Variability of layered circulation in South China Sea
by Yao Tang
THESIS
2019
M.Phil. Environment and Sustainability
x, 50 pages : illustrations (some color), color maps ; 30 cm
Abstract
This research aims to investigate spatiotemporal variability of the three-dimensional cyclonic-anticyclonic-cyclonic (CAC) circulation in upper (h<750 m), middle (750m 1500 m) layer over the South China Sea (SCS) basin (h100 m), respectively, which
remains largely unknown. A 20-year (1992-2011) daily data from CMOMS (China Sea Multi-Scale Ocean Modeling System) is utilized to conduct the investigation. We find that: (1) intensity
of circulation and its variability weakens with increase in depth, while large variability of
circulation occurs mainly over the continental margin of the basin; (2) seasonality dominates
variability of circulation in the upper layer, while intra-seasonal variation at periods of 4.5- and 6-month in the middle layer and 7-month period in deep layer are most energetic; (3) the CAC...[ Read more ]
This research aims to investigate spatiotemporal variability of the three-dimensional cyclonic-anticyclonic-cyclonic (CAC) circulation in upper (h<750 m), middle (750m 1500 m) layer over the South China Sea (SCS) basin (h>100 m), respectively, which
remains largely unknown. A 20-year (1992-2011) daily data from CMOMS (China Sea Multi-Scale Ocean Modeling System) is utilized to conduct the investigation. We find that: (1) intensity
of circulation and its variability weakens with increase in depth, while large variability of
circulation occurs mainly over the continental margin of the basin; (2) seasonality dominates
variability of circulation in the upper layer, while intra-seasonal variation at periods of 4.5- and 6-month in the middle layer and 7-month period in deep layer are most energetic; (3) the CAC
circulation is composed of hotspots of positive and negative vorticity in each layer that account
for significant percentage of overall CAC circulation. In upper layer, there are three positive
vorticity hotspots located in the western and northwestern margins (hotspot 1), northeast (hotspot
2), and central basin (hotspot 3). These three hotspots contribute to near 90% of basin-wide
cyclonic circulation. Beneath hotspot1 and hotspot2 in upper layer, there exist two negative
vorticities at west and east of middle layer, which explain >80% of anti-cyclonic circulation in
middle layer. The single hotspot, situated in the southwestern corner of deep basin, accounts
for >20% of total deep cyclonic circulation; (4) the CAC circulation exhibits an inter-annual
variation with an intensifying trend over the 20 years. These spatiotemporal variability of CAC
circulation are largely induced by the variation of wind stress curl and planetary vorticity flux in
Luzon Strait as well as the interplay between circulation and complex basin topography. In light
of the increasing marine environment concern, implication of results in this study will improve
our understanding of the physics, biochemistry processes in the SCS.
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