Study of whistlers in saturn magnetosphere in the presence of parallel a.c. electric field

The electromagnetic whistler waves generated by lightning was observed in the magnetosphere of Saturn through the Cassini Radio and Plasma Wave Science Survey (RPWS). On July 1, 2004, two whistlers were observed as the spacecraft flew over the rings, and the third was observed at a radial distance of 6.19 RS (the radius of Saturn) as it entered the orbit on October 28, 2004. In present work we have investigated those whistlers waves which are pertaining in background plasma propagating in the direction of the magnetic field of Saturn. We use non-uniform, anisotropic, multi-component plasma waves to study linear growth. Using the kinetic approach method, the expressions of dispersion relation and growth rate are derived. A model of magnetic field strength has been used for different latitudes at a radial distance of 8 R_s (1 R_s = 60,268 km). Various parameters affecting the growth of whistler waves with relativistic effect in bi-Maxwellian background has been studied. Parametric analysis inferred that growth rate of whistler waves increases with increasing value of temperature anisotropy and AC frequency, but the growth rate remains same as the angle of propagation with respect to B_o (Magnetic field at equator) increases. We find that temperature anisotropy (T⊥/T∥ ~ 1.5) can account for linear temporal growth rate of whistler mode waves, which provides a majority of the observed frequency-integrated power. Higher frequency chorus emissions differ from lower frequency whistler mode emissions and are sometimes associated with simultaneously observed low frequency electromagnetic ion cyclotron waves. These electromagnetic ion cyclotrons appear to modulate a slow frequency drift (~15 Hz / s), which develops into a nonlinear growth with much greater frequency drift, only related to high frequency chorus. (author)