-Planets
Interaction (SPI) framework and interpretation of Wolff and Patrone
(2010), we calculated the corresponding variations of the most important
storage of the specific potential energy (PE) within the Sun that could
be released by the exchanges between two rotating, fluid-mass elements
that conserve its angular momentum. This energy comes about as a result
of the roto-translational dynamics of the cell around the solar system
barycenter. We find that the maximum variations of this PE storage
correspond remarkably well with the occurrences of well-documented Grand
Minima (GM) solar events throughout the available proxy solar magnetic
activity records for the past 1000 yr. It is also clear that the maximum
changes in PE precede the GM events in that we can identify precursor
warnings to the imminent weakening of solar activity for an extended
period. The dynamical explanation of these PE minima is connected to
the minima of the Sun’s position relative to the barycenter as well
as the significant amount of time the Sun’s inertial motion revolving
near and close to the barycenter. We presented our calculation of PE
forward by another 1000 yr until 3000 AD. If the assumption of the
solar activity minima corresponding to PE minima is correct, then we
can identify quite a few significant future solar activity GM events
with a clustering of PE minima pulses starting at around 2150 AD,
2310 AD, 2500 AD, 2700 AD and 2850 AD.
---------------------------------------------------------
Title: A review of Holocene solar-linked climatic variation
on centennial to millennial timescales: Physical processes,
interpretative frameworks and a new multiple cross-wavelet transform
algorithm
Authors: Soon, Willie; Velasco Herrera, Victor M.; Selvaraj, Kandasamy;
Traversi, Rita; Usoskin, Ilya; Chen, Chen-Tung Arthur; Lou, Jiann-Yuh;
Kao, Shuh-Ji; Carter, Robert M.; Pipin, Valery; Severi, Mirko;
Becagli, Silvia
2014ESRv..134....1S Altcode:
We report on the existence and nature of Holocene solar and climatic
variations on centennial to millennial timescales. We introduce a new
solar activity proxy, based on nitrate (NO<SUB>3</SUB><SUP>-</SUP>)
concentration from the Talos Dome ice core, East Antarctica. We also
use a new algorithm for computing multiple-cross wavelet spectra in
time-frequency space that is generalized for multiple time series
(beyond two). Our results provide a new interpretive framework for
relating Holocene solar activity variations on centennial to millennial
timescales to co-varying climate proxies drawn from a widespread
area around the globe. Climatic proxies used represent variation in
the North Atlantic Ocean, Western Pacific Warm Pool, Southern Ocean
and the East Asian monsoon regions. Our wavelet analysis identifies
fundamental solar modes at 2300-yr (Hallstattzeit), 1000-yr (Eddy),
and 500-yr (unnamed) periodicities, leaves open the possibility
that the 1500-1800-yr cycle may either be fundamental or derived,
and identifies intermediary derived cycles at 700-yr and 300-yr that
may mark rectified responses of the Atlantic thermohaline circulation
to external solar modulation and pacing. Dating uncertainties suggest
that the 1500-yr and 1800-yr cycles described in the literature may
represent either the same or two separate cycles, but in either case,
and irrespective too of whether it is a fundamental or derived mode in
the sense of Dima and Lohmann (2009), the 1500-1800-yr periodicity is
widely represented in a large number of paleoclimate proxy records. It
is obviously premature to reject possible links between changing solar
activity at these multiple scales and the variations that are commonly
observed in paleoclimatic records.
---------------------------------------------------------
Title: Arctic albedo changes are small compared with changes in
cloud cover in the tropics
Authors: Legates, David R.; Eschenbach, Willis; Soon, Willie
2014PNAS..111E2157L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar irradiance modulation of Equator-to-Pole (Arctic)
temperature gradients: Empirical evidence for climate variation on
multi-decadal timescales
Authors: Soon, Willie; Legates, David R.
2013JASTP..93...45S Altcode:
Using thermometer-based air temperature records for the period
1850-2010, we present empirical evidence for a direct relationship
between total solar irradiance (TSI) and the Equator-to-Pole (Arctic)
surface temperature gradient (EPTG). Modulation of the EPTG by
TSI is also shown to exist, in variable ways, for each of the four
seasons. Interpretation of the positive relationship between the TSI
and EPTG indices suggests that solar-forced changes in the EPTG may
represent a hemispheric-scale relaxation response of the system to a
reduced Equator-to-Pole temperature gradient, which occurs in response
to an increasing gradient of incoming solar insolation. Physical
bases for the TSI-EPTG relationship are discussed with respect to
their connections with large-scale climate dynamics, especially
a critical relationship with the total meridional poleward energy
transport. Overall, evidence suggests that a net increase in the TSI,
or in the projected solar insolation gradient which reflects any net
increase in solar radiation, has caused an increase in both oceanic and
atmospheric heat transport to the Arctic in the warm period since the
1970s, resulting in a reduced temperature gradient between the Equator
and the Arctic. We suggest that this new interpretative framework, which
involves the extrinsic modulation of the total meridional energy flux
beyond the implicit assumptions of the Bjerknes Compensation rule, may
lead to a better understanding of how global and regional climate has
varied through the Holocene and even the Quaternary (the most recent
2.6 million years of Earth's history). Similarly, a reassessment is
now required of the underlying mechanisms that may have governed the
equable climate dynamics of the Eocene (35-55 million years ago) and
late Cretaceous (65-100 million years ago), both of which were warm
geological epochs. This newly discovered relationship between TSI
and the EPTG represents the "missing link" that was implicit in the
empirical relationship that Soon (2009) recently demonstrated to exist
between multi-decadal TSI and Arctic and North Atlantic climatic change.
