Showing papers on "Monsoon published in 1980"

On the Maximum Cloud Zone and the ITCZ over Indian, Longitudes during the Southwest Monsoon

Abstract: An investigation is presented of the daily variation of the maximum cloud zone (MCZ) and the 7W mb trough in the Northern Hemisphere over the Indian longitudes 70–90°E during April–October for 1973–77. It is found that during June–September there are two favorable locations for a MCZ over these longitudes–on a majority of days the MCZ is present in the monsoon zone north of 15°N, and often a secondary MCZ occurs in the equatorial region (0–10°N). The monsoon MCZ gets established by northward movement of the MCZ occurring over the equatorial Indian ocean in April and May. The secondary MCZ appears intermittently, and is characterized by long spells of persistence only when the monsoon MCZ is absent. In each of the seasons studied, the MCZ temporarily disappeared from the mean summer monsoon location (15–28°N) about four weeks after it was established near the beginning of July. It is reestablished by the northward movement of the secondary MCZ, which becomes active during the absence of the monsoo...

Some aspects of the large scale fluctuations of summer monsoon rainfall over India in relation to fluctuations in the planetary and regional scale circulation parameters

Abstract: Year-to-year fluctuations of summer monsoon (June–September) rainfall of India are studied in relation to planetary and regional scale features. Anomalous epochs in the monsoon rainfall have been found to coincide with the epochs having anomalous patterns of temperature distribution in the northern hemispheric extratropics as well as with the spells of years having anomalous patterns of sea surface temperature distribution in the equatorial Pacific Ocean (EL-Nino phenomenon). Relationship between monsoonal rainfall and regional atmospheric circulation features is studied by compositing data of five good and five bad monsoon rainfall years over India. A comparison of the two data sets yields interesting relationships between the anomalous patterns of rainfall on the one hand and atmospheric parameters on the other. On the average parameters of monsoon depressions are more or less the same among the two types of composites. The most important distinguishing feature of good monsoon years is the greater frequency of cyclogenesis (monsoon lows included) on the regional scale which keeps the monsoon trough near its normal position and with concomitant higher cyclonic vorticity in the trough zone contributes to greater seasonal rainfall on the regional scale during good monsoon years.

Large-Scale Droughts/Floods and Monsoon Circulation

Abstract: An objective numerical drought index based on monthly monsoon rainfall and duration has been developed for assessment of drought intensity. The drought intensity equation serves the dual purpose of assessing the intensity of drought as well as flood. The Drought Area Index (DAI) is defined as the percentage area of India having a mean monsoon index ≤ −2 (i.e., moderate or higher drought severity). Likewise, the Flood Area Index (FAI) is the percentage area of India with mean monsoon index ≥ +2 (i.e., moderate or more severe wetness), where the mean monsoon index is the mean drought index for the four monsoon months. A year is defined as a large-scale drought or flood year when DAI or FAI ≥ 25. Using the evolved criteria, years of large-scale drought and flood over India have been identified during the period 1891–1975. The method adopted for defining large-scale drought or flood does bear out the actual experience. Power spectrum analysis reveals a weak triennial cycle in DAI series and a highly ...

The Structure and Vorticity Budget of an Early Summer Monsoon Trough (Mei-Yu) over Southeastern China and Japan

Abstract: One of the most persistent rain-making events over East Asia is the development of an early summer monsoon trough (Mei-Yu) which extends from southeastern China to southern Japan. This work studies the structure and vorticity budget of a Mei-Yu system for the period 10–15 June 1975. Subjectively analyzed grid-point data are time composited with respect to the trough axis along three cross sections over southeastern China (western section), southern East China Sea (central section) and southern Japan (eastern section), respectively, during the mature and decaying stages of the trough. The results indicate that the structure of the eastern and central sections resembles a typical midlatitude baroclinic front with strong vertical tilt toward an upper level cold core and a strong horizontal temperature gradient. On the other band, the western section resembles a semitropical disturbance with an equivalent barotropic, warm core structure, a weak horizontal temperature gradient, and a rather strong hor...

The albedo of a tropical evergreen forest

Abstract: The diurnal variation of the average albedo, during 1970, over a tropical dry evergreen forest and a nearby clearing was investigated. The study is based on a most comprehensive set of solar radiation data in Southeast Asia. A strong dependence of the albedo on the zenith angle is evident. This dependence is subdued during cloudy days. The average midday albedo for the winter monsoon season is 10.6 for the forest and 13.4 for the clearing; for the summer monsoon it is 12.0 for the forest and 14.6 for the clearing. Generally, results show great uniformity. The largest standard deviations are 0.05 with a more representative value in the range 0.01–0.02.

