Diurnal variation of Atmospheric Electric Potential Gradient at Colaba (Bombay) examined for the Universal Component and relationship with meteorological elements

Abstract

The atmospheric electric potential gradient (P.G.) data of Colaba (Bombay) are averaged over the period 1936 to 1955 to obtain the mean diurnal variation for the different months of the year. The diurnal variations are regular and for large amplitude only for the winter months of November to February. The diurnal variations for these months are harmonically analysed to see if the universal component of the diurnal variation found for the ocean areas as well as some land stations by Mauchly (1923), is manifested in the variations at Colaba. The phase of the 24-hourwave is found to differ from that found by Mauchly by 5 to 10 hours. It is concluded that

the universal component of the diurnal variation in P .G .does not readily manifest itself at Colaba.

The relationships between diurnal variation of P .G. and those of the meteorological elements, barometric pressure, air temperature and relative humidity are next examined. The statistical correlation coefficient between P.G. and barometric pressure variations is +0.71, that between P.G. and air temperature variations -0.67 and the value between P.G. and relative humidity is +0.57.

A confirmation of the relationships is sought for in the phase relationships of the significant harmonic components of the diurnal variations of P .G. and the meteorological elements for the winter months. For the P .G. diurnal variation both the 24:hour wave and the 12-hour wave are almost equally significant. For barometric {16a) pressure it is the 12-hour component which is significant, while the 24-hour components predominate in the diurnal variations of air temperature and relative humidity. It is found that the 12-hour waves of P.G. and barometric pressure variations are very nearly in phase. The 24-hour waves of P.G. and air temperature are in antiphase while

those of P.G. and relative humidity are nearly in phase.

Assuming the electrical state of the atmosphere to be in quasi-static eqnilibrium an attempt is made to examine possible ways by which meteorological elements can influence P.G.