Low‐latitude Es capable of controlling the onset of equatorial spread F

Abstract

AbstractTo investigate their role on the occurrence of equatorial spread F (ESF), the low‐latitude E region in the evening hours has been characterized in terms of sporadic E (Es) activity based on ionosonde observations from Sriharikota, a low‐latitude station in India. While prior to the sunset, either Chapman type E layer, or Es, or a combination of the two was observed, after sunset, when observed, the E layer was exclusively Es. Es, however, could be either blanketing or nonblanketing type. Observations revealed that while the occurrence of ESF had a broad relationship with the type of Es, a detailed investigation suggested that (1) ESF occurred (did not occur) irrespective of Es type if the virtual height of the F layer base (h'F) was greater than ~360 km (less than ~290 km), and (2) ESF occurrence depended strongly on the type of Es if 290 km < h'F < 360 km. Model computation shows that low‐latitude Es can significantly influence the growth of the Rayleigh‐Taylor instability for the cases corresponding to category 2 by increasing the total field‐line integrated Pedersen conductivity, consistent with the observations. The results presented in this paper highlight under what circumstances the low‐latitude Es would play a critical role in the occurrence of ESF, which can be used to understand the day‐to‐day variability of ESF.