天津城区暴雪的环流形势与雷达特征分析

利用常规观测资料和天津新一代天气雷达资料,对20022017年发生在天津城区的4次暴雪天气过程进行了分析,结果表明:4次暴雪过程均属于回流型降雪,但环流形势和影响系统却不尽相同;暴雪主要产生在500 hPa和700 hPa高空槽、850 hPa切变线东移的形势下;水汽主要来源于700 hPa西南急流及850 hPa低空和925 hPa超低空急流的水汽输送。回流东北风在天津地区形成冷空气垫,有利于西南暖湿气流的爬升,加强了地面的动力抬升作用。通过对暴雪过程的雷达径向速度场分析看到,暴雪过程具有零速度等值线闭合特征,此特征是冬季降雪过程独有的特征,反映了近地面层与中高层之间的风切变,闭合越完整表明切变越强烈,可以直观地预警暴雪量级。另外,高仰角上中尺度辐合线维持时间的长短与降雪量之间对应关系较好,可以作为预警降雪量级的一个指标。VWP图上从观测到西北风出现到降雪结束平均需要12 h,这可以作为暴雪结束时间的预报指标。     

贵州铜仁一次罕见暴雪过程分析

本文将利用常规探测资料、NCEP再分析资料和多普勒雷达资料,对2018年12月29～30日铜仁市暴雪过程的环流形势特征与成因进行分析,结果表明：此次暴雪过程发生在高空南支槽、多波动槽东移、700hPa西南暖湿急流输送及850hPa东北回流冷垫的环流背景下,表现出持续时间长、范围广、强度大、积雪深的特征;强降雪阶段对流层低层有来自孟湾的源源不断的水汽输送,湿层厚度增强,且有较强的水汽辐合;700hPa较强的垂直上升运动及对流层中低层较强的垂直风切变利于暴雪天气的发生;强降雪时刻暴雪区800hPa以上位于高层冷平流、低层暖平流的叠加区域,为不稳定大气;此次降雪具有对流性和持续性特征,雷达反射率回波云团具有列车效应。     

冷垫背景下冻雨和极端大暴雪成因机制分析

利用常规气象资料、通辽市和赤峰市多普勒雷达资料、气候极端降雪以及NCEP的FNL(1°×1°)逐6 h再分析资料,对2020年11月17-19日内蒙古中东部极端回流大暴雪天气进行分析。研究表明：500 hPa东移高空槽前暖湿气流、 700 hPa西南急流以及暖式切变线为降雪提供了丰富的水汽和动力辐合抬升机制,地面至850 hPa均为偏东风冷垫,中高空西南暖湿空气沿低层冷垫爬升产生锋生,是造成此次大暴雪的主要原因。降雪最强时段,从低层到高层均为上升运动,中低层水汽几乎接近饱和状态,深厚湿层有利于产生高效率的强降雪;通辽探空图有冰相层、逆温层、融化层、中性层等多种特殊层结,并有明显表征冻雨的“象鼻”层结曲线;低层东北风急流与中高层西南急流形成强的垂直风切变和温度差,动力锋生在降雪期间一直维持,动力锋生最强阶段和降雪最强时刻相对应。雷达反射率有0℃层亮带,50～55 dBz带状强回波;基本径向速度低层长时间维持东北急流构成的冷垫,并有一对正负速度中心的风速核,形成“牛眼”结构,“牛眼”结构代表边界层出现急流核;雷达基本径向速度图低层东北风,中高层西南急流,很好地反映了西南暖湿急流在冷垫上爬升...     

鲁南初冬一次罕见特大暴雪的成因分析

利用常规气象观测资料和NCEP/NCAR逐6 h再分析资料,对2015年11月23—24日山东南部出现的一次罕见特大暴雪天气过程进行诊断分析。结果表明：1）这是一次典型的回流形势降雪,850 hPa东南风急流影响的鲁南地区降雪强度较大,而东北风急流影响的区域降雪强度较弱。2）700 hPa强西南低空急流、850 hPa东南低空急流为鲁南地区降雪提供了充沛的水汽,水汽通量的强辐合区域即为大暴雪的发生区域。3）暴雪区上空散度呈现出弱辐散—强辐合—强辐散的垂直结构;暴雪落区与高空的强辐合中心以及强上升运动中心吻合度较高。4）暴雪期间,850～925 hPa之间维持一个逆温层;强冷空气使得925 hPa以下边界层温度锐降导致降雨迅速转雪,降雪持续时间长是鲁南地区产生异常强降雪的重要原因。     

