Showing papers on "Monsoon published in 1982"

Glacial to interglacial contrasts in the northern Indian Ocean

Abstract: Differences between the 18O/16O ratios of planktonic foraminifera deposited during the last glacial maximum, about 18,000 yr ago, and those deposited during the Holocene show that in the Indian Ocean, the south-west monsoon was weaker than today but that the north-east monsoon was stronger. The upwelling observed in modern conditions along the southern coast of Arabia had disappeared because of the low speed of the southwestern winds during glacial summers. The reduction in rainfall and runoff over the continent caused a reduction of the salinity gradient in the Bay of Bengal and along the western coast of India. Increased precipitation fell on the sea south of 10° N, while strong evaporation over the northernmost Arabian Sea produced an enhanced salinity gradient in that area.

The Sensitivity of the African-Asian Monsoonal Climate to Orbital Parameter Changes for 9000 Years B.P. in a Low-Resolution General Circulation Model.

Abstract: The earth's orbital parameters, precession, obliquity and eccentricity, produce solar radiation differences (compared to present) of ∼7% at the solstices 9000 years before present (B.P.): more radiation in June-July-August, less in December-January-February. When this amplified seasonal cycle of solar radiation is used to drive a low-resolution general circulation model, an intensified monsoon circulation is simulated for Northern Hemisphere summer. The annual- and global-average land surface temperature and the annual- and global-average precipitation are the same for the simulated 9000 years B.P. climate and the present climate. Certain features of the simulated monsoon climate from this orbital-parameter sensitivity experiment agree with the paleoclimatic evidence.

Oceanography of the northern Arabian Sea

Abstract: The euphotic zone of the northern Arabian Sea ranges from 20 to 60 m with an average depth of about 40 m. Surface temperatures range from 22.5 to 28.5°C, increasing from north to south. At 1000 m, the temperature is about 15°C lower than at the surface. Maximum difference in temperature is found during the SW monsoon. Salinity also decreases from north to south. High salinity in the northern region is probably due to the excess of evaporation over precipitation and runoff, and to high salinity water coming from the Persian Gulf. There is little seasonal effect on the salinity, but there are large differences in the dissolved oxygen at the surface during the SW monsoon. There are two oxygen minima, the first between 100 and 400 m and the second between 800 and 1500 m. The formation of the first oxygen minimum is probably due to high organic production in the euphotic zone, sinking of a large amount of organic matter, the lack of horizontal advection due to the land-locked nature of the sea, and the presence of high salinity water in the upper layers. High oxygen at intermediate depths and the second oxygen minimum in the range 800 to 1500 m probably occur as a result of physical processes peculiar to this part of the Arabian Sea. The flow pattern consists of several eddies and meanders. Inorganic phosphorus is high in the surface layer and still higher at greater depths. Nitrate-nitrogen is low at the surface and increases with depth. Ratios between apparent oxygen utilization (AOU), and changes in carbon, silicon, nitrogen, and phosphorus by atoms were 280:108:40:16:1. Using this relationship it was possible to estimate nitrate reduction at the intermediate depth range and the residence time of water in the oxygen-deficient layer. The rate of primary production in the northern Arabian Sea was 835 mg C m−2day−1 or 530 × 106 tonnes of carbon each year. The average chlorophyll in the euphotic zone was also high. About 25% of the total photosynthetic production of the Arabian Sea occurs in the northern part in about 8% of the area. Zooplankton biomass was also several times that in the rest of the Arabian Sea, and was largely confined to the upper 200 m. Benthic biomass, on the other hand, was lower than in the other regions of the Indian Ocean.

