PUBLICATIONS

The Society has published the following books:

· Theorems on Cyclones
· Works of Sir Gilbert Walker
· Proceedings of TROPMET – 92
· Proceedings of TROPMET – 93
· Proceedings of TROPMET – 95
· Proceedings of TROPMET – 97
· Proceedings of INTROMET – 97
· Proceedings of TROPMET – 99
· Proceedings of TROPMET – 2000


ABSTRACTS OF VAYU MANDAL VOL. 30, NO 1 &2, JANUARY-JUNE, 2000

1. ENSO AND MONSOON

U.S. De
India Meteorological Department, Pune-411 005

El-Nino and Southern Oscillation were known as important atmospheric and oceanic phenomenon for well over a century. It is only during the recent years that the concept of ENSO has developed through interdisciplinary research in the field of meteorology and oceanography. It was Rasmusson and Carpenter1 who first used the term ENSO. Southern Oscillation was a key parameter in the long range prediction of Indian Summer Monsoon since the days of Sir Gilbert Walker. Investigations in the past two decades have shown that El-Nino and Southern Oscillation often occur together re-enforcing each other giving rise to the epochs of warm sea surface temperature in the Pacific and negative Southern Oscillation Index. Such major ENSO events produce circulation and rainfall anomalies on a global scale, as a consequence, the normal weather and climate in the equatorial Pacific and in the monsoon region of Asia gets disrupted. ENSO has a periodicity of 2 to 10 years and is a variability in a climate system of global dimension. Indian monsoon responds to these phenomena albeit in a complex manner. In the present century, there were 17 ENSO events which affected the Indian summer monsoon. The ENSO events of 1982-83, 1986-87 had the effect of producing major drought over the country while the El-Nino which started in the beginning of 1997 did not have a similar significant impact on the summer monsoon rainfall.

Investigations carried out over China shows an inverse relationship between SST over the equatorial eastern Pacific and summer rainfall over East China. However, there is still some uncertainty about whether the Atlantic Ocean does undergo El-Nino like oscillations (Webster)2. The timing of onset of El-Nino/ENSO events and its impact on the Indian summer monsoon and East Asian monsoon varies and important aspect of this interaction will be highlighted in this overview.

Key words : Drought, Eastern Equatorial Pacific, El-Nino/ENSO, Thermocline

2. Monsoon activity over Gujarat : Effect of temperature and rainfall of June

D. P. Dubey
Meteorologist Meteorological Centre, Bhopal

Monsoon rainfall over India has significant temporal as well as spatial variability. It is not uncommon to find some areas of deficient rainfall even when the country as a whole point to be normal monsoon season. Similarly there are excess rainfall zones during bad monsoon performance of all India scale. Considering the large variability of monsoon rainfall over India, an attempt has been made to develop a regression model of prediction of southwest monsoon rainfall over smaller areas i.e. sub-division wise over Gujarat region and Saurastra & Kutch. The mean maximum temperature and rainfall over Gujarat region during the month of June is considered as two potential predictors for assimilation of sub-division wise rainfall. The model is validated for independent data from 1991 to 1995.

3. Study on characteristic features and anomalous vertical and horizontal wind shears of the easterly jet stream during the contrasting years of monsoon

G. Krishnakumar , G. V. Mallan* and Mata Mahakur*
* Meteorological Office, Pune
* Regional Meteorological Centre, Mumbai.
** Indian Institute of Tropical Meteorology, Pune

Tropical Easterly Jet (TEJ) Stream is one of the most prominent components of the monsoon circulation. Using upper air data of stations for the years of contrasting monsoons, the characteristic features were analysed. Maximum wind and anomalous shears were found with respect to TEJ. An attempt is made to study the structure of the TEJ with its development, intensity and variation. Frequency and intensity of synoptic systems are also discussed. The influence of TEJ in the development and intensification of monsoon depressions are examined during the period of study in this paper.

