UVCS/SOHO PAPERS - 2003


2003-32:   Spectral Line Profile Correction of the Detector Effect: for a SOHO/UVCS Spectrometer

Akinari NAKAGAWA

OPTICAL REVIEW Vol. 10, No. 1 (2003) 47-52. The Optical Society of Japan

It has been noticed that observed spectral line profiles by the SOHO ultraviolet coronagraph spectrometer (SOHO/UVCS) are contaminated by a so-called detector effect, and an iterative correction of observed profiles by convolution with a zero-integral function has been employed to remove this unwanted effect on UVCS detectors. It is shown here that this iteration procedure using a zero-integral function can be replaced by an only-once application of convolution. For zero-integral functions of exp[-|x|/L]-type, the convolution function in this method is proved to have exactly the same, but narrower (steeper), functional form as the original one. These results are also valid, with some modifications, for the discrete case used in numerical calculation.

2003-31:   The Effect of Proton Temperature Anisotropy on the Solar Minimum Corona and Wind


Vásquez, Alberto M.; van Ballegooijen, Adriaan A.; Raymond, John C.

The Astrophysical Journal, Volume 598, Issue 2, pp. 1361-1374.

A semiempirical, axisymmetric model of the solar minimum corona is developed by solving the equations for conservation of mass and momentum with prescribed anisotropic temperature distributions. In the high-latitude regions, the proton temperature anisotropy is strong and the associated mirror force plays an important role in driving the fast solar wind; the critical point where the outflow velocity equals the parallel sound speed (v=c∥) is reached already at 1.5 Rsolar from Sun center. The slow wind arises from a region with open-field lines and weak anisotropy surrounding the equatorial streamer belt. The model parameters were chosen to reproduce the observed latitudinal extent of the equatorial streamer in the corona and at large distance from the Sun. We find that the magnetic cusp of the closed-field streamer core lies at about 1.95 Rsolar. The transition from fast to slow wind is due to a decrease in temperature anisotropy combined with the nonmonotonic behavior of the nonradial expansion factor in flow tubes that pass near the streamer cusp. In the slow wind, the plasma β is of order unity and the critical point lies at about 5 Rsolar, well beyond the magnetic cusp. The predicted outflow velocities are consistent with O5+ Doppler dimming measurements from UVCS/SOHO. We also find good agreement with polarized brightness (pB) measurements from LASCO/SOHO and H I Lyα images from UVCS/SOHO.


2003-30:   Origin of the Solar Wind and Open Magnetic Structures


Habbal, Shadia Rifai


Stars as Suns: Activity, Evolution and Planets, International Astronomical Union. Symposium no. 219, held 21-25 July, 2003 in Sydney, Australia.


Following Parker’s theoretical prediction in 1958 of a subsonic-supersonic solar wind outflow from the Sun space observations soon confirmed its presence at Earth’s orbit. The first EUV and X-ray observations of the Sun in the early 1970’s revealed the complexity of coronal structures dominated by arch-like closed magnetic structures with the exception of dim regions named coronal holes where the EUV and X-ray emissions were significantly reduced. Based originally on the chance occurrence of reduced x-ray emission at the Sun with fast solar wind streams measured at Earth’s orbit coronal holes were soon associated with regions of open magnetic flux and the source of the fast solar wind despite the absence of coronal magnetic field measurements. With the advent of radio occultation and white light measurements the first coronal velocity inferences from UVCS/SOHO the over-the-poles solar wind plasma measurements by Ulysses and polarimetric coronal measurements the widely held view that coronal holes are the sole source of the fast solar wind was revisited. These observations will be highlighted and evidence for the coexistence of open and closed magnetic structures throughout the corona and the implications for the source of the fast and the slow solar wind will be discussed

2003-29:   Interplume as source of the fast solar wind


Teriaca, L.; Poletto, G.; Romoli, M.; Biesecker, D. A.

Memorie della Societa Astronomica Italiana, v.74, p.713 (2003).

High speed solar wind is known to originate in polar coronal holes which, however, are made up of two components: bright, high density regions known as plumes and dark, weakly emitting low density regions known as interplumes. Recent space observations have shown that the width of UV lines is larger in interplume regions. Moreover, observations of the ratio of the O VI doublet lines at 1032 and 1037 Å, at 1.7 Rsun, suggest higher outflows in interplume regions than in plumes at that altitude. In this work we examine SUMER and UVCS observations of a north polar coronal hole taken on 1996 June 3, over the altitude range between 1 and 2 Rsun and, through a Doppler dimming analysis of our data, we show that interplume areas may be really identified as sources of fast wind streams. The behavior of plumes, on the contrary, can be interpreted in terms of static structures embedded in the interplume ambient. We conclude comparing our results with the predictions of theoretical models of the solar wind.

2003-28:   A Transient Heating Model for Coronal Structure and Dynamics 


Spadaro, D.; Lanza, A. F.; Lanzafame, A. C.; Karpen, J. T.; Antiochos, S. K.; Klimchuk, J. A.; MacNeice, P. J.