Short-Term Planetary-Scale Interactions over the Tropics and Midlatitudes during Northern Winter. Part I: Contrasts between Active and Inactive Periods

Abstract: Objectively analyzed 200 mb winds of four winters are used to study the short-term (several days) teleconnections between planetary-scale circulation components over the monsoon region. The composited structures suggest that during very actively northeasterly monsoon (surge) periods, the midlatitude and tropical circulation components vary in a coherent way. The jet streak and local Hadley circulation over East Asia, the divergent flow over the maritime continent, and the equatorial Walker circulations over the Pacific and Indian Oceans all strengthen steadily, while the secondary jet streak over West Asia weakens. During inactive (break) periods the midlatitude circulation components all exhibit reversed changes, while the variations in the tropics are less coherent, although still showing reversed tendencies. The results basically verify the short-term teleconnection model proposed by Chang and Lau (1980), but more complex processes in the acceleration of the midlatitude jet streaks are indicated. In addition, the contrast between the very active and break monsoon periods suggests the relative importance of tropical versus midlatitudinal forcings in different regions of the monsoon circulation.

An Apparent Relationship between Eurasian Spring Snow Cover and the Advance Period of the Indian Summer Monsoon

Abstract: Satellite images and Northern Hemisphere snow cover charts have been used to derive the Eurasian spring (March-May) snow cover area for the period 1967–78. The advance period of summer monsoon from the extreme southern tip of peninsular India to northwest India was derived from the Indian Daily Weather Reports. Year-to-year variations of the advance period of the Indian summer monsoon were compared with the Eurasian spring snow cover area and also with the Eurasian snowmelt, from March to May. This preliminary study revealed that springs with extensive snow cover area over Eurasia were followed by a longer advance period of the Indian summer monsoon. Further, an inverse relationship (negative correlation) is found between spring snowmelt and the advance period, that is, springs with more snowmelt over Eurasia were related with a shorter advance period of the Indian summer monsoon.

Thermodynamic and Circulation Characteristics, of Winter Monsoon Tropical Mesoscale Convection

Abstract: During the December 1978 field phase of the International Winter Monsoon Experiment (Winter MONEX), a regular diurnal cycle of deep convective activity occurred over the South China Sea immediately to the north of Borneo. The convection was initiated during the late night hours by convergence of the low-level northeast monsoon flow with the land breeze along Borneo's north coast. The precipitation feature that developed was characterized during its mature stage by a nearly continuous stratiform cloud, referred to here as a mesoscale anvil, of ∼ 100–500 km dimension extending from the mid-troposphere (∼5 km) to near the tropopause (∼ 17 km). Using rawinsonde data from the sounding network, thermodynamic and Circulation characteristics of the convection are documented. Mesoscale upward motion is found to within the anvils, with a MCSOMC downdraft below producing a warm, dry region over a lame area just above the boundary layer. Air flow relative to the anvil on both its leading and trailing edges i...

The Mid-Cretaceous Earth: Paleogeography; Ocean Circulation and Temperature; Atmospheric Circulation

Abstract: A reconstruction of the global paleogeography of the mid-Cretaceous (100 m.y. ago), including adjustment of continental outlines to account for microplate movements, cmstal shortening, and accretion in mid-Cretaceous and later orogenic regions, is described and a map presented. On the modified continents, coastlines and significant mountain ranges are added. This paleogeography is used as a framework for a reconstruction of ocean surface circulation and temperature distribution. Then the main features of the atmospheric circulation are deduced using the paleogeography and ocean temperatures as boundary conditions. Relative to the present, these features are: a much weaker westerly wind belt and greater seasonality of wind patterns leading to more extreme surface climates over the continents; slightly equatorward positions of the subtropical anticyclones; and monsoonal regimes over the continental margins bordering "Tethys" and the central Atlantic. A comparison of the results with climatic evidence from t...

