Diurnal variations of the atmospheric electric field and conductivity at Maitri, Antarctica

Surface measurements of the atmospheric electric potential gradient and conductivity have been made at the Indian station, Maitri (70 degrees 45'52S, 11 degrees 44'3E, 117 m above mean sea level), Antarctica, from January 10 to February 24, 1997. The diurnal variation curve of potential gradient averaged for 20 fair weather days is single periodic with a maximum at 1300 UT and another secondary but distinct maximum at 1900 UT and a minimum at 0100 UT. The mean value of the potential gradient is 83 V m(-1) and the maximum and minimum values are 1.55 and 0.73 times the mean value, respectively. The total conductivity is 2.1 x 10(-14) S m(-1), and does not show any significant diurnal variation. The diurnal variation of the potential gradient observed at Maitri is similar to the one observed a few days later in the southern Indian Ocean and to the one reported by Kamra et al. [1994] with a few hours difference in phase in the northern Indian Ocean. The results are discussed in terms of the seasonal variation of the longitudinal distribution of thunderstorm activity. It is proposed that the diurnal variation of flash activity when averaged over several days or weeks may cause a peak at an averaged time in the diurnal variation of ionospheric potential.