The Effects of Midlatitude Waves over and around the Tibetan Plateau on Submonthly Variability of the East Asian Summer Monsoon
The Effects of Midlatitude Waves over and around the Tibetan Plateau on Submonthly Variability of the East Asian Summer Monsoon
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DOI：
10.1175/2009mwr2826.1
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发表时间：
2009-07-01
影响因子：
3.2
通讯作者：
Yasunari, Tetsuzo
中科院分区：
文献类型：
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作者：
Fujinami, Hatsuki;Yasunari, Tetsuzo
利用插值长波辐射（OLR）和NCEP-NCAR再分析资料，分析了1979-2004年长江淮河流域（YHRBs）亚月尺度（7-25 d）对流变化及其相关大尺度大气环流。yhrb上空对流异常与上层流函数异常在各格点上的相关性表现出两种截然不同的模式。在高原背风处，由向东移动的上层波包和高原相关的对流形成低空涡旋。沿亚洲急流的罗斯比波列表现了两种模式的高层环流异常。NET年亚洲急流以北向弧形结构为主，AT年以纬向急流为主。这些差异可能会改变罗斯比波列的传播路线。此外，AT波的纬向波数（类似于7-8）大于NET波的纬向波数（类似于6），意味着AT波型比NET波型相对于地面的纬向相速度更快。这些差异可能解释了在NET模式中yhrb以北的波经向放大和在AT模式中向东穿过高原的波运动。
Convective variability at submonthly time scales (7-25 days) over the Yangtze and Huaihe River basins (YHRBs) and associated large-scale atmospheric circulation during the mei-yu season were examined using interpolated outgoing longwave radiation (OLR) and NCEP-NCAR reanalysis data for 12 yr having active submonthly convective fluctuation over the YHRBs within the period 1979-2004. Correlations between convection anomalies over the YHRBs and upper-level streamfunction anomalies at every grid point show two contrasting patterns. One pattern exhibits high correlations along the northern to eastern peripheries of the Tibetan Plateau (defined as the NET pattern), whereas the other has high correlations across the Tibetan Plateau (defined as the AT pattern). Composite analysis of the NET pattern shows slow southward migration of convection anomalies from the northeastern periphery of the Tibetan Plateau to southern China, in relation to southward migration of the mei-yu front caused by simultaneous amplification of upper- and low-level waves north of the YHRBs. In the AT pattern, convection anomalies migrate eastward from the western Tibetan Plateau to the YHRBs. A low-level vortex is created at the lee of the plateau by eastward-moving upper-level wave packets and associated convection from the plateau. Rossby wave trains along the Asian jet characterize the upper-level circulation anomalies in the two patterns. The basic state of the Asian jet during the mei-yu season differs between the two patterns, especially around the Tibetan Plateau. The Asian jet has a northward arclike structure in NET years, while a zonal jet dominates in AT years. These differences could alter the Rossby wave train propagation route. Furthermore, the larger zonal wavenumber of AT waves (similar to 7-8) than of NET waves (similar to 6) means faster zonal phase speed relative to the ground in the AT pattern than in the NET pattern. These differences likely explain the meridional amplification of waves north of the YHRBs in the NET pattern and the eastward wave movement across the plateau in the AT pattern.