Y. Q. Hu, R. Esser, and S. R. Habbal
JGR, 102, 17419.
We explore the energy requirements for the fast solar wind when the anisotropy
in the proton temperature is taken into account. Using a one-dimensional,
two-fluid model with anisotropic proton temperature, we present high-speed
solar wind solutions which meet most of the empirical constraints currently
available from in situ measurements in interplanetary space and very recent
remote sensing observations of the inner corona. Included in the model is
the momentum exerted on the flow by Alfvén waves, as well as heating
due to their damping. However, to produce solutions consistent with these
empirical constraints, additional heat input to both electrons and protons,
as well as momentum addition to the protons, are found to be needed. These
are described by ad hoc functions with adjustable parameters. While classical
thermal conduction is adopted for both electrons and protons in the inner
corona in the model computations, the corresponding heat fluxes in the outer
corona are limited to values comparable to current observations. The fast
solar wind solutions thus obtained differ from each other mainly in their
thermal properties within 0.3 AU from the Sun, a region that is still poorly
probed by in situ and remote sensing measurements. To satisfy observational
constraints, we find that the inclusion of a proton temperature anisotropy
in the modeling of the solar wind requires that either the protons be highly
anisotropic in the inner corona or that there exist a mechanism, in addition
to adiabatic expansion, to cool them in the direction parallel to the magnetic
field. Given these observational constraints and in the absence of knowledge
of an efficient cooling mechanism, our model computations imply that the maximum
temperature of the protons in the parallel direction has to be limited to
106K in the corona. Furthermore, because of the strong coupling
between electrons and protons, and between the parallel and perpendicular
motions, at the coronal base, the electron temperature as well as the perpendicular
proton temperature cannot be much higher than 106K there. Although
thermal anisotropy of the protons is found to have little influence on the
dynamics of the fast solar wind, its inclusion imposes new requirements on
the unknown coronal heating mechanisms.
Cranmer, S. R., Field, G. B., and Kohl, J. L.
ASP Conf. Ser. 154, page 592
Cranmer, S. R., Field, G. B., Noci, G., and Kohl, J. L.
ESA SP-415, page 89
Verneta, A. I.
ESA SP-404, 709
1997-35: Signature of open magnetic field lines in the extended solar corona and of solar wind acceleration
E. Antonucci, S. Giordano, C. Benna,
J.L. Kohl, G. Noci, J. Michels, S. Fineschi.
ESA SP-404, 175-182
1997-34: The quiescent corona and slow solar wind
G. Noci, J.L. Kohl, E. Antonucci,
G. Tondello, M.C.E. Huber, S. Fineschi, L.D. Gardner, C.M. Korendyke, P.
Nicolosi, M. Romoli, D. Spadaro, L. Maccari, J.C. Raymond, O.H.W. Siegmund,
C. Benna, A. Ciaravella, S. Giordano, J. Michels, A. Modigliani, G. Naletto,
A. Panasyuk, C. Pernechele, G. Poletto, P.L. Smith, L. Strachan.
ESA SP-404, 75-84
1997-33: Spectroscopic observations of the extended corona during the SOHO whole sun month
L. Strachan, J.C. Raymond,
A.V. Panasyuk, S. Fineschi, L.D. Gardner, E. Antonucci, S. Giordano, M. Romoli,
G. Noci, and J.L. Kohl
1997, Fifth SOHO Workshop ESA SP-404, 691-696
1997-32: Physical Parameters in Plume and Interplume Regions from UVCS Observations
Corti, G. et al.
ESA SP-404, 289
1997-31: Ultraviolet spectroscopy of a coronal mass ejection with UVCS
A. Ciaravella, J. Raymond,
S. Fineschi, M. Romoli, C. Benna, L. Gardner, S. Giordano, R. O'Neal, J.
Michels, E. Antonucci, G. Noci, J. Kohl
ESA SP-404, 279-282
1997-30: Solar wind acceleration in the solar corona
S. Giordano, E. Antonucci,
C. Benna, J.L. Kohl, G. Noci, J. Michels and S. Fineschi.
ESA, SP-415, 327-330
1997-28: Intercomparison between UVCS/WLC and LASCO/C2 measured polarized brightness
M. Romoli, D. Biesecker, C. Benna, S. Fineschi, P.L. Lamy, A. Llebaria, J.L. Kohl, G. Noci.
1997, Fifth SOHO Workshop ESA SP-404, 637-639
1997-27: UVCS/SOHO empirical models of solar coronal holes
S.R. Cranmer, J.L.Kohl, G.