ApJ, Volume 582, Issue 1, pp. 486-494.

A wealth of observational evidence for flows and intensity variations in nonflaring coronal loops leads to the conclusion that coronal heating is intrinsically unsteady and concentrated near the chromosphere. We have investigated the hydrodynamic behavior of coronal loops undergoing transient heating with one-dimensional numerical simulations in which the timescale assumed for the heating variations (3000 s) is comparable to the coronal radiative cooling time and the assumed heating location and scale height (10 Mm) are consistent with the values derived from TRACE studies. The model loops represent typical active region loops: 40-80 Mm in length, reaching peak temperatures up to 6 MK. We use ARGOS, our state-of-the-art numerical code with adaptive mesh refinement, in order to resolve adequately the dynamic chromospheric-coronal transition region sections of the loop. The major new results from our work are the following: (1) During much of the cooling phase, the loops exhibit densities significantly larger than those predicted by the well-known loop scaling laws, thus potentially explaining recent TRACE observations of overdense loops. (2) Throughout the transient heating interval, downflows appear in the lower transition region (T~0.1 MK) whose key signature would be persistent, redshifted UV and EUV line emission, as have long been observed. (3) Strongly unequal heating in the two legs of the loop drives siphon flows from the more strongly heated footpoint to the other end, thus explaining the substantial bulk flows in loops recently observed by the Coronal Diagnostic Spectrometer and the Solar Ultraviolet Measurement of Emission Radiation instrument. We discuss the implications of our studies for the physical origins of coronal heating and related dynamic phenomena.

2003-27:    Outflow Velocities in the Onset Region of the Solar Wind


Gabriel, Alan H.; Bely-Dubau, Françoise; Antonucci, Ester

Stars as Suns: Activity, Evolution and Planets, International Astronomical Union. Symposium no. 219, held 21-25 July, 2003 in Sydney, Australia


It is well established that the fast solar wind originates during the solar minimum from the polar coronal holes. The object is to investigate this wind onset region to identify the solar structures responsible. We report here the first measurements of outflow velocities between 1.0 and 1.3 Ro in solar plumes using XUV spectral lines from SUMER/SOHO and the Doppler dimming technique. In contrast to what has been suggested by several other observers using SOHO data we conclude that the wind velocity in plumes is greater than in the interplume regions. This tendency diminishes with height so that it may vanish or even reverse at greater distances. We show that one half of the solar wind observed at 1 A.U. from Ulysses originates from the solar plumes at 1.1 Ro. We are extending these observations to 4 Ro using the UVCS/SOHO spectro-coronagraph to understand the connection with plumes seen at greater distances. Initial indications suggest a change in the physical nature of plumes around 2.0 Ro raising questions concerning their relation to the frequently seen white-light plumes at large distances. We explore the possible connection between polar plumes the supergranule network and coronal heating in non-hole regions

2003-26:    Acceleration region of the slow solar wind in corona


Abbo, L.; Antonucci, E.; Mickic, Z.; Riley, P.; Dodero, M. A.; Romoli, M.

Memorie della Societa Astronomica Italiana, v.74, p.733 (2003).

We present the results of a study concerning the physical parameters of the plasma of the extended corona in the low-latitude and equatorial regions, in order to investigate the sources of the slow solar wind during the minimum of solar activity. The equatorial streamer belt has been observed with the Ultraviolet Coronagraph Spectrometer (UVCS) onboard SOHO from August 19 to September 1, 1996. The spectroscopic diagnostic technique applied in this study, based on the OVI 1032, 1037 Ålines, allows us to determine both the solar wind velocity and the electron density of the extended corona. The main result of the analysis is the identification of the acceleration region of the slow wind, whose outflow velocity is measured in the range from 1.7 up to 3.5 solar radii.

2003-25:    Physical parameters of coronal streamers near the maximum phase of solar cycle


Bemporad, A.; Poletto, G.; Romoli, M.

Memorie della Societa Astronomica Italiana, v.74, p.721 (2003).

During june 10-17, 2000 the Ultraviolet Coronograph Spectrometer (UVCS) aboard the Solar and Heliospheric Observatory observed a streamer complex. Data were acquired at the time of a SOHO-Sun-Ulysses quadrature. We identify two streamers for which we derive electron densities, temperatures and elemental abundances and we point out differences and analogies between the two structures. We also derive the coronal Fe/O, which we consider a proxy for the FIP effect and we compare it with Fe/O values measured in situ by SWICS.

2003-24:    The Temerature of the Solar Conora

Noci, G.

Memorie della Societa Astronomica Italiana, v.74, p.704 (2003)

This paper is a historical survey of the temperature determinations in the solar corona. After the description of the early results, it focuses on coronal holes; it discusses the discrepancies of the past and comments on the nearly general present agreement.