---------------------------------------------------------
Title: Variation in surface air temperature of China during the
20th century
Authors: Soon, Willie; Dutta, Koushik; Legates, David R.; Velasco,
Victor; Zhang, Weijia
2011JASTP..73.2331S Altcode:
The 20th century surface air temperature (SAT) records of China from
various sources are analyzed using data which include the recently
released Twentieth Century Reanalysis Project dataset. Two key features
of the Chinese records are confirmed: (1) significant 1920s and 1940s
warming in the temperature records, and (2) evidence for a persistent
multidecadal modulation of the Chinese surface temperature records in
co-variations with both incoming solar radiation at the top of the
atmosphere as well as the modulated solar radiation reaching ground
surface. New evidence is presented for this Sun-climate link for the
instrumental record from 1880 to 2002. Additionally, two non-local
physical aspects of solar radiation-induced modulation of the Chinese
SAT record are documented and discussed.Teleconnections that provide
a persistent and systematic modulation of the temperature response
of the Tibetan Plateau and/or the tropospheric air column above the
Eurasian continent (e.g., 30°N-70°N; 0°-120°E) are described. These
teleconnections may originate from the solar irradiance-Arctic-North
Atlantic overturning circulation mechanism proposed by Soon (2009). Also
considered is the modulation of large-scale land-sea thermal contrasts
both in terms of meridional and zonal gradients between the subtropical
western Pacific and mid-latitude North Pacific and the continental
landmass of China. The Circum-global teleconnection (CGT) pattern
of summer circulation of Ding and Wang (2005) provides a physical
framework for study of the Sun-climate connection over East Asia. Our
results highlight the importance of solar radiation reaching the ground
and the concomitant importance of changes in atmospheric transparency
or cloudiness or both in motivating a true physical explanation of
any Sun-climate connection. We conclude that ground surface solar
radiation is an important modulating factor for Chinese SAT changes
on multidecadal to centennial timescales. Therefore, a comprehensive
view of local and remote factors of climate change in China must take
account of this as well as other natural and anthropogenic forcings.
---------------------------------------------------------
Title: Temporal derivative of Total Solar Irradiance and anomalous
Indian summer monsoon: An empirical evidence for a Sun-climate
connection
Authors: Agnihotri, Rajesh; Dutta, Koushik; Soon, Willie
2011JASTP..73.1980A Altcode:
Identifying the pattern of natural climate variability is of
immense importance to delineate the effects of anthropogenic climate
changes. Global and regional climates are suspected to vary, in unison
or with delays, with the Total Solar Irradiance (TSI) at decadal to
centennial timescales. Here we show that the Indian summer monsoon
rainfall correlates well with the temporal derivative of TSI on
multi-decadal timescales. This linkage between the temporal derivative
of TSI and the Indian summer monsoon is tested and corroborated both
for the instrumental period (1871-2006) and for the last ∼300 years
using a speleothem δ<SUP>18</SUP>O record representing rainfall
in southwestern India. Our analyses indicate that anomalous dry
periods of the Indian monsoon are mostly coincident with negative
TSI derivative. This study thus demonstrates the potential of ‘TSI
derivative’ as an important indicator of natural monsoon variability
on an interdecadal timescale.
---------------------------------------------------------
Title: Differential rotation of some HK-Project stars and the
butterfly diagrams
Authors: Katsova, M. M.; Livshits, M. A.; Soon, W.; Baliunas, S. L.;
Sokoloff, D. D.
2010NewA...15..274K Altcode:
We analyze the long-term variability of the chromospheric radiation of
20 stars monitored in the course of the HK-Project at the Mount Wilson
Observatory. We apply the modified wavelet algorithm for this set of
gapped time series. Besides the mean rotational periods for all these
stars, we find reliable changes of the rotational periods from year to
year for a few stars. Epochs of slower rotation occur when the activity
level of the star is high, and the relationship repeats again during
the next maximum of an activity cycle. Such an effect is traced in two
stars with activity cycles that are not perfectly regular (but labeled
"Good" under the classification in [Baliunas, S.L., Donahue, R.A.,
Soon, W.H., Horne, J.H., Frazer, J., Woodard-Eklund, L., Bradford, M.,
Rao, L.M., Wilson, O.C., Zhang, Q. et al., 1995. ApJ 438, 269.]) but
the two stars have mean activity levels exceed that of the Sun. The
averaged rotational period of HD 115404 is 18.5 days but sometimes
the period increases up to 21.5 days. The sign of the differential
rotation is the same as the Sun's, and the value ΔΩ / < Ω > =
- 0.14. For the star HD 149661, this ratio is -0.074. Characteristic
changes of rotational periods occur over around three years when the
amplitude of the rotational modulation is large. These changes can
be transformed into latitude-time butterfly diagrams with minimal a
priori assumptions. We compare these results with those for the Sun
as a star and conclude that epochs when surface inhomogeneities rotate
slower are synchronous with the reversal of the global magnetic dipole.
---------------------------------------------------------
Title: The Sun-Climate Connection: A journey from
solar-stellar-galactic astrophysics, to weather-climate continuum
and paleoclimatic-geological insights (Invited)
Authors: Soon, W.
2009AGUFMGC11A0681S Altcode:
I will take a brief tour through some of the latest developments in
solar-stellar-glactic astronomy which include understanding of the
intrinsic variability of the Sun's magnetism, the weather-climate
continuum, and paleoproxies of climate variability and change from
the geological archives. Insights from the orbital theory for the
transition between ice ages and warm interglacial climate will also
be discussed and applied in terms of the framework of the latitudinal
insolation gradient that has been recently proposed by Davis and Brewer
(2009). Empirical evidence and interpretation for solar climatic
responses on a wide range of spatial and temporal scales will be
presented. Related challenges and implications will be discussed.
---------------------------------------------------------
Title: Multiple and changing cycles of active stars. II. Results
Authors: Oláh, K.; Kolláth, Z.; Granzer, T.; Strassmeier, K. G.;
Lanza, A. F.; Järvinen, S.; Korhonen, H.; Baliunas, S. L.; Soon,
W.; Messina, S.; Cutispoto, G.
2009A&A...501..703O Altcode: 2009arXiv0904.1747O
Aims: We study the time variations in the cycles of 20 active stars
based on decade-long photometric or spectroscopic observations. <BR
/>Methods: A method of time-frequency analysis, as discussed in a
companion paper, is applied to the data. <BR />Results: Fifteen stars
definitely show multiple cycles, but the records of the rest are too
short to verify a timescale for a second cycle. The cycles typically
show systematic changes. For three stars, we found two cycles in each
of them that are not harmonics and vary in parallel, indicating a
common physical mechanism arising from a dynamo construct. The positive
relation between the rotational and cycle periods is confirmed for the
inhomogeneous set of active stars. <BR />Conclusions: Stellar activity
cycles are generally multiple and variable.
---------------------------------------------------------
Title: Differential rotation of some HK Project stars and the
butterfly diagrams
Authors: Katsova, M. M.; Livshits, M. A.; Soon, W.; Sokoloff, D. D.
