UVCS/SOHO PAPERS - 2002

2002-47:    The effect of time-dependent coronal heating on the solar wind

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

2002-46:    The effect of transition region heating on the solar wind from coronal holes

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

ApJ, volume 566, pp 562-576.

Using a 16 moment solar wind model extending from the chromosphere to 1 AU, we study how the solar wind is affected by direct deposition of energy in the transition region, in both radially expanding geometries and rapidly expanding coronal holes. Energy is required in the transition region to lift the plasma up to the corona, where additional coronal heating takes place. The amount of energy deposited determines the transition region pressure and the number of particles reaching the corona and, hence, how the solar wind energy flux is divided between gravitational potential and kinetic energy. We find that when only protons are heated perpendicularly to the magnetic field in a rapidly expanding coronal hole, the protons quickly become collisionless and therefore conduct very little energy into the transition region, leading to a wind much faster than what is observed. Only by additional deposition of energy in the transition region can a reasonable mass flux and flow speed at 1 AU be obtained. Radiative loss in the transition region is negligible in these low-mass flux solutions. In a radially expanding geometry the same form of coronal heating results in a downward heat flux to the transition region substantially larger than what is needed to heat the upwelling plasma, resulting in a higher transition region pressure, a slow, massive solar wind, and radiative loss playing a dominant role in the transition region energy budget. No additional energy input is needed in the transition region in this case. In the coronal hole geometry the solar wind response to transition region heating is highly nonlinear, and even a tiny input of energy can have a very large influence on the asymptotic properties of the wind. By contrast, the radially expanding wind is quite insensitive to additional deposition of energy in the transition region.

2002-45:    Ion Effective Temperatures in Polar Coronal Holes: Observations versus Ion-Cyclotron Resonance

Patsourakos, S.; Habbal, S. R.; Hu, Y. Q.

ApJL, 581, L125-L127

The resonant cyclotron interaction between ion-cyclotron waves and solar wind species is considered nowadays to be a strong candidate for heating and acceleration of protons, ?-particles, and heavy ions. A crucial physical parameter for determining the amount and the location of significant heating and acceleration, which the different solar wind ions receive from the waves in the frame of the ion-cyclotron mechanism, is their charge-to-mass ratio q/m. Therefore, comparisons of ion temperatures derived from spectroscopic observations and calculated by ion-cyclotron models, for ions that span a broad range in q/m, would provide a rigorous test for such models. By using an ion-cyclotron model, we calculate the effective temperatures for 10 different ions that cover the range 0.16-0.37 in q/m. Effective temperatures correspond to unresolved thermal motions and wave motions. The good agreement between our calculations, based on the specific mechanism that we employed here (ion-cyclotron resonance) and on spectroscopic observations of effective temperatures in polar coronal holes, provides support that the above mechanism accounts for the energetics and kinematics of fast solar wind heavy ions. However, such an agreement does not prove that other potential mechanisms can be excluded.    [ ]

2002-44:     A theoretical model for O⁵⁺ (O⁷⁺) ions in the fast solar wind

Y. Chen, R. Esser and Y. Hu

J.G.R. 107(A11), 1368, doi:10.1029/2002JA009341

We present a theoretical model for O$5+$ (O$7+$) ions as test particles in the fast solar wind, using a previous turbulence-driven four-fluid model to establish the background solar wind, which consistsof electrons, protons, alpha particles and O$6+$ ions. The O$5+$ (O$7+$) ions in our model and the O$6+$ ions in the background are driven by the same mechanism, say, the resonant cyclotron interaction or an exponential heating addition. The ionization and recombination processes of O ions are taken into account.It is shown that the differential flow speeds between O$6+$ and O$5+$ or O$7+$, which are found to be in the range of 0.3 to 2, play very different roles in the formation of O charge states. This is due to discrepancy between the freezing-in distances of the two ion species. O$7+$ forms predominantly below 1.2 $R_S$ too close to the Sun to develop a differentialstreaming between O ions. O$5+$, on the other hand, freezes-in at about $1.8$ $R_S$ where differentia! l flows are well developed and therefore important for the formation of O$5+$ ions. [ ]

2002-43:     Constraints on ion outflow speeds and electron distribution function in the corona derived from SUMER electron temperatures and SWICS ion fractions

Esser, R., and Edgar, R. J.

Adv. Space Res. 30, 481-86

It has been a puzzle for quite some time that spectroscopic measurements in the inner corona indicate electron temperatures far too low to produce the ion fractions observed in the in situ solar wind. In the present paper we show that in order to reconcile the two sets of measurements, a number of conditions have to exist in the inner corona: 1) the electron distribution function has to be Maxwellian or close to Maxwellian close to the coronal base; 2) the non-Maxwellian character of the distribution has to develop rapidly as a function of height and has to reach close to interplanetary properties inside of a few solar radii; 3) ions of different elements have to flow with significantly different speeds to separate their ``freezing-in'' distances sufficiently so they can encounter different distribution functions. We chose a set of observationally constrained coronal plasma parameters to demonstrate that these conditions are general requirements if both coronal electron temperatures and in situ ion fractions are correct. However, the details of the required distribution functions are very sensitive to the exact electron temperature, density and ion flow speed profiles in the region of the corona where the ions predominantly form. [4551]

2002-42:     SOHO, Yohkoh, Ulysses and Trace: The four solar missions in perspective, and available resources

Domingo, V.