2003-23:    Preliminary analysis of a CME observed by SOHO and Ulysses experiments

Bemporad, A.; Poletto, G.; Romoli,l M.; Suess, S. T.

In: Solar variability as an input to the Earth's environment. International Solar Cycle Studies (ISCS) Symposium, 23 - 28 June 2003, Tatranská Lomnica, Slovak Republic. Ed.: A. Wilson. ESA SP-535, Noordwijk: ESA Publications Division, ISBN 92-9092-845-X, 2003, p. 567 - 570.

Over the last week of November 2002 SOHO/LASCO observed several Coronal Mass Ejections, most of which occurring in the NW quadrant. At that time SOHO/UVCS was involved in a SOHO-Sun-Ulysses quadrature campaign, making observations off the west limb of the Sun, at a northern latitude of 27°. Here we focus on data taken at 1.7 solar radii, over a time interval of ≈7 hours, on 26/27 November, 2002, when a large streamer disruption was imaged by LASCO C2 and C3 coronagraphs. UVCS spectra revealed the presence of lines from both high and low ionization ions, such as C III, O VI, Si VIII, IX and XII, Fe X and XVIII, which brighten at different times, with a different time scale and at different positions and are apparently related to different phenomena. In particular, the intensity increase and fast disappearance of the C III 977 Å line represents the passage through the UVCS slit of cold material released in a jet imaged by EIT in the He II 304 Å line. The persistent presence of the Fe XVIII 974 Å line is not easily related to any special feature crossing the UVCS slit. We suggest to interpret this behavior in terms of the reconnection events which lead to the formation of loops observed in the EIT He II 304 Å line.

2003-22:    The ASCE EUV Polarimeter

Romoli,l M.; Fineschi, S.; Uslenghi, M.; Corti, G.; Pace, E.; Ciaravella, A.; Tondello, G.; Noci, G.; Gardner, L.; Kohl, L.

Memorie della Societa Astronomica Italiana, v.74, p.835 (2003).

The SOHO mission has achieved important results in the physics of solar wind and coronal mass ejection acceleration, but most of the processes that drive this acceleration have not yet been explained. The Advanced Spectroscopic and Coronagraphic Explorer (ASCE) mission will carry on-board spectroscopic and polarimetric instrumentation of new generation that is designed to address the fundamental questions on this processes. Following a brief description of ASCE scientific objectives and instrumentation, the EUV polarimetric channel is described. The EUV Polarimeter (EUVP) is designed to measure for the first time the magnetic field vector in the extended corona through the Hanle effect, and the anisotropy of the ion velocity. The EUVP represents the contribution of the Italian solar physics community to the ASCE mission.

2003-21:    The Advanced Spectroscopic and Coronagraphic Explorer: science payload design concept

Gardner, L.D., Kohl, J.L., Daigneau, P.S., Smith, P.L., Strachan, L., Jr., Howard, R.A., Socker, D.G., Davila, J.M., Noci, G., Romoli, M., & Fineschi, S.

Proc. SPIE 4843, pp 1-7.

The Advanced Spectroscopic and Coronagraphic Explorer (ASCE) was proposed in 2001 to NASA's Medium-Class Explorer (MIDEX) Program by the Smithsonian Astrophysical Observatory in collaboration with the Naval Research Laboratory, Goddard Space Flight Center, and the Italian Space Agency. It is one of four missions selected for Phase A study in 2002. ASCE is composed of three instrument units: an Advanced Ultraviolet Coronagraph Spectrograph (AUVCS), an Advanced Large Aperture Visible light Spectroscopic Coronagraph (ALASCO), and an Advanced Solar Disk Spectrometer (ASDS). ASCE makes use of a 13 m long boom that is extended on orbit and positions the external occulters of AUVCS and ALASCO nearly 15 m in front of their respective telescope mirrors. The optical design concepts for the instruments will be discussed.
Keywords: Solar Corona, UV Spectroscopy, Magnetic Fields, Coronagraphs, UV Optics, Polarization

manuscript (PDF)    [ ]

2003-20:     Solar wind acceleration in low density regions

Teriaca, L., Poletto, G., Romoli, M., and Biesecker, D.

SOLAR WIND TEN: Proceedings of the Tenth International Solar Wind Conference. AIP Conference Proceedings, Volume 679, pp. 327-330 (2003).

Recent space observations have shown that the width of UV lines is larger in interplume regions (Giordano/etal:1997, Banerjee/etal:2000) while observations of the ratio of the O VI doublet lines at 1032 and 1037 A, at the altitude of 1.7 solar radii, suggest higher outflows in interplume regions than in plumes (Giordano/etal:2000). These results seem to locate the source of the fast solar wind in the interplume regions. The present work aims at identifying the outflow speed vs. altitude profile of the OVI ions, at heights up to 2 solar radii, both in plumes and interplume regions. To this end, we examined SUMER and UVCS data taken in the North polar coronal hole on June 3, 1996 over the altitude range between 1 and 2 solar
radii. A Doppler dimming analysis applied to our data allows us to determine the outflow speed in interplume regions throughout the range covered by the observations. Our results favor interplumes as sources of fast wind. However, models mimicking observations in plume regions will also be discussed. []

2003-19:     Elemental Abundances for the 1996 Streamer Belt

M. Uzzo, Y. -K. Ko, J. C. Raymond, P. Wurz, and F. M. Ipavich

ApJ, Volume 585, Issue 2, pp. 1062-1072.

