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第 242回 大気海洋物理学・気候力学セミナー のおしらせ

日　時： 6月 27日(木) 午前 09:30
場　所： 環境科学院 D棟2階 D201号室

発表者： 阿部泰人(低温科学研究所/PD)
\\Hiroto Abe (PD)
題名： 熱帯収束帯の南北変位によって励起された海洋ロスビー波
\\Oceanic Rossby waves induced by the meridional shift of the ITCZ in association with the ENSO events

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熱帯収束帯の南北変位によって励起された海洋ロスビー波
\\Oceanic Rossby waves induced by the meridional shift of the ITCZ in association with the ENSO events
\\(阿部泰人 \\Hiroto Abe）発表要旨 :

This study investigated the eastern Pacific Inter-Tropical Convergence
Zone (ITCZ) as an atmospheric forcing to the ocean, using various
observed and reanalysis data sets over 29 years. In climatology, a zonal
band of positive wind stress curls (WSCs) with a 10°meridional width was
exhibited along the ITCZ. A southward shift of the positive WSC band
during the El Nin~o phase, induced negative (positive) WSC anomalies
(WSCAs) along the northern (southern) portion of the ITCZ, and vice
versa during the La Nin~a phase. This meridional dipole accounted for
more than 25% of interannual variances of the WSCAs, based on the
analysis during the period from 1993 to 2008. The negative (positive)
WSCAs in the northern portion of the ITCZ during the El Nin~o (La Nin~a)
phase were collocated with positive (negative) sea surface height
anomalies (SSHAs) that propagated westward as a Rossby wave all the way
to western North Pacific. This finding indicates that this
off-equatorial Rossby wave is induced by the WSCAs around the ITCZ,
instead of reflection of an equatorial Kelvin wave on the eastern
coastal boundary. To examine the factor in forming the off-equatorial
Rossby wave, we conducted a numerical model. The 1.5-layer reduced
gravity model simulated major patterns of the observed SSHAs well. While
the Rossby waves emitted from the eastern coastal boundary decayed
mostly until they arrived 140°W, the SSH amplitude was recovered by the
wind forcing west of 140°W. Thus, the ITCZ acts as an atmospheric bridge
to connect the equatorial and off-equatorial oceanic waves.

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