New Insights into the Daytime Thermospheric Wave Dynamics over Low-Latitudes Obtained Using Radio Technique: Response to the Solar Flux and Seasonal Variations

Abstract:

Gravity waves (GWs) play an important role in the redistribution of energy and momentum in the Earth’s atmosphere. Knowledge on their spatial and temporal variations with respect to seasons and solar flux is vital in order to understand the coupling processes in the upper atmosphere. A novel approach using radio technique is implemented wherein information on the phase offsets observed between the height variations of isoelectron densities in the daytime obtained from a digisonde in a low-latitude location, Ahmedabad (23⁰ N, 72.5⁰ E; 14.9⁰ N MLAT), India, yielded information on the vertical propagation characteristics of GWs. Radio measurements enable unhindered study of gravity wave dynamics around the year. As winds over a given location flow in different directions in different seasons, the season dependent preferential directions of propagation of GWs over Ahmedabad have been inferred. Propagation characteristics of GWs during geomagnetic disturbed times are found to be different than those in the quiet times. These differences in the GW propagation characteristics during geomagnetic disturbed times as compared to the corresponding seasonal quiet time values show good semblance with those in the variations in integrated AE index. This enhancement in the energy input at high-latitudes having a strong correlation with low-latitude GW propagation characteristics, provides direct evidence on the high- to low-latitude coupling. Further, GW activity and their vertical propagation characteristics increase with an increase in solar flux. Even though the GWs are nearly omnipresent in the daytime thermosphere, they do not propagate vertically on every day. New insights on the understanding of the upper atmospheric interactions during daytime with regard to neutral GW characteristics will be presented in detail.