Showing papers on "Monsoon published in 1991"

Forcing mechanisms of the Indian Ocean monsoon

Abstract: Sediments in the Arabian Sea provide biological, biogeochemical and lithogenic evidence of past changes in the Indian Ocean summer monsoon winds. For the past 350,000 years, this system has been externally forced by cyclical changes in solar radiation, and internally phase-locked to the transport of latent heat from the southern subtropical Indian Ocean to the Tibetan Plateau. In contrast to the results of general circulation models, these geological data suggest that the climate change associated with variability in global ice volume is not a primary factor in determining the strength and timing of the monsoon winds.

A 13,000-year climate record from western tibet

Abstract: ALTHOUGH the Tibetan plateau is important in influencing the atmospheric circulation of the Northern Hemisphere1–3, there are only a few continuous palaeoclimate records available, and these are limited to the plateau's northeastern margin4–6. Here we present a 13,000-yr record from Sumxi Co (western Tibet), constructed from both lake-core and shoreline studies, which shows that conditions in the early–middle Holocene were warmer and wetter than at present. These results confirm model predictions of an intensified monsoon over the region at ∼9,000 yr BP, owing to an orbitally induced increase in summer insolation7,8. We also find evidence for warm, humid pulses at ∼12,500 and ∼10,000 yr BP, in phase with the steps of the last deglaciation, and for a return to cold, dry conditions at ∼11-10,000 yr BP, none of which can be explained by orbital variations. The existence of the cold episode confirms that the cooling associated with the Younger Dry as event occurred in continental China6,9, and provides further evidence of the global nature of this event10

Wind-driven coastal upwelling along the western boundary of the Bay of Bengal during the southwest monsoon

Abstract: A hydrographic survey during the southwest monsoon (July–August 1989) showed that along most of the western boundary of the Bay of Bengal, in an approximately 40 km wide band, isopycnals from depths up to about 70 m surfaced due to upwelling forced by local winds, in a fashion similar to that observed along eastern boundaries. Below the upwelling band there were often signatures of downwelling, suggestive of an undercurrent. There were no indications of a large-scale remotely forced western boundary current. Geostrophic velocity in the upwelling band was in the direction of the winds. The dynamic topography outside the upwelling band had cellular structures possibly indicating the presence of shelf waves with longshore wavelength of 400–500 km. The near-surface stratification was dominated by salinity, a consequence of high freshwater input to the Bay. The upwelling led to a coastward increase in salinity, except near the northern end where the freshwater influx from the Ganges and the Brahmaputra rivers overwhelmed other processes and gave rise to a freshwater plume offshore of the upwelling band. This plume moved equatorward against local winds.

Influence of monsoonally-forced Ekman dynamics upon surface layer depth and plankton biomass distribution in the Arabian Sea

Abstract: Oceanic surface layer properties in the central Arabian Sea at the height of the northeast 1986, 1987 and southwest 1987 monsoons are described. Data from two research cruises on the R.R.S. Charles Darwin are combined with Comprehensive Ocean—Atmosphere Data Set (COADS) winds and a simple model to consider the influence of the monsoons on the surface layers of the Arabian Sea. In December 1986 (NE monsoon) the top of the thermocline was fairly uniform with a mean depth of approximately 60 m. In contrast, this depth varied with latitude in the SW monsoon, with the shallowest depths occurring under the region of maximum winds and the maximum depths to the south of the monsoon jet. This situation is tied to the Ekman flow which leads to open ocean upwelling to the north of the wind maximum, thus suppressing the development of the mixed layer. The thermocline to the south is deepened by a combination of Ekman pumping and advection of dense fluid from the north. A simple two-dimensional model incorporating a non-penetrative mixed layer and a slab Ekman layer flow is used to examine the factors involved in the evolution of the surface layers during the monsoons. The combination of upwelling and surface layer deepening leads to latitudinal gradients in phytoplankton biomass. The major effect in the SW monsoon is the upwelling induced by Ekman dynamics and a consequent shoaling of the nitracline in the northern Arabian Sea. Vertical mixing and the associated deepening of the surface layer dominate phytoplankton distributions in the NE monsoons.

