VARIATIONS IN THE ATMOSPHERIC ELECTRIC-FIELD AND METEOROLOGICAL PARAMETERS AT A TROPICAL COASTAL URBAN STATION DURING 1936-40 AND 1962-66

The seasonal and diurnal variations in the vertical component of the a tmospheric electric field, air temperature, relative humidity and hori zontal wind speed were studied using the surface data for the two peri ods (1936-40) and (1962-66) recorded at the tropical urban station. Co laba. Bombay (18-degrees-51'N, 72-degrees-49'E, 11 m ASL), located on the west coast of India. The atmospheric electric field during the lat ter period (1962-66) is significantly higher (up to 42.3%) than the ea rlier period (1936-40). This has been attributed to the enhanced parti culate concentrations in the atmosphere. The increase noticed in the a tmospheric electric field is a maximum during winter and minimum durin g the monsoon. The atmospheric electric field exhibited a marked semi- diurnal oscillation with peaks at 0900 LST and 2200 LST during winter, pre-monsoon and post-monsoon seasons of both the periods. During the monsoon season the double oscillation is not marked. The variations no ticed in the surface air temperature and the relative humidity are in agreement with those observed in the atmospheric electric field. The h orizontal wind speed showed a decrease which has been attributed to th e surface roughness resulting from urbanization.