Showing papers on "Monsoon published in 1985"

Aspects of the 40–50 Day Oscillation during the Northern Summer as Inferred from Outgoing Longwave Radiation

Abstract: Intraseasonal variability Of tropical convection over the Indian Ocean/Pacific region during northern summer is studied using outgoing longwave radiation (OLR). OLR anomalies are found to propagate eastward along the equator from the Indian 0cean to the western Pacific and northward towards the Indian subcontinent and southern China. It is found that the dominant mode of tropical convection consists of a dipole with centers located over the Indian 0cean and the western Pacific/South China Set. This dipole undergoes complex structural changes over a broad period range centered around 40–50 days. During a typical oscillation, an anomaly first develops over the equatorial Indian Ocean. This anomaly then extends eastward to the equatorial western and central Pacific to form an elongated convection zone, while its center is displaced progressively northward from the Indian Ocean into the Indian subcontinent by an anomaly of the opposite sign. The elongated convection zone over the western Pacific then...

Climate dynamics of the tropics

Abstract: 1. Introduction.- References.- 2. Diurnal Forcings and Local Circulations.- 2.1. Insolation and Heat Budget Forcing.- 2.2. Atmospheric Tides.- 2.3. Circulations on the Local and Meso-Scale.- 2.4. Diurnal Marches of Sea-Air Exchange, Cloudiness, and Precipitation.- 2.5. Synthesis.- References.- 3. Planetary Scale Atmospheric Circulation.- 3.1. Mean Meridional Distribution of Temperature and Humidity.- 3.2. Zonal Wind Regime.- 3.3. Mean Meridional Circulation.- 3.4. Maintenance of the Global Circulation: Angular Momentum.- 3.5. Maintenance of the Global Circulation: Kinetic Energy.- 3.6. Synthesis.- References.- 4. Ocean Circulation.- 4.1. Wind Stress and Motion Field in the Upper Ocean.- 4.2. The Subtropical Gyres.- 4.3. Equatorial Current Systems.- 4.3.1. Overview of Surface Circulation.- 4.3.2. Balance of Forces.- 4.3.3. The North Equatorial Countercurrent.- 4.3.4. Wind Stress, Vertical Motion, Thermocline and Surface Topography.- 4.3.5. The Equatorial Undercurrent.- 4.3.6. Equatorial Waves and Remote Forcing.- 4.3.7. Recent Discoveries of Subsurface Currents.- 4.4. The Monsoon Ocean.- 4.5. Deep Circulation.- 4.6. Synthesis.- References.- 5. Heat and Water Budgets.- 5.1. Basic Theory.- 5.2. Net Radiation at the Top of the Atmosphere.- 5.3. Oceanic Heat Budget.- 5.4. Atmospheric Heat Budget.- 5.5. Water Budget.- 5.6. Relative Roles of Oceanic Versus Atmospheric Heat Transports.- 5.7. Synthesis.- References.- 6. Regional Circulation Systems.- 6.1. Overview of the Global Tropics.- 6.2. Jet Streams.- 6.2.1. Basic Dynamics.- 6.2.2. Subtropical Westerly Jet.- 6.2.3. Tropical Easterly Jet.- 6.2.4. West African Mid-Tropospheric Jet.- 6.2.5. East African Low Level Jet.- 6.3. Subtropical Highs.- 6.4. Trades.- 6.5. Trade Inversion.- 6.5.1. Spatial Patterns.- 6.5.2. Origin and Maintenance.- 6.5.3. Climatic Implications.- 6.6. Mid-Tropospheric Inversions.- 6.7. Equatorial Trough Zone.- 6.7.1. The Large-Scale Setting.- 6.7.2. Structure of the Intertropical Convergence Zone.- 6.7.2.1. Atlantic and Pacific Oceans.- 6.7.2.2. Indian Ocean.- 6.7.2.3. Africa.- 6.7.2.4. On Atmospheric and Oceanic Controls.- 6.7.3. Dynamics of Cross-Equatorial Flow.- 6.7.4. Equatorial Dry Zone.- 6.8. Monsoons.- 6.8.1. Definition and Global Perspective.- 6.8.2. Africa.- 6.8.3. Indian Ocean Sector.- 6.8.4. On the Heat and Moisture Budget of the Indian Monsoons.- 6.8.5. Numerical Modelling of the Indian Summer Monsoon.- 6.9. Zonal Circulations.- 6.10. Upper-Tropospheric Anticyclones.- 6.11. Wind Regimes of the Equatorial Stratosphere.- 6.12. Synthesis.- References.- 7. Climatology of Weather Systems.- 7.1. Clouds and Convection.- 7.2. Tropical Storms.- 7.3. Waves in the Easterlies.- 7.4. Squall Lines.- 7.5. Dust Storms of the Sudan.- 7.6. Monsoon Depressions.- 7.7. Subtropical Cyclones.- 7.8. Temporales of Pacific Central America.- 7.9. Cold Surges.- 7.10. Interannual Variability.- 7.11. Synthesis.- References.- 8. Interannual Variability of the Atmosphere-Ocean System.- 8.1. Surface Patterns of the Southern Oscillation.- 8.2. El Nino.- 8.3. Upper-Air Patterns of the Southern Oscillation.- 8.4. Rainfall Anomalies in Indonesia.- 8.5. Vagaries of the Indian Monsoon.- 8.6. The Secas of Northeast Brazil.- 8.7. Rainfall Variations in the Central American - Caribbean Region.- 8.8. Drought and Flood Regimes in Subsaharan Africa.- 8.9. Climate Anomalies at the Angola Coast.- 8.10. Hydrometeorological Anomalies in the Zaire (Congo) Basin.- 8.11. Time Scales of Climate Variability.- 8.12. Synthesis.- References.- 9. Climate Prediction.- 9.1. Indian Monsoon.- 9.2. Indonesian Rainfall.- 9.3. Hong Kong Climate.- 9.4. Southern Africa.- 9.5. Kenya Rainfall.- 9.6. Sahel Drought.- 9.7. The Droughts of Northeast Brazil.- 9.8. Rivers of Northern South America.- 9.9. El Nino.- 9.10. Tropical Storms.- 9.11. Numerical Modelling.- 9.12. Biological Consequences.- 9.13. Synthesis and Outlook.- References.- 10. The Human Impact.- 10.1. Deforestation.- 10.2. Land Use and Surface Albedo.- 10.3. Effects of Dust on Climate.- 10.4. Intentional Climate Modification.- 10.5. Ocean Climate and Fisheries.- 10.6. India.- 10.7. Northeast Brazil.- 10.8. Subsaharan Africa.- 10.9. The Use of Climate Prediction.- 10.10. Synthesis.- References.- 11. Tropical Glaciers and Climate.- 11.1. Spatial Patterns.- 11.2. History of Glacier Variations.- 11.3. Climatic Forcing and Terminus Response.- 11.4. Ice Cores.- 11.5. Synthesis.- References.- 12. Past Climates Of The Tropics.- 12.1. Causes of Climate Variations.- 12.2. Vegetation.- 12.3. Lakes.- 12.4. Glaciers.- 12.5. Deep-Sea Cores.- 12.6. Pacific and Australasia.- 12.7. The Indian Ocean and Surrounding Continents.- 12.8. Africa and the Adjacent Tropical Atlantic.- 12.9. Americas.- 12.10. Numerical Modelling.- 12.11. Synthesis.- References.- Author Index.