13. onset of monsoonal related upwelling in the western arabian sea as revealed by planktonic foraminifers1

Abstract: Quantitative analysis of the late Cenozoic planktonic foraminiferal record from western Arabian Sea Site 722 revealed long term trends in the history of oceanography and climate. The modern western Arabian Sea surface waters are highly influenced by the monsoonal wind system. Summer upwelling, a result of southwestern winds, occurs along the coast of Somalia which produces distinct foraminiferal assemblages which are dominated by G. bulloides d'Orbigny. Consequently, variations in the distribution record of G. bulloides through time monitor the upwelling history associated with monsoonal activities. G. bulloides was a minor constituent of the foraminiferal fauna from the bottom of the hole (-14.5 Ma) until about 8.6 Ma ago. Then a rapid shift occurred toward higher values, up to 53% at 7.4 Ma. We interpret this rapid increase as a major step in the evolution of the monsoonal history. It is either the establishment of the system or at least a strong intensification of the monsoonal winds. At 5.5 Ma a significant drop of the G. bulloides relative abundance occurred which may indicate less upwelling, or alternatively other biota may have been favored in this period. From 5.0 Ma to Recent the G. bulloides record indicates that upwelling has occurred with minor fluctuations.

Biological control of surface temperature in the Arabian Sea

Abstract: In the Arabian Sea, the southwest monsoon promotes seasonal upwelling of deep water, which supplies nutrients to the surface layer and leads to a marked increase in phytoplankton growth. Remotely sensed data on ocean color are used here to show that the resulting distribution of phytoplankton exerts a controlling influence on the seasonal evolution of sea surface temperature. This results in a corresponding modification of ocean-atmosphere heat exchange on regional and seasonal scales. It is shown that this biological mechanism may provide an important regulating influence on ocean-atmosphere interactions.

Enhanced particle fluxes in Bay of Bengal induced by injection of fresh water

Abstract: THE melting of ice sheets during deglaciation results in the injection of large amounts of fresh water into the oceans1. To investigate how such injections might influence particle fluxes in the ocean, and hence the uptake of atmospheric CO2, we deployed three sediment-trap moorings (two traps in each mooring) in the northern, central and southern parts of the Bay of Bengal, respectively. The Bay of Bengal is suitable for such a study, because some of the world's largest rivers2 supply pulses of fresh water and sediment to the bay, resulting in large seasonal changes in surface salinity3. We find that the maximum river discharge, which occurs during the southwest monsoon, coincides with the maximum observed flux of participate matter. From north to south, the carbonate flux increases, whereas fluxes of opal, organic carbon and particulate matter decrease. The overall flux pattern seems to be controlled by the seasonally varying input from the rivers and the accompanying shift in marine biogenic production. We conclude that fresh-water pulses during deglaciation may therefore have caused similar shifts in marine biogenic production, resulting in short-term episodes of increased oceanic uptake of atmospheric CO2.

The coastal current off Western India during the Northeast monsoon

Abstract: Hydrographic data collected during December 1987 and January 1988 are used to describe the poleward coastal current along the west coast of India that flows against weak winds during the northeast monsoon. Near the southern end of the coast, at about 10°N, the current was approximately 400 km wide, 200 m deep and carried the low salinity Equatorial Surface Water. The isopycnals tilted down on approaching the coast. Near the northern end of the coast, at about 22°N, the flow was restricted mainly to the vicinity of the continental slope; the current was a narrow (100 km), 400 m deep jet with a transport of about 7 × 106 m3 s−1. Along most of the coastline, a southward moving undercurrent was inferred from the distribution of salinity, temperature and dynamic topography. To understand the driving mechanism of the current, the annual cycle of the contribution of the longshore pressure gradient and that of the winds to the near-surface momentum balance was examined using available climatologies. It is seen that the longshore pressure gradient overwhelms the winds during the northeast monsoon, whereas during the southwest monsoon the winds dominate. In the Leeuwin Current off western Australia, the only other known eastern boundary current that flows against the winds, the pressure gradient dominates the winds throughout the year. The overall structure of the northeast monsoon coastal current is consistent with that predicted in the analytic model proposed by McCreary et al. (1986, Journal of Marine Research, 44, 71–92) to explain the Leeuwin Current. In the model a poleward baroclinic pressure gradient is generated by a density gradient along the coast. The latter is known to exist along the west coast of India. However, it seems likely that the current is also influenced by a barotropic pressure gradient.

