Characteristics and Mechanisms of Persistent Wet–Cold Events with Different Cold-air Paths in South China

We investigate the characteristics and mechanisms of persistent wet–cold events(PWCEs)with different types of coldair paths.Results show that the cumulative single-station frequency of the PWCEs in the western part of South China is higher than that in the eastern part.The pattern of single-station frequency of the PWCEs are“Yangtze River(YR)uniform”and“east–west inverse”.The YR uniform pattern is the dominant mode,so we focus on this pattern.The cold-air paths for PWCEs of the YR uniform pattern are divided into three types—namely,the west,northwest and north types—among which the west type accounts for the largest proportion.The differences in atmospheric circulation of the PWCEs under the three types of paths are obvious.The thermal inversion layer in the lower troposphere is favorable for precipitation during the PWCEs.The positive water vapor budget for the three types of PWCEs mainly appears at the southern boundary.

Analysis of Characteristics of Snow Accumulation and Its Meteorological Influencing Factors during a Snowstorm Process in Ulanqab City

Based on the data of national observation stations of CMISS system,artificial encrypted observation data of snow depth,ERA5 reanalysis data,the snowfall process in Ulanqab City from March 17 to 19,2022 was analyzed.It is found that the influencing system of the snowfall process was upper-air trough combined with ground inverted trough.Snowfall was not proportional to snow depth,and the relationship between the maximum snow depth and total snowfall varied in different value intervals.A large intensity of snowfall was a necessary condition for the formation of abundant accumulated snow when ground temperature was higher than 0℃.After the formation of accumulated snow,ground temperature changed less,and it was easy to produce accumulated snow as ground temperature was lower.The lower the temperature,the more conducive to the generation of accumulated snow.

Spatial and Temporal Distribution Characteristics of Snowstorm in Ulanqab City in Recent 30 Years

Based on the data of daily snowfall and weather phenomena of 11 national meteorological stations in Ulanqab City from 1991 to 2020,the spatial and temporal distribution characteristics of snowstorm were analyzed.The results show that the snowstorm in Ulanqab had obvious seasonal distribution characteristics,mainly happening in spring(March-May)and autumn(September-November).It also had obvious regional distribution in space,and the snowstorm center appeared in Chahar Right Wing Middle Banner and Jining District,namely the east side of the Yinshan Mountain.In the past 30 years,the amount of snowstorm in the whole year in Ulanqab showed a certain fluctuation trend,and the number of snowstorm days had shown an obvious upward trend since 2011.

Analysis of a Type Ⅱ Snowstorm Process in the Early Spring of 2022 in Ulanqab

Based on the observation data of meteorological stations,Doppler radar observation data of Ulanqab City,and ERA-5 reanalysis data,a snowstorm process in Ulanqab City from March 17 to 18,2022 was analyzed.The results show that this was a type Ⅱ snowstorm process generated under the joint influence of upper trough and ground low inverted trough and frontal cyclone.The main period of snowfall can be divided into two time stages,and the total snowfall was more in the south and less in the north,which was consistent with that of average specific humidity field.Water vapor conditions provided by strong water vapor transport and convergence,strong upward movement shown by large vertical velocity field,and the suction action of high-and low-layer divergence and convergence were the reasons for the hourly heavy snowfall on the 18^(th).During the process,radar echoes were mainly sheet-shaped,and composite reflectivity was 15-25 dBZ in most areas.The zero speed line in the first period was positively"S"-shaped,and there was warm advection and southwest wind.On the morning of the 18^(th),after the cold front transited the city,Ulanqab City was gradually controlled by northwest wind,and the snow tended to end.

