Annual Report 2000-2001

Scientific Research

Monsoon and Tropical Climate (MONTCLIM)

The Monsoon and Tropical Climate Programme is directed towards undertaking studies on monsoon climate variability/change, modelling atmospheric processes and technology development for atmospheric science research. In order to study the effect of weather and climate in tropics, efforts are being made to improve parameterisation of land-ocean-atmospheric processes in the Atmospheric General Circulation Models (AGCM).

Climate modelling:

The spatial and temporal variability of error growth rates in predicting climate system using coupled ocean atmosphere model indicated that the fast growth rate is characteristic of small scales of motion, independent of seasons. Also, the initial errors in small scale quickly travel to the dominant mode in spring, while the coupled system does not allow it to do so in autumn or winter. A conceptual model to study how the intra-seasonal oscillations (ISO) could influence the seasonal mean monsoon has been developed. The evolution of 30-60 days mode shows that the ISO is characterised by a systematic northward propagation of the tropical convergence zone. Whereas, 10-20 days mode is rather regional in character with its significant anomalies confined to the Bay of Bengal.

Several numerical experiments were undertaken with general circulation model at different resolutions (T63L19, T42L09 & T80L18) using different types of envelope orography to simulate the large scale features of Indian summer monsoon and movement of tropical cyclones. The NCMRWF operational model (T80L18) results indicate that performance of 2-D filters is superior to 1-D filter.

The development of the climate version of the NCMRWF model has been completed. The initial results indicated that the model realistically simulates most of the major features of the Indian summer monsoon.

Tropical Cyclone Simulation:

A multi-level axi-symmetric primitive equation model has been developed and tested with different cumulus parameterisation schemes, to study the evolution of cyclonic circulation over Bay of Bengal. Sensitivity experiments indicated that the increase of sea surface temperature contributes to faster development and stronger cyclonic systems. One numerical experiment using a Mesoscale Model (MM5) was carried out to simulate the cyclonic systems and the track positions over Bay of Bengal occurred during November 1996. The results on strength and track of the cyclone are encouraging.

The numerical experiments using axi-symmetric model of tropical cyclone with Arakawa-Schubert scheme for convection indicated that (a) the size of the incipient system (about 250 km radius) play an important role in the process of intensification; (b) a basic characteristic of intensifying system is centrally organised convection at the initial state whereas non-intensifying systems exhibited large scale divergence activity in the core region at the initial stage; (c) strong correspondence between intensification and sustained and organised cloud activity near the center, and (d) the scale selective intensification appears to arise from a delicate combination of the vertical distribution of temperature and humidity.

Land-Atmosphere:

Preparation of monthly mean gridded (1o X 1o) data sets on land surface characteristics of the Indian Subcontinent is completed. A one-dimensional land surface scheme of energy, momentum, water and CO2 exchanges between the atmosphere and land surface has been developed. The sensitivity experiments demonstrate that vegetation exerts a mitigating influence on both the land surface and atmosphere. Experiments with a `Regional Atmospheric Modelling System (RAMS)' suggest that the model performs better with an interactive biosphere-hydrological land surface scheme. The impact of interactive hydrology vis-a-vis specified hydrology on the seasonal mean simulation using Climate Community Model indicated that surface processes play a significant role in the simulation of the monsoon features.

The quality checked data generated during the `Land Surface Processes Experiment (LASPEX)' over Sabarmati River Basin in Gujarat are made available to the scientific community for further analysis. The initial scientific results presented at the LASPEX workshop are under publication. The data sets are utilised to validate different land surface parameterisation schemes in a 1-D soil-vegetation boundary layer model, 2-D Meso-scale model and a 3-D limited area model. The seasonal variation in radiation flux, soil heat flux, sensible and latent heat fluxes are well simulated by the models. The impact studies indicated that inclusion of land surface processes scheme in 3-D model enhanced the predicted latent heat flux and sensible heat flux gradients over land and these gradients, there by increased the low-level convection. These results further demonstrate the importance of the parameterisation of the land surface processes in the short-range prediction/simulation of summer monsoon circulation features and rainfall over India.

Ocean-atmosphere:

A global ocean general circulation model was developed for the first time in India. The model is able to respond to wind stress and reproduces the structure of temperature, salinity and density fields. Further, model simulation indicated the realistic intra-seasonal as well as interannual variations of sea surface temperature. The development of a coupled ocean-atmospheric model is in progress. A simple model of the meridional circulation has been formulated. Trail integration of the model show that the model tracer fields are sensitive to the meridional velocity field. The work related to the seasonal variations of the meridional circulation, in the upper 400 meters of the ocean is in progress. Surface flux measurements in the Ocean-Atmosphere boundary layer during INDOEX (Indian Ocean Experiment) field phase were undertaken. A 4-meter micro meteorological tower with sensors mounted at 3-levels was installed on the ship. Both fast and slow sensors were used. The data collected are being analysed. Agrometeorology

Field experiments and modelling studies on the effect of weather and climate on the crop growth, pest and disease development and yields are being undertaken under this sub-programme. The data generated has been used to develop sub?routines for agrometeorological processes, testing and validation. Initiated studies on land surface processes over Wheat crop at Anand. Modelling the effect of weather and climate on cotton growth and yield is underway. A weather based Rice blast disease forecasting system in the Kangra region of Himachal Pradesh was developed.