Noci, L.Strachan, A.V. Panasyuk, M. Romoli, S. Fineschi, D. Dobrzycka, J.C.
Raymond, R.M. Suleiman and R.H. O'Neal
1997, Fifth SOHO Workshop ESA SP-404, 295-298
1997-26: K-Corona polarized brightness and electron density measurement with the visible light polarimeter of UVCS
M. Romoli, C. Benna, S. Cranmer,
S. Fineschi, L.D. Gardner, L. Strachan, J.L. Kohl, G. Noci.
1997, Fifth SOHO Workshop ESA SP-404, 633-636
1997-25: SOHO observations of the north polar solar wind
G. Peres, A Ciaravella, R.
Betta, S. Orlando, F. Reale, J. Kohl, G. Noci, S. Fineschi, M. Romoli, P.
Brekke, A. Fludra, J.B. Gurman, P. Lemaire, U. Schuhle.
1997, Fifth SOHO Workshop ESA SP-404, 587-590
1997-24: Ultraviolet observations of coronal mass ejections
A. Ciaravella, J.C. Raymond,
C. Benna, S. Fineschi, L.D. Gardner, S. Giordano, R.H. O'Neal, F. Reale,
M. Romoli, J. Michels, E. Antonucci, J.L Kohl, G. Noci.
1997, ESLAB Symposium, ESA SP-415, 543
1997-23: Ultraviolet Coronagraph Spectrometer Observation of the 1996 December 23 Coronal Mass Ejection
CIARAVELLA, A.; RAYMOND, J. C.;
FINESCHI, S.; ROMOLI, M.; BENNA, C.; GARDNER, L.; GIORDANO, S.; MICHELS,
J.; O'NEAL, R.; ANTONUCCI, E.; KOHL, J.; NOCI, G.
1997, Ap.J. Letters, 491, L59
The Ultraviolet Coronagraph Spectrometer (UVCS) aboard the Solar and Heliospheric Observatory (SOHO) observed a spectacular coronal mass ejection (CME) caused by a prominence eruption on 1996 December 23. The evolution of the ejected prominence material was followed for 1 hr and 50 minutes. The observation consists of a series of 5 minute exposures, at a fixed heliocentric distance of 1.5 R _{solar} in several spectral ranges. The Lyman lines of hydrogen brighten more than 2 orders of magnitude during the CME. The C III 977.02 A line is very bright, and many other low-temperature lines have been detected. Line intensities and profiles provide important diagnostics for the physical and dynamical parameters of the ejected plasma. Lines widths show nonthermal line broadening due to a plasma expansion with velocity larger than 50 km s-1. The Ly alpha inside the CME region shows red and blue shifts, up to 0.2 A (50 km s-1) and 0.8 A (200 km s-1), respectively. A preliminary estimate shows a flat emission measure distribution 3 or 4 orders of magnitude smaller than typical prominence emission measures. Essentially the same structure in space and velocity is seen in the Lyman lines, in C III (10^{5} K) and in O VI (3x10^{5} K).
1997-22: Ultraviolet Coronagraph Spectrometer Observations of Density Fluctuations in the Solar Wind
OFMAN, L.; ROMOLI, M.; POLETTO, G.;
NOCI, G.; KOHL, J. L.
1997, Ap.J. Letters, 491, L111
Recent Ultraviolet Coronagraph Spectrometer (UVCS) white-light channel (WLC) observations on board the Solar and Heliospheric Observatory (SOHO) indicate quasi-periodic variations in the polarized brightness (pB) in the polar coronal holes. This is the first observation of possible signatures of compressional waves high above the limb (at heliocentric distances in the range 1.9-2.45 Rsolar). The Fourier power spectrum of the pB time series at 1.9 Rsolar shows significant peak at about 6 minutes and possible fluctuations on longer timescales (20-50 minutes). The observation at 1.9 Rsolar is the only currently available WLC data set with sufficient cadence to resolve the 6 minute period. These preliminary observations may result from density fluctuations caused by compressional waves propagating in polar coronal holes. We stress that our results are preliminary, and we plan future high-cadence observations in both plume and interplume regions of coronal holes. Recently, Ofman & Davila used a 2.5 D MHD model and found that Alfven waves with an amplitude of 20-70 km s-1 at the base of the coronal hole can generate nonlinear, high-amplitude compressional waves that can contribute significantly to the acceleration of the fast solar wind. The nonlinear solitary-like waves appear as fluctuations in the density and the radial outflow velocity and contribute significantly to solar wind acceleration in open magnetic field structures. The motivation for the reported observations is the MHD model prediction.
