Geomagnetic variations & near and far Space Environment of Earth
To a first approximation, properties of the earth’s magnetic field resemble that of a dipole like magnet with its origin from the dynamo mechanism within the earth’s outer core. The absolute measure of the magnetic field at any location on the Earth is the combination of the sources in the Earth’s core, in the Earth’s crust and in the near and far space environment of the earth such as ionosphere and magnetosphere. The main magnetic field contributes to almost 99% of the observed magnetic field, changes associated with this field is the secular variation or long-term variation. In addition to the main field variations, as suggested by the hypothesis of Stewart in 1882, daily oscillations are due to the currents in the ionized atmosphere of the earth.
Stewart’s ideas on these variations were attributed to the currents flowing in the upper atmosphere due to periodic air motions in the presence of magnetic field. Later this proposition was referred as atmospheric dynamo theory of solar quiet (Sq) and lunar (L) variations. Schuster confirmed the inference of Stewart and Breit and Tuve, Appleton and Barnett confirmed this proposition experimentally in 1924. Thus the measurement of the magnetic field at any point on the surface of our planet Earth, is considered as a less expensive experimental basic tool to study and infer the geophysical processes taking place inside the Earth and its near and far space environment.
Chapman and Bartels (1940) and Vestine (1960) represented the source of the regular magnetic variation in terms of a current sheet at an altitude of ~100 km above the earth’s surface with two vertices, at around 350 latitude. Regular and systematic variations of the magnetic components at many observatories around the globe have subsequently brought out by researchers in 1950s the important finding of the equatorial electrojet, a phenomenon representing the enhanced flow of east-west current over the magnetic equator.
The geographical location of India in the global scenario is ideal for monitoring the developments in the Equatorial Electrojet activities and its associated effect in the Global Sq current system. The existing extensive network of magnetic observatories through Russia from magnetic pole to peninsular India centered along 1450 geomagnetic meridian provides unique data set of magnetic variations from pole to dip equator.
At any point on the surface of the Earth, the magnetic field is a vector, having amplitude and direction. The magnitude of the field is represented by the Total field F. The three components of the magnetic field are Horizontal Intensity ‘H’, Vertical Intensity ‘Z’ and the Declination component ‘D’ of the location defining the angle between the true north and the magnetic north. Observations of these recordings are done on a continuous basis at magnetic observatories with the help of magnetometers specially designed to monitor the sensitive aspects of the changes in the earth’s magnetic field.
Magnetic observatories operated by the Institute are equipped with both modern Digital Fluxgate magnetometers and classical analogue recording instruments to record the continuous measurements of the Earth’s magnetic field uninterruptedly. A semi-permanent magnetic observatory is operated at the Indian Antarctic station at Maitri. The magnetic measurements from the Indian longitudinal chain form a unique database in view of investigating the ionosphere – magnetosphere-coupling processes, as the entire network can cover the locations spanning equator to the North Pole in the Indo-Russian longitude.
PUBLICATION AND DISSEMINATION OF MAGNETIC DATA
Uninterrupted observations of absolute and variation measurements are carried out regularly at the magnetic Observatories operated by the Institute, with latitudinal coverage from dip equator in the southern end of India to the north in the vicinity of the Sq-focal latitude, and from east to west coast of India.
Calibrations of Instruments at the observatories are carried out time to time to match the international data standard for consistency and accuracy of observations. Modern Absolute Magnetometers PPM & DIM are used in addition to classical instruments for absolute measurements and ensure better accuracy in field values by providing inter-comparison facility with existing classical instruments.
B. veena, D. M. Daga, V. J. Jacob and Staff at Magnetic Observatories
Processing and publication of the data from the Magnetic Observatories also forms the responsibility of this division. The Institute has succeeded in getting near real-time variation data transmission from the Digital Fluxgate Magnetometers set up at four of the Magnetic Observatories to H.Q. at Navi Mumbai.
Preparation of the final hourly data of D, H, and Z elements is done at H.Q, Navi Mumbai. Absolute hourly values are prepared in final format for publication in book form and digital form and also for deposition with the World Data Centre. One minute digital variation data received from the Magnetic Observatories are compiled and processed as one minute final absolute values at H.Q. on a routine basis.
Analogue and Digital data from the magnetic observatories operated by the Institute are processed at H.Q. on a regular basis. Absolute measurements recorded at all Indian stations with modern Absolute Magnetometers (PPM/VPPM, DIM) are used to compute baseline values for deriving final absolute values. Near real time data received from INTERMAGNET System (at Alibag) are processed and e-mailed to the Intermagnet GIN on daily basis. One minute Definitive data are prepared and sent for inclusion in the Annual CD-ROM of the Intermagnet community.
B.Veena, R. L. Asinkar, D. K. Meshram, S. Bhardwaj, M. M. Jadhav, S. Kumar, P. Birthare, A. S. Kulkarni, R. Rawat, P. Patro, S. Sawardekar
Hourly values, one minute digital magnetic data and magnetogram copies are supplied on regular requests to scientists and research students from Scientific Institutions and several Universities from India and abroad for investigational work.
Printed data bulletins are dispatched regularly to the Scientific Organisations / Institutions and Agencies with reference to the mailing list.
Principal magnetic storm days are classified to prepare the magnetic Storm Sudden Commencement amplitudes and ranges and forwarded to World Data Centre, Colorado for inclusion in Geophysical Data Bulletin.
Final Absolute Hourly values, One minute digital magnetic data (Variation as well as Definitive) and computed Equatorial Electrojet strength are supplied on requests to scientists and research students from Scientific Institutions and several Universities from India and abroad for investigational work
Prime magnetic observatory at Alibag serves as a calibration centre for magnetic instruments from organisations like SOI and NGRI. Several magnetic compasses from the Indian Naval services, Pawan Hans and Indian Coast Guard Air stations are calibrated at Alibag magnetic Observatory on a regular basis.