| Session Details | |
| Section | ST - Solar & Terrestrial Sciences |
| Session Title | Coupling Processes in the Equatorial Atmosphere |
| Main Convener | Prof. D. Narayana Rao (Dept. of Space, Govt. of India, India) |
| Co-convener(s) | Prof. Toshitaka Tsuda (Kyoto University, Japan) |
| Session Description | Equatorial atmosphere hosts many important and unique atmospheric dynamical and chemical processes as it receives maximum amount of solar radiation over the globe. A variety of atmospheric waves such as gravity waves, atmospheric tides and planetary scale waves are generated in this equatorial region through latent heating of the atmosphere by cumulus convection in the lower atmosphere and solar insolation absorption of Ultra Violet (UV) rays by ozone molecules in the stratosphere and Infrared radiation (IR) by water and Carbon-di-oxide molecules in the troposphere respectively. The dynamics associated with these waves help to couple the entire atmosphere vertically from boundary layer to thermosphere/ionosphere and laterally from equator to pole as well as all the longitudinal regions. The energy and momentum of the vertically upward propagating waves are deposited at high altitudes when they dissipate by processes such as (i) wave mean flow interaction, (ii) nonlinear wave-wave interaction (iii) critical level absorption, (iv) wave damping/saturation through convective or mechanical instabilities, (v) radiative and frictional damping through Newtonian cooling and viscous drag respectively (vi) wave diffusion etc. Equatorial Quasi-Biennial Oscillation (QBO) in the lower stratosphere and Semi Annual Oscillation (SAO) in the upper stratosphere and mesosphere and the negative drags of the lower mesosphere are the best examples of wave-mean flow interaction. Not only the waves drive the general circulation of the middle atmosphere, but also they play an indispensable role in driving various electrodynamical processes of the ionosphere through wind induced dynamo mechanisms in the presence of the earth’s magnetic field. The generation of primary east-west electric field in the E region ionosphere is believed to be due to the dynamo mechanism induced by various atmospheric tidal oscillation modes that penetrate above 100 km and generated in the lower atmosphere. Further, triggering of Spread-F events, Counter Equatorial Electrojects over the magnetic equatorial regions is some times due to the effect of vertically propagating, large-amplitude high frequency gravity waves that are generated in the lower atmosphere as a result of the latent heating of the atmosphere through convection. And the long period modulation of the intensity of E region irregularities and electrical currents is believed sometimes due to the effect of penetrating planetary scale equatorial waves (~2-30 days) generated in the lower atmosphere through convective heating. As the exact physical mechanisms that govern the tropical E-region 150 km and quasi-periodic echoes are yet to be identified, wind dynamics (prevailing in the E region) associated with lower atmospheric internal gravity waves and tidal modes are considered important to explain these E region electrodynamical processes. |