Summer Monsoon Experiment—A Review

Abstract: This paper presents a short summary of the Summer Monsoon Experiment (MONEX). The review is largely based on those papers that have made use of the summer MONEX observations during 1979. 0bservational aspects of this study emphasize the annual march of the monsoon rainfall belt from Indonesia to the foothills of the Himalayas, from the northern winter to the northern summer season and a reverse motion thereafter. The excellent FGGE/MONEX data sets have provided a detailed definition of the divergent wind; these are summarized with reference to the Hadley and the Walker circulations. The manner in which monsoonal circulations respond to the evolving differential heating fields are presented via the mutual interactions among the rotational and divergent wind components. Specific examples of heat sources from the studies of Luo and Yanai highlight their contrast over different regions of the monsoon including the Tibetan Plateau. A problem of considerable interest in this context is the cooling of t...

Global Water Vapor Flux and Maintenance during FGGE

Abstract: The relative humidity, temperature and wind fields generated by the First Global GARP Experiment (FGGE) III-b analysis of the Geophysical Fluid Dynamics Laboratory (GFDL) are used to examine the global precipitable water distribution, and the water vapor transport and maintenance for two extreme seasons of atmospheric circulation, i.e., December–February and June–August 1979. It has been observed that the major water vapor content exists in tropical areas, especially over three regions: equatorial Africa, the northern part of South America, and equatorial western Pacific in December-February; equatorial Africa, Central America and the northern part of South America, and monsoon areas in June-August. The water vapor transport was analyzed to explore how the high water vapor content of these areas is maintained by the large-scale atmospheric circulation. It is concluded that 1) the nondivergent stationary mode describes most of the atmospheric water vapor transport; 2) the stationary divergent mode...

