Author name code: brekke ADS astronomy entries on 2022-09-14 author:"Brekke, Pal" ------------------------------------------------------------------------ Title: Norway's most celebrated scientist Authors: Southwood, David; Brekke, Pâl Bibcode: 2017A&G....58e5.28S Altcode: David Southwood and Pål Brekke celebrate the life of Kristian Birkeland. Title: The Total Solar Eclipse on Svalbard 2015 Authors: Sigernes, F.; Ellingsen, P. G.; Holmen, S. E.; Brekke, P.; Danielsen, A.; Olsen, B.; Syrjäsuo, M.; Chen, X.; Dyrland, M. E.; Partamies, N.; Baddeley, L. J.; Lorentzen, D. A.; Krogtoft, M. A.; Dragland, T.; Mortensson, H.; Smistad, L.; Oksavik, K.; Heinselman, C. J.; Habbal, S. R. Bibcode: 2015AGUFMSH52A..02S Altcode: This work reports the results from a multi-instrumental campaign that was planned and executed to record the Total Solar Eclipse that occurred on Friday 20th of March 2015 in Longyearbyen (78oN, 15oE) on Svalbard, Norway. Both airborne hyperspectral- and ground-based camera systems were used to image the event. A novel video accumulation filter technique is presented that reveals small scale chromospheric features. The result is fused with a High Dynamic Range (HDR) image of the Corona taken from the old Auroral Station in Adventdalen. The Kjell Henriksen Observatory (KHO) was also operative, but did not detect any dayside auroral signatures. The background sky condition was too bright during totality for the auroral cameras. The airborne hyperspectral data is used to cluster and classify active solar regions with prominences from the background continuum. Title: National Report Norway: Arctic Access to Space Authors: Brekke, P. Bibcode: 2015ESASP.730...43B Altcode: Norway has long traditions as a space nation, much due to our northern latitude. Our space science activities are concentrated into relatively few areas. This concentration is necessary due to limited resources, both in funding and personnel. The main scientific activities are within Solar-terrestrial physics and cosmology. The first field has been a priority since before the space age and is still the major priority. The usage of the ground infrastructure in Northern Norway and on Svalbard is essential in studying the middle and upper atmosphere and the interaction with the Sun. This includes the utilization of sounding rockets, both small and large, and ground based installations like radars, lidars and other optical instrumentation. The planned use of Svalbard as a launch site for large stratospheric balloons may allow the cosmology community access to our northern infrastructure. The solar physics community is also heavily involved in the HINODE and IRIS missions and Norway is supporting downlink of data via the Svalbard Station for these missions. The sounding rocket program is in close collaboration with many countries like Germany, USA, France, Canada and Japan. Two scientific sounding rocket programs are currently being pursued: The ICI series (from Svalbard) and MaxiDusty (from Andoya). A series of scientific publications have recently appeared from the ECOMA campaign a few years ago. A significant improvement of today's polar and ionospheric research infrastructure in Northern Norway and Svalbard has recently been put on the ESFRI roadmap for European research infrastructure through the 5105 and EISCAT 3D initiatives. The Norwegian government has recently decided to upgrade the VLBI facilities at Svalbard. Title: Variable Cascade Dynamics and Intermittency in the Solar Wind at 1 AU Authors: Sigernes, F.; Ellingsen, P. G.; Holmen, S. E.; Brekke, P.; Danielsen, A.; Olsen, B.; Syrjäsuo, M.; Chen, X.; Dyrland, M. E.; Partamies, N.; Baddeley, L. J.; Lorentzen, D. A.; Krogtoft, M. A.; Dragland, T.; Mortensson, H.; Smistad, L.; Oksavik, K.; Heinselman, C. J.; Habbal, S. R. Bibcode: 2014AGUFMSH52A..02S Altcode: This work reports the results from a multi-instrumental campaign that was planned and executed to record the Total Solar Eclipse that occurred on Friday 20th of March 2015 in Longyearbyen (78oN, 15oE) on Svalbard, Norway. Both airborne hyperspectral- and ground-based camera systems were used to image the event. A novel video accumulation filter technique is presented that reveals small scale chromospheric features. The result is fused with a High Dynamic Range (HDR) image of the Corona taken from the old Auroral Station in Adventdalen. The Kjell Henriksen Observatory (KHO) was also operative, but did not detect any dayside auroral signatures. The background sky condition was too bright during totality for the auroral cameras. The airborne hyperspectral data is used to cluster and classify active solar regions with prominences from the background continuum. Title: The Interface Region Imaging Spectrograph (IRIS) Authors: De Pontieu, B.; Title, A. M.; Lemen, J. R.; Kushner, G. D.; Akin, D. J.; Allard, B.; Berger, T.; Boerner, P.; Cheung, M.; Chou, C.; Drake, J. F.; Duncan, D. W.; Freeland, S.; Heyman, G. F.; Hoffman, C.; Hurlburt, N. E.; Lindgren, R. W.; Mathur, D.; Rehse, R.; Sabolish, D.; Seguin, R.; Schrijver, C. J.; Tarbell, T. D.; Wülser, J. -P.; Wolfson, C. J.; Yanari, C.; Mudge, J.; Nguyen-Phuc, N.; Timmons, R.; van Bezooijen, R.; Weingrod, I.; Brookner, R.; Butcher, G.; Dougherty, B.; Eder, J.; Knagenhjelm, V.; Larsen, S.; Mansir, D.; Phan, L.; Boyle, P.; Cheimets, P. N.; DeLuca, E. E.; Golub, L.; Gates, R.; Hertz, E.; McKillop, S.; Park, S.; Perry, T.; Podgorski, W. A.; Reeves, K.; Saar, S.; Testa, P.; Tian, H.; Weber, M.; Dunn, C.; Eccles, S.; Jaeggli, S. A.; Kankelborg, C. C.; Mashburn, K.; Pust, N.; Springer, L.; Carvalho, R.; Kleint, L.; Marmie, J.; Mazmanian, E.; Pereira, T. M. D.; Sawyer, S.; Strong, J.; Worden, S. P.; Carlsson, M.; Hansteen, V. H.; Leenaarts, J.; Wiesmann, M.; Aloise, J.; Chu, K. -C.; Bush, R. I.; Scherrer, P. H.; Brekke, P.; Martinez-Sykora, J.; Lites, B. W.; McIntosh, S. W.; Uitenbroek, H.; Okamoto, T. J.; Gummin, M. A.; Auker, G.; Jerram, P.; Pool, P.; Waltham, N. Bibcode: 2014SoPh..289.2733D Altcode: 2014arXiv1401.2491D; 2014SoPh..tmp...25D The Interface Region Imaging Spectrograph (IRIS) small explorer spacecraft provides simultaneous spectra and images of the photosphere, chromosphere, transition region, and corona with 0.33 - 0.4 arcsec spatial resolution, two-second temporal resolution, and 1 km s−1 velocity resolution over a field-of-view of up to 175 arcsec × 175 arcsec. IRIS was launched into a Sun-synchronous orbit on 27 June 2013 using a Pegasus-XL rocket and consists of a 19-cm UV telescope that feeds a slit-based dual-bandpass imaging spectrograph. IRIS obtains spectra in passbands from 1332 - 1358 Å, 1389 - 1407 Å, and 2783 - 2834 Å, including bright spectral lines formed in the chromosphere (Mg II h 2803 Å and Mg II k 2796 Å) and transition region (C II 1334/1335 Å and Si IV 1394/1403 Å). Slit-jaw images in four different passbands (C II 1330, Si IV 1400, Mg II k 2796, and Mg II wing 2830 Å) can be taken simultaneously with spectral rasters that sample regions up to 130 arcsec × 175 arcsec at a variety of spatial samplings (from 0.33 arcsec and up). IRIS is sensitive to emission from plasma at temperatures between 5000 K and 10 MK and will advance our understanding of the flow of mass and energy through an interface region, formed by the chromosphere and transition region, between the photosphere and corona. This highly structured and dynamic region not only acts as the conduit of all mass and energy feeding into the corona and solar wind, it also requires an order of magnitude more energy to heat than the corona and solar wind combined. The IRIS investigation includes a strong numerical modeling component based on advanced radiative-MHD codes to facilitate interpretation of observations of this complex region. Approximately eight Gbytes of data (after compression) are acquired by IRIS each day and made available for unrestricted use within a few days of the observation. Title: Secrets of the Northern Lights Authors: Brekke, Pål Bibcode: 2013S&T...125b..18B Altcode: No abstract at ADS Title: Our Explosive Sun Authors: Brekke, Pål Bibcode: 2012oes..book.....B Altcode: No abstract at ADS Title: Two methods to forecast auroral displays Authors: Sigernes, Fred; Dyrland, Margit; Brekke, Pål; Chernouss, Sergey; Lorentzen, Dag Arne; Oksavik, Kjellmar; Sterling Deehr, Charles Bibcode: 2011JSWSC...1A..03S Altcode: This work compares the methods by Starkov (1994a) and Zhang & Paxton (2008), that calculate the size and location of the auroral ovals as a function of planetary Kp index. The ovals are mapped in position and time onto a solar illuminated surface model of the Earth. It displays both the night- and dayside together with the location of the twilight zone as Earth rotates under the ovals. The graphical display serves as a tool to forecast auroral activity based on the predicted value of the Kp index. The forecast is installed as a service at http://kho.unis.no/. The Zhang & Paxton (2008) ovals are wider in latitude than the Starkov (1994a) ovals. The nightside model ovals coincide fairly well in shape for low to normal auroral conditions. The equatorward border of the diffuse aurora is well defined by both methods on the nightside for Kp ≤ 7. The dayside needs further studies in order to conclude. Title: Norwegian National Report- Arctic Access to Space Authors: Brekke, P. Bibcode: 2011ESASP.700...23B Altcode: No abstract at ADS Title: Solar radiation and human health Authors: Juzeniene, Asta; Brekke, Pål; Dahlback, Arne; Andersson-Engels, Stefan; Reichrath, Jörg; Moan, Kristin; Holick, Michael F.; Grant, William B.; Moan, Johan Bibcode: 2011RPPh...74f6701J Altcode: The Sun has played a major role in the development of life on Earth. In Western culture, people are warned against Sun exposure because of its adverse effects: erythema, photoimmunosuppression, photoageing, photocarcinogenesis, cataracts and photokeratitis. However, Sun exposure is also beneficial, since moderate doses give beneficial physiological effects: vitamin D synthesis, reduction of blood pressure and mental health. Shortage of Sun exposure may be even more dangerous to human health than excessive exposure. Avoiding Sun exposure leads to vitamin D deficiency which is associated not only with rickets and osteomalacia, but also with increased risk of cardiovascular disease, multiple sclerosis, rheumatoid arthritis, diabetes, influenza, many types of cancer and adverse pregnancy outcomes. Solar radiation induces nitric oxide release in tissue and immediate pigment darkening which certainly play important roles, although these are still unknown. Action spectra relevant for health are described. We will also review what is known about spectral and intensity variations of terrestrial solar radiation as well as its penetration through the atmosphere and into human skin and tissue. Title: International Living With a Star Authors: Brekke, Pål Bibcode: 2005ESASP.590..623B Altcode: 2005erbp.conf..623B The response of our space environment to the constantly changing Sun is known as "Space Weather". Sudden ejections of plasma and magnetic field structures from the Sun's atmosphere called coronal mass ejections (CMEs) together with sudden bursts of radiation termed solar flares all cause space weather effects at the Earth. The International Living With a Star (ILWS) programme is a space weather focused and applications driven research programme. Its goal is to develop the scientific understanding necessary to effectively address those aspects of the connected Sun-Earth system that directly affects life and society. Recent large solar storms caused damages to power systems and satellites and disturbed important navigation and communication systems. Furthermore, accurate monitoring of the energy output from the Sun is important for understanding how the Sun contributes to the observed warming of our planet. The Sun is a variable star we better learn how to live with. Title: Space Weather Effects on SOHO and its Leading Role as a Space Weather Wãtchdog Authors: Brekke, P.; Fleck, B.; Haugan, S. V.; van Overbeek, T.; Schweitzer, H.; Simonin, B. Bibcode: 2005mcsp.conf...83B Altcode: No abstract at ADS Title: Closing remarks on the Sun influence on climate changes. Authors: Brekke, P. Bibcode: 2005MmSAI..76..913B Altcode: Numerous attempts have been made over the years to link various aspects of solar variability to changes in the Earth's climate. Since the Sun's output of electromagnetic radiation and energetic particles varies, and since the Sun is the ultimate driver for the climate system, it seems natural to link the two together and look for the source of climate variability in the Sun itself. In recent years there has been a growing concern about the possible anthropogenic forcing of climate change through the increasing atmospheric content of greenhouse gases. This has made the connection between solar variability and global climate change a very controversial research area. This conference brings together the solar and climate community to present the most recent results gained on the knowledge of solar variability and the effects on the Earth's climate system. From the presentations it appears that the understanding have come a long way, with the Sun driving global warming in the early part of the last century and anthropogenic effects taking over in the second half. However, it is also evident that we need to improve our knowledge about historic solar and temperature proxy data. Furthermore we need to better understand the atmospheric response to variations in the ultraviolet and extreme ultraviolet radiation and the physics of cloud formation. Title: The Suns Halloween Scare and the Media Frenzy Authors: Brekke, P. Bibcode: 2004AGUSMSH32A..01B Altcode: SOHO appeared to be in everyone's focus this fall as the Sun turned from an almost spotless orb into an ominously scarred source of mighty fireworks in just a few days. Over two weeks, it featured three unusually large sunspot groups (including the largest one of this solar cycle), 11 X-class flares (including the strongest ever recorded), numerous halo CMEs (two with near-record speeds) and two significant proton storms which lasted for a combined five days. Satellites, power grids, radio communication and navigation systems were significantly affected in this period. The events caused unprecedented attention from the media and the public. Images from SOHO as well as quotes from SOHO scientists appeared in nearly every major news outlet (CNN, BBC, Associated Press, Reuters, to mention a few). Stories including SOHO images made the front page of newspapers and were featured prominently on including USA Today and The Washington Post. NASA estimated that the story reached "all" US newspapers and 2000 US TV channels. Media coverage in Europe was also impressive. The attention wiped out all existing SOHO web traffic records Title: The Role of the Sun in Climatic Change Authors: Kirby, A.; Brekke, P. Bibcode: 2003ESASP.519E...2K Altcode: 2003niyf.conf....2K No abstract at ADS Title: Search for a chromospheric resonator above sunspots Authors: Brynildsen, N.; Maltby, P.; Brekke, P.; Redvik, T.; Kjeldseth-Moe, O. Bibcode: 2003AdSpR..32.1097B Altcode: We have recently observed thirteen sunspots, both with CDS on SOHO and TRACE. For each sunspot we investigate the oscillations in the chromosphere, transition region and corona. Above the umbra the power spectra show one dominant peak corresponding to a period of 3 minutes. The intensity oscillation amplitude increases with increasing