Astrophys. & Space Sci. 282, p.171-188

Four solar observing spacecraft, now in operation, have obtained and continue to obtain data during the late phase of solar cycle 22 and hopefully most of cycle 23. The data are available for scientific analysis, practically in an unrestricted manner. A large pool of software suited for the processing and to help programming any data analysis is freely available. An almost random list of results that are being obtained with this data is presented as an example of what can be done by analysing the data from these spacecraft, either alone or combining results among them, with ground observatories, or with other spacecraft, such as those that measure particles and fields in interplanetary space or in geospace, to study solar physics or solar-terrestrial relations. [4601]

2002-41:    What Can We Learn from Constructing CME Models: Magnetic Interface

J. Lin and J. Wang

Solar-Terrestrial Magnetic Activity and Space Environment
COSPAR Colloquia Ser. 14, eds. H. Wang and R. Xu,

In most cases, the magnetic interface can be identified with the magnetic separatrix where activities are always expected. This is not always true although activities are tightly related to the interactions among different magnetic systems topologically separated by the magnetic interface. In the present work, we investigated the magnetic interface on the base of current CME models for the first time. The relations and differences between the magnetic interface and the magnetic separatrix were carefully studied, and potential significance of these relations and differences to the observation and solar activity forecasting were discussed. [ ]

2002-40:    UV and Soft X-Ray Polar Coronal Jets

D. Dobrzycka, J.C. Raymond, S. R. Cranmer, and J. Li

Multi-Wavelength Observations of Coronal Structure and Dynamics
COSPAR Colloquia Ser. 13, ed. P.Martens D.Cauffman, p.23

We present results of simultaneous SXT and UVCS observations of jetsfrom polar coronal holes. Although we did not identify the UVcounterparts of the X-ray jets, on one occasion UVCS recordedHI Ly$alpha$ profile variations consistent with a UV jet at theposition of the X-ray jet but prior to that event. We discuss thepossible relation between the UV and X--ray events and consider themagnetic reconnection models developed for X--ray jets, as a model forUV jet formation. The rough estimates of the total energies of theX-ray and UV jets show the energies to be comparable. [4662]

2002-39:     Low-latitude solar wind during the Fall 1998 SOHO-Ulysses quadrature

Poletto, G.; Suess, S. T.; Biesecker, D. A.; Esser, R. Gloeckler, G.; Ko, Y.-K.; Zurbuchen, T. H.

J. Geophys. Res., 107(A10), 1300, doi: 10.1029/2001JA000275

The Fall 1998 Solar-Heliospheric Observatory SOHO-Ulysses quadrature occurred when Ulysses was at 5.2 AU, 17.4 degrees South of the equator, and off the West limb of the Sun. SOHO coronal observations, at heliocentric distances of a few solar radii, showed that the line through the solar center and Ulysses crossed, over the first days of observations, a dark, weakly emitting area and through the northern edge of a streamer complex during the second half of the quadrature campaign. Ulysses in situ observations showed this transition to correspond to a decrease from higher speed wind typical of coronal hole flow to low speed wind. Physical parameters of the low latitude coronal plasma sampled over the the campaign are determined using constraints from what is the same plasma measured later in situ and simulating the intensities of the Hydrogen Lyman-alpha and O VI 1032 and 1037 A lines, measured by the Ultraviolet Coronagraph Spectrometer UVCS on SOHO. It appears that low latitude wind from small coronal holes and polar wind have different characteristics in the corona, differences well known at interplanetary distances through in situ experiments. Small, low altitude coronal holes have a higher expansion factor than typical polar holes and their plasma moves at a lower speed than plasma from polar holes, reaching, at 3.5 Rsun, only about 1/5 of the terminal speed. Wind emanating from bright regions, above streamer complexes, is, at the altitudes we analyzed i.e. 3.5 and 4.5 R_sun, about a factor 3 slower than the low latitude coronal hole wind, implying a shift to even higher altitudes in the region where plasma gets accelerated. We surmise that open field regions, interspersed amidst closed coronal loops/streamers, may be at least partially responsible for the well known slow wind variability. As in polar fast wind, O VI ions move faster than protons, over the range of altitudes we sampled, and are frozen-in at temperatures of about 1.3-1.5 106 K, depending on the site where the outflow originates. An Oxygen abundance variation from a value of 8.55, in low latiude holes, to 8.73 in bright areas, has also been inferred variation. []

2002-38:     UV line intensity and flow velocity distributions in two coronal mass ejections as deduced by UVCS-SOHO observations

Ventura, R.; Spadaro, D.; Uzzo, M.; Suleiman, R.

A&A, 383, pp.1032-1048

The Ultraviolet Coronagraph Spectrometer (UVCS) instrument onboard the SOHO satellite observed two coronal mass ejections on November 2 and 3, 2000, related to the eruptions of a large filament structure in an active region close to the west limb of the Sun, and of a prominence near the South Pole, respectively. Intensity and profile of the O VI resonance doublet lines at 1032 and 1037 A and of Ly beta (1026 AA) line, together with the intensity of some other minor ions, were observed using the O VI channel of UVCS. We analysed these spectroscopic observations in order to get information about the distributions of ionic densities and flow velocities in the solar coronal plasma ejected during these transient events. Emission in ions ranging from C II to O VI indicates a temperature range between 104.5 and 105.5 K. The morphology of the bright emission regions suggests the development of several strands of plasma irregularly distributed inside the CME structures, whose temporal evolution is significantly different from each other. The velocities determined for each bright element also give a complex picture of the plasma kinematics characterizing these coronal mass ejections [4428]

2002-37:    Heating in Coronal Funnels by Ion Cyclotron Waves

Li, X.

