Electronic Collision Frequency in the F Region at Sunrise & Sunset

Abstract

The variation of the effective collision frequency of electrons veff with solar zenith angle <img src='/image/spc_char/lembda.gif' border=0> has been studied around sunrise and sunset by group retardation method [Appleton, E. V., <i>Nature, Lond., </i> 135(1935), 618] at different radio frequencies. The variation is found to be steeper at sunrise than at sunset. Taking a linear relationship between 'veff' and <i>f</i>², the square of radio frequency, a rough estimate of the electron temperature <i>T_e </i>has been made. The resulting values of <i>T_e </i> at sunrise and sunset are found to be 1113 and 987^o K., respectively.