Spatial estimates of Rayleigh-Taylor instability at geomagnetic equator from satellite scintillation observations at Delhi

Abstract

From scintillations recorded at Delhi (42° dip) using signals from a pair of geostationary satellites, viz. ETS-II (130°E) and SYMPHONIE (49°E) at VHF during March-April 1979, and ETS-II(VHF) and MARISAT (73°E) at L-band from October 1986, spatial estimates and characteristics of the post-sunset Rayleight-Taylor instability (RTI) triggered on certain days at the geomagnetic equator are made. It is assumed that there exists a strong electromagnetic coupling of the ionospheric phenomenon at the geomagnetic equator with those at higher latitudes in the post-sunset periods due to rising plasma bubbles and plumes in the equatorial ionosphere. Occasionally, it is found that severe magnetic storms trigger instability of very large spatial extents giving rise to scintillation producing irregularities characterize by uniform scale-size. The estimates of RTI spatial extents are limited by the observing geometry and hence, they are at least of the same order as the distance separating the subionospheric points for the appropriate satellite pair. For ETS-II and SYMPHONIE pair the subionospheric points are separated by 1000 km approximately, while it is about 800 km for ETS-II and MARISAT pair. The present limited data indicate that increased magnetic activity might inhibit growth of RTI and hence scintillation production, especially during high solar activity.