Arabian Sea Cooling: A Preliminary Heat Budget

Abstract: To assess the importance of possible feedbacks between ocean and atmosphere in the Arabian Sea, we computed a preliminary heat budget for the upper ocean layer. The observed total heat loss during the Southwest Monsoon between April and August is essentially balanced by three phenomena: positive heat gain from the atmosphere, negative northward heat flux across the equator, and heat loss due to upwelling along the coasts of East Africa and Arabia. Upwelling constitutes the dominant factor and the question is discussed as to which processes replenish the cold upwelled water on a seasonal time scale. The average annual heating rate above and beyond seasonal fluctuations is found to be 24 W m−2. This net heat input must be compensated by ocean currents. The manner in which the ocean accomplishes this remains to be clarified.

Himalayan and Trans-Himalayan Glacier Fluctuations and the South Asian Monsoon Record

Abstract: Termini fluctuations for glaciers in the Himalayas and Trans-Himalayas are examined for the period AD 1850 to 1960. This period can be characterized as one of general retreat. Differentiation by ge...

Evolution of sea surface temperature in the somali basin during the southwest monsoon of 1979.

Abstract: Satellite and research vessel observations of sea surface temperature during the southwest monsoon of 1979 show the development of large wedge-shaped areas of cold water along the Somali coast at both 5° and 10°N during June and July. The cold water associated with the large northern and southern Somali eddy systems could be traced several hundred kilometers offshore. By late August the cold wedge at 5°N translated northeastward as far as 10°N at speeds of 15 to 30 centimeters per second, indicating a coalescence of the systems.

Somali current: evolution of surface flow.

Abstract: The transition of the Somali Current from northeast monsoon conditions to southwest monsoon conditions was observed from April through August 1979. The northeastward flow associated with the Somali Current of the southwest monsoon progressed from the equator in April to 4 ° N in August. The separation of the current from the coast, as observed at the northern boundary of the northeastward flow, did not intrude north continuously, but rather in distinct steps. South of 4 ° N, the circulation was characterized by the incorporation of increasing amounts of somewhat more saline water from the south and east into the boundary current. A clockwise gyre with northeastward flow along the coast developed between 6 ° and 10 ° N during June.

Climatic Variations in the Eastern Mediterranean Sea Area

Abstract: A very dry climate which prevailed during the last glacial maximum of the Pleistocene from India to the Sahara, was replaced by variable weather conditions with alternating more or less humid phases, starting from the Pleistocene-Holocene transition period and lasting up to about 3000 years ago, when present arid conditions set in. A particularly wet phase is recognized throughout the region some 5000 years ago. Phase shifts within the region and in particular changes in rain distribution patterns, are interpreted as due to shifting spheres of influence of the monsoonal circulation, of Atlantic depressions and moisture originating from the Mediterranean Sea. The condition of the Mediterranean Sea itself, which is influenced by runoff and melt waters from the European Continent and by the Nile floods, as well as by the eustatic sea-level changes, is not a good indicator of local climate conditions.

Low-Frequency Transitions of a Simple Monsoon System

Abstract: Seasonal, diurnal and synoptic time scales, plus a subseasonal modulation of synoptic events, appear to dominate the temporal structure of monsoon systems. Observational studies indicate that the latter low-frequency variation modulates or groups synoptic disturbances, producing periods of intense activity (the “active” monsoon) separated by distinct lulls (the “break” monsoon) Together with the “onset” and “retreat” of the monsoon, the modulations introduce into the system time scales which are far more rapid than that which would be expected from the evolving latitudinal variation of insolation. As observations indicate that the seasonal cycle and low-frequency transients occur in large spatial scales a model is used which appears to simulate the large-scale mean seasonal structure of the monsoon. Such a model is a zonally symmetric moist primitive equation model coupled to an interactive and mobile ocean. With such a model the hypothesis is tested that the basic character of the low-frequency ...