temperature, reaches a maximum for lines emitting close to 1-2 × 10 5 K, and decreases for higher temperatures. Part of the wave energy penetrates into the corona, channeled into small areas that appear to coincide with the endpoints of sunspot coronal loops. The observations support the hypothesis that the oscillations are caused by upwardly propagating acoustic waves and show no signs of the resonances, equally spaced ≈1 mHz in frequency, predicted by the chromospheric resonator theories. Title: UV spectroscopy with SOHO Authors: Harra, L. K.; Brekke, P. Bibcode: 2003AdSpR..32..965H Altcode: The UV spectroscopy from SOHO has provided new and exciting results from a wide range of phenomena observed on the Sun. Determination of plasma parameters such as velocity, density, temperatures, line widths and abundances have provided new physical insight into fundamental problems in solar physics. These include magnetic reconnection, quiet Sun coronal heating, active region dynamics, flows in solar flares, formation of the solar wind, determination of coronal mass ejection onset, characteristics of coronal waves and the twisting of magnetic structures. This paper will review these results and discuss what can be achieved with future spectroscopic instrumentation. Title: Sunspot Oscillations and Acoustic Wave Propagation Authors: Brekke, P.; Brynildsen, N.; Maltby, P.; Fredvik, T.; Kjeldseth-Moe, O. Bibcode: 2003SPD....34.0401B Altcode: 2003BAAS...35..810B Observations with the Coronal Diagnostic Spectrometer of 3 min oscillations in sunspot umbrae support the hypothesis that they are caused by upwardly propagating acoustic waves. This is evident from the asymmetry of oscillation amplitudes in the red and blue wings of spectral lines, where the oscillations are decidedly more pronounced in the blue than in the red line wing. Additional evidence include the fact that the relation between oscillations in intensity and velocity agree with that predicted for an acoustic wave with regard to phase as well as magnitude. Finally, the observed phase difference between lines formed at different temperatures points to an upward propagating disturbance, and the value of dominant frequency of the oscillations, close to 6 mHz, is above the acoustic cutoff frequency in the sunspot atmosphere. SOHO is a mission of international cooperation between ESA and NASA. This study was supported by the Research Council of Norway. Title: The 6 mHz Oscillations above Sunspots Authors: Brekke, P.; Brynildsen, N.; Maltby, P.; Fredvik, T.; Kjeldseth-Moe, O. Bibcode: 2002AAS...200.8806B Altcode: 2002BAAS...34..790B Sunspot oscillations in the transition region and corona are observed simultaneously with CDS on SOHO and TRACE. Results obtained from investigations of ten sunspots in 2001 and 2002 are presented. We find that the oscillation amplitude above the umbra increases with increasing temperature, reaches a maximum for lines emitted close to 200 000 K, and decreases for higher temperatures. Part of the wave energy penetrates into the corona, channeled into small areas that appear to coincide with the endpoints of sunspot coronal loops. The observed power spectra show one dominating peak, near 6 mHz, and not several, equally spaced resonances as predicted by theories based on the idea of a chromospheric resonator. We conclude that the observations are compatible with upwardly propagating acoustic waves. Title: Variability and dynamic state of active region loops Authors: Fredvik, T.; Kjeldseth-Moe, O.; Haugan, S. V. H.; Brekke, P.; Gurman, J. B.; Wilhelm, K. Bibcode: 2002AdSpR..30..635F Altcode: A set of 218 consecutive CDS rasters taken at the solar limb on October 26-28 1999 has been used to investigate the variability and plasma dynamics of active region loops. Each raster contains simultaneous images in 6 different lines, covering the full temperature range of CDS, 10 000 K (He I) to 2.7 MK (Fe XVI). Activity is seen to go on without breaks at temperatures below 1 MK for the full 39 hours of the series. Transition region loops or extended sections of loops, 50-200 Mm long, appear and disappear in intervals as short as 11 minutes, the observing cadence. In the corona the emission is less variable, but significant changes are seen. Measured Doppler shifts correspond to typical plasma velocities of 20 km s -1 to 100 km s -1, at temperatures 10 000 K to 450 000 K, and siphon flows may occur in some of the loops. High velocities are frequently seen where the emitted intensities are weak, often on the outer edges of loops as defined in that particular spectral line. At coronal temperatures, 1 MK and higher, systematic loop velocities occur only occasionally. Simultaneous observations with EIT and SUMER were made during part of the raster series and are compared with the CDS result. Title: Space Weather Effects and how Soho has Improved the Warnings Authors: Brekke, P. Bibcode: 2002stma.conf..385B Altcode: No abstract at ADS Title: Solar eruptions - the effects on the Earth's environment Authors: Brekke, P. Bibcode: 2002HiA....12..384B Altcode: The response of our space environment to the constantly changing Sun is known as "Space Weather". The Solar and Heliospheric Observatory (SOHO) has obtained significant new information about coronal mass ejections (CMEs), the source of the most severe disturbances in the Earth's environment. Most of the time space weather is of little concern in our everyday lives. However, when the space environment is disturbed by the variable outputs of the Sun, technologies that we depend on both in orbit and on the ground can be affected. The increasing deployment of radiation-, current-, and field-sensitive technological systems over the last few decades and the increasing presence of complex systems in space combine to make society more vulnerable to solar-terrestrial disturbances. Thus, our society is much more sensitive to space weather activity today compared to the last solar maximum. By observing the Sun 24 hours per day, SOHO has proved to be an important "space weather watchdog". The importance of real-time monitoring of the Sun will be pointed out and a number of enterprises affected by space weather will be discussed. Title: EUV irradiance measurements from SOHO during Cycle 23 Authors: Brekke, P.; Thompson, W.; Pap, J.; McMullin, D. Bibcode: 2002cosp...34E..97B Altcode: 2002cosp.meetE..97B EUV irradiance variability of the double peak feature of cycle 23 is presented. EUV irradiance measurements are being made from SOHO on a regular basis by the Solar Extreme-Ultra-Violet Monitor (SEM) and the Coronal Diagnostic Spectrometer (CDS). SEM continuously measures the full solar disk absolute photon flux at the prominent and scientifically important He II 304 A line, as well as the absolute integral flux between 1 and 500 A. CDS produces full disk spectra in two bands in the range 307-380 A and 515-632 A. The "Sun as a Star" spectrum has been made roughly once a month starting 25 March 1997 to present. As well as irradiance values, the most recent observations also provide moderate resolution solar images to help quantify the important sources of irradiance variability. The EUV irradiance variability is compared to measurements of total irradiance from VIRGO and other solar cycle indices such as sunspot number, magnetic field measurements, and the 10.7 radio flux. Title: The Sun During The Ulysses Fast Latitude Scan and Northern Polar Pass As Seen By Soho Authors: Fleck, B.; Brekke, P.; Haugan, S. V. H. Bibcode: 2002EGSGA..27.3839F Altcode: In 2001, during the Ulysses fast latitude scan (January - September) and second north- ern polar pass (September - December), the Sun showed a remarkable resurgence of solar activity after its rapid drop-off following the activity maximum in the summer of 2000. In early April active region 9393, the largest active region of the current cycle, produced a series of events, among them the biggest X-ray flare on record. In the fall there were three severe proton storms, one of them the third largest on record since measurements began in 1976. It is interesting to note that five out of the eight proton storms with flux densities greater than 10,000 cm-2 s-1 sr-1 (>10 MeV) since 1976 occurred in cycle 23, and three of these five in 2001. The overall change in solar ac- tivity in 2001 will be reviewed and some of the most dramatic events from that year discussed. Title: From Solar Min To Solar Max: Half A Solar Cycle of Soho Observations Authors: Brekke, P. Bibcode: 2002EGSGA..27.1316B Altcode: The Solar and Heliospheric Observatory (SOHO) has provided an unparalleled breadth and depth of information about the Sun, from its interior, through the hot and dynamic atmosphere, out to the solar wind. Analysis of the helioseismology data from SOHO has shed new light on a number of structural and dynamic phenomena in the solar interior, such as the absence of differential rotation in the radiative zone, subsur- face zonal and meridional flows, sub-convection-zone mixing, a possible circumpolar jet, and very slow polar rotation. Evidence for an upward transfer of magnetic energy from the Sun's surface toward the corona has been established. The ultraviolet in- struments have revealed an extremely dynamic solar atmosphere where plasma flows play an important role. Electrons in coronal holes were found to be relatively `cool', whereas heavy ions are extremely hot and have highly anisotropic velocity distribu- tions. The source regions for the high speed solar wind has been identified and the acceleration profiles of both the slow and fast solar wind have been measured. This presentation will summarize some of the findings from the SOHO mission from the past six years. Title: The Solar Inner Corona and Transition Region Observed with SOHO Authors: Brekke, P. Bibcode: 2002cosp...34E..98B Altcode: 2002cosp.meetE..98B Recent sophisticated space missions have clearly changed our view of the solar transition region. In particular the ESA/NASA Solar and Heliospheric Observatory (SOHO) and NASA's TRACE satellite has provided a unique opportunity to explore solar atmosphere in detail. The combination of high spatial, spectral and temporal observations has made it possible to derive three dimensional images of emission, velocity and line widths of solar features. Active region loop structures at transition region temperatures appear to be extremely time variable and dynamic, a result with profound implications for our understanding and modeling of the upper solar atmosphere. Large line of sight Dopplershifts have also been observed in these structures. A 3 minute transition region oscillation has been observed above sunspots suggesting upward-propagating acoustic waves. Clear evidences of velocity oscillations in the internetwork regions has also been observed in both the chromosphere and the transition region. The longstanding puzzling problem, the apparent net redshift of emission lines in the transition region has been revisited. The extensive wavelength coverage of the SOHO spectrometers has made it possible to extend the measurements to much higher temperatures compared to previous instruments. The combination of magnetograms, EUV spectral imaging and the high resolution broad-band images from TRACE has also given us new insight concerning the structure of the transition region and it's relation with the photospheric magnetic filed. In this review I will present some recent results based on SOHO observation with particular emphasis on the dynamics of active regions loop systems. Title: Space Weather Effects on SOHO Authors: Brekke, P.; Fleck, B.; Haugan, S.; Schweitzer, H.; Chaloupy, M. Bibcode: 2002cosp...34E2156B Altcode: 2002cosp.meetE2156B Since its launch on 2 December 1995, the Solar and Heliospheric Observatory (SOHO) has provided an unparalleled breadth and depth of information about the Sun, from its interior, through the hot and dynamic atmosphere, and out to the solar wind. SOHO is in a halo orbit around L1 Lagrangian point where it views the Sun 24 hours a day. Thus, it is situated outside the Earth's protective magnetosphere which shields other satellites from high energy particles from the Sun. We present a summary of the observed effects on the instruments and electronics on SOHO throughout the mission. In particular we will focus on a number of large particle events during the recent years while the Sun was approaching maximum activity, and how they affected both the scientific data as well as hardware components. Title: Search for a chromospheric resonator above sunspots Authors: Brynildsen, N.; Maltby, P.; Brekke, P.; Fredvik, T.; Kjeldseth-Moe, O. Bibcode: 2002cosp...34E.178B Altcode: 2002cosp.meetE.178B We have recently observed eleven sunspots, both with CDS on SOHO and TRACE as part of our on-going investigations of the sunspot atmosphere. For each sunspot we investigate the oscillations in the chromosphere, transition region and corona. The observed power spectra show one dominating peak corresponding to a period of 3 minutes. The oscillation amplitude above the umbra increases with increasing temperature, reaches a maximum for lines emitting close to 200 000 K, and decreases for higher temperatures. Part of the wave energy penetrates into the corona, channeled into small areas that appear to coincide with the endpoints of sunspot coronal loops. The observations support the hypothesis that the oscillations are caused by upwardly propagating acoustic waves and show no signs of equally spaced resonances as predicted by theories based on the idea of a chromospheric resonator. Title: The SUMER spectral atlas of solar-disk features Authors: Curdt, W.; Brekke, P.; Feldman, U.; Wilhelm, K.; Dwivedi, B. N.; Schühle, U.; Lemaire, P. Bibcode: 2001AIPC..598...45C Altcode: 2001sgc..conf...45C A far-ultraviolet and extreme-ultraviolet (FUV, EUV) spectral atlas of the Sun between 670 Å and 1609 Å in first order of diffraction has been derived from observations obtained with the SUMER (Solar Ultraviolet Measurements of Emitted Radiation) spectrograph on the spacecraft SOHO (Solar and Heliospheric Observatory) [1]. The atlas contains spectra of the average quiet Sun, a coronal hole and a sunspot on disk. Different physical parameters prevalent in the bright network (BN) and in the cell interior (CI)-contributing in a distinct manner to the average quiet-Sun emission-have their imprint on the BN/CI ratio, which is also shown for the entire spectral range. With a few exceptions, all major lines are given with their identifications and wavelengths. Lines that appear in second order are superimposed on the first order spectra, but below 500 Å the responsivity of the normal-incidence optical system is very low. The spectra include emissions from atoms and ions in the temperature range 6 103 K to 2 106 K, i.e., continua and mission lines emitted from the lower chromosphere to the corona. This spectral atlas, with its broad wavelength coverage, provides a rich source of new diagnostic tools for studying the physical parameters in the chromosphere, the transition region and the corona. In particular, the wavelength range below 1100 Å as observed by SUMER represents a significant improvement over the spectra produced in the past. In view of the manifold appearance and temporal variation of the solar atmosphere it is obvious that our atlas can only be a-hopefully typical-snapshot. The spectral radiances are determined with a relative uncertainty of 0.15 to 0.30 (1σ), and the wavelength scale is