Diurnal and seasonal variations of the small-, intermediate-, and large-ion concentrations and their contributions to polar conductivity

Simultaneous measurements of the concentrations of small, intermediate and large ions and of polar conductivity of both polarities were made at a height of 1 m above ground at Pune (18° 32'N, 73° 51'E, 559 m above msl), India during February 1990 to January 1991. Diurnal and seasonal variations of concentrations of ions of all three categories show their peak values in the morning hours throughout the year. Concentrations of all categories of ions are higher during the nighttime as compared to that during the daytime and are higher in winter than in other seasons. Although small-ion concentrations show only a small change, intermediate- and large-ion concentrations undergo a change of up to 1 to 2 orders of magnitude over a period of a year. Most of the time, our observations do not exhibit any inverse relationship between the small- and large-ion concentrations. The results have been explained in terms of the stability of the lower atmosphere and accumulation of radioactive gases, aerosols, etc., below nocturnal inversions. The diurnal and seasonal variations of the percentage contribution of three different categories of ions to the polar conductivity show that although contribution of small ions is dominant for most of the day, contributions of intermediate and large ions become very large in the morning hours, especially in winter. Diurnal variations of the mean values of polar conductivity calculated from the ion concentrations are compared with those of the measured values of polar conductivity. The two values show good agreement during the daytime when the polar conductivity is small. However, the measured values of polar conductivity are always higher than its calculated values during nighttime or in the morning hours when polar conductivity is large