Low frequency plasma waves in the solar wind: from ecliptic plane to the solar polar regions

Abstract

<B>Traveling from the ecliptic to the solar polar regions, Ulysses observed wave activity below the local electron cyclotron frequency, f_ce. In regions near the heliospheric current sheet (hereafter HCS regions), two wave modes are observed: (1) whistler mode electromagnetic waves near interplanetary shocks and during periods of rapidly increasing solar wind velocity, and (2) apparently electrostatic waves occurring during the periods when gradually decreasing solar wind velocity is observed. At high heliographic latitudes, in the region with relatively steady high speed solar wind streams, wave activity is consistently observed near and below f_ce with little time variability of the spectra. It is found that in the periods when intense waves of the second type are observed in the HCS regions, the electron heat flux decreases. This may imply that these low frequency waves limit the intensity of the heat flux through wave particle scattering.</B>