2009AIPC.1094..672K Altcode: 2009csss...15..672K
We analyze the long-term variability of the chromospheric radiation of
20 stars monitored in the course of HK Project. We apply the modified
wavelet algorithm for this set of gapped data. Besides the rotational
periods for all these stars, we find reliable changes of the periods
from year to year for a few stars. Epochs of the slower rotation occur
when the activity level of the star is high, and they come again during
the next maximum of a cycle. Such an effect is traced in two “Good”
stars, whose cycles are not quite regular, but they are more active
than the Sun. So, the mean period of rotation of the star HD 115404
is 18.5 days, and sometimes it does increase up to 21.5 days. The
sign of the differential rotation is the same as one for the Sun,
and ΔΩ/<Ω> = -0.14. For the star HD 149661, this ratio
is -0.074. Characteristic changes of rotational periods occur over
around three years when the amplitude of the rotational modulation is
large. These changes can be transformed into the butterfly diagrams
without a priori assumptions. We compare these results with those for
the Sun as a star and conclude that epochs when surface inhomogeneities
rotate slower are synchronous with reversal of the global magnetic
dipole.
---------------------------------------------------------
Title: Changing stellar activity cycles
Authors: Oláh, K.; Strassmeier, K. G.; Granzer, T.; Soon, W.;
Baliunas, S. L.
2007AN....328.1072O Altcode:
We investigated continuous long-term photometric datasets of thirteen
active stars, Ca II variability of one single main-sequence star, and
10.7cm radio data of the Sun, with simple Fourier- and time-frequency
analysis. The data reflect the strength of the activity manifested
in magnetic spots. All studied stars show multiple (2 to 4) cycles of
different lengths. The time-frequency analysis reveals, that in several
cases of the sample one or two of the cycles exhibit continuous changes
(increase or decrease). For four stars (V711 Tau, IL Hya, HK Lac,
HD 100180) and for the Sun we find that the cycle length changes are
strong, amounting to 10-50% during the observed time intervals. The
cycle lengths are generally longer for stars with longer rotational
periods.
---------------------------------------------------------
Title: Some Issues of Solar Irradiance Variability and Climatic
Responses: A Brief Review
Authors: Soon, W.
2007AGUFMGC42A..05S Altcode:
In this paper, I will overview the difficulties surrounding a
physical understanding of solar irradiance variability to contrast
the superficial results from parametric fitting procedures. Related
problems and consequences will be discussed. I will also offer some
thoughts and empirical evidence for solar climatic responses on a
range of spatial and temporal scales.
---------------------------------------------------------
Title: Patterns of Photometric and Chromospheric Variation among
Sun-like Stars: A 20 Year Perspective
Authors: Lockwood, G. W.; Skiff, B. A.; Henry, Gregory W.; Henry,
Stephen; Radick, R. R.; Baliunas, S. L.; Donahue, R. A.; Soon, W.
2007ApJS..171..260L Altcode: 2007astro.ph..3408L
We examine patterns of variation of 32 primarily main-sequence Sun-like
stars [selected at project onset as stars on or near the main sequence
and color index 0.42<=(B-V)<=1.4], extending our previous 7-12
yr time series to 13-20 yr by combining Strömgren b, y photometry from
Lowell Observatory with similar data from Fairborn Observatory. Parallel
chromospheric Ca II H and K emission data from the Mount Wilson
Observatory span the entire interval. The extended data strengthen
the relationship between chromospheric and brightness variability at
visible wavelengths derived previously. We show that the full range of
photometric variation has probably now been observed for a majority of
the program stars. Twenty-seven stars are deemed variable according
to an objective statistical criterion. On a year-to-year timescale,
young active stars become fainter when their Ca II emission increases,
while older less active stars such as the Sun become brighter when
their Ca II emission increases. The Sun's total irradiance variation,
scaled to the b and y stellar filter photometry, still appears to be
somewhat smaller than stars in our limited sample with similar mean
chromospheric activity, but we now regard this discrepancy as probably
due mainly to our limited stellar sample.
---------------------------------------------------------
Title: Anharmonic and standing dynamo waves: theory and observation
of stellar magnetic activity
Authors: Baliunas, S.; Frick, P.; Moss, D.; Popova, E.; Sokoloff,
D.; Soon, W.
2006MNRAS.365..181B Altcode: 2005MNRAS.tmp.1044B
The familiar decadal cycle of solar activity is one expression of
interannual variability of surface magnetism observed in stars on or
near the lower main sequence. From studies of time-series of CaII
H and K emission fluxes that go back more than 35 yr and have been
accumulated for such stars at the Mount Wilson Observatory by the HK
Project, we define a quantitative measure, called anharmonicity, of
the cyclic component of interannual magnetic variability. Anharmonicity
provides a connection between observed variations in magnetic activity
and the two-dimensional description of a Parker dynamo model. We
explore the parameter space of the Parker dynamo model and find an
excellent counterpart in the records of several of the lowest-mass
(late K-type to early M-type) active stars in the HK Project sample to
the solutions containing highly anharmonic, standing dynamo waves. We
interpret anharmonicity apparent in the records as resulting from
non-propagating or standing dynamo waves, which operate in a regime that
is substantially supercriticial. There, for the majority of a cycle, or
pulse of decadal-to-interdecadal variability, the large-scale magnetic
fields are generated and maintained by winding of field by differential
rotation rather than by the joint action of differential rotation and
helical convection. Among the less active stars (the Sun is considered
such a star in the HK Project sample) we find a correspondence between
anharmonicity and Parker dynamo model solutions that include simple
harmonic, migratory and/or intermediate-type dynamo wave patterns over
a broad range of dynamo parameters.
---------------------------------------------------------
Title: Variable solar irradiance as a plausible agent for multidecadal
variations in the Arctic-wide surface air temperature record of the
past 130 years
Authors: Soon, Willie W. -H.
2005GeoRL..3216712S Altcode:
This letter offers new evidence motivating a more serious consideration
of the potential Arctic temperature responses as a consequence of
the decadal, multidecadal and longer-term persistent forcing by
the ever-changing solar irradiance both in terms of total solar
irradiance (TSI, i.e., integrated over all wavelengths) and the
related UV irradiance. The support for such a solar modulator can
be minimally derived from the large (>75%) explained variance
for the decadally-smoothed Arctic surface air temperatures (SATs) by
TSI and from the time-frequency structures of the TSI and Arctic SAT
variability as examined by wavelet analyses. The reconstructed Arctic
SAT time series based on the inverse wavelet transform, which includes
decadal (5-15 years) and multidecadal (40-80 years) variations and a
longer-term trend, contains nonstationary but persistent features that
are highly correlated with the Sun's intrinsic magnetic variability
especially on multidecadal time scales.
---------------------------------------------------------
Title: Anharmonicity of Stellar Cycles: A Wavelet Quantification
Authors: Baliunas, S.; Frick, P.; Moss, D.; Popova, E.; Sokoloff,
D.; Soon, W.
