甘肃省长江流域大(暴)雨引发泥石流危险程度评价

运用甘肃省长江流域11个气象站1971—2000年30 a整编气象资料及5个农业气象观测站1981—2000年1 m土层内的土壤湿度资料,分析了该地大(暴)雨发生频率及大(暴)雨易发时段不同深度层次的土壤含水量、可容纳水量的变化,构建了评价当地大(暴)雨引发泥石流的评价指数。结果表明,在发生大雨时,西汉水流域的泥石流发生可能性大于白龙江流域。发生暴雨时,白龙江发生泥石流的可能性大于西汉水流域。

宝天高速公路西段大(暴)雨引发泥石流危险程度评价

大（暴）雨可能引发的泥石流等地质灾害,是宝天高速公路西段安全运行的最大威胁.根据宝天高速公路西段1965-2008年麦积国家基本气象站、街子气象哨降水资料及1980-2008年天水农业气象试验站历年土壤水分含量观测资料,分析了宝天高速公路沿线降水、大（暴）雨及土壤含水量分布规律,建立了大（暴）雨引发泥石流可能发生的危险性的评价模式.结果表明：天宝高速公路西段是地质灾害高危险区,也是天水市地区的大（暴）雨中心.自20世纪60年代以来,宝天高速公路段的年降水呈20 a周期变化,大（暴）雨出现次数与年降水量距平百分率呈正相关.大（暴）雨的出现具有明显的季节性,在大（暴）雨出现的4-10月,100 cm土层土壤最大水分容纳量为86-172 mm,40 cm土层为41-69 mm.大（暴）雨引发泥石流的危险性7月最高,4月最低.7-10月泥石流发生的危险程度高于4-6月,主汛期是该线路段泥石流等地质灾害的重点防御时段.

和政县近30年大(暴)雨气候演变特征及灾害分析

利用1983—2012年气象资料,分析了和政县大(暴)雨灾害的演变特征,结果表明,和政县出现暴雨的频率较低,年均仅为0.5次,但大雨出现频率高,年均3.6次,且大(暴)雨日数呈明显的增长趋势,尤其近10 a暴雨日数剧增,由暴洪灾害造成的直接经济损失占各类气象灾害总损失的36%,居和政县气象灾害之首。

一次大(暴)雨天气过程分析

利用常规气象资料、区域自动站雨量资料、FY-2D卫星资料,对2012年7月20—22日内蒙古锡林郭勒盟出现的一次大(暴)雨天气过程进行了综合分析。结果表明:此次大(暴)雨是由高空低涡、地面气旋共同影响产生的,700 hPa西南涡是这次大(暴)雨的影响系统,北部下滑冷空气的加入和西南暖湿气流的加强是影响系统加强维持的原因。低层强盛的低空急流将南方西南暖湿气流源源不断地向大雨区输送。各物理量场的高低空合理配置和高能、高湿是此次降水出现必备的动力和能量条件。

Comparison of two types of persistent heavy rainfall events during sixteen warm seasons in the Sichuan Basin

Based on hourly precipitation from national surface stations,persistent heavy rainfall events(PHREs)over the Sichuan Basin(SCB)are explored during the warm season(May to September)from 2000 to 2015 to compare synoptic circulations and maintenance mechanisms between different PHRE types.There are two main types of PHREs:one is characterized by a rain belt west of 106°E over the SCB(WSB-PHREs),and the other features a rain belt east of 106°E over the SCB(ESB-PHREs).In total,there are 18 ESB-PHREs and 10 WSB-PHREs during the study period.Overall,the rain belts of WSB-PHREs are along the terrain distribution east of the Tibetan Plateau,while the precipitation intensity of ESB-PHREs is stronger.For the two types of PHREs,the shortwave trough over the SCB and the western Pacific subtropical high act as their favorable background environments,particularly for ESB-PHREs.The water vapor of WSB-PHREs is mainly transported from the South China Sea,whereas for ESB-PHREs the South China Sea and Bay of Bengal are their main moisture sources.The composite vorticity budgets of southwest vortices during their mature stage indicate that the convergence effect is a dominant factor for maintaining the two types of PHREs,and the strong vertical vorticity advection is also favorable,but the relative contribution of vertical advection is larger for WSB-PHREs.

