A study of precursors to equatorial spread F using the giant meterwave radio telescope

Abstract

This paper reports the results of an experiment to identify a possible precursor to equatorial spread F (ESF) with the Giant Meterwave Radio Telescope (GMRT) (latitude: 19.10°N, longitude: 74.05°E geographic; dip: 23°N magnetic) near Pune by simultaneously recording the amplitude and phase of the signal from the radio source 3C218 (RA:09h 15m, Declination: -11 °) at 235, 327, 610, and 1420 MHz in the postsunset-premidnight period 18.5-22.5 LT on 26, 29, and 31 March 2004. Patches of scintillations both in amplitude and phase were observed on 26 and 29 March 2004 at 235, 327, and 610 MHz frequencies starting around 20 LT (LT = UT + 05:00) and extending until 22 LT while the records for 31 March 2004 do not show any scintillations. Significant amplitude scintillations were not observed at 1420 MHz. The most remarkable feature was the presence of large-scale periodic structures in phase prior to onset of amplitude scintillations. The Total Electron Content (TEC) as observed on a GPS link also looking through the same ionospheric volume showed periodic variation of carrier phase prior to onset of scintillations and bite-outs in TEC, which implies that before the onset of ESF, the large-scale wave structures propagate to the height of maximum ionization and beyond. Copyright 2008 by the American Geophysical Union.