石家庄一次秋季罕见暴雪天气过程物理诊断

利用NCEP再分析资料,采用天气学诊断方法,对2009年11月10—12日石家庄地区出现的一次历史同期罕见区域性暴雪天气过程的环流特征和物理量场进行了探讨。结果表明:此次暴雪天气过程属典型的东北回流型降雪,地面从贝加尔湖南下冷高压与中国河套低压倒槽、700 hPa暖式切变线和500 hPa高空槽是主要影响系统。低空西南急流与超低空东北急流耦合,在为暴雪提供水汽和热量输送的同时加强了抬升运动。水汽的垂直输送导致局地比湿显著增大,深厚的湿层和强烈的水汽辐合为暴雪提供了充沛的水汽条件。"高空辐散、低空辐合"以及强劲的上升运动是暴雪的动力条件,降雪强度最大时段对应上升运动的强盛发展阶段。暴雪开始阶段云水含量的时空演变特征,一方面显示了水汽的迅速增加与爬升,另一方面也说明了地形的强迫抬升作用不容忽视。850 hPa温度低于700 hPa,有利于水汽经过此层时被凝华成固态。逆温层提前24 h出现,而且暴雪最强时段内两层温差均为5℃以上,这对暴雪预报具有指示意义。     

石家庄一次秋季罕见暴雪天气过程物理诊断分析

利用NCEP再分析资料,采用天气学诊断方法,对2009年11月10—12日石家庄地区出现的一次历史同期罕见区域性暴雪天气过程的环流特征和物理量场进行了探讨。结果表明：此次暴雪天气过程属典型的东北回流型降雪,地面从贝加尔湖南下冷高压与河套低压倒槽、700 hPa暖式切变线、500 hPa高空槽是主要影响系统。低空西南急流与超低空东北急流耦合,在为暴雪提供水汽和热量输送的同时加强了抬升运动。水汽的垂直输送导致局地比湿显著增大,深厚的湿层和强烈的水汽辐合为暴雪提供了充沛的水汽条件。“高空辐散、低空辐合”以及强劲的上升运动是暴雪的动力条件,降雪强度最大时段对应上升运动的强盛发展阶段。暴雪开始阶段云水含量的时空演变特征,一方面显示了水汽的迅速增加与爬升,另一方面也说明了地形的强迫抬升作用不容忽视。850 hPa温度低于700 hPa,有利于水汽经过此层时被凝华成固态。逆温层提前24 h出现,而且暴雪最强时段内两层温差均为5 ℃以上,这对暴雪预报具有指示意义。     

2016年初冬河南区域暴雪过程诊断分析

针对2016年初冬河南省首场区域强暴雪过程，利用常规观测资料、L波段雷达探空资料和NCEP再分析资料等，从影响系统和物理量诊断方面深入分析其发生发展机制，结果表明:宽广的纬向型环流中不断有短波槽东移，东北冷涡深厚且维持时间较长，是暴雪发生的大尺度环流背景；中高层偏南气流，低层偏北气流的流场配置起至关重要的作用:850～925 hPa东北急流迫使暖湿空气抬升为暴雪发生提供“冷垫”的同时，与500～700 hPa西南急流形成强垂直风切变和深厚的锋生区，加强的斜升运动和锋面次级环流，对暴雪起增幅作用；700 hPa作为关键层，西南暖湿急流输送水汽的同时与冷涡后部冷空气交汇于黄淮地区形成的辐合切变线，是暴雪发生的重要动力抬升机制，其南北摆动形成了河南中西部和东南部两个降雪大值中心；暴雪区随着“冷空气楔”逐步南压时，其上层始终存在湿正压项大于零且湿斜压项小于零的湿位涡绝对值高值中心，有利于对称不稳定能量的释放和暴雪的发生。     

