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NEWS Monsoons: Past, present and future*

During the past three decades, there has developments were discussed in a discus- the meteorological observational network been a remarkable progress in the under- sion meeting on ‘Monsoon: Past, present was established. During this period it was standing of the variability of the monsoon. and future’ held in Orange County apparent that the prosperity of India was Monsoon variability occurs on many time (Coorg) in November 1997. inexorably linked to the summer monsoon scales. They span the range of a few In his opening remarks, R. Narasimha rainfall all over India. The long-range weeks to a few thousand years. In the (Indian Institute of Science and JNCASR) forecasting of the monsoon began more last three decades, observations and com- stressed the need to consolidate the know- than 100 years ago when H. F. Blandford puter models have identified the mecha- ledge we have gained during the past discovered an association between snow- nisms that govern the variability of the three decades about the variability of the fall in Eurasia and the Indian summer monsoons on different time scales. These monsoon; D. R. Sikka (former director, monsoon rainfall. Gilbert Walker, ,who Indian Institute of Topical Meteorology, was the Director General of Observatories Pune) provided a historical perspective in the early part of this century, discov- *A report of the discussion meeting on ‘Mon- of monsoon research in India over the ered the association between all India soons: Past, Present and Future’ held from last 120 years. He suggested that the monsoon rainfall and the large-scale November 20 to November 22, 1997 in monsoon research in India had three oscillation in surface pressure in the south- Orange County (Coorg). This meeting was co- sponsored by Indian Academy of Sciences and different epochs. These epochs were ern hemisphere. He termed the see-s.aw Jawaharlal Nehru Centre for Advanced Scien- 1875-1947, 1948-1980 and 1980-1997, in surface pressure between the West tific Research (JNCASR). During the first epoch (i.e. 1875-1947) Pacific Ocean and East Pacific Ocean in

