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Zhiyong Meng and Dan Yao

Abstract

On 21 July 2012, severe wind damage occurred in Beijing, China, during a heavy rainfall event. Through a damage survey that had the most detailed information in all of the published tornado damage surveys so far in China, this work showed significant evidence that the wind damage was caused by a mesocyclonic tornado rated as a category 3 storm on the enhanced Fujita scale (EF3) that was observed by people but of which not a single picture was taken. This was the first tornado ever reported or documented in Beijing. The most influential evidence indicating a tornado included a narrow damage swath 30–400 m wide and ~10 km long and convergent surface winds at multiple places along the swath. The radar analyses examined here show that the tornado was embedded in a strong mesocyclone. The initial linear and later sinusoidal tornado track was likely due to the intensification and expansion of the mesocyclone. The location, timing, and intensity variation of the wind damage were precisely collocated with those of a tornadic vortex signature. Descending reflectivity cores as well as their associated jetlets and counterrotating vortices were detected both before tornadogenesis and prior to the reintensification of the tornado damage. A tornadic debris signature was also detected in the later stages of the tornado. Compared to the U.S. climatology of forecast parameters for different storm categories, this storm developed in an environment that was favorable for the formation of supercells or weakly tornadic supercells rather than significantly tornadic supercells.

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Yijia Hu, Yimin Zhu, Zhong Zhong, and Yao Ha

Abstract

The prediction of mei-yu onset date (MOD) in the middle and lower reaches of the Yangtze River valley (MLYRV) is an important and challenging task for those making seasonal climate predictions in China. In this paper, the atmospheric and oceanic conditions in the preceding winter and spring related to MOD are analyzed. It is found that the MOD is associated with the intensity of the Ural high and the East Asian trough in high latitudes, with the intensity of the upper-level westerly jet in middle latitudes, and with the contrast of land–sea temperature and pressure in the preceding winter and spring, which are proxies for the intensity of the East Asian winter monsoon (EAWM). It is suggested that the intensity of the EAWM is the most crucial factor affecting the MOD. Years with an early MOD usually correspond to strong EAWMs in the preceding winter, and vice versa. The EAWM can affect the MOD by influencing the East Asian summer monsoon (EASM) through tropical ocean–atmosphere and tropical–extratropical interactions. Based on the above analysis, a physics-based statistical forecast model is established using multivariable linear regression techniques. The hindcast of MOD during the 13 yr from 1998 to 2010 is carried out to evaluate the performance of this forecast model. The MOD can be predicted successfully in 8 out of the 13 yr. The forecast model predicts the MOD in the years with strong mei-yu intensity more accurately than in those with weak mei-yu intensity, especially for cases of extreme flooding. This is useful in the prevention of flooding disasters.

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Zhiyong Meng, Lanqiang Bai, Murong Zhang, Zhifang Wu, Zhaohui Li, Meijuan Pu, Yongguang Zheng, Xiaohua Wang, Dan Yao, Ming Xue, Kun Zhao, Zhaoming Li, Siqi Peng, and Liye Li

Abstract

An EF4 supercellular tornado hit Funing County, Yancheng, Jiangsu Province, China, from about 1410 to 1500 local standard time 23 June 2016, causing 98 fatalities and 846 injuries. It was the deadliest tornado in the past 40 years in China. This paper documents the storm environment, evolution of the radar signatures, real-time operational tornado warning services, and the damage distribution during this event. The tornado was spawned from a supercell that developed ahead of an upper-level trough extending southwestward from a low pressure vortex in northeast China and dissipated following the occlusion of the tornado vortex. The radar-based rotational velocity of the mesocyclone peaked at 42.2 m s−1. The strength of the tornado vortex signature (gate-to-gate azimuthal radial velocity difference) peaked at 84.5 m s−1. Surface observations at 1-min intervals from a mesoscale network of in situ surface weather stations revealed the surface wind pattern associated with the mesocyclone, such as convergent and rotational flows. The tornado formed after the peak updraft strength of the supercell, producing a damage swath that was 34.5 km long and with a maximum width of 4.1 km. The review of the tornado warning process for this event reveals that there is much work to be done to develop operational tornado forecast and warning services for China.

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