ApJ 571, pp.L67-L70

Plasma heating by ion cyclotron waves in rapidly expanding flow tubes in the transition region, referred to as coronal funnels, is investigated in a three-fluid plasma consisting of protons, electrons, and α-particles. Ion cyclotron waves are able to heat the plasma from 6×104 to 106 K over a distance range of 104 km by directly heating α-particles. Although only α-particles dissipate the waves, the strong Coulomb coupling between α-particles and protons and between protons and electrons makes it possible for protons and electrons to be heated also to more than 106 K. However, owing to the extreme heating of the α-particles, the particles are not in thermal equilibrium: α-particles can be much hotter and faster than protons. Beyond 1.02Rs, the particles return to thermal equilibrium when the electrons reach about 106 K, which is canonically defined as the base of the corona. These results lead to the following implications: (1) If spectral lines formed at Te<106 K are observed at different heights, the inferred outflow velocities may vary by a factor of 5-6. (2) If minor ions are indeed much faster than protons and electrons at Te<106 K, one cannot reliably determine the bulk outflow velocity of the solar wind in that region by using minor ion outflow velocities. [4549]

2002-36:    Damping of Low-Frequency Alfvén Waves in Fast Polar Coronal Winds from the Rotating Sun

Lou, Yu-Qing

ApJL, 571, pp.L187-L190.

Steady fast solar winds with high speeds of ~750-800 km s-1 persist from polar coronal holes and meandering coronal holes that extend to lower latitudes. Observations of Ulysses and earlier spacecraft confirmed the presence of large-amplitude transverse magnetic field fluctuations in the fast solar wind, characterized by outward-traveling Alfvénic correlations with velocity fluctuations. Observations of the Solar and Heliospheric Observatory revealed gross correlations among the networks of outflow patterns (Ne VIII λ770), chromospheric heating (Si II λ1533), chromosphere-corona transition (C IV λ1548), and supergranule boundaries where intense magnetic field fibrils concentrate. In the theory of fast-wind heating and acceleration by MHD waves, it is known that compressive MHD waves damp rapidly close to the Sun, while Alfvén waves of low frequencies are not readily damped over many solar radii. In addition to the Alfvén wave pressure effect, the theory of fast wind requires a proper damping of Alfvén waves in the radial range of supersonic flow. We examine physical effects of the slow solar rotation on coupling compressive MHD waves and Alfvén waves that eventually lead to an effective damping of primary Alfvén waves. For high frequencies, this MHD wave coupling is weak, while for lower frequencies, this MHD wave coupling can become fairly effective. The emphasis of our estimates will be on fast polar solar winds, but the basic idea should be applicable to stellar winds from rotating stars with open magnetic fields in general. [4442]

2002-35:    Soho Contribution to Prominence Science

Patsourakos, S., & Vial, J.-C.

Sol. Phys. 208, pp.253-281

We present the main current issues concerning prominence studies. We recall the large range of plasma parameters found in prominences which makes the work of the MHD modeler more difficult. We also summarize the capabilities of the SOHO instrumentation. We present and discuss the most recent SOHO results concerning the determination of temperature, densities, and velocities. We put some emphasis on the different morphologies observed, the diagnostic capabilities of the Lyman lines profiles when accompanied by improved non-LTE modeling, and the information gathered from the first prominence oscillations measured from space. We also make an account of eruptive prominences. We finally discuss what could be done with present and future SOHO data to improve our understanding of prominences. [4562]

2002-34:     Spectroradiometry for Solar Physics in Space

Smith, Peter L., and Huber, M. C. E.

ISSI SR-002, pp.21-36
The Radiometric Calibration of SOHO

To access the *.pdf version of this file click on the link: Smith & Huber [4667]

2002-33:     Spectroradiometry of Spatially-Resolved Plasma Structures

Wilhelm, K.

ISSI SR-002, pp.37-50
The Radiometric Calibration of SOHO

To access the *.pdf version of this file click on the link: Wilhelm [4589]

2002-32:    Summary of Cleanliness Discussion: Where was the SOHO Cleanliness Programme Really Effective?

Schuehle, U., Thomas, R., Kent, B.J., Clette, F., Defise, J.-M., Delaboudiniere, J.-P., Froehlich, C., Gardner, L.D., Kohl, J.L., Hochedez, J.-F., & Moses, J.D.

