Low-frequency coupled atmosphere-ocean variability in the southern Indian Ocean |
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| Authors: | FENG Junqiao HU Dunxin YU Lejiang |
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| Institution: | Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, Key Laboratory of Ocean Circulation and Waves, Chinese Academy of Sciences, Qingdao 266071;Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, Key Laboratory of Ocean Circulation and Waves, Chinese Academy of Sciences, Qingdao 266071;Applied Hydrometeorological Research Institute, Nanjing University of
Information Science and Technology, Nanjing 210044 |
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| Abstract: | The low-frequency atmosphere--ocean coupled variability of the southern
Indian Ocean (SIO) was investigated using observation data over 1958--2010.
These data were obtained from ECMWF for sea level pressure (SLP) and wind,
from NCEP/NCAR for heat fluxes, and from the Hadley Center for SST. To
obtain the coupled air-sea variability, we performed SVD analyses on SST and
SLP. The primary coupled mode represents 43% of the total square
covariance and is featured by weak westerly winds along 45--30S.
This weakened subtropical anticyclone forces fluctuations in a well-known
subtropical dipole structure in the SST via wind-induced processes. The SST
changes in response to atmosphere forcing and is predictable with a
lead-time of 1--2 months. Atmosphere--ocean coupling of this mode is
strongest during the austral summer. Its principle component is
characterized by mixed interannual and interdecadal fluctuations. There is a
strong relationship between the first mode and Antarctic Oscillation (AAO).
The AAO can influence the coupled processes in the SIO by modulating the
subtropical high. The second mode, accounting for 30% of the total square
covariance, represents a 25-year period interdecadal oscillation in the
strength of the subtropical anticyclone that is accompanied by fluctuations
of a monopole structure in the SST along the 35--25S band. It is
caused by subsidence of the atmosphere. The present study also shows that
physical processes of both local thermodynamic and ocean circulation in the
SIO have a crucial role in the formation of the atmosphere--ocean
covariability. |
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| Keywords: | southern Indian Ocean SST SLP Antarctic Oscillation |
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