Large-scale structure of the solar wind assuming kappa velocity distribution.
Abstract
We will present new measurements of the solar wind electron density, total temperature and kappa index obtained from spectroscopic analysis of the electrostatic noise recorded by the radio low-frequency receiver (~1 to 50 kHz) with the electric dipole antenna on the Ulysses spacecraft, as this probe flew by pole-to-pole during a minimum solar activity (cycle 22 to 23). These electron measurements are obtained by fitting a model of the voltage power spectrum to the voltage measured at the antenna terminals. This method, generically known as ''quasi thermal noise spectroscopy'', is a powerful tool to measure in situ the electron thermodynamic quantities in natural plasmas, and has been used in the solar wind, planetary ionospheres and plasmaspheres or cometary tails. The present work improves on previous ones by modeling the electron velocity distribution by a generalized Lorentzian or ''kappa'' distribution. This model is especially adapted in the solar wind, whose electron velocity distribution has a conspicuous suprathermal tail. The 3 fitted parameters are the electron density, temperature and kappa index of the distribution, and we will discuss their variations with heliocentric distance and latitude. We will especially focus on the total temperature variation with distance during the solar minimum at high latitudes and compare it with the temperature profile predicted by a kinetic collisionless model of the solar wind.
- Publication:
-
EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003
- Bibcode:
- 2003EAEJA.....3217M