accurate to typically 10 mÅ, which is the level achievable with semi-automatic processing. The SUMER solar-disk spectral atlas will be published in the near future by Curdt et al. [2]. It includes profiles of the average quiet Sun, an equatorial coronal hole, and a sunspot. As an example we show in Fig. 1 the spectral range from 1300 Å to 1342 Å with the prominent O I and C II lines. Resolved emission lines are indicated by a mark, the measured wavelength in angstrom, and the identification, if available. Marks point to line lists available in the literature, where additional information about a specific line can be found [3-7]. New lines or identifications are indicated. Lines observed in first order and in second-order of diffraction are distinguished. Only the three least-significant digits of the wavelength values are given. If available, unidentified lines are characterized by the temperature classification defined in [3] (a: Te<3 105 b: Te~3 105 c: Te~4 105 d: 6 105<Te <9 105 e: Te~1.4 106 f: Te~1.8 106). The vertical axes are scaled to spectral radiance in units of mW sr-1 m-2 Å-1 on the left the radiometric calibration for first order lines is given, on the right for second order lines. Note, that second order lines are always superimposed on a first order background. We have taken care of the type of photocathode (bare or KBr) when applying the radiometric calibration to different sections of the spectrum. Also displayed in green is the BN/CI ratio in an attempt to characterize the quiet-Sun chromospheric network structure. A pre-print of the SUMER spectral atlas and a line list is available at http://www.linmpi.mpg.de/~curdt. . Title: The SUMER spectral atlas of solar-disk features Authors: Curdt, W.; Brekke, P.; Feldman, U.; Wilhelm, K.; Dwivedi, B. N.; Schühle, U.; Lemaire, P. Bibcode: 2001A&A...375..591C Altcode: A far-ultraviolet and extreme-ultraviolet (FUV, EUV) spectral atlas of the Sun between 670 Å and 1609 Å in the first order of diffraction has been derived from observations obtained with the SUMER (Solar Ultraviolet Measurements of Emitted Radiation) spectrograph on the spacecraft SOHO (Solar and Heliospheric Observatory). The atlas contains spectra of the average quiet Sun, a coronal hole and a sunspot on the disk. Different physical parameters prevalent in the bright network (BN) and in the cell interior (CI) - contributing in a distinct manner to the average quiet-Sun emission - have their imprint on the BN/CI ratio, which is also shown for almost the entire spectral range. With a few exceptions, all major lines are given with their identifications and wavelengths. Lines that appear in second order are superimposed on the first order spectra. These lines are clearly marked in the atlas. The spectra include emissions from atoms and ions in the temperature range 6*E3 K to 2*E6 K, i.e., continua and emission lines emitted from the lower chromosphere to the corona. This spectral atlas, with its broad wavelength coverage, provides a rich source of new diagnostic tools to study the physical parameters in the chromosphere, the transition region and the corona. In particular, the wavelength range below 1100 Å as observed by SUMER represents a significant improvement over the spectra produced in the past. In view of the manifold appearance and temporal variation of the solar atmosphere, it is obvious that our atlas can only be a - hopefully typical - snapshot. Brief descriptions of the data reduction and calibration procedures are given. The spectral radiances are determined with a relative uncertainty of 0.15 to 0.30 (1sigma ) and the wavelength scale is accurate to typically 10 mÅ. The atlas is also available in a machine readable form. Table A.1 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/375/591 Title: VizieR Online Data Catalog: SUMER Spectral Atlas of Solar Disk Features (Curdt+, 2001) Authors: Curdt, W.; Brekke, P.; Feldman, U.; Wilhelm, K.; Dwivedi, B. N.; Schuhle, U.; Lemaire, P. Bibcode: 2001yCat..33750591C Altcode: List of spectral lines in the wavelength range from 668Å to 1611Å identified in SUMER (Solar Ultraviolet Measurements of Emitted Radiation, spectrograph on the spacecraft SOHO) spectra of the average quiet Sun (QS), a coronal hole (CH) and a sunspot on disk (SS). Spectral lines observed in second order of diffraction which are also given here, extend the lower wavelength limit to below 500Å. For each entry we give the observed wavelengths in angstrom, the identification, the transition, the peak of spectral radiance, Lpeak, in mW/(sr*m2*Å) (incl. background), and a cross-reference to other line lists available in the literature (cf., Sect. 5.1). For second-order lines radiance entries are generally not provided, since the background separation in both orders of diffraction is a non-trivial task, which can not be automated. Only a few radiance values of strong second-order lines with negligible first-order contribution are given, which are marked by an asterisk (*). (1 data file). Title: From solar min to solar max: half a solar cycle of SOHO observations Authors: Brekke, P.; Fleck, B. Bibcode: 2001ICRC...27I..21B Altcode: The Solar and Heliospheric Observatory (SOHO) has provided an unparalleled breadth and depth of information about the Sun, from its interior, through the hot and dynamic atmosphere, out to the solar wind. Analysis of the helioseismology data from SOHO has shed new light on a number of structural and dynamic phenomena in the solar interior, such as the absence of differential rotation in the radiative zone, subsurface zonal and meridional flows, subconvection-zone mixing, a possible circumpolar jet, and very slow polar rotation. Evidence for an upward transfer of magnetic energy from the Sun's surface toward the corona has been established. The ultraviolet instruments have revealed an extremely dynamic solar atmosphere where plasma flows play an important role. Electrons in coronal holes were found to be relatively `cool', whereas heavy ions are extremely hot and have highly anisotropic velocity distributions. The source regions for the high speed solar wind has been identified and the acceleration profiles of both the slow and fast solar wind have been measured. This paper tries to summarize some of the findings from the SOHO mission from the past five years. Title: Impact of SOHO, TRACE and Yohkoh on Solar Physics (CD-ROM Directory: contribs/brekke) Authors: Brekke, P. Bibcode: 2001ASPC..223..311B Altcode: 2001csss...11..311B No abstract at ADS Title: Recent insights into the physics of the sun and heliosphere : highlights from SOHO and other space missions : IAU Symposium 203, proceedings of the 24th General Assembly of the IAU held at Manchester, United Kingdom, 7-11 August 2000 Authors: Brekke, Pål; Fleck, Bernhard; Gurman, Joseph B. Bibcode: 2001IAUS..203.....B Altcode: No abstract at ADS Title: Transition Region Flows Authors: Brekke, P. Bibcode: 2000eaa..bookE2266B Altcode: Ultraviolet emission lines emitted from the SOLAR TRANSITION REGION are often shifted from their expected rest wavelengths. Shifts of spectral lines are due to the so-called DOPPLER EFFECT, where the source of emission is moving either away from or towards the observer, causing a change in the apparent wavelength. The shifted emission lines are most often interpreted as a flow of plasma along ... Title: Solar Spectroscopy: Ultraviolet and Extreme Ultraviolet Emission Authors: Brekke, P. Bibcode: 2000eaa..bookE2233B Altcode: Vacuum ultraviolet (VUV) emission is defined as that electromagnetic radiation with wavelengths shorter than 2000 Å. Its name comes from the fact that light shorter than 2000 Å is strongly absorbed by most gases and, in particular, the atmosphere. VUV is usually divided into far ultraviolet (FUV) extending from 1200 to 2000 Å and the extreme ultraviolet (EUV) in the range 300 to 1200 Å. The spec... Title: EUV Full-Sun Imaged Spectral Atlas Using the SOHO Coronal Diagnostic Spectrometer Authors: Thompson, William T.; Brekke, Pål Bibcode: 2000SoPh..195...45T Altcode: The Coronal Diagnostic Spectrometer (CDS) aboard the Solar and Heliospheric Observatory (SOHO) carries out a regular program of measuring the full-disk irradiance using the Normal Incidence Spectrograph (NIS). The full-disk solar spectrum is returned in the wavelength bands 308-379 Å and 513-633 Å, with a spectral resolution between 0.3 and 0.6 Å. A recent modification to the CDS on-board software allows simultaneous moderate resolution monochromatic images to be made of the stronger lines in these wavelength ranges. We report on observations made 23 April 1998, 21 May 1998, and 22 June 1998. A total of 69 monochromatic full-Sun images are extracted from the spectral line data. For the first time, spectrally resolved images of the full Sun in He ii 303.8 Å and Si xi 303.3 Å are presented and compared. Velocity maps of the Sun in singly ionized helium are presented. Correlations of intensity to velocity over a wide range of transition region and coronal temperatures are shown. Lines from He i to Fe xiv show statistical red shifts of 1-7 km s−1 between active regions and quiet Sun areas. Velocity maps of Mg ix and x are presented, showing strong upflow and downflow regions associated with active regions, but not correlated with the brightest emission. Changes in line width are also presented in He i, with discussion of similar features in other lines of comparable temperature. Corrections which need to be applied to CDS/NIS data to extract meaningful velocities and line widths are presented and discussed. The identifications of the lines in the CDS spectrum are examined. The spatial and spectral variation of the background component of the CDS spectrum is examined. Title: The Extreme-Ultraviolet Solar Irradiance Spectrum Observed with the Coronal Diagnostic Spectrometer (CDS) on SOHO Authors: Brekke, P.; Thompson, W. T.; Woods, T. N.; Eparvier, F. G. Bibcode: 2000ApJ...536..959B Altcode: We present a calibrated solar EUV irradiance spectrum in the ranges 307-380 Å and 515-632 Å. The ``Sun as a star'' spectrum was recorded by the Coronal Diagnostic Spectrometer (CDS) on SOHO on 1997 May 15 using the normal incidence spectrometer (NIS) with a spectral resolution between 0.3 and 0.6 Å. The relatively high spectral resolution allows the separation of blends and the differentiation of weak emission lines. The full-disk spectrum is compared with simultaneous well-calibrated EUV irradiance measurements from a NASA/LASP rocket payload to validate the preflight calibration of CDS. Significant errors in the preflight calibration were found, and a new calibration has been established for the CDS/NIS system. The present spectrum includes emission lines formed in the temperature range 104 to over 106 K. Line fluxes for the most prominent lines are extracted for the calibration and for the solar irradiance studies. This measurement should represent well solar minimum conditions as the daily 10.7 cm radio flux was 73 (units of 10-22 W m-2 Hz-1). A modest spatial resolution, constrained by the observing mode used, allows for the discrimination between quiet and active sun. The calibrated quiet-Sun irradiance spectrum is compared with previous measurements. Title: Observed Variability and Dynamics of Active Region Loops Authors: Haugan, S. V. H.; Brekke, P.; Fredvik, T.; Kjeldseth-Moe, O.; Wilhelm, K.; Gurman, J. B. Bibcode: 2000SPD....31.0205H Altcode: 2000BAAS...32..811H A series of 218 rasters taken with the Coronal Diagnostic Spectrometer (CDS) on SOHO demonstrates the strong time variability and dynamical state of the plasma in active region loops at transition region temperatures, i.e. 10 000 K to 500 000 K, first reported by Kjeldseth-Moe and Brekke (1998). The continuous raster series, which covered 39 hours, show how transition region loops or sections of loops, 50-200 Mm in length, appear and disappear in intervals as short as 10 minutes, the observing cadence. At the same temperatures plasma velocities of 20 km s-1 to 100 km s-1 are indicated from observed Doppler shifts. Siphon flows may occur in some of the loops, but in other loops patterns are less obvious. High velocities are frequently seen where the emitted intensities are weak, often on the ``outside'' of the loops as defined by the emission in that particular spectral line. At coronal temperatures the emission is less time variable, but significant changes are seen. Systematic loop velocities occur only occasionally in the corona. Simultaneous observations with EIT and SUMER were made during part of the raster series and is compared with the CDS result. Title: EUV irradiance variations measured with the SOHO Coronal Diagnostic Spectrometer Authors: Brekke, P.; Thompson, W. T. Bibcode: 2000SPD....3102114B Altcode: 2000BAAS...32S.831B The Coronal Diagnostic Spectrometer aboard the Solar and Heliospheric Observatory observes the solar EUV spectrum in two bands between 308--379 { Angstroms} and 513--633 { Angstroms}. The full Sun irradiance can be measured by rastering the instrument over the solar disk. Measurements of the solar irradiance have been made starting 25 March 1997 and continuing to the present, ranging from very quiet to very active Sun. These measurements are the only current EUV spectral irradiance measurements taken on a regular basis. As well as irradiance values, the most recent observations also provide moderate resolution solar images to help quantify the important sources of the irradiance variability. The dependence of individual spectral lines on the solar cycle is presented, spanning the temperature range from 3 x 104 K to 2.7 x 106 K. The important spectral lines of He II and Si XI at 304 { Angstroms} are observed in second order and separated. The high spectral resolution of these measurements, combined with the coverage of a significant proportion of the solar cycle, provide a unique dataset for understanding solar variability in the EUV. In addition, these data are important input for interpreting data from broadband and lower resolution irradiance monitors, such as the SOHO SEM and TIMED. Title: Four years of SOHO discoveries - some highlights. Authors: Fleck, B.; Brekke, P.; Haugan, S.; Duarte, L. S.; Domingo, V.; Gurman, J. B.; Poland, A. I. Bibcode: 2000ESABu.102...68F Altcode: Analysis of the helioseismic data from SOHO has shed new light on solar and heliosheric physics: the structure and dynamics of the solar interior, the heating and dynamics of the solar corona, and the acceleration and composition of the solar wind. Title: EUV Irradiance Variations Measured with the SOHO Coronal Diagnostic Spectrometer Authors: Thompson, W. T.; Brekke, P. Bibcode: 2000ESASP.463..435T Altcode: 2000sctc.proc..435T No abstract at ADS Title: Signatures of Magnetic Reconnection and Observed EUV Emission Line Profiles in An Active Region Authors: Brekke, P.; Brynildsen, N.; Kjeldseth-Moe, O.; Maltby, P.; Wilhelm, K. Bibcode: 2000AdSpR..26..457B Altcode: We report on observations with SUMER on SOHO of high-velocity events, also called explosive events. The high spatial and spectral resolutions of SUMER allow simultaneous observations of EUV emission lines formed at different temperatures within the transition region. Complex line profiles with three separate line components appear to be a characteristic feature of many high-velocity events based on a survey of Si IV λ1393 observations. The present study is based on 551 spectra of the active region NOAA 7995 obtained on 17 November 1996. We find that the complex line