• B M Pathan

      Articles written in Journal of Earth System Science

    • Comparative study of scintillations at the magnetic equator and at the crest region of the equatorial anomaly in Indian zone

      Boby Mathew B M Pathan K N Iyer D R K Rao

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      Using simultaneous long-term observations of ionospheric scintillation at equator and anomaly crest region in the same longitude (Indian) zone comparative features of scintillation occurrence are brought out. The salient features are: (a) predominantly pre-midnight occurrence of scintillation at equator during winter and equinox seasons, (b) increase of pre-midnight scintillation occurrence with solar activity (c) shifting of occurrence peak during summer from post-midnight in low to pre-midnight in high solar activity periods (d) similarity of scintillation behaviour at these locations during winter and equinoxes but dissimilarity during summer. The solar activity response and magnetic effects indicate that the scintillations at the anomaly crest region in winter and equinox, particularly during high solar activity periods, are of equatorial origin while the summer events may be of local or mid-latitude origin.

    • IMF BY dependence of the extent of substorm westward electrojet

      T Arun Ajay Dhar K Emperumal B M Pathan

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      In this paper the duskward extension of the westward auroral electrojet is investigated for substorm intervals on the basis of magnetograms recorded at the Indian Antarctic station, Maitri. The database comprises three years from 1998–2000. Based on an initial study of the magnetograms, an arbitrary local time of 2030 MLT is fixed to define the early manifestation of the substorm westward electrojet. Using this criterion 12 substorms are identified and the possible causes examined. Many of these events are observed to be associated with a moderate to intense ring current. The hourly average of the GSM BY-component of the interplanetary magnetic field (IMF) for the hour preceding the substorm onset at Maitri is negative for most of the events. It is suggested that the azimuthal shift of the auroral electrojets in the southern hemisphere resulting from a negative BY-component of the IMF influences the extent of the substorm westward electrojet. This finding implies that the IMF may have a role in controlling the longitudinal extent of substorm occurrence.

    • First results from imaging riometer installed at Indian Antarctic station Maitri

      Jayanta K Behera A K Sinha Anand K Singh Rahul Rawat Geeta Vichare Ajay Dhar B M Pathan K U Nair C Selvaraj P Elango

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      Cosmic noise absorption (CNA) measurred by imaging riometer, is an excellent tool to passively study the high latitude D-region ionospheric conditions and dynamics. An imaging riometer has been installed at Indian Antarctic station Maitri (geographic 70.75°S, 11.75°E; corrected geomagnetic 63.11°S, 53.59°E) in February 2010. This is the first paper using the imaging riometer data from Maitri. The present paper introduces the details of this facility, including its instrumentation, related CNA theory and its applications. Sidereal shift of around 2 hours in the diurnal pattern validates the data obtained from the newly installed instrument. Moreover, the strength of cosmic noise signal on quiet days also varies with months. This is apparently due to solar ionization of D-region ionosphere causing enhanced electron density where collision frequency is already high. The main objective of installing the imaging riometer at Maitri is to study magneotspheric–ionospheric coupling during substorm processes. In the current study, we present two typical examples of disturbed time CNA associated with storm-time and non-storm time substorm. Results reveal that CNA is more pronounced during storm-time substorm as compared to nonstorm-time substorm. The level of CNA strongly depends upon the strengthening of convectional electric field and the duration of southward turning of interplanetary magnetic field before the substorm onset.

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