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IONOSPHERE

The ionosphere is defined as a region of the partially ionized gas extending from around 90kms to heights wherein neutrals still dominate the population and the atmosphere is in state of hydrostatic equilibrium. Solar radiation in EUV and X-ray range are primarily responsible for the ionization of this region which carries the diurnal currents largely imposed on it by tidal motions originating from lower heights.

Traditionally, it has been assumed that currents in the ionosphere do not affect the lower atmosphere but with the development of the concept of the Global Electric Circuit (GEC), series investigations are going on to assess the transport of electric currents from the ionosphere and above in to region of the neutral atmosphere right up to the surface of the earth. The probable role of the GEC in the solar-terrestrial-weather relations has resulted in the study of atmospheric electric field and Schumann resonance at EGRL. GEC measurements are also carried out by the scientists of the Institute at Antarctica as the clean environment offers so essential for such studies.

The ionosphere electric fields and currents have a significant contribution from large scale processes accruing directly or indirectly from the interaction of the out flowing solar plasma with the geomagnetic field. The structure of the currents in the ionsphere depends not only on the level of ionization but also on the local geometry of the geomagnetic field line. Hence there is a significant enhancement of ionospheric currents around the latitude of the dip equator leading to the so called Equatorial Electro Jet (EEJ) which stands out above the background Sq. current system. EEJ is of special interest to the Institute but also to the space physics community as a whole. The establishment of the THUMBA rocket launching facility at Trivandrum was essentially dictated by the desire to make a comprehensive study of the EEJ.

Only the height integrated effects of currents in the ionosphere are recorded by surface magnetometers hence the 3-D structure of the current system require the use of rocket and satellite based measurements. The Institute works with satellite data and carries out numerical modeling of the ionspheric current system as apart of its research activities.

EEJ not only manifests itself in the magnetic field variations but also controls the dynamics of the ionosphere up to the latitude of the so called Appleton anomaly region. A variety of instabilities are associated with the dynamics region and these are studied with ground based ionosonde, coherent and incoherent radars, airglow, low altitude satellites and also through radio wave scintillations. The irregularities in the ionosphere degrade satellite communication and hence radio wave scintillations are studied extensive studied using the GPS satellites.



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