鲁西北地区一次秋季强对流天气的雷达识别分析

利用SA雷达探测和高空探空资料,结合防雹作业数据和灾情信息,对2016年9月11日发生在鲁西北地区的强对流天气过程中两个对流单体进行雷达识别分析。结果表明:两个对流单体发展迅速,在4-7个体扫(约25-45min)内,垂直液态水含量(VIL)分别跃增了27kg·m^-2、16kg·m^-2,达到64kg·m^-2、57kg·m^-2;在反射率因子图上都具有典型的冰雹回波特征:存在较明显的强回波墙、回波穹窿、有界弱回波区;实施防雹作业后,对流单体回波顶高、VIL、风暴质心高度、冰雹概率、强冰雹概率等指标持续下降,进一步证实了开展防雹作业可有效地减小降雹灾害。     

Diurnal cycles of precipitation over subtropical China in IPCC AR5 AMIP simulations

Atmospheric Intercomparison Project simulations of the summertime diurnal cycle of precipitation and low-level winds over subtropical China by Intergovernmental Panel on Climate Change Fifth Assessment Report models were evaluated. By analyzing the diurnal variation of convective and stratiform components, results confirmed that major biases in rainfall diurnal cycles over subtropical China are due to convection parameterization and further pointed to the diurnal variation of convective rainfall being closely related to the closure of the convective scheme. All models captured the early-morning peak of total rainfall over the East China Sea, but most models had problems in simulating diurnal rainfall variations over land areas of subtropical China. When total rainfall was divided into stratiform and convective rainfall, all models successfully simulated the diurnal variation of stratiform rainfall with a maximum in the early morning. The models, overestimating noon-time （nocturnal） total rainfall over land, generally simulated too much convective rainfall, which peaked close to noon （midnight）, sharing some similarities in the closures of their deep convection schemes. The better performance of the Meteorological Research Institute atmospherer. ocean coupled global climate model version 3 （MRI-CGCM3） is attributed to the well captured ratio of the two kinds of rainfall, but not diurnal variations of the two components. Therefore, a proper ratio of convective and stratiform rainfall to total rainfall is also important to improve simulated diurnal rainfall variation.     

The Variability of Spring Sand-Dust Storm Frequency in Northeast Asia from 1980 to 2011

The characteristic distributions of regional sand-dust storm(SDS) weather processes over Northeast Asia from 1980 to 2011 were investigated using the shared WMO surface station meteorological data,atmospheric sounding data,China high density weather data,NCEP/NCAR reanalysis data,as well as the archived original weather maps of China.The concentration-weighted trajectory(CWT) method was used to calculate the SDS frequency from the discrete station data and to track the large-scale regional SDS weather processes in Northeast Asia.A spline trend analysis method was employed to investigate the variability of the SDS weather systems.The results show that during 1980-2011,the SDS weather processes exhibit both a historical persistence and abrupt transitions with an approximate 10-yr high-low occurrence oscillation.Through composite analysis of atmospheric circulation during high and low SDS years,it is found that the SDS occurrences are closely related to the anomalies of arctic vortex and midlatitude westerly,and the circulation patterns around the Lake Baikal.During the high frequency years,the meridianal flows in the upper and mid troposphere above the high SDS corridor in East Asia(from the Lake Balkhash along Northwest and North China,Korean Peninsula,and Japan Islands) are apparently stronger than the meridianal flows during the low SDS frequency years,favoring the development and transport of SDSs in the midlatitude regions.     

Environmental Influences on the Intensity Change of Tropical Cyclones in the Western North Pacific

The atmospheric and oceanic conditions are examined during different stages of the lifecycle of western North Pacific tropical cyclones (TCs), with the intention to understand how the environment affects the intensity change of TCs in this area. It is found that the intensification usually occurs when the underlying sea surface temperature (SST) is higher than 26℃. TCs usually experience a rapid intensification when the SST is higher than 27.5℃ while lower than 29.5℃. However, TCs decay or only maintain its intensity when the SST is lower than 26℃. The intensifying TCs usually experience a low-to-moderate vertical wind shear (2-10 ms-1 ). The larger the vertical wind shear, the slower the TCs strengthen. In addition, the convective available potential energy (CAPE) is much smaller in the developing stage than in the formation stage of TCs. For the rapidly intensifying TCs, the changes of SST, CAPE, and vertical wind shear are usually small, indicating that the rapid intensification of TCs occurs when the evolution of the environment is relatively slow.     

一次冷涡背景下强对流不稳定条件的成因分析

利用常规观测资料及NCEP再分析资料,在分析环流背景、探空资料的基础上,通过选取不同的高度和温度,对比研究四种CAPE以及CAPE场与地面要素场的关系,对发生在辽宁沈阳的一次冷涡背景下的强对流天气进行不稳定条件成因分析.结果表明,水汽潜热是不稳定能量的主要组成部分,冷涡背景下低层暖湿平流、高层冷干平流有利于不稳定能量的累积,从而导致强对流天气的发生;对流温度CAPE可以反映午后发生强对流所必需的不稳定能量,对强对流天气预报具有一定指示意义.     

