The response of the equatorial ionosphere to fast stream solar coronal holes during 2008 deep solar minimum over Indian region

Abstract

In this paper, we report ionospheric response to fast stream solar coronal holes during 2008 deep solar minimum year using ground-based multi-instruments over Indian region. To examine this, we analyzed foF2 (MHz) and hpF2(km) from Canadian Advanced Digital Ionosonde and total electron content (TEC) from GPS receiver over Tirunelveli (8.73°N, 77.70°E; dip 0.5°N) along with equatorial electrojet (EEJ) strength. Our analysis shows good correlation between solar wind and foF2/TEC, while hpF2 is poorly correlated. However, moderate correlation exists between solar wind and EEJ strength. When we performed periodogram analysis, we observed 9 and 13 day periods as dominant periods in foF2 and TEC. Interestingly, the occurrence pattern of plasma irregularities also resembles these periodic oscillations. Since it is believed that lower atmospheric waves are dominant forces for ionospheric variabilities during deep solar minimum, we examined the mesosphere/lower thermosphere region temperature using Thermosphere Ionosphere Mesosphere Energetics and Dynamics Sounding of the Atmosphere using Broadband Emission Radiometry and winds using medium frequency radar along with outgoing longwave radiation in the troposphere altitudes to rule out the sources for these periodic oscillations in the lower atmosphere. Using cross-wavelet and cross-coherence spectra of both solar wind and ionospheric/atmospheric parameters, we suggest that ionospheric periodicities are similar to that of solar wind. Based on these results, we suggest that while the periodic oscillations are associated with the disturbance dynamo winds/electric fields that are propagated to equatorial latitudes, the differences in their temporal/seasonal variations are attributed to the variations in the composition/recombination changes.