ISSI SR-002, pp.289-310
The Radiometric Calibration of SOHO

To access the *.pdf version of this file click on the link: Schuehle et al. [4595]

2002-31:     White Light Inter-calibrations of UVCS, LASCO and Spartan 201/WLC

R. A. Frazin, M. Romoli, J. L. Kohl, L. D. Gardner, D. Wang, R. A. Howard and T. A. Kucera

ISSI SR-002, pp.249-264
The Radiometric Calibration of SOHO

To access the *.pdf version of this file click on the link: Frazin et al. [4664]

2002-30:     In-Flight Radiometric Calibration of the UVCS White Light Channel

M. Romoli, R. A. Frazin, J. L. Kohl, L. D. Gardner, S. R. Cranmer, K. Reardon, and S. Fineschi et al.

ISSI SR-002, pp.181-202
The Radiometric Calibration of SOHO

To access the *.pdf version of this file click on the link: M. Romoli et al. [4665]

2002-29:     UV Radiometric Calibration of UVCS

L. D. Gardner, P. L. Smith, J. L. Kohl, N. Atkins, A. Ciaravella, M. P. Miralles, A. Panasyuk, J. C. Raymond, L. Strachan, Jr., and R. Suleiman

ISSI SR-002, pp.161-180
The Radiometric Calibration of SOHO

To access the *.pdf version of this file click on the link: L. D. Gardner et al. [4666]

2002-28:     Source Standards for the Radiometric Calibration of Astronomical Instruments in the VUV Spectral Range Traceable to the Primary Standard BESSY

Hollandt, J., Kuehne, M., Huber, M.C.E., & Wende, B

ISSI SR-002, pp.51-68
The Radiometric Calibration of SOHO

To access the *.pdf version of this file click on the link: Hollandt et al. [4590]

2002-27:    

Calibration and Intercalibration of SOHO's Vacuum-Ultraviolet Instrumentation

Wilhelm, K.

ISSI SR-002, pp.69-90
The Radiometric Calibration of SOHO

abstract (PDF)

To access the *.pdf version of this file click on the link: Wilhelm2 [4170]

2002-26:     The Eruptive Processes in the Solar Atmosphere and the Theories

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

Chinese Science Bulletin, 47, pp.1601-12

We concentrate on currently the most popular theoretical research and models on solar eruptive processes. Evaluations of the early theories and their development are also conducted. We discuss thechallenges that the current theoretical researches onthe solar activities are facing with and the constraintsthey impose on the model constructions. [4668]

2002-25:     Space Observations of the Solar Atmosphere

Spadaro, D.

Solar Variability and Geomagnetism,(ed. W.Schroeder, pp.7-36
Lectures from the IAGA-IASPEI Joint Scientific Assembly, Hanoi 2001 [4411]

2002-24:     Vacuum Ultraviolet Observations of the Solar Upper Atmosphere

Wilhelm, K.

Solar Variability and Geomagnetism, (ed. W.Schroeder)
Lectures from the IAGA-IASPEI Joint Scientific Assembly, Hanoi 2001 [4412]

2002-23:     Two-dimensional Structure of a Polar Coronal Hole a Solar Minimum: New Semiempirical Methodology for Deriving Plasma Parameters

Zangrilli, L.; Poletto, G.; Nicolosi, P.; Noci, G.; Romoli, M.

ApJ, 574, Issue 1, pp. 477-494.

We develop a new technique to determine the plasma parameters in a polar coronal hole. This method makes use of the line intensities of the H I Lyα λ1215.6 line and of the O VI λλ1031.9, 1037.6 doublet, measured with the Ultraviolet Coronagraph Spectrometer (UVCS) on board the ESA-NASA solar spacecraft Solar and Heliospheric Observatory (SOHO) during 1996 August. The observed intensities are self-consistently reproduced with a two-dimensional semiempirical coronal hole model, for heliocentric distances between 1.4 and 2.6 Rsolar and latitudes between 90° (north pole) and 40°. Electron densities are derived by separating the O VI doublet collisional components from those due to resonant scattering. The calculated electron density radial profiles are consistent with typical polar coronal hole data and show only a moderate increase with latitude decreasing, in regions close to the equatorial streamer. The outflow speeds of protons and O VI ions are determined by means of the Doppler dimming technique. In the Doppler dimming analysis we use kinetic temperatures Tk derived from UVCS observations of the line profiles, whenever available, or we keep Tk as a free parameter if not provided by data. Mass flux conservation along the magnetic field lines is studied adopting a simple analytical model for the geometry of the magnetic flux tubes. Our model shows that protons and O VI ions accelerate outward, but their outflow speed turns out to decrease slowly as latitude decreases. The O VI speed, initially comparable to the speed of protons, exceeds the proton speed beyond about 1.7 Rsolar. Anisotropic O VI kinetic temperatures, T&par; and T⊥, turn out to be necessary to ensure the consistency of the model parameters with mass flux conservation, while the H kinetic temperature distribution is kept isotropic. Results from our model are compared with those from other two-dimensional models recently developed. [4669]

2002-22:     Energetics and Propagations of Coronal Mass Ejections in Different Plasma Environments

Lin, J.

Chinese J. Astron. Astrophys., 2, pp. 539-556, 2002

Based on previous work, we investigate the propagation of CMEs in amore realistic plasma environment. Slightly faster reconnection isrequired in this atmosphere in order to allow the flux rope to break freethan in the isothermal environment. The average Alfven Mach number$M_A$ for the inflow into the reconnection site ought to be at least0.013 in order to give a plausible eruption (compared to $M_A=0.005$ inthe isothermal atmosphere). Taking $M_A=0.1$, we find that the energyoutput and the electric field inducedinside the current sheet match the temporal behavior inferred for theenergetic, long duration X-ray events associated with CMEs. The results indicate that the catastrophic loss of equilibrium in the coronal magnetic field constitutes the most promising mechanism for the major solar eruptions, and that the more energetic the eruption is, the earlier theassociated flare peaks. Variations of the output power against thestrength of the background field revealed by our calculations implicitlysuggest the poor correlation of slow CMEs to solar flares. This workalso further confirms the explanation we proposed for the peculiar motionof giant X-ray arches and anomalous post-flare loops. The motion patternsof these features and the heights where they are observed are determinedby the local Alfven speed and its variation with the height. [4670]

2002-21:     Tomography of the Solar Corona: II. Reconstruction of the 3D Electron Density Distribution from Polarized White-Light Images

Frazin, R. A., and Janzen, P.

