Weakening of Interannual Variability in the Summer East Asian Upper-tropospheric Westerly Jet since the Mid-1990s |
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Authors: | LU Riyu YE Hong and Jong-Ghap JHUN |
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Institution: | State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029,State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029,School of Earth and Environmental Sciences, Seoul National University, Seoul, Korea |
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Abstract: | In this study, we found that the intensity of interannual variability in the
summer upper-tropospheric zonal wind has significantly weakened over
Northeast Asia and the subtropical western North Pacific (WNP) since the
mid-1990s, concurrent with the previously documented decrease of the
westerly jet over North China and Northwest China. Corresponding to this
weakening of zonal wind variability, the meridional displacement of the East
Asian westerly jet (EAJ) manifested as the leading mode of zonal wind
variability over the WNP and East Asia (WNP--EA) before the mid-1990s but
not afterward. The energetics of the anomalous pattern associated with the
meridional displacement of the EAJ suggests that barotropic energy
conversion, from basic flow to anomalous patterns, has led to the weakening
of the variability in the EAJ meridional displacement and to a change in the
leading dominant mode since the mid-1990s. The barotropic energy conversion
efficiently maintained the anomalies associated with the variability in the
EAJ meridional displacement during 1979--1993 but acted to dampen the
anomalies during 1994--2008. A further investigation of the energetics
suggests that the difference in the patterns of the circulation anomaly
associated with either the first leading mode or the meridional displacement
of the EAJ, i.e., a southwest--northeast tilted pattern during 1979--1993
and a zonally oriented pattern during 1994--2008, has contributed greatly to
the change in barotropic energy conversion. |
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Keywords: | East Asian jet mid-1990s interannual variability energetics |
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