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MESOSPHERE AND LOWER THERMOSPHERE

The first 90kms or so of the atmosphere is controlled by neutral dynamics leading to the development of gravity waves, tides and planetary scale motions. These oscillations interact with each other and wave coupling processes lead to annual, semi-annual as well as inter-annual trends that include the quasi-biennial oscillations. Dynamics in this region is of great interest to researches in geomagnetism as the large scale oscillations originating in this region propagate upward and reach the region of ionized plasma above 100kms with enhanced amplitudes. They generate large scale electric fields and consequently currents that are recorded as slowly varying geomagnetic field variation in ground magnetic observatories. It is impossible to understand the geomagnetic variations recorded on ground and by rockets and low orbit satellites with a grip on dynamics of the neutral atmosphere. We monitor the dynamics in the region between 70 to 100kms using medium frequency partial reflection radars and atmospheric airglow emissions.

The Indian Institute of Geomagnetism maintains a regional centre called Equatorial Geophysical Research Laboratory (EGRL) at Tirunelveli wherein a variety of scientific experiments are conducted in the pursuit of understanding middle and upper atmospheric phenomena.



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