Search Publications
Hubble Space Telescope observations of the Martian aphelion cloud belt prior to the Pathfinder mission: Seasonal and interannual variations
Wolff, Michael J.; James, Philip B.; Lee, Steven W. +1 more
The presence of a globally extant equatorial belt of water ice clouds on Mars is quantitatively investigated using data from three seasons of our Hubble Space Telescope synoptic monitoring program (1993-1997). A subset of the 1996-1997 images covers the landing site of the Mars Pathfinder including a set of images taken after touchdown. Using mult…
Cyclotron resonance in coronal holes: 1. Heating and acceleration of protons, O5+, and Mg9+
Hollweg, Joseph V.
The resonant heating and acceleration of protons and selected heavy ions in coronal holes are investigated by calculating trajectories of individual test particles under the influence of gravity, the electrostatic electric field, the mirror force, and the resonant acceleration due to interaction with dispersive ion cyclotron waves. The transverse …
Interplanetary Lyman α line profiles derived from SWAN/SOHO hydrogen cell measurements: Full-sky Velocity Field
Bertaux, Jean-Loup; Lallement, Rosine; Quémerais, Eric +3 more
We present here an analysis of 1 year of data obtained by the solar wind anisotropies (SWAN) instrument on board the SOHO spacecraft orbiting around the L1 Lagrange point at 1.5×106km sunward from Earth. This instrument is measuring the interplanetary Lyman α background due to solar photons backscattered by hydrogen atoms in the interpl…
Changes of the boot-shaped coronal hole boundary during Whole Sun Month near sunspot minimum
Hoeksema, J. T.; Scherrer, P. H.; Zhao, X. P.
The August 27, 1996, boot-shaped coronal hole is shown to rotate nearly rigidly at a rate of 13.25°/day, greater than the equatorial rotation rate of bipolar magnetic regions such as active regions and plages. The day-to-day variation of the coronal hole border is determined by comparing the rigid rotation projection of the disk-center hole bounda…
Quasi-thermal noise in a drifting plasma: Theory and application to solar wind diagnostic on Ulysses
McComas, D. J.; Moncuquet, Michel; Issautier, Karine +2 more
The present paper provides the basic principles and analytic expressions of the quasi-thermal noise spectroscopy extended to measure the plasma bulk speed, as a tool for in situ space plasma diagnostics. This method is based on the analysis of the electrostatic field spectrum produced by the quasi-thermal fluctuations of the electrons and by the D…
A two-fluid, MHD coronal model
Wu, S. T.; McComas, D. J.; Poletto, G. +2 more
We describe first results from a numerical two-fluid MHD model of the global structure of the solar corona. The model is two-fluid in the sense that it accounts for the collisional energy exchange between protons and electrons. As in our single-fluid model, volumetric heat and momentum sources are required to produce high speed wind from coronal h…
Potential wells, the cyclotron resonance, and ion heating in coronal holes
Hollweg, Joseph V.
We consider the motions of protons and O5+ ions in coronal holes. We first consider the effects of a potential well, which arises from the combination of gravity, the electrostatic electric field, and the mirror force. We show that if the potential well is time dependent, then ions which are initially trapped will undergo a time-average…
A study of solar wind acceleration based on gyrotropic transport equations
Leer, Egil; Olsen, Espen Lyngdal
The gyrotropic transport equations are used to describe an electron-proton solar wind from the 500,000 K level in the upper transition region and out to 30 solar radii. These equations allow for different temperatures parallel and perpendicular to the magnetic field, as well as transport of parallel and perpendicular thermal energy along the field…
Microwave enhancement and variability in the elephant's trunk coronal hole: Comparison with SOHO observations
Thompson, B. J.; Gopalswamy, N.; Shibasaki, K. +2 more
We report on an investigation of the microwave enhancement and its variability in the elephant's trunk coronal hole observed during the Whole Sun Month campaign (August 10 to September 9, 1996). The microwave images from the Nobeyama radioheliograph were compared with magnetograms and EUV images obtained simultaneously by the Michelson Doppler ima…
Energy spectra of 50-keV to 20-MeV protons accelerated at corotating interaction regions at Ulysses
Simnett, G. M.; Lario, D.; Balogh, A. +6 more
We analyze here the energy spectra of 50-keV to 20-MeV protons accelerated at corotating shocks observed at Ulysses in the southern heliosphere during 1992 and 1993. In general, our results are inconsistent with the predictions of two models based on diffusive shock acceleration theory (Fisk and Lee [1980] and Jones and Ellison [1991]). The main r…