Analysis on the TBB Bright Temperature and Vertical Helicity in a Heavy Rain at Anqiu in 2010

In order to get insight into the mechanism of summer rainstorm occurred in central Shandong Province and further improve the prediction accuracy,the FY-2E satellite TBB data and 6 h of NCEP/NCAR 1°×1° reanalysis data were used to carry out the weather dynamics diagnosis and TBB cloud image analysis of a heavy rain happened in Anqiu City on July 18,2010.The results showed that the Anqiu torrential rain was caused by common effects of the subtropical high and upper trough and ground cyclone system;TBB strong low clouds moved with cloud band along the low level jet direction,and closely associated with water vapor and energy belt,while the heavy rain occurred in the north of TBB light in low temperature zone,making the unstable energy release above the Anqiu area;the changes of the vertical spiral degrees at center could well guide the movement of the ground cyclonic center.

Analysis of Heavy Rainstorm in Dongting Lake on July 4, 2014

This paper analyzes the heavy rainstorm in northeast Dongting Lake on June 4, 2014. Results indicate the weather situation, radar echo and the satellite imagery of the strong precipitation. Besides, the warm and wet water vapor in Dongting Lake also contributes to this heavy rainstorm. As the astronomical precipitation cycle in this precipitation is outstanding, it is essential to pay attention to and use the astronomical precipitation forecast method.

HELICITY ANALYSIS FOR HIGH-WIND AND UNCOMMON RAINSTORM PROCESSES OVER YUNNAN IN EARLY SUMMER

Helicity was applied to analyze several high-wind and rainstorm processes, which occurred from May to June, 2001 over Yunnan in early summer. The results of diagnostic analyses show that the rainstorm occurs in the area in which hp is positive at 700 hPa and energy is unstable. The change of helicity can reflect the movement and development of synoptic system and the position and intensity of the rainstorm. The value of hp is a negative center at the upper level and a positive at the lower level over the rainstorm position; moreover it can reflect the characteristics of vertical distribution and rotational motion.

ON THE RELATIONSHIPS BETWEEN THE SUMMER RAINFALL IN CHINA AND THE ATMOSPHERIC HEAT SOURCES OVER THE EASTERN TIBETAN PLATEAU AND THE WESTERN PACIFIC WARM POOL

The relationships between the summer rainfall in China and the atmospheric heat sources over the eastern Tibetan Plateau and the western Pacific warm pool were analyzed comparatively, using the NCEP/NCAR reanalysis daily data. The strong (weak) heat source in summer over the eastern Tibetan Plateau will lead to abundant (scarce) summer rainfall in the Yangtze River basin, and scarce/abundant summer rainfall in the eastern part of Southern China. While the strong (weak) heat source in summer over the western Pacific warm pool will lead to another pattern of abundant (scarce) summer rainfall in the middle-lower reaches of the Yangtze River and scarce (abundant) summer rainfall in Southern China and in the region of northern Jiangsu to southern Shandong. Comparatively, the heat source over the eastern Tibetan Plateau affects a larger area of summer rainfall than the heat source over the western Pacific. In both cases of the heat source anomalies over the eastern Tibetan Plateau and over the western Pacific, there exist EAP-like teleconnection patterns in East Asia. The summer rainfall in China is influenced directly by the abnormal vertical motion, which is related closely to the abnormal heat sources in the atmosphere. The ridge line of the western Pacific High locates far south (north) in summer in the case of strong (weak) heat sources over the two areas mentioned above.

THE THEORY OF MOIST POTENTIAL VORTICITY AND ITS APPLICATION IN THE DIAGNOSIS OF TYPHOON RAINFALL AND INTENSITY

This paper tests the impacts of cloud-induced mass forcing on the moist potential vorticity （MPV） anomaly associated with torrential rains caused by Typhoon No.9914 （Dan） by using fine model simulation data outputted by the Fifth-Generation NCAR / Penn State Mesoscale Model （MMS）. The diagnostic results show that the positive MPV anomaly region, which is obtained by integrating the MPV from 600 hPa to 300 hPa in the vertical, roughly coincides with the precipitation at their synchronous stages either in position or in the distribution pattem, and the maximum positive MPV area of Dan is located mainly between 600 hPa and 300 hPa, which is much higher than torrential rain cases. Further analyses also showed that the value of positive MPV anomaly increased or decreased with the development of Dan, and the positive MPV anomaly may also be served as a tracer to indicate the evolution of tropical cyclone intensity.

