Sporadic E over Allahabad during the extremely prolonged low solar activity period of 2007-2009

Abstract

In this paper, the characteristics of sporadic E (Es) layer echoes, observed using a Canadian Advanced Digital Ionosonde (CADI) from equatorial ionization anomaly crest region of Allahabad (25.3ºN, 81.5ºE, and dip latitude 16.3ºN) during extremely prolonged low solar activity period of 2007-2009, have been investigated. Quarter hourly ionograms have been used to study the Es characteristics, viz. the top frequency reflected by the Es layer (ftEs), the blanketing frequency (fbEs), virtual height of Es (h’Es) and their local time and seasonal variations. Also, the occurrence statistics of Es and total blanketing type Es are presented. The most notable feature of the sporadic Es layer at Allahabad is the high percentage occurrence during daytime in the summer months. Interestingly, observation shows that the occurrence of total blanketing type Es layer is more during the nighttime of summer months than in other times and other months. Height migration of h’Es shows descending pattern indicating the role of tidal winds. These results are finally compared with those reported earlier and discussed in the light of current understanding of the solar cycle and seasonal variability of the temperate latitude Es.