profiles of explosive events may be represented by a composite line profile consisting of three Gaussian line components. Both positive and negative line-of-sight velocities are found to be significantly larger at 6.3 ×105 K than at 1.5 - 1.7 ×105 K. We briefly confront the observations with signatures predicted from magnetic reconnections, disturbances originating in the corona and flows in an extremely structured transition region Title: Structure and Dynamics in the Atmosphere Above Sunspot Regions Authors: Brynildsen, N.; Brekke, P.; Haugan, S. V. H.; Kjeldseth-Moe, O.; Maltby, P.; Wikstøl, Ø. Bibcode: 2000AdSpR..25.1743B Altcode: Based on simultaneous observations of 10 EUV emission lines with the Coronal Diagnostic Spectrometer - CDS on the Solar and Heliospheric Observatory - SOHO we study the spatial distributions of both line emission and line-of-sight velocity in the atmosphere above 17 sunspots. We find that both the enhanced EUV line emissions and the velocities are distributed non-uniformly over the sunspot regions. Areas with enhanced line emission tend to be red shifted, but they seldom coincide exactly with areas with enhanced velocity. Bright sunspot plumes with motion directed away from the observer are observed in most of the sunspot regions Title: Solar Eruptions-the effects on the Earth's environment Authors: Brekke, P. Bibcode: 2000IAUJD...7E...9B Altcode: The response of our space environment to the constantly changing Sun is known as "Space Weather". The Solar and Heliospheric Observatory (SOHO) has obtained significant new information about coronal mass ejections (CME's), the source to the most severe disturbances in the Earth's environment. Most of the time space weather is of little concern in our everyday lives. However, when the space environment is disturbed by the variable outputs of the Sun, technologies that we depend on both in orbit and on the ground can be affected. The increasing deployment of radiation-, current-, and field-sensitive technological systems over the last few decades and the increasing presence of complex systems in space combine to make society more vulnerable to solar-terrestrial disturbances. Thus, our society is much more sensitive to space weather activity today compared to the last solar maximum. By observing the Sun 24 hours per day SOHO has proved to be an important ``space weather watchdog''. The importance of real-time monitoring of the Sun will be pointed out and a number of enterprises affected by space weather will be discussed. Title: Observations of Transition Region Plasma Authors: Brekke, Pâl Bibcode: 1999SoPh..190..379B Altcode: Recent space missions have changed our view of the solar transition region. In particular the ESA/NASA Solar and Heliospheric Observatory (SOHO) and NASA's TRACE satellite have provided a unique opportunity to explore the solar atmosphere in detail. The combination of high spatial, spectral and temporal observations has made it possible to derive three dimensional images of the emission and velocity structures of solar features. Active region loop structures at transition region temperatures appear to be extremely time variable and dynamic, a result with profound implications for our understanding and modeling of the upper solar atmosphere. Large Dopplershifts have also been observed in these structures. A 3-minute transition region oscillation has been observed above sunspots suggesting upward-propagating acoustic waves. Clear evidence of velocity oscillations in the internetwork regions has also been observed in both the chromosphere and the transition region. The longstanding and puzzling problem of the apparent net red shift of emission lines from the transition region has been revisited. The extensive wavelength coverage of the SOHO spectrometers has made it possible to extend the measurements to much higher temperatures compared to previous instruments. The combination of magnetograms, EUV spectral imaging and the high resolution broad-band images from TRACE has also given us new insight concerning the structure of the transition region and its relation with the photospheric magnetic field. Title: The SUMER EUV Atlas in the Spectral Range 670 A - 1498 A Authors: Curdt, W.; Brekke, P.; Schühle, U.; Wilhelm, K.; Dwivedi, B. N. Bibcode: 1999ESASP.446..251C Altcode: 1999soho....8..251C An extreme ultraviolet spectral atlas between 660 and 1600 A (first order) of a quiet Sun, a coronal hole, and a Sun spot region has been derived from observations with the SUMER (Solar Ultraviolet Measurements of Emitted Radiation) instrument on SOHO. More than 1000 emission lines are given with the best available identification. The spectra are radiometrically calibrated. Lines in second order are superimposed on this spectrum. The spectral scans include emissions from atoms and ions in the temperature range from 6 000 to 2000 000 K, i.e., continua and emission lines emitted from the lower chromosphere to the corona. This broad wavelength coverage provides an important new diagnostic tool for studying the essential physical parameters throughout the upper solar atmosphere. In particular, the wavelength range shortward of 1100 A as observed by SUMER represents a significant improvement over the spectra produced in the past. A brief description of the data reduction and calibration procedures is given. The absolute intensities are determined with an uncertainty of better than +- 15% in most of the range presented, and the wavelength scale is accurate to better than 0.01 A. The atlas will also be available in machine readable form. Title: The Time Variable Solar Atmosphere - Dynamical and Variable Active Region Loops Observed with CDS on SOHO. Authors: Kjeldseth-Moe, O.; Brekke, P. Bibcode: 1999ASPC..184..286K Altcode: The Coronal Diagnostic Spectrometer, CDS, on SOHO has detected an upper solar atmosphere that is much more dynamic and time variable than previously expected. Loops in active regions, particularly in emission lines formed at temperatures 105 K to 1 MK, traditionally thought of as the transition region, are seen to change significantly over an hour. Loops appear or disappear, the emission along their length change, or they change shape or expand outward, all on time scales of 10-20 minutes. The structural variability is accompanied by high Doppler shifts, especially in the 2-5x105 K temperature range. Velocities corresponding to the shifts typically amount to +/- 50-100 km-1. We find that existing theoretical models for loops cannot explain the observations. However, models with extreme fine structure, combined with episodic heating and magneto-acoustic wave disturbances propagating in the loop legs seem promising. The rapidly changing conditions that we observe give a new conception of loop systems that has never before been seriously considered. Title: EUV Observations of Sunspot Regions with CDS on SOHO Authors: Brynildsen, N.; Brekke, P.; Haugan, S. V. H.; Kjeldseth-Moe, O.; Maltby, P. Bibcode: 1999ASPC..184..266B Altcode: The spatial distributions of line emission and line-of-sight velocity in seventeen different sunspot regions are studied, based on observations with the Coronal Diagnostic Spectrometer - CDS on SOHO. Ten EUV emission lines, formed in the chromosphere, transition region, and corona are observed. Enhanced EUV line emissions in the transition region are distributed non-uniformly over the active regions and are located both inside and outside sunspots. Most sunspot regions show strongly enhanced transition region line emission above the spot, i.e. sunspot plumes are reinvented. From wavelength shifts we derive the line-of-sight velocity, relative to the average velocity in the rastered area, 120" x 120". In sunspot plumes we find that the motion is directed away from the observer and increases with increasing line formation temperature, T, reaches a maximum up to 40 km s-1 close to log T ≅ 5.5, then decreases abruptly. The spatial extent of both emission features and flow regions increase with increasing temperature within the transition region. The observations show a marked difference between the transition region and the low corona, both regarding the spatial distributions of line emission and line-of-sight velocity. Title: A Transition Region Eruption Observed with CDS, TRACE and EIT Authors: Brekke, P.; Kjeldseth-Moe, O.; Fredvik, T.; Haugan, S. V. H.; Tarbell, T. D.; Gurman, J. B. Bibcode: 1999AAS...194.5905B Altcode: 1999BAAS...31..918B An ejection of plasma on the west limb has been observed with CDS, TRACE and EIT on 19 May 1998. The start of the eruption coincided with a weak flare observed with GOES. Erupting material rose to 120 Mm above the solar surface in 17 min, and then fell back to the solar surface. Vertical velocities of 200 km s(-1) are estimated from a series of TRACE images in the C(+3) resonance lines at 155 nm and from EIT images in the 19.5 nm band, while Doppler shifts of the transition region lines observed with CDS yield maximum horizontal velocities of 300 km s(-1) at the top of the plasma trajectories. The similar appearance and time variation of the eruption as seen with all three instruments indicate the presence of a multi-temperature plasma in spatial regions less than 1-2 arc seconds, with temperatures ranging from 10(5) K to 1.5 MK. The material did not have the momentum to break loose from the Sun and was not associated with any CME observed with LASCO. However, we may speculate that CMEs are similar to the eruption observed, with even higher speeds involved. Title: Time Variation of Active Region Loops Observed with CDS on SOHO Authors: Fredvik, T.; Kjeldseth-Moe, O.; Brekke, P.; Haugan, S. V. H. Bibcode: 1999AAS...194.5904F Altcode: 1999BAAS...31R.918F The emission from plasma filled loops, 10(4) K < T <1.5 MK, above active regions are much more time variable than previously considered. These loops, which define the solar atmosphere above active regions in this temperature range, appear or disappear, the emission along their length change, or they change shape or expand outward, all on time scales of 10-20 minutes. In this paper we report on an investigation with CDS on SOHO of 20 loop systems observed on the solar limb between September 1997 and May 1998. We describe the apparent isothermal appearance of many loops and discuss to what extent loops radiating in different emission lines, i.e. at different temperatures, are co-located within their recorded widths. Finally, we demonstrate the time variability of loop systems at different temperatures, and show how the rapidly changing conditions require a new conception of loop systems that has never before been seriously considered. Title: Multi-wavelength observations of the onset phase of a coronal mass ejection Authors: Innes, D. E.; Inhester, B.; Srivastava, N.; Brekke, P.; Harrison, R. A.; Matthews, S. A.; Noëns, J. C.; Schmieder, B.; Thompson, B. J. Bibcode: 1999SoPh..186..337I Altcode: The structure and dynamics of the initial phases of a coronal mass ejection (CME) seen in soft X-ray, extreme ultraviolet and optical emission are described. The event occurred on the SW limb of the Sun in active region AR 8026 on 9 April 1997. Just prior to the CME there was a class C1.5 flare. Images taken with the Extreme Ultraviolet Imaging Telescope (EIT) reveal the emergence of a candle-flame shaped extreme ultraviolet (EUV) cavity at the time of the flare. Yohkoh images, taken about 15 min later, show that this cavity is filled with hot X-ray emitting gas. It is most likely that this is the site of the flare. Almost simultaneous to the flare, an Hα surge or small filament eruption occurs about 50 arc sec northwards along the limb from the EUV cavity. At both the site of the core of the hot, EUV cavity and the filament ejection are X-ray jets. These jets seem to be connected by hot loops near their bases. Both jets disappear within a few minutes of one another. Title: SOHO Observations of the Structure and Dynamics of Sunspot Region Atmospheres Authors: Brynildsen, N.; Maltby, P.; Brekke, P.; Haugan, S. V. H.; Kjeldseth-Moe, O. Bibcode: 1999SoPh..186..141B Altcode: We present results from a study of the spatial distributions of line emission and relative line-of-sight velocity in the atmosphere above 17 sunspot regions, from the chromosphere, through the transition region and into the corona, based on simultaneous observations of ten EUV emission lines with the Coronal Diagnostic Spectrometer - CDS on SOHO. We find that the spatial distributions are nonuniform over the sunspot region and introduce the notation 'sunspot loop' to describe an enhanced transition region emission feature that looks like a magnetic loop, extending from inside the sunspot to the surrounding regions. We find little evidence for the siphon flow. Attention is given to the time variations since we observe both a rapid variation with a characteristic time of a few to several minutes and a slow variation with a time constant of several hours to ≈ 1 day. The most prominent features in the transition region intensity maps are the sunspot plumes. We introduce an updated criterion for the presence of plumes and find that 15 out of 17 sunspots contain a plume in the temperature range logT≈5.2-5.6. The relative line-of-sight velocity in sunspot plumes is high and directed into the Sun in the transition region. Almost all the sunspot regions contain one or a few prominent, strongly redshifted velocity channels, several of the channels extend from the sunspot plume to considerable distances from the sunspot. The flow appears to be maintained by plasmas at transition region temperatures, moving from regions located at a greater height outside the sunspots and towards the sunspot. The spatial correlation is high to moderate between emission lines formed in the transition region lines, but low between the transition region lines and the coronal lines. From detailed comparisons of intensity and velocity maps we find transition region emission features without any sign of coronal emission in the vicinity. A possible explanation is that the emission originates in magnetic flux tubes that are too cold to emit coronal emission. The comparisons suggest that gas at transition region temperature occur in loops different from loops with coronal temperature. However, we cannot exclude the presence of transition region temperatures close to the footpoints of flux tubes emitting at coronal temperatures. Regions with enhanced transition region line emission tend to be redshifted, but the correlation between line emission and relative line-of-sight velocity is weak. We extend our conditional probability studies and confirm that there is a tendency for line profiles with large intensities and red shifts (blue shifts) above the average to constitute an increasing (decreasing) fraction of the profiles as the wavelength shift increases. Title: EUV Full Sun Imaged Spectral Atlas Using the SOHO Coronal Diagnostic Spectrometer Authors: Thompson, W. T.; Brekke, P. Bibcode: 1999AAS...194.1607T Altcode: 1999BAAS...31R.850T The Coronal Diagnostic Spectrometer (CDS) aboard the Solar and Heliospheric Observatory (SOHO) carries out a regular program of measuring the full-disk irradiance using the Normal Incidence Spectrograph (NIS). The full-disk solar spectrum is returned in the wavelength bands 308-379 { Angstroms} and 513-633 { Angstroms}, with a spectral resolution between 0.3 and 0.6 { Angstroms}. A recent modification to the CDS on-board software allows simultaneous moderate