The phytoplankton bloom in the northwestern Arabian Sea during the southwest monsoon of 1979

Abstract: The biological variability of the northwestern Arabian Sea during the 1979 southwest monsoon has been investigated by the synthesis of satellite ocean color remote sensing with analysis of in situ hydrographic and meteorological data sets and the results of wind-driven modeling of upper ocean circulation. The phytoplankton bloom in the northwestern Arabian Sea peaked during August-September, extended from the Oman coast to about 65°E, and lagged the development of open-sea upwelling by at least 1 month. In total, the pigment distributions, hydrographic data, and model results all suggest that the bloom was driven by spatially distinct upward nutrient fluxes to the euphotic zone forced by the physical processes of coastal upwelling and offshore Ekman pumping. Coastal upwelling was evident from May through September, yielded the most extreme concentrations of phytoplankton biomass, and along the Arabian coast was limited to the continental shelf in the promotion of high concentrations of phytoplankton. Upward Ekman pumping to the northwest of the Somali Jet axis stimulated the development of a broad open-sea phytoplankton bloom oceanward of the Oman shelf. Vertical mixing during the 1979 southwest monsoon was apparently not a primary cause of the regional-scale phytoplankton bloom.

The Monsoon Year — A New Concept of the Climatic Year in the Tropics

Abstract: The concept of “monsoon year” is proposed as a unit year of climatic anomalies (i.e., the climatic year) in the tropics. This monsoon year is defined as one year starting just before the northern summer monsoon season. It is also argued that this climatic year in the tropics is physically based upon the characteristic nature of the coupled ocean/land/atmosphere system over the Asian monsoon/Pacific Ocean sector.

On the remote forcing of the circulation in the Bay of Bengal

Abstract: The paper presents a hypothesis that the remote forcing is one of the mechanisms that determine the semiannual reversal of the upper ocean circulation in the Bay of Bengal. A simple reduced-gravity oceanic model is used to explain the hypothesis. Three numerical experiments have been performed to compare the oceanic responses to a remote forcing, a local forcing, and a combined forcing. It is found that the long Rossby waves excited by the remotely forced Kelvin waves contribute substantially to the variability of the local circulation. This research indicates that equatorial Kelvin waves are one of the major factors determining the circulation in the eastern equatorial Indian Ocean.

Evidence of Secular Variations in Indian Monsoon Rainfall–Circulation Relationships

Abstract: Detailed correlation analysis of the all-India monsoon rainfall and mean sea-level seasonal pressure at Bombay (19°N, 73°E) up to three lags on either side of the monsoon wren during the last 30 years (1951–80) indicates a systematic relationship. The winter-to-premonsoon (March, April, May–Deceinber, January, February; MAM–DJF) seasonal pressure tendency at Bombay shows a correlation coefficient (CC) of −0.70 (significant at 0.1% level) with the Indian monsoon rainfall. Further examination of this relationship over a long period of 144 years (1847–1990), using sliding correlation analysis, reveals some interesting features. The sliding CCs were positive before 1870, negative during 1871–1900, positive in the years 1901–40, and again negative later on, showing systematic turning points around the years 1870, 1900, and 1940. In light of other corroborative evidence, these climatic regimes can be identified as “meridional monsoon” periods during 1871–1900 and after 1940, and as “zonal monsoon” peri...

Methane flux to the atmosphere from the Arabian Sea

Abstract: ATMOSPHERIC concentrations of methane, an important greenhouse gas, have increased significantly over the past few decades1,2. Although attention has been focused on anthropogenic sources, data from ice cores show that large changes in atmospheric methane concentrations have occurred over glacial–interglacial time scales, indicating that there is significant variability in natural methane fluxes3,4. The surface waters of the oceans are often supersaturated with methane, which implies that the oceans are a net source, although their contribution to the global methane budget is small relative to other sources4. Here we report high concentrations of methane in the Arabian Sea, and calculate that the flux of methane to the atmosphere is up to five times greater than the previously reported average ocean flux. Methane production is associated with high phytoplankton biomass, which is closely coupled with the monsoon-driven upwelling of nutrient-rich water. We calculate that the Arabian Sea (representing 0.43% of the total surface area of the world's oceans) could account for between 1.3 and 133% of the current estimates of the open-ocean source of methane. Our results do not alter the view that the oceans are a relatively minor source of atmospheric methane, but the magnitude of the methane fluxes from the Arabian Sea and the link with the monsoon suggest that this region may be particularly sensitive to climate change, with a greater potential for feedback responses than its surface area might suggest.

