Electrostatic noise bands and whistler bursts observed in DEMETER satellite at low latitude and their ground observation

Abstract

Very low frequency (VLF) electric and magnetic field data recorded in DEMETER satellite corresponding to 30 nighttime passes over Indian longitudes during the period from 01 September to 09 December, 2010 are analyzed. The quick-look data show the existence of two intense electrostatic noise bands, one high frequency band between 04 and 18 kHz and other low frequency band below 01 kHz in majority of passes. The noise bands are electrostatic because no similar data are seen in the magnetic channel of the satellite. The characteristics of high frequency noise bands are similar to the lower hybrid resonance (LHR) bands observed in earlier satellite experiments. The data also show the occurrence of intense VLF noise bursts of duration two to three hours in the low latitude ionosphere which are analyzed thoroughly and found containing numerous first-hop magnetospherically reflected (MR) whistlers. There are some welldefined large dispersion whistlers also which appear to have propagated to the satellite in hybrid mode of propagation. A comparison with the ground data observed simultaneously at Agra station indicate insignificant and feeble nature of whistlers recorded on the ground suggesting that satellite whistlers propagated in nonducted mode of propagation and did not reach the ground. Various possibilities for the rare occurrence of VLF bursts are discussed.