Analysis of Snowstorm Process in Northeast China during 5-9 November, 2021

In November 2021, Northeast China had more precipitation than in the same period. Among them, Heilongjiang and Jilin provinces in the Northeast China were the highest precipitation in the same period. I study a snowfall weather process from November 5 to 9, which mainly includes dynamic situation, synoptic background and situation. The results show that: In the middle and high latitudes of Eurasia, circulation is adjusted from zonal to meridional with large fluctuations. The northerly wind behind the trough continuously transports the polar cold air to the south. The northwest airflow behind the trough led the cold air to erupt to the southeast. In the process of moving southward, the cold air meets the warm and humid air in front of the trough, causing snowfall in the northeast. The southerly airflow and southeasterly airflow on the east side of the vortex continued to transport warm and humid airflow from the Yellow Sea and the Sea of Japan, which enhanced the snowfall.

Reflection on China's Disaster Prevention and Mitigation Construction after Rainstorm and Snowstorm

On July 10,2004,Beijing was hit by the rainstorm that has not been seen for many years,which caused water accumulation in many places of the urban area,power supply interruption in many places,and traffic paralysis for nearly 5 h. On July 12,2004,the rainstorm in Shanghai lasted less than 1 h,but it caused 7 deaths,more than 20 injuries,extensive power outages and traffic paralysis. At the end of 2005,the continuous snowfall in Weihai City of Shandong Province for half a month caused direct economic losses of over 200 million yuan,and the continuous heavy snowfall had a serious impact on people’s lives. From July 17 to 23,2021,Henan Province suffered a rare extremely heavy rainstorm in history,with a direct economic loss of 120.6 billion yuan. Faced with such urban meteorological disasters and other types of urban disasters,combined with the current situation of disaster prevention and reduction in China,what will managers,decision-makers,and experts and scholars think about from them.

中国雪都阿尔泰山暖区暴雪水汽特征分析

为进一步做好中国雪都阿勒泰山冬季冰雪旅游暴雪预报预警服务,利用阿尔泰山固态降水数据、NCEP/NCAR再分析和GDAS数据,应用天气学诊断和不同水汽分析方法对2021年阿尔泰山区3次暴雪过程环流背景和水汽特征进行分析。结果表明:①3次暴雪过程均为新疆北部典型的暖区暴雪过程。②欧拉方法分析表明,该区水汽主要源于大西洋及其沿岸,阿尔泰山西边界为水汽输入,东边界和南边界为水汽输出,中、低层的水汽输入量与暴雪量关系密切,水汽通量散度辐合区位于对流层低层。③HYSPLIT(拉格朗日)方法分析表明,水汽源地主要来自北冰洋、欧洲,其次是中亚和加拿大,与上述结论明显不同;对暴雪区综合贡献较大的是对流层低层的水汽。④构建了阿尔泰山区暴雪过程水汽贡献模型,700 hPa及以上水汽自源地到达关键区后主要从偏西(西南)路径输入暴雪区,700 hPa以下水汽到达关键区后,在环流合适时主要从东南路径输入暴雪区,但从偏西(西南)和西北路径输入暴雪区的水汽也不容忽视;水汽主要在对流层低层聚集,并辐合抬升。

气象灾害下民航机场韧性指数研究

为探究气象灾害下不同机场的韧性表现与引起韧性差异的原因,首先,提出基于机场功能水平的机场韧性定义,涵盖抵抗性、鲁棒性、恢复性3个子特性;然后,通过航班数据计算气象灾害下机场功能水平,得出机场韧性及子特性指数,从而反映机场的韧性水平;最后,以暴风雪灾害为例,分析美国受影响机场的韧性指数分布特征及不同机场韧性指数差异的原因,进一步分析冬季风暴、洪水、热带风暴、龙卷风灾害下受影响机场韧性指数特点以及灾害类型对机场韧性指数的影响。研究结果表明:机场韧性指数的差异主要由抵抗性指数引起;暴风雪灾害下引起机场韧性指数差异的关键因素为吞吐量、飞机机身维修计划等级、发动机维护水平;机场在冬季风暴、洪水与在暴风雪灾害下的韧性指数基本一致,韧性指数相对差值最低分别为7.519%、5.521%,平均相对差值为23.021%、21.037%,机场韧性指数计算方法可较准确地反映机场韧性属性。