ApJ, 570, 408-422

For Pt.I see ApJ 530, p.1026-35 (2000). Solar rotational tomography is used to determine the three-dimensional electron density distribution of the solar corona from 2.4 to 6.0 R_sun. The robust, regularized, positive estimation method, described in a previous paper, is demonstrated on test cases and on LASCO-C2 data. Because the solar rotational pole is inclined to the plane of the ecliptic by about 7 degrees , the tomographic inversion requires a full three-dimensional treatment instead of a series of two-dimensional inversions. The LASCO data are taken from the first Whole Sun Month, which was a period of low solar activity. [4671]

2002-20:    Lyman alpha intensities in a polar coronal hole from a 2D model

Zangrilli, L.; Poletto, G.; Nicolosi, P.; and Noci, G.

Adv. Space Res. 30, p.523-528
Heating and Energetics of the Solar Corona and Solar Wind

We simulate the coronal H I Lyman alpha intensity for heliocentric distances between 1.5 and 2.5 R(.), and latitudes between 90 degrees (North pole) and 30 degrees, making use of a 2D semiempirical coronal hole model. Observations are made with the UltraViolet Coronagraph Spectrometer (UVCS) on board the ESA-NASA solar satellite SOHO (SOlar and Heliospheric Observatory). Model electron densities are derived from the collisional part of the O VI lambda 1037.6 AA line and the proton outflow speed is calculated from mass flux conservation along the magnetic field lines. The expansion factor and the direction of the magnetic flux tubes have been derived by adopting a simple analytical magnetic field configuration. The intensities of the Ly alpha line predicted by the model are compared with the observed intensities [4663]

2002-19:     Catastrophic and Non-Catastrophic Mechanisms for Coronal Mass Ejections

J. Lin and A. A.van Ballegooijen

Ap. J., Vol. 576, pp. 485-492, 2002.

It has been suggested that coronal mass ejections (CMEs) are triggered by the loss of equilibrium of a coronal magnetic field configuration containing atwisted flux rope. We propose that there are two types ofCMEs, fast CMEs that are triggered by a catastrophic loss of equilibrium,and slow CMEs that do not involve a true catastrophe but nevertheless showrapid evolution of the system. As an extension of the work by Forbes andIsenberg (1991), we investigated the evolution of a magnetic configuration taking into account deviations from ideal MHD. We find that thenon-ideal-MHD evolution makes it easier for the catastrophic loss ofequilibrium to occur, and the catastrophic behavior of the system is nolonger constrained by the radius of the flux rope. For ideal-MHD evolutionwe find that non-catastrophic solutions can account for slow CMEs. We alsodiscuss the conditions under which the ideal-MHD approximation holds. [4672]

2002-18:     Effect of flow-tube geometry on solar wind properties

Y. Chen and Y. Hu

Astrophys. Space Sci., 282, 447-460, 2002.

A mathematical description of the solar wind flow-tubegeometry is proposed. The expansion factor of the flow tube $f(r)$ ($=a/r2$, $r$ is the heliocentric distance and $a$ is the flow-tube cross-section area)increases monotonically from 1 at the coronal base to $f_m$ at $r_c$, and approaches its asymptotic value $f_infty$ nearly in a width of $2sigma_c$. The flow tube with $f_m = f_infty$ is demonstrated to beapproximately equivalent to that given by Kopp and Holzer (1976) for the fast solar wind, and it presumably represents slow wind tubes as $f_m$ is substantially larger than $f_infty$. In terms of an Alfven wave-driven solar wind model, the effect of the flow-tube geometry on solar wind properties is examined. It is found that with the same flow conditions at the coronal base an expansion factor which increases monotonically with the radial distance results in a fast solar wind solution, whereas a flow tube which undergoes an expansion-contraction-reexpansion pro! cess creates a slow solar wind solution. Among the four flow-tube parameters the maximum expansion factor $f_m$ has the strongest effect, and the associated Laval-nozzle formed by the contraction and reexpansion of the flow tube plays a crucial role in determining solar wind properties. It is suggested that one must take the effect of the flow-tube geometry into account while constructing reasonable flow-tube models for the slow solar wind. [4673]

2002-17:    The radiometric calibration and intercalibration of SOHO

Huber, M. C. E.; Pauluhn, A.; von Steiger, R.