基于多种探测资料对华北中部一次回流暴雪过程的分析

2020年1月5日07时至6日04时（北京时,下同）华北中部出现一次回流暴雪天气,过程最大降雪量15.5 mm。文中应用ERA5再分析和多种高分辨率观测资料分析了此次暴雪的大尺度天气背景和本地动、热力状况,探讨了暴雪落区、强度演变和降雪微物理特征及成因。结果表明,受河套地区地面倒槽和东北平原高压影响,900 hPa以下东北气流（被称为“回流”）自东北平原经渤海抵达华北平原,早于降雪7 h开始影响华北中部,受太行山阻挡在华北平原形成浅薄的近地面中尺度辐合线,对应暴雪落区;暴雪落区位于500 hPa高空槽前、700 hPa南北走向切变线东侧,850 hPa受西南低涡外围东南气流影响。降雪前1 h石家庄市观测到800 m以下转为东北风,1 km以下气温迅速下降至?5—?1℃,形成“冷垫”;暴雪区上空700 hPa附近低空急流较降雪早2 h出现,随后急流变厚、向下伸展至2 km高度,其下部暖湿空气沿“冷垫”爬升触发降雪,急流风速增至极值（19 m/s）和急流指数达峰值（约8）与大于1 mm/h强降雪时段重合,此时700 hPa上下为上升运动和水汽输送的大值中心。本次降雪粒子直径多为0.35—0.55 mm,降雪强度与粒子数浓度呈线性正相关;降雪云层位于1.3—5.5 km高度,大致以3 km （约?10℃）为分界线,下层为冰雪混合层,上层为冰雪层,冰雪层相对湿度与地面雪花粒子浓度及降雪强度呈正相关。基于雨滴谱仪探测资料反演的地面反射率因子与降雪强度拟合关系为Z=149.85R1.14。      

铜仁市暴雪天气的环流配置及物理量特征分析

铜仁市暴雪发生的频次低,2005年至今仅发生5次,因此准确的量级和落区预报难度较大。本文选取2004-2021年铜仁市出现的5场暴雪天气过程,就大尺度环流形势、高低空天气系统配置和物理量特征进行分析,找出暴雪环流形势以及物理量预报指标。结果显示：铜仁市暴雪发生时,500hPa中高纬为两槽一脊形势,我国东北地区-日本海低槽加深发展,中低纬孟湾附近有南支低槽系统东移;海平面场上贝加尔湖西部冷高中心强度为1060hPa,大于1030hPa的等压线线进入铜仁市。暴雪落区出现在500hPa高空槽和南支槽前、700hPa西南急流左侧或低涡切变线南侧、850hPa东北急流或东北风前部的风速辐合区内。暴雪日500hPa温度平均低于-16℃,700hPa温度为-2～-6℃,850hPa温度-6～-8℃,地面气温为0～-4℃,地面气温越低降雪持续时间越长。暴雪发生时大气中层700～500hPa上升运动明显增强,这可作为降雪增大的预示指标;散度场总体表现为低空辐合、高空辐散的特征,当辐合层次伸展更高时,有利于暴雪天气的持续;水汽通量散度辐合主要在850hPa,平均值为-3.6×10-6﹒g﹒cm-2﹒hPa-1﹒s-1; 500hPa比湿值≥1.5g/kg是暴雪发生的参考指标。     

山西一次低空偏东风暴雪天气结构特征分析

应用常规地面、探空观测资料和NCEP 1°×1°再分析资料,对2011年11月28-29日山西低空偏东风暴雪天气结构特征进行了探讨。结果表明:(1)这次低空偏东风暴雪是由高空西风槽、低空切变线、地面回流和倒槽共同影响造成。降雪前约18 h,山西925~850 hPa上空出现东北风;降雪前约12 h,山西中南部地面出现较强东北风,强降雪期间地面东北风强劲;降水开始前,低空东北风是干冷性质,降水开始后低空东北风是湿冷垫。(2)暴雪的水汽来源主要是源于西太平洋的偏东风水汽输送在北部湾附近转向的西南水汽与南支槽前的西南气流在西南地区汇合北上,再与西风槽前西南水汽结合;强降雪出现在700 hPa水汽通量中心西北侧等值线密集区且风向气旋性辐合的偏南气流区域。(3)强降雪伴随山西上空深厚湿层、500 hPa以下明显水汽辐合,以及800 hPa以上对流层中强上升气流,而上升区下是明显的下沉气流,这是由低空偏东风的契入产生的。(4)强降雪期间300 hPa西风急流不断东移南压,山西位于其入口区右侧,出现强辐散,有利于地面河套倒槽发展、维持,以及垂直上升运动的增强。     

