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Ben-Da Lin

Abstract

A linear primitive equation model has been used to simulate the behavior of summer stationary waves in the Northern Hemisphere. Many basic features of the observed summer stationary waves have been reproduced quite well with this model. The role of different forcing mechanisms for the summer stationary waves has been compared. It is found that latent heating plays the dominant role for the formation and maintenance of the summer monsoon circulation in the subtropics, but in high latitudes, where advective processes become more important, topography and sensible heat flux from the surface produce more realistic surface wave patterns than does the latent heating. The performance of the model for different latitude domains is discussed in some detail.

The effects of the mean wind structure on the behavior of stationary waves, especially on horizontal propagation, have been examined. It is found that in summer the latitudinal propagation of stationary waves is mainly northward and hence the influence of low latitudes on high latitudes is more significant than the influence of high latitudes on low latitudes. The mean wind structure, especially the zero wind line in high latitudes, has significant effect on the northward propagation of stationary waves.

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Ben-Da Lin

Abstract

A primitive equation linear wave model is developed to examine the effects of mean zonal wind structure on the vertical propagation of stationary planetary waves and to identify the characteristics of the winter stationary waves forced by realistic topography and diabatic heating. An analytic mean zonal wind model is used to facilitate changing the wind structure parameters for comparative experiments. A more realistic mean wind profile is used to simulate the observed behavior of stationary waves more closely.

The experiments confirm the sensitivity of vertical wave propagation to the mean wind structure, especially to the latitudinal curvature of the mean wind. The role of the polar night jet in channeling the planetary waves as they propagate vertically is emphasized. At is found that the latitudinal location of the polar night jet also has a significant influence upon the wave propagation. A mechanism is proposed to explain the possible connections between the change in the location of the polar night jet and stratospheric sudden warmings during winter.

The model with topographic forcing reproduces quite realistic wave patterns both in the troposphere and stratosphere, whereas the model with diabatic heating does not have this ability, indicating that topographic forcing plays a more important role than diabatic heating for maintaining the stationary waves during winter, especially in the stratosphere.

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Yali Luo, Renhe Zhang, Qilin Wan, Bin Wang, Wai Kin Wong, Zhiqun Hu, Ben Jong-Dao Jou, Yanluan Lin, Richard H. Johnson, Chih-Pei Chang, Yuejian Zhu, Xubin Zhang, Hui Wang, Rudi Xia, Juhui Ma, Da-Lin Zhang, Mei Gao, Yijun Zhang, Xi Liu, Yangruixue Chen, Huijun Huang, Xinghua Bao, Zheng Ruan, Zhehu Cui, Zhiyong Meng, Jiaxiang Sun, Mengwen Wu, Hongyan Wang, Xindong Peng, Weimiao Qian, Kun Zhao, and Yanjiao Xiao

Abstract

During the presummer rainy season (April–June), southern China often experiences frequent occurrences of extreme rainfall, leading to severe flooding and inundations. To expedite the efforts in improving the quantitative precipitation forecast (QPF) of the presummer rainy season rainfall, the China Meteorological Administration (CMA) initiated a nationally coordinated research project, namely, the Southern China Monsoon Rainfall Experiment (SCMREX) that was endorsed by the World Meteorological Organization (WMO) as a research and development project (RDP) of the World Weather Research Programme (WWRP). The SCMREX RDP (2013–18) consists of four major components: field campaign, database management, studies on physical mechanisms of heavy rainfall events, and convection-permitting numerical experiments including impact of data assimilation, evaluation/improvement of model physics, and ensemble prediction. The pilot field campaigns were carried out from early May to mid-June of 2013–15. This paper: i) describes the scientific objectives, pilot field campaigns, and data sharing of SCMREX; ii) provides an overview of heavy rainfall events during the SCMREX-2014 intensive observing period; and iii) presents examples of preliminary research results and explains future research opportunities.

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