The northwestern Indian Ocean during the monsoons of 1979: distribution, abundance, and feeding of zooplankton

Abstract: Upwelling induced by the separation of the Somali Current from the coast of east Africa is associated with low surface temperatures, high concentrations of nitrate, and blooms of phytoplankton. Coefficients of concordance, based upon 17 taxa of zooplankton collected at 33 stations in the southwest monsoon and 15 stations in the northeast monsoon, were consistently larger for the southwest monsoon and indicative of a general response of the zooplankton in the northwestern Indian Ocean. The largest coefficients of concordance in the southwest monsoon were among adult females of Paracalanus denudatus, Paracalanus parvus , and Paracalanus aculeatus and of Calanoides carinatus and Eucalanus spp. Coefficients of concordance among copepodids of six taxa had a trend similar to adult females in the southwest monsoon. During the southwest monsoon, total biomass of zooplankton was significantly greater within areas of upwelling than outside; adult females and copepodids of C. carinatus and Eucalanus spp. were significantly more abundant within the upwelling regions, along with adult females of Clausocalanus furcatus and Clausocalanus minor . The upwelling regions, which are associated with a reproductively active population of the large-bodied C. carinatus , are the primary features affecting distributions of zooplankton during the southwest monsoon and the main difference between monsoons. The ontogenetic migration of C. carinatus is essentially an annual life-history strategy and therefore on the same temporal scale as the reversals in the monsoonal winds and associated upwelling. The ability of C. carinatus to ingest readily the diatoms that dominate the upwelling regions and to store lipid is crucial to its dominance of the areas of upwelling both in numbers and biomass.

Characteristics of precipitation during the monsoon season in high-mountain areas of the Nepal Himalaya*

Abstract: Precipitation phenomena during some summer monsoon seasons were observed in high-mountain areas of the Nepal Himalaya. The main results obtained from these observations are as follows. (a) Precipitation along the main valley of Dudh Kosi decreases with altitude in the range from 2800 m to 4500 m a.m.s.l. (b) The total amount of precipitation around peaks and ridges is 4 or 5 times larger than that around valley bottoms. (c) The frequency and amount of precipitation around peaks and ridges are concentrated during the day-time when cumulus convection is predominant, while those around valley bottoms are concentrated during the evening up to midnight. (d) A linear relation between the surface air temperature and the percentage of occurrences of snowfall to all the cases of precipitation was obtained from the observations at the station (4958 m) near Glacier AX010 in Shorong Himal.

Water-Mass Distributions at Intermediate Layers off the Somali Coast during the Onset of the Southwest Monsoon, 1979

Abstract: Hydrographic observations at intermediate depth in the Somali Basin have been made during and after the transition from the northeast monsoon to the southwest monsoon, 1979. The data are discussed in relation to measurements of absolute currents during the same time period. Earlier water-mass identification by Warren et al. (1966) is confirmed and extended by introducing a well-defined Equatorial Water Mass. The distribution of water masses and its temporal evolution with the changing monsoonal wind field is analyzed on three different spatial scales. Equatorial and near-coastal undercurrents are an important factor in the large-scale redistribution of water masses in the intermediate layers. Cross-equatorial exchange of water, in particular highly saline Red Sea water, is largely confined to a narrow region off the East African Coast. No obvious response of these currents to the onset of the southwest monsoon is detected. In the mesoscale range anticyclonic subsurface eddies containing Equatoria...

Variability of the Somali Current System during the Onset of the Southwest Monsoon, 1979

Abstract: An array of six current-meter moorings and several coastal temperature recorders was deployed on the shelf and continental slope off northern Somalia from March to July 1979; a seventh mooring was placed near 2°S. In addition, four deep-sea moorings were deployed for a period of one month in May–June farther offshore. Already during the late northeast monsoon in March the Somali Current north of 5°N was flowing northeastward in the top 150 m. Underneath, in the depth range 150–400 m, a narrow southward undercurrent was observed from March to June. After the first onset of the southwest monsoon, which occurred around 5 May when winds shifted from easterly to southwesterly parallel to the coast, the near-surface temperatures on the shelf decreased immediately with no detectable phase difference between 6 and 10°N, but no change was observed in the offshore circulation pattern. The final monsoon onset around 10 June was characterized by a drastic increase in wind speeds and the establishment of a st...