Successfully completed the initial development of an agrometeorological data bank at the Central Research Institute for Dryland Agriculture (CRIDA), Hyderabad. The facility is to collect, compile and archive various types of crop and weather data generated under agrometeorology projects supported by Indian Council of Agricultural Research and DST. New projects were initiated to study the nitrogen flux from rice wheat system in northwest India, methane emission from rice fields in the northeastern region, agroclimatic variability in the Uttar Pradesh - Bihar plains and modelling environmental modulations in rate of development of Soybean genotypes. Experiments on methane emission from natural wet lands are under progress. Radio Acoustic Sounding System (RASS)

A multi-institutional supported project on the indigenous development of Wind Profiler /Radio Acoustic Sounding System has been completed. The system will have the ability to provide temperature profile (up to 5 km) and wind profile (up to 10?16 km) in the atmosphere. The initial validation tests of system have been done with available upper air wind data. The results are encouraging and needs further tuning. The Project Advisory and Monitoring Committee suggested that this prototype system to be permanently installed at Pune to carry out detailed validation tests and specific experiments by the atmospheric scientists in collaboration with India Meteorological Department. Accordingly, arrangements were made to shift the system to Pune. The site developmental work to install the system is in progress. Indian Climate Research Programme (ICRP)

The objectives of the Indian Climate Research Programme (ICRP) are, (i) analysis of observational data from ground-based, ship-based and satellite-based measurements, (ii) modelling studies with coupled ocean-atmospheric general circulation models and (iii) identification of the climate component of agricultural productivity, impact of climate on environment and climate change, etc. A number of projects were evolved and supported.

The first field observational experiment under the ICRP, called the Bay of Bengal Monsoon Experiment (BOBMEX), was carried out successfully. BOBMEX was aimed at measurements of important variables of the atmosphere, ocean and their interface to gain deeper insight into some of the processes that govern the variability of organised convection over the Bay. Simultaneous time series observations were carried out in the northern and southern Bay of Bengal from ships and met ocean buoys. About 80 scientists from 15 different institutions in India collaborated during the BOBMEX to make observations in most hostile conditions of the raging monsoon. The initial results indicated the following.

During the BOBMEX field phase there were several active spells of convection over the Bay, separated by weak spells. Observations with high resolution rediosonde, launched for the first time over northern Bay, showed that the magnitudes of the Convective Available Potential Energy (CAPE) and the Convective Inhibition Energy (CINE) were comparable to those for the atmosphere over the West Pacific warm pool. CAPE decreased by 2-3 kJkg-1 following convection, and recovered in a time period of one or two days. The surface wind speed was generally higher than 8 ms-1. The thermohaline structure as well as its time-evolution during the BOBMEX field phase was found to be different in the north Bay from the south Bay. Over both the regions the sea surface temperature (SST) and sea surface salinity decreased during rain events and increased in cloud free conditions. Over the season as a whole, the upper layer salinity decreased for the north Bay and increased for the south Bay. The variation in SST during 1999 was found to be of smaller amplitude than in 1998. The quality checked atmospheric and oceanographic data sets were provided to the scientific community. Further analysis of the surface fluxes and currents is expected to give insight into the nature of coupling. Twelve research papers based on the data analysis from BOBMEX-Pilot study were published as a special issue of the Proceedings of the Indian Academy of Sciences, Earth and Planetary Sciences (Vol. 109, No.2. June 2000).

Prepared the science plan on Arabian Sea Monsoon Experiment (ARMEX). The technical programme to carryout ARMEX during 2002 is under preparation. Initiated studies on (a) Monsoon dynamics, energitics and variability, (b) Development of optimised atmospheric general circulation model, (c) Impact of natural processes and anthropogenic activities on the atmospheric chemistry, (d) ENSO-Snow-Monsoon interactions and (e) Differential absorption LIDAR sensing of Ozone. Fortnightly samples of atmospheric precipitation and ground water were collected from 12 locations in and around Mangalore (Karnataka). Measurements of physiochemical parameters and aerosols are in progress. The development of a coupled ocean-atmospheric model is in progress.

A brainstorming session on `Weather Modification Research' was organised at Indian Institute of Tropical Meteorology, Pune. Expert comments on the technical paper on `Forest fire and transboundary haze pollution' were obtained to evolve a new programme. A training workshop on `Agroclimatic analysis and Database Management Techniques' was organised for 20 young scientists for two weeks duration at CRIDA, Hyderabad.