ESA SP-508, pp.213-214
SOHO 11 Symposium From Solar Min to Max: Half a Solar Cycle with SOHO

The radiometric calibration of spectrometric telescopes assures that the observed spectral radiance (or irradiance) is measured on a scale that is defined by the radiometric standards realised and used in terrestrial laboratories. All SOHO instruments therefore have been calibrated by use of source and detector standards that are traceable to the primary radiometric standards. As any calibration, the laboratory calibration has uncertainties. Moreover, environmental influences, namely molecular and particulate contamination on the ground and effects by photon and particle radiaton in space, do change the responsivity of the instruments. In two workshops held at the International Space Science Institute in Bern the individual instrument calibrations were discussed and reconciled. The outcome of the workshops, to which all instrument groups contributed, is summarised in a book that is presented here before it goes to press. [4530]

2002-16:     Cyclical Variations in the Plasma Properties of Coronal Holes

Miralles, M. P.; Cranmer, S. R.; Kohl, J. L.

ESA SP-508, pp.351-359
Invited Paper SOHO 11 Symposium - Davos, Switzerland, 11-15 March 2002

Full text
Abstract
[4674]

2002-15:     Spectroscopic diagnostics of CME material

J.C. Raymond

ESA SP-508, pp.421-430
Invited Paper SOHO 11 Symposium - Davos, Switzerland, 11-15 March 2002

Full text (PDF)
Abstract
[4675]

2002-14:     Solar Wind Acceleration in Coronal Holes

Steven R. Cranmer

ESA SP-508, pp.361-366
Invited Paper SOHO 11 Symposium - Davos, Switzerland, 11-15 March 2002

Full text (PDF)
Abstract
[4676]

2002-13:     The Radiometric Calibration and Intercalibration of SOHO

M.C.E. Huber, A. Pauluhn and R. von Steiger

ESA SP-508, pp.213-214
Contributed Paper SOHO 11 Symposium - Davos, Switzerland, 11-15 March 2002

Abstract
[4502]

2002-12:     Coronal Hole-Streamer Interface and the Source of the Slow Wind

L. Abbo and E. Antonucci

ESA SP-508, pp.477-480
Contributed Paper SOHO 11 Symposium - Davos, Switzerland, 11-15 March 2002

Abstract
[4678]

2002-11:     Temporal Profile of Polar Wind from SOHO-Sun-Ulysses Quadrature Data: Preliminary Results

R. A. Cuadrado, G. Poletto, L. Teriaca and S. T. Suess

ESA SP-508, pp.481-484
Contributed Paper SOHO 11 Symposium - Davos, Switzerland, 11-15 March 2002

Abstract
[4679]

2002-10:     Latitudinal Profile of Heavy Ion Outflows in a Energy input to O VI ions and protons in the fast solar wind

L. Zangrilli, G. Poletto, P. Nicolosi, G. Noci and M. Romoli

ESA SP-508, pp.493-496
Contributed Paper SOHO 11 Symposium - Davos, Switzerland, 11-15 March 2002

Abstract
[4680]

2002-09:     Coronal Holes and the High-Speed Solar Wind

S. R. Cranmer

Space Science Rev., 101, pp.229-294

Coronal holes are the lowest density plasma components of the Sun's outer atmosphere, and are associated with rapidly expanding magnetic fields and the acceleration of the high-speed solar wind. Spectroscopic and polarimetric observations of the extended corona, coupled with interplanetary particle and radio sounding measurements going back several decades, have put strong constraints on possible explanations for how the plasma in coronal holes receives its extreme kinetic properties. The Ultraviolet Coronagraph Spectrometer (UVCS) aboard the Solar and Heliospheric Observatory (SOHO) spacecraft has revealed surprisingly large temperatures, outflow speeds, and velocity distribution anisotropies for positive ions in coronal holes. We review recent observations, modeling techniques, and proposed heating and acceleration processes for protons, electrons, and heavy ions. We emphasize that an understanding of the acceleration region of the wind (in the nearly collisionless extended corona) is indispensable for building a complete picture of the physics of coronal holes. [4681]

2002-08:     Solar and Heliospheric Observatory Ultraviolet Coronagraph Spectrometer and Yohkoh Soft X-Ray Telescope Observations of the High-Temperature Corona above an Active Region Complex

Ko, Yuan-Kuen; Raymond, John C.; Li, Jing; Ciaravella, Angela; Michels, Joseph; Fineschi, Silvano; Wu, Rai

ApJ, 578, pp. 979-995

We present the results of Solar and Heliospheric Observatory Ultraviolet Coronagraph Spectrometer (SOHO/UVCS) and Yohkoh Soft X-Ray Telescope (SXT) observations above an active region complex (AR 8194, 8195, and 8198) at the southeast limb on 1998 April 6-7. This active region complex appears to be the base of a small streamer seen by the Large Angle and Spectrometric Coronagraph Experiment (LASCO/C2) at the southeast limb. The UVCS was offset-pointed to observe low in the corona from 1.22 up to 1.6 R_solar with normal pointing. High-temperature lines such as [Fe XVIII] λ974 and Ne IX λ1248 were present in this region, implying that the electron temperature is higher than that in the quiet-Sun corona. This region of the corona is also seen as particularly bright in the Yohkoh/SXT, SOHO EUV Imaging Telescope high-temperature filter (Fe XV λ284) and SOHO/LASCO C1. The electron temperature analysis indicates a two-temperature structure, one of ~1.5×10⁶ K, which is similar to that observed in quiet-Sun streamers, and the other at a high temperature of ~3.0×10⁶ K. This two-temperature region likely corresponds to two distinct coronal regions overlapping in the line of sight. We compare the electron temperature and emission measure results from the SOHO/UVCS data with those from the Yohkoh/SXT data. The absolute elemental abundances show a general first ionization potential effect and decrease with height for all the elements. This is consistent with the effect of gravitational settling, which, however, cannot totally account for the observed elemental abundances. Other mechanisms that are likely to affect the coronal elemental abundance are discussed. [4682]

2002-07:     Elemental Abundances and Post-Coronal Mass Ejection Current Sheet in a Very Hot Active Region

Ciaravella, A.; Raymond, J. C.; Li, J.; Reiser, P.; Gardner, L. D.; Ko, Y.-K.; Fineschi, S.