Late-Quaternary climatic change on the American North Pacific Coast

Abstract: The late Quaternary climate of the North Pacific, where according to modelling the solar radiation in the early Holocene at the time of the summer solstice is high and in the late Holocene is relatively low, is investigated. Quantitative temperature and precipitation estimates from southern Alaska are compared with estimates from western Washington and British Columbia. Data extending over more than 10,000 years show a broadly consistent pattern of climatic change in general agreement with predicted variations in solar radiation and their effect on atmospheric circulation and seasonal duration of pressure systems over the North Pacific Ocean. In the early Holocene, the subtropical North Pacific anticyclone annually regulated climate for a longer period at higher latitudes than at present, so that warmth and dryness increased in southern Alaska. The Aleutian low-pressure center intensified during the late Holocene, resulting in colder and more humid coastal climate and increased frequency of glacier growth in the cordillera.

Seasonal relationships between indian summer monsoon rainfall and the southern oscillation

Abstract: Association between the all-India summer monsoon (June to September) rainfall and an index of the Southern Oscillation (SO) is studied in relation to the vagaries of the monsoon rainfall and the seasonal characteristics of the SO. The SOI values of different months and standard seasons show opposite tendencies during deficient and excess years of all-India monsoon rainfall. The correlation coefficients between the all-India monsoon rainfall series and the SOIs of summer monsoon, autumn and winter minus spring seasons are significant at the 1 per cent level.

The Atmospheric Heat Source over the Tibetan Plateau: May–August 1979

Abstract: Estimates of the time and space variability of the atmospheric heat source over Tibet are presented for the summer of 1979. These estimates rely on new data from the People's Republic of China allowing a better assessment of the surface heat fluxes, and on new satellite data from Nimbus-7 giving the radiation balance at the top of the atmosphere. The estimates of the atmospheric heat source turned out to be considerably smaller than those provided earlier in the literature, mainly because of different assumptions of the drag coefficient. The atmospheric heat source over Tibet is mainly modulated by the release of latent heat. Over the southeastern and southwestern plateau regions the heat source appears to be in phase with the precipitation yield of the Indian summer monsoon, whereas central Tibet reveals an out-of-phase behavior. Over western Tibet there appears to be hardly any net import of moisture from outside the region, whereas the maintenance of the hydrological cycle over eastern Tibet requires moisture flux convergence from outside the region of up to 40 percent of the mean rainfall, in agreement with what is known about the surface hydrology of Tibet.

Influence of Local Land-Surface Processes on the Indian Monsoon: A Numerical Study

Abstract: Integrations made with general circulation models to investigate the influence of changes in the land-surface fluxes, over the Indian subcontinent, on the monsoon circulation and rainfall are presented. The experiments conducted include: (1) a control, (2) increased land-surface albedo, (3) increased land-surface albedo and reduced land-surface roughness, and (4) increased land-surface albedo, reduced surface roughness, and no evapotranspiration. A comparison of ensemble means of the data is provided; a decrease in rainfall is observed when the surface albedo is increased and the surface roughness reduced. Low surface roughness makes the horizontal transport of planetary boundary layer (PBL) westerly, reducing cross-isobaric moisture and thereby rainfall. Evapotranspiration had no influence on rainfall because of the PBL motion and moisture convergence. The correlation between surface albedo, surface roughness and vegetation is examined.

Tropical 45 Day Oscillations during the 1979 Northern Hemisphere Summer

Abstract: Based on FGGE 1,cvel IIIb data, the structural features of 45 day perturbations over a tropical belt (15°N-15°S) during the 1979 summer are detailed. At the equator, 45 day perturbations which are primarily associated with the zonal wind components of wavenumber 1, propagate eastward (8° of longitude per day) and upward (0.7 km per day), probably indicating downward energy flux. In the Southern Hemisphere tropics (0°–15°S), the 45 day zonal mean wind perturbations propagate downward with an approximate phase speed of 0.8 km per day. In the Northern Hemisphere tropics, they are largely of standing character with the maximum amplitude (3 m s−1) near 200 mb at 15°N. There exists a strong association between monsoon activity over South Asia and changes in the intensity of the equatorial Walker circulation. When active monsoons occur over South Asia, the Walker circulation becomes stronger than usual with prominent 850 mb easterlies (200 mb easterlies) over the eastern Pacific east of the date line an...