“12·14”山东暴雪过程降水相态的多源观测分析

基于毫米波云雷达、降水天气现象仪、风廓线雷达、双偏振雷达、自动气象站等多源观测资料及欧洲中期天气预报中心(European Centre for Medium-Range Weather Forecasts,ECMWF)第五代大气再分析(ECMWF Reanalysis v5,ERA5)资料,对2023年12月14日山东暴雪过程的环流背景和降水粒子微物理参数进行分析,探讨新型观测资料在降水相态监测与预报中的应用。结果表明:(1)此次过程受高空槽、低空西南急流和江淮气旋影响,伴随地面气温下降和中层暖层消退,出现雨、雨夹雪、冰粒和雪等相态。(2)降水天气现象仪探测发现,雪和雨的下落末速度均较小,雪粒子直径超过8 mm,雨粒子直径大多在4 mm以下。(3)毫米波云雷达观测到反射率因子、径向速度、谱宽和垂直液态水含量降低时,雨夹雪转为雪。(4)风廓线雷达显示雨夹雪和冰粒阶段对应强的低空西南急流和最大垂直速度(4~5 m·s^(-1)),转雪时3 km以下垂直速度降低至2 m·s^(-1)左右。(5)相关系数(C c)、差分反射率(Z DR)和水平极化反射率因子(Z h)等双偏振参量可判断融化层亮带,亮带的下降和消失可指示此次过程雨向雪的转换。

“23·12”山东半岛特大海效应暴雪特征及成因

采用地面气象观测站、多普勒天气雷达、闪电、积雪深度人工加密观测资料、常规观测及欧洲中期天气预报中心(European Centre for Medium-Range Weather Forecasts,ECMWF)第五代大气再分析(ECMWF Reanalysis v5,ERA5)资料,对2023年12月15—22日山东半岛特大海效应暴雪过程的降雪特征及极端性成因进行了分析。结果表明:(1)此次过程有4站积雪深度突破本站历史极值,有1站2 d的日降雪量为山东半岛海效应降雪有气象记录以来的最大值,文登积雪深度达74 cm,超过山东所有国家级地面气象观测站纪录,是一次极端海效应暴雪事件。(2)欧亚中高纬度阻塞形势下两次异常强冷空气持续影响渤海和山东半岛地区,850 hPa温度最低降至-21~-20℃,冷空气强度明显强于往年12月海效应暴雪过程,造成降雪持续时间长、累计降雪量大。异常强冷空气是此次极端暴雪过程产生的关键因素,渤海海面温度(简称“海温”)异常偏高是有利的海温背景。(3)冷空气强、海温偏高造成海气温差偏大,700 hPa以下产生对流不稳定,使得降雪强度大;强降雪发生在海气温差快速增大阶段。(4)925 hPa以下存在来自渤海的北—东北风与内陆地区的西北风构成的切变线,产生强上升运动,切变线长时间维持形成“列车效应”。(5)主要降雪时段强垂直上升运动、高相对湿度层的温度为-20~-12℃,适宜树枝状冰晶形成和维持,有利于产生大的积雪和降雪含水比;2 m气温持续低于-5℃,0 cm地温在降雪开始时即降至0℃以下,且两次强降雪过程仅间隔1 d,均有利于降雪累积产生极端积雪深度。

Effect of Snowstorm on Winter Wheat Production in Tacheng Basin in 2009

Located in Eurasia inland,Tacheng Basin belongs to arid and semi-arid climate region in middle temperate zone,and the main crops include winter wheat,spring wheat,maize,seeding-watermelon,sugar beet and so on,while winter wheat is the main food crop.From November 2009 to March 2010,a snowstorm which occurred every 60 years appeared in Tacheng Basin,and there was more snowfall in five continuous months,while this snowfall broke through the extreme value in history and reached a historic high.Based on the comparison between practical monitoring data and history data of winter wheat,the effects of snowstorm on winter wheat production were analyzed.

