Abstract
An analysis based on July-August precipitation reveals that there is a tripole pattern of the precipitation distribution, that is, significantly increased rainfall over North China (NC) is related to the increased rainfall over the Indian subcontinent (IS) and the decreased rainfall over the southeastern Tibetan Plateau (TP) and vice versa, that corresponds to the Indian summer monsoon (ISM) and TP heating pattern, which are interactive. Therefore, it is necessary to investigate the effect of NC rainfall-related atmospheric circulation and the physical linkage with the two thermal forcings together. The linear baroclinic model (LBM) is applied to determine the dynamics of the process. The results show that an enhanced ISM is accompanied by reduced TP heating, favors convection and easterly anomaly over the IS, and produces a Gill-type Rossby wave that affects the vorticity over North Africa. Meanwhile, there is another Rossby wave originating in North Africa and moving eastward to the Pacific Ocean, which interferes with circulation at mid- to high-latitudes, i.e., it strengthens the cyclone over the Baikal region and stretches the western Pacific subtropical high (WPSH) northward to northeastern Asia, and results in abundant water vapor transported to NC. Furthermore, the strong convection over the IS excites the Kelvin waves over the equatorial region, which moves eastward and generates anticyclones over Philippines, consequently leading to the Pacific-Japan (PJ) pattern. The PJ pattern cooperates with the wave train at midlatitudes, resulting in abundant water vapor being transported to NC. The summer rainfall over NC is therefore modulated by synergistic effect of both the ISM and TP heating.
Highlights
North China (NC) is located at mid-to high-latitudes between the Baikal region and the northwestern Pacific Ocean; the climate variability here in summer is very large and is affected by atmospheric circulation anomalies such as blockings at high-latitudes over both the tropical and extratropical regions [1], westerly wave trains [2], western Pacific subtropical high (WPSH) [3], and Asian summer monsoons [4,5,6]
Various studies documented that the Indian summer monsoon (ISM) affected the summer climate in East Asia through a midlatitude wave train along the East Asian upper tropospheric westerly jet stream, causing differences in atmospheric circulation and water vapor transport [18, 19]. e results further revealed that an enhanced ISM could generate anomalous cyclonic circulation over the Mediterranean Sea in the upper layer [20, 21] and stimulated a continuous downstream air flow, i.e., a silk road pattern [22], with a barotropic anticyclonic anomaly over East Asia, leading to more water vapor being transported northward along the western periphery of the WPSH [23]
We addressed the tripole pattern for rainfall over the Indian subcontinent (IS) and the southeastern Tibetan Plateau (TP) and NC. e increased precipitation over the IS caused by strengthened ISM is often accompanied by the release of latent heating similar to that in the southeastern TP [53], which means that the diabatic heating can represent precipitation to a large extent. erefore, we use the linear baroclinic model (LBM) to verify the effect of thermal forcing and investigate how it determines the rainfall distribution
Summary
North China (NC) is located at mid-to high-latitudes between the Baikal region and the northwestern Pacific Ocean; the climate variability here in summer is very large and is affected by atmospheric circulation anomalies such as blockings at high-latitudes over both the tropical and extratropical regions [1], westerly wave trains [2], western Pacific subtropical high (WPSH) [3], and Asian summer monsoons [4,5,6]. Various studies documented that the ISM affected the summer climate in East Asia through a midlatitude wave train along the East Asian upper tropospheric westerly jet stream, causing differences in atmospheric circulation and water vapor transport [18, 19]. The TP has a considerable influence on the boreal circulation and precipitation as a significant surface and atmospheric heating source in summer [29, 30], which, is considered
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