Summer Persistence Barrier of Sea Surface Temperature Anomalies in the Central Western North Pacific |
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Authors: | ZHAO Xi LI Jianping and ZHANG Wenjun |
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Institution: | Laboratory of Ocean Circulation and Waves, Institute of Oceanology,
Chinese Academy of Sciences, Qingdao 266071,
National Key Laboratory of Numerical Modeling for Atmospheric Sciences
and Geophysical Fluid Dynamics,
Institute of Atmospheric Physics, Chinese Academy of Science, Beijing 100029,
State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology,
Chinese Academy of Sciences, Guangzhou 51030;National Key Laboratory of Numerical Modeling for Atmospheric Sciences
and Geophysical Fluid Dynamics,
Institute of Atmospheric Physics, Chinese Academy of Science, Beijing 100029;Key Laboratory of Meteorological Disaster of Ministry of Education and College of Atmospheric Sciences,
Nanjing University of Information Science and Technology, Nanjing 210044, National Key Laboratory of Numerical Modeling for Atmospheric Sciences
and Geophysical Fluid Dynamics,
Institute of Atmospheric Physics, Chinese Academy of Science, Beijing 100029 |
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Abstract: | The persistence barrier of sea surface temperature anomalies (SSTAs) in the
North Pacific was investigated and compared with the ENSO spring persistence
barrier. The results show that SSTAs in the central western North Pacific
(CWNP) have a persistence barrier in summer: the persistence of SSTAs in the
CWNP shows a significant decline in summer regardless of the starting month.
Mechanisms of the summer persistence barrier in the CWNP are different from
those of the spring persistence barrier of SSTAs in the central and eastern
equatorial Pacific. The phase locking of SSTAs to the annual cycle does not
explain the CWNP summer persistence barrier.
Remote ENSO forcing has little linear influence on the CWNP summer
persistence barrier, compared with local upper-ocean process and atmospheric
forcing in the North Pacific. Starting in wintertime, SSTAs extend down to
the deep winter mixed layer then become sequestered beneath the shallow
summer mixed layer, which is decoupled from the surface layer. Thus,
wintertime SSTAs do not persist through the following summer. Starting in
summertime, persistence of summer SSTAs until autumn can be explained by the
atmospheric forcing through a positive SSTAs--cloud/radiation feedback
mechanism because the shallow summertime mixed layer is decoupled from the
temperature anomalies at depth, then the following autumn--winter--spring,
SSTAs persist. Thus, summer SSTAs in the CWNP have a long persistence,
showing a significant decline in the following summer. In this way, SSTAs in
the CWNP show a persistence barrier in summer regardless of the starting
month. |
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Keywords: | SST anomalies persistence barrier oceanic mixed layer atmospheric forcing positive cloud feedback on SSTAs |
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