First results from imaging riometer installed at Indian Antarctic station Maitri

Abstract

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.

Auroral electrojets during severely disturbed geomagnetic condition on 24 August 2005

“…(i) depression near midnight-dawn hours due to the westward electrojet which may, however, expand up to the pre-noon hours (Feldstein et al, 2006;Behera et al, 2014), (ii) enhancement near dusk hours due to the eastward electrojet (Guo et al, 2014 and references therein) and (iii) occasional enhancement or depression near noon due to extension of the polar electrojet towards the auroral latitudes (Feldstein et al, 2006). Positive and negative envelops of H-components variations from globally distributed auroral stations (respectively AU and AL indices) represent the maximum intensities of the eastward and westward auroral electrojets.…”

Ionization and NO production in the polar mesosphere during high-speed solar wind streams: model validation and comparison with NO enhancements observed by Odin-SMR

“…The timing of the HSS arrivals, defined as the time when the solar wind speed increased through 500 m s −1 , and the related Odin-SMR observations are summarized in Ta The solar wind speeds reached in our selected events, 600-700 km s −1 , correspond to speeds between the mean and upper quartile in the study of Meredith et al (2011). The imaging riometer at Maitri (Behera et al, 2012) registered longlasting absorption events on the days following the HSS arrivals -these are summarized in Table 2 in terms of average CNA between 07:00 and 11:00 MLT, which is the time of day when CNA is expected to be most sensitive to the HSSrelated EEP. The measured values in Table 2 can be compared with our models -for winter, the mean, UQ and LQ-HSS models give averages of 0.83, 0.45 and 0.04 dB CNA, respectively, for the 07:00-11:00 MLT time interval.…”

India's Contribution to Geomagnetism and Allied Studies in Antarctica-A Review

“…Results reveal that CNA is more pronounced during stormtime substorm as compared to non-storm time substorm or, isolated. Further, initial results confirm that the level of CNA strongly depends upon the strengthening of convection electric field and the duration of southward turning of interplanetary magnetic field before the substorm onset (Behera et al, 2014).…”