1997-21: The
Lyman alpha line from the solar wind acceleration region: Results from an
eight-moment approximation two-fluid solar wind model
E. L. Olsen
1997, Geophys. Res. Letters, 24, 2873
1997-20: First Results from the SOHO Ultraviolet Coronagraph Spectrometer
J.L. Kohl, G. Noci, E. Antonucci,
G. Tondello, M.C.E. Huber, S. Fineschi, L.D. Gardner, G. Naletto, P. Nicolosi,
J.C. Raymond, M. Romoli, D. Spadaro, B. Martin, J. Michels, C. Benna, A.
Ciaravella, S. Cranmer, M. Karovska, S. Giordano, A. Modigliani, A. Panasyuk,
C. Pernechele, G. Poletto, O.H.W. Siegmund, P.L. Smith, L. Strachan
1997, Solar Physics, 175, 613 (1997)
The SOHO Ultraviolet Coronagraph Spectrometer (UVCS/SOHO) is being used to observe the extended solar corona from 1.25 to 10 solar radius from Sun center. Initial observations of polar coronal holes and equatorial streamers are described. The observations include measurements of spectral line profiles for H I Ly alpha and Ly beta, O VI 1032 A and 1037 A, Mg X 625 A, Fe XII 1242 A and several others. Intensities for Mg X 610 A, Si XII 499 A and 520 A, S X 1196 A,and 22 others have been observed. Preliminary results for derived H, O, Mg and Fe velocity distributions and initial indications of outflow velocities for O are described.
1997-19: Plume and interplume regions and solar wind acceleration in polar coronal holes between 1.5 and 3.5 R
S. Giordano, E. Antonucci,
C. Benna, M. Romoli, G. Noci, J.L. Kohl, S. Fineschi, J. Michels, G. Naletto.
1997, Fifth SOHO Workshop ESA SP-404, 413-416
1997-18: Velocity Fields in the Solar Corona Mass Ejections as Observed with UVCS-SOHO
E. Antonucci, J.L. Kohl, G. Noci,
G. Tondello, M.C.E. Huber, L.D. Gardner, P. Nicolosi, S. Fineschi, J.C. Raymond,
M. Romoli, D. Spadaro, O.H.W. Siegmund, C. Benna, A. Ciaravella, S. Giordano,
J. Michels, A. Modigliani, A. Panasyuk, C. Pernechele, P.L. Smith, L. Strachan,
R. Ventura
1997, Ap.J. Letters 1997, 490, L183
This paper presents the observations of the first two coronal mass ejections (CMEs) obtained with the Ultraviolet Coronagraph Spetrometer of SOHO. Both CMEs where observed at high spectral resolution in the ultraviolet domain. The first event on June 6--7 1996 was observed in H I Ly 1216 and Ly 1026, O VI 1032 and 1037, Si XII 499 and 521 and imaged within 1.5 and 5 solar radius. The second event on December 23 1996 was observed in several H I lines and cool lines such as C III 977, N III 990--992 and O V 630. The analysis of line profiles has allowed us to determine the l.o.s. velocities of the extended corona during a mass ejection. In particular there is evidence for mass motions consistent with untwisting magnetic fields around an erupted fluxtube in one of the events and line of sight velocities of 200 in the early phase of the second event presumably related to the expansion of the leading arch of the transient.
1997-17: Origins of the Slow and the Ubiquitous Fast Solar Wind
HABBAL, S. R.; WOO, R.; FINESCHI,
S.; O'NEAL, R.; KOHL, J.; NOCI, G. KORENDYKE, C.
1997, Ap.J. Letters, 489, L103
We present in this Letter the first coordinated radio occultation measurements and ultraviolet observations of the inner corona below 5.5Rs, obtained during the Galileo solar conjunction in 1997 January, to establish the origin of the slow solar wind. Limits on the flow speed are derived from the Doppler dimming of the resonantly scattered component of the oxygen 1032 and 1037.6 A lines as measured with the ultraviolet coronagraph spectrometer (UVCS) on the Solar and Heliospheric Observatory (SOHO). White light images of the corona from the large-angle spectroscopic coronagraph (LASCO) on SOHO taken simultaneously are used to place the Doppler radio scintillation and ultraviolet measurements in the context of coronal structures. These combined observations provide the first direct confirmation of the view recently proposed by Woo & Martin that the slow solar wind is associated with the axes, also known as stalks, of streamers. Furthermore, the ultraviolet observations also show how the fast solar wind is ubiquitous in the inner corona and that a velocity shear between the fast and slow solar wind develops along the streamer stalks.
