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Guo R.-F.,Yunnan Meteorological Observatory | Xiao Z.-N.,China Meteorological Administration Training Center | Li Y.,Chinese Academy of Meteorological Sciences | Shi W.-J.,Nanjing Institute of Information Engineering
Journal of Tropical Meteorology

Using data available from the Retrieval System Based on Yearbooks of Tropical Cyclones over the Western North Pacific, NCEP/NCAR reanalysis daily data and observed precipitation data for 1959 to 2007 in Yunnan, a province located in a low-latitude plateau, this work analyzes the climatic characteristics and the corresponding large-scale circulation patterns related to the western North Pacific westward moving TCs (WMTCs). Its impacts on the rainfall in the Yunnan Plateau are studied. Results show that WMTCs happen almost every year, mainly from July to September. It shows a downward trend in decadal variation. Nearly the entire Yunnan area is affected by them but the eastern part experiences the most severe influences. Most of the WMTCs migrate from the South China Sea, primarily make landfall in Hainan and Guangdong and enter the Northern Bay. The tracks of these typhoons can be classified into five categories, in which the most significant impact results from those making landfall in Guangdong. All categories of the tropical cyclones can induce province-wide heavy rainfall in Yunnan. Super typhoons bring about the heaviest and most extensive rainfall over the low-latitude plateau while the associated circulation pattern is marked with a dominant 500 hPa meridional circulation at middle latitudes, an active monsoon depression and Intertropical Convection Zone (ITCZ) at low latitudes and a westward-located South Asia High at 100 hPa, which is favorable for tropical cyclones to travel westward. WMTCs tend to go westward into the interior part of China if the subtropical high extends its westernmost ridge point to the northeast of Yunnan, or expands its periphery anti-cyclonic circulation to the Tibetan Plateau, or merges with the Qinghai-Tibetan high. Source

Liu Y.,Yunnan University of Finance and Economics | Peng G.,Yunnan Meteorological Observatory | Zhao N.,Yunnan Meteorological Observatory
Emerging Economies, Risk and Development, and Intelligent Technology - Proceedings of the 5th International Conference on Risk Analysis and Crisis Response, RACR 2015

This paper constructed a comprehensive drought index mainly with Thornthwaite dryness index, supplemented by self-defined effective precipitation index, based on using fuzzy information theory and transcendental limit probability theory with data in 125 Yunnan Meteorological stations from 1959 to 2005 divided into 5 periods to evaluate drought risks in Yunnan Province. Results show that: each year from January to March the risks of drought disasters are highest, drought probabilities in most areas are 60%–100%, and heavy drought probabilities are 20%–60% (even up to 90% in some areas); from November to December, the risks of drought disasters are relatively lower, drought probabilities in most areas are 30%–60%, heavy drought probabilities are 20%–60%; from June to August, there is almost no drought risk; from September to October, the drought probabilities of the whole province are less than 5%, and heavy drought probabilities are nearly none; from April to early June, the drought probabilities in about half of province are 10%–20%, 29% of the province are 20%–40%, 21% of the province are 40%–80%, and the heavy drought probabilities are less than 5%. © 2015 Taylor & Francis Group, London. Source

Zhang T.-F.,Yunnan Meteorological Observatory | Duan X.,Yunnan Meteorological Institute | Zhang J.,Yunnan Meteorological Observatory | Yin L.-Y.,Yunnan Meteorological Observatory | Liu L.,Yunnan Meteorological Observatory
Journal of Tropical Meteorology

Based on cloud-ground lightning data and Doppler weather radar echo products, both the characteristics and the relations of lightning and radar echoes for strong convective rainstorms over Yunnan are analyzed during the flood season of 2007. The results show that most rainstorms are convective in which lightning is mostly negative and the negative lightning number accounts for more than 90% of the total. Although the correlation between precipitation and the lightning number is small on the rainstorm day, the large day-lightning frequency usually produces heavy precipitation. Hourly evolution of precipitation and lightning frequency shows peak-style characteristics. And their evolution is very coherent in strong rainstorm, but lightning often occurs before precipitation, whose peaks are in phase with or 1-to-2-hour lagged behind that of lightning frequency. Meanwhile the peaks of positive frequency are in phase with or fall behind that of precipitation. When the wind field is heterogeneous in radial velocity, it is conducive to both the development of convection echoes and occurrence of lightning. Strong lightning-producing convective rainstorms correspond to strong echo fields and usually result in reflectivity above 30 dBZ and echo top ET of more than 9 km, respectively. Source

Liang H.-L.,Yunnan Meteorological Observatory | Xu Y.-Y.,Yunnan Meteorological Observatory | Daun W.,Meteorological Science Institute of Yunnan
Journal of Tropical Meteorology

Recent studies indicated that except for the land-sea thermal contrast, there also existed the land-land thermal contrast. The composite analysis and t-test method are used to further study the local thermal contrast variation over the Asian continent, and to discuss the association of seasonal variation of land thermal state with circulation over East Asia, the early summer and summer monsoon activity, and the precipitation anomaly in China in the decadal scale. Results show that the positive meridional temperature anomaly transports downward from upper tropospheric layers in middle-high latitudes north of 25°N in the positive years. In the zonal direction, the Tibetan Plateau heating in the successive spring acts as a force to influence the atmosphere, leading to the rapid temperature warming over eastern Chinese continent, which could increase the land-sea thermal contrast with the negative SSTA. Accordingly, the monsoon activity in early summer over East Asian establishes earlier and the summer monsoon intensity becomes stronger. The early summer precipitation is more-than-normal over the Yangtze River, and the summer precipitation is more-than-normal over the north China and the southwest China. The situation is contrary in the negative years. Source

Zhu L.,Yunnan Meteorological Observatory | Zhang T.,Yunnan Meteorological Observatory | Ding Z.,Nanjing University of Information Science and Technology
Journal of Natural Disasters

1° × 1°NCEP reanalyzed data and MM5V3.6 numerical model were used to simulate two typical local extra torrential rain events happened in Yunnan Province which located in lower latitude plateau of China. High space-time resolution data from MM5V3.6 numerical model was utilized to draw T-ln P diagram and calculate LI index, CAPE index, CIN index and equivalent potential vortex (EPV). These physical quantities were used to analyze the conditional instability, convective instability and conditional symmetrical instability of the two local extra torrential rain events. Results indicate that, the two local extra torrential rain events have different instability mechanism. When atmosphere is stratification stable and convective stable or weak unstable, the conditional symmetrical instability may lead to heavy precipitation. Source

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