A power regression model for long range forecast of southwest monsoon rainfall over India

Abstract: A detailed analysis of southwest monsoon (June to September) rainfall over India of several decades vis-a-vis the regional and global antecedent signals in numerous permutations and combinations has led the authors to conclude that a long range forecast based on one, two, three or four parameters as attempted by several workers in the past, cannot be reliable on all occasions as indeed has proved to be the case. The parametric and power regression models utilizing 16 parameters, described in the present paper, suggest that it is a tapestry of several parameters and interactive nature of the regional and global climatic forcings that govern the quality and quantity of the monsoon. A detailed analysis of non-linear interactions among the antecedent climatic conditions and the monsoon has led the authors to introduce the concept of proportionate weightage to the signals of different parameters. This has led to the development of a power regression model, which is able to quantify the effect of each parameter. Details of the model are presented, Based on the model, the India Meteorological Department has been issuing the operational long range forecast of monsoon rainfall over India as a whole during the past 3 years, 1988 to 1990, and these forecasts have proved to be correct.

The warm pool in the Indian Ocean

Abstract: The structure of the warm pool (region with temperature greater than 28°C) in the equatorial Indian Ocean is examined and compared with its counterpart in the Pacific Ocean using the climatology of Levitus. Though the Pacific warm pool is larger and warmer, a peculiarity of the pool in the Indian Ocean is its seasonal variation. The surface area of the pool changes from 24 × 106 km2 in April to 8 × 106 km2 in September due to interaction with the southwest monsoon. The annual cycles of sea surface temperature at locations covered by the pool during at least a part of the year show the following modes: (i) a cycle with no significant variation (observed in the western equatorial Pacific and central and eastern equatorial Indian Ocean), (ii) a single maximum/minimum (northern and southern part of the Pacific warm pool and the south Indian Ocean), (iii) two maxima/minima (Arabian Sea, western equatorial Indian Ocean and southern Bay of Bengal), and (iv) a rapid rise, a steady phase and a rapid fall (northern Bay of Bengal).

The environmental-effects of the uplift of the qinghai-xizang plateau

Abstract: The intense upheaval of the Qinghai-Xizang Plateau took place 2 Ma BP. The terraces of the Yellow River in the Lanzhou Region and its upper sections provide a record of the uplift of the Plateau. The interaction of glaciation cycles resulting from climatic changes and pulsating tectonic upheavals are both involved in the record of environmental change across the Plateau. Three tectonic-climatic events which are termed respectively the Qinghai-Xizang Movement, the Huanghe (Yellow River) Movement and the Gonghe Movement occurred 2-1.5, 1.0 and 0.15 Ma BP. The upheaval of the Qinghai-Xizang Plateau was the trigger mechanism of the Asian Monsoon. The Loess Plateau was formed in the monsoon triangle of east Asia. Human origins and human evolution may have been stimulated by the uplift of the Qinghai-Xizang Plateau.

Lithogenic fluxes to the deep Arabian sea measured by sediment traps

Abstract: Particle fluxes measured continously for one year at three locations in the Arabian Sea using time-series sediment traps show that lithogenic sedimentation processes are strongly coupled to biological processes. The vertical flux of lithogenic matter is controlled by episodic production and fluxes of biogenic matter. Illite and quartz are the dominant clay minerals in the traps at all three locations. Smectites generally range between 2 and 8%, but show higher fluxes up to 25% in the central and eastern Arabian Sea during the southwest monsoon period. Most of the river discharge is retained on the continental shelf, and less than 5% of the annual input of lithogenic material to the Arabian Sea is deposited in the deeper part as hemipelagic sediments.

One Million Year Record of Summer Monsoon Winds and Continental Aridity from the Owen Ridge (Site 722), Northwest Arabian Sea

