Characteristics of intense space weather events as observed from a low latitude station during solar minimum

摘要

Using a dual‐frequency high‐resolution software‐based GPS receiver, TEC and phase have been monitored from Calcutta, India situated near the northern crest of the Equatorial Ionization Anomaly for studying some Space Weather events during 2008–2010. Data from a dual‐frequency Ionospheric TEC and Scintillation Monitor operational at this station under the international SCINDA program of the U.S. Air Force have also been used. This paper presents two cases of intense Space Weather events occurring in the equatorial latitudes under magnetically quiet conditions during the abnormally prolonged minimum of solar cycle 24. High values of S_4 with maximum ～0.8 were noted on GPS links located almost due south of Calcutta (22.58°N, 88.38°E geographic; magnetic dip: 32°N) when the look angles of the satellites are more‐or‐less aligned with the axis of the anisotropic field‐aligned irregularities over the magnetic equator. Associated bite‐outs in TEC of amplitude 40 units were recorded in the local post‐sunset hours. Well‐defined patches of phase scintillations and associated cycle slips were identified. On these days, higher values of ambient ionization were noted and the diurnal maximum of the electrojet strength was found to be delayed followed by a significant rise of the F region with a high upward drift velocity over the magnetic equator around sunset indicated by ionosonde. Measurements of in situ ion density using LEO DMSP corroborate the F region height rise. Presence of irregularities in ionization density distributions around 450km was found from C/NOFS measurements.