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Oceanic Rossby Waves over Eastern Tropical Pacific of Both Hemispheres Forced by Anomalous Surface Winds after Mature Phase of ENSO

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Title: Oceanic Rossby Waves over Eastern Tropical Pacific of Both Hemispheres Forced by Anomalous Surface Winds after Mature Phase of ENSO
Authors: Abe, Hiroto Browse this author →KAKEN DB
Tanimoto, Youichi Browse this author →KAKEN DB
Hasegawa, Takuya Browse this author
Ebuchi, Naoto Browse this author →KAKEN DB
Keywords: Intertropical convergence zone
Sea/ocean surface
Atmosphere-ocean interaction
Ekman pumping/transport
Rossby waves
Issue Date: 10-Nov-2016
Publisher: American Meteorological Society
Journal Title: Journal of Physical Oceanography
Volume: 46
Issue: 11
Start Page: 3397
End Page: 3414
Publisher DOI: 10.1175/JPO-D-15-0118.1
Abstract: The present study examined ENSO-related wind forcing contribution to off-equatorial Rossby wave formations in the eastern tropical regions of the North and South Pacific using satellite altimeter data and atmospheric reanalysis data during the period of 1993–2013. After mature phases of ENSO events, the sea surface height anomaly fields showed that off-equatorial Rossby waves propagated westward along 11°N and 8°S from the eastern Pacific. Starting longitudes of the westward propagation were distant from the eastern coast, especially for weak El Niño events in the 2000s, in contrast to the strong 1997/98 El Niño event in which the propagations started from the coast. Based on observational data, it was hypothesized that the Rossby waves could be formed by off-equatorial zonal belts of wind stress curl anomalies (WSCAs) in 135°–90°W rather than by wave emissions from the eastern coast. A numerical model forced only by WSCAs, that is, without wave emissions from the coast, successfully reproduced observed features of the Rossby waves in 180°–120°W, supporting the study’s hypothesis. During mature phases of El Niño events, equatorially symmetric negative sea level pressure anomalies (SLPAs) resulting from hydrostatic adjustment to the underlying warm sea surface temperature anomalies dominated over the eastern tropical Pacific. Anomalous surface easterlies blowing around the negative SLPA area as geostrophic winds were a major contributor in forming the anticyclonic WSCAs. The polarity of the anomalies is reversed during La Niña events. Therefore, spatial patterns of the SLPAs associated with the ENSO events are necessary to understand the Rossby wave formations.
Rights: © Copyright 2016-11-10 AMS
Type: article
Appears in Collections:低温科学研究所 (Institute of Low Temperature Science) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

Submitter: 阿部 泰人

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