1997-16: Composition of Coronal Streamers from the SOHO Ultraviolet Coronagraph Spectrometer
J.C. Raymond, J.L. Kohl, G. Noci,
E. Antonucci, G. Tondello, M.C.E. Huber, L.D. Gardner, P. Nicolosi, S. Fineschi,
M. Romoli, D. Spadaro, O.H.W. Siegmund, C. Benna, A. Ciaravella, S. Cranmer,
S. Giordano, M. Karovska, R. Martin, J. Michels, A. Modigliani, G. Naletto,
A. Panasyuk, C. Pernechele, G. Poletto, P.L. Smith, R.M. Suleiman, L. Strachan
1997, Solar Physics 175, 645
The Ultraviolet Coronagraph Spectrometer on the SOHO satellite covers the 940-1350 A range as well as the 470-630 A range in second order. It has detected coronal emission lines of H, N, O, Mg, Al, Si, S, Ar, Ca, Fe, and Ni, particularly in coronal streamers. Resonance scattering of emission lines from the solar disk dominates the intensities of a few lines, but electron collisional excitation produces most of the lines observed. Resonance, intercombination and forbidden lines are seen, and their relative line intensities are diagnostics for the ionization state and elemental abundances of the coronal gas. The elemental composition of the solar corona and solar wind vary, with the abundance of each element related to the ionization potential of its neutral atom (First Ionization Potential-FIP). It is often difficult to obtain absolute abundances, rather than abundances relative to O or Si. In this paper, we study the ionization state of the gas in two coronal streamers, and we determine the absolute abundances of oxygen and other elements in the streamers. The ionization state is close to that of a Log T = 6.2 plasma. The abundances vary among, and even within, streamers. The helium abundance is lower than photospheric, and the FIP effect is present. In the core of a quiescent equatorial streamer, oxygen and other high-FIP elements are depleted by an order of magnitude compared with photospheric abundances, while the depletion along the edges of the streamer is only a factor of 3. The abundances along the edges of the streamer (`legs') closely resemble elemental abundances measured in the slow solar wind, supporting the identification of streamers as the source of that wind component.
1997-15: First Results from UVCS
G. Noci, J.L. Kohl, E. Antonucci,
G. Tondello, M.C.E. Huber, S. Fineschi, L.D. Gardner, G. Naletto, P. Nicolosi,
J.C. Raymond, M. Romoli, D. Spadaro, A.A. Van Ballegooijen, C. Benna, A.
Ciaravella, S. Giordano, A. Modigliani, A. Panasyuk, C. Pernechele, G. Poletto,
O.H.W. Siegmund, P.L. Smith, L. Strachan
1997, Advances in Space Research 20, 2219
We present here the first results obtained by the Ultraviolet Coronagraph Spectrometer (UVCS) operating on board the SOHO satellite. The UVCS started to observe the extended corona at the end of January 1996; it routinely obtains coronal spectra in the 1145 A - 1287 A, 984 A- 1080 A ranges, and intensity data in the visible continuum. Through the composition of slit images it also produces monocromatic images of the extended corona. The performance of the instrument is excellent and the data obtained up to now are of great interest. We briefly describe preliminary results concerning polar coronal holes, streamers and a coronal mass ejection, in particular: the very large r.m.s. velocities of ions in polar holes (hundreds km/sec for O VI and Mg X); the puzzling difference between the H I Ly image and that in the O VI resonance doublet, for most streamers; the different signatures of the core and external layers of the streamers in the width of the ion lines and in the O VI doublet ratio, indicating larger line-of-sight (l.o.s.) and outflow velocities in the latter.