Stochastic dynamic model for long range prediction of monsoon rainfall in Peninsular India

Abstract: An attempt has been made to develop a Stochastic dynamic model that could be used for forecasting monsoon rainfall, June to September, in the larger sub-division of India, viz., Peninsula. For building such a model the atmosphere bas been considered as a linear dynamic system that converts various inputs into the output, say the rainfall. In this study the 500 mb mean April sub-tropical ridge position along Long. 75° E has been used as input to the atmosphere. The input~ output data for the recent 38 years (1939-1976) have been utilised for developing the model which utilises the dynamics of the atmosphere and also that of the ARIMA process to forecast the rainfall. The performance of the model has been found good during the sample and the test (1977 to 1980) periods. Even in rank drought and excess rainfall years the closeness of the predicted and realised values stands out well. In terms of seven categories currently being used by the India Meteorological Department for describing its long range forecasts, the skill score of the model forecast for the test period has been found equal to one which is the highest that a forecast formula can have. This suggests that the Stochastic Dynamic Model developed here can therefore, be used for issuing more accurate long range monsoon rainfall forecasts about a month ahead of the season for the Peninsula. This would provide enough time for planning adequate strategies for mitigating the disastrous effects that are produced due to the large vagaries of monsoon.

Fluctuations in the deficiency of the summer monsoon over India, and their effect on economy

Abstract: To assess the deficiency in the activity of the monsoon over India during the season, an index for the country based on the percentage area with a specified percentage seasonal rainfall deficiency and termed the Monsoon Deficiency Index (MDI), has been utilized. The statistical properties of the MDI series for the period 1871–1978 have been examined. The series which can be taken to be homogeneous and random has a high variability. MDI is generally not observed to persist at a high level; a high value is invariably followed by a low value. The deficiency over the country is considered as largescale and is termed as monsoon failure when the MDI value equals or exceeds the nineth decile viz. 40, of the mixed gamma distribution fitted to the MDI series. Using this criterion, the years of monsoon failure have been identified. The monsoon failures are found to occur randomly. The effect of monsoon deficiency on the Indian economy has been assessed.

Abundance, breeding and growth of the ocypodid crab Dotilla myctiroides (Milne-Edwards) on a West Malaysian beach

Abstract: The ocypodid crab, Dotilla myctiroides, was studied on the south-west coast of peninsular Malaysia The mean numbers and biomass over a year along a transect from high to low water ranged from 37·5 to 579 crabs m−2 and from 2·22 to 50·79 g m−2 (wet weight) respectively Berried females were found in all months of the year but two peaks of activity were apparent, from November to February and May to July It is suggested that this may be related to changes in food abundance associated with the effects of monsoon winds on sea currents Laboratory growth studies indicated that maximum life span was approximately 13 months (from first crab stage) for males and 10 months for females Growth rate decreased with increasing size of crab Egg number increased with size of female

Fluctuations in northeast monsoon rainfall of Tamil Nadu

Abstract: The average rainfall series of Tamil Nadu for the NE monsoon months of October-December and the season as a whole were analysed for trends, periodicities and variability using standard statistical methods. The trend analysis showed that there are no long-term trends of increasing or decreasing rainfall in the individual months or the season as a whole. The power spectrum analysis of rainfall series showed peaks at frequencies corresponding to the time periods of 2-2.44 yr and 3.66-4.40 yr.

Response to annually reversing monsoon winds at the southern boundary of the Somali Current

Abstract: The transient monsoon current system of the northwestern Indian Ocean provides a unique opportunity to investigate the dynamics of rapid western boundary currents. In 1979, part of the Indian Ocean Experiment (INDEX) focused on the southern boundary of the annually reversing Somali Current where interaction with the East Africa Coastal Current is an important feature. This study presents current measurements in the southern boundary area and investigates a simple vorticity model that suggests that the location of the southern boundary and the rapid switching action of the currents may, in part, be topographically controlled. It seems reasonable that the convergence-deflection area may be limited in range by larger scale forcing, but within this range topographic forcing along the coast of Kenya places a local constraint on the occurrence of the deflection in location as well as in time. This has significant implications on understanding the transient processes associated with rapid boundary currents where redirection may play a major role.

