On the unique divergent response of the equatorial electrojet vertical polarization electric field to different solar flare events

The response of ionospheric E region to different flare events is investigated using coherent HF backscatter radar to bring out divergent observations. The study reveals the following aspects: (i) increase of absolute mean Doppler frequency by similar to 25-52% during the initial phase of the morning time flares of 9 September 2005 with concurrent fall in backscattered power and (ii) decrease of absolute mean Doppler frequency by similar to 11.6-16.2% during the initial phase of the flare of 20 February 2002 with concurrent fall in backscattered power. The Doppler frequency is directly related to vertical polarization electric field. Therefore, these observations are unique and in contrast to earlier works which have, in general, reported only a decrease in equatorial electrojet (EEJ) vertical polarization electric field during the initial phase of flare events. The present study also brings out the possible important role played by the height-integrated conductivities in producing the divergent response of the EEJ. The large reduction in backscattered power for weak M class flare events is also observed in this study. In view of the importance of the ionosphere as a major source of error in GPS-based navigation, the present result assumes significance.