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Characteristics of the winter monsoon over the Malaysian region

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Title:Characteristics of the winter monsoon over the Malaysian region
Authors:Lim, Joo Tick
Keywords:Monsoons -- Malaysia
Rain and rainfall -- Malaysia
Date Issued:1979
Abstract:Two periods, a strong and weak monsoon periods, are chosen from the winter monsoon of 1974/75 for the study of some characteristics of the monsoon over the Malaysian region. In the strong monsoon period, it is found that a time lag of about three days existed between the cold surge arrival at Hong Kong and the occurrence of heavy rainfall over the east coast of Peninsular Malaysia. Interaction between the quasi-stationary near-equatorial trough and monsoon surge caused the heavy rainfall over Malaysia. Mean maps of various radiative parameters for Southeast Asia for the two periods are analyzed. Of interest is the albedo map for the surge period, which indicates the maximum albedo (convective activity) areas were confined largely to the Peninsular Malaysia-South Thailand-South Bay of Bengal region. Composite maps of surface wind speed, air temperature, dew-point and sea surface temperature (SST) over the South China Sea are prepared. It is found that a strong wind band was aligned along the general wind direction during the monsoon surge. The strong wind band formed the main surface branch of the Hadley cell while the intense convective activity region, which lay downwind of the strong wind band, became the main ascending branch. In general, the distributions of SST, air temperature and dewpoint during the strong monsoon period showed large gradients north of 15N. To south of 15N, they were relatively uniform. In the weak monsoon period, the distributions of these parameters, with the exception of SST, were influenced greatly by the presence of a tropical storm. Surface heat exchanges are computed for several locations over the South China Sea using the bulk aerodynamic equations. It is noted that during the strong monsoon period, the intake of latent heat and sensible heat by the atmosphere decreased by more than half when the northeasterlies traversed from the northern South China Sea to the Peninsular Malaysia-South Thailand region, although wind speed remained as strong as in the north. A detailed study is made of the near-equatorial trough. It is found that the trough has a double-convergence structure with primary convergence located in the trough northern flank. The trough thermal structure resembles that of the typhoon and evidence points to CISK as the principal mechanism for its development and maintenance. Hourly surface wind observations along the Malaysian coasts are analyzed to determine the characteristics of the coastal winds and the extent of local influence. During the weak monsoon period, land/sea breeze circulations prevailed everywhere, while during the strong monsoon period, the mesoscale circulations existed in most areas except northeastern Peninsular Malaysia. The coastal winds had three main diurnal variations which can be analyzed by a two-dimensional analytical model. Theoretical analyses indicate that the coastal wind characteristics are determined largely by the synoptic winds, Coriolis parameter, temperature difference between land and sea, and surface friction. During the monsoon surge, the mountain ranges and near-equatorial trough restricted the strong monsoon conditions to northeastern Peninsular Malaysia, where a rains regime dominated. Here strong winds and cloudy skies suppressed all local effects and rainfall occurred mostly during the night and early morning. Elsewhere, a showers regime prevailed. The observed diurnal rainfall variations were generally the result of interactions among the various local factors and synoptic winds. In the weak monsoon period, a showers regime prevailed throughout Peninsular and East Malaysia.
Thesis (Ph. D.)--University of Hawaii at Manoa, 1979.
Bibliography: leaves 87-93.
xvi, 218 leaves ill., maps 29 cm
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Appears in Collections: Ph.D. - Meteorology

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