2004SoPh..224..179B Altcode: 2005SoPh..224..179B
Two quantitative measures for the anharmonicity of stellar cycles,
as recorded in the Ca II H and K chromospheric activity data as well
as in simple dynamo models, are presented and discussed.
---------------------------------------------------------
Title: Time-spectra of chromospheric activity of old solar-type stars:
detection of rotational signals from double wavelet analysis
Authors: Frick, Peter; Soon, Willie; Popova, Elena; Baliunas, Sallie
2004NewA....9..599F Altcode:
We introduce a novel technique, called the double wavelet analysis
(DWA), for the determination of stellar rotation periods from time
serial data. This first paper aims narrowly at the discussion,
introduction and application of the DWA technique to records
of surface magnetism in solar-type (relatively old) lower main
sequence stars that are obtained by the Mount Wilson Observatory
(MWO) HK Project. The technique takes a series of careful steps
that seek to optimize wavelet parameters and normalization schemes,
ultimately allowing fine-tuned, arguably more accurate, estimates of
rotation-modulated signals (with, e.g., periods of days to months)
in records that contain longer periodicities such as stellar magnetic
activity cycles (with, e.g., period of years). The apparent rotation
periods estimated from the DWA technique are generally consistent
with results from both ;first-pass; (i.e., ordinary) global wavelet
spectrum and earlier classical periodogram analyses. But there are
surprises as well. For example, the rotation period of the ancient
subdwarf Goombridge 1830 (HD 103095), previously identified as ≈31
days, suggests under the DWA technique a significantly slower period
of 60 days. DWA spectra also generally reveal a shift in the cycle
period toward high frequencies (hence shorter periods) compared to
the first-pass wavelet spectrum. For solar-type stars analyzed here,
the character of the DWA spectrum and slope of the first-pass global
wavelet spectrum produce a classification scheme that allows a star's
record to be placed into one of three categories.
---------------------------------------------------------
Title: Evolution of morphological features of CMEs deduced from
catastrophe model of solar eruptions
Authors: Lin, J.; Soon, W.
2004NewA....9..611L Altcode:
We describe the evolution of morphological features of the magnetic
configuration of CME according to the catastrophe model developed
previously. For the parameters chosen for the present work, roughly
half of the total mass is nominally contained in the initial flux
rope, while the remaining plasma is brought by magnetic reconnection
from the corona into the current sheet and from there into the CME
bubble. The physical attributes of the difference in the observable
features between CME bubble and flare loop system were studied. We
tentatively identified distinguishable evolutionary features like the
outer shell, the expanding bubble and the flux rope with the leading
edge, void and core of the 3-component CME structure. The role of
magnetic reconnection is discussed as a possible mechanism for the
heating of the prominence material during eruptions. Several aspects
of this explanation that need improvement are outlined.
---------------------------------------------------------
Title: Stellar Magnetic Activity, the Earth and Exoplanets: How
Future Space Missions Can Contribute to Understanding Solar Activity
and Solar-terrestrial Influences
Authors: Baliunas, S. L.; Soon, W. W. -H.
2004AAS...204.0809B Altcode: 2004BAAS...36..790B
The solar spectral and particle output varies over time scales of
minutes to eons; some of those variations are documented or claimed
to have influenced the terrestrial environment. The origins of solar
variability include the progress of fusion through time and the complex
interaction of the interior gas and magnetic fields. The Mount Wilson
HK Project has yielded information on stellar magnetic activity
on more than 2,000 stars going as far back as 38 years in order to
put solar magnetic activity in a physical perspective unavailable
from theory and models alone. We discuss how future space missions
like Space Interferometry Mission (SIM) and Stellar Imager (SI) would
contribute to understanding solar variability that has influenced -- and
should continue to influence -- life and the environment on earth. <P
/>This research funded in part by MIT-MSG 5710001241, JPL 1236821, AF
49620-02-1-0194, a grant from NASA HQ and GSFC to SAO for the SI Vision
Mission Study, NASA NAG5-7635, NRC COBASE, CRDF 322, Richard Lounsberry
Foundation, Langley-Abbot, Rollins, Scholarly Studies and James Arthur
Funds (Smithsonian Institution) and several generous individuals.
---------------------------------------------------------
Title: Estimation and representation of long-term (>40 year) trends
of Northern-Hemisphere-gridded surface temperature: A note of caution
Authors: Soon, Willie W. -H.; Legates, David R.; Baliunas, Sallie L.
2004GeoRL..31.3209S Altcode: 2004GeoRL..3103209S
Several quantitative estimates of surface instrumental temperature
trends in the late 20th century are compared by using published
results and our independent analyses. These estimates highlight a
significant sensitivity to the method of analysis, the treatment of
data, and the choice of data presentation (i.e., size of the smoothing
filter window). Providing an accurate description of both quantitative
uncertainties and sensitivity to the treatment of data is recommended
as well as avoiding subjective data-padding procedures.
---------------------------------------------------------
Title: Year Without a Summer
Authors: Soon, Willie; Yaskell, Steven
2003Mercu..32c..13S Altcode:
A weak solar maximum, a major volcanic eruption, and possibly even
the wobbling of the Sun conspired to make the summer of 1816 one of
the most miserable ever recorded.
---------------------------------------------------------
Title: Theories of solar eruptions: a review
Authors: Lin, J.; Soon, W.; Baliunas, S. L.
2003NewAR..47...53L Altcode:
This review highlights current theoretical research on eruptive
phenomena in the solar atmosphere. We start by looking back upon the
early theories and their development. Any theory and model of solar
eruptions must explain two key aspects of eruption physics. The first
aspect concerns the original cause of the eruption and the second
pertains to the nature of the morphological features that form during
its evolution. Those features include rapid ejection of large-scale
magnetic flux and plasma into interplanetary space, and the separating
of ribbons of H α emission on the solar disk joined by a rising arcade
of soft X-ray and H α loops, with hard X-ray emission at their summits
and feet. We intercompare relevant theories and models by discussing
their advantages as well as by pointing out important aspects that
need improvement.
---------------------------------------------------------
Title: Proxy climatic and environmental changes of the past 1000 years
Authors: Soon, W.; Baliunas, S. L.
2003ClRe...23...89S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Reconstructing climatic and environmental changes of the past
1000 years: A reappraisal
Authors: Soon, W.; Baliunas, S. L.; Idso, C.; Idso, S.; Legates, D.
2003En&En..14..233S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Maunder Minimum and the Variable Sun-Earth Connection
Authors: Soon, Willie Wei-Hock; Yaskell, Steven H.