resolution monochromatic images to be made of the stronger lines in these wavelength ranges. We report on observations made 23 April 1998, 21 May 1998, and 22 June 1998. A total of 69 monochromatic full-sun images are extracted from the spectral line data. For the first time, spectrally resolved images of the full Sun in He II 303.8 { Angstroms} and Si XI 303.3 { Angstroms} are presented and compared. Velocity maps of the Sun in neutral and singly ionized helium are presented. Correlations of intensity to velocity over a wide range of transition region and coronal temperatures are shown. Velocity maps of Mg IX and X are presented. Title: Solar Wind Outflow and the Chromospheric Magnetic Network Authors: Hassler, Donald M.; Dammasch, Ingolf E.; Lemaire, Philippe; Brekke, Pal; Curdt, Werner; Mason, Helen E.; Vial, Jean-Claude; Wilhelm, Klaus Bibcode: 1999Sci...283..810H Altcode: No abstract at ADS Title: An eruption in the transition region observed with CDS and TRACE, on May 19, 1998. Authors: Brekke, P.; Kjeldseth-Moe, O.; Tarbell, T. Bibcode: 1999joso.proc..170B Altcode: The authors present simultaneous CDS and TRACE observations in the EUV of an eruption of May 19, 1998. A large ejection of plasma was seen on the west limb and could be followed in EUV rasters in transition region lines with CDS and in high cadence images in the C+3 155 nm line from TRACE. The onset of the eruption coincided with a weak flare observed with GOES. The eruption extended to 120000 km above the solar surface after 17 min and then fell back to the solar surface. At the leading edge of the eruption CDS observed Doppler shifts of 300 km s-1 away from the observer (i.e. parallel to the solar surface) in the O+4 line at 62.9 nm. High cadence observations with TRACE indicate that the plasma velocities perpendicular to the line of sight (i.e. along the solar vertical) reached similar values, i.e. 200 km s-1. Perhaps this was a "coronal mass ejection" that did not make it? Title: Jets and Eruptions in the Transition Region Observed with CDS, EIT and TRACE Authors: Brekke, P.; Kjeldseth-Moe, O.; Tarbell, T.; Gurman, J. Bibcode: 1999ASPC..183..357B Altcode: 1999hrsp.conf..357B No abstract at ADS Title: The evolution of solar bipolar jets observed in the UV by SUMER on SOHO. Authors: Mendoza-Torres, J. E.; Wilhelm, K.; Innes, D. E.; Curd, W.; Kliem, B.; Brekke, P. Bibcode: 1998larm.confE..17M Altcode: Observations of bipolar jets made in the UV by SUMER onboard SOHO are presented. The observations were carried out in the interval 74.9-79.0 nm which contains some chromospheric and transition region lines. The theory predicts that under the conditions of the solar chromosphere the reconnection of magnetic lines accelerates plasma into two oppositely directed jets. In the chromosphere, as well as in other solar layers, different phenomena, where plasma acceleration take place, are observed. Of them the UV jets, observed by SUMER, represent one of the most clear evidences of the link between magnetic reconnection and plasma acceleration. The jets are clearly revealed by a considerably intensity increase and large doppler shifts of the line wings. It should be noted that the enhancement of only one wing also occurs and that the central component of the line also undergoes velocity shifts and amplitude enhancement. The behavior of the wings found in this work is consistent with results obtained for other events (Innes et al. 1997) namely: 1)The wings are observed during few minutes 2) The doppler velocities of the line wings (red and blue) are similar to each other and typical values are of the order of 100 km/sec, 3) In general, the blue component is more long-lived than the red one, 4)the red component is, in general, more intense than the blue one. In this work, an analysis of the velocities of the three spectral components (the central and the wings) as a function of the location on the slit, used for the observations, is also done. The ratios of two OV (density sensitive) and two OIV (temperature sensitive) lines, whose wavelengths are in the observed range, are also analyzed. An important result is that these parameters show gradients along the slit. An analysis of the spatial distributions and the correlations between them is done. A discussion of these results, in relation with the appearance and the evolution of the jets, will be done. Title: Time Variability of Active Region Loops Observed with the Coronal Diagnostic Spectrometer (Cds) on SOHO Authors: Kjeldseth-Moe, O.; Brekke, P. Bibcode: 1998SoPh..182...73K Altcode: Monochromatic images from the Coronal Diagnostic Spectrometer (CDS) of loops above active regions show clear evidence of rapid time variability. The rapidly changing conditions that we observe give a new conception of loop systems that has never before been seriously considered. Loop systems, particularly in emission lines formed at temperatures in the 1-5 × 105 K range, traditionally thought of as transition region temperatures, are seen to change significantly over a period of 1 hour. Loops may appear or disappear in certain emission lines, may show rapid variations in the distribution of the emission along their lengths, or may change shape or expand outward, all on time scales of 10-20 min. At other temperatures below 1.5 MK the variability appears less striking, but is still pronounced. At high temperatures, i.e., T ≥ 1.5 MK, conditions are normally much more stable. Examples exist, however, of loop systems showing violent changes in images at all temperatures up to Fe xvi formed at 2.7 MK. The structural variability is accompanied by high Doppler shifts, especially in the O v line. Corresponding velocities typically amount to 50-100 km s-1, but values as high as 300 km s-1 have been recorded. Animations with illustrative examples of loop variability have been prepared and are found on the enclosed CD-ROM. In addition we briefly discuss other structural and dynamical properties of active region loops, particularly those with temperatures below 1.5 MK. Theoretical models of loops cannot explain the present observations, but models that combine extreme fine structure, episodic heating and magneto-acoustic wave disturbances propagating in the loop legs seem promissing. Title: Flows in Sunspot Plumes Detected with SOHO Authors: Brynildsen, N.; Maltby, P.; Brekke, P.; Fredvik, T.; Haugan, S. V. H.; Kjeldseth-Moe, O.; Wikstol, O. Bibcode: 1998ApJ...504L.135B Altcode: 1998astro.ph..5249B In the Letter, ``Flows in Sunspot Plumes Detected with the Solar and Heliospheric Observatory'' by N. Brynildsen, P. Maltby, P. Brekke, T. Fredvik, S. V. H. Haugan, O. Kjeldseth-Moe, and Ø. Wikstøl (ApJ, 502, L85 [1998]), the following correction should be made:

In the last line on page L86, which reads ``peak line intensity I>=5 are located (1) above the umbra or, '' an ``Ī'' should be inserted so that the revised line reads ``peak line intensity I>=5Ī are located (1) above the umbra or.'' Title: Flows in Sunspot Plumes Detected with the Solar and Heliospheric Observatory Authors: Brynildsen, N.; Maltby, P.; Brekke, P.; Fredvik, T.; Haugan, S. V. H.; Kjeldseth-Moe, O.; Wikstøl, Ø. Bibcode: 1998ApJ...502L..85B Altcode: Bright extreme-UV sunspot plumes have been observed in eight out of 11 different sunspot regions with the Coronal Diagnostic Spectrometer on Solar and Heliospheric Observatory. From wavelength shifts, we derive the line-of-sight velocity relative to the average velocity in the rastered area, 120''×120''. In sunspot plumes, we find that the motion is directed away from the observer and increases with increasing line formation temperature, reaches a maximum between 15 and 41 km s-1 close to log logT~5.5, then decreases abruptly. The flow field in the corona is not well correlated with the flow in the transition region, and we discuss briefly the implication of this finding. Title: SOHO Observations of the Connection Between Line Profile Parameters in Active and Quiet Regions and the Net Red Shift in EUV Emission Lines Authors: Brynildsen, N.; Brekke, P.; Fredvik, T.; Haugan, S. V. H.; Kjeldseth-Moe, O.; Maltby, P.; Harrison, R. A.; Wilhelm, K. Bibcode: 1998SoPh..181...23B Altcode: We present high spatial and spectral resolution observations of one active and one quiet-Sun region, obtained with CDS and SUMER on SOHO. The connections between the line profile parameters are studied and a systematic wavelength shift towards the red with increasing peak line intensity (line broadening) is detected. The large scatter in the data calls for another approach. We apply conditional probability analysis to a series of EUV emission lines and find significant correlations between line profile parameters. For a given interval in wavelength shift we find that: (1) line profiles with large intensities (line widths) and red shifts above the average constitute an increasing fraction of the profiles as the relative wavelength shift increases, (2) line profiles with large intensities (line widths) and blue shifts compared to the average, on the other hand, constitute a decreasing fraction of the profiles as the relative wavelength shift increases. These results extend the findings of an earlier quiet-Sun study from one to several emission lines and expand the validity to include the active region. Interestingly, the active region observations show correlations between peak line intensity and wavelength shift in the coronal lines. Title: EUV Spectroscopy of the Sunspot Region NOAA 7981 Using SOHO - II. Velocities and Line Profiles Authors: Brynildsen, N.; Brekke, P.; Fredvik, T.; Haugan, S. V. H.; Kjeldseth-Moe, O.; Maltby, P.; Harrison, R. A.; Pike, C. D.; Rimmele, T.; Thompson, W. T.; Wilhelm, K. Bibcode: 1998SoPh..179..279B Altcode: We have studied the dynamics in the sunspot transition region between the chromosphere and the corona and investigated the extension of the flow field into the corona. Based on EUV spectra of a medium size sunspot and its surroundings, NOAA 7981, observed with CDS and SUMER on SOHO, we derive line-of-sight velocities and study the line profiles for a series of emission lines. Title: Extreme-Ultraviolet Sunspot Plumes Observed with SOHO Authors: Maltby, P.; Brynildsen, N.; Brekke, P.; Haugan, S. V. H.; Kjeldseth-Moe, O.; Wikstøl, Ø.; Rimmele, T. Bibcode: 1998ApJ...496L.117M Altcode: 1998astro.ph..1144M Bright EUV sunspot plumes have been observed in five out of nine sunspot regions with the Coronal Diagnostic Spectrometer on the Solar and Heliospheric Observatory. In the other four regions, the brightest line emissions may appear inside the sunspot but are mainly concentrated in small regions outside the sunspot areas. These results are in contrast to those obtained during the Solar Maximum Mission but are compatible with the Skylab mission results. The present observations show that sunspot plumes are formed in the upper part of the transition region, occur in both magnetic unipolar and bipolar regions, and may extend from the umbra into the penumbra. Title: EUV Spectroscopy of the Sunspot Region NOAA 7981 Using SOHO - I. Line Emission and Time Dependence Authors: Brynildsen, N.; Brekke, P.; Fredvik, T.; Haugan, S. V. H.; Kjeldseth-Moe, O.; Maltby, P.; Harrison, R. A.; Pike, C. D.; Rimmele, T.; Thompson, W. T.; Wilhelm, K. Bibcode: 1998SoPh..179...43B Altcode: EUV spectra of a medium-size sunspot and its surroundings, NOAA 7981, were obtained on 2 August 1996 with the Coronal Diagnostic Spectrometer (CDS) and the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) on the Solar and Heliospheric Observatory (SOHO). The spectral lines formed in the transition region and corona show considerable structure and large deviations from a uniform spatial distribution over the active region. Enhanced EUV emissions in transition region lines are concentrated in small regions outside the umbra of the sunspot throughout most of the observing sequence. Only during a short, active period do we find an enhanced line emission that reaches into the umbra. Preliminary values for the umbral intensity are given. Title: Plasma jets in the solar atmosphere observed in EUV emission lines by SUMER on SOHO Authors: Wilhelm, K.; Innes, E. E.; Curdt, W.; Kliem, B.; Brekke, P. Bibcode: 1998ESASP.421..103W Altcode: 1998sjcp.conf..103W No abstract at ADS Title: Three Dimensional EUV Imaging of Sunspot Regions Observed with SOHO Authors: Brynildsen, N.; Brekke, P.; Haugan, S. V. H.; Kjeldseth-Moe, O.; Maltby, P.; Harrison, R. A.; Rimmele, T.; Wilhelm, K. Bibcode: 1998ASPC..155..171B Altcode: 1998sasp.conf..171B No abstract at ADS Title: Active Region Structures and Dynamics in the Transition Region and Corona (Invited review) Authors: Brekke, P. Bibcode: 1998ASPC..155..150B Altcode: 1998sasp.conf..150B No abstract at ADS Title: Inconstancy of the Transition Region - Variable and Dynamic Active Region Loops Authors: Kjeldseth-Moe, O.; Brekke, P.; Haugan, S. V. H. Bibcode: 1998ESASP.417..153K Altcode: 1998cesh.conf..153K No abstract at ADS Title: Chromospheric and Photospheric Activity of the Sun as a Star Using SOLSTICE Data Authors: Catalano, S.; Lanza, A. F.; Brekke, P.; Rottman, Gary J.; Hoyng, P. Bibcode: 1998ASPC..154..584C Altcode: 1998csss...10..584C The distribution of photospheric and chromospheric active regions (spots and plages) on the surface of stars is mainly recovered from the deconvolution of light or line flux curves. Here we check the reliability of the maximum entropy technique to derive surface maps from the rotational modulation of the continuum and line fluxes observed in active stars. We compare the solar chromospheric map obtained from the deconvolution of daily average of the C 2 line flux at 133.5 nm measured by SOLSTICE, and solar Hα images contemporaneously obtained at Catania observatory. Hα plages may not exactly overlay C 2 plages, however the agreement between the reconstructed and the direct images is strikingly good. Only small (<20circ-30circ in diameter) or low contrast (Delta I/I < 0.3) structures are not recovered. We use also the Wolf sunspot number to study the longitude distribution of the active regions in photosphere and chromosphere, contrasting the solar behaviour with that of other active stars. Title: Velocity Fields of a Filament Region Observed with Ground-Based Telescopes and from SOHO Authors: Mein, P.; Schmieder, B.; Malherbe, J. -M.; Wiik, J. E.; Engvold, O.; Brekke, P.; Zirker, J. B.; Poland, A. I.; Delaboudiniere, J. -P.; Staiger, J. Bibcode: 1998ASPC..150..135M Altcode: 1998npsp.conf..135M; 1998IAUCo.167..135M No abstract at ADS Title: Active Regions Observed in Extreme Ultraviolet Light by the Coronal Diagnostic Spectrometer on SOHO Authors: Fludra, A.; Brekke, P.; Harrison, R. A.; Mason, H. E.; Pike, C. D.; Thompson, W. T.; Young, P. R. Bibcode: 1997SoPh..175..487F Altcode: We present observations of five active regions made by the Coronal Diagnostic Spectrometer (CDS) on the Solar and Heliospheric Observatory (SOHO). CDS observes the Sun in the extreme ultraviolet range 150-780 Å. Examples of active region loops seen in spectral lines emitted at various temperatures are shown. Several classes of loops are identified: those that are seen in all temperatures up to 2 x 106 K; loops seen at 106 K but not reaching 1.6 x 106 K; those at temperatures 2- 4 x 10-5 K and occasionally at 6 x 10-5 K but not reaching 106 K. An increasing loop size with temperature and the relationship between the cool and hot structures is discussed. CDS observations reveal the existence of loops and other unresolved