The purpose of this paper is to explore the observed physical characteristics of the solar corona streamer belt from 1996 June 1 to August 5. The UV spectral data was collected by the UltraViolet Coronagraph Spectrometer (UVCS) instrument aboard the SOlar and Heliospheric Observatory (SOHO) spacecraft. From this data the abundances of oxygen, silicon, and magnesium were determined on an almost daily basis during this time period at both the west and east limbs. The streamer belt was composed of both active and quiescent streamers, which allows for the comparison of these two categories of magnetic field structures. The depletion of these three elemental abundances in the core of quiescent streamers was found as in previous observations. The variance in abundance with solar rotation was investigated due to the long time frame considered here. The First Ionization Potential (FIP) effect was present in the data and the danger of exploring this phenomena by the traditional FIP bias was also covered. A comparison to {\it in situ} elemental abundance data from the Charge, Element and Isotope Analysis System (CELIAS) instrument on SOHO provides evidence suggesting that active region streamers and the outer ``leg'' structural component of quiescent streamers are definite contributors to the slow solar wind. [ ]

2003-18:     Evolution of A Semi-Circular Flux Rope with Two Ends Anchored in the Photosphere

J. Lin and A. A.van Ballegooijen

JGR, Volume 107, Issue A12, pp. SSH 3-1, CiteID 1438, DOI 10.1029/2002JA009486.

We investigated a coronal magnetic configuration including a semi-circular flux rope with two ends anchored in the photosphere. The background fieldis produced by two source regions on the photosphere. We study theevolution of this configuration in response to the gradual change in the background field, which is modeled by varying either the strength of the source or the distance between the source regions on the photosphere. Our results indicate that the evolution due to the change in source strength shows the likelihood of catastrophic loss of equilibrium, and that the evolution due to the change in the distance is smooth and does not manifest any tendency to lose equilibrium. In the former case, the current sheet starts developing fairly early, it forms even before the evolution reaches the maximum current state. We notice that the effect of the curvature of flux rope on the evolution of the system issignificant, such that the equilibrium curve does not form acusp-catastrop! hic structure but a simple fold-catastrophic structure evenif the evolution is ideal MHD and a current sheet attached to the boundary surface occurs. The curvature strengthens the magnetic compression between the flux rope and the photosphere, and makes the loss of equilibrium easier. But the question of how the system behaves after loss ofequilibrium is still open since the flux rope is not likely to remain semi-circular at the stage of fast evolution. [ ]

2003-17:    Past and Recent Observations of the Solar Upper Atmosphere at Vacuum-Ultraviolet Wavelengths

Wilhelm, K.

J. Atmos. Sol. Terr. Phys. 65, pp.167-189 [ ]

2003-16:    CHIANTI - An Atomic Database for Emission Lines. VI. Proton Rates and Other Improvements

Young, P.R., Del Zanna, G., Landi, E., Dere, K.P., Mason, H.E., Landini, M.

ApJS 144, pp.135-152

The CHIANTI atomic database contains atomic energy levels, wavelengths, radiative transition probabilities, and electron excitation data for a large number of ions of astrophysical interest. Version 4 has been released, and proton excitation data are now included, principally for ground configuration levels that are close in energy. The fitting procedure for excitation data, both electrons and protons, has been extended to allow nine-point spline fits in addition to the previous five-point spline fits. This allows higher quality fits to data from close-coupling calculations where resonances can lead to significant structure in the Maxwellian-averaged collision strengths. The effects of photoexcitation and stimulated emission by a blackbody radiation field in a spherical geometry on the level balance equations of the CHIANTI ions can now be studied following modifications to the CHIANTI software. With the addition of H I, He I, and N I, the first neutral species have been added to CHIANTI. Many updates to existing ion data sets are described, while several new ions have been added to the database, including Ar IV, Fe VI, and Ni XXI. The two-photon continuum is now included in the spectral synthesis routines, and a new code for calculating the relativistic free-free continuum has been added. The treatment of the free-bound continuum has also been updated. [ ]

2003-15:     Spatial and temporal behavior of the oxygen abundance in a streamer complex

Bemporad, A., Poletto, G., Romoli, M.