1997-14 Measurements of H I and O VI velocity distributions in the extended corona with UVCS/SOHO and UVCS/SPARTAN
J.L. Kohl, G. Noci, E. Antonucci,
G. Tondello, M.C.E. Huber, L.D. Gardner, P. Nicolosi, S. Fineschi, J.C. Raymond,
M. Romoli, D. Spadaro, O.H.W. Siegmund, C. Benna, A. Ciaravella, S.R. Cranmer,
S. Giordano, M. Karovska, R. Martin, J. Michels, A. Modigliani, G. Naletto,
A. Panasyuk, C. Pernechele, G. Poletto, P.L. Smith, L. Strachan
1997, Advances in Space Research 20, no. 1, 3
Ultraviolet Coronagraph Spectrometer on the Solar and Heliospheric Observatory, UVCS/SOHO, and the Ultraviolet Coronal Spectrometer on the Spartan 201 satellite, UVCS/Spartan, have been used to measure H I 1215.67 A line profiles in polar coronal holes of the Sun at projected heliocentric heights between 1.5 and 3.0 R_s. UVCS/SOHO also measured line profiles for H I 1025.72 A, O VI 1032/1037 A, and Mg X 625 A. The reported UVCS/SOHO observations were made between 5 April and 21 June 1996 and the UVCS/Spartan observations were made between 11 and 12 April 1993. Both sets of measurements indicate that a significant fraction of the protons along the line of sight in coronal holes have velocities larger than those for a Maxwellian velocity distribution at the expected electron temperature. Most probable speeds for O velocity distributions along the lines of sight are smaller than those of H at 1.5 R_s, are comparable at about 1.7 R_s and become significantly larger than the H velocities above 2 R_s. There is a tendency for the O line of sight velocity distribution in concentrations of polar plumes to be more narrow than those in regions away from such concentrations. UVCS/SOHO has identified 31 spectral lines in the extended solar corona.
1997-13: First results from UVCS: Dynamics of the extended corona
E. Antonucci, G. Noci, J.L. Kohl,
G. Tondello, M.C.E. Huber, S. Giordano, C. Benna, A. Ciaravella, S. Fineschi,
L.D. Gardner, R. Martin, J. Michels, G. Naletto, P. Nicolosi, A. Panasyuk,
J.C. Raymond, M. Romoli, D. Spadaro, L. Strachan & A. Van Ballegooijen
1997, Advances in the Physics of Sunspots 1st Advances in Solar Physics Euroconference. eds. B. Schmieder, J.C. del Toro Iniesta, M. Vasquez ASP Conference Series 118, p.273
1997-12: Influence of Heavy Ions on the High Speed Solar Wind
Xing Li, Ruth Esser, Shadia R. Habbal
and You-Qiu Hu
1997, J. Geophys. Res., 102, 17,419
We present the results of a parameter study of the influence of heavy ions on the background solar wind, choosing doubly ionized helium, or alpha particles, and O+6, as examples. Using a three-fluid solar wind model, we keep the input parameters to the electrons and protons unchanged, and investigate the effects of changing the abundance of the minor ions at the coronal base, as well as their energy source. Our results confirm earlier studies that alpha particles can have a dramatic effect on the thermodynamic and flow properties of the protons in the solar wind. The maximum helium abundance for which the changes in the energy input to the alphas has no effect on the protons is $5 10^{-4}$, which is well below the photospheric value. For larger abundances, the sensitivity of the changes of the flow speed and proton mass flux to changes in the energy input to alphas increases sharply with increasing abundance. When the alpha particles are not heated, the increase in the abundance leads to an increase in flow speed, a decrease in proton mass flux, and an increase in proton temperature at 1 AU. However, as the heat input to the alphas increases, the dependence of these parameters on the abundance goes through a transition and starts to follow the opposite pattern, namely a decrease in flow speed and proton temperature at 1 AU, and an increase in proton mass flux. Although less pronounced, the same behavior is found when the O+6 ions replace the alphas. We also find that when the energy input to the minor ions is distributed over an extended heliocentric distance the influence of the minor ions on the protons is strongly reduced. This parameter study shows that, for currently known photospheric elemental abundances, the flow properties of minor ions cannot be investigated independently of those of the bulk proton-electron solar wind. The effect of minor ions on the electron-proton bulk solar wind is determined primarily by the interactions occurring very close to the coronal base. Hence, including physical processes responsible for the preferential heating of minor ions to temperatures exceeding those of protons in the inner corona, cannot be done without considering the subsequent implications for the protons and electrons in a self-consistent manner.
1997-11: Alfvenic fluctuations in fast and slow solar winds
S. Orlando, Y.-Q. Lou, G. Peres,
and R. Rosner.