structures in active regions, at temperatures between 1.5- 4 x 10-5 K, which do not have counterparts in lines emitted above 8 x 10-5 K. Bright compact sources only seen in the transition region lines are investigated. These sources can have lifetimes of up to several days and are located in the vicinity of sunspots. We study the variability of active region sources on time scales from 30 sec to several days. We find oscillatory behaviour of Hei and Ov line intensities in an active region on time scales of 5-10 min. Title: Doppler Shifts in the Quiet-Sun Transition Region and Corona Observed with SUMER on SOHO Authors: Brekke, P.; Hassler, D. M.; Wilhelm, K. Bibcode: 1997SoPh..175..349B Altcode: New observations of systematic red shifts of transition region and coronal lines obtained with SUMER (Solar Ultraviolet Measurements of Emitted Radiation) on SOHO (the Solar and Heliospheric Observatory) are presented. With the extensive wavelength coverage of SUMER it is possible to extend the measurements of the red shifts to much higher temperatures compared to previous instruments. We find lines formed in the upper transition region (e.g. Ov, Sv, and Svi) to be red-shifted similar to lower temperature lines (T ≤ 1.8 x 10-5 K). Even hotter lines such as Ovi, Neviii and Mgx show systematic red shifts on the order of 5 km s-1 in the quiet Sun. This is a new and significant result since previous measurements of the red shifts were less well constrained. Title: High-Velocity Flows in an Active Region Loop System Observed with the Coronal Diagnostic Spectrometer (Cds) on SOHO Authors: Brekke, P.; Kjeldseth-Moe, O.; Harrison, R. A. Bibcode: 1997SoPh..175..511B Altcode: EUV spectra of coronal loops above an active region show clear evidence of strong dynamical activity. We present an example where the Ov 629 Å line, formed at 240 000 K, is shifted from its reference position corresponding to line-of-sight velocities greater than 50 km s-1 with the shift extending over a large fraction of a loop. The observations were made with the Coronal Diagnostic Spectrometer (CDS) on the Solar and Heliospheric Observatory (SOHO), and are from active region NOAA 7981 on the east solar limb on 27 July 1996. An animation has been prepared showing the variation of the shift or flow velocity along the loop. This animation is to be found on the enclosed CD-ROM and gives a clear impression of the dynamical condition present in the loop. The appearance of the loop system in different lines formed over a range in temperature as well as the observed dynamics indicates that loops at different temperatures are not closely co-located. Finally, the results are discussed and related to mechanisms that may cause line shifts. Title: Bursts of Explosive Events in the Solar Network Authors: Innes, D. E.; Brekke, P.; Germerott, D.; Wilhelm, K. Bibcode: 1997SoPh..175..341I Altcode: Observations of the quiet-Sun network in the UV emission line Siiv 1393 Å over a time period of two hours are presented. Bursts of explosive events, highly Doppler-shifted emission, seem to be sporadically emitted from the brighter regions of the network lanes. Individual events have typical lifetimes of ≈ 1-6 min and come in bursts of up to 30 min. The most spectacular burst in this dataset, shown in the accompanying movie, lasts ≈ 30 min and shows a wide variety of line profiles with both red and blue shifts ≈180 km s1. There appears to be no characteristic form or evolutionary pattern to the line profiles in either the individual events or series of events. There are about twice as many blue shifts as red shifts. Title: Eruptive prominence and associated CME observed with SUMER, CDS and LASCO (SOHO) Authors: Wiik, J. E.; Schmieder, B.; Kucera, T.; Poland, A.; Brekke, P.; Simnett, G. Bibcode: 1997SoPh..175..411W Altcode: Observations of an eruptive prominence were obtained on 1 May 1996, with the SUMER and CDS instruments aboard SOHO during the preparatory phase of the Joint Observing Programme JOP12. A coronal mass ejection observed with LASCO is associated temporally and spatially with this prominence. The main objective of JOP12 is to study the dynamics of prominences and the prominence-corona interface. By analysing the spectra of Oiv and Siiv lines observed with SUMER and the spectra of 15 lines with CDS, Doppler shifts, temperatures and electron densities (ratio of Oiv 1401 to 1399Å) were derived in different structures of the prominence. The eruptive part of the prominence consists of a bubble (plasmoid) of material already at transition region temperatures with red shifts up to 100 km s-1 and an electron density of the order of 1010cm-3. The whole prominence was very active. It developed both a large helical loop and several smaller loops consisting of twisted threads or multiple ropes. These may be studied in the SUMER movie (movie 2). The profiles of the SUMER lines show a large dispersion of velocities (±50 km s-1) and the ratio of the Oiv lines indicates a large dispersion in electron density (3 x 109cm-3 to 3x 1011cm-3). The CME observed by LASCO left the corona some tens of minutes before the prominence erupted. This is evidence that the prominence eruptions are probably the result of the removal of the restraining coronal magnetic fields which are in part responsible for the original stability of the prominence. Title: Initial Comparison of MDI Photospheric Magnetic Movies and CDS Transition Region Movies in Quiet Sun Authors: Tarbell, T.; Brekke, P.; Fludra, A.; Deforest, C.; Saba, J.; Covington, J. Bibcode: 1997SPD....28.0111T Altcode: 1997BAAS...29..881T We present simultaneous, coaligned movies of photospheric magnetic fields and transition region (TR) intensities in very quiet sun near disk center obtained by SOHO in January, 1997. For example, the 22 Jan 1997 CDS movies show He I 584 (2x10(4) K) and O V 630 (2.4 x 10(5) K) from 16:51 to 19:54 UT, with a 310 x 240 arcsecond field of view, 105 second cadence, and 1.7 arcsecond pixels. MDI photospheric longitudinal magnetograms, with 60 second cadence and 0.6 arcsecond pixels, have been coaligned with these. Bright TR emission correlates more strongly with close bipoles in the photospheric magnetic field than with magnetic flux alone. Some strong photospheric flux tubes are barely visible in the TR emission, appearing only occasionally in connections with nearby weak opposite polarity fields. Bright transient emissions in the TR are located at places of cancelling opposite polarities in photospheric magnetic fields. The flux cancellation continues for tens of minutes or hours in the magnetic movies. Searches for more rapid magnetic counterparts to these TR transients and for emerging magnetic flux regions in the movies are under way. This work was supported by NASA grant NAG5-3077 at Stanford and Lockheed Martin. Title: The Non-Uniformity in the Sunspot Transition Region Authors: Brynildsen, N.; Brekke, P.; Fredvik, T.; Haugan, S. V. H.; Kjeldseth-Moe, O.; Maltby, P.; Harrison, R. A.; Rimmele, T.; Wilhelm, K. Bibcode: 1997ESASP.404..257B Altcode: 1997cswn.conf..257B No abstract at ADS Title: Transition Region Velocities and Line Profiles in the Sunspot Region 7981 Authors: Brynildsen, N.; Brekke, P.; Fredvik, T.; Haugan, S. V. H.; Kjeldseth-Moe, O.; Maltby, P.; Harrison, R. A.; Pike, C. D.; Rimmele, T. Thompson, W. T.; Wilhelm, K. Bibcode: 1997ESASP.404..251B Altcode: 1997cswn.conf..251B No abstract at ADS Title: CDS Observations of the Connection Between Line Intensity and Doppler Shift in the Active Region NOAA 7981 Authors: Fredvik, T.; Brynildsen, N.; Maltby, P.; Kjeldseth-Moe, O.; Brekke, P.; Haugen, S. V. H.; Harrison, R. A. Bibcode: 1997ESASP.404..391F Altcode: 1997cswn.conf..391F No abstract at ADS Title: Flows with High Velocities in an Active Region Loop Observed with the Coronal Diagnostic Spectrometer Authors: Kjeldseth-Moe, O.; Brekke, P.; Harrison, R. A. Bibcode: 1997ESASP.404..457K Altcode: 1997cswn.conf..457K No abstract at ADS Title: First Results from SOHO on Waves Near the Solar Transition Region Authors: Steffens, S.; Deubner, F. -L.; Fleck, B.; Wilhelm, K.; Schuhle, U.; Curdt, W.; Harrison, R.; Gurman, J.; Thompson, B. J.; Brekke, P.; Delaboudiniere, J. -P.; Lemaire, P.; Hessel, B.; Rutten, R. J. Bibcode: 1997ASPC..118..284S Altcode: 1997fasp.conf..284S We present first results from simultaneous observations with the CDS, EIT and SUMER instruments {please see Solar Physics 162 (1995) for a description of the instruments} onboard SOHO and the VTT at Tenerife. Our aim is to study the wave propagation, shock formation, and transmission properties of the upper chromosphere and transition region. The preliminary results presented here include the variation of velocity power spectra with height, difference in power between internetwork and network regions, and variations in mean flows displayed by different spectral lines. Title: The Net Redshifts in EUV Emission Lines and the Connection Between Intensity and Doppler Shift Authors: Brynildsen, N.; Fredvik, T.; Maltby, P.; Kjeldseth-Moe, O.; Brekke, P.; Haugan, S. V. H.; Harrison, R. A.; Wilhelm, K. Bibcode: 1997ESASP.404..263B Altcode: 1997cswn.conf..263B No abstract at ADS Title: EUV Line Emission and Time Dependence in the Sunspot Region NOAA 7981 Authors: Brynildsen, N.; Brekke, P.; Fredvik, T.; Haugan, S. V. H.; Kjeldseth-Moe, O.; Maltby, P.; Harrison, R. A.; Pike, C. D.; Rimmele, T.; Thompson, W. T.; Wilhelm, K. Bibcode: 1997ESASP.404..245B Altcode: 1997cswn.conf..245B No abstract at ADS Title: First Results of the SUMER Telescope and Spectrometer on SOHO - I. Spectra and Spectroradiometry Authors: Wilhelm, K.; Lemaire, P.; Curdt, W.; Schühle, U.; Marsch, E.; Poland, A. I.; Jordan, S. D.; Thomas, R. J.; Hassler, D. M.; Huber, M. C. E.; Vial, J. -C.; Kühne, M.; Siegmund, O. H. W.; Gabriel, A.; Timothy, J. G.; Grewing, M.; Feldman, U.; Hollandt, J.; Brekke, P. Bibcode: 1997SoPh..170...75W Altcode: SUMER - the Solar Ultraviolet Measurements of the Emitted Radiation instrument on the Solar and Heliospheric Observatory (SOHO) - observed its first light on January 24, 1996, and subsequently obtained a detailed spectrum with detector B in the wavelength range from 660 to 1490 Å (in first order) inside and above the limb in the north polar coronal hole. Using detector A of the instrument, this range was later extended to 1610 Å. The second-order spectra of detectors A and B cover 330 to 805 Å and are superimposed on the first-order spectra. Many more features and areas of the Sun and their spectra have been observed since, including coronal holes, polar plumes and active regions. The atoms and ions emitting this radiation exist at temperatures below 2 × 106 K and are thus ideally suited to investigate the solar transition region where the temperature increases from chromospheric to coronal values. SUMER can also be operated in a manner such that it makes images or spectroheliograms of different sizes in selected spectral lines. A detailed line profile with spectral resolution elements between 22 and 45 mÅ is produced for each line at each spatial location along the slit. From the line width, intensity and wavelength position we are able to deduce temperature, density, and velocity of the emitting atoms and ions for each emission line and spatial element in the spectroheliogram. Because of the high spectral resolution and low noise of SUMER, we have been able to detect faint lines not previously observed and, in addition, to determine their spectral profiles. SUMER has already recorded over 2000 extreme ultraviolet emission lines and many identifications have been made on the disk and in the corona. Title: SOHO observations of the north polar solar wind Authors: Peres, G.; Ciaravella, A.; Betta, R.; Orlando, S.; Reale, F.; Kohl, J.; Noci, G.; Fineschi, S.; Romoli, M.; Brekke, P.; Fludra, A.; Gurman, J. B.; Lemaire, P.; Schuhle, U. Bibcode: 1997ESASP.404..587P Altcode: 1997cswn.conf..587P No abstract at ADS Title: Systematic Redshifts in the Quiet Sun Transition Region and Corona Observed with SUMER on SOHO Authors: Brekke, P.; Hassler, D. M.; Wilhelm, K. Bibcode: 1997ESASP.404..229B Altcode: 1997cswn.conf..229B No abstract at ADS Title: Flows and Dynamics in the Corona Observed with the Coronal Diagnostic Spectrometer (cds) Authors: Brekke, P.; Kjeldseth-Moe, O.; Brynildsen, N.; Maltby, P.; Haugan, S. V. H.; Harrison, R. A.; Thompson, W. T.; Pike, C. D. Bibcode: 1997SoPh..170..163B Altcode: EUV spectra obtained with the Coronal Diagnostic Spectrometer (CDS) on the Solar and Heliospheric Observatory (SOHO) show significant flows of plasma in active region loops, both at coronal and transition region temperatures. Wavelength shifts in the coronal lines Mgix 368 Å and Mgx 624 Å corresponding to upflows in the plasma reaching velocities of 50 km s-1 have been observed in an active region. Smaller velocities are detected in the coronal lines Fexvi 360 Å and Sixii 520 Å. Flows reaching 100 km s-1 are observed in spectral lines formed at transition region temperatures, i.e., Ov 629 Å and Oiii 599 Å, demonstrating that both the transition region and the corona are clearly dynamic in nature. Some high velocity events show even higher velocities with line profiles corresponding to a velocity dispersion of 300-400 km s-1. Even in the quiet Sun there are velocity fluctuations of 20 km s-1 in transition region lines. Velocities of the magnitude presented in this paper have never previously been observed in coronal lines except in explosive events and flares. Thus, the preliminary results from the CDS spectrometer promise to put constraints on existing models of the flows and energy balance in the solar atmosphere. The present results are compared to previous attempts to observe flows in the corona. Title: The EUV Solar Irradiance Spectrum Observed with the Coronal Diagnostic Spectrometer (CDS) on SOHO Authors: Brekke, P.; Thompson, W. T. Bibcode: 1997ESASP.404..235B Altcode: 1997cswn.conf..235B No abstract at ADS Title: The Ultraviolet Spectrum of a 3B Class Flare Observed with SOLSTICE Authors: Brekke, P.; Rottman, G. J.; Fontenla, J.; Judge, P. G. Bibcode: 1996ApJ...468..418B Altcode: An observation of the ultraviolet spectrum (1200-1800 Å) during the impulsive phase of a very extended 3B-X3 class solar flare on 1992 February 27 was obtained with the Solar-Stellar Irradiance Comparison Experiment (SOLSTICE). This observation is combined with ground-based Hα, magnetogram, and microwave data as well as hard X-ray measurements from the Ulysses spacecraft. This flare shows a dramatic enhancement of lines formed in the solar transition region. The irradiance (emitted flux density from the entire solar disk) of the resonance lines of C iv and Si iv increased by a factor of 12-13 during the impulsive phase of the flare. These irradiance enhancements are comparable with those measured during stellar flares. By taking into account the emitting flare area we infer that the radiance (specific intensity) of the flaring plasma was at least a factor of 15,000 brighter than the average solar disk radiance just prior to the event. Assuming the flare site's initial radiance was that of a typical active region, it then must have brightened by a factor of at least 3400. Such enhancement far exceeds previous published values (e.g., OSO 8, Skylab, and SMM) and indicates that many observations were affected by limited dynamic range. Thus, the SOLSTICE observation may be the first measurement of the true UV enhancement during the impulsive phase of very bright solar flares.