‘ CURRENT SCIENCE, VOL. 74, NO. 3,lO FEBRUARY 1998 187 NEWS the southern hemisphere as the southern between the objectives of ICRP and the ded in a general circulation model. He oscillation. The southern oscillation is international programmes such as the claimed that such models provide a more linked to the variations in the east-west World Climate Research Programme accurate prediction of the spatial structure circulation in the tropics. The east-west (WCRP) and the International Geosphere of all India monsoon rainfall. This lecture circulation in the tropics is called the Biosphere Programme (IGBP), Gadgil was followed by a spirited discussion Walker circulation in honour of the remarked that the emphasis in ICRP will about the reliability of climate models. pioneering contribution made by Gilbert be on the monsoon climate that is a Some of the participants argued that the Walker. During the period 1947-1 980, special feature of our region. spatial and temporal variability of Indian several international observational pro- Murari Lal (Indian Institute of Tech- monsoon rainfall predicted by these grammes were launched to understand nology, New Delhi) provided an overview models differs substantially from the the monsoon, Some of these were the of the simulations by coupled ocean- observations and hence one cannot rely International Indian Ocean Experiment atmosphere models. He highlighted the upon the predictions by these models (IIOE) in 1964, Indo-Soviet Monsoon variations in the Indian monsoon rainfall regarding the monsoon in the next Experiment (ISMEX) in 1973, and predicted by these models with an em- century. Some other participants argued, Monsoon Experiment (MONEX) in 1979. phasis on future climate. In these models however, that some of the climate models These experiments and routine observa- it is assumed that the amount of carbon have shown systematic and steady tions provided the first detailed picture dioxide in the atmosphere will continue improvement in their ability to simulate of the vertical structure of the thermo- to increase at the rate of 1.5 to 4.5 ppm the spatial and temporal variability of the dynamical variables during the monsoon per year over that next hundred years. Indian monsoon rainfall. All the pardci- season. The launching of the Indian These models also assume that the amount pants agreed, however, that there is il remote sensing satellite (INSAT) in early of sulphate aerosols in the atmosphere need to characterize more precisely the 1980s provided, for first time, an oppor- will also increase exponentially due to sulphate aerosol loading over India based tunity to monitor continuously the pro- the increasing use of coal in China, on the sulphur content of the Indian coal gress of the monsoon over the continent Europe, America, Australia . and India. and the projections regarding increase in as well as the oceans. In the early 1990s Specifically, these models assume that coal consumption in India over the next the first indigenous observational experi- the maximum sulphate aerosol loading in hundred years. ment called MONTBLEX (Monsoon India will increase from the present value G. E3. Pant (Director, Indian Institute trough Boundary Layer Experiment) was of 8 mg/m2 to 40 mg/m2 in fifty years. of Tropical Meteorology, Pune) discussed launched. This experiment provided the If the increase in CO, alone is incorpo- the climate change in the Himalayas over first detailed measurement of the fluxes rated in these models, they indicate that the past thousand years as revealed by near the surface during the monsoon. the all India summer monsoon rainfall data from tree rings. The analysis of Sikka concluded his talk by pointing out will increase from the present value of climate variation was based on 600 that monsoon research in India has entered 87 cm to around 112 cm by the year coniferous tree samples in Kashmir, a new phase with the launching of the 2050. This would imply an increase in Himachal Pradesh and Uttar Pradesh. The Indian Climate Research Programme the all India monsoon rainfall by more tree ring data does not indicate any tern- . (ICRP) in 1997. than 25% in the next 50 years. This perature trend over the past two hundred Sulochana Gadgil (Indian Institute of increase is wE11 above the inherent inter- years in the Himalayas. This is in contrast Science, Bangalore) made a brief annual variability in the model. When to the increase in surface temperature presentation on the ICRP. She indicated the effect of increase in sulphate aerosol seen over the past hundred years in the that this programme was launched to is incorporated in these models, they in- data from the plains of India. harness the expertise available in India dicate a decrease in all India monsoon Chaya Sharma (Birbal Sahni Institute in atmospheric, oceanic and space rainfall! This is due to the cooling of of Palaeobotany, Lucknow) provided an sciences and utilize the facilities available the continental surface on account of the overview of the reconstruction of past for observation and modelling in the reflection of solar radiation by the climate using pollen data, The pollen Department of Ocean Development sulphate aerosols. Murari La1 cautioned, analysis covered the regions from (DOD), CSIR and the universities. The however, that the results obtained from Kashmir in the Western Himalayas, . major objectives of the ICRP are: (i) to these models cannot be used for making Katmandu in the Central Himalayas to document the spatial and temporal van- policy decisions since some of the pa- Sikkim in the Eastern Himalayas. In the abiIity of the monsoon climate, (ii) to rameters (such as sulphate aerosol load- Kashmir valley, pollen analysis suggests understand the physical processes that ing) used in the model are not known a cooler period around 10,000 years lead to climate variability, and (iii) to accurately. In addition, most of the models before present, followed by a gradual understand the impact of climate change show large variations in the Indian mon- warming between 7000 and 4000 years on natural and managed ecosystem. soon rainfall depending upon the numeri- before present. Pollen studies in Ladakh In order to attain the objectives enu- cal techniques used and the manner in indicate that during the last 30,000 years merated above, it is proposed to undertake which clouds and mountains are incor- the climate there was cold and dry. There analysis of existing data, gather new data porated in the model. Many of thcse were, however, brief periods when warm from satellites and buoys, and organize models do not reproduce correctly the climate lasting about 2000 to 3000 years special observational experiments in the spatial pattern of the present-day monsoon existed. About 1000 years ago there was Bay of Bengal. Sulochana Gadgil pointed rainfall. He advocated the use of high- a transition from moist to relatively dry out that there is considerable overlap resolution regional climate model embed- conditions in the western Himalayas. I

