On the origin of the large scale zonal modulation of the equatorial spread F
Abstract
Coordinated VHF radar (Gadanki, 13.5 degree North, 79.2 degree East, 6.5 degree North magnetic latitude) and ionosonde (Sriharikota, 13.7 degree North, 80.1 degree East, 6.7 degree North magnetic latitude) observations have been used to study the zonal pattern of the equatorial spread F (ESF). Long term investigations have revealed the presence of large scale wave structure (LSWS), modulating the zonal pattern of the equatorial spread F. Two different categories of observations, one where radar plumes were observed soon after the F region sunset, and another where radar plumes were observed with a delay of more than 1 hour with respect to the F region sunset, have been investigated. The average peak F region base height (h’F) corresponding to the first category was 20 km more than that for the second category, indicating the presence of a standing large scale wave structure. Observations made using the ionosonde located at Sriharikota, a low latitude station just 100 km east of Gadanki, revealed drastically different sporadic E (Es) features for the two different categories of events. While blanketing type Es were found to disappear at ~18:45 LT corresponding to the first category of events, continuous blanketing type Es were observed even after 19:45 LT for the second category of events. Hence it is argued that the large scale zonal Pedersen and Hall conductivity variation of the low latitude E region, owing to the Es, resulted in the zonal variation of post sunset height rise of the F layer and the ESF. Model computation was carried out to simulate the influence of the low latitude Es which is connected to the F region via magnetic field lines, on the height rise of the F layer during post sunset period. Model simulation clearly reveals that the spatial variation in the low latitude Es is capable of producing the LSWS in the F region.
- Publication:
-
40th COSPAR Scientific Assembly
- Pub Date:
- 2014
- Bibcode:
- 2014cosp...40E1348J