Variation of surface Currents Offshore from Rayong Rivermouth from NRCT Buoy Data in 1994
Absornuda Stripping, Supichai Tangjaitrong
Sirichai Dharmvanij, Chaiyong Yuangthong
and Pakorn Purimatikant
Marine Science Department, Faculty of Science
Chulalongkom University, Bangkok 10330, Thailand.
Presented at the 16th Asian Conference on Remote Sensing,
20-24 Nov. 1995, at Suranaree University of Technology Nakhon
Ratchasima, Thailand.
Abstract
The monthly current rose data at 3 metre depth, Lat. 120 29' 42" N, Long. 1010 14 '16'' E. in 1994 from the TOBIS buoy, under the SEAWATCH program of the National Research Council of Thailand, at the offshore of the Rayong Rivermouth were analysed with the mean wind data to study the pattern of wind-driven currents. In North monsoon, from October to January, the sea currents mainly flow to 300° from North with the mean speed of 10.65 cm/sec. In South monsoon season, from February to May, the currents principally flow to 120° from North, with the mean speed of 11.775 cm/sec. During the Southwest monsoon season, from June to September, the principal currents flow to 90° (to East), with the mean speed of 12.10 cm/sec.
Introduction
The continuous current date in the sea are important especially for the study on transport of energy and matter, among others. The data from the ship are only discrete and not continuos for a long term study. The National Research Council of Thailand moored 7 Buoys in the Gulf of Thailand under the SEAWATCH program.
Data and Method of Study.
One of the TOBIS buoy of NRCT by the OCEANOR was moored offshore of the Rayong Rivemouth at the Lat. 12 0 29' 42" N, Long. 1010 14' 16 E. The current data at 3 metre depth under the sea surface in 1994 were plotted per month by the software ORKAN to show the current rose method. The data were missing in January, June, July and December 1994. From the climatological data for 1981 to 1994 by the Meteorological Department, at Rayong, Lat. 120 38 N, Long. 1010 21'E were used to study the wind direction and velocity. The sea current data are related to the wind regime to study the variation of surface wind-driven currents here.
Results
Table 1 is the wind speed and direction at each month average from 1981 to 1994 at Rayong s station. The Northerly winds blow during October to January the Southerly winds blow during February to May, and the Southwesterly winds blow during June to September.
Table 1. Wind speed and direction to at Rayong from 1981 to 1994.
(Data from Meteorological Department)
| Wind (Knots) |
Jan |
Feb |
Mar |
Apr |
May |
Jun |
Jul |
Aug |
Sep |
Oct |
Nov |
Dec |
| Mean speed |
3.10 |
4.60 |
5.10 |
4.50 |
5.60 |
8.60 |
8.00 |
8.70 |
4.60 |
2.90 |
2.90 |
3.20 |
| Prevailing |
N |
S |
S |
S |
S |
SW |
SW |
SW |
SW |
N |
N |
N |
| Max. speed |
24 |
33 |
30 |
35 |
40 |
45 |
40 |
50 |
35 |
35 |
24 |
24 |
February 1994 (Southerly wind), Fig. 1, the principal surface current flow to 300° form North, and second maxima to 120° with the mean speed of 12.5 cm/s. This month is the transition period from Northerly wind to Southerly wind.
Figure 1
March 1994 (Southerly wind), Fig. 2, the principal surface currents flow to 300° and the second maxima to 120°, with the mean speed of 12.0 cm/s.
Figure 2
April 1994 ((Southerly wind), Fig. 3, the principal surface currents flow to 300° and the second maxima to 120°, with the mean speed of 11.5 cm/s.
Figure 3
