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B. K. MUKHERJEE
and
Bh. V. RAMANA MURTY

Abstract

Examination of the available rocketsonde data for the tropical station, Thumba, India, has shown that warmings, less pronounced than in the case of middle and high-latitude stations but of noticeable magnitude, and coolings of similar magnitude occurred in the mesopheric and upper stratospheric levels during the period, December 1970–March 1971. This was the only winter period when observations were made at the station during all of the 4 mo. No prominent change in wind has been observed in association with the warnings, however.

The maximum warming observed over a period of 1 week in the upper stratosphere was 26°C at 45 km. The upper mesosphere had been subjected to a continuous process of warming for over 3 weeks in December–January 1971 during which period the temperature rose by 48°C at 70 km. There is no definitive indication that these warmings were of the propagating type. However, they appear to have moved in the vertical at a rate of 3–5 km/day.

The temperature behavior of the lower stratosphere (50 mb) and the upper troposphere (300 mb) in the winter of 1970–71 was different than that which was observed in the preceding 2 winters.

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B. K. Mukherjee
,
R. S. Reddy
, and
Bh V. Ramana Murty

Abstract

Temperature and wind data for the troposphere, stratosphere and mesosphere obtained from rocket-sonde/radiosonde/rawin observations made at a tropical station (Thumba, 8°32′15″N, 76°51′48″E) during five summer monsoons (1971–73, 1975–76) with differential monsoon activity were examined.

There is agreement between the occurrence of high-level warmings and monsoon activity in four out of five monsoons studied. There were no warmings in the year with very weak monsoon activity. The temperatures of the stratopause and the tropopause were significantly warmer in 1972 when the monsoon was very weak than in other years when the monsoon was active or very active.

There is a high positive correlation between the monsoonal activity (precipitation departure from normal over Indian subcontinent) and the 25 km mean zonal wind, and a strong negative correlation with the winds near 16 and 50 km. The change in the sign of correlation coefficient was due to the observed phase change with altitude of the quasi-biennial oscillation.

The study indicated the possibility of a relationship between stratospheric quasi-biennial structure and the Indian monsoon rainfall.

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R. S. Reddy
,
B. K. Mukherjee
,
K. Indira
, and
Bh V. Ramana Murty

Abstract

An investigation of the dates of occurrence of heaviest rainfall is very important for flood forecasting. We have considered this aspect in the present study by examining the daily rainfall data for four coastal stations Kakinada, Masulipatnam, Nellore and Visakhapatnam for the month of October for a 10-year period 1973–82. The data have been analyzed by considering the heaviest rainfalls for each station separately. We have defined the heaviest rainfall as that which exceeds two or more times the mean rainfall of the month. The study shows that heaviest rainfalls occur during the period 16–23 October. This feature is repeated year after year, constituting a rainfall singularity for the region.

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B. K. Mukherjee
,
K. Indira
,
R. S. Reddy
, and
Bh V. Ramana Murty

Abstract

In an earlier study a relationship was pointed out between phases of the quasi-biennial oscillation (QBO) in the lower stratospheric (30 mb) zonal wind and percentage departures of summer monsoon rainfall of India. That study was based on analysis of wind data for Thumba (8°32′N, 76°52′E) and the rainfall data for India for a short-period (1971–76). Wind data for Balboa (9°N, 80°W), which is also an equatorial station, and rainfall activity over India are now examined for a longer period (1951–82). About 15% of the variability in rainfall over India during the summer monsoon is associated with the pattern of the QBO.

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