Diurnal and seasonal variations of point discharge current during thunderstorms at a tropical inland station

The data of point discharge current (PDC) measurements during a total of 65 thunderstorms at Pune (18°32â²N, 73°51â²E) are analyzed to study the PDC local diurnal variation and some issues related with the current. The analysis shows that about 83 of the total quarter hours occupied by PDC are localized between 1400 hrs LT and 2400 hrs LT and the remaining 17 are sparsely distributed over midnight to early hours in the morning. The net result of this study revealed that PDC is the dominant agent for the negative charging of the earth's surface and should be identified as an active element participating in global electrical circuit. The phase relationship between the positive and negative current during the diurnal period suggests that the active period of current of one polarity has a preferred time of occurrence over the other and by the late night hours the positive charge showed its sustained occurrence over the negative one. The seasonal relationship between storm averaged PDC and monthly mean maximum surface air temperature has also been examined. The comparison of seasonal average amplitude of PDC has suggested a strong positive correlation with the monthly mean maximum surface air temperature. The average amplitude of PDC during thunderstorm in premonsoon season is found to be about three times higher than those during the monsoon season. An examination of association between duration and amplitude variation of PDC showed that storms that are closer to the station within 4 km have longer duration and stronger current amplitude than when they are more than 4 km away.