The Si III multiplet near 1295 Å also shows remarkable enhancement, but other allowed lines of C II, Si III (1206 Å), N V, and He II show more moderate enhancements, the weakest being H I Lyα, the irradiance of which increases only 6%. Some of the differences between the various enhancements are certainly caused by the timing of the observations since the scanning spectrometer observed different spectral features over periods of 4 minutes. Other differences due to line formation processes are being investigated but are consistent with density effects in the line emission coefficients. The inferred Lyα radiance enhancement is consistent with current post-impulsive phase flare models. However, the formation of the C IV and Si IV lines, formed during the impulsive phase of the flare, remains unknown. During the impulsive phase of the flare the strong transition region lines are systematically redshifted by 50 km s-1. Title: Intercombinations and Allowed Transitions in O IV Authors: Brage, Tomas; Judge, P. G.; Brekke, P. Bibcode: 1996ApJ...464.1030B Altcode: We report on large-scale ab initio multiconfiguration Hartree-Fock calculations for important multiplets including the UV 0.01 multiplet, 2s22p2PJ-2s2p2 4Pj', in O IV. The resulting transition probabilities should be accurate to ±5%-10% for intersystem lines and 1% or better for permitted lines.

We present new calculations of line emission coefficients using these transition probabilities and collisional rate coefficients published by Zhang, Graziani, & Pradhan in 1994. We readdress the use of these lines as diagnostics of electron densities, paying particular attention to uncertainties in density determinations. We find (1) the absolute uncertainties in derived densities are difficult to assess, but are at least ±40% controlled by uncertainties in collision strengths; (2) our new calculations bring observed and computed line ratios into better agreement (earlier papers yielding systematically different densities make the agreement worse); (3) there is additional evidence for strong blends in the 1404.8 emission feature, as argued by other authors, and/or evidence for inaccurate laboratory wavelengths; and (4) the computed branching ratios are in good agreement with observed ratios to within observational uncertainties of ±7%.

We determine electron densities in a variety of solar features from HRTS data from the first and second flights of this instrument. The derived electron densities vary remarkably little between quiet Sun network and active regions, but resonance line intensities vary dramatically, and we discuss reasons for this. Finally, we discuss how new high-quality data from the SUMER instrument to be flown on Solar and Heliosphereic Observatory (SO HO) could be used to address outstanding problems concerning blends and heating of the solar transition region. Title: High Velocity Event Observed with CDS on SOHO Authors: Kjeldseth-Moe, O.; Brynildsen, N.; Brekke, P.; Harrison, R. A. Bibcode: 1996AAS...188.3714K Altcode: 1996BAAS...28..880K The Coronal Diagnostic Spectrometer, CDS, on SOHO has observed its first strong High Velocity Event. The event occurred on 22 March 1996 at approximately 13.36 UT and was located in the leg of an active region loop. The spectral signature is extremely wide emission lines corresponding to a velocity dispersion of approximately 300-450 km/s. As measured in the 386 A line from Mg IX, the emission also seems shifted in wavelength with a redshift corresponding to 65 km/s. The intensity contrast in the line is a factor 2 compared to the surrounding areas. The spatial extent is small, less than or corresponding to the angular resolution of CDS of 4". The event occur in all available lines from He I to Fe XV, i.e. over a temperature range from 10 000 K to 2.2 MK. This is a new result which has not been reported before. The relation of this type of event to the well studied explosive events is discussed. Title: A Solar EUV Spectral Atlas Observed with SUMER Authors: Brekke, P.; Wilhelm, K.; Lemaire, P.; Curdt, W.; Schuhle, U.; Poland, A.; Kucera, T.; Hassler, D. M.; Siegmund, O. H. W. Bibcode: 1996AAS...188.3713B Altcode: 1996BAAS...28..879B We present the first solar EUV spectral atlas in the wavelength range 500 -- 1600 { Angstroms}. The spectra were recorded with the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) which is part of the ESA/NASA Solar and Heliospheric Observatory (SOHO). The solar spectrum below 1200 { Angstroms} is not very well known. Thus, the present spectral atlas, and SUMER observations in general, represents a new important diagnostic tool to study essential physical parameters of the solar atmosphere. It includes emission from atoms and ions in the temperature range 10(4) to 2 x 10(6) K. Thus, emission lines and continua emitted from the lower chromosphere to the lower corona can be studied. The atlas is also useful as a planning tool for SUMER studies to determine useful dwell times, possible blends, and to select proper data extraction windows. The angular resolution of SUMER is close to 1 arcsec, but the atlas presented here represents an average along part of the 1-arcsec wide slit, typically 30 arcsec. The spectral resolving power of the instrument is lambda /Delta lambda = 17770-38300. For more details about the SUMER instrument we refer to Wilhelm et al. (Solar Physics, 162, 189, 1995). The spectral data in this atlas were obtained with the spectrometer slit positioned at the center of the solar disk with a dwell time of 300 s to bring up weak lines and continua. The full spectral range was put together from a number of exposures each covering approximately 20 { Angstroms} in 1st order on the coated, and therefore most sensitive, part (KrB) of the detector. 1st and 2nd order spectra are superimposed. The spectral atlas is available in a computer readable format together with a IDL program to read and display the data using a widget interface. The atlas and the programs can be obtained via the World Wide Web (http://hydra.mpae.gwdg.de/mpae_projects/SUMER/sumer.html) or by contacting one of the authors. Title: Ultraviolet (1200 to 1800 Angstroms) Emission during the Impulsive Phase of a Class 3B-X3 Solar Flare Observed with SOLSTICE Authors: Brekke, P.; Rottman, C. J.; Fontenla, J.; Judge, P. G. Bibcode: 1996mpsa.conf..213B Altcode: 1996IAUCo.153..213B No abstract at ADS Title: The UV "sun as a star" flare spectrum observed with SOLSTICE Authors: Brekke, P.; Rottman, G. J.; Fontenla, J.; Judge, P. G. Bibcode: 1996ASPC..109..111B Altcode: 1996csss....9..111B No abstract at ADS Title: On the Failure of Standard Emission Measure Analysis for Solar Extreme-Ultraviolet and Ultraviolet Irradiance Spectra Authors: Judge, P. G.; Woods, T. N.; Brekke, P.; Rottman, G. J. Bibcode: 1995ApJ...455L..85J Altcode: We perform emission measure analysis of new and accurate UV ( lambda > 1200 A) and extreme-ultraviolet (EUV) ( lambda <= 1200 A) irradiance ("Sun-as-a-star") emission-line spectra of the Sun. Our data consist of (1) daily averaged UV irradiances from the SOLSTICE on the UARS spacecraft and (2) EUV irradiances obtained on the same date from a \frac {1}{4} m spectrograph flown on a sounding rocket. Both instruments have a spectral resolution of roughly 1 A. The absolute uncertainties in these data are at most +/-15% (+/-2 sigma ), one of the highest photometric accuracies yet achieved. We find large, highly significant and systematic discrepancies in the emission measure analysis of transition region lines which can only be accounted for by a breakdown of one or more standard assumptions. All strong lines above 1000 A, which are from the Li and Na isoelectronic sequences, are too strong by factors of between 2.5 and 7 compared with their counterparts in the EUV region. Previous studies were tantalizingly close to finding these discrepancies, but those data lacked the wavelength coverage and relative photometric precision necessary for definitive conclusions. We argue that either dynamical effects, inaccurate treatments of atomic processes, and/or Lyman continuum absorption are the culprits. However, we favor the former explanation. In any event, this study should have implications for models of the solar transition region, for observing programs with the CDS and SUMER instruments on SOHO, and for analysis of UV spectra for stars across the cool half of the H-R diagram. Finally, the discrepancy is not seen for the "coronal" Li-like ions. Title: The Coronal Diagnostic Spectrometer for the Solar and Heliospheric Observatory Authors: Harrison, R. A.; Sawyer, E. C.; Carter, M. K.; Cruise, A. M.; Cutler, R. M.; Fludra, A.; Hayes, R. W.; Kent, B. J.; Lang, J.; Parker, D. J.; Payne, J.; Pike, C. D.; Peskett, S. C.; Richards, A. G.; Gulhane, J. L.; Norman, K.; Breeveld, A. A.; Breeveld, E. R.; Al Janabi, K. F.; Mccalden, A. J.; Parkinson, J. H.; Self, D. G.; Thomas, P. D.; Poland, A. I.; Thomas, R. J.; Thompson, W. T.; Kjeldseth-Moe, O.; Brekke, P.; Karud, J.; Maltby, P.; Aschenbach, B.; Bräuninger, H.; Kühne, M.; Hollandt, J.; Siegmund, O. H. W.; Huber, M. C. E.; Gabriel, A. H.; Mason, H. E.; Bromage, B. J. I. Bibcode: 1995SoPh..162..233H Altcode: The Coronal Diagnostic Spectrometer is designed to probe the solar atmosphere through the detection of spectral emission lines in the extreme ultraviolet wavelength range 150 - 800 å. By observing the intensities of selected lines and line profiles, we may derive temperature, density, flow and abundance information for the plasmas in the solar atmosphere. Spatial and temporal resolutions of down to a few arcseconds and seconds, respectively, allow such studies to be made within the fine-scale structure of the solar corona. Futhermore, coverage of large wavelength bands provides the capability for simultaneously observing the properties of plasmas across the wide temperature ranges of the solar atmosphere. Title: Observed Redshifts in the Solar Transition Region above Active and Quiet Regions Authors: Achour, H.; Brekke, P.; Kjeldseth-Moe, O.; Maltby, P. Bibcode: 1995ApJ...453..945A Altcode: Solar UV spectral observations show a redshifted emission at temperatures between the chromosphere and the corona. We have measured the magnitude of the redshift as a function of the temperature using solar spectrograms from the High Resolution Telescope and Spectrograph HRTS. The velocity derived from the average redshift is found to increase up to a temperature T ≍ 1.35 x 105 K in both quiet and active regions, then decrease with increasing temperature, with the rate of decrease depending critically on the laboratory wavelengths adopted for the transition region lines. This result illustrates the need for improved laboratory measurements.

