基于多源观测资料对张家口一次雨雪天气降水相态特征的分析

利用ERA5再分析资料及云雷达、微波辐射计和SA双偏振多普勒雷达等多源观测资料,分析2020年11月17—19日张家口地区一次雨雪天气的降水相态演变特征。结果表明:在高空低槽、中低层低涡与地面倒槽配合下,高空槽后西北气流引导冷空气南下造成气温迅速下降,导致降水相态变化。过程前期整层大气均为强暖平流,且地面气温较高,降水相态为雨。18日傍晚冷平流发展强烈,各层温度迅速降低,整层变为冷层,导致降水相态转换为雪。散度和垂直速度的诊断表明降雨时段的动力强迫主要位于高层,降雪时段则主要位于低层。云雷达高分辨率资料可以反映0℃层变化,大于10 dBZ的质心变化可以指示降水强度变化,降雨时的基本速度最大可达6~8 m·s^(-1),而降雪时则小于2 m·s^(-1)。微波辐射计高分辨率时空资料可以准确判断雨雪转换时间,降水开始之前3~5 h积分水汽含量出现跃升与峰值。双偏振雷达和微波辐射计结合可以对降水粒子相态实现准确判断,可用于降水相态转换的临近预报。     

沙颍河流域一次基于高分辨资料的降水相态分析

利用常规气象资料、NCEP 0. 25°×0. 25°分析资料以及微波辐射计、风廓线雷达等高分辨率资料,采用诊断和统计方法,对2017年2月21日沙颍河流域一次雨雪过程中降水相态进行分析。结果表明:在高空低槽与东路冷空气共同作用造成雨雪天气的背景下,925 h Pa及以下冷高压底部的偏北冷空气造成低层持续降温,导致降水相态变化。过程前期700 h Pa以下为强暖平流,冷平流在900 h Pa以下且较为浅薄,温度层结为冷层-暖层-冷层-暖层,冰晶粒子下落融化形成雨滴。降水中后期冷平流发展强烈导致温度迅速下降,整层温度变为冷层,导致相态为雪;即使下游局部地区仍有暖层,但暖层浅薄、低层冷层深厚,相态也为雪。雨雪转换时0℃层高度下降明显,降雨阶段0℃层在抬升凝结高度以上,降雪阶段0℃层降到抬升凝结高度以下; 0℃层亮带回波在相态转换时出现明显变化,其亮带高度逐渐降低。微波辐射计的温湿廓线、云底高度以及液态水等在雨雪转换中均有显著变化,液态水含量在雨雪转变时迅速增大。风廓线风场定性反映了冷空气持续南下,低层冷垫增厚,导致相态转变以及降水强度增加;风廓线速度定量反映出降雨和降雪之间的差异,降雨速度范围为1. 5～7. 0 m·s-1,降雪速度范围在0. 25～1. 5 m·s-1;雨雪转换时下落速度明显减小,可用于相态转变的监测和预报。     

黔北一次冰雹天气过程C波段双偏振雷达资料分析

【目的】为进一步探索C波段双偏振雷达参数指标的本地化运用。【方法】利用习水C波段双偏振雷达资料、地面自动站资料、探空资料,对2022年3月16日发生在黔北的一次冰雹天气过程成因以及双偏振雷达回波特征进行分析。【结果】（1）此次强对流天气发生在500 hPa前倾槽前、低层低涡切变东南侧,中低空急流的北侧及地面低压倒槽内,同时午后升温及中高层干冷平流入侵,使得层结更趋于上干冷下暖湿的不稳定层结,冷锋前沿的地面辐合线为过程提供了触发机制。（2）过程由多单体风暴引发,最大反射率因子达65 dBz,40 mm冰雹出现了三体散射,剖面图中出现了悬垂结构和有界弱回波区,低层观测到辐合速度对。（3）对比30 mm和40 mm的冰雹双偏振参数发现：融化层以上冰雹Z_DR在-1~0.2 dB,CC值在0.90~0.99之间,K_DP均为0;从融化层以下,30 mm冰雹CC值在0.70~0.90,40 mm冰雹CC值在0.80~0.97,两者有所区别,Z_DR也有明显增加,在0~4 dB之间;由于融化层以下大雨滴的混合,K_DP在0~3.1 °·km^-1之间。（4）大冰雹偏振参数出现明显Z_DR柱、K_DP柱,CC谷,CC图中出现明显的非均匀波束充塞,Z_DR和CC图中有明显的三体散射现象。【结论】该文仅是对一次多单体天气过程个例的偏振参数特征粗略分析,未来仍需分析更多个例用以完善C波段双偏振天气雷达在强对流天气中各种偏振参数的标准,为实际业务提供更精准的参考。     