CHARACTERISTICS AND TRENDS OF CLIMATIC EXTREMES IN CHINA DURING 1959–2014

The spatial and temporal variations of daily maximum temperature(Tmax), daily minimum temperature(Tmin), daily maximum precipitation(Pmax) and daily maximum wind speed(WSmax) were examined in China using Mann-Kendall test and linear regression method. The results indicated that for China as a whole, Tmax, Tmin and Pmax had significant increasing trends at rates of 0.15℃ per decade, 0.45℃ per decade and 0.58 mm per decade,respectively, while WSmax had decreased significantly at 1.18 m·s~(-1) per decade during 1959—2014. In all regions of China, Tmin increased and WSmax decreased significantly. Spatially, Tmax increased significantly at most of the stations in South China(SC), northwestern North China(NC), northeastern Northeast China(NEC), eastern Northwest China(NWC) and eastern Southwest China(SWC), and the increasing trends were significant in NC, SC, NWC and SWC on the regional average. Tmin increased significantly at most of the stations in China, with notable increase in NEC, northern and southeastern NC and northwestern and eastern NWC. Pmax showed no significant trend at most of the stations in China, and on the regional average it decreased significantly in NC but increased in SC, NWC and the mid-lower Yangtze River valley(YR). WSmax decreased significantly at the vast majority of stations in China, with remarkable decrease in northern NC, northern and central YR, central and southern SC and in parts of central NEC and western NWC. With global climate change and rapidly economic development, China has become more vulnerable to climatic extremes and meteorological disasters, so more strategies of mitigation and/or adaptation of climatic extremes,such as environmentally-friendly and low-cost energy production systems and the enhancement of engineering defense measures are necessary for government and social publics.     

Revisiting the Concentration Observations and Source Apportionment of Atmospheric Ammonia

正While China’s Air Pollution Prevention and Control Action Plan on particulate matter since 2013 has reduced sulfate significantly, aerosol ammonium nitrate remains high in East China. As the high nitrate abundances are strongly linked with ammonia, reducing ammonia emissions is becoming increasingly important to improve the air quality of China. Although satellite data provide evidence of substantial increases in atmospheric ammonia concentrations over major agricultural regions, long-term surface observation of ammonia concentrations are sparse. In addition, there is still no consensus on     

LOW-FREQUENCY CIRCULATION AND EXTENDED-RANGE FORECAST IN CONNECTION WITH AUTUMN EXTREME HEAVY RAINFALL PROCESS IN HAINAN

Observed daily precipitation data from the National Meteorological Observatory in Hainan province and daily data from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis-2 dataset from 1981 to 2014 are used to analyze the relationship between Hainan extreme heavy rainfall processes in autumn (referred to as EHRPs) and 10–30 d low-frequency circulation. Based on the key low-frequency signals and the NCEP Climate Forecast System Version 2 (CFSv2) model forecasting products, a dynamical-statistical method is established for the extended-range forecast of EHRPs. The results suggest that EHRPs have a close relationship with the 10–30 d low-frequency oscillation of 850 hPa zonal wind over Hainan Island and to its north, and that they basically occur during the trough phase of the low-frequency oscillation of zonal wind. The latitudinal propagation of the low-frequency wave train in the middle-high latitudes and the meridional propagation of the low-frequency wave train along the coast of East Asia contribute to the ‘north high (cold), south low (warm)’ pattern near Hainan Island, which results in the zonal wind over Hainan Island and to its north reaching its trough, consequently leading to EHRPs. Considering the link between low-frequency circulation and EHRPs, a low-frequency wave train index (LWTI) is defined and adopted to forecast EHRPs by using NCEP CFSv2 forecasting products. EHRPs are predicted to occur during peak phases of LWTI with value larger than 1 for three or more consecutive forecast days. Hindcast experiments for EHRPs in 2015–2016 indicate that EHRPs can be predicted 8–24 d in advance, with an average period of validity of 16.7 d.     

AN ATTRIBUTION ANALYSIS OF CHANGES IN POTENTIAL EVAPOTRANSPIRATION IN THE BEIJING–TIANJIN–HEBEI REGION UNDER CLIMATE CHANGE

Based on the measurements obtained at 64 national meteorological stations in the Beijing–Tianjin–Hebei (BTH) region between 1970 and 2013, the potential evapotranspiration (ET0) in this region was estimated using the Penman–Monteith equation and its sensitivity to maximum temperature (Tmax), minimum temperature (Tmin), wind speed (Vw), net radiation (Rn) and water vapor pressure (Pwv) was analyzed, respectively. The results are shown as follows. (1) The climatic elements in the BTH region underwent significant changes in the study period. Vw and Rn decreased significantly, whereas Tmin, Tmax and Pwv increased considerably. (2) In the BTH region, ET0 also exhibited a significant decreasing trend, and the sensitivity of ET0 to the climatic elements exhibited seasonal characteristics. Of all the climatic elements, ET0 was most sensitive to Pwv in the fall and winter and Rn in the spring and summer. On the annual scale, ET0 was most sensitive to Pwv, followed by Rn, Vw, Tmax and Tmin. In addition, the sensitivity coefficient of ET0 with respect to Pwv had a negative value for all the areas, indicating that increases in Pwv can prevent ET0 from increasing. (3) The sensitivity of ET0 to Tmin and Tmax was significantly lower than its sensitivity to other climatic elements. However, increases in temperature can lead to changes in Pwv and Rn. The temperature should be considered the key intrinsic climatic element that has caused the "evaporation paradox" phenomenon in the BTH region.     

ANALYSIS OF “BIMODAL PATTERN” STORM ACTIVITY CHARACTERISTICS OF THE BAY OF BENGAL

Storms that occur at the Bay of Bengal (BoB) are of a bimodal pattern, which is different from that of the other sea areas. By using the NCEP, SST and JTWC data, the causes of the bimodal pattern storm activity of the BoB are diagnosed and analyzed in this paper. The result shows that the seasonal variation of general atmosphere circulation in East Asia has a regulating and controlling impact on the BoB storm activity, and the “bimodal period” of the storm activity corresponds exactly to the seasonal conversion period of atmospheric circulation. The minor wind speed of shear spring and autumn contributed to the storm, which was a crucial factor for the generation and occurrence of the “bimodal pattern” storm activity in the BoB. The analysis on sea surface temperature (SST) shows that the SSTs of all the year around in the BoB area meet the conditions required for the generation of tropical cyclones (TCs). However, the SSTs in the central area of the bay are higher than that of the surrounding areas in spring and autumn, which facilitates the occurrence of a “two-peak” storm activity pattern. The genesis potential index (GPI) quantifies and reflects the environmental conditions for the generation of the BoB storms. For GPI, the intense low-level vortex disturbance in the troposphere and high-humidity atmosphere are the sufficient conditions for storms, while large maximum wind velocity of the ground vortex radius and small vertical wind shear are the necessary conditions of storms.     

Information for Authors

正AIMS AND SCOPE Atmospheric and Oceanic Science Letters (AOSL) publishes short research letters on all disciplines of the atmosphere sciences and physical oceanography.     

Information for Authors

AIMS AND SCOPE
Atmospheric and Oceanic Science Letters （AOSL） publishes short research letters on all disciplines of the atmosphere sciences and physical oceanography. Contributions from all over the world are welcome.     

Information for Authors

AIMS AND SCOPE Atmospheric and Oceanic Science Letters （AOSL） pub- lishes short research letters on all disciplines of the atmos- phere sciences and physical oceanography. Contributions from all over the world are welcome.     

INFORMATION FOR AUTHORS

正Aims Scope Advances in Atmospheric Sciences(AAS)is an international journal on the dynamics,physics,and chemistry of the atmosphere and ocean with papers across the full range of the atmospheric sciences,co-published bimonthly by Science Press and Springer.The journal includes Articles,Note and Correspondence,and Letters.Contributions from all over the world are welcome.