Low frequency variability of the 20°C isotherm topography in the western equatorial Indian Ocean

Abstract: Monthly maps of the mean 20°C isotherm topography in the western Indian Ocean have been compiled from historical data. They reveal strong annual and semi-annual fluctuations. The yearly cycle has significant phase lags across the area investigated that reflects the different circulation patterns during and in between the two monsoon periods. In particular, the different development of the Somali Current north and south of 5°N can be seen in these data. The flow in the southern part reverses 1 month prior to the large scale onset of the SW-monsoon but otherwise follows the monsoonal windfield. In the northern part southward flow is found only for 2 months during the height of the NE-monsoon. The Somali eddy spins up immediately after the SW-monsoon onset but remains strong for 2 months after the winds weaken. The semi-annual fluctuations are in phase from 10°N to 10°S and can be related to the zonal winds over the equator. Eastward surface currents cause thermocline upwelling during boreal spring and fall which has maxima along the coast and at 5° north and south of the equator. It can feed the currents at a rate of 15×106 m3 s−1 during a 3-month period.

Discoveries of Rice in Prehistoric Sites in Korea

Abstract: Korea is a small peninsula with an area of 220,839 square kilometers. It is a mountainous land, with only one-fifth of the area available for cultivation. The peninsula belongs to the temperate zone, but the north is colder and more arid while the south is humid and hot in the summer, like the monsoon zone of southeast Asia and Japan. The south has a yearly rainfall of 800 to 1,000 millimeters, and 60 percent of the precipitation occurs in the summer months from June to early September.

Cross-equator flow from australia and monsoon over china

Abstract: In this paper, we have analysed the wind data and synoptic circulation pattern over West Pacific and Southeast Asia. It is shown that there is a cross-equator jet flow from Australia which prevails the East China and determines the precipitation in China. This flow is defined as cross-equator flow from Australia and low level jet over China.It has very important effect on the summer precipitation over China. The effects on precipitation in China of Southwest monsoon coming from India and southwest monsoon coming from West Pacific have been analysed by some authors. In this paper it is pointed out that the cross-equator flow which lies between these two flows mentioned above and comes from Australia of South Hemisphere effects the summer monsoon rainfall over China.It is noticed that exploration of this flow will help to research in a deep going way on structure of summer monsoon over East Asia and help to change our ideas about this subject.

The Wind Stress Patterns over the Indian Ocean During the Summer Monsoon of 1979

Abstract: A detailed analysis of the wind stress patterns over the Indian Ocean was made from 1 May to 31 July 1979. A combination of cloud motion and ship data obtained once per day was used to diagnose the surface-wind patterns to a degree of detail not possible in the past for an individual season. These data show the monsoon development and the fluctuations of the Somali Jet and the Southern Hemispheric tradewinds. Wind stress patterns produced by two traveling tropical storms are discussed. These combined to exert an unusually high westerly wind stress on the equator before the monsoon developed.

On the Dynamics of the East African Jet. III: Arabian Sea Branch

Abstract: Barotropic simulations of the East African jet are extended to include the Arabian Sea branch of the flow and to allow for flow over the mountains of Africa. Large-scale mass source-sink forcing, present to the east of the model orography, drives the low-level circulation. Many features of the southeast trades, cross-equatorial flow and southwest monsoon are simulated. Among them are the separation of the jet from the African highlands, a wind speed maximum over the Arabian Sea and a reinforcement of the southwest monsoon by the Arabian northerlies. Splitting of the jet over the Arabian Sea is not simulated. Starting from a state of rest, a well-developed southwest monsoon is achieved in a week of simulated time. Inclusion of a prescribed Southern Hemisphere midlatitude disturbance excites a significant response in the cross-equatorial flow, even though flow is permitted over the African mountains. Downstream, the surges excite a response over both the Arabian Sea and the Bay of Bengal. The bay r...

