Solar - Terrestrial Physics
The group working on the ionosphere and the magnetic field of the Earth has experimental facilities at the KodaikanalObservatory. These observations conducted from about four degrees north ofthe magnetic equator around the fringe of the equatorial electrojet beltin the Indian sector, provide useful insights into dynamical aspects of the ionosphere.
Round the clock monitoring of the ionosphere is done with a IPS-42 digital ionosonde (which replaced an analog model C-3 ionosonde that was in operation since mid 50's) and of the geomagneic field with aLa Cour variometer (since 1949). The ionospheric and geomagnetic data are used by scientists at home and abroad for investigation of wide range of problems in the inter-disciplinary field of Solar Terrestrial Physics. In addition an HF Doppler radar is operated to monitor the small scale ionospheric vertical plasma motions with high sensitivity (10's of meters) and time resolution (6 sec) associated with a variety of geophysical phenomena. These include geomagnetic sudden commencements, substorms and storms. The La Cour variometer was replaced some time ago by a digital DMI fluxgate magnetmeter to provide geomagnetic data with high time resolution (1 min) and sesitivity (1 nT).
Geomagnetic and Geodynamic Facilities
The kinematics and structure at the extremeties of the Indian continental plate are being studied by installing broadband seismometersand GPS receivers in Hanle, Ladakh and Kodaikanal. Through a special permission,the GPS data is decoded, after a mandatory time-lapse, using the c-code giving about 1 mm precision in the geodetic position of these stations.