1997, J. Geophys. Res. 102, 24,139
We compute properties of Alfvenic fluctuations within a wide frequency range (that is, $10^{-6}\hbox{ s}^{-1}\lsim f\lsim 10^{-2}\hbox{ s}^{-1}$) in both high- and low-speed magnetized radial solar winds. In particular, the radial and frequency variations of the normalized cross helicity $\sigma_c$, the Alfven ratio ${\cal R}_A$, and other relevant quantities associated with Alfvenic fluctuations are presented and analyzed. Due to the existence of the Alfven critical radius $r_A$ and a characteristic frequency $f_c$ for a given magnetized solar wind profile, continuous reflection effects are clearly manifest at frequencies lower than several times of $f_c$. Since outward propagating Alfvenic fluctuations have been detected in the high-latitude solar wind (which is fast and steady), such continuous reflection effects in the low-frequency end of the fluctuation spectrum may be found in the Ulysses data. In order to strengthen our case, comparisons are carried out between our theoretical results and previous data analyses of observations from the Helios 1 and 2 spacecraft in the radial range of $0.29\hbox{ AU}\lsim r\lsim 1.0\hbox{ AU}$. Stronger evidence for continuous reflection effects of low-frequency Alfvenic fluctuations is found in the high-speed solar wind close to the Sun than in the low-speed solar wind in general.
1997-10: Study of Coronal Transients in UV Line Emission
R. Martin, L. Maccari and G. Noci
1997, Solar Physics 172, 215
We investigate the expected emission from coronal transients in the following spectral lines observable with the Ultraviolet Coronagraph Spectrometer (UVCS) onboard SOHO: H I Ly alpha 1216 A, O VI 1032--1037 A, N V 1239--1243 A, Mg X 610--625 A, Si XII 499--521 A, and Fe XII 1242 A. We calculate line intensities and profiles for typical CME conditions, and we analyse their relation with the properties of the perturbed coronal region. We find that significant changes in UV line intensities are produced during a coronal transient. An overall decrease of the H I Ly alpha intensity is found, which is mainly due to the Doppler dimming produced by the increase in plasma outflow velocity. The emission from heavy ions is instead mainly affected by variations in plasma density and temperature. We expect to compare these results with the future UVCS observations of coronal transients.
1997-09: Possible Signatures of Nonlinear MHD Waves in the Solar Wind: UVCS Observations and Models
Ofman, L., Romoli, M., Davila, J. M., Poletto, G., Kohl, J., Noci, G.
ESA, SP-404, 571
1997-08: Inferences on Coronal Magnetic Fields from SOHO UVCS Observations
Poletto, G., Romoli, M., Suess,
S.-T., Wang, A.-H., Wu, S.-T.
1997, Solar Phys. 174, 53
The characteristics of the magnetic field ubiquitously permeating the coronal plasma are still largely unknown. In this paper we analyze some aspects of coronal physics, related to the magentic field behavior, which forthcoming SOHO UVCS observations can help better understand. To this end, three coronal structures will be examined: streamers, coronal mass ejections (CMEs), and coronal holes. As to streamers and CMEs, we show, via simulations of the Ly-a and white-light emission from these objects, calculated on the basis of recent theoretical models (Wang et al., 1995), how new data from SOHO can help in advancing our knowledge of the streamer/CME magnetic configuration. Our discussion highlights also those observational signatures which might offer clues on reconnection processes in streamers' current shhets. Coronal holes (CH) are discussed in the last section of the paper. Little is known about CH flux tube geometry, which is closely related to the behavior of the solar wind at small heliocentric distances. Indirect evidence for the flux tube spreading factors, within a few solar radii, is here examined.
1997-07: Future space instrumentation for solar physics
E. Antonucci and G. Simnett
1997, Lecture Notes in Physics, 'Solar and Heliospheric Plasma Physics', edited by G.M. Simnett, C.E. Alessandrakis and L. Vlahos, Springer, 261-278
1997-06: Optical performances of the UVCS/SOHO spectrometer
Claudio Pernechele, Giampiero Naletto,
Piergiorgio Nicolosi, Giuseppe Tondello: University of Padua Silvano Fineschi,
Marco Romoli, Giancarlo Noci: University of Florence Daniele Spadaro: Astrophysical
Observatory of Catania John L. Kohl: Harvard-Smithsonian Astrophysical Observatory
1997, Appl. Opt. 36, 813-26
Optical performances of the Spectrometer Assembly for the Ultraviolet Coronagraph Spectrometer of the Solar and Heliospheric Observatory mission have been tested. The flight unit of the Spectrometer Assembly, consisting of the structure equipped with the entrance slits assembly, the grating drive mechanisms mounting two toroidal gratings and the photon counting detectors, has been integrated and aligned; also the flight unit of the White Light Channel has been integrated and aligned in the Spectrometer Assembly. Tests with both visible and UV radiation have been performed: aberration and stray light measurements have shown satisfactory performances of the instrument almost in compliance with the scientific requirements; also some measurements of the polarimeter modulation curve and the relative error have shown performances within the specified requirements.