On the role of large scale energetics in the onset and maintenance of summer monsoon -I: Moisture budget

Abstract: The effect of large scale moisture and moist static energy (MSE) budget on the onset and activities of summer monsoon is investigated. The data base for this study consists of twice daily First GARP Global Experiment (FGGE) level IIIb analysis of temperature, relative humidity, geopotential and wind fields for a tropical belt from 20 deg. S to 40 deg. Nand 0 deg. E to 150 deg. E, during May-July 1979. The daily variation, vertical distribution and period averages of the various terms in latent heat energy (LHE) and MSE budget equation are closely examined to find out their influence on the activities of monsoon. The study indicates significant increase in the net LHE, horizontal. Convergence of moisture and diabatic moisture sink (indicator of excess condensation than evaporation) about two week before the onset pf monsoon over Kerala coast. Further, a decreasing trend is observed in horizontal convergence of moisture and moisture sink about one week before the break monsoon condition, which started over India on 16 July 1979. However, the various terms of the MSE budget equation do not depict my significant trend with the advance of the monsoon. The vertical distribution, period averages and the boundary fluxes also confirm the above findings.

Wave to wave and wave to zonal mean flow kinetic energy exchanges during contrasting monsoon years

Abstract: Fourier analysis of the monthly mean northern hemispheric geopotential heights for the levels 700 mb and 300 mb are undertaken for the months of April through to August The wave to wave and wave to zonal mean flow kinetic energy interactions are computed for specified latitude bands of the northern hemisphere during the pre-monsoon period (April to May) and monsoon period (June through to August) for bad monsoon years (1972, 1974, 1979) and for years of good monsoon rainfall over India (1967, 1973, 1977) Planetary scale waves (waves 1 to 4) are the major kinetic energy source in the upper atmosphere during the monsoon months Waves 1 and 2 in particular are a greater source of kinetic energy to other waves via both wave to wave interactions as well as wave to zonal mean flow interactions in good monsoon years than in bad monsoon years The zonal mean flow shows significantly larger gains in the kinetic energy with a strengthening of zonal westerlies in good monsoon years than in bad monsoon years

Mesoscale Features and Cloud Organization on 10–12 December 1978 over the South China Sea

Abstract: Aircraft data from Winter MONEX have been combined with other data to study mesoscale features, and organization of cumulus clouds, on 10–12 December 1978. A moderate cold surge in the northeasterly monsoon flow, toward cloudiness in an equatorial trough off Borneo, peaked on 11 December. Clouds in the northeasterly monsoon flow were similar to those in the trades, with variations in convective regime on length scales on the order of 100 km. Marked mid-tropospheric subsidence was accompanied by low-level divergence near 20°N. During 10 December, anvil clouds near Borneo expanded; cumulus congestus and cumulonimbus formed on the periphery of this area. The approach of the low-level northeasterlies to the area of anvils was marked by a diminution of subsidence, conditional instability, and a weak field of low-level convergence, with randomly organized cumulus of increasing height. A low-level easterly jet was found in this transition zone, downstream from cloudiness over the Philippines. South of V...

Studies of the Indian summer monsoon with a coarse‐mesh general circulation model, part II

Abstract: A previous paper (Part I) discussed the performance of a coarse-mesh general circulation model in studies of the Indian summer monsoon. Part II herein describes impacts on the simulated monsoon climate due to prescribed changes in the lower boundary conditions: lowering and flattening of the Himalayan Mountains and cold and warm sea-surface temperature (SST) anomalies in the Arabian Sea. Results indicate that it is the Himalayas that are responsible for the observed north-westerly flow aloft over northern India before onset and the delay in precipitation onset there until late June or July. SST anomalies, which are held constant throughout four-month simulations, affect local precipitation computations via changes in stability and cause impacts of the opposite sign immediately downwind. Neither of the two anomalies tested resulted in statistically significant precipitation impacts over India.