ESA-SP 506, Proc. of the 10th Meeting of the European Solar Physics Society
Solar variability from Core to Outer Frontiers

The determination of the abundance of trace elements in different solar structures and in the solar wind may be crucial for the identification of the solar wind sources. In the last few years, SOHO data allowed an evaluation of the oxygen abundance at previously unattainable coronal levels \citep{Zangrilli01}. Analyses of streamer data taken at the minimum of the solar activity cycle raised the question of whether streamers' legs might be the site where slow wind originates, because the oxygen abundance in the lateral branches of the streamer, at coronal levels, turned out to be similar to the slow wind abundance. In this work we analyse UVCS streamers observations, taken at 1.6 R_sun, near the maximum phase of the activity cycle, to check whether the behavior found at minimum is shared by streamers at maximum. We derive also the abundance of oxygen in different streamers and, within a streamer, across its axis, to get more information on the spatial variability of the oxygen abundance. Our results show that the oxygen abundance in different streamers may be significantly different and may vary in time, implying that a more thorough analysis is needed before drawing conclusions about the site where slow wind originates. [ ]

2003-14:    The nascent solar wind: origin and acceleration

Teriaca, L., Poletto, G., Romoli, M., and Biesecker, D.

ApJ, volume 588, Issue 1, pp. 566-577.

High speed solar wind is known to originate in polar coronal holes which, however, are made up of two components: bright, high density regions known as plumes, and dark, weakly emitting low density regions known as interplumes. Recent space observations have shown that the width of UV lines is larger in interplume regions while observations of the ratio of the O VI doublet lines at 1032 and 1037 A, at 1.7 solar radii, suggest higher outflows in interplume regions than in plumes at that altitude. These results favor interplumes regions as sources of the fast solar wind. The present work aims at investigating the outflow speed vs. altitude properties of the O VI and H I ions, at heights below 2 solar radii, both in plumes and interplume regions. To this end, we examined SUMER and UVCS observations of a north polar coronal hole taken on 1996 June 3, over the altitude range between 1 and 2 solar radii and, through a Doppler dimming analysis of our data, we show that interplume areas may be really identified as sources of fast wind streams. The behavior of plumes, on the contrary, can be interpreted in terms of static structures embedded in the interplume ambient. We conclude comparing our results with the predictions of theoretical models of the solar wind and giving an empirical estimate of the heating rate, per particle, for H I and O VI ions, in interplume regions at 1.75 and 2.0 solar radii. [ ]

2003-13:     Theories of Solar Eruptions: A Review (Invited)

J. Lin, W. Soon, and S. L. Baliunas

New Astronomy Reviews, Volume 47, Issue 2, p. 53-84..

This review highlights current theoretical research on eruptive phenomena in the solar atmosphere. We start by looking backupon the early theories and their development. Any theory and model of solar eruptions must explain two key aspects of eruption physics. The first aspect concerns the original cause of the eruption and the second pertains to the nature of the morphological features that form during its evolution. Those features include rapidejection of large-scale magnetic flux and plasma into interplanetary space, and the separating of ribbons of ha emission on the solar disk joined by a rising arcade of soft X-ray and ha loops, with hard X-ray emission at their summits and feet. We intercompare relevant theories and models by discussing their advantages as well as by pointing out important aspects that need improvement. [ ]

2003-12:     Far UV Spectra of the Coronal Mass Ejection Associated with the 2002 April 21 X-Class Flare

J.C. Raymond, A. Ciaravella, D. Dobrzycka, L. Strachan, Y.-K. Ko and M. Uzzo

ApJ, volume 597, Issue 2, pp. 1106-1117.

The X-class solar flare on 2002 21 April was observed with many instruments, and it produced a very fast Coronal Mass Ejection (CME). We present observations of the CME made with the UltraViolet Coronagraph Spectrometer (UVCS). The spectra provide physical parameters of the pre-CME streamer and Doppler velocities during the streamer blowout. The blowout appears as a rapid fading of the O VI emission at zero velocity and the rapid acceleration of sheets of gas to 800 km s-1. A small, transient brightening in the [Fe XVIII] 974 A line shows rapidly moving hot plasma, perhaps related to reconnection heating associated with ejection of the CME. Observations of a remarkably similar CME observed on 2002 23 August are included for comparison.

full text (.ps) [ ]

2003-11:     Doubly Ionized Carbon Observed in the Plasma Tail of Comet Kudo-Fujikawa

Povich, M. C., Raymond, J. C., Jones, G. H. Uzzo, M, Ko, Y-K, Feldman, P. D., Smith, P.L., Marsden, B, Woods, T.

Science, Volume 302, Issue 5652, pp. 1949-1952.

 Comet C/2002 X5 (Kudo-Fujikawa) was observed near its perihelion of 0.19 astronomical unit by the Ultraviolet Coronagraph Spectrometer aboard the Solar and Heliospheric Observatory spacecraft. Images of the comet reconstructed from high-resolution spectra reveal a quasi-spherical cloud of neutral hydrogen and a variable tail of C+ and C2+ that disconnects from the comet and subsequently regenerates. The high abundance of C2+ and C+, at least 24% relative to water, cannot be explained by photodissociation of carbon monoxide and is instead attributed to the evaporation and subsequent photoionization of atomic carbon from organic refractory compounds present in the cometary dust grains. This result serves to strengthen the connection between comets and the material from which the Solar System formed. 

