Showing papers on "Monsoon published in 1969"

A major low-level air current near the Indian Ocean during the northern summer

Abstract: It is demonstrated that high-energy flow, in the form of low-level southerly jet streams which have been reported earlier over Kenya, is only one part of a much more extensive current of air which flows rapidly around the western half of the Indian Ocean during the northern summer. The high speeds are associated with the concentration of the cross-equatorial airflow into the zone from longitude 38 deg E to about 55 deg E instead of being rather evenly distributed from 40 deg to 60 deg or 80 deg E as illustrated in many climatological atlases and charts of mean flow during the season. The high-speed current is shown to flow intermittently from the vicinity of Mauritius through Madagascar, Kenya, eastern Ethiopia, Somalia and thence across the Indian Ocean to the west coast of India and beyond. The stream is occasionally reinforced by northward flow through the Mozambique Channel. The high-speed air current, or system of low-level jet streams, is closely associated with the Intertropical Convergence Zone over the Arabian Sea and western India, and variations in the strength of the stream over Kenya during a two month period were related to the rainfall which western India received from the south-west monsoon.

Some measurements of current off the Somali Coast during the Northeast Monsoon

Abstract: Geostrophic and direct current measurements off the Somali coast during the northeast monsoon of 1964–1965 indicate a large subsurface north-going current across a 9°N section between 52° and 53°30′E and a south-going current of similar characteristics between 53°30′ and 55°30′E. The characteristics of the flow suggest the existence of an anticyclonic gyre having a transport of approximately 70×106 m3/sec, the center being near that of the gyre found during the southwest monsoon.

Unsteady wind‐driven ocean currents

Abstract: The linear theory of unsteady wind-driven currents in a horizontally stratified ocean is reviewed in general and applied in detail to the northern part of the Indian Ocean, for several reasons the most suitable area for comparison with observed current changes. The ocean is predicted to respond to the onset of the Southwest Monsoon principally in two modes as far as vertical distribution of current is concerned; to a somewhat lesser extent in the barotropic mode with uniform distribution, and to a somewhat greater extent in the first baroclinic mode with current distribution roughly as in Fig. 1, concentrated predominantly in the uppermost 200 m. Calculations for a zonal distribution of winds, which rather rapidly make a reversal of direction and increase of strength somewhat north of the Equator characteristic of monsoon onset, predict that the barotropic and baroclinic modes are both propagated to the west at comparable speeds of the order of 1 m s−1; the marked contrast here with other oceans (in the comparability of speeds) is given particularly detailed study. When the associated patterns of current flux reach the coast of East Africa, they become concentrated into the Somali current, which flows northward along the coast only during the Northern Hemisphere summer (after monsoon onset) but during that time is comparable in volume flow (about 5 × 107 m3 s−1) to other western boundary currents such as the Gulf Stream. Theory indicates one month (of which two-thirds is needed for propagation of current patterns and one-third for their concentration into a boundary current) as the characteristic time scale for formation of the Somali current, in contra-distinction to the ‘decades’ predicted by the same type of theory for the Gulf Stream (Veronis and Stommel 1956). The flow is calculated to reach 40 per cent of a typical maximum value (observed in August) within a month of monsoon onset (May). The linear theory predicts the current as extending as far north as 6°N, but non-linear terms are generally found in computational studies (Bryan 1963; Veronis 1966) to bring about some ‘inertial overshoot’ in concentrated boundary currents, which may explain why the current does not in fact separate until about 9°N. In the non-equatorial oceans, however, non-linear effects are expected to be much greater.

The tropopause over India

Abstract: The frequency of occurrence of the polar and tropical tropopause at different stations in India in different months is studied. The seasonal and latitudinal height variations of the tropical tropopause are examined. A break in the tropical tropopause just at the latitude of the easterly jet stream is suggested. The lower southern tropopause is called the monsoon tropopause. A few comments on the possible characteristics of the monsoon tropopause are given.

Air-mass dynamics or subsidence processes in the Arabian Sea monsoon

Abstract: Soundings over the Arabian Sea during the International Indian Ocean Expedition period and climatological data over the west coast of India have been discussed to determine the cause of the low-level inversion and the influence of the Western Ghats on the inversion and precipitation. There does not appear relation between maximum divergence and lowest height of base of inversion as presumed by Flohnet al. The pattern of precipitation frequency on the west coast as seen from Fig. 2 of Ramage does not show the same trend either as the number of rainy days or rainfall at the coastal observatories. The depth of the moist layer and the height of base of inversion increase as the Western Ghats are approached, such changes not occurring off west Kathiawar-Kutch-Sind where there are no orographic barriers on the coast. The air-mass considerations to explain the low-level inversion over the Arabian Sea, would appear substantially valid even now.

Hydrogeology of a volcanic island che ju do, korea

Abstract: Che Ju Do is a volcanic island off shore from the Korean Peninsula. The island is an extinct volcano, petrologically a part of the intra-pacific province of the olivine-basalt-trachyte association. The last volcanic activity has been reported in old manuscripts. Climate of the island is primarily influenced by the Pacific monsoon pattern and the north-west winter Siberian winds. A highly permeable basaltic surface of the mountainous central part of the island, coincident with the highest precipitation in the area, results in good recharge of ground water. Ground water appears as perched horizons on impermeable planes between lava flows, but most of the reserves are stored in a basal fresh water lens, which floats upon and displaces the sea water beneath the island.

Role of the synoptic scale on convection over southeast asia during the summer monsoon.

Abstract: : Using Udorn and Saigon as reference stations, an investigation is made of convective activity over Southeast Asia during July 1967. Particular emphasis is placed on the role of the large synoptic scale on convective activity. Periods of suppressed and increased convective activity were isolated using the radar index. Vertical profiles of virtual equivalent potential temperature for these periods portray characteristic variations between suppressed and increased convective conditions. Time cross sections for Udorn show a correlation between depth and strength of the southwest monsoonal air current over Southeast Asia and convective activity. Examination of the synoptic analyses for the periods of suppressed and increased convection reveal that convection is suppressed when the monsoonal current is disrupted, whereas convection is increased when the depth and strength of the monsoonal current is increased. (Author)

Satellite evidence of sea-air interactions during the indian monsoon

Abstract: A cloud-free zone adjoining the Indian Peninsula, observed from Gemini XI on Sept 14, 1966, is attributable to upwelling A possible connection between a weak southwest monsoon, coastal upwelling, and below-normal rainfall is suggested The photograph reveals a region remarkably free from clouds around Peninsular India The cloudless zone is 60 to 100 km in width along the west coast and continues around the southern tip of India into the Bay of Bengal The cloudless zone is at its maximum width in the Bay estending toward the northern half of the coastal seas of Ceylon Here, the cloudless zone is about 3" of longitude (300 km) wide along the Indian coast This zone is, strictly speaking, not totally cloud-free because of a whiff of cirrus spreading about Farther north along the east coast of India, the cloudless zone decreases in width to about 150 km Gemini XI passed over this region when the area was under the influence of a weak monsoon Normally during such periods cloud is negligible but we find from figure 1 that there was extensive clouding in the seas This could be perhaps attributed mainly to the upper air troughs, one over the Arabian Sea and another over the Bay of Bengal, at 850 and 700 mb It is very unfortunate that this peculiar cloud pattern, which might have provoked serious thinking among several meteorologists, was observed over an oceanic region having, normally, a poor observational network The purpose of this note is to present all the available relevant observational materials, published and un- published, and initiate a discussion on the possible causes for the cloud phenomenon How far this phenomenon is important to the study of the monsoon circulation is also considered