188 CURRENT SCIENCE, VOL. 74, NO. 3, 10 FEBRUARY 1998 L

NEWS -~~ ~~

R. Ramesh (Physical Research Labora- that C, plants (mainly tropical grasses) ocean can cause a dramatic change in tory, Ahmedabad) reviewed the data thrive under arid conditions while C, the CO, of the atmosphere. During the available on past monsoons and the ability plants dominate when wetter conditions last glaciaI maximum (around 18,000 of climate models to simulate past prevail. The ratios of I3C to ''C in the years ago), the CO, of the atmosphere monsoon. He showed that during the last C, and C, plants are different because was around 200ppm which was lower glacial maximum (which occurred around of the differences in the photosynthetic than the pre-industrial value of 280ppm 18,000 years ago), there was an increase pathways of carbon fixation. He 'showed and the present value of 360ppm. The in the salinity of the surface waters in the variations in the 13C to I2C ratio in equatorial ocean is a source of CO, for the Bay of Bengal. There is evidence peat samples collected From a pit dug in the atmosphere while the ocean in the that the surface winds in the Arabian sea the Nilgiris. He used this data to show southern hemisphere acts as a sink. Naqvi were 50% below the present values. This that this region had arid climate during highlighted the effect of deep-ocean indicates a reduction in monsoon rainfall the last glacial maximum (about 18,000 circulation and nitrogen cycle on the CO, during the last glacial maximum. Around years ago) and a wet period around 9000 content of the atmosphere. 9000 years ago the solar radiation incident years ago, In the discussions that foIiowed the in the tropics was about 7% more than S. W. A. Naqvi (National Institute of presentation on palaeoclimate, many present and the proxy data indicate that Oceanography, Goa) discussed the regu- participants underscored the need to ex- the monsoon rainfall was more than the lation of the amount of CO, in the tend the observations to other regions of present. The simulations of past monsoon atmosphere by the oceans. The amount India so that the large-scale signal of using general circulation models show a of carbon stored in the ocean is more climate variations can be deduced. linear relationship between the solar ra- than 50 times the amount of carbon stored Many participants highbghted that corals diation incident at the top of the atmos- in the atmosphere. Hence the exchange in the Indian seas may provide high- phere in the tropics and the monsoon of CO, between the ocean and the resolution data on past climate changes rainfall. Some models show that a 1% atmosphere has a profound influence on in the Indian region. The simulation of change in solar radiation causes a 2.5% the concentration of CO, in the atmos- past climate using climate models was change in monsoon rainfall. phere. At the present lime around 7 billion considered necessary in order to gain R. Sukumar (Indian Institute of Science, tons of CO, is pumped into the atmos- confidence in our ability to predict future Bangalore) presented results based on the phere by the burning of fossil fuels and climate. use of stable carbon isotope ratio as deforestation. Out of the 7 billion tons, indicators of past climate based on the 2 billion tons is absorbed by the oceans different ecological requirements of and 3 billion tons accumulates in the different plant types. He discussed the atmosphere and causes an increase of J. Srinivasan, Centre .For Atmospheric classification of plants into C, and C, CO, in the atmosphere at the rate of and Oceanic Sciences and Department of types on the basis of their photosynthetic around 1.5 ppm per year. Any change in Mechanical Engineering, Indian Institute pathways of carbon fixation. He showed the rate of absorption of CO, by the of Science, Bangalore 560 012, India.

National Centre for Ultrafast Processes

During the last decade there has been techniques are used in these studies for The Department of Science and Tech- enormous interest to study processes understanding transient phenomena. nology (DST), Government of India has occurring in the solid state and condensed Study of ultrafast processes paves the established a National Centre for Ultrafast phase in real time by using techniques way to control the product of chemical Processes at Madras University. A particularly in the picosecond (10-l2 s) reactions, angular distribution of photo- separate building with laboratories, hostel and femtosecond s) domains. Many electrons and the evolution of vibrational and other infrastructure will be exclu- biological, chemical and other transport wave pockets of diatomic molecules. Dur- sively established for NCUFP in the phenomena are known to occur from ing the last two decades, lasers with Taramani Campus of the University with millisecond to a few hundred femto- ultrashort light pulses have been deve- the support of the Government of Tamil seconds. In order to understand the loped which are now available with pulses Nadu. The Centre will have major facili- fundamental dynamic processes for the shorter than 100 femtoseconds. Using ties for (i) lifetime measurements by time development of new materials, study of these lasers impressive pulse shaping and correlated single photon counting, (ii) nano- the fast processes in various areas of tailoring techniques have emerged that second pulsed laser systems for absorption physics, chemistry and biology has make it possible to control molecular and emission studies, and (iii) flash pho- become important. Towards this, new dynamics. Investigations on ultrafast tolysis equipment using flqh lamps. lasers and techniques have been developed phenomena are aimed at developing Facilities also being established include during the last two decades for investi- technologies in the cutting edge of (i) picosecond emission spectrometer and gating the dynamics of the ultrafast pro- materials research: new catalysts for (ii) picosecond pump probe laser system. cesses and physical properties occurring chemical transformation, nanophase in clusters of atoms and molecules in materials, biotechnological process P. Natarajan, Department of Inorganic real time in condensed phase and in solid materials and molecular electronic and Chemistry, University of Madras, Guindy state. Time resolved laser Spectroscopic photonic systems. Campus, Chennai 600 025, India.

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