河西走廊沙尘暴50 a频率突变检测分析

 利用1958年至2007年民勤、敦煌、武威、张掖、景泰的沙尘暴春季发生频次资料,运用滑动t检验和滑动F检验进行突变检测分析,根据检验结果综合确定突变点及其突变强度,寻求沙尘暴发生频率突变规律及产生原因,为沙尘暴发生频率的变化趋势研究和预测提供参考。滑动t检测结果显示,5站点的沙尘暴春季频率突变数量呈现往东部递增的趋势;降低突变较多;升高突变年份集中在20世纪60年代末期和90年代末期,降低突变主要出现在1983年及2002年前后;均值降低突变强度大于升高突变。滑动Ｆ检验结果显示突变均是方差降低突变;河西走廊中东部的沙尘频率波动性差异较其他地区更为显著;方差突变出现在80年代中期及90年代初期,其余时间的波动性的差异维持在一个较低的水平。当对沙尘暴发生频率进行滑动t及滑动F检验时,两种情况下的降低突变检测结果存在一定的对应关系。河西走廊地区的沙尘暴发生频率突变与地面风速、大风日数、降水量及平均气温的突变存在密切联系,可作为沙尘暴频率突变的预测因子。     

基于HEC-HMS模型的时间步长对次洪模拟的影响分析

运用HEC-HMS水文模型,初步建立了适用于晋江西溪流域的暴雨洪水模型。在此基础上,采用15 min和60 min两个模拟时间步长,研究模拟时间步长的变化对模拟结果的影响,进而寻求最佳的时间步长和模拟结果。结果表明:时间步长对模拟结果存在一定的影响,当改变时间步长时,需要通过参数的调整,才可得到相似的模拟结果,在其他参数不变的情况下,模拟时间步长减小,蓄量常数(K)呈逐渐增大的趋势。同时,当采用较短的模拟时间步长时,模型的模拟效率得到提高。     

东濮凹陷文南—刘庄地区沙二下亚段浅湖风暴沉积

风暴沉积是一种特殊的事件沉积,反映了区域特定时期的古地理环境和古气候变化.通过区域古地理研究和精细地层对比,探讨了东濮凹陷文南—刘庄地区沙二下亚段沉积时期浅湖风暴沉积证据及特征,在此基础上总结了风暴沉积模式.结果表明:沙二下亚段沉积时期湖盆沉积层序主要受气候条件控制,气候频繁变化导致风暴沉积广泛分布、多期发育;风暴沉积主要发育在湖侵体系域和高水位体系域,沉积早期发育在深水区,而到沉积晚期分布范围扩大;风暴沉积一般发生在每期砂组的边界附近,作为短期、等时的一种事件沉积,可以用来作为层序划分的辅助标志;研究区风暴沉积模式主要有Ⅰ类和Ⅱ类两种;Ⅰ类风暴沉积为类深水风暴沉积,发育A-D段沉积的类鲍马序列层序,但粒度要较深水风暴沉积细得多,多见于漫湖沉积环境相对深水区;Ⅱ类风暴沉积不发育Ⅰ类风暴的B和D段沉积;风暴流在风暴停止时越靠近湖盆中央,其沉积特征就越类似深水风暴沉积,反之则越类似Ⅱ类风暴沉积.     

基于FY-4A卫星数据的强对流云团识别与监测

为解决强对流监测问题,克服地区亮温特征对卫星监测的影响,利用FY 4A卫星L1数据,结合滑动窗口方法和多通道动态阈值自动识别法,对典型强对流云团进行识别与监测。结果表明：1）多通道动态阈值自动识别方法结合滑动窗口方法,可避免人为设置阈值的主观性,整合强对流的区域识别结果,实现全国强对流云团监测。2）此方法具有良好的强对流云团识别效果,识别正确率达到89%;3）FY 4A卫星识别结果与雷达反射率高值区基本一致,能够准确监测强对流云团发生发展和移动的过程,具有较高的识别精度。     

On the Origin of the 1999 Leonid Storm as Deduced from Photographic Observations

Photographic multi-station observations of 18 Leonid meteorsobtained by the Spanish Photographic Meteor Network are presented. For each meteoroidthe radiant position, trajectory data and orbital parameters are discussed and compared totheoretical radiant positions and orbital elements of particles ejected from 55P/Tempel–Tuttle in 1899.We discuss the role of mean velocity imprecision in the dispersion of some orbital parameters,specially the semimajor axis. Finally, by applying the dust trail theory we have adjusted the1999 Leonidstorm orbits to a defined semimajor axis value to test the quality of photographic observations.