PROGRAM: P-18
Title:
IONOSPHERIC RESPONSE OF SOUTHERN HEMISPHERE TO SEVERE GEOMAGNETIC STORMS DURING SOLAR CYCLE 23Abstract:
The ionosphere is a highly coupled neutral plasma system where photochemistry and plasma dynamics plays an important role. The variations of ionospheric parameters can be regular having distinct periodicity of 11 years, 1 year, 6 months or 24 hours or sudden caused principally by geomagnetic storms due to the coupling of earth’s magnetic field and solar events. (Maruyama et al., 2004). Studies on these sudden ionospheric variations are essential as it plays a crucial role in radio wave propagation, satellite tracking and navigation. In the present study, the spatial and temporal variations of the ionospheric F2 layer critical frequency (foF2) in response to intense geomagnetic storms of 23rd solar cycle (1996-2008) over five stations of southern hemisphere are studied. The severe geomagnetic storms of the cycle was identified from the Disturbance Storm Time index (Dst) such that Dst ≤ -200 nT. The analysis reveals a domination of negative ionospheric response for all stations during the main phase of the geomagnetic storm followed by an enhancement during the recovery phase. The ionospheric foF2 effects are more dominant after the main phase of the storm when the Dst dips to its modest minimum than during the sudden storm commencement of the storm. A pre-storm enhancement is also noticed for equatorial station in some cases of extreme geomagnetic storms. Mid and high-mid latitude stations shows a pattern of foF2 variation similar to that of Dst with modest time lag.
Acknowledgements:
Authors sincerely acknowledge the Space Weather Services, Australia, and World Data Center for Geomagnetism, Kyoto respectively for providing the ionospheric foF2, Dst data.
References:
Maruyama, Takashi. Guanyi, M.A. & Nakamura Maho (2004) 3-3 Ionospheric Storm and Variation of Total Electron Content 3-3-1 Observations of TEC Disturbances with. J. Natl. Inst. Inf. Commun. Technol., 56 (1–4), 349– 368.