江淮气旋暴雪和海效应暴雪个例的微物理特征对比

利用雨滴谱等多源观测资料,对2023年12月山东江淮气旋暴雪和海效应暴雪的微物理特征进行了对比分析。结果表明:(1)相比于海效应暴雪,江淮气旋暴雪云系云顶高度较高,云顶亮温较低,对流强度较强。(2)江淮气旋暴雪的粒子数浓度高、粒子谱较窄、粒子体积较小、降雪强度较大;海效应暴雪的粒子数浓度低、粒子谱较宽、粒子体积较大、降雪强度较小。(3)江淮气旋暴雪的粒子下落末速度以单峰型为主,海效应暴雪则多为双峰型;江淮气旋暴雪的粒子下落末速度及其谱宽均大于海效应暴雪。(4)江淮气旋暴雪含有较多的霰粒、冰粒、雪花,海效应暴雪则以雪花及其聚合体为主。(5)两次暴雪的等效反射率因子(Z e)-降雪强度(I s)关系有较大差异。在降雪强度相同时,海效应暴雪的Z e更大。

一次极端暴雪事件中罕见冻雨成因分析

使用常规观测、自动气象站、雷达回波及ERA5 0.25°×0.25°再分析等资料,对2021年11月8-9日发生在黑龙江省一次极端暴雪事件中罕见冻雨过程进行分析。结果表明:冻雨发生在降水强度较大时段,地面气温普遍低于0℃。垂直温度分布呈典型的“冷-暖-冷”层结特征,近地层存在强逆温层,探空温度>0℃的面积比<0℃的大。近地层冷垫是冷高压南侵时,受江淮气旋和地形阻挡,在海拔较低的松花江干流地区堆积形成。融化层在850 hPa低涡前部,西南或偏南低空急流携带暖湿空气像楔子一样插在冷空气中,持续的暖平流特征明显,地面冷垫与中层暖层之间有明显的锋区特征。电线积冰直径与融化层持续长短有很大的相关性。冻雨的形成符合“冰相融化”机制,在冻雨区具有回波强度增大的特征。

1979~2017年冬季新疆北部各区域型暴雪日水汽输送特征分析

北疆地处内陆干旱半干旱区,降水的多少对其影响十分巨大。尤其在全球变暖背景下,北疆地区的降水异常增多。本研究利用1979~2017年北疆40个站点冬季降水资料、ECMWF ERA-Interim和NCEP/NCAR再分析资料,基于HYSPLIT v4.9模式讨论北疆4个区域型暴雪日的水汽输送特征及可能影响机制。研究发现:(1)各区域型水汽以西边界输入为主,但西天山型有少量水汽从北边界输入,天山型有部分水汽从南边界高层输入;(2)北部型、西部型和西天山型的水汽通道均位于中纬西风带,但具体位置有所差异。北部型以地中海和黑海水汽输送为主,贡献率为58.8%;西部型以里海西南侧水汽输送为主,贡献率为70.8%;西天山型以黑海和里海东南侧水汽输送为主,总贡献率为72.9%;天山型的水汽源地主要位于印度、伊朗附近,贡献率为64.2%;(3)各区域型位势高度的距平南北均呈现“正—负”分布,西东均呈现“负—正—负”分布,但中心强度、位置及范围有所不同,这种差异导致影响区域的不同。