Abstract: The upper 38 m of Hole 722B sediments (Owen Ridge, northwest Arabian Sea) was sampled at 20 cm intervals and used to develop records of lithogenic percent, mass accumulation rate, and grain size spanning the past 1 m.y. Over this interval, the lithogenic component of Owen Ridge sediments can be used to infer variability in the strength of Arabian Sea summer monsoon winds (median grain size) and the aridity of surrounding dust source-areas (mass accumulation rate; MAR in g/cm k.y."'). The lithogenic MAR has strong 100, 41, and 23 k.y. cyclicities and is forced primarily by changes in source-area aridity associated with glacial-interglacial cycles. The lithogenic grain size, on the other hand, exhibits higher frequency variability (23 k.y.) and is forced by the strength of summer monsoon winds which, in turn, are forced by the effective sensible heating of the Indian-Asian landmass and by the availability of latent heat from the Southern Hemisphere Indian Ocean. These forcing mechanisms combine to produce a wind-strength record which has no strong relationship to glacial-interglacial cycles. Discussion of the mechanisms responsible for production of primary Milankovitch cyclicities in lithogenic records from the Owen Ridge is presented elsewhere (Clemens and Prell, 1990). Here we examine the 1 m.y. record from Hole 722B focusing on different aspects of the lithogenic components including an abrupt change in the monsoon wind-strength record at 500 k.y., core-to-core reproducibility, comparison with magnetic susceptibility, coherency with a wind-strength record from the Pacific Ocean, and combination frequencies in the wind-strength record. The Hole 722B lithogenic grain-size record shows an abrupt change at 500 k.y. possibly indicating decreased monsoon wind-strength over the interval from 500 k.y. to present. The grain-size decrease appears to be coincident with a loss of spectral power near the 41 k.y. periodicity. However, the grain-size decrease is not paralleled in the Globigerina bulloides upwelling record, an independent record of summer monsoon wind-strength (Prell, this volume). These observations leave us with competing hypotheses possibly involving: (1) a decrease in the sensitivity of monsoon windstrength to obliquity forcing, (2) decoupling of the grain size and G. bulloides records via a decoupling of the nutrient supply from wind-driven upwelling, and/or (3) a change in dust source-area or the patterns of dust transporting winds. Comparison of the lithogenic grain size and weight percent records from Hole 722B with those from a nearby core shows that the major and most minor events are well replicated. These close matches establish our confidence in the lithogenic extraction techniques and measurements. Further, reproducibility on a core-to-core scale indicates that the eolian depositional signal is regionally strong, coherent, and well preserved. The lithogenic weight percent and magnetic susceptibility are extremely well correlated in both the time and frequency domains. From this we infer that the magnetically susceptible component of Owen Ridge sediments is of terrestrial origin and transported to the Owen Ridge via summer monsoon winds. Because of the high correlation with the lithogenic percent record, the magnetic susceptibility record can be cast in terms of lithogenic MAR and used as a high resolution proxy for continental aridity. In addition to primary Milankovitch periodicities, the Hole 722B grain-size record exhibits periodicity at 52 k.y. and at 29 k.y. Both periodicities are also found in the grain-size record from piston core RC11-210 in the equatorial Pacific Ocean. Comparison of the two grain-size records shows significant coherence and zero phase relationships over both the 52 and 29 k.y. periodicities suggesting that the strengths of the Indian Ocean monsoon and the Pacific southeasterly trade winds share common forcing mechanisms. Two possible origins for the 52 and 29 k.y. periodicities in the Hole 722B wind-strength record are (1) direct Milankovitch forcing (54 and 29 k.y. components of obliquity) and (2) combination periodicities resulting from nonlinear interactions within the climate system. We find that the 52 and 29 k.y. periodicities show stronger coherency with crossproducts of eccentricity and obliquity (29 k.y.) and precession and obliquity (52 k.y.) than with direct obliquity forcing. Our working hypothesis attributes these periodicities to nonlinear interaction between external insolation forcing and internal climatic feedback mechanisms involving an interdependence of continental snow/ice-mass (albedo) and the hydrological cycle (latent heat availability).

Response of a monsoon forest‐savanna boundary to fire protection, Weipa, northern Australia

Abstract: A numerical floristic analysis of samples across a monsoon forest‐savanna boundary, from an area that had been actively protected from fire for 15 years, at Weipa, northern Australia, revealed three communities: (i) a monsoon forest with a low closed canopy composed mainly of tree species with extra‐Australian tropical affinities and a sparse ground layer; (ii) an ecotone with a distinct closed microphyll shrub layer beneath the open canopy of savanna trees; and (iii) a savanna dominated by Eucalyptus tetrodonta. The development of the ecotone has occurred since fire protection and is of limited extent within the fire protected block. The monsoon forest occurred on soils with significantly higher concentrations of bauxitic pisoliths than the other two communities. Soils under the monsoon forest had significantly higher concentrations of total K, S, C, N, exchangeable K and Ca, and higher pH and electrical conductivity than for soils of either of the other communities. A positive relationship between woody basal area and concentrations of surface soil total P, N, C, exchangeable Ca, CEC and gravel was detected across a 20 m transect from the ecotone community into the savanna. The invasion of monsoon forest seedlings was greatest in the ecotone, with few occurring in the savanna. It appears that the expansion of the monsoon forest requires the development of a layer of shrubs. The mechanism of this facilitation is unclear, although the possible role of nutrient enrichment by the shrubs requires further investigation.