ApJ, 575, pp.1116-1130

A peculiar young active region was observed in 1998 March with the Ultraviolet Coronagraph Spectrometer (UVCS) over the southwest limb. The spectra showed strong emission in the 974 Angstrom line of fluorine-like iron, [Fe XVIII], which is brightest at an electron temperature of 10^6.8 K, and lines of Ne IX, [Ca XIV], [Ca XV], Fe XVII, [Ni XIV], and [Ni XV]. It is the only active region so far observed to show such high temperatures 0.5 R_solar above the solar limb. We derive the emission measure and estimate elemental abundances. The active region produced a number of coronal mass ejections (CMEs). After one CME on March 23, a bright post-CME arcade was seen in EIT and Yohkoh/SXT images. Between the arcade and the CME core, UVCS detected a very narrow, very hot feature, most prominently in the [Fe XVIII] line. This feature seems to be the reconnection current sheet predicted by flux rope models of CMEs. Its thickness, luminosity, and duration seem to be consistent with the expectations of the flux rope models for CME. The elemental abundances in the bright feature are enhanced by a factor of 2 compared to those in the surrounding active region, i.e., a first ionization potential enhancement of 7-8 compared to the usual factor of 3-4. [4558]

2002-06:     Polar Coronal Jets

Dobrzycka, D.; Raymond, J. C.; Cranmer, S. R.

Adv. in Space Research, 29, 337

We present ultraviolet spectroscopy of polar coronal jets obtained with the Ultraviolet Coronagraph Spectrometer aboard the Solar and Heliospheric Observatory. They correlate with the Extreme--Ultraviolet Imaging Telescope Fe XII 195A and Large Angle Spectrometric Coronagraph white-light jet events. We found that the jets typically undergo two phases: at the first phase the O VI lines show a brief intensity enhancement and narrowing, while the H I Lyman alpha line is not enhanced, and the second phase, about 25 minutes later, when the H I Lyman alpha line shows maximum intensity enhancement and narrowing, while the O VI line is relatively unchanged. We modeled the observable properties of the jets from 1997 August 5, detected at 1.71 Rs. We interpret the first phase as the fast, dense centroid of the jet passing by the slit, and the second phase as a passage of cooler, lower density material following the centroid. Possible scenarios of the electron temperature variations needed to account for observed conditions on 1997 August 5 indicate that some heating is required. We computed models of the temperature and nonequilibrium ionization state of an expanding plasma using various forms for the heating rates. We discuss the model results and estimate the initial electron temperature and heating rate required to reproduce the observed O VI ionization state. We also place some constraints on the origin of the jet material based on the inferred plasma properties. [4683]

2002-05:     Polar Coronal Jets at Solar Minimum

Dobrzycka, D.; Cranmer, S. R.; Raymond, J. C.; Biesecker, D. A.; Gurman, J. B.

ApJ, 565, 621

We present an analysis of six polar coronal jets observed by the Ultraviolet Coronagraph Spectrometer UVCS at solar minimum 1996. Four of the events were also recorded by the Extreme--Ultraviolet Imaging Telescope EIT and/or the Large Angle Spectrometric Coronagraph LASCO C2 coronagraph. We compared the polar coronal jets observed during the ascending phase of the solar cycle 1997 with those at solar minimum. We modeled the observable properties of the jet from 1996 June 11, detected at 1.5R_odot. It represents a type of polar jet in which ionH1 Lyalpha and ionO6 get brighter at the same time. The model reproduced the line properties with an electron density enhancement of a factor of 2 with a resulting density of 4.8times106 cm-3, an outflow velocity enhancement of a factor of 3 yielding velocity of 200kms-1, and an electron temperature decrease of a factor of 0.36 with a resulting temperature of 5.3times 105K. We derived the jets electron densities from the LASCO C2 white light observations. They are a factor of 1.5 higher than in the interplume corona and comparable to those in plume regions. We developed a model for the origin of polar jets based on Wangs 1994 model for plumes. We envisioned that jets may be the result of short-lived bursts of base heating, while plumes may be the result of base heating events that last longer than several hours. Models with the base heatflux near 3 times 105 rm ergcm-2s-1 come closest to matching the observations, though they are not entirely consistent. [4426]

2002-04:     UVCS/SOHO observations of a CME-driven shock: Consequences on ion heating mechanisms behind a coronal shock