The separate contributions of line squalls, thunderstorms and the monsoon to the total rainfall in nigeria

Abstract: Using thunderstorm and rainfall information from five Nigerian stations for a five year period, the separate contributions of line squalls, thunderstorms and ordinary monsoons to the total rainfall and their variations with latitude are investigated. Total and thunderstorm rainfall decreases with increasing latitude but monsoon precipitation decreases exponentially while line squall rainfall is at a maximum around 9°N. Rainfall from thunderstorms shows a single annual peak in July/August at stations north of about 8°N whereas line squall precipitation exhibits a double maximum for all stations south of 12°N. It is also shown that, in the mean, line squalls are the most important rain producing systems, giving 47-6 per cent of the mean total annual precipitation compared with 39 per cent and 13-4 per cent from thunderstorms and ordinary monsoon rain, respectively.

Cross-Equatorial Influence of Winter Hemisphere Subtropical Cold Surges

Abstract: Two case studies are presented of winter hemisphere cold surges affecting the summer hemisphere tropics. One case has been chosen from each of the Northern and Southern Hemispheres. In both instances, the subtropical rise in pressure is tracked equatorward. This leads to a pressure rise at the equator and the establishment of a west–east pressure gradient at low latitudes in the opposite hemisphere. These effects lead in turn to an enhanced cross-equatorial component of flow and enhanced monsoon westerly flow in the summer hemisphere. Both enhanced wind flow effects are observed through a deep layer from the surface up to at least 500 mb. In both cases, the sequence of events also includes the development of a tropical cyclone in the summer hemisphere monsoon trough. The generality of the above sequence of events is investigated with time series data for several seasons. It is shown that day-to-day changes in equatorial pressure are significantly correlated to pressure changes in the winter hemis...

Monthly-mean wind stress along the coast of the north Indian Ocean

Abstract: Monthly-mean wind stress and its longshore and offshore components have been computed using the bulk aerodynamic method for each of a string of 36 two-degree-latitude by two-degree-longitude squares along the coast of the north Indian Ocean. The data source for the computation is the sixty-year mean resultant winds of Hastenrath and Lamb. The main features exhibited by the components, taking the longshore components as positive (negative) when the Ekman transport is away from (towards) the coast, are: (1) Along the coasts of Somalia and Arabia, the magnitude of the wind stress is among the highest in the north Indian Ocean, and its direction is generally parallel to the coastline. This results in a longshore component which is large (as high as 2·5 dyne/cm2) and positive during the southwest monsoon, and weaker (less than 0·6 dyne/cm2) and negative during the northeast monsoon. (2) Though weak (less than 0·2 dyne/cm2) during the northeast monsoon, the monthly-mean longshore component along the west coast of India remains positive throughout the year. The magnitude of the offshore component during the southwest monsoon is much larger than that of the longshore component. (3) The behaviour of the wind stress components along the east coast of India is similar to that along the Somalia-Arabia coast, but the magnitudes are much smaller.

On the structure of the 30 to 50 day mode over the globe during FGGE

Abstract: 6 vertical levels of the entire 365-day global FGGE Illb analysis for 5 variables are subjected to a time-series analysis and a frequency filter to investigate the structure of the 30- to 50-day mode. This study isolates regions where the amplitude of these low-frequency oscillations are large; the vertical structures across these large amplitude regions are also presented. The seasonal variation of the maximum 30–50 day filtered wind in the lower troposphere is highlighted. The major results for the FGGE year show that the 30- to 50-day mode has its largest amplitude in the upper troposphere of polar latitudes and in the summer monsoon region. During the northern winter, active regions are also located over the equatorial belt of the central Pacific ocean. The phase propagation on the pressure surfaces are examined simply from an analysis of a time sequence of low-frequency weather maps. The vertical phase propagation is illustrated by pressure-time plots of the low-frequency data sets at individual locations. This analysis suggests vertical propagation over convective areas and a lack of it over most other regions. A highlight of this study is a phenomenon we have labelled as “low-frequency storms”. Here we illustrate long-lasting, low-frequency, weather systems that propagate meridionally (1) over the summer monsoon regions from the equator to the Himalayas and (2) over the eastern Pacific ocean from the equator northwards during the northern winter season. An example of such a long-lasting system is traced to 60° N; subsequently, it appears to move zonally from the gulf of Alaska across the Canadian Arctic, north Atlantic, and Europe prior to its dissipation over Siberia. The potential for interactions between these low-frequency systems and polar front cyclones is another interesting aspect of this investigation. The low-frequency oscillations and motions are considered important since their amplitude in the troposphere is large (8 ms -1 ) and they are well-defined within their scales of motion (on the order of 4000 km or larger). DOI: 10.1111/j.1600-0870.1985.tb00432.x

