General Circulation in the Malacca Strait and Andaman Sea: A Numerical Model Study

Abstract

In the Andaman Sea and Malacca Strait, as in other parts of the Indian Ocean, the seasonal change of the wind plays a most important role: the south-west (hereafter SW) is monsoon active from June through September and the north-east (hereafter NE) monsoon is active from December through February. During the NE monsoon the winds are directed from the north and northeast to the south-west, and during the SW monsoon from the south-west to the north-east. Strong winds between June and September lead to maximum rainfall over most parts of the Indian subcontinent. These areas are also greatly influenced by the tides. The circulation in the Andaman Sea and the Malacca Strait is simulated with a three-dimensional baroclinic primitive equation model. In order to run the model, the HAMSOM model is used. The model is forced by tides at the open boundaries as well as by wind and heat flux. We use also the NCEP/NCAR data. The M2-tide amplitudes are bigger in the shallow areas in the northwest part coast of Andaman Sea and in the Malacca Strait. The phases of M2 tide shows that the M2 tidal wave come from Indian Ocean and bifurcates to the Andaman Sea and Malacca Strait. The current ellipses of M2-tide are also stronger in the shallow areas both in the Andaman Sea and Malacca Strait. There are two types of tidal distribution in the Andaman Sea and Malacca Strait. In the Indian Ocean part and in the middle of the Malacca Strait, the type is mixed tide prevailing semi diurnal, while in the Andaman Sea and the southern part of the Malacca Strait the type is semi diurnal tide. Generally, the general circulation caused by tides, heat flux and wind both for NE and SW monsoon shows the same pattern. These general circulation patterns, vertical structure of temperature and salinity in the Malacca Strait are compared with the observations carried out by other researchers. Based on those comparisons, the results of the model are reasonable. It means, the HAMSOM model can be used for the simulation of the Andaman Sea and Malacca Strait.

On the Holocene evolution of the Ayeyawady megadelta

“…Indeed, tidal modeling suggests that a tidal shear front (e.g., Wang et al, 2017) may be present in this region that shows a drastic change from weak and more isotropic tidal currents west of Bogale promontory to highly oriented strong currents in the Gulf of Mottama (Rizal et al, 2012). Such a shear front would explain both the unusual channel-drift couplet and the fact that the Ayeyawady was able to build its delta west of the gulf.…”

“…However, such an energy fence may be broken by prevailing westerly currents during Figure 5. (a) Bathymetry of the northern Andaman Sea shelf and SRTM-derived DEM for the Ayeyawady delta region on land with regional faults and associated splay faults (Morley, 2007); arrow pairs indicate regional compression (white) or extension (red); (b) tidal range lines (black), cotidal lines (white) and tidal current magnitudes (ellipses) for the dominant M2 tide component (Rizal et al, 2012); (c) sketch of the Ayeyawady delta plain evolution phases and associated subaqueous deltas. the summer monsoon when water and sediment discharge from the Ayeyawady peaks to provide suspended sediment to the Mottama clinoform.…”

“…Tidal currents combine with the wind-driven circulation. Wind currents are clockwise during the summer monsoon and reversed during the winter monsoon (Rizal et al, 2012). The macrotidal regime maintains turbid conditions year-round with the turbidity front oscillating ∼ 150 km in the Gulf of Mottama in phase with the spring-neap tidal cycle (Ramaswamy et al, 2004).…”

“…The Ayeyawady delta may already be sediment deficient (Hedley et al, 2010) and the anticipated sediment deficit after damming could increase its vulnerability to such transient events as well as to long-term sea level rise (Giosan et al, 2014). Strong tidal currents in the northern Andaman Sea (Rizal et al, 2012) amplify some aspects of delta vulnerability, such as salinization (Taft and Evers, 2016), whereas other aspects such as sediment redistribution along the coast or sediment trapping within the subaerial delta (e.g., Hoitink et al, 2017) may be attenuated. Better knowledge on how the delta has formed and functioned will help future efforts to maintain its viability.…”

Phylogeography ofPadina boryana(Dictyotales, Phaeophyceae) around the Thai-Malay Peninsula

“…The Gulf of Thailand is affected strongly by the South China Sea current during the Southwest monsoon season whereas the Andaman Sea faces the equatorial current coming from the west. Water in the Andaman Sea can flow through and mix with water masses north of Sumatra (Rizal et al, 2012;Yi-Neng et al, 2012) but not flow into the Gulf of Thailand because of the Malacca Strait barrier. Also, the occurrence of clockwise and counter-clockwise currents in the upper Gulf of Thailand (Buranapratheprat, 2008) will reduce connectivity to the open ocean.…”