Characteristics of the Upper Troposphere, Tropopause and the Lower Stratosphere over Trivandrum

Abstract

Using the data from radiosonde ascents at Trivandrum in the years 1948-51 and from afternoon pilot balloon ascents ov-er Nagercoil in 1944-50 the structure of the atmosphere over Trivandrum with special reference to the upper troposphere, tropopause and lower stratosphere has been studied. Tables of temperatures and air densities are given and temperatures over Trivandrum are compared with those over Madras, Poona and Agra and at the same latitude over East Africa. Diagrams giving a composite picture of the wind and temperature distribution, four seasonal mean tephigrams and temperature- height curves for the ten ascents reaching the trcpopause are also given and discussed. The patterns of wind distribution in January, April, July and October compared with the four basic currents in the tropics classified by Riehl.

The chief results of  the study are-

(i) The annual range of temperature is small and is maximum at the 200-100 mb level.

(ii) The tropopause occurs at or slightly above the 100-mb level and appears to be lower in June to October than in     the    rest of  the year.  The average counter-lapse of  temperature in  the lower stratosphere up to 20 km is -2°C km -1.

(iii) The maximum lapse rate of  temperature occurs between 300 and 200-mb levels. There is a marked decrease of lapse rate at the 150-mb level, about 2 km below the tropopause.

(iv) Winds with easterly components are the most predominant, westerly winds occurring mainly between surface and the 400-mb level during June to October. Easterly components are prominent and strong above the 300-mb level in June to October and increase in force with height up to the tropopause and decrease with height at higher levels.

(v) There is a large negative gradient of temperature between  Trivandrum and Madras  in  the 200-100 mb region in all the seasons and to a lesser degree between Trivandrum and north IndIa in winter and above the 600-mb level in summer. There is a positive gradient of temperature between Trivandrum and north India (Agra) in the SW monsoon season up to the 200-mb level, specially in the 500-300 mb region.