Investigation of Solar Flare Effects on GPS TEC and their positional dependence at Low, Mid and High Latitudes

The state and dynamics of the earth’s ionosphere is completely controlled by the solar radiations. The amount of solar radiation incident on the ionosphere varies considerably with the solar activity, so does the ionospheric variability. In this chapter we investigate the influences of solar flares on the ionospheric variability, since during solar flares huge amounts of radiation fluxes are released from the sun. To investigate the effect of solar flares on the ionosphere we consider the solar flares that were observed during 1998-2011. We have taken the three latitude station one each in mid, low and high latitude region. The solar X-ray flux in the 0.1 – 0.8 nm band were taken from the measurements of Geostationary Operational Environmental Satellite while as the solar EUV flux in the 24 – 34 nm band were taken from the Solar EUV monitor (SEM) onboard SOHO spacecraft. The correlative study of these fluxes was carried out with GPS derived Total Electron Content (TEC) at three latitude station viz Davis (68.57⁰S, 77.96⁰E), Usuda (36.13⁰N, 138.36⁰E) and IISC Bangalore (13.02⁰N, 77,57⁰E). From our study we found that peak values and peak enhancements of the radiation fluxes correlate well with the peak values and peak enhancements of TEC. However the correlation between peak enhancements of fluxes and TEC are much stronger than the correlation between peak values themselves. We then adjusted the solar radiation fluxes to the CMD, where CMD is Central Meridian Distance and takes care of flare location on the solar disc, and then investigated the correlation of CMD adjusted fluxes with the TEC. We found that the correlation between fluxes and TEC is extraordinarily improved as the fluxes are adjusted to CMD. Therefore location of flare has a considerable role in deciding how much impact it will produce on the ionosphere.