Morphological changes of the beaches of Goa

Abstract: Morphological variations of 2 of the major beaches of Goa have been found to be cyclic over a period of approximately 1 yr. These beaches attain their maximum sediment storage around April/May. They are then subjected to rapid rates of erosion with the onset of the southwest monsoon wind and wave conditions followed by slower rates during the subsequent period of the monsoon. This continues till August when the beaches have minimum sediment storage. The wave climates during the postmonsoon and winter months help the beaches in recovering gradually after passing through a secondary phase of erosion associated closely with the onset of the northeast monsoon, during November/December.

Fluctuations of Global Surface Pressure Patterns during the Past 100 Years and Their Relation to the Asian Monsoon Part I. Northern Summer (July)

Abstract: In order to detect the fluctuations of the global circulation patterns and their relation to the Asian summer monsoon, an empirical orthogonal function (EOF) analysis was applied to the July monthly mean smoothed surface pressure data for 106 years (1871-1976) covering most of the globe. The 1st component (31% of the total variance) shows a contrasting spatial pattern between the Southern Hemisphere through the equatorial zone and the Northern Hemisphere mid-latitudes. This mode may represent the major re-distribution of the global-scale pressure patterns from the "Little Ice Age" to the recent warmer period. The 2nd component (19% of the total variance) reflects a pressure seesaw between the subtropical oceans and the Afro-Eurasian continents, which seems to be largely responsible for the strength of the Asian monsoon. These two dominant modes seem to correspond well with the long-term global-scale SST change. The 3rd component (14% of the total variance) represents a north-south (or east-west) shift of the main centers of action, and is also closely connected with the monsoon circulation. The EOF analysis of the original year-to-year data has revealed that the mode of the Southern Oscillation is also dominant as a fluctuation with periods less than 10 years, which is well correlated with the shorterperiod fluctuations of the monsoon.

Some characteristic features of the low-level jet field over the Arabian Sea during the Indian summer monsoon

Abstract: Some characteristic features of the low-level jet over the Arabian Sea have been studied by using the Indo-Soviet Monsoon Experiment- 1973 and Monsoon Experiment- 1977 data. The meridional wind profiles show two distinct jet maxima over the extreme western Arabian Sea. The lower maximum occurs near 1.0 km in the north and lies well within the pronounced inversion layer. The upper wind maximum lies near 2.0 km toward the south above the inversion. Towards the east, the profiles indicate a stronger low-level maximum and the absence of the upper level wind maximum in the south. Thus, the downwind changes occurring in the wind field over the western Arabian Sea indicate a possible dynamic coupling between the two jet cores in this region. The low-level wind structure over the Arabian Sea indicates cold air advection to the south and warm air advection to the north of the jet core. Strong negative thermal wind shear is evident in the jet core.

Year-in-advance Forecasting of the Indian Monsoon Rainfall

Abstract: The paper starts out by discussing factors which influence the Indian monsoon rainfall—including Northern Hemispheric temperature changes, long-period soli–lunar tides, and the tidelike phenomena associated with the wobble of the Earth relative to its spin-axis. When the effects of these factors on precipitation are quantified and integrated into a thermodynamical–statistical model, long-range climatic forecasts can be made that are better than chance or than predicting ‘normal’ up to two or more years in advance.Climatic changes have had profound effects on the peoples of India through the controlling influence of the monsoon on Indian agriculture. We now have a technological tool, never before available, that might lessen the impact of variations of the monsoon by forecasting these variations one to two years in advance. The two-years-in-advance 1982 monsoon rainfall forecast for June and July, using the same station models that produced the excellent 1981 forecast, indicates that there is a two-to-one chance that the 1982 Indian monsoon rainfall will be less, in general, in June and July, than it was in 1981. The question which we wish to ask the reader is: How can this new technology be used? For example, how can this type of information be used for planning and policy-making in order to ensure less uncertainty about food supplies in the future than in the past?This region cannot depend upon the monsoon to bring plentiful rain every year, and, therefore, it is essential that we should continue to improve our forecasting capability and that others learn to make optimum use of these forecasts.