Seasonal Structure of a Simple Monsoon System

Abstract: With a structure based on observational studies which indicate that the monsoon occurs on extremely large spatial scales and shows distinct seasonal character, a model is developed with the aim of discerning the basic driving mechanisms of the mean seasonal monsoon. It is argued that for the macroscale monsoon an appropriate facsimile is a zonally, symmetric, moist and primitive equation atmosphere coupled to an interactive and mobile ocean. Via experimentation with the model a hypothesis is tested which states that the character of the mean seasonal monsoon is determined by an interplay between the basic drive of the monsoon system (i.e., the differential heating between an interactive ocean and continental regimes) and the hydrologic cycle. A seasonal structure of a simple monsoon system was developed and its character discussed. With full hydrology and an ocean-continent differential beating, the model displays many features of the observed mean monsoon. Comparisons between moist and dry and o...

Mass Balance of Glacier AX010 in Shorong Himal, East Nepal during the Summer Monsoon Season

Abstract: Observation of mass balance of Glacier AX010 at the southern front of the Nepal Himalayas was made from June to September in 1978. Since much of the annual accumulation due to the monsoon. and ablation occur simultaneously in the summer, the separate measurement of the amounts of accu mulation and ablation is difficult in this area. Accumulation is estimated from the precipitation on the basis of the relation between the probability of occurrences of solid precipitation ana surface air temperature, and ablation is obtained from the difference between the accumulation and the observational results of the balance. The probability of occurrences of solid precipitation had different linear relations with the air temperature between daytime and nighttime. The relation of air temperature to the estimated ablation is expressed by a power function. Although the change of accumulation depended on air temperature, the ablation was much more sensitive to the change of air temperature. The average summer balance over the whole area of the glacier was negative, but the positive summer balance in recent years is deduced. It is concluded that the fluctuation of the summer temperature on glaciers in the Nepal Himalayas under the influence of the summer monsoon is important for the variation of mass balance.

On some aspects of interaction between middle latitude westerlies and monsoon circulation

Abstract: Day to day zonal index between 30-50 deg. N has been computed and discussed in relation to the break monsoon conditions. Relation between the mean zonal index and general distribution of the precipitation in the central parts of the country, has been investigated. Distortion in the 500 mb flow pattern across Tibet due to the interaction between westerly trough and monsoon Circulation has also been discussed.

Tank irrigation in semi-arid tropical India

Abstract: Small water reservoirs behind earthen dams are called tanks in India. Tanks supply many villages with drinking water, but their primary purpose is for irrigation. Tank irrigation is an old established practice in most of the semi-arid tropical parts of India and of some other countries. In India, the monsoon rains fall erratically during a few months in the year, and irrigation tanks serve to store and regulate the flow of water for agricultural use. In southern India this is primarily for the production of rice.

Importance of Upper Tropospheric Thermal Anomalies for Long-Range Forecasting of Indian Summer Monsoon Activity

Abstract: Upper tropospheric monthly mean values of geopotential height at selected Indian stations during the pre-months of April and May, and the monsoon months of June, July and August, have been used to study the interannual variation in the upper tropospheric thermal field for the years 1968–77. The 300–100 mb thickness anomalies averaged over these stations reveal that 1) the anomalies observed during the pre-monsoon period of April-May generally persist through the subsequent monsoon months of June, July and August; and 2) a warm (cold) anomaly over northern India during the pre-monsoon months is followed by above-normal (below-normal) monsoon rainfall activity. The study may be useful in long-range forecasting of Indian summer monsoon rainfall activity.

Does the Early or Late Onset of Monsoon Provide Any Clue to Subsequent Rainfall During the Monsoon Season

Abstract: The association between the onset of the monsoon and the subsequent rainfall distribution over three west coast subdivisions of India, viz., Kerala, coastal Karnataka and Konkan, has been examined for the 50-year period (1921–70). The results revealed that the rainfall received in these subdivisions during the early monsoon month of June and the monsoon season as a whole is independent of onset date.

A hypothesis on onset, advance and withdrawal of the Indian summer monsoon

Abstract: The paper defines the intertropical convergence zone. (ITCZ) in the Indian monsoon region during the northern summer, identifies it with the northern boundary of the advancing monsoon and suggests that its seasonal movement can serve as an indicator of onset, advance and withdrawal of the monsoon. Evidence suggesting the movement of the ITCZ which is associated with the equatorial trough of low pressure is indirectly furnished by an analysis of the isallobaric or height-tendency field which reveals a distinct gradient towards the north/south during period of advance/withdrawal of the monsoon. A comparative study of the dates of onset of monsoon during two successive years appears to suggest that some of the problems encountered in using rainfall as the sole criterion for determining the onset and advance of the monsoon may be over-come by using the ITCZ concept as proposed in the present paper. Attention is drawn to the effects of synoptic-scale disturbances on the normal dates of onset, advance and withdrawal of the monsoon.

