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UPPER ATMOSPHERE

The Earth’s upper atmosphere can be broadly divided into three domains:


1. A region dominated by neutral dynamics (Mesosphere and Lower Thermosphere),
2. A region where both neutral dynamics as well as plasma electrodynamics are relevant (Ionosphere),
3. A region totally dominated by plasma processes (Magnetosphere).

Global Electric Circuit (GEC):
The radars are used to probe the dynamics of the neutral atmosphere at various altitudes, and the electrical coupling between different regions of the ionosphere.

Dynamics of the middle and upper atmosphere:
The first 90 km 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 100 km 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 short term geomagnetic variations recorded on ground without having proper understanding of the middle atmospheric dynamics.
Regular monitoring of the middle atmosphere in the height range between 70 to 100 km using medium frequency partial reflection radars and atmospheric airglow emissions helps in understand its coupling to the ionospheric processes like EEJ, EIA and ESF irregularitie

Geomagnetic Pulsations:
Pulsation or short period fluctuations of the measured geomagnetic field, on time scales less than an hour, are used to study space plasma processes in different regions of the magnetosphere, alongside theoretical investigations.

 

Equatorial Electrojet (EEJ):
The Equatorial Electrojet is the high concentration of ionospheric current flowing from west to east in a narrow belt flanking the dip equator in the sunward hemisphere. Being the major current system in the equatorial region, it controls the dynamics and electrodynamics of the ionospheric plasma at low latitudes. The detailed investigation employs satellite as well as ground magnetic field observations.

Ionospheres Irregularities:
Imaging of structures and irregularities in the ionospheres plasma, produced by plasma instabilities, is carried out using ground-based radio and airglow techniques. Radio wave signals transmitted from the Global Positioning System (GPS) satellites have provided additional tools for probing ionospheres structures. Theoretical studies in this area are also being pursued. Gravity waves are also investigated using airglow observations.

Solar wind – Magnetosphere – Ionosphere Coupling:
Theoretical models of various plasma processes that are involved in Solar wind Magnetosphere – Ionosphere coupling are being developed in conjunction with the analysis of ground and satellite data. Development of various magneto-hydrodynamical (MHD) computer simulation codes is being undertaken to investigate the substorm phenomenon.

Space Weather Prediction:
The objective of this programme is to improve the capability of providing timely specification and forecasting of conditions on the Sun, and in the solar wind, magnetosphere, ionosphere, and thermosphere that can impair the performance and reliability of space-borne and ground-based technological systems.

 


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