Key words : Tropical Easterly Jet, Wind Shear, Contrasting Monsoon

4. Some aspects of zonal wind profiles along west-coast of India during monsoon

R. V. Sharma , Thakur Prasad and Shravan Kumar
Regional Meteorological Centre,
Colaba Mumbai ­ 400005.

The wind profile over a station follows a systematic change from one season to another as a part of general circulation. As a result, different wind features are observed over various places in different seasons. It is, therefore, worthwhile to note such changes over some important stations in different seasons. Based on five years data from 1981 to 1985, the zonal wind profiles during monsoon season over three coastal stations, namely, Thiruvananthapuram, Goa and Mumbai have been analysed and discussed. An attempt has also been made to find relationship between lower and upper tropospheric winds during monsoon season over the southern peninsula of India.

Key words : Wind Profile , Correlation Coefficient , Tropospheric Winds

5. Spatial coherence in drought occurrences over districts of Maharashtra and their relation with droughts over larger spatial extent

P.G. Gore and K.C. Sinha Ray
India Meteorological Department, Pune 411005, India


Drought is generally a widespread phenomena and adjoining areas experience high probability of simultaneous occurrence of drought. In this paper nature and extent of the occurrence of drought over the districts of Maharashtra has been studied with the concept of probability of simultaneous occurrence of drought over a district with adjoining districts as well as the state and country for the period 1901-1998. A high degree of spatial coherence in drought occurrence is noticed over some of the districts of Vidarbha. The study will help to understand occurrence of drought in various spatial scales and their relation with each other. It would help the farmers towards drought preparedness.

Key words : Spatial coherence, Drought, ‘key’ district, Probability, Recurrence period.

6. Rainfall over Hyderabad – A climatological study

C.V.V. Bhadram and R. Narayanaswamy
Meteorological Centre, Hyderabad -500 016


Based on 50 - year (1949-1998) rainfall data of Hyderabad, the daily normal, mean monthly, seasonal and annual rainfalls have been analysed and the results presented graphically are discussed. Diurnal variation of rainfall for monsoon months showed maximum intensity in the evening and night. By applying Gumbel distribution, the return period of 24 - hour peak rainfall for Hyderabad is found to be 125 years.

Key words : Normal rainfall, Diurnal variation, Extreme values, Return period.

7. Land slides in India

T.K. Ray, D.Sinha* and P. Guhathakurta*
Meteorological Office, New Delhi * Regional Metrological Centre, Guwahati


Land slides are one of the natural disasters which kills and destroys without forewarning. Though localized it is one of the major killers when taken countrywise or even on the larger scale. Ironically, not much studies have been made on this natural calamity which is quite within the range of reasonable predictability.

8. Changes in trends of pH over BAPMoN stations in India

R.R. Shende
India Meteorological Department, Pune-411 005

Monthly mean pH values have been determined for the rainwater samples collected at all ten BAPMoN (Background Air Pollution Monitoring Network) stations in India. These values for the years 1985-94 have been compared to the earlier collected pH data for the period 1974-84. It is observed that there is over-all decreasing trend in pH values at nine BAPMoN stations except Minicoy, which shows increase in acidic values and decrease in alkaline values.

A few stations like Allahabad, Pune and Vishakhapatnam show a considerable decrease in pH values, which is indicative of rapid industrialization of these cities.

Key words - Background air pollution monitoring, Trend.

9. Study of surface winds at paradeep

J R. Prasad, Sudarshan Mishra and T R Sivaramakrishnan*
Cyclone Detection Radar Station, Sector 21, Paradeep- 754 143, Orissa

Surface wind data was collected for Paradeep (20.30 N / 86.70 E ) using high wind speed recorder at the Radar station round the clock since 1990. Analysis of the data so collected has been made and mean wind profiles typical of the various months and seasons have been worked out. The extreme values have been identified. April to August and November are the periods of uniform winds, throughout day and night (from Southwest in April to August and from Northeast in November). There is a diurnal trend in surface winds during the months December to March. October is the month for variable winds and the frequency distribution is near normal.

The mean wind speeds for each month have been spelt. Occasions of calm winds (zero wind speed) are more than 20% in the months of October, November and December and least (about 3%) in April & May. The probability of getting high winds (speed exceeding 20 kts) is greatest in the month of May followed by August. The results have been discussed and the synoptic situations as well as the impact of tropical cyclones on the mean values have been touched upon.

Key words : Mean wind direction, Mean wind speed, Strong winds, Frequency distribution.