The Coast of China

Abstract: The 32,000 km coastline of China can be classified into two major types: the bedrock embayed coast and the plains coast. The distribution of these types is controlled by geological and tectonic setting, particularly zones of uplift and subsidence. The sedmentary processes along the coast of China are greatly affected by the large rivers which deliver enormous amounts of sediment. The sediment supplied is redistributed by monsoon waves and tidal currents.Within tropical and subtropical climate zones, the growth of mangrove and corals is also an important factor in coast-line formation. The coastal research in China is combined with various coastal engineering projects, which require information on coastal processes for the installation of port facilities. Thus practical requirements advances the understanding of coastal dynamic geomorphology.

Observations on the hydrography and inshore plankton of the bay of Bengal of Balasore

Abstract: The hydrographical features and the inshore plankton of the northern part of the Bay of Bengal was studied from the Balasore coast. The hydrology is mainly governed by the monsoons and river systems flowing into the bay. The surface temperature showed a bimodal pattern with a summer and autumn maximum. The salinity was below the oceanic average with the lowest value during October. The coastal water was found to be rich in nutrients, with peak values during the southwest monsoon. Three phytoplankton blooms followed by zooplankton maxima were observed between early spring and late fall.

Limnological Studies of a Freshwater Fish Pond at Burdwan,West Bengal,India

Abstract: Seasonal variation of the physicochemical factors and plankton community in a freshwater fish pond at Burdwan, West Bengal were studied from January to December, 1971. Water temperature varied from 20.0°C in January to 32.6°C in June. Total plankton volume varied from 8.7 to 14.2 ml and the maxima were recorded in February (spring) and July (monsoon) and the minima appeared in April (summer) and November (autumn). It was observed that the spring maximum was dominated by zooplankton while the monsoon maximum was dominated by phytoplankton. The rotifers constituted the most abundant group of zooplankton. Water-blooms of blue-green algae were recorded from the monsoon period to autumn. A positive correlation between the phosphate content of the water and the zooplankton was observed.

NOTES AND CORRESPONDENCE A Quasi-Stationary Appearance of 30 to 40 Day Period in the Cloudiness Fluctuations during the Summer Monsoon over India

Abstract: By using the cloudiness data from 1966 to 1972, a quasi-stationary appearance of 30 to 40 day period was confirmed during the summer monsoon season over India, which is recently found in the data for 1973 as a predominant mode of the monsoon fluctuations (Yasunari, 1979). In the same manner as the result of Yasunari (1979), the fluctuation of this mode shows a northward movement over India-Indian Ocean area in each year. This periodicity seems to appear annually except for the severe drought years such as 1972.

A study of the air and sea surface temperatures over the Indian Ocean

Abstract: Several studies on the air and sea surface temperatures over Indian Ocean : particularly over west Arabian Sea have been reported (Verploegh 1960; Colon 1964; Bunker 1965; 1970, 1974; Shukla 1975, 1977). The present paper is a study of the air and sea surface temperatures over the Arabian Sea and Bay of Bengal during the seven year period 1961 to 1967. Its purpose is to demarcate, with the recent date, Indian Ocean into separate zones each of a particular character with reference to the variation of the air and sea surface temperatures through the year as also the warmer than air-sea and colder than air-sea conditions during the southwest monsoon season. An attempt to examine the association of the anomalies of sea surface temperatures over the Arabian Sea to the variation in the activity of monsoon over India in the respective years has also been made.

Distribution of winter precipitation brought about by the passage of depressions over the japanese islands

