Locally and remotely forced atmospheric circulation anomalies of Ningaloo Niño/Niña
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A recently identified climate mode called Ningaloo Niño (Niña) is associated with positive (negative) sea surface temperature (SST) anomalies off the west coast of Australia and negative (positive) sea level pressure (SLP) anomalies in the overlying atmosphere. By conducting a series of numerical experiments with an atmospheric general circulation model, generation mechanisms of the atmospheric circulation anomalies accompanied by Ningaloo Niño/Niña are examined. Even when SST is allowed to vary interannually only in the eastern South Indian Ocean, negative (positive) SLP anomalies are formed off the west coast of Australia in Ningaloo Niño (Niña) years, supporting the existence of local ocean–atmosphere interaction. When the model is forced by SST anomalies outside of the eastern South Indian Ocean, negative (positive) SLP anomalies are also generated in Ningaloo Niño (Niña) years owing to a Matsuno–Gill type response to atmospheric convection anomalies in the tropical Pacific. It is found that the latter impact is stronger in the current atmospheric general circulation model. Regarding climatic impacts, it is shown that Ningaloo Niño (Niña) induces wet (dry) anomalies over the northwestern part of Australia even when SST anomalies outside of the eastern South Indian Ocean are excluded from the SST forcing.
KeywordsNingaloo Niño/Niña Interannual variation Southeastern Indian Ocean Atmospheric general circulation model
Constructive comments from three anonymous reviewers helped us to improve our manuscript. The AGCM was run on the supercomputers of Information Technology Center, the University of Tokyo under the cooperative research with Atmosphere and Ocean Research Institute, the University of Tokyo. The NCEP/NCAR reanalysis data and GPCC precipitation data are provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA, from their web site at http://www.esrl.noaa.gov/psd/. NOAA_ERSST_V3 data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA, from their web site at http://www.esrl.noaa.gov/psd/. The second author is supported by Research Fellowship of Japan Society for the Promotion of Science (JSPS) for Young Scientists and the Program for Leading Graduate Schools, MEXT, Japan.
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