“12·14”山东暴雪过程的极端性特征及成因

利用国家级地面气象观测站、风廓线雷达、X波段双偏振相控阵雷达等多源观测资料和欧洲中期天气预报中心(European Centre for Medium-Range Weather Forecasts,ECMWF)第五代大气再分析(ECMWF Reanalysis v5,ERA5)资料,总结了2023年12月13—14日山东大范围暴雪、局地大暴雪(简称“12·14”暴雪)极端性的特征和成因,并与2021年11月7日山东极端暴雪过程(简称“11·7”暴雪)对比分析了降雪量和雪水比差异的原因。结果表明:(1)典型的暖平流型天气形势是产生极端暴雪有利的环流背景条件,低层切变线和风速辐合区在鲁西北叠加,形成强烈而持久的上升运动。(2)低空急流异常偏强,降水强度不仅与低空急流的强度有关,而且与其厚度有关。当3.0 km高度保持低空急流的强度时,10 m·s^(-1)风速到达的高度越低,降雪强度越大。(3)700 hPa比湿超过4 g·kg-1、850 hPa比湿超过3 g·kg-1的持续时间均长达10 h以上,为极端暴雪过程提供了充足的水汽。850 hPa比湿和比湿平流远远高于“12·14”暴雪过程,是“11·7”过程最大累计降雪量大于“12·14”过程的原因之一。(4)“12·14”暴雪过程垂直运动旺盛,最大上升速度位于不稳定层顶的前沿,处于-20~-10℃层,有利于树枝状冰晶生长,降雪效率高。对流层整层温度低于0℃,雪花下落过程中没有融化,雪水比高,积雪深度大。“11·7”暴雪过程初期最大上升运动中心高度低,形成更多柱状冰晶,经过暖层时融化,雪水比低,积雪深度小于“12·14”暴雪过程。

四种检验方法在山东暴雪预报中的应用对比

利用山东122个国家级地面气象观测站2017—2021年中1—3月和11—12月“24 h降雪量p≥10.0 mm”的暴雪实况资料,采用二分类法、邻域空间检验法(以下简称“邻域法”)、时间偏移法和量级模糊法等4种方法对山东暴雪预报进行检验与对比。结果表明:(1)山东暴雪具有明显的时空分布特征,暴雪主要出现在半岛北部地区,鲁东南和半岛南部产生暴雪的概率最小;暴雪出现次数的年际变化和月际变化较大,最多年份出现98次,最少年份仅有5次,2月是高发月,占全年暴雪总次数的38.5%。(2)现行业务中应用最广泛的二分类法检验的预报命中率较低,其中24 h预报命中率仅为12.08%,主要原因是该方法受到空间、时间和量级的多重影响,不能精细准确地反映预报能力。(3)邻域法、时间偏移法和量级模糊法对24 h的暴雪预报命中率分别为14.40%、14.69%和30.05%;相较于二分类法,这3种检验方法的预报命中率均有较大幅度提高,空报率和漏报率均有较大幅度下降。(4)融合邻域法、时间偏移法和量级模糊法的综合检验法,能从空间、时间和量级3个维度区分出预报差异,检验结果更加精细准确,有利于引导预报员放下“检验评分低”的思想包袱,做出更加科学客观的预报,进一步提升预报服务效果。

“12 ·14”山东暴雪过程积雪深度特征及成因

利用常规观测、积雪深度逐时加密观测资料和欧洲中期天气预报中心(European Centre for Medium-Range Weather Forecasts,ECMWF)第五代大气再分析(ECMWF Reanalysis v5,ERA5)资料,对2023年12月13—15日山东一次极端暴雪天气过程积雪特征及其成因进行分析,得到以下结论:(1)此次过程是一次江淮气旋暴雪天气过程,具有持续时间长、降水相态复杂、基础温度低、降温幅度大和积雪深度厚等特征。(2)最大小时新增积雪深度可达8 cm;过程平均雪水比为0.7 cm·mm^(-1),呈“西大东小”的分布特征。(3)有积雪的站近地面温度从开始降雪到地面产生积雪,气温和雪面温度均呈下降趋势,0 cm地温在降雪前期降温明显,积雪形成后地温不再明显变化。无积雪的站在整个降雪时段内近地面温度可分为4种情况。(4)雪水比随气温变化最明显;积雪形成之后地温对雪水比大小影响不大;当雪水比小于0.75 cm·mm^(-1)时,雪水比随雪面温度降低而增大,当雪水比大于0.76 cm·mm^(-1)后,雪面温度不再有明显变化。