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

A&A, 383, pp.267-274

We report the observation of a 1100 km s^-1 CME-driven shock with the UltraViolet Coronagraph Spectrometer (UVCS) telescope operating on board SOHO on March 3, 2000. The shock speed was derived from the type II radio burst drift rate and from UVCS observations that can yield the density profile just before the passage of the shock. A CME projected speed of 920 km s^-1 was deduced from the Large Angle Spectrometric Coronagraph (LASCO) white light images, indicating that the CME leading edge was lagging behind at about 20% of the shock speed. The spectral profiles of both the O VI and Lyalpha lines were Doppler dimmed and broadened at the passage of the shock by the emission from shocked material along the line of sight. The observed line broadening for both protons and oxygen ions was modeled by adopting a mechanism in which the heating is due to the nondeflection of the ions at the shock ramp in a quasi-perpendicular shock wave. This specific ion heating model was able to reproduce the observed spectroscopic properties of the shocked plasma. [4685]

2002-03:     Empirical Densities, Kinetic Temperatures, and Outflow Velocities in the Equatorial Streamer Belt at Solar Minimum

Strachan, L.; Suleiman, R.; Panasyuk, A. V.; Biesecker, D. A.; Kohl, J. L.

ApJ, 571, pp.1008-1014.

We use combined Ultraviolet Coronagraph Spectrometer and Large Angle Spectroscopic Coronagraph data to determine the O⁵⁺ outflow velocities as a function of height along the axis of an equatorial streamer at solar minimum and as a function of latitude (at 2.3 R_solar from Sun center). The results show that outflow increases rather abruptly in the region between 3.6 and 4.1 R_solar near the streamer cusp and gradually increases to ~90 km s^-1 at ~5 R_solar in the streamer stalk beyond the cusp. The latitudinal variation at 2.3 R_solar shows that there is no outflow (within the measurement uncertainties) in the center of the streamer, called the core, and that a steep increase in outflow occurs just beyond the streamer legs, where the O VI λ1032 intensity relative to H I λ1216 (Ly-alpha;) is higher than in the core. Velocity variations in both height and latitude show that the transitions from no measurable outflow to positive outflow are relatively sharp and thus can be used to infer the location of the transition from closed to open field lines in streamer magnetic field topologies. Such information, including the densities and kinetic temperatures derived from the observations, provides hard constraints for realistic theoretical models of streamers and the source regions of the slow solar wind. [4446]

2002-02:     Far-Ultraviolet Observations of Comet 2P/Encke at Perihelion

Raymond, J. C.; Uzzo, M.; Ko, Y.-K.; Mancuso, S.; Wu, R.; Gardner, L.; Kohl, J. L.; Marsden, B.; Smith, P. L.

ApJ, 564, pp.1054-1060.

Comet 2P/Encke was observed with UVCS/SOHO near perihelion (2000 September 9 and 11) in the Lyman lines of hydrogen. We present a Lyα image reconstructed from a series of long-slit spectra, along with the intensity ratios of Lyα, Lyβ, and Lyγ. The narrow Lyα profile indicates that the observed photons are scattered from hydrogen atoms produced by dissociation of H2O and OH, though a broader profile far from the coma suggests a contribution from hydrogen atoms produced by charge transfer with solar wind protons. The outgassing rate derived from the Lyα intensity distribution is in excellent agreement with Sekanina's model of two active vents. We also present upper limits for the outgassing rates of the noble gases helium, neon, and argon. [4425]

2002-01:     The Helium Focusing Cone of the Local Interstellar Medium Close to the Sun

Michels, J. G.; Raymond, J. C.; Bertaux, J. L.; Quemerais, E.; Lallement, R.; Ko, Y.-K.; Spadaro, D.; Gardner, L. D.;Giordano, S.; O'Neal, R.; Fineschi, S.; Kohl, J. L.; Benna, C.; Ciaravella, A.; Romoli, M.; Judge, D.

ApJ, 568, pp.385-395.

The Solar and Heliospheric Observatory (SOHO) Ultraviolet Coronagraph Spectrometer is used to observe the interplanetary He focusing cone within 1 AU. Taken over 2 yr and from differing orbit positions, the series of observations includes measurements of He I 584 A and Ly-beta intensities. The cone itself is spatially well defined, and the He I intensity within the cone was ~45 R in 1996 December, compared with ~1 R for lines of sight outward from 1 AU. Between 1996 December and 1998 June, the focusing cone dimmed by a factor of 3.3 as the level of solar activity rose. This is the first time that interstellar helium is observed so near the Sun. Measured intensities are compared to a detailed temperature and density model of interstellar helium in the solar system. The model includes EUV ionization but does not include ionization by electron impact from solar wind electrons. There are several features in the data model comparison that we attribute to the absence of electron impact ionization in the model. The absolute maximum intensity of 45 R first measured in 1996 December calls for an ionization 45 % more intense than the EUV photoionization alone as measured by the Solar EUV Monitor/Charge, Element, and Isotope Analysis System (SEM/CELIAS) on SOHO. Important day-to-day variations of the intensity are observed, as well as a general decrease as the solar activity rises (both absolute and divided by a model with a constant ionization). This general decrease is even larger than predicted by a model run with the SEM/CELIAS photoionization rate alone, in spite of a factor of 1.5 increase of this rate from 1996 December to 1998 June. At this time, an additional ionization rate of 0.56x10^-7 s^-1 (compared with 1.00x10^-7 s^-1 from solar EUV) is required to fit the measured low intensity. We attribute this additional rate to solar wind electron impact ionization of the atoms. This shows that the helium intensity pattern is a very sensitive indicator of the electron density and temperature near the Sun. [4397]