Tropical Indian Region Research Articles

Diurnal variation of deep cloud systems over the Indian region using INSAT-1B pixel data

Among the various time scales of deep clouds, diurnal variation is found to be prominent over the tropics. The present study examines the diurnal variation in the number and area cover associated with the cloud systems over the tropical Indian region using INSAT-1B pixel data. Three periods, namely, April–May 1988, July–August 1988, and January–February 1989 are considered. The dependence of diurnal characteristics on the temperature threshold, life duration and size of cloud systems, and land-sea contrast has been explored. The diurnal characteristics of cloud systems living for more than a day have been studied for the first time. It is shown that cloud systems exhibit strong diurnal dependence at the coldest temperature threshold used (201 K). Also, the diurnal variation is more for larger cloud systems and for longer living systems. In general, more deep cloud activity is found from the satellite data during the pre-dawn and early morning hours. Precipitation is enhanced during morning to early noon hours. Further, using data from a recent field experiment, clear evidence of diurnal variation in precipitation over the Bay of Bengal is also presented.

Observations of tropical convection events using Indian MST radar: First results

AbstractMesoscale convective events, associated with severe weather, play a significant role in troposphere‐stratosphere coupling processes. Deep convection occurs very often at tropical latitudes. The convection events result in the transport of energy from the lower troposphere to the upper troposphere and stratosphere, and may also affect global circulation. In the Indian tropical region, meteorological convection events are a common occurrence during the months of May to December. In the present study, very‐high‐frequency radar located at Gadanki (13.45°N, 79.18°E), a tropical station in India, is used to make observations of winds, turbulence and stable‐layer structures, during the passage of convective events over the radar site under different synoptic situations.Radar observations of vertical velocity show enhanced up and down draughts during the passage of convection events. Height and time cross‐sections of radar‐observed signal‐to‐noise ratio clearly show distinct regions of enhanced signal intensity, indicating height and time Structures of enhanced atmospheric turbulence associated with the convection. It is also noted that stable‐layer structures associated with the tropical tropopause are not well defined during the passage of convection. This suggests ‘weakening’ of stable‐layer structures during the convective activity. The present observations also show enhanced mass flux, both in upward and downward directions, through the tropopause, indicating mass exchange between troposphere and stratosphere during the period of convective activity.

Digital change detection of forest conversion of a dry tropical Indian forest region

Abstract Monitoring of the changes in the forest cover has been quite important because of its significant impact on climatic change. The following study was undertaken to monitor the conversion of vegetation cover to categories of different canopy cover in an area that has undergone very rapid industrialization in the recent past. 1982 and 1989 same season MSS data was registered and the atmospheric haze was reduced using a regression method. Conversion of the vegetation categories to the other categories was detected from the colour-sliced PC2 image of the subtracted bands.

Methane flux measurements from paddy fields in the tropical Indian region

Methane flux measurements have been made from paddy fields in the Thanjavur region in southern India from September 1991 to January 1992. This is a major rice growing area having plenty of river and rain water. A perspex chamber was used to cover the plants. Samples from this chamber were collected using a metal bellows pump in small sample bottles. The methane flux values estimated from the analysis of these samples are mostly in the range of 15–25 mg m −2h −1. These preliminary results, from natural fields, give higher flux values than estimates from some other regions in India, as well as average values for the mid-latitude region, but values lower than from China.

Middle atmospheric oscillation over India and its possible association with Indian summer monsoon

In this paper the middle atmospheric oscillations of the zonal wind in upper stratosphere and lower mesosphere have been analysed and studied using the rocket sonde wind data of Thumba and Balasore
 
 It was observed that in the mean, picture, t e semi-annual oscillation at on was predominant in the equatorial Indian region (i, e.,over Thumba ) while the annual wave was predominant over tropical Indian region (i.e over Balasore), During good monsoon year, a strong semi-annual wave over tropical Indian region was observed . The amplitude of this semi-annual wave was also found to be significantly higher over the equatorial Indian region during good monsoon year, The study seem3 to reveal a close association of the middle atmospheric oscillations over India with the summer monsoon.

Angular momentum transport and temperature Gradient in the middle atmosphere over the tropical Indian region

The paper deals with the momentum transport and temperature gradient of the middle atmosphere over Balasore and SHAR and their seasonal variation .Weekly RH.200 rocket data for the period 1979-1984 over Balasore and 1979-1982.over SHAR were used to estimate the angular momentum transport and temperature gradient. The results Indicated that the convergence of the westerly momentum by the mean motion towards the equator during post monsoon to pre-monsoon through winter restricted the penetration of the summer hemispheric easterlies Into the winter hemisphere In the lower mesospheric region. During the monsoon, southward eddy transport maintained the mesospheric easterly jet core located poleward of the equator. The temperature gradient and the wind shear analysis showed the barotropic nature of the lower tratosphere throughout the year over tropical Indian region.

Vertical Motions within the Indian Tropical Middle Atmosphere

Abstract Computations of vertical motions in the middle atmosphere over the Indian tropical region have been made based on the thermodynamic equation with the geostrophic approximation. The authors have used the once weekly rocketsonde temperature and wind data for the tropical station Thumba India, (8°32′N, 76°52′E) for the four summers (1972, 1973, 1975 and 1976) and two winters (1971 and 1972) which are also years of varying monsoon activity. In the tropical middle atmosphere, downward motion (subsidence) is the dominant feature when the motion field is considered in a longer time scale. The trend of fluctuations in vertical motion suggests wave structures in the tropical middle atmosphere. The magnitude of the extreme values of the vertical motion in the stratosphere over the high latitudes is larger, by a factor of 2 or more, than those obtained over the low latitudes (tropics). Whereas the magnitude of the vertical motion in high latitudes is associated with stratospheric warmings during winter, the...