The cloud-microphysical cause of torrential rainfall amplification associated with Bilis(0604)

After its landfall in China＇s mainland in 2006, Typhoon Bilis brought about torrential rainfall amplification at the edge of Guangdong, Jiangxi, and Hunan provinces, causing severe disasters. From a cloud-microphysical perspective, we discuss the differences of cloud-microphysical processes before and during the precipitation amplification and possible causes of the rain- fall amplification by using high-resolution simulation data. The results show that the cloud-microphysical characteristics dur- ing the above two periods are significantly different. With the distinct increase in the rainfall intensity, the cloud hydrometeor contents increase markedly, especially those of the ice-phase hydrometeors including ice, snow and graupel, contributing more to the surface rainfall. The clouds develop highly and vigorously. Comparisons of conversion rates of the cloud hydrometeors between the above two periods show that the distinct increases in the cloud water content caused by the distinct enhancement of the water vapor condensation rate contribute to the surface rainfall mainly in two ways. First, the rain water content increas- es significantly by accretion of cloud water by rain water, which thus contributes to the surface rainfall. Second, the accretion of cloud water by snow increases significantly the content of snow, which is then converted to graupel by accretion of snow by graupel. And then the graupel melts into rain water, which subsequently contributes to the surface rainfall amplification. In summary, a flow chart is given to clarify the cloud-micropbysical cause of the torrential rainfall amplification associated with Bills.

Extreme precipitation events in East China and associated moisture transport pathways

Interannual variation of summer precipitation in East China, and frequency of rainstorms during the monsoon season from 1961 to 2010, are analyzed in this study. It is found that the two variables show opposite trends on a decadal time scale: frequency of rainstorms increases significantly after the 1990 s, while summer precipitation in East China decreases during the same period. Analysis of the spatial distribution of summer rainstorm frequency from 1961 to 2010 indicates that it decreases from the southeast to the northwest at the east edge of the large-scale topography associated with the plateaus. Spatial distribution of rainstorms with daily rainfall greater than 50 mm is characterized by a "high in the southeast and low in the northwest" pattern, similar to the staircase distribution of the topography. However, the spatial distribution of variation in both summer precipitation and frequency of extreme rainstorms under global warming differs significantly from the three-step staircase topography. It is shown that moisture characteristics of summer precipitation and extreme rainstorms during the monsoon season in East China, including moisture transport pathways, moist flow pattern, and spatial structure of the merging area of moist flows, differ significantly. Areas of frequent rainstorms include the Yangtze River Valley and South China. Column-integrated moisture transport and its spatial structure could be summarized as a "merging" of three branches of intense moist flows from low and middle latitude oceans, and "convergence" of column-integrated moisture fluxes. The merging area for moist flow associated with rainstorms in the high frequency region is located slightly to the south of the monsoonal precipitation or non-rainstorm precipitation, with significantly strong moisture convergence. In addition, the summer moist flow pattern in East China has a great influence on the frequency of extreme rainstorms. Moisture flux vectors in the region of frequent rainstorms correspond to vortical flow pattern. A comparison of moisture flux vectors associated with non-rainstorms and rainstorms indicates that the moist vortex associated with rainstorms is smaller in size and located to the south of the precipitation maximum, while the moist vortex associated with non-rainstorms is larger and located to the north. It is shown that column-integrated moist transport vortices and the structure of moist flux convergence have significant impacts on the north-south oscillation of frequent rainstorm areas in East China, which is synchronized with the maximum vorticity of moisture transport and the minimum of convergence on the decadal time scale. Synthesis of moisture transport pathways and related circulation impacts leads to a conceptual model of moisture flow associated with rainstorms.