Late quaternary forcing of Indian Ocean summer-monsoon winds : a comparison of Fourier model and general circulation model results

Abstract: Past fluctuations in the strength of summer monsoon winds in the Arabian Sea can be inferred from the grain size of lithogenic material blown in from the peripheral deserts. We partition a 400 kiloyear (kyr) time series of inferred wind strength into its dominant frequency components, and develop a Fourier model to evaluate the relative influence of potential monsoon forcing mechanisms operating over these dominant frequencies. Our results indicate that the primary external and internal forcing mechanisms determining the timing and strength of Arabian Sea monsoon winds over the late Quaternary are (1) solar insolation and (2) latent heat collected from the southern subtropical Indian Ocean and released over the Asian Plateau. Our results further suggest that the extent of glacial conditions plays only a minor role in determining the timing and strength of the Arabian Sea paleomonsoon. In contrast, sensitivity experiments using the National Center for Atmospheric Research community climate model (NCAR CCM) indicate that glacial boundary conditions play a dominant role in forcing the strength of Arabian Sea paleomonsoon winds. Such inconsistencies are illustrated by comparing CCM wind strengths to those inferred from geological data. CCM monsoon winds in the Arabian Sea are uniformly strong during interglacial oxygen isotope stages 1 and 5 and weak during glacial stage 2. The geological record, in contrast, indicates strong and weak monsoons during both glacial and interglacial stages. Examining CCM monsoon strength in the context of latent heat flux versus regional sea surface temperatures (SST) suggests that these discrepancies may be attributed to incorrect ocean-atmosphere heat transfer in the southern hemisphere, possibly associated with the effects of prescribed model SST fields.

Interannual Variability of the Australian Summer Monsoon Onset: Possible Influence of Indian Summer Monsoon and El Niño

Abstract: The date of Australian summer monsoon onset (ASMO) is found to be well correlated with the monsoon rainfall of India during the preceding June to September. Years of below (above) normal Indian summer monsoon rainfall (ISMR) are followed by delayed (early) ASMO. Sea surface temperature (SST) anomalies during the September to November season over the tropical Indian Ocean, the equatorial eastern Pacific Ocean, and the ocean north of Australia also correlate significantly with the date of the following ASMO. Delays in ASMO are associated with cold SST north of Australia and warm SST in the tropical Indian and equatorial cast Pacific oceans. Previous studies have shown that a warm SST is created over the tropical Indian Ocean in years of poor ISMR. We hypothesize that a warm SST anomaly over the Indian Ocean delays the seasonal southward and eastward migration of the cloudiness maximum. A delay in the southeastward movement of cloudiness results in a delayed ASMO. A similar hypothesis already has be...

The sensitivity of sub-Saharan precipitation to Atlantic SST

Abstract: The climate model of the Goddard Institute for Space Studies (Hansen et al., 1983) is used to study the sensitivity of sub-Saharan rainfall to Atlantic Ocean SST. Initial changes of SST in the South Atlantic Ocean on March 1st are shown to reduce the June–August sub-Saharan precipitation totals using the model version with an interactive ocean that updates SST. Evidence is offered in support of theories that link Sahel drought with anomalously warm SST in the eastern South Atlantic and the study compares the model's response to spatially coherent SST anomalies with the response to random SST perturbations. The physical processes whereby SST and sea-level pressure synoptics influence the African summer monsoon are discussed in reference to the simulations. Predictibility of Sahel summer rainfall based on spring SST patterns or spring atmospheric circulation patterns is implied by the results. The SST/Sahel drought links are discussed for projections of future climate characteristics.

Sensible climates in monsoon Asia.

Abstract: This study identifies characteristics of the geographical distribution of sensible climates and their diurnal and annual variations, and presents a classification of bioclimates in monsoon Asia by using Kawamura's discomfort index formula During the hottest month, tropical areas and areas in central and South China are uncomfortable for humans throughout the day and night, and temperate zones in lowlands are uncomfortable during the daytime Tropical zones are uncomfortable all year long and temperate zones in lowlands are uncomfortable during summer Four climatic types were distinguished in monsoon Asia Climatic type I, hyperthermal throughout the year, occurs in the tropics south of latitude 20° N Climatic type II, hyperthermal in the hottest month and comfortable in the coldest month, extends over latitudes from 20° to 30° N except in the highlands Climatic type III, hyperthermal in the hottest month and hypothermal in the coldest month, encompasses temperate zones of East Asia and subtropical arid areas of northwestern India Climatic type V, comfortable in the hottest month and hypothermal in coldest month, occurs near the southeast coast of the Soviet Union and in the highlands of the Himalayas