1997-05: Do First Results from SOHO UVCS Indicate that the Solar Wind is Accelerated by Solitary Waves?
L. Ofman (Hughes STX/NASA GSFC)
and J.M. Davila (NASA GSFC)
1997, Astrophysical Journal Letters 476, L51-54
The Ultraviolet Coronograph Spectrometer (UVCS) on board the recently launched US-European SOHO satellite has found O VI and H I emission lines with a broad component that corresponds to 300 km/s unresolved motions at about 0.7 solar radii above the photosphere. These motions appear to be independent of ion mass. We suggest that the large Doppler broadening of the ion emission lines observed by the UVCS are signatures of solitary waves in the solar wind plasma. According to our recent 2.5D (i.e., 2D with three components of the velocity and the magnetic field) MHD simulations these waves may contribute significantly to the solar wind acceleration and may generate velocity fluctuations with a magnitude that agrees with the above observations.
1997-04: Absolute Abundances in Streamers from UVCS
Raymond, J., SUleiman, R., van Ballegooijen, A., Kohl, J.
ESA, SP-415, 383
1997-03: Effects of High Ion Temperatures on Spectral Line Diagnostics in the Source Region of the High Speed Solar Wind
N. S. Brickhouse and R. Esser
1997, Astrophys. J. 479, 470-76
Theoretical work on solar wind acceleration has suggested that the proton and electron temperatures at the base of the solar coronal hole region are not thermally equilibrated but that instead the proton temperature may exceed the electron temperature significantly. Recently, Kohl, Strachan, & Gardner (1996) have measured both broad and narrow components of the H Ly-alpha profile, and have suggested that the broad component may be the signature of high proton temperatures, 4 to 6 x 10^{6} K or more. Since proton impact excitation can contribute to the emission line excitation processes, high proton temperatures have important implications for some spectral line emissivities that are useful for electron temperature and density determinations. The diagnostics most affected are those which are sensitive to the distribution of population within the fine structure of the ground state configuration. We discuss selected case studies. For modest proton temperatures (Tp = 3 Te) we have found effects on temperature diagnostics to be less than 30% but effects on some density diagnostics may be as large as an order of magnitude.
1997-02: Hot Protons in the Inner Corona and Their Effect on the Flow Properties of the Solar Wind
Ruth Esser, Shadia R. Habbal, W.
A. Coles, and J. V. Hollweg
1997, J. Geophys. Res., 102, 7063
Following recent observations which indicate the presence of extremely high flow speeds in the inner corona, 700 - 800 km s^{-1} below 10 R_S, and the possible presence of very high proton temperatures, 3 x 10^{6} \leq T_p \leq 8.5 \times 10^{6} K, we present a parameter study which shows that if the high proton temperatures in the inner corona are genuine, then flow speeds of 700 to 800 km s^{-1} can readily be achieved at 10 R_S or even closer to the coronal base. If one allows for both heat and momentum deposition in the inner corona, the rapid acceleration close to the coronal base can be achieved with proton temperatures well below the upper limit placed by the observations.
1997-01: Interdependence of Solar Wind Models and Solar Wind Observations
Ruth Esser and Nancy S. Brickhouse
1997, in Proceedings of the Workshop "Scientific Basis for Robotic Exploration Close to the Sun", Ed. S. R. Habbal, AIP, in press
A brief overview of the observations in the inner corona is presented together with three different solar wind models. It is shown that the very high flow speeds derived from the observations in the inner corona can be modeled if either the proton temperature is extremely high, or if there exists a mechanism that adds momentum to the flow much closer to the coronal base than in traditional Alfven wave driven models. These high flow speeds and the possibility that the proton temperature is very high have an influence on observations used to infer plasma parameters in the inner corona. This point is illustrated choosing the line ratio density diagnostic as an example.