OCEAN DYNAMICS IN THE REGION BETWEEN AUSTRALIA AND INDONESIA AND ITS INFLUENCE ON THE VARIATION OF SEA-SURFACE TEMPERATURE IN A GLOBAL GENERAL-CIRCULATION MODEL
Td. Qu et al., OCEAN DYNAMICS IN THE REGION BETWEEN AUSTRALIA AND INDONESIA AND ITS INFLUENCE ON THE VARIATION OF SEA-SURFACE TEMPERATURE IN A GLOBAL GENERAL-CIRCULATION MODEL, J GEO RES-O, 99(C9), 1994, pp. 18433-18445
Variation of sea surface temperature (SST) in the region between Austr
alia and Indonesia is of crucial importance to Australian winter rainf
all. To gain insight into how the SST is maintained and changed, the p
resent study provides a comprehensive description of ocean dynamics in
the region, using results from a seasonal ocean general circulation m
odel run by Semtner and Chervin [1988, 1992]. We also investigate the
heat budget of the surface layer (0-50 m). Indonesian topography is he
avily simplified in this model, but some simple results which probably
do not depend strongly on topographic detail are obtained. The curren
ts in the model are verified by comparison to observed annual mean and
seasonal thermal structures and circulations determined from the expe
ndable bathythermograph data collected in the region since 1983. We fo
und a distinctive difference in the model circulations and heat budget
s in two regions: one between the coast of Indonesia and 13-degrees-S
(called the northern region) and the other between the northwest coast
of Australia and 13-degrees-S (called the southern region). Net surfa
ce heat fluxes in the model's northern region are low compared to thos
e in most climatologies, possibly because the model does not allow for
strong tidal mixing within the Indonesian archipelago. The annual mea
n vertical velocity in the upper 500 m shows strong upwelling in the n
orthern region and weak downwelling in the southern region. The annual
variation in the vertical motion near the surface (<50 m) is driven b
y local wind stress in both regions. Within the depth range of the the
rmocline, vertical motion is dominated by a remotely forced semiannual
signal in the northern region and a local response to wind stress in
the southern region. The surface heat flux and advection in the annual
mean heat budget are very small, at least an order of magnitude small
er than those in the seasonal budget. In the southern region the model
may represent the ocean heat budget quite well: here the primary cont
rol on the seasonal variation on SST is the surface heat flux. However
, about half of the flux is balanced by advection in the southern regi
on. This suggests that ocean circulation could also play a role in the
generation of the SST anomalies north of Australia, which are critica
l for Australian climate variation as documented by Nicholls (1989). I
n the northern region, cold advection due to upwelling is largely canc
elled by warm advection from within the Indonesian archipelago. This m
ay explain the fact that observed sea surface temperature depressions
south of Indonesia are quite small compared to those in other eastern-
boundary upwelling regions. However, model heat fluxes in the northern
region may be in error owing to the absence of tidal mixing. In the m
odel the largest terms show that heat transport by Indonesian throughf
low and Ekman current is the main heating process and this process is
largely balanced by cooling due to upwelling near the coast of Indones
ia, and by release of heat to the atmosphere near the northwest coast
of Australia.