2003-10:     Solar wind characteristics from SOHO-Sun-Ulysses quadrature observations

G. Poletto and S. T. Suess

SOLAR WIND TEN: Proceedings of the Tenth International Solar Wind Conference. AIP Conference Proceedings, Volume 679, pp. 102-105 (2003).

Coronal and solar wind studies made at the time the same plasma is first observed remotely in the corona, and, later on, in situ, provide the best way to determine the evolution of plasma as it is being accelerated from the corona out to interplanetary distances. We have used this technique to derive solar wind characteristics from the analysis of data acquired by SOHO and Ulysses when the SOHO-Sun-Ulysses included angle is 90 degrees: that is, when SOHO, the Sun and Ulysses are in quadrature. As an example of the information that can be derived from observations acquired at these times, we summarize here the results obtained from the study of the December 1998 quadrature, when we focussed on the behavior of slow wind from low-latitude regions, and anticipate some results from the June 2000 quadrature, which is being analyzed, when we focussed on establishing a relationship between coronal and wind abundances of different elements. We conclude by illustrating briefly the objectives of future quadrature studies. [ ]

2003-09:    Plasma Properties above coronal active regions inferred from SOHO/UVCS and radio spectrograph observations

S. Mancuso, J.C. Raymond, J. Kohl, Y.-K. Ko, M. Uzzo and R. Wu

Astronomy & Astrophysics, v.400, p.347-353 (2003) .

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2003-08:     Dynamical and Physical Properties of a Post-CME Current Sheet

Ko, Y.-K., J. C. Raymond, J. Lin, G. Lawrence, J. Li, A. Fludra

ApJ, volume 594, Issue 2, pp. 1068-1084.

On January 8, 2002, a coronal mass ejection (CME) occurred at the east limb which has constant acceleration of 0.19 km/s above 2.76 Ro. Its plane-of-sky speed reached as high as 1800 km/s by 14 Ro. There is strong evidence that it underwent a much larger acceleration ($sim$ 1 km/s$2$) below 2.76 Ro. Following this fast CME, thin threads of material were formed, as seen in the white light corona, with continuous outflow that lasted more than two days as it gradually moved toward the north.We interpret it as a current sheet left behind the CME. Two groups of post-CME loops were formed at the limbwhich grew in height. UV/EUV spectra were taken on January 10 by it Solar and Heliospheric ObservatoryUltraviolet Coronagraph Spectrometer (SOHO/UVCS) and Coronal Diagnostic Spectrometer (SOHO/CDS) as part of theSOHO Joint Observing Program (JOP) 151. The UV spectra at 1.53 Ro show a small region ($sim$ 70 arcsec) ofenhanced low temperature emission and a high temperature region ($sim$ 190 arcsec) where lines from highlyionized ions such as Fe$+17$ and Ca$+13$ are observed. This high temperature emission ($sim$ 4 million degrees) was along the direction of the current sheet seen in the white light corona. We combine the data from UVCS, Large Angle andSpectrometric Coronagraph Experiment (LASCO), EUV Imaging Telescope (EIT) and CDS on SOHO to obtain the dynamical properties (outflow speed and acceleration) of this CME and the current sheet it left behind, aswell as the physical properties (electron temperature, electron density and elemental abundances) inthe current sheet. Implications for its formation and magnetic properties are discussed. []

2003-07:     Physical Parameters of the Feb 11, 2000 Coronal Mass Ejection: UV Spectra vs White Light Images

A. Ciaravella, J. C. Raymond, A. van Ballegooijen, L. Strachan, A. Vourlidas , J. Li , J. Chen & A. Panasyuk

ApJ, volume 597, Issue 2, pp. 1118-1134.

We present spectra of a three-part CME observed by the UltraViolet Coronagraph Spectrometer (UVCS/SOHO) on Feb. 11, 2000. Images of the CME in different spectral lines show how the morphology depends on the temperature, density and outflow speed of the ejected plasma. The H I Lyman-alpha is the line that best resembles the white light data, although it can be rather different where the outflow speed severely dims its radiative component. We estimate the ranges of temperature, density, and the plane-of-the-sky, outflow and line of sight speeds in the front, prominence core and void.

The plasma in the front was denser, cooler and more depleted in O and Si than the ambient coronal streamer. These characteristics indicate that it originated in the closed field core of the pre-CME streamer. The leading edge was not the projection of a simple spherical shell onto the plane of the sky. Line profiles suggest a wide loop-like structure, though a more complete shell that was brighter in some areas could also match the data. The prominence has a structure in temperature and density with the hotter top end emitting in the Mg X and Si XII lines while the bottom end was much cooler and visible just in the H I Lyman lines. Emission in the void was rather faint. The outflow speed obtained from Doppler dimming of the radiative lines, the line of sight speed measured from the Doppler shift of the lines and the plane of the sky speed estimated from the comparison of the images taken at 2.3 and 2.6 Rsun give speeds much lower than those estimated at higher heights (>4 Rsun) from the LASCO and indicate a stronger acceleration at the lower heights.