南昌地区雷击事件雷达回波特征分析

【目的】南昌地区地处亚热带地区,为了更好地监测预警雷电天气,提醒人们减少雷击事件的发生。【方法】使用南昌市历史雷击事件资料、江西雷达拼图资料和南昌、九江SA雷达基数据等资料,采用天气学、雷达气象学等原理及方法,对南昌地区雷击事件的雷达回波特征进行分析。【结果】（1）2013—2022年雷击事件共出现23次,孤立单体回波有2段闪电高发期,超级单体、飑线回波带和短带回波只有1个闪电高发期。（2）500 hPa高空槽、中层切变及西南急流等天气系统重叠最易产生雷击事件。（3）飑线回波带是由多个对流单体、强回波单体甚至超级单体回波排列组成的带状回波;短带回波长度比飑线回波带要短,回波强度也偏弱。【结论】上述结论为南昌地区雷电天气的监测预警提供分析依据。     

苏南两次回流天气过程形势特征和降水相态分析

利用常规观测资料、0.25°×0.25° FNL资料、微波辐射计资料和风廓线雷达资料，对发生在苏南的两次回流天气过程的环流特征、大气层结特征等进行分析。结果表明：高纬度地区500 hPa是两槽一脊的环流形势，近地面层持续受东北风影响，西南暖湿气流在底层冷垫上爬升，是回流降雪天气形势；从东北平原回流南下的冷空气湿度小，在降水中只起到了"冷垫"的作用。中低层西南暖湿气流差异导致两次降雪强度存在差异；近地面层的降温在雨和雪的区分判别上影响更大，统计2012—2022年初苏南地区8个降雪个例发现，苏南地区，满足T₈₅₀≤-4 ℃，T₉₂₅≤-3 ℃，T_{1 000}≤1 ℃，T_{2 m}≤2 ℃这样的温度阈值条件时开始雨转降雪；当1 515 gpm≤H_700-850≤1 575 gpm，1 289 gpm≤H_{850-1 000}≤1 317 gpm时，相态易由雨转雪。中低层西南气流、底层东北风的加强，2 000 m左右高度风场的转变，短波槽（或切变线）触发了不稳定能量的释放，导致降雪发生；当中低层西南气流减弱转为西北气流后，大气水汽含量降低，降雪结束。     

一次强寒潮引发的浙北不同地区雨雪气象条件差异

雨雪相态的转化是浙江省冬季降水预报服务的重点和难点。利用NCEP再分析格点资料、浙江省自动气象站和两部风廓线雷达观测资料,对2016年1月一次强寒潮在浙江北部地区导致不同的降水相态进行气象要素的对比分析。结果发现:高空强冷平流、中低层强暖湿气流为雨雪过程提供了良好的动力和水汽条件。对比分析发现:在同等强度的冷空气影响下,浙江北部沿海地区雨夹雪或雪需要大气低层的气温比内陆地区更低。根据不同降水相态下T_(2 m)、Φ_(850-1 000)和Φ_(925-1 000)指标差异对沿海地区和内陆地区分别建立雨雪判别指标。检验表明统计指标对浙北地区雨雪相态预报有较好的指示意义,且风廓线雷达资料500 m以下边界层平均垂直速度变化可以辅助判定地面雨雪的相态变化和地面降雪的强弱。     

