Malini Aggarwal1 * , H. P. Joshi1 , K. N.
Iyer1 , A. K. Patra,2 and
Smitha V. Thampi3
1Department of Physics, Saurashtra University, Rajkot,
India
2 National Atmospheric Research Laboratory, Gadanki,
Tirupati, India
3 Space Physics Laboratory, VSSC, Trivandrum, India
Abstract. An important component of ionospheric plasma irregularity stud- ies at low latitudes involves the study of the plasma bubbles which produce intense scintillations of trans-ionospheric satellite signals. In order to investi- gate the dynamics of plasma density irregularities of different scale sizes, a cam- paign of multi-technique observations was conducted during 11 to 15 Sep.05 at Gadanki (geog.13.45o N, 79.17o E, dip latitude 6.4 N), an Indian station. A low latitude spread F event occurred during the campaign on the night of 15 Sep.05. The observations were made using dual frequency GPS receiver and VHF coher- ent backscatter radar from Gadanki and two ionosondes with some latitudinal separation, from Trivandrum and SHAR. Range type spread F on ionograms and radar plume signatures on range-time-intensity maps of the VHF radar were observed. Using the GPS receiver, the amplitude scintillation index (S4 ) enhancements by 0.36 and 0.39 with two depletions in total electron content (5 and 12 TECU) are seen. The vertical plasma drift velocity is observed by ionosonde to be high (35 m/s) which maximized around 1915 LT, which coin- cided with onset of range type spread F over the magnetic equator, Trivandrum. The irregularities are observed first at Trivandrum at 1915 hrs, thereafter by GPS receiver and later by VHF radar (off-equatorial station) indicating that the observed bubble is drifting eastward.
Keywords: equatorial spread F - scintillation - GPS - VHF radar - ionosonde