To explore the formation mechanism of severe dense fog (SDF), we compare the similarities and differences in surface meteorological conditions and boundary layer structures among SDF, dense fog (DF) and heavy haze (HH) events based on observations from tethered balloon soundings, microwave radiometers, wind profiler radars and conventional ground-based meteorological stations, as well as analysis fields from the European Center for Medium-Range Weather Forecasts. In addition, we investigate the roles and mechanisms of ultra low-level jets (ULLJs) and vertical wind shear in the formation of the SDF. The results indicate that during the formation and development stages of the SDF, the maximum surface cooling exceeds 4°C, whereas no obvious cooling was observed during DF and HH events. Additionally, during the formation and maintenance stages of the SDF, the boundary layer was characterized by strong temperature inversion, an “upper-level dry and lower-level wet” (UDLW) structure, the presence of an ULLJ, and pronounced vertical wind shear. Similar ULLJs (or strong wind speeds) and vertical wind shear also occurred during DF and HH events. The latter featured a deep and strong inversion, but without the UDLW structure. The above differences indicate the following formation mechanisms of the SDF. (1) On SDF days, northerly (non-northerly) winds prevailed above (below) the jet, forming an UDLW structure that favors surface radiative cooling and humidification. In contrast, on DF and HH days, southerly winds prevailed above the jet, which was not conducive to the formation of the UDLW structure and surface radiative cooling. (2) The SDF days featured vertical wind shear that resulted in a distinct “upper-level stable and lower-level turbulent” structure in the surface layer, whereas the boundary layer remained generally stable on HH days. Consequently, the key factor determining whether the HH evolves into the SDF is the vertical wind profile within the boundary layer, which governs the formation of the UDLW structure and further creates the cooling, moistening and turbulence conditions favorable for the formation and maintenance of SDF.

As one of the important sources of aerosols, new particle formation events can affect the spatiotemporal dis-tribution of CCN. To analyze the characteristics of new particle formation (NPF) events and their effects on cloud condensation nuclei (CCN) during the summer at Mt.Tian, the data of aerosol size distribution and CCN number concentrations were measured using an aerosol wide-range particle size spectrometer and a cloud condensation nuclei counter from August 4 to 25, 2019, and combined with meteorological data and polycyclic aromatic hydrocarbons (PAHs) data. NPF events at Mt.Tian occurred seven days during the observation period, accounting for 32% of the observation days, and usually occurred at 13:00 and ended at 17:00 (Beijