2011年汛期预测回顾

2011年夏季(6—8月),全国降水偏少,气温偏高,高温日数偏多,区域性、阶段性旱涝灾害重,旱涝转换快,登陆热带气旋(中心附近最大风力≥8级)强度弱,灾害损失偏轻。本文对2011年夏季(6—8月)天气气候异常特征进行了成因分析,并对2011年的汛期预测进行了回顾和总结。总的来说,2011年汛期预测总体趋势与实况接近,但是对于长江中下游的降水偏多估计不足。     

超声波传感器雪深测量与人工观测对比试验分析

通过对2010年2、3月佳木斯国家基准气候观测站人工观测与超声波雪深传感器测量获取数据对比、分析不同天气条件下（高风速、低风速、低温度）两种方法获得的数据差值的变化情况。结果表明：观测结果差异的大小主要受温度和风速两个因素的影响。低温环境下温度会影响超声波的行程时间使得超声波传感器的测量精度受到影响,通过温度补偿的方法对雪深进行订正可以提高超声波传感器的测量精度,两者的差值较小,且观测资料有较好的可比性;高风速时,风速会影响超声波脉冲,使其偏离传感器的下方,同时超声波的速度也会受到影响,从而影响测量结果,使得两者的差值较大。     

鹰潭市一次冻雨暴雪天气过程分析

利用常规气象资料、T213资料等,对鹰潭市2008年2月1-2日出现的冻雨、暴雪天气过程进行分析。结果表明,暴雪出现在500hPa槽前、700hPa急流轴与切变线之间、850hPa切变线附近和地面冷高压底部的区域。高空低槽东移,700hPa西南急流的南压,使得700hPa温度下降为-3．7℃,温度条件变化有利于产生降雪。中低层辐合、高层辐散及较强的上升运动,为强降雪提供较好的动力条件。850—700hPa的逆温层有利于冻雨、暴雪出现,当700hPa温度≥-1℃时,出现冻雨;当温度≤-3℃时,出现暴雪。对流层中层较好的水汽输送,是暴雪发生的重要原因之一。     

Decadal Relationship Between Atmospheric Heat Source and Winter-Spring Snow Cover over the Tibetan Plateau and Rainfall in East China

By using a reverse computation method and the NCEP/NCAR daily reanalysis data from 1960 to 2004, the atmospheric heat source （AHS） was calculated and analyzed. The results show that AHS over the Tibetan Plateau （TP） and its neighboring areas takes on a persistent downtrend in spring and summer during the foregone 50 years, especially the latest 20 years. Snow depth at 50 stations over the TP in winter and spring presents an increase, especially the spring snow depth exhibits a sharp increase in the late 1970s. A close negative correlation exists between snow cover and AHS over the TP and its neighboring areas, as revealed by an SVD analysis, namely if there is more snow over the TP in winter and spring, then the weaker AHS would appear over the TP in spring and summer. The SVD analysis between AHS over the TP in spring and summer and rainfall at 160 stations indicates that the former has a negative correlation with summer precipitation in the middle and lower reaches of the Yangtze River, and a positive correlation with that in South China and North China. The SVD analysis of both snow cover over the TP in winter and spring and rainfall at the same 160 stations indicates that the former has a marked positive correlation with precipitation in the middle and lower reaches of the Yangtze River, and a reversed correlation in South China and North China. On the decadal scale, the AHS and winter and spring snow cover over the TP have a close correlation with the decadal precipitation pattern shift （southern flood and northern drought） in East China. The mechanism on how the AHS over the TP influences rainfall in East China is discussed. The weakening of AHS over the TP in spring and summer reduces the thermodynamic difference between ocean and continent, leading to a weaker East Asian summer monsoon, which brings more water vapor to the Yangtze River Valley and less water vapor to North China. Meanwhile, the weakening of AHS over the TP renders the position of the subtropical high further westward and the r     

山东半岛一次持续性强冷流降雪过程的成因分析

利用NCEP/NCAR逐日6 h再分析资料和观测资料,诊断分析了2005年12月3～21日山东半岛北部沿海地区发生的罕见持续性强降雪过程.结果表明: 降雪以西北气流下的冷流降雪为主,具有典型冷流降雪分布特征;有利的大气环流形势造成强冷空气频繁,经过渤海暖海面时产生较大海气温差,是降雪持续时间长、强度大的直接原因;一定的海气温差是冷流降雪的重要指标,产生冷流降雪时山东北部近海海域的海气温差常在22K以上;冷流暴雪产生在高能舌、对流层低层辐合、中层辐散的上升运动区,上升运动层浅薄;水汽来源于渤海,水汽辐合层位于超低层(925 hPa高度以下);对流层中低层的垂直速度、散度场、涡度场的动力耦合结构配置有利于暴雪的形成和维持;特殊的低山丘陵地形强迫抬升是冷流降雪的触发机制,对暴雪的产生起到增幅作用.     

2008年初四川盆地极端低温雨雪灾害的水汽汇合机制探讨

利用NCEP/NCAR资料研究了2008年1月中下旬四川盆地的极端低温雨雪灾害。结果表明:四川盆地的低温雨雪天气与南来的水汽变化及长江流域的锋生作用有密切关系,在对流层中低层700 hPa上,四川盆地长时间存在稳定的水汽辐合区,水汽辐合的时段基本与盆地冷空气活动时间段一致,这为低温降水的发生提供了水汽条件。另一方面,长江流域长时间存在一个"东西带状"分布的锋生带,这个锋生带的稳定使南来的西南水汽在四川盆地及长江流域以南地区受阻,从而形成了水汽长时间封闭,并引起了中低层的对流不稳定。因此,低层"东西向带状"锋生的长期维持使南来水汽受封闭是产生此次灾害的重要物理机制之一。     

2008年桂西低温雨雪冻害特点及成因分析

利用观测实况、数值预报产品等资料,通过一般统计学和天气学诊断分析的方法,对2008年1~2桂西低温雨雪冻害极端天气事件进行分析,揭示了该次灾害有平均气温低、持续时间长、冻雨和冰冻影响及受灾特别严重等特点,造成灾害的主要成因为蒙古高压长期稳定偏强,高纬乌拉尔山高压和巴湖横槽不断重建崩溃,低纬南支西风槽异常活跃,冷暖空气在华南地区上空交绥等大气环流异常。     

低温雨雪冰冻灾害对桂林市农业的影响

2008年1月12日至2月20日,桂林市区及各县遭受了1951年以来持续时间最长,平均气温低,覆盖范围广,破坏力强的低温雨雪冰冻灾害性天气。对交通、电力、通信等行业,特别是农作物造成严重灾害。通过分析这次冰冻雨雪天气过程的特征及各种农作物的受灾情况,总结经验,为今后的农业生产提供指导和依据。     

桂北冬季地面气象观测注意事项

对2008年11月大规模低温雨雪冰冻灾害天气过程的地面气象观测工作的注意事项及技术细节进行了分析。     

A New Triple-Moment Blowing Snow Model

This paper presents a new triple-moment blowing snow model PIEKTUK-T by including predictive equations for three moments of the gamma size distribution. Specifically, predictive equations for the total number concentration, total mass mixing ratio, and total radar reflectivity for blowing snow are included. Tests in the context of idealized experiments and observed case studies demonstrate that the triple-moment model performs better than the double-moment model PIEKTUK-D in predicting the evolution of the number concentration, mixing ratio, shape parameter, and visibility in blowing snow, provided that the fall velocities for the total number concentration, mass mixing ratio, and radar reflectivity are weighted by the same order of the respective moments in both models. The power law relationship between the radar reflectivity factor and particle extinction coefficient found in PIEKTUK-T is consistent with one observed in snow storms. Coupling of the triple-moment blowing snow model to an atmospheric model would allow realistic studies of the effect of blowing snow on weather and climate.