EDP Sciences
Free access
Volume 425, Number 1, October I 2004
Page(s) 281 - 285
Section The Sun
DOI http://dx.doi.org/10.1051/0004-6361:20040174

A&A 425, 281-285 (2004)
DOI: 10.1051/0004-6361:20040174

The jump of reverse drift rate of V-shaped structure and the large-scale inhomogeneity of plasma density in the solar atmosphere

F. Y. Xu1, 2 and H. A. Wu1, 2

1  Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008, PR China
    e-mail: pmoxfy@163.com
2  National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, PR China

(Received 16 October 2002 / Accepted 31 March 2004 )

A rare solar radio V-shaped structure was observed on August 25, 1999 by the 4.5-7.5 GHz spectrograph of the Purple Mountain Observatory, China. It consists of a reverse drift component followed by a normal drift one, which seems to be an unusual frequency drift event because of the jump of reverse drift rate from 3.22 to 1.53 GHz/s and the fastest drift rate of -3.53 GHz/s. According to their different drift rates, the V-shaped structure can be divided into three parts. By the consideration of plasma emission of an electron beam, a three-component solar atmospheric model with large and small scale lengths $\lambda $, $\lambda _{1}$ and $\lambda _{2}$ to describe the equilibrium solar atmosphere and local inhomogeneity as well as the energy loss of the electron beam due to electron-electron collision is proposed. The local scale lengths $\lambda _{1}=5.5\times 10^{9}$, $\lambda _{2}=7.7\times 10^{9}$ cm and $\overline{v}_{1}=0.41$ c, $\overline{v}_{2}=0.25$ c at Parts 1 and 2 of the reverse drift component are obtained. The variations of scale length of $\lambda
_{1}<\lambda _{2}$ and $\overline{v}_{1}>\overline{v}_{2}$, especially $\overline{v}_{1}>\overline{v}_{2}$, could be responsible for the jump of drift rate. The normal drift rate would be interpreted as the increase of average energy $E^{\prime
}$ of the electron beam at the mirror due to the decrease in electrons of lower energy via energy loss of collision. The three-component solar atmospheric model and the energy loss of the electron beam are discussed.

Key words: sun: flares -- Sun: radio radiation

© ESO 2004