Surface circulation over the shelf off the east coast of India during the south west monsoon

Abstract: From the hydrographic data collected on board R V Gaveshant in the western Bay of Bengal during Aug.-Sept. 1978, fields of temperature, salinity aud density have been constructed and the probable flow regime has been deduced. The studies indicate strong upwelling in the southern regions off the east coast of India. Vertical temperature and salinity structures north of Visakhapatnam show a predominant estuarine character and upwelling is not evident. In the northern regions, the flow is directed south and is consonant with that derived from wind stress curl distribution.

Quasi-Biennial Oscillation in Stratospheric Zonal Wind and Indian Summer Monsoon

Abstract: In an earlier study a relationship was pointed out between phases of the quasi-biennial oscillation (QBO) in the lower stratospheric (30 mb) zonal wind and percentage departures of summer monsoon rainfall of India. That study was based on analysis of wind data for Thumba (8°32′N, 76°52′E) and the rainfall data for India for a short-period (1971–76). Wind data for Balboa (9°N, 80°W), which is also an equatorial station, and rainfall activity over India are now examined for a longer period (1951–82). About 15% of the variability in rainfall over India during the summer monsoon is associated with the pattern of the QBO.

July-August rainfall in West-Central Kenya

Abstract: The annual rainfall distribution in west-central Kenya (34°−38°E, 1°N–1°S) exhibits marked spatial variation because of the complicated nature of the local topography. The annual distributions are classified into a number of types on the basis of ‘rainfall seasons’. Over parts of the area of study, precipitation falling in July and August makes an important contribution to the yearly total (up to 33 per cent). The spatial variation of the rainfall in this period, during the so-called ‘dry season’ over much of Kenya (between the two main ‘monsoon’ rains) is examined in some detail, especially its relationship with altitude. The distribution of the July and August rainfall indicates that it is associated with a westerly airstream overlying the lowest layers of the atmosphere.

Synoptic and satellite aspects of the southwestern u.s. summer ‘monsoon’

Abstract: Satellite infrared imagery for three years (1980, 1981, 1982) are analysed using a colour enhancement technique to derive a cloud climatology of the southwest United States summer ‘monsoon’ Diurnally-stratified and weekly statistics are obtained for different cloud levels and used as an index of the monsoon intensity in each year Strong diurnal variations in cloudiness, related to surface heating, are identified for July and August, as are marked interannual differences These regional-scale cloud variations are found to correlate more closely with the 700mb wind direction than with the height of the 700 mb pressure surface when considered for a representative station (Winslow, Arizona) A satellite-based definition of ‘monsoon’ best considers variations of the total cloud rather than of any individual cloud level(s) Several surface and 700 mb synoptic circulation indices are identified and related statistically to the intraseasonal cloudiness changes The most significant association is found for the variations in latitude of the Bermuda high pressure ridge that presumably relates to changes in subsidence However, the sign of this relationship may reverse in years when other circulation systems, notably the North Pacific anticyclone, also influence the desert Southwest Consideration of the zonal westerly index between 45 and 65°N tends to improve the correlation between the Bermuda ridge and summer monsoon cloudiness over the region Such cloud-circulation studies have implications not only for climate dynamics but also for ongoing solar energy research in the American Southwest

Surface currents in the Mozambique channel

Abstract: The average surface current conditions of the Mozambique Channel and adjacent waters derived from shipdrift data are described for the two seasons November to April and May to October for a 1° grid. The South Equatorial Current was most intense during the southwest monsoon season while the East Madagascar Current and the Mozambique/Agulhas Current had maximum current speed during the northeast monsoon season.