2003mmvs.book.....S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Global warming
Authors: Soon, W.; Baliunas, S. L.
2003PrPhG..27..448S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Gauging the Sun: Comparative photometric and magnetic activity
measurements of sunlike stars, 1984-2001
Authors: Lockwood, G. W.; Hall, J. C.; Skiff, B. A.; Henry, G. W.;
Radick, R. R.; Baliunas, S. L.; Soon, W.; Donahue, R. A.
2002AAS...200.0709L Altcode: 2002BAAS...34..651L
Visible light photometric observations of a small sample of
sunlike stars with mean chromospheric activity levels similar to or
slightly lower than the Sun's suggest that total solar irradiance
variations on activity cycle timescales may be comparatively small
(Lockwood et al. 1992, Nature 360, 653; Radick et al. 1998, ApJS 118,
239). The Sun's irradiance variation over the past two cycles is
0.04% rms compared with 0.1% rms for the stellar sample measured at
Lowell from 1984 to 1995. This assertion can now be tested using new
photometric measurements from Fairborn Observatory automated telescopes
(1993-2001) that extend the duration of stellar observations to 17
years. Chromospheric activity measurements for these stars come from
the Mount Wilson HK program (1966-2001) and the Lowell Observatory
Solar Stellar Spectrograph program (1993-2001). In this presentation
we will describe efforts to merge the overlapping Lowell and Fairborn
photometry and the Mt. Wilson and Lowell HK measurements with the
goal of reducing the uncertainties in previous efforts to characterize
stellar photometric variations near the limit of detection.
---------------------------------------------------------
Title: Sources of solar variability responsibile for global warming
of the upper ocean on decadal period scales
Authors: White, W.; Dettinger, M.; Soon, W.; Baliunas, S.
2002cosp...34E1318W Altcode: 2002cosp.meetE1318W
Global-average warming and cooling of upper ocean temperature on decadal
period scales of ~0.1 K are aligned with decadal changes in the SunSs
irradiance of ~0.5 W m-2 throughout the 20th Century at lags ranging
from 0 to 18 months. This apparent upper ocean temperature response
to solar forcing is ~3 times that expected from the Stefan-Boltzmann
radiation balance for the EarthSs surface. Yet, this global-average
temperature change is a small residual in the spatial integration
of relatively large temperature changes of O(1.0 K) associated with
a global pattern of variability that is similar to that of the El
Nino-Southern Oscillation (Tourre et al., 2001). Since the latter
exhibits global-average warming and cooling of 0.2 K in the absence
of solar forcing (White et al., 2001), the SunSs decadal signal
needs simply to excite this particular decadal mode in the EarthSs
ocean-atmosphere-terrestrial system in order to produce the observed
global-average temperature change. The question is, by what mechanism
does it do this? Here we examine the global-average diabatic heat
storage budget for the upper ocean on decadal period scales using the
NCEP/NCAR atmospheric reanalysis and the SIO oceanic reanalysis. First,
we find the global-average variability dominated by the tropical
global-average. Second, we find the peak tropical warm phase associated
with higher troposphere moisture content and cloud fraction, driven
by an increase in outgoing sensible-plus-latent heat flux and
outgoing longwave-minusshortwave radiative heat flux of comparable
magnitudes. The sources of the anomalous warming tendency during the
onset phase is the reduction in the net poleward Ekman heat flux out
of the tropics and the reduction in outgoing sensible-plus-latent
heat flux of similar magnitude, both in response to reduced trade
wind intensity. Thus, the increase in cloud fraction during the peak
tropical warm phase does not heat the underlying ocean, as assumed
by Marsh and Svensmark (2000). Rather, the reduction in trade wind
intensity during the onset phase is consistent with that simulated
by Haigh (1996) in response to heating of the lower stratosphere by
the UV portion of the total solar irradiance spectrum. Here we find
a slow downward propagation of zonal wind anomalies from the lower
stratosphere to the lower troposphere contributing to this reduction
in trade wind intensity.
---------------------------------------------------------
Title: Reply to Comments on "Modeling climatic effects of
anthropogenic CO2 emissions: Unknowns and uncertainties
Authors: Risbey, James; Soon, W.; Baliunas, S.; Idso, S. B.;
Kondratyev, K. Ya.; Posmentier, E. S.
2002ClRe...22..187R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Modeling climatic effects of anthropogenic CO2 emissions:
Unknows and uncerta inties
Authors: Soon, W.; Baliunas, S.; Demirchan, K. S.; Idso, S. B.;
Kondratyev, K. Ya.; Posmentier, E. S.
2001ClRe...18..259S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Global Climate Change: Conceptual Aspects, 2001
Authors: Kondratyev, K. Ya.; Adamenko, V. N.; Demirchian, K. S.;
Baliunas, S.; Boehmer-Christiansen, S.; Idso, S. B.; Kukla, G.;
Posmentier, E. S.; Soon, W.
2001rass.rept.....K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The impact of anthropogenic CO2 emissions: Unknows and
uncertainties
Authors: Soon, W.; Baliunas, S.; Demirchan, K. S.; Idso, S. B.;
Kondratyev, K. Ya.; Posmentier, E. S.
2001PRGS..133....1S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar and Space Weather (or SOLSPA) EuroConference: The Solar
and Terrestrial Climate
Authors: Soon, W.
2001sefp.conf...91S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Curious case of the carbon forest source
Authors: Baliunas, S.; Soon, W.
2000WCRp....6f...3B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Millennial climate
Authors: Baliunas, S.; Soon, W.
2000WCRp....6b...3B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: 100000110011 (Computer Year 2099)
Authors: Baliunas, S.; Soon, W.
2000WCRp....5v...3B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Man vs. Milky Way revisited
Authors: Baliunas, S.; Soon, W.
2000WCRp....5s...3B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Climate hypersensitivity to solar forcing?
Authors: Soon, W.; Posmentier, E.; Baliunas, S.
2000AnGeo..18..583S Altcode:
We compare the equilibrium climate responses of a quasi-dynamical
energy balance model to radiative forcing by equivalent changes in
CO2, solar total irradiance (Stot) and solar UV (SUV). The response is
largest in the SUV case, in which the imposed UV radiative forcing is
preferentially absorbed in the layer above 250 mb, in contrast to the
weak response from global-columnar radiative loading by increases in
CO2 or Stot. The hypersensitive response of the climate system to solar
UV forcing is caused by strongly coupled feedback involving vertical
static stability, tropical thick cirrus ice clouds and stratospheric
ozone. This mechanism offers a plausible explanation of the apparent
hypersensitivity of climate to solar forcing, as suggested by analyses
of recent climatic records. The model hypersensitivity strongly depends
on climate parameters, especially cloud radiative properties, but
is effective for arguably realistic values of these parameters. The
proposed solar forcing mechanism should be further confirmed using
other models (e.g., general circulation models) that may better capture
radiative and dynamical couplings of the troposphere and stratosphere.