2023年和2005年山东两次极端海效应暴雪的对比

利用常规气象观测资料、降水天气现象仪资料、美国国家海洋和大气管理局(National Oceanic and Atmospheric Administration,NOAA)资料、欧洲中期天气预报中心(European Centre for Medium-Range Weather Forecasts,ECMWF)第五代大气再分析(ECMWF Reanalysis v5,ERA5)资料等对2023年12月山东半岛的海效应特大暴雪和2005年12月持续性海效应强降雪过程的高空形势、海气温差、低层切变线、大气水凝物等进行了综合分析。结果表明:(1)亚欧大陆强大的经向高压脊和脊前冷涡环流是发生海效应暴雪的大尺度环流背景。2005年高压脊宽广、稳定少动是海效应强降雪持续时间长的主要原因,2023年高压脊、冷涡的经向特征更加显著,冷空气爆发力强。(2)2005、2023年渤海海面温度较常年偏高;2023年偏高2.5℃的范围更广,12月20—21日海气温差超过30℃。(3)出现暴雪时,山东半岛北部存在偏西风和北—东北风之间的风场辐合;荣成站出现暴雪时,低层需要更强劲的引导气流。(4)2023年12月20—21日,云体主要由冰晶和雪晶构成,较多雪晶位于上升气流上方,与冰粒子分布区域重叠,说明除了水汽凝华外,冰雪晶粒子之间的聚合作用对雪粒子的增长有很大帮助,聚合产生的枝状雪粒子有利于积雪深度增大,文登站雨滴谱也表明,21—22日雪粒子直径偏大的特征更明显。

2024年1月大气环流和天气分析

2024年1月大气环流的主要特征是:北半球极涡呈偶极型分布,欧亚中高纬环流呈纬向“两槽一脊”型,东亚大槽偏东。1月,全国平均降水量为16.3 mm,较常年同期(14.1 mm)偏多15.6%;全国平均气温-3.8℃,较常年同期(-4.8℃)偏高1.0℃。月内气温起伏较大,出现了1次全国型寒潮过程和2次大范围持续性雾-霾天气过程。其中20—22日的寒潮天气过程具有影响范围广、降温幅度大、大风持续时间长、暴雪极端性强等特点。

基于拉格朗日方法的鲁南一次回流大暴雪的水汽来源分析

利用拉格朗日轨迹模式HYSPLIT,结合E-P诊断法,以及区域源汇归因法,研究了2015年鲁南一次回流大暴雪的水汽来源及输送路径。结果表明,影响暴雪过程的水汽路径有3条:一条是回流路径,沿中低空的回流冷空气经渤海、黄海输送至鲁南;另一条是南支路径,沿槽前西南气流经华南、华中向北输送至鲁南;第三条是偏西路径,沿平直的西风气流从黄土高原东侧输送至鲁南。源汇区定量分析显示,回流暴雪的水汽源地有6个,分别是渤海黄海区域、华东中北部区域、中南区域、南海区域、亚洲大陆南部和北部。对比不同源地的水汽贡献发现,中南区域与渤海黄海区域对回流暴雪的贡献最大,这与两者初期较高的源区水汽摄取量密切相关。华东中北部区域虽然初期水汽摄取较少,但由于其沿途水汽损耗较低并且在目标区域降水转化率较高,因此最终的水汽贡献不容忽视。尽管亚洲大陆南部和北部区域初期水汽吸收量明显高于华东中北部区域的,但过高的沿途水汽损耗,最终导致它们的实际水汽贡献低于华东中北部区域的贡献率。中国南海区域的水汽贡献最小,一方面是由较高的水汽损耗所致,另一方面还与初期较低的水汽吸收量有关。