We find that the differential re shift between an active region and the surroundings increases smoothly with temperature, reaches a maximum velocity difference of 7 km s 1 at 1.35 × 105 K and falls abruptly to zero at 2.3 × 105 K. This observation is independent of the laboratory wavelengths. Suggestions regarding the origin of the redshift are confronted with the results. Title: The OV 1371.29A/1218.35A emission-line ratio in solar and stellar spectra Authors: Keenan, F. P.; Brekke, P.; Byrne, P. B.; Greer, C. J. Bibcode: 1995MNRAS.276..915K Altcode: New calculations of the theoretical electron-density-sensitive emission-line ratio R=I(2s2p ^1P-2p^2 ^1D)/I(2s^2 ^1S-2s2p ^3P_1)=I(1371.29A)/I(1218.35A) in OV are presented, which are significantly different from those deduced previously, principally due to the adoption of improved atomic data in the present analysis. Electron densities estimated from the current diagnostics, in conjunction with observed values of R measured from solar spectra obtained by the S082B spectrograph on board Skylab and by the High Resolution Telescope and Spectrograph (HRTS) on board a sounding rocket flight, are found to be in good agreement with densities determined from line ratios in species formed at similar electron temperatures to OV, such as OIV and NIV. These results provide experimental support for the accuracy of the diagnostic calculations presented in this paper, and hence the atomic data used in their derivation. The observed value of R for the M0Ve flare star AU Mic, determined from observations made by the Goddard High Resolution Spectrometer on board the Hubble Space Telescope, is within 4 per cent of the expected low-density limit, implying that logN_e<=10.4 for the OV emitting region of the AU Mic atmosphere. This is similar to density estimates made for AU Mic using other methods. Title: Needs for Improved Laboratory Wavelength Measurements in the EUV Authors: Brekke, P.; Hassler, D. M. Bibcode: 1995ASPC...81..589B Altcode: 1995lahr.conf..589B No abstract at ADS Title: An Ultraviolet Spectral Atlas of the Sun 1190 - 1730 A Authors: Brekke, P. Bibcode: 1995ASPC...81..102B Altcode: 1995lahr.conf..102B No abstract at ADS Title: CDS quicklook display software Authors: Brekke, P.; Haugan, S. V. H.; Brynildsen, Nils Bibcode: 1994ESASP.373..437B Altcode: 1994soho....3..437B No abstract at ADS Title: Observed redshifts of transition region/Corona lines Authors: Brekke, P. Bibcode: 1994SSRv...70...97B Altcode: Solar UV observations reveal a redshifted emission at transition region temperatures, commonly interpreted as a net downflow of plasma. In earlier investigations the magnitude of the redshift has been found to increase with temperature, reaching a maximum at T=105 K, and then to decrease towards higher temperatures. These observations, mostly from Skylab, suggested no significant shift of the O V line at 1218 Å formed at 2.4×105 K. The variation of the downflow velocity with temperature is, however, uncertain since there are few reliable observations of lines formed at higher temperatures. Using spectrograms from the High Resolution Telescope and Spectrograph — HRTS we find an average net redshift of the O V lines at 1218 Å and 1371 Å at all locations extending from disk center to solar limb. A discrepancy between the observed flow velocity in the two lines is probably caused by uncertainty in the available laboratory wavelength of the intercombination line at 1218 Å (2s2 1S0-2s2p3P1). The observed shift in O V is compared with corresponding measurements of lines formed at other temperatures (Si IV, C IV, N IV, O IV, and Fe XII). Large variations in the shift are found along the instrument slit. Thus, blueshifts are also observed with the sites of the largest upflow located in the sunspot umbrae and in a quiet region close to an active region. Title: Fine structure and the emission filling factor Authors: Kjeldseth-Moe, O.; Brynildsen, N.; Brekke, P.; Maltby, P. Bibcode: 1994SSRv...70...89K Altcode: There is observational evidence for an extreme fine structure in the solar transition region, much smaller than 1″ in size (Dereet al., 1987, 1988) Corresponding to this extreme fine structure there appear to be an equally complex dynamical structure. We review the evidence for such dynamical extreme fine structure as demonstrated by the frequent appearance of multiple velocities, i.e. distinctly different velocities in the transition region occurring within the angular resolution element. Multiple velocities are prominent in active regions and particularly near sunspots, where velocity components may be supersonic. However, multiple velocities are frequent also in quiet regions. The consequences of such fine structure for modeling the transition region will be outlined. Finally the appropriate CDS and SUMER observations needed to extend our knowledge of a finely structured transition region and corona, spatially or in time, are discussed. Title: New Radiometric Values of the Solar Ultraviolet Continuum Radiation from 1500 to 1700 Angstrom Authors: Brekke, P.; Kjeldseth-Moe, O. Bibcode: 1994ApJ...431L..55B Altcode: A high-resolution stigmatic spectrometer, the High Resolution Telescope and Spectrograph (HRTS), has been calibrated against broad-band irradiance measurements of the Sun with the Solar Ultraviolet Irradiance Monitor (SUSIM) and the Solar-Stellar Irradiance Comparison Experiment (SOLSTICE), resulting in a new value for the radiance of the solar UV continuum from 1500 to 1700 A. Previous HRTS results were based on a comparison with the Skylab SO82B calibration rocket, CALROC, and agreed, within the stated accuracy of +/- 25%, with other independently calibrated UV radiance measurements over the last 20 years. The new calibration increases the derived radiance in this wavelength range by a factor of 1.35-1.5 over previous measurements. The difference is systematic over the wavelength range and cannot be explained by contributions to the irradiance from spectral lines or enhanced emission in active regions. The new radiance values are significant for solar atmospheric models as well as for related studies of stellar models, since the radiance at these wavelengths reflects the value of the minimum temperature at the top of the photosphere. Title: The solar UV continuum 1440-1680 Å and its center-to-limb variation Authors: Brekke, P.; Kjeldseth-Moe, O. Bibcode: 1994SoPh..150...19B Altcode: The solar UV continuum has been derived from intensity-calibrated observations with the High-Resolution Telescope and Spectrograph - HRTS - on its second rocket flight in 1978. A database has been constructed using the spatially-resolved solar spectrum 1180-1700 å along a slit extending from near disk center to the solar limb and crossing a sunspot and two active regions. The angular resolution is approximately 1.8″. Title: Observed Redshift of O V and Downflows in the Transition Region Authors: Brekke, P. Bibcode: 1994emsp.conf...57B Altcode: No abstract at ADS Title: The HRTS Spectral Database in Oslo Authors: Brekke, P. Bibcode: 1994emsp.conf..209B Altcode: No abstract at ADS Title: An Ultraviolet Spectral Atlas of the Sun between 1190 and 1730 Angstrom Authors: Brekke, P. Bibcode: 1993ApJS...87..443B Altcode: An ultraviolet spectral atlas of different solar regions in the wavelength region 1190-1730 A is presented. The data were obtained with the High Resolution Telescope and Spectrograph during a rocket flight in 1978. The spectral resolution of the instrument was 0.05 A while a spatial resolution of approximately 1.8 arcsec was achieved. The atlas contains spectra of three different quiet regions including pointings at disk center and the extreme limb. Data from an active region close to the solar limb and a prominence have also been included together with an atlas of a so-called explosive event. The selected areas are averaged over several arcsec, ranging from 3.5 to 220 arcsec. The absolute intensities are determined with an accuracy of +/- 30 percent except for the strongest emission lines that are synthesized from spectra with different exposure times. The atlas is available in a machine-readable form together with an IDL program to interactively measure line widths, total intensities, and solar wavelengths. Title: Multiple Flows and the Fine Structure of the Transition Region around Sunspots Authors: Kjeldseth-Moe, O.; Brynildsen, N.; Brekke, P.; Maltby, P.; Brueckner, G. E. Bibcode: 1993SoPh..145..257K Altcode: The fine structure in the flow field in the transition region above and surrounding a sunspot is determined fromCIV 1548 å line profiles, observed with the High Resolution Telescope and Spectrograph (HRTS) during the Spacelab 2 mission. The observed line profiles show one, two, or three distinct velocity components within the resolution element of 1″ × 1″. Supersonic flows occur in small regions where the line profile has two or three components. The line component that shows supersonic speed often is weaker than the subsonic line component, which may explain why some observers have been unable to detect the supersonic flow component. The broadening of individual line components shows non-thermal velocities close to 20 km s−1. This suggests that turbulence is less important than usually considered. Title: Observed Redshifts in O V and Downflows in the Solar Transition Region Authors: Brekke, P. Bibcode: 1993ApJ...408..735B Altcode: Spectrograms from HRTS are used to find an average net redshift of the O V lines at 1218 and 1371 A at all locations extending from disk center to solar limb. The observed shift in O V is compared with measurements of the O IV line at 1401 A and the Si IV line at 1402 A. Large variations in the shift are found along the instrument slit. Blueshifts are also observed with the sites of the largest upflow located in the sunspot umbrae and in a quiet region close to an active region. The present result could put new constraints on numerical models of flows in the solar transition region and will also be of importance for modeling stellar atmospheres. The spatial variation of line-of-sight velocities in the O V line at 1371A and the SI IV line at 1402 A is illustrated. Title: Multiple flows in the solar transition region. Authors: Brekke, P.; Brynildsen, N.; Kjeldseth-Moe, O.; Maltby, P.; Brueckner, G. E. Bibcode: 1992ESASP.346..211B Altcode: 1992ssts.rept..211B The solar transition region between the chromosphere and the corona shows clear evidence of a fine scale structure that is much smaller than the best available instrumental resolution in the UV of 1×1 arcsec. Previous studies have suggested filling factors of 0.01 - 0.001, with the solar gas being restricted to thin, extended fibrills. New evidence of the fine scale structure is found from its dynamical characteristics, the presence of multiple flows. In multiple flows the solar gas in small volumes show several distinct velocities, resulting in line profiles with more than one velocity component within the spatial resolution element. Multiple velocities are particularly prominent above sunspots, but by no means restricted to these regions. Instead they are clearly a general feature in the solar transition region, occurring in quiet as well as active regions. Title: Observed structure and dynamics of the solar chromosphere and transition region based on high resolution ultraviolet spectrograms Authors: Brekke, Pål Ording Lie Bibcode: 1992PhDT.......306B Altcode: No abstract at ADS Title: Data reduction of HRTS spectral images. Authors: Wahlstrøm, C.; Brekke, P. Bibcode: 1992lest.rept...31W Altcode: A description of the data reduction of the spectral images from High Resolution Telescope and Spectrograph (HRTS) is given. Title: An Ultraviolet Spectral Atlas of a Sunspot and an Active Region 1190--1730 Angstrom Authors: Brekke, P.; Kjeldseth-Moe, O.; Bartoe, J. -D. F.; Brueckner, G. E. Bibcode: 1991ApJS...75.1337B Altcode: An ultraviolet spectral atlas of a sunspot with high spectral and spatial resolution in the wavelength region 1190-1730 A is presented. The atlas contains spectra of three different areas in the sunspot and also of an active region and a quiet region. The selected areas are averaged over several arcsec, ranging from 3.5 arcsec in the sunspot to 18 arcsec in the quiet region. Brief descriptions of the data reduction and calibration procedures are given. The absolute intensities are determined with an accuracy of + or - 30 percent and the wavelength scale is accurate to better than 0.01 A. The transition region lines show the most extreme example known of downflowing gas above a sunspot, a phenomenon which seems to be commonly connected to sunspots. Title: The Solar UV Continuum 1440 - 1680 Å Authors: Kjeldseth-Moe, O.; Brekke, P.; Bartoe, J. -D. F.; Brueckner, G. E. Bibcode: 1991BAAS...23.1060K Altcode: No abstract at ADS Title: Dynamical Evidence of Fine Structure in the Solar Transition Region Authors: Brekke, P.; Kjeldseth-Moe, O.; Bartoe, J. -D. F.; Brueckner, G. E. Bibcode: 1991BAAS...23.1060B Altcode: No abstract at ADS Title: Dynamics in the solar transition region. Authors: Brekke, P.; Brynildsen, N. Bibcode: 1991cwlt.conf...71B Altcode: The authors present an analysis of the dynamical evidence for extreme fine structure in the transition region using the Si IV line at 1402 Å. Gas velocities, line widths and intensities are measured from the line profiles by fitting the profiles to a set of Gaussian components using a least squares method. Both quiet and active regions are studied. The relation of the observed supersonic flow velocities to possible shocks in the flow is briefly discussed. Title: Multiple flow velocities in the transition region Authors: Brekke, P.; Brynildsen, N.; Kjeldseth-Moe, O.; Maltby, P.; Bartoe, J. -D. F.; Brueckner, G. E. Bibcode: 1991AdSpR..11e.251B Altcode: 1991AdSpR..11..251B Observations with the High Resolution Telescope and Spectrograph (HRTS) of the C IV lines at 1550 Å above sunspots reveal the co-existence of several distinct high velocity gas components within the instrument resolution element of 1 × 1 arc second. A further investigation of the HRTS material demonstrates that such multiple gas velocities are not restricted to the temperature region around 105 K, where the C IV lines are formed, but that the gas flows with essentially unchanged speed through all temperature layers from 2.5 × 105 K to 104 K. Furthermore the phenomenon is not restricted to sunspots, but occurs also in other solar regions, often most easily distinguished in active regions. We describe the characteristics of the velocity fields, analyze the mass fluxes and discuss the requirements they place on the resolving power of future space instruments. Title: Multiple downflow velocities above sunspotss Authors: Brekke, P.; Kjeldseth-Moe, O.; Brueckner, G. E. Bibcode: 1990Ap&SS.170..135B Altcode: Supersonic transition zone downflow appears to be commonly occurring above sunspots. The downflow has been observed in 29 emission lines in the ultra-violet spectrum with the High Resolution Telescope and Spectrograph (HRTS) on two rocket flights and on 5 consecutive days during the Spacelab-2 mission. Spectra from the second rocket flight, contain the most extreme example of downflow, showing speeds up to 180 km s-1 and extending over 60 are sec along the slit. The observations demonstrate the existence of several different distinctive flow speeds within the 1 arc sec resolution element throughout the temperature range 7000 240 000 K. Title: An Ultraviolet Spectral Atlas of a Sunspot and an Active Region 1190-1730Å Authors: Brekke, P.; Kjeldseth-Moe, O.; Bartoe, J. -D. F.; Brueckner, G. E. Bibcode: 1990BAAS...22..793B Altcode: No abstract at ADS Title: Observed Line Profiles and Mass Fluxes in the Transition Region above Sunspots Authors: Maltby, P.; Brekke, P.; Brynildsen, N.; Kjeldseth-Moe, O.; Bartoe, J. -D. F.; Brueckner, G. E. Bibcode: 1990PDHO....7..244M Altcode: 1990dysu.conf..244M; 1990ESPM....6..244M Spectrograms obtained with the HRTS show strong mass flows through the transition zone that are particularly prominent above sunspot regions. Most characteristic for the flow associated with sunspots are regions with supersonic downflows, but upward flowing gas is also observed with generally smaller velocities. The flow pattern changes from one day to the next and even within a time span of minutes. An apparent lack of balance between up- and downflowing massfluxes is found. Generally the net massflux appears to be directed downward. Possible reasons for this result are briefly discussed in terms of observability and line emission area filling factor. Title: Transition Region Massflows Associated with Sunspots Authors: Kjeldseth-Moe, O.; Brekke, P.; Brynildsen, N.; Maltby, P.; Brueckner, G. E.; Bartoe, J. -D. F. Bibcode: 1989BAAS...21.1178K Altcode: No abstract at ADS Title: Bildebehandling av solspektra fra romfergen. Authors: Brekke, P.; Brynildsen, N. Bibcode: 1989ATi....22...49B Altcode: No abstract at ADS Title: Gas Flows in the Transition Region above Sunspots Authors: Kjeldseth-Moe, O.; Brynildsen, N.; Brekke, P.; Engvold, O.; Maltby, P.; Bartoe, J. -D. F.; Brueckner, G. E.; Cook, J. W.; Dere, K. P.; Socker, D. G. Bibcode: 1988ApJ...334.1066K Altcode: Strong downflows and moderate upflows in the transition region over a sunspot have been observed with the HRTS on Spacelab 2 in 1985. The flows are persistent in the sense that they are seen in the same spot for 5 days. The downflows are prominent in regions of limited extent (4arcsec - 6arcsec), and flow velocities are in the range 40 - 80 km s-1 and are thus supersonic. Upward flows have smaller velocities, 5 - 20 km s-1, but may extend over a larger area. In the downflowing regions there is always an appreciable amount of gas at rest in the line of sight. Flow speeds derived from the profiles of different lines formed in the transition region between 30,000 and 230,000K are very similar implying constant downflow in this temperature range. Title: Ultraviolet Rocket-Spectra of a Sunspot Authors: Brekke, P.; Kjeldseth-Moe, O.; Bartoe, J. -D. F.; Brueckner, G. E. Bibcode: 1987ESASP.270..341B Altcode: 1987erbp.symp..341B Downflows in the transition zone above a sunspot were observed with a high resolution telescope and spectrograph on a rocket. The rocket spectra on photographic film were digitized. Noise caused by film grains was removed by Fourier filtering. The spectral images were corrected for geometrical distortions and calibrated to give the solar intensity as a function of wavelength. Maximum speeds of 200 km/sec are reached in the flows which extend over 60 arc-sec along the slit. Components with distinct, but lower velocities also appear. The variations with temperature of the characteristic flow speeds are studied. Title: Gasflows in the transition region above sunspots. Authors: Kjeldseth-Moe, O.; Brynildsen, N.; Brekke, P.; Bartoe, J. -D. F.; Brueckner, G. E. Bibcode: 1987ESASP.275...27K Altcode: 1987sspp.symp...27K Gas flows in the transition region in and above sunspots were observed with the High Resolution Telescope and Spectrograph on two rocket flights and during the Spacelab 2 mission. Supersonic downflows of mass from the corona appear to be generally occurring in sunspots. The downflows are often concentrated in regions with typical diameters of 4000 km on the Sun, suggesting a flow in a looplike structure. However, the total flow pattern often has an elongated sheetlike structure of much larger extent. Flow speeds are typically 80 km/sec and show small variation with the temperature of the radiating gas. Much higher flow-speeds (180 km/sec) also occur. Studies of the areas surrounding the sunspot in the Spacelab material reveal the presence of upflows over extended regions with flow-speeds of 10 to 30 km/sec. It is not clear whether the amount of upward flowing gas is sufficient to compensate for the mass flux in the downflows.