Christina Oikonomou

Study of the effect of 17–18 March 2015 geomagnetic storm on the Indian longitudes using GPS and C/NOFS

The largest geomagnetic storm in solar cycle 24 occurred during March 17-18, 2015 where the main phase of the storm commenced from 07:00 UT of March 17, 2015 and reached the Dst negative minimum at 22:00 UT. The present paper reports observations of TEC, amplitude and phase scintillations from different GPS stations of India during the storm of March 17 and highlights its effects on GPS. It also presents the global ESF occurrence during the storm using total ion density drift measurements from C/NOFS satellite. TEC enhancements were noted from stations along 77oE meridian around 10:00 UT on March 17 compared to March 16 and 18 indicating positive storm effects arising out of equatorward neutral wind in the local morning-noon sector of the main phase. Intense scintillation observations from Calcutta were most extensive during 15:00-16:00 UT, March 17 and the receiver recorded a longitude deviation of 5.2 m during this time. Cycle slips of the order of 8 s could be observed during periods of intense phase scintillations on the same night. Intense scintillation observation from Palampur is an exceptional phenomenon attributed to the dramatic enhancement of the electric field due to PPEF leading to a very high upward ion velocity over the magnetic equator as recorded by C/NOFS. The total ion density measured globally by C/NOFS reveals two distinct longitude regions of ESF occurrence during the storm: i) East Pacific sector and ii) Indian longitude during the storm. The time and longitude of ESF occurrence could be predicted using the time of southward turning of IMF Bz.

Study of topside electron density profiles obtained by cosmic satellites and an ionosonde over Cyprus during a four year period

The determination of the ionospheric electron density profile below the electron density peak (bottomside) has been traditionally conducted by ground-based ionosondes, which probe the ionosphere up to the maximum electron density and define the profile above the peak (topside) using functions which extrapolate the profile above the peak. An alternative modern technique for measuring electron density profiles is the GPS Radio Occultation, conducted by means of signals transmitted by GPS satellites and received by LEO satellites. The FORMOSAT-3/COSMIC (Constellation Observing System for Meteorology, Ionosphere, and Climate) is such a system operating since 2006. In this paper a comparison of the topside electron density profiles over Cyprus is investigated in terms of these two different measurement techniques, within a period of four years. The ability of the International Reference Ionosphere model (IRI-2012) to represent the topside electron density profile is also examined.