北京延庆山区降雪云物理特征的垂直观测和数值模拟研究

基于风廓线雷达、云雷达、粒子谱仪、微波辐射计和自动站等垂直观测设备,结合中尺度数值模式WRF对2017年3月23~24日北京延庆海坨山地区的一次降雪过程进行了观测和数值模拟研究。研究结果表明:垂直探测仪器结合中尺度数值模式可以获得降雪的宏观结构和微物理信息,有助于对降雪的深入研究。此次降雪过程由中高层西南及偏南暖湿气流与低层东南偏冷空气交汇造成动力和水汽辐合抬升形成,4~5 km高度处的风切变有利于降雪的增强。上升气流有助于水汽的输送、冰雪转化以及雪晶凝华、聚合,冰晶数浓度中心对应着上升运动顶部。然而此次降雪云系低层过冷云水含量不足,降雪回波<20 dBZ,回波顶高<7 km,雪花垂直下落速度<2 m s-1,地面降水量大值与低层强回波区对应。降雪粒子谱分布范围较窄,以直径1 mm左右的小粒子为主,相态主要为干雪,基本不存在混合相态。     

一次强寒潮过程的多相态降水分析

综合利用常规观测资料、双偏振雷达和雨滴谱仪探测资料,对2020年3月28日发生在常州地区的一次罕见强寒潮引起的降雨、雨夹雪和雪不同相态降水天气进行了分析。结果表明：(1)此次3月末罕见强寒潮和降水主要是在高空槽、中低层切变线和西南急流与地面冷高压配合下,强冷平流入侵以及850 hPa明显干层的蒸发(或升华)吸热的共同作用引起的,中低层温度的急剧下降,导致降水相态发生变化。(2)双偏振雷达监测到3种降水相态呈现出不同的偏振变量特征：降雨相态向雨夹雪转变时,反射率因子Z增大,差分反射率因子Z_DR增大,相关系数C_C有明显的低值带状分布,呈现出Z>30 dBz,Z_DR>1 dB,C_C<0.95组成的雨雪相态混合区域;而纯雪则为Z>22 dBz,Z_DR<1 dB,C_C>0.98。(3)雨滴谱仪显示降雨阶段主要由高浓度小粒子构成,雨滴速度-尺度谱呈现为倾斜的带状;雨夹雪阶段数浓度减小,粒径范围较宽,质量加权平均直径明显增大,雨滴速度...     

一次江淮地区突发降雪的多源观测特征及其成因分析

利用激光雨滴谱仪资料、地面观测资料、合肥双偏振雷达资料和欧洲中心ERA5再分析资料，对2022年1月26日发生在江淮之间一次短时强降雪天气过程中滴谱变化和雷达回波特征进行分析，并探讨雨雪相态变化的成因，结果表明：（1）本次江淮之间突发的强降雪过程中，雨雪转换迅速，降水相态变化时间提前于地面温度变化，合肥地区温度变化明显强于周边地区。（2）此次短时强降雪发生在锋生强迫过程形成的高架雷暴中，强烈的上升运动、降水粒子的融化和蒸发引起温度负变化，导致降温过程自上而下产生，表现为地面温度下降落后于雨雪相态的变化。（3）降雪过程先后出现降雨、雨夹雪、纯雪3个阶段，雨（雪）滴谱的时间演变特征变化明显；转雪后降水粒子的下落末速度降低、粒径增大、滴谱明显变宽。（4）雷达观测显示此次降雪回波顶高度较高，超过6.5km，低空1km有强度超过50dBZ强反射率因子带并延伸到地面。反射率因子、相关系数（CC）和降水粒子产品（HCL）在降雪过程的发展中有明显特征。     