Transition from the Southern to Northern Hemisphere Summer Monsoon

Abstract: During the period from 15 February to 20 June 1979, the northward migration of the zones of low outgoing longwave radiation was most clearly defined over the convectively active continental regions of equatorial Africa, the maritime continent, and equatorial South America. Regionally, the withdrawal of the Southern Hemisphere summer monsoon over Indonesia and Australia was followed by the first establishment of the summer monsoon over the Malaysian Peninsula during the midtransition around 15 April, which is about two months earlier than the monsoon onset over central India. In investigating the wind changes during the transition period, smoothed time-series data were constructed by adding three components of winds; viz., the annual mean winds, which are approximately symmetric about the equator; and the yearly and half-yearly wind harmonics that are asymmetric about the equator with a distinct seasonal character. The 200 mb wind patterns during the midtransition exhibit new symmetric character w...

The concentration of particulate aluminum and clay minerals in aerosols from the northern Arabian Sea

Abstract: Aerosol samples have been collected from the northern Arabian Sea during the northeast monsoon. Total atmospheric Al concentrations ranged between 323 and 20,300 ng m-3 of air; these are among the highest found over marine regions and demonstrate that the atmosphere is an important pathway for the transport of crustal material to the northern Arabian Sea and the Gulf of Oman. The clay mineralogy of the soil-sized particulates in the aerosol is similar to that of the surface sediments underlying the collection region but is different from that of the other sediments in the Arabian Sea. The clay mineral data provide evidence supporting previously proposed theories that the relatively high concentrations of chlorite in the sediments of the northern Arabian Sea and the Gulf of man are a consequence of the atmospheric transport of crustal material from the adjacent land masses.

Interannual and long-term variability of the summer monsoon and its possible link with northern hemispheric surface air temperature

Abstract: Some statistical properties of the summer monsoon seasonal rainfall for India during the last 100 years (1881–1980) are presented. The most recent decade of 1971–1980 shows the lowest value of standard-decadal average monsoon rainfall (86.40 cm) and is also characterised by the second highest value of coefficient of variation in monsoon rainfall (12.4 %). The combined last two standard-decadal period of 1961–1980 was the period of the largest coefficient of variation and the lowest average monsoon rainfall for India.

The south to north progression of rainfall anomalies across India during the summer monsoon season

Abstract: The low frequency spatio-temporal intraseasonal evolution of monsoon rainfall over India is studied by considering the pentad rainfall averages taken over 2.5° wide and 5.0° long blocks lying across the central longitudinal and latitudinal transacts. The time-latitude cross sections show south to north progressions of rainfall anomalies with a recurrence period of about 40 days. The progressions show considerable inter-annual and intra-seasonal variation in frequency, amplitude and rate of progression. The extended empirical orthogonal function analysis shows that the first two most important functions correspond to this northward progression of rain anomalies recurring after an interval of about 40 days. The rate of progression of anomalies is about 0.5° Lat./day. The time-longitude cross sections show the movement of rainfall anomalies towards both directions east and the west, with slight preference towards the east. The importance of these signals in rainfall forecasting is foreseen.

Onset of the south-west monsoon and sea-surface temperature anomalies in the Arabian Sea

Abstract: In 1979, the year of the Global Weather Experiment, the atmosphere and ocean of the monsoon region were particularly well observed For this reason, the onset period of the monsoon, 11–19 June 1979, was selected for international comparison of numerical prediction models1 Previous studies2–4 have demonstrated that successful predictions for this period are difficult to achieve I report here two examples of numerical predictions that highlight the role of sea-surface temperatures, namely a control forecast using climatological sea-surface temperatures and an anomaly forecast using more realistic (and warmer) surface temperatures specified for the eastern Arabian Sea It is shown that the use of the more accurate sea-surface temperatures enables a better prediction of the development of a monsoon depression to be obtained

The Somali Current in autumn 1984, before the onset of the north-east monsoon

Abstract: The Somali Current undergoes vigorous variations during the course of the south-west monsoon Although the initial phases of this response were fairly intensively studied during the FGGE Indian Ocean Experiment (INDEX) in 19791,2, relatively little is known about what happens in the late summer monsoon and the transition to the winter monsoon In October 1984, we carried out measurements in the Somali Current regime with a shipboard acoustic Doppler current profiler which showed that a continuous Somali Current did not exist at this time: instead, the cross-equatorial flow with a transport of 12 × l06 m3 s−1 in the upper 100 m identified by relatively low surface salinities, was found to turn offshore south of 2° N Between 6 and 11° N, a large closed anticyclonic gyre, marked by relatively high surface salinities, was found with a transport of 32 × 106 m3 s−1 in the upper 250 m, which is significantly greater than previously estimated from geostrophic calculations