---------------------------------------------------------
Title: The Trouble with Ozone
Authors: Baliunas, S.; Soon, W.
2000WCRp....5o...3B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Photometric and Ca II H and K Spectroscopic Variations in
Nearby Sun-like Stars with Planets. III.
Authors: Henry, Gregory W.; Baliunas, Sallie L.; Donahue, Robert A.;
Fekel, Francis C.; Soon, Willie
2000ApJ...531..415H Altcode:
We present the results of an analysis of time-series photometry, Ca
II H and K spectrophotometry, and high-dispersion visible spectra of
nine nearby Sun-like stars recently identified as having planets. For
the six stars whose presumed planets have orbital periods of less than
4 months (τ Boo, 51 Peg, υ And, ρ<SUP>1</SUP> Cnc, ρ CrB, and 70
Vir), sine-curve fits to the photometric data show no variations with
semiamplitude greater than 1 or 2 parts in 10<SUP>4</SUP>. Photometric
variations in 47 UMa are similarly small, although our photometric data
of this star are slightly affected by variability of the comparison
star. Nonvariability at this level of precision is sufficient to
rule out surface magnetic activity as the cause of the observed
radial-velocity variations in these seven stars and makes nonradial
pulsations unlikely as well. Thus, our photometry provides indirect
but strong support for true reflex motions-planets-in these seven
stars, but cannot yet so support the planetary hypothesis for the two
additional stars, 16 Cyg B and Gl 411. Continued photometric monitoring
of the short-period systems may soon result in the direct detection of
these planets in reflected light. We have used our photometric fluxes
to search for possible transits of the extrasolar planets. Transits
definitely do not occur in τ Boo, 51 Peg, υ And, and ρ<SUP>1</SUP>
Cnc, and probably do not occur in ρ CrB and 70 Vir. Our transit-search
results are inconclusive for 47 UMa, and we cannot address the issue for
16 Cyg B and Gl 411. The precision of our photometry is sufficient to
detect transits of planets even if they are not gas giants, as currently
assumed, but much smaller objects with rocky compositions. The chance
of finding at least one transit in the six stars is ~40%. We find
significant year-to-year photometric variability only in τ Boo,
which is not only the youngest star in the sample but also the star
with the shallowest convective zone. The interseasonal range in its
yearly mean photometric flux is ~0.002 mag, roughly twice the 0.0008
mag decadal variation in the Sun's total irradiance. Monitoring of
the relative Ca II H and K fluxes began between 1966 and 1968 for 51
Peg, τ Boo, ρ CrB, and Gl 411, between 1990 and 1993 for 47 UMa,
70 Vir, 16 Cyg B, and ρ<SUP>1</SUP> Cnc, and in 1996 for υ And. The
data have been newly recalibrated for improved long-term instrumental
stability, resulting in better precision of the Ca II records. Five of
the nine stars in this study have little or no detectable year-to-year
variation in Ca II flux. The remaining four show moderate or pronounced
variability: τ Boo, whose radial-velocity and photometric variations
have comparatively high amplitudes; Gl 411, whose planetary companion
was inferred astrometrically, not spectroscopically; ρ<SUP>1</SUP>
Cnc, which may undergo decadal cyclic activity; and υ And, which shows
moderate year-to-year variability. Except for 47 UMa, intraseasonal
variability consistent with rotation was detected in the Ca II records
of all stars. However, the rotation periods determined for υ And,
70 Vir, and 16 Cyg B are of low confidence. An examination of the
recalibrated Ca II records for 51 Peg finds a rotation period of 22
days, in contrast to our previous result of 37 days. Ages have been
estimated from the mean Ca II flux and, where possible, the rotation
period. We find general consistency with the ages determined by others
comparing properties determined from high-resolution spectroscopy
to evolutionary models, although the uncertainties are, in general,
large. Based on observations made at Mount Wilson Observatory, operated
by the Mount Wilson Institute, under an agreement with the Carnegie
Institution of Washington and the automatic photoelectric telescope
at Fairborn Observatory in the Patagonia Mountains of southern Arizona.
---------------------------------------------------------
Title: Calculating the Climatic Impacts of Increased CO<SUB>2</SUB>:
the Issue of Model Validation
Authors: Soon, W.; Baliunas, S.; Idso, S. B.; Kondratyev, K. Ya.;
Posmentier, E. S.
2000ESASP.463..243S Altcode: 2000sctc.proc..243S
No abstract at ADS
---------------------------------------------------------
Title: The rains of Ranchipur
Authors: Baliunas, S.; Soon, W.
2000WCRp....5j...3B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The sun also warms
Authors: Baliunas, S.; Soon, W.
2000stcl.rept...21B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Variations of solar coronal hole area and terrestrial lower
tropospheric air temperature from 1979 to mid-1998: astronomical
forcings of change in earth's climate?
Authors: Soon, W.; Baliunas, S.; Posmentier, E. S.; Okeke, P.
2000NewA....4..563S Altcode:
The temperature anomaly of the terrestrial lower troposphere,
inferred from the Microwave Sounding Unit (MSU) radiometers, is
found to be inversely correlated with the area of the Sun covered
by coronal holes. The correlation between the monthly time series of
global tropospheric temperature anomaly and total coronal hole area
from January 1979 to April 1998 has a Pearson coefficient of -0.46,
which is different from zero at a 95% confidence level. Physical
reasonings for the explained and unexplained parts of the correlation
are discussed. The coronal hole area is a physical proxy for both the
global-scale, 22-yr geometrical and shorter-term, dynamical components
of the cosmic ray modulation, as well as the corpuscular emission of
the Sun. Other solar parameters that may indicate a solar radiative
effect on climate are also evaluated. It is concluded that variable
fluxes either of solar charged particles or cosmic rays modulated by
the solar wind, or both, may influence the terrestrial tropospheric
temperature on timescale of months to years.
---------------------------------------------------------
Title: Generations of Hurricanes
Authors: Baliunas, S.; Soon, W.
1999WCRp....5f...3B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Almighty Chance and the Dance of El Nino
Authors: Baliunas, S.; Soon, W.
1999WCRp....5d...3B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Pioneers in the Greenhouse Effect
Authors: Baliunas, S.; Soon, W.