2003-06:     Empirically Determined Anisotropic Velocity Distributions and Outflows of O^5+ Ions in a Coronal Streamer at Solar Minimum

R. A. Frazin, S. R. Cranmer & J. L. Kohl

ApJ, volume 597, Issue 2, pp. 1145-1157.

Empirical constraints on the O^5+ velocity distributions and outflow speeds in a solar minimum equatorial streamer between 2.6 and 5.1 R_sun are determined using a spectral synthesis code that includes O VI Doppler dimming. These constraints follow directly from UV spectra taken on 12 October 1996 with the Ultraviolet Coronagraph Spectrometer (UVCS) on the SOHO satellite and 3D electron densities derived from tomography applied to a time series of polarized white-light images taken with the Large Angle and Spectrometric Coronagraph (LASCO) on SOHO. Four conclusions result from this work: 1) our analysis shows O^5+ velocity distribution anisotropy in the streamer legs and stalk and also shows that the microscopic velocity distribution (which excludes wave motions that equally affect all charged particles) is anisotropic, where the most probable speed perpendicular to the magnetic field direction exceeds that in the parallel direction; 2) there is preferential heating of the O^5+ ions over the protons in the streamer stalk and legs. 3) There is no evidence for preferential O^5+ heating in the core; 4) the outflow velocity of the O^5+ ions is determined at heights above 4.6 R_sun. All results have a confidence level of at least 70 %.

manuscript (PDF)

2003-05:    Temporal evolution of a streamer complex: coronal and in situ plasma parameters

Bemporad, A., G. Poletto, S. T. Suess, Y.-K. Ko, S. Parenti, P. Riley, M. Romoli, and T. Z. Zurbuchen

ApJ, submitted, Volume 593, Issue 2, pp. 1146-1163.

In this paper we report on observations acquired by the UVCS spectrograph on SOHO, from 10 to 17 June 2000, at the time of a SOHO-Sun-Ulysses quadrature. UVCS took data at 1.6 and 1.9 solar radii, with a slit normal to the solar radius and centered along the radial to Ulysses. A streamer complex was sampled by UVCS, throughout the quadrature campaign, giving us the opportunity to derive plasma parameters in different streamers, and to compare them with plasma properties measured in situ. LASCO images above 2 solar radii helped us understand the temporal evolution of the streamer complex. We derive densities, temperatures and elemental abundances in two streamers, which have different temperatures and element abundances. In spite of these differences, both structures have the same FIP bias. The Fe/O ratio, which may be considered a proxy for the FIP effect, was measured in situ by SWICS. Values of Fe/O measured in the corona, at the sites where in situ plasma originated, agree with in situ Fe/O values.

2003-04:    Ultraviolet spectroscopy of narrow coronal mass ejections

D. Dobrzycka, J.C. Raymond, D.A. Biesecker, J. Li, and A. Ciaravella

ApJ, Volume 588, Issue 1, pp. 586-595.

We present Ultraviolet Coronagraph Spectrometer (UVCS) observations of5 narrow coronal mass ejections (CMEs) that were among 15 narrow CMEsoriginally selected by Gilbert et al. (2001). Two events (1999 March27, April 15) were structured, i.e. in white light data theyexhibited well defined interior features, and three (1999 May 9, May21, June 3) were unstructured, i.e. appeared featureless. In UVCSdata the events were seen as 4-13 deg wide enhancements of thestrongest coronal lines HI Lyman alpha and OVI 1032, 1037 A.We derived electron densities for severalof the events from the Large Angle Spectrometric Coronagraph (LASCO)C2 white light observations. They are comparable to or smaller thandensities inferred for other CMEs. We modeled the observableproperties of examples of the structured (1999 April 15) andunstructured (1999 May 9) narrow CMEs at different heights in thecorona between 1.5 Rs and 2 Rs. The derived electrontemperatures, densities and outflow speeds are! similar for those twotypes of ejections. They were compared with properties of polarcoronal jets and other CMEs. We discuss different scenarios of narrowCME formation either as a jet formed by reconnection onto open fieldlines or CME ejected by expansion of closed field structures. Overall, we conclude that the existing observations do not definitively placethe narrow CMEs into the jet or the CME picture, but the accelerationof the 1999 April 15 event resembles acceleration seen in many CMEs,rather than constant speeds or deceleration observed in jets.

2003-03:    Alfvenic Turbulence in the Extended Solar Corona: Kinetic Effects and Proton Heating

S. R. Cranmer and A. van Ballegooijen

ApJ, volume 594, Issue 1, pp. 573-591.

