Large-Scale Structure of the Solar Wind: Electron Density, Temperature and Kappa Deduced from ULYSSES Radio Measurements by Quasi-Thermal Noise Spectroscopy.
Abstract
We will revisit and discuss the electron density and temperature derived from the electrostatic noise measurement made with the URAP-RAR dipole electric antenna on Ulysses, as this probe flew by pole-to-pole during the minimum solar activity (1994-95). The electron parameters are obtained by fitting a model of the voltage power spectrum to the voltage measured at the terminals of an electric antenna. This method is generically known as ``quasi thermal noise spectroscopy''. In the present work, the model of spectrum is depending on only 3 parameters and computed by assuming that the electron velocity distribution is a generalized Lorentzian or ``kappa'' distribution. The 3 fitted parameters are thus the electron density, temperature and kappa value of the distribution, and we will discuss their variations with heliocentric distance, latitude and temporal solar activity. We will also compare these new results to those obtained by our team from the same data set but assuming instead a classical ''core + halo'' distribution for the electron velocity, that is a sum of two Maxwellian distributions. With this later method, the only temperature that could be determined with enough precision was the core temperature, while our new processing provides the total temperature of the solar wind electrons. We will finally focus on the total temperature gradient with distance we find when using such a kappa distribution.
- Publication:
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AGU Spring Meeting Abstracts
- Pub Date:
- May 2004
- Bibcode:
- 2004AGUSMSH21A..09M
- Keywords:
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- 2164 Solar wind plasma;
- 2194 Instruments and techniques