A study on the low-latitude daytime E region plasma irregularitiesusing coordinated VHF radar, rocket-borne, and ionosondeobservations

摘要

In this paper we study the off-electrojet low-latitude daytime E region plasmairregularities using first multi-instrument observations in India made during July 2004 bythe MST radar from Gadanki (13.5°N, 79.2°E, magnetic latitude 6.4°N), Langmuir probeon board the RH-300 Mk II rocket, and ionosonde from Sriharikota (13.6°N, 80.2°E,magnetic latitude 6.4°N). Radar echoes were confined to altitudes below 105 km and wereobserved in the form of a descending echoing layer with the descent rate of 1 km/h. Virtualheight of the E layer, as observed by ionosonde, shows identical descending behavior. Adetailed analysis based on the radar and ionosonde observations shows that the radarechoes are related to the range spread in the ionogram. Rocket observations made on23 July 2004 revealed weak plasma irregularities with scale sizes more than 100 m and nonoticeable irregularity at shorter scales. The spectral slope of the irregularities observed bythe rocket probe is found to be —4 for scales in between 1 km and 100 m. During therocket launch, radar did not detect any echo conforming that the small-scale irregularitieswere not present. Examination of concurrent observations of neutral wind made byTIMED Doppler interferometry suggests that zonal wind plays a crucial role in formingelectron density layers, which become unstable via the gradient drift instability withbackground electric field or/and zonal neutral wind generating low-latitude E regionplasma irregularities.