Abstract: The winter climate of Japan is dominated by the northwesterly monsoon, which brings: abundant precipitation in the form of snow to the regions facing the Japan Sea. Most climatological studies on winter precipitation have concentrated upon the relationship betweenn the heavy precipitation near the Japan Sea and the winter monsoon, but a considerable amount of precipitation is brought about also by the passage of depressions or fronts. The purpose of this paper is to reveal some characteristics of the precipitation brought about by the passage of depressions, especially its areal distributions and the time variation of precipitation intensity. The results obtained are summarized as follows: 1) The depressions which pass over the Japanese Islands in winter may be classified into two types: the Japan Sea Low type, in which depression forms over the southwest of the Japan Sea, moves northeastward, and passes through the Soya or the Tsugaru Strait, andd the Pacific Coast type, in which depression rises over the East China Sea and travels eastward along the Pacific Coast of Japan (Fig. 1). 2) The Pacific side has little precipitation during the passage of Japan Sea Lows. The distribution of precipitation associated with these depressions is similar to that of monsoonall precipitation. Furthermore, it is fairly irrespective to the location of the depression. On.n the other hand, Pacific Coast Lows bring more precipitation to the Pacific side than to the Japan Sea side, and the distribution of precipitation changes as the depression moves eastward. The ordinary monsoonal precipitation pattern disappears during the passage of a. Pacific Coast Low, and then recovers once more after the passage (Figs. 2, 3 and 4). 3) There are conspicuous regional differences in the characteristics of precipitation during the passage of depressions. On the basis of the depression type which brings precipitation and the period of the maximum intensity of precipitation, eight major regions can be identified.as follows (Figs. 5, 7 and 9). On the Pacific side: (a) West of Kanto-more precipitation occurs during the passage of a Pacific Coast Low than during the passage of a Japan Sea Low. The intensity of precipitation increases rapidly as the depression approaches, reaches a maximum just before the arrival of de pression, and decreases with the depression moving away to the east. (b) Inland Honshu-similar to region (a), except that period of maximum intensity of pre cipitation is longer. (c) Tohoku-similar to region (b), except that the intensity of precipitation decreases much more slowly after the depression has passed. (d) Hokkaido-there is little difference in the amounts of precipitation brought by the two types of depression, and either type produces a little precipitation, i, e. this region is not so affected by the passage of depressions. On the Japan Sea side: (e) San-in-more precipitation occurs during the passage of a Pacific Coast Low than during the passage of a Japan Sea Low, but unlike the Pacific side regions, the maximum intensity of precipitation occurs after the depression has passed. (f) Hokuriku-there is little difference in the amounts of precipitation brought by the two types of depression. More precipitation is brought to this region by the winter monsoon than by depressions. (g) Tohoku-more precipitation occurs during the passage of a Japan Sea Low than during the passage of a Pacific Coast Low. Precipitation reaches maximum intensity before a Japan Sea Low arrives; that is, while it is still located over the central Japan Sea. (h) Hokkaido-similar to region (g), except that the absolute amount of precipitation is less than in any other region except the Pacific side of Hokkaido, and there is no distinct period of maximum precipitation intensity.

The Burst of the 1978 Indian Summer Monsoon as Seen from METEOSAT

Abstract: Low-level wind fields over the western Indian Ocean west of 65°E have been determined from the analysis of METEOSAT images from 10 to 22 May 1978 (one field every two days). The data show the abrupt change in the low-level airflow circulation which takes place over the western Indian Ocean during the burst of the monsoon. The burst of the monsoon along the African coast is characterized by the sudden establishment of the Somali low-level jet and associated strong cross-equatorial flow. This modification which augurs the beginning of the monsoon season over India is closely related to the first rainfalls over the southern part of the western coast of India which occur with a lag of 3–4 days.

Monsoon cyclogenesis and large scale flow patterns over South Asia

Abstract: An important problem of monsoon meteorology is understanding the mechanism of formation of monsoon disturbances over north Bay of Bengal. Using the linear stability analysis approach we have investigated in three different ways the stability of July mean monsoon zonal flow for the growth of disturbances. We have used a two-layer quasigeostrophic model and conducted combined barotropic­ baroclinic stability analysis. In the first approach, we included cumulus heating into our model through CISK mechanism. We obtained growing modes in the lower troposphere. One of thew modes has scale, structure and growth rate which agree well with those of the observed monsoon disturbances. In another study, we superposed a long stationary wave (the planetary monsoon wave) on the basic zonal flow and repeated the stability analysis. No heating was included in this case. This analysis also yielded growing disturbances in the basic flow. It turns out that one of these modes resembles well with the observed disturbances in respect of horizontal scale, growth rate and structure. Lastly, we examined the basic flow for instabili­ties when both cumulus heating and long wave are present. As expected there was enhancement in the growth rate and amplitude of perturbation as compared to their values in the earlier two cases. We have also studied the variability of monsoon cyclogenesis by considering the large-scale flow field over the monsoon region during active and break monsoon phases. We have conducted the above stability analysis of monsoon flow during break monsoon and just prior to distur­bance formation. It is found that the flow during break monsoon is stable whereas the flow just prior to depression formation is found to be unstable and yields disturbances with realistic scales and growth rates.