NOAA Images of the Plumes in the south China Sea : Some Preliminary Observations
Methods and Results
The data were obtained from the NOAA - 12 and NOAA - 14 satellites through the HRPT Reception System developed by Dundee Satellite Systems. HRPT (High Picture Transmission) refers to the standard format in which the data is transmitted from the satellite. The data is displayed using the STARS AVHRR Processing System provided by Sea Scan. The visible and thermal images were processed using the PCI Easi - pace software. There was no attempt to make any atmospheric or geometric corrections and only density slicing was applied to enhance the variabilities of the plume and surface temperature patterns. The surface temperature differences and suspended sediments variations were used since their relative gradients are sufficient to indicate the plume shapes and flows.
The longest river in the region is the Mekong river which is 4, 189 km with its estuary located in southern Vietnam. As the Mekong River would have much influence in the South China Sea, images of it were first studied. NOAA images in the months of December-January and July-August in the years 1995-1996 were selected and cloud-free images analysed. Channels 1 and 5 of the images were used and pseudo - coloured to show the variations in the plume stages and sea surface temperature.
As expected the images indicate the flow of the plume which was greatly influenced by the monsoonal winds.
Discussion and conclusions
Drinkwater (1986) described the profound effects of the river input which can extend to over a thousand kilometers. In the South China Sea, the effect of the Coriolis force would have some effects on the flow of the Mekong River plume. During the Southwest monsoon season, the plume would therefore be exerted by two forces, the south west widns and the Coriolis force. The plume flows in the north east direction and the extent of the plume flow is estimate d to be about 100-200 km. Conversely during the Northeast monsoon, the north east winds is stronger than the influence of the Coriolis force. Such an image is yet to be analysed and which would show the direction of the plume flowing in the southwesterly direction and perhaps extending as far down to about 300 km. In additio, the tidal flow in the area will affect the flow and consequently the timely image that would be required in this study is when the plume is flowing during the ebb tide. This is when the river runoff is high and the plume is more distinct. This kind of image is still being sorted for further analysis.
The effects of the freshwater runoff of the Mekong River which effected by the Northeast winds could bring large abundance of shrimps into the coastal wat4ers of the Eastern Peninsular Malaysia. This corresponds to the seasonality of shrimps in the Terengganu waters of the area. The shrimps are abundant during the Northeast monsoon season (Ibrahim Johari and Syed Abdullah, pers. Comm..) and they seem to disappear after the monsoons. The distance between the Mekong estuary and the Terengganu coast is about 300 nautical miles (560 km).
This study is a preliminary one and more images of the plumes in the area are required for analyses to further confirm this phenomenon. The extent of the plume flow is important in this area for it will show the actual the interactions of the water masses and the effects they have on the marine living resources.