We present a model of magnetohydrodynamic (MHD) turbulence in the extended solar corona that contains the effects of collisionless dissipation and anisotropic particle heating. Recent observations have shown that preferential heating and acceleration of positive ions occurs in the first few solar radii of the high-speed solar wind. Measurements made by the Ultraviolet Coronagraph Spectrometer aboard SOHO have revived interest in the idea that ions are energized by the dissipation of ion cyclotron resonant waves, but such high-frequency (i.e., small wavelength) fluctuations have not been observed. A turbulent cascade is one possible way of generating small-scale fluctuations from a pre-existing population of low-frequency MHD waves. We model this cascade as a combination of advection and diffusion in wavenumber space. The dominant spectral transfer occurs in the direction perpendicular to the background magnetic field. As expected from earlier models, this leads to a highly anisotropic fluctuation spectrum with a rapidly decaying tail in the parallel wavenumber direction. The wave power that decays to high enough frequencies to become ion cyclotron resonant depends on the relative strengths of advection and diffusion in the cascade. For the most realistic values of these parameters, though, there is insufficient power to heat protons and heavy ions. The dominant oblique fluctuations (with dispersion properties of kinetic Alfven waves) undergo Landau damping, which implies strong parallel electron heating. We discuss the probable nonlinear evolution of the electron velocity distributions into parallel beams and discrete phase-space holes (similar to those seen in the terrestrial magnetosphere) which can possibly heat protons via stochastic interactions.

2003-02:    Formation of minor ion charge states in the fast solar wind: roles of differential flow speeds of ions of the same element

Y. Chen, R. Esser & Y. Hu

ApJ 582, 467-74

To investigate the possibility of differential flow speeds between ions of the same element and their roles in the determination of ionic fractions, this paper extends our latest minor ion model to a five-fluid model, describing the behavior of five species of minor ions of one given element in the fast solar wind. We solve the five sets of mass, momentum and energy equations simultaneously to include the effects of ionization, recombination and heating. The five species of minor ions are taken as test particles flowing in a background plasma consisting of electrons, protons and alpha particles. The parameters of the background gas are calculated using a previous three-fluid wave-driven magneto-hydrodynamic model for the fast solar wind. These background parameters are modeled as closely as possible to observed values. Using this background of fast solar wind parameters, the five-fluid minor ion model has no problem reproducing the frozen-in charge state distribution! s observed in the fast solar wind for C and O ions, while the modeled ionic fractions of Si, Mg, and Fe show significant shifts to lower charge states compared with the observed values. It is found that the majority of C and O ions are frozen-in below 1.2 solar radii, while most Si, Mg and Fe ions are frozen-in beyond 1.3 to 1.5 solar radii. Comparing the cases with and withoutdifferential flows shows that even though differential flow speeds between ions of the same element do develop beyond a certain heliocentricdistance (e.g., 1.2 solar radii for Si ions), they can not account for the high ion charge states observed in situ.

2003-01:    Helium Abundance in the corona and solar wind: Gyrotropic Modeling from the Chromosphere to 1 AU

O. Lie-Svendsen, V. H. Hansteen and E. Leer

ApJ, Volume 596, Issue 1, pp. 621-645.

We have developed a solar wind model including helium that extends from the chromosphere to 1 AU. The model is based on the gyrotropic approximation to the 16-moment set of fluid transport equations, which allows it to accommodate temperature anisotropies, as well as nonclassical heat transport. We find that, as in a pure electron-proton solar wind, the flow geometry close to the Sun also has a large impact on helium. In a radially expanding flow, downward proton heat conduction from the corona leads to a high transition region pressure and a large thermal force that pulls helium ions into the corona. In this case α-particles may easily become the dominant species in the corona, resulting in a polar wind type of solar wind in which the light protons are accelerated outward in the electric field set up by the α-particles and electrons. By contrast, applying the same form for the coronal heating in a rapidly expanding geometry intended to simulate a coronal hole, protons become collisionless closer to the Sun, and therefore the downward proton heat flux is smaller, resulting in a lower transition region pressure and a lower thermal force on helium. In this case the helium abundance is low everywhere and helium is unimportant for the acceleration of the solar wind. For the low coronal proton and α-particle densities found in the rapidly expanding flow, where asymptotic flow speeds are typically significantly higher than the gravitational escape speed at the solar surface, the solar wind helium mass flux is determined by the amount of helium available at the top of the chromosphere. In the radially expanding flow, with asymptotic flow speeds lower than the escape speed, the helium mass flux depends on the amount of energy available in the corona to lift helium out of the gravitational potential. In both cases the frictional coupling between helium and hydrogen in the chromosphere, using currently accepted elastic cross sections, is too weak to pull a sufficient number of helium atoms up to the top of the chromosphere and thus obtain a mass flux in agreement with observations. A better understanding of the chromosphere is therefore called for.