2016年怀化2次低温雨雪天气过程对比分析

利用地面、高空常规观测资料、NCEP1°×1°再分析资料以及CB型多普勒雷达资料,从天气实况、环流形势、物理量场和雷达回波等方面对2016年影响怀化的2次低温雨雪天气过程进行对比分析。结果表明：“1.22”过程500 hPa中高纬呈西高东低形势,“3.9”过程呈两槽一脊形势。2次过程影响系统均包含有高空槽、低空急流、切变线和地面冷锋。“1.22”过程冷空气强度强于“3.9”过程,降雪更明显、气温更低,“3.9”过程水汽条件更好,降雨更强。700 hPa温度和地面2 m气温对怀化预报降水相态有重要指示意义。物理量方面,2次过程中南部降水量强于北部,“3.9”过程降雨量更大,表明中层水汽输送、水汽辐合以及涡度场对雨雪过程发生发展、强度和落区具有指示意义。雷达回波方面,2次过程降雪阶段主要以层状云降水回波为主。深厚的强冷空气对“1.22”过程中的降雪和低温、强暖湿气流对“3.9”过程的较强降水起着重要作用。同时,地形对降雪相态以及降水强度有一定的影响。     

1,800 Years of abrupt climate change, severe fire, and accelerated erosion, Sierra Nevada, California, USA

This paper provides both a detailed history of environmental change in the Sierra Nevada over the past 1,800 years and evidence for climate teleconnections between the Sierra Nevada and Greenland during the late Holocene. A review of Greenland ice core data suggests that the magnitudes of abrupt changes in temperature and precipitation increased beginning c. 3,700 and 3,000 years ago, respectively. Precipitation increased abruptly 1,300 years ago. Comparing paleotemperature data from Cirque Peak, CA with paleoprecipitation data from Pyramid Lake, NV suggests that hot temperatures occurred at the beginnings of most severe droughts in the Sierra Nevada over the past 1,800 years. Severe fires and erosion also occurred at Coburn Lake, CA at the beginning of all severe droughts in the Sierra Nevada over the past 1,800 years. This suggests that abrupt climate change during the late Holocene caused vegetation and mountain slopes in some areas to be out of equilibrium with abruptly changed climates. Finally, the ending of drought conditions in Greenland coincided with the beginning of drought conditions in the Sierra Nevada over the past 1,800 years, perhaps as a result of the rapidly changed locations of the Earth??s major precipitation belts during abrupt climate change events.     

The microstructure of selected, small, isolated, cumulus clouds near Red Deer, Alberta

Physical experiments designed to explore the potential of rain augmentation through airborne glaciogenic seeding on small, isolated non-precipitating cumuliform clouds near Red Deer, Alberta were carried out during the period 1982–1985. The microstructure of 90 cumulus congestus clouds have been documented through repeated in-situ sampling using a cloud physics instrumented aircraft platform. Observations from the inspection passes of 57 clouds seeded with either dry ice pellets or silver iodide pyrotechnics, and all the passes of 33 natural clouds are presented.Measurements of the cloud droplet concentration indicate that Alberta cumulus clouds are typically continental in nature, with an average droplet concentration of 535 cm⁻³ and an average droplet diameter of 10.6 μm. Alberta clouds have average liquid water contents of 0.57 g m⁻³, with a peak 1-sec value of 3.17 g m⁻³. The 1-km average liquid water contents are 0.83 g m⁻³, with a peak value of 2.81 g m⁻³. Cloud lifetimes vary between 11 and 20 minutes. Concentrations of naturally occurring ice crystals are found to be low. The average maximum 1-km ice concentration was 31⁻¹, and the peak 1-km concentration was 73.11⁻¹ in the natural cloud dataset. Evidence of precipitation-sized particles was detected in 21% (7 of 33) of the clouds, and precipitation below cloud base was detected in 6% (2 of 33) of the clouds.A comparison of the Alberta cloud characteristics to the cumulus clouds from different locations showed that there are some distinct differences between Alberta clouds and the clouds from the other regions.     

