The electric field of overhead thunderclouds

Abstract

In a previous paper* I drew attention to the fact that, owing to the peculiar geographical position of Bombay, almost all the “ heat ” thunderstorms which form during the pre-monsoon and the post-monsoon periods over the hills to the east of the Colaba Observatory, between the sea coast and the Western Ghats, develop a westerly movement and pass over the station. When the air has attained a certain state in regard to its moisture content and lapse-rate, these thunderstorms are initiated by the strong instability produced through the heating of the surface layers over the hills by intense insolation. Their westerly movement was explained by means of the schematic diagram given in fig. 4 of the paper mentioned above. There is no definite evidence whether the “ trigger action ” is caused by a kind of katabatic flow down the Western Ghats advancing as a wedge, but such an assumption would not be inconsistent with this schematic diagram.