Spatial Features of L-Band Equinoctial Scintillations From Equator to Low Midlatitude at Around 95°E During 2015-2016

The nature and extent of the irregularities causing L-band nighttime scintillations at a group of five stations Dibrugarh (27.5 degrees N, 95 degrees E, 43 degrees dip), Kohima (25.6 degrees N, 94.1 degrees E, 39 degrees dip), Aizawl (23.7 degrees N, 92.8 degrees E, 36 degrees dip), Port Blair (11.6 degrees N, 92.7 degrees E, 9 degrees dip), and Cocos Islands (12.2 degrees S, 96.8 degrees E, 43 degrees dip) from the northern low midlatitudes to southern midlatitudes along 95 degrees E meridian is investigated. Global Navigation Satellite System/Global Positioning System/ionosonde measurements during the equinoctial months of 2015-2016 have been utilized. The northernmost station Dibrugarh and the southernmost station Cocos Islands are magnetically conjugate. Scintillations occur more frequently around the equatorial ionization anomaly crest where the background charge density (total electron content crest-to-trough ratio) plays an important role. It is also observed that L-band scintillations around this sector decrease considerably from equinoctial months of 2015 to equinoctial months of 2016. The anomalous El Nino-Southern Oscillation and quasi-biennial oscillation recorded during the 2015-2016 winter might have contributed partly to the suppression of irregularities (and hence scintillations) in the succeeding equinox. Strong pre-midnight scintillations when triggered by equatorial spread F occur simultaneously at all stations. The zonal/vertical drift velocities of irregularities estimated from the time delay of occurrence of scintillations decrease from postsunset to midnight hours. On the other hand, simultaneous sporadic E and post-midnight scintillations occur over Dibrugarh and Cocos Islands in the absence of scintillations at the equator. Azimuthal position of post-midnight scintillations at these two locations suggests that they are the manifestation of a frontal structure of sporadic E.