Performance of CMORPH,TMPA, and PERSIANN rainfall datasets over plain,mountainous, and glacial regions of Pakistan

The present study aims at the assessment of six satellite rainfall estimates (SREs) in Pakistan. For each assessed products, both real-time (RT) and post adjusted (Adj) versions are considered to highlight their potential benefits in the rainfall estimation at annual, monthly, and daily temporal scales. Three geomorphological climatic zones, i.e., plain, mountainous, and glacial are taken under considerations for the determination of relative potentials of these SREs over Pakistan at global and regional scales. All SREs, in general, have well captured the annual north-south rainfall decreasing patterns and rainfall amounts over the typical arid regions of the country. Regarding the zonal approach, the performance of all SREs has remained good over mountainous region comparative to arid regions. This poor performance in accurate rainfall estimation of all the six SREs over arid regions has made their use questionable in these regions. Over glacier region, all SREs have highly overestimated the rainfall. One possible cause of this overestimation may be due to the low surface temperature and radiation absorption over snow and ice cover, resulting in their misidentification with rainy clouds as daily false alarm ratio has increased from mountainous to glacial regions. Among RT products, CMORPH-RT is the most biased product. The Bias was almost removed on CMORPH-Adj thanks to the gauge adjustment. On a general way, all Adj versions outperformed their respective RT versions at all considered temporal scales and have confirmed the positive effects of gauge adjustment. CMORPH-Adj and TMPA-Adj have shown the best agreement with in situ data in terms of Bias, RMSE, and CC over the entire study area.     

BDA方案对台风背景高温天气预报的改进

广州地Ⅸ的高温天气主要是受副热带高压和台风外围下沉气流的影响所致.文中采用BDA(Bogus Data Assimila-tion)方法,探讨BDA方案对广州地区台风背景条件下高温预报的改进能力.选取2005年7月中旬广州地区出现的高温天气进行研究.这是比较典型的受副热带高压和台风(海棠)共同影响造成高温的天气过程.分析有无采用BDA方案的模式初始场.结果表明:采用BDA方案同化Bogus模型可以调整台风中心位置和强度,使所得到的初始场中心位置与观测更为接近,台风强度(气压梯度力、风速)比末用Bogus的情况强,与观测值更为接近.数值模拟的结果表明,采用了BDA方案的敏感试验可以更好地预撤台风路径和台风中心强度变化,从而更好地预报高温天气,对高温区分布、日平均温度大小等的预报都有改进.文中对引起这种预报差异的原因进行了讨论,并探讨高温预报改进的可能机制.大气下沉运动的增强是高温预报改进的主要原因.敏感试验由于广州中低层大气的水汽减少,大气的下沉增强,致使天空的云量减少,对太阳短波辐射的阻挡减小,从而地面吸收热量增多,温度升高,输送给大气的感热增加,大气气温升高.采用BDA方案可以改进模式在台风"海棠"过程对广州高温的预报.     

Roughness length of sea,sand, and snow

Profiles of wind speed in driving sand and snow show roughness length increasing as the square of the friction velocity, in accordance with Charnock's relation for the roughness length of the sea.     

Distribution,speciation, and budget of atmospheric mercury

Total gaseous mercury (TGM) concentrations over the Atlantic Ocean and over Central Europe were measured repeatedly in the years 1978–1981. The latitudinal TGM distribution showed a pronounced and reproducible interhemispherical difference with higher TGM concentrations in the Northern Hemisphere. TGM was found to be vertically well mixed within the troposphere. The TGM concentration seems to increase with time at a rate of 10±8%/yr in the Northern and 8±3%/yr in the Southern Hemisphere. Measurements of mercury speciation showed that elemental mercury is the main TGM component contributing more than 92% and 83% of TGM in marine and continental air, respectively. The tropospheric mercury burden was calculated to be 6×10⁹g. The interhemispheric distribution and temporal and spatial variability of TGM imply a tropospheric residence time of TGM of about 1 yr. Sink strengths calculated independently from the measured mercury concentration on particles and in rainwater are consistent with the above figures.