1999WCRp....4s....B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Pioneers in the Greenhouse Effect
Authors: Baliunas, S.; Soon, W.
1999WCRp....4S...6B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Mysteries of Carbon Dioxide
Authors: Baliunas, S.; Soon, W.
1999WCRp....4R...6B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Aerosols are Cool
Authors: Baliunas, S.; Soon, W.
1999WCRp....4k...6B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Aerosols are Cool
Authors: Baliunas, S.; Soon, W.
1999WCRp....4Q...6B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Lifetime of Surface Features and Stellar Rotation: A Wavelet
Time-Frequency Approach
Authors: Soon, Willie; Frick, Peter; Baliunas, Sallie
1999ApJ...510L.135S Altcode: 1998astro.ph.11114S
We explore subtle variations in disk-integrated measurements spanning
<~18 yr of stellar surface magnetism by using a newly developed
time-frequency gapped wavelet algorithm. We present results based on
analysis of the Mount Wilson Ca II H and K emission fluxes in four,
magnetically active stars (HD 1835 [G2 V], HD 82885 [G8 IV-V], HD
149661 [K0 V], and HD 190007 [K4 V]) and sensitivity tests using
artificial data. When the wavelet basis is appropriately modified
(i.e., when the time-frequency resolution is optimized), the results
are consistent with the existence of spatially localized and long-lived
Ca II features (assumed here as activity regions that tend to recur
in narrowly confined latitude bands), especially in HD 1835 and HD
82885. This interpretation is based on the observed persistence of
relatively localized Ca II wavelet power at a narrow range of rotational
timescales, enduring as long as >~10 yr.
---------------------------------------------------------
Title: Silvery-blue Cloudlets of the Night
Authors: Baliunas, S.; Soon, W.
1999WCRp....4....5B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Environmental effects of increased atmospheric carbon dioxide
Authors: Soon, W.; Baliunas, S.; Robinson, A.; Robinson, Z. W.
1999ClRe...13..149S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Cold World: Model Analysis shows icy trend
Authors: Baliunas, S.; Soon, W.
1998WCRp....4g...6B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Cycles of the Sun.
Authors: Soon, W.; Yaskell, S. H.
1998AsNow..12S..15S Altcode: 1998AstNw..12S..15S
Edward Maunder noted that the Sun has times of very low sunspot
activity. Is the Earth's climate affected by this?
---------------------------------------------------------
Title: The Miner's Canary is Still Singing
Authors: Baliunas, S.; Soon, W.
1998WCRp....4c...6B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The summer of our discontent
Authors: Baliunas, S.; Soon, W.
1998WCRp....3c..10B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The life and times of Alfonso Nino and family
Authors: Baliunas, S.; Soon, W.
1998WCRp....3s..10B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Milky Way and the clouds of Earth
Authors: Baliunas, S.; Soon, W.
1998WCRp....3o..10B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Nature speaks of many things, Of missing flux and butterfly
wings
Authors: Baliunas, S.; Soon, W.
1998WCRp....3k...6B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Environmental effects of increased atmospheric carbon dioxide
Authors: Robinson, A.; Baliunas, S. L.; Soon, W.; Robinson, Z. W.
1998MeSen...3..171R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Activity Cycles in Lower Main Sequence and POST Main Sequence
Stars: The HK Project
Authors: Baliunas, Sallie L.; Donahue, Robert A.; Soon, Willie; Henry,
Gregory W.
1998ASPC..154..153B Altcode: 1998csss...10..153B
In 1966, Olin Wilson began making monthly measurements at Mount Wilson
Observatory of the relative fluxes in the Ca II H (396.8 nm) and K
(393.3 nm) emission cores of approximately 100 stars on or near the
lower main sequence. In the late 1970's the Ca II fluxes of nearly
1,000 lower main-sequence stars were sampled, and by 1980 the program
had expanded to include near-nightly observations of the stars in
Wilson's sample. In 1984 the project was again extended to include the
measurement of post-main sequence stars. Today, the project monitors the
Ca II fluxes of 400 dwarf and giant stars, with great emphasis on stars
close in mass and age to the Sun. The relative Ca II fluxes are thought
to closely correspond to the strength and coverage of surface magnetism
on such stars. Three general classes of long-term variations of surface
magnetism have been seen in lower main sequence and post main sequence
stars: 1. substantial fluctuations on time scales of a few years,
with little observed repitition of periodicity; 2. nearly-periodic
variations with time scales of a decade or more, with some variability
in the amplitude, length and shape of each successive cycle; 3. either
low-amplitude modulation on time scales of several decades or more,
or essentially no long-term variability. In the lower main-sequence
stars both the class of long-term variability and the time-averaged
level of Ca II fluxes are influenced primarily by a star's angular
momentum. In a related matter, most of the detected extra-solar planets
(with orbital periods ranging from 3 to 1200 days) orbit sun-like stars
with long-term Ca II flux records that are virtually flat (Class 3,
above). The lack of variability is an observational bias that enhances
detection of extra-solar planets orbiting sun-like stars.
---------------------------------------------------------
Title: Maunder's Minimum: Cycles of the Sun
Authors: Soon, W.; Yaskell, S. H.
1998AsNow..12...15S Altcode: 1998AstN...12...15S; 1998AstNw..12...15S
No abstract at ADS
---------------------------------------------------------
Title: Wavelet Analysis of Stellar Chromospheric Activity Variations
Authors: Frick, P.; Baliunas, S. L.; Galyagin, D.; Sokoloff, D.;
Soon, W.
1997ApJ...483..426F Altcode:
Observations of chromospheric activity variations for some lower
main-sequence stars from the Mount Wilson Observatory's HK project
reveal a cyclic behavior comparable to the sunspot cycle. Even in
the relatively short interval that they have been observed, those
stars show stellar cycles and other features, like grand minima. The
quasi-periodic nature of such variations is not completely compatible
with the standard Fourier analysis, so we applied a wavelet analysis
to study the nature of regularities in the data. We computed wavelet
transforms and energy spectra for the 25 yr records of surface magnetic
activity in four stars: HD 3651, HD 10700, HD 10476, and HD 201091. We
present a modified wavelet technique that is suitable for analysis of
data with gaps and find that the common aliasing problems due to the
finite length of the observations and irregularly spaced gaps between
data can be reduced on both large and small scales by applying this
algorithm.
