Abstract
Abstract. A thin and highly dense sporadic E layer, which can occasionally block the upper ionospheric layers, is called blanketing sporadic E (Esb). We present the statistical seasonal local time occurrence pattern of Esb at equatorial station Tirunelveli (8.7° N, 77.8° E, dip latitude 0.7° N) during the extended minimum of solar cycle 24 (2007–2009). In spite of nearly the same average solar activity during both 2007 and 2009, considerable differences are noticed in the seasonal occurrence of Esb during this period. The percentage of Esb occurrence is found to be the highest during the summer solstice (≥ 50%) for both 2007 and 2009, which is in general accordance with the earlier studies. The occurrences of Esb during the vernal equinox (~ 33%) and January–February (~ 28%) are substantial in 2009 as compared to those during the same seasons in 2007. We find that, during winter (January–February), ~ 75% of Esb occurred during or just after the period of sudden stratospheric warming (SSW). We suggest that enhanced Esb occurrence during winter (January–February) and the vernal equinox of 2009 could be associated with SSW-driven changes in the E region ambient conditions. Furthermore, the close association of Esb with counter equatorial electrojet (CEEJ) suggested by earlier studies is re-examined carefully using the scenario of Esb occurrence on non-CEEJ days. Such an exercise is crucial as we are unaware whether the physical mechanisms driving Esb and CEEJ are linked or not. We find that, of all the seasons, the association of Esb and CEEJ is strongest during winter (November–December).
Highlights
The ionospheric E region is characterized by the presence of thin layers of enhanced ionization at heights of 100– 120 km, known as sporadic E (Es)
It should be noted that the occurrence of Esb is primarily seen between 10:00 and 20:00 Indian Standard Time (IST), we calculate the seasonal local time percentage occurrence of Esb for this period
We propose that the physical process involving formation of Esb and counter equatorial electrojet (CEEJ) are closely linked (Reddy and Devasia, 1981) and the presence of east–west winds with vertical shear assists the formation of Esb during
Summary
The ionospheric E region is characterized by the presence of thin layers of enhanced ionization at heights of 100– 120 km, known as sporadic E (Es). Es is patchy and transparent to the radio waves reflected from layers at higher altitudes (Rishbeth and Garriott, 1969). Sometimes these layers are highly dense, known as blanketing type sporadic E (Esb), which effectively blocks the upper ionospheric layers to the radio waves. Mid- and high-latitudes has been studied for over half a century, yet its seasonal occurrence pattern globally remains a puzzling feature. Mid- and high-latitudes has been studied for over half a century, yet its seasonal occurrence pattern globally remains a puzzling feature. Whitehead (1989, 1997a, b) has discussed unsolved problems in understanding the formation of Esb at different latitudes
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
