Occurrence features of Intermediate Descending Layers [IL] over the equatorial location of Thiruvananthapuram

Abstract

A study has been carried out on the various aspects of occurrence of Intermediate Descending Layers [IL] on the bottom side of the F region over the magnetic equatorial location of Thiruvananthapuram [8.5 0 N; 77 0 E; dip lat of 0.5 0 N] in India for the period from 2000−2008 using ionosonde observations. Diurnally, the IL occurrence exhibits a double peak pattern with maximum occurrence in the post noon [15–17 IST], followed by early morning [7–9 IST]. The IL has a solsticial maximum [both summer and winter] probability of occurrence [∼70% during 2006 and 20% during 2002] with minima during equinoxes [∼10% during 2002 and 40% during 2006]. The solar cycle variability of IL is brought out in the present study using data from solar cycle 23. The occurrence is found to be high during solar minimum period [70%] and low during solar maximum period [10%]. The diurnal and seasonal behaviour of IL parameters like the peak frequency and the base height are also reported in this study. The role of gravity waves in determining the above stated features of occurrence is being proposed.