---------------------------------------------------------
Title: Time scales and trends in the central England temperature data
(1659-1990): A wavelet analysis
Authors: Baliunas, Sallie; Frick, Peter; Sokoloff, Dmitry; Soon, Willie
1997GeoRL..24.1351B Altcode:
We have applied the standard wavelet and the adaptive wavelet transform
algorithms to the record of the Central England Temperature (CET) from
1659-1990. Peaks in the CET spectra include 7.5±1.0 yr, 14.4±1.0
yr, 23.5±2.0 yr, as well as a previously unreported variation at
102±15 yr. Our wavelet analysis of CET agrees with previous results
from Singular Spectrum Analysis (SSA) by Plaut et al. [1995] and gives
additional results of variability on longer timescales. The interdecadal
and century-scale variability in CET is strongly dependent on the
interval of analysis. Estimates of a data trend are also shown to
be sensitive to the cutoff timescale of the filter. A cooling of ≈
0.3°C during 1659-1720 is found relative to the temperatures during
the 1800s. The complex time dependence of the actual data cautions
against using model-derived representations of natural variability on
such long timescales.
---------------------------------------------------------
Title: Magnetic Field and Rotation in Lower Main-Sequence Stars:
an Empirical Time-dependent Magnetic Bode's Relation?
Authors: Baliunas, Sallie; Sokoloff, Dmitry; Soon, Willie
1996ApJ...457L..99B Altcode:
We find a significant correlation between the magnetic and rotational
moments for a sample of 112 lower main-sequence stars. The rotational
moment is calculated from measurements of the rotation period in most
of the stars (not from the projected rotational velocity inferred
from Doppler broadening). The magnetic moment is computed from a
database of homogeneous measurements of the mean level of Ca II H
and K emission fluxes sampled for most of the stars over an interval
of 25 yr. The slope connecting the logarithm of the magnetic moment
and the logarithm of the rotational moment is about +0.5--0.6, with a
Pearson correlation coefficient of about +0.9. The scatter of points
from the mean relation has a component that is natural and caused by
decade-long surface variability.
---------------------------------------------------------
Title: The Sun-Climate Connection
Authors: Baliunas, Sallie; Soon, Willie
1996S&T....92...38B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Interpretation of stellar Ca II activity cycles.
Authors: Baliunas, S. L.; Nesme-Ribes, E.; Sokoloff, D.; Soon, W.
1996sube.conf...57B Altcode:
Twenty-five year records of Ca II H and K chromospheric emission
fluxes measured in lower main-sequence stars reveal surface magnetic
activity cycles which are comparable to that of the Sun's. The observed
variations can be interpreted in terms of stellar dynamo theory. The
authors find the ratio of the period of stellar cycle to the period
of stellar axial rotation, P<SUB>cyc</SUB>/P<SUB>rot</SUB>, to be
representative of a stellar dynamo number, D.
---------------------------------------------------------
Title: Chaos in the Sun: Is Solar Cycle Understandable? How Can
Watching Stars Help?
Authors: Soon, W.
1996cfas.book..110S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Are Variations in the Length of the Activity Cycle Related
to Changes in Brightness in Solar-Type Stars?
Authors: Baliunas, Sallie; Soon, Willie
1995ApJ...450..896B Altcode:
We compare the average level of chromospheric activity and cycle
length for solar-type stars as determined from 25 yr records of Ca
II fluxes and from the sunspot record from 1750 to 1990. Both sets
of data show an inverse relation between the cycle length and average
activity level, with only a minor difference in the slopes. In turn,
the amplitude of Ca II variability is positively correlated with
the photometric brightness change during an activity cycle. The
relationship between those observables provides a physical basis for
the close correlation between the length of the sunspot cycle and
mean terrestrial temperature over the last few centuries as shown by
Friis-Christensen & Lassen. <P />Solar brightness variations over
the last several centuries can be estimated from this relationship by
including stars with low Ca II fluxes which, we assume, are in states
resembling the phase of solar activity known as the Maunder minimum
(circa 1645-1715). Although the value of the slope connecting the
mean level of Ca II activity and the cycle length is sensitive to the
statistical treatment of the data, a lower limit to the slope can be
determined reliably. This lower limit yields an increase of 0.4% of
solar brightness from the solar Maunder minimum to the cyclic phase
of sunspot activity which immediately followed the Maunder minimum.
---------------------------------------------------------
Title: A Study of Variability in a Sample of G and K Giants
Authors: Choi, Hyung-Jin; Soon, Willie; Donahue, Robert A.; Baliunas,
Sallie L.; Henry, Gregory W.
1995PASP..107..744C Altcode:
Eight years of Ca II surface activity records from Mount Wilson
Observatory measured for 12 bright G-K III stars have been analyzed
in order to detect periodic variations attributable to rotation. We
also present photometric V-band data for these stars from the
Fairborn 0.25m Automatic Photometric Telescope (APT) that yielded
a photometric period in one case and rms deviations from apparently
constant brightness levels for the remaining 11 stars. The Ca II data
yielded rotation periods for 10 out of 12 giant stars. We demonstrate
that the photometric variability and non-variability of these stars
can be predicted from their Rossby numbers calculated from our observed
rotation periods and convective turnover times scaled up from the main
sequence. (SECTION: Stars)
---------------------------------------------------------
Title: Chromospheric Activity and Age of Solar-Type Stars
Authors: Baliunas, S. L.; Donahue, R. A.; Soon, W.; Gilliland, R.;
Soderblom, D. R.
1995AAS...186.2109B Altcode: 1995BAAS...27..839B
Main-sequence stars near one solar mass show an average level of Ca
II H and K emission and rotation that decrease with age. Although the
mechanism governing surface magnetism and rotation is not theoretically
well-understood, the measurement of rotation or average activity
level can yield an estimate of the age of a solar-mass star. Several
empirically-determined functions of the decay of rotation and activity
have been developed over the last several decades, but more have
concentrated on stars much younger than the Sun, whose Ca II activity
and rotation have been relatively easy to measure. Observations of the
Ca II H and K emission were obtained of solar-mass stars in the old
open clusters NGC 752 and M 67 with the KPNO 4-m telescope and HYDRA
spectrograph. Those spectra yield a large (>50) smaple of stars
close to one solar mass and close to the age of the Sun. Those spectra
have been calibrated to the system of measurement of Ca II H and K
emission fluxes of nearly 1000 lower main sequence stars obtained at
Mount Wilson Observatory. The combined sample of Ca II fluxes yield:
(1) a refined calibration of age as a function of activity, using
rotation as an indicator of age; (2) the range of Ca II activity at a
given age, caused by variations of surface magnetic activity over time
scales of decades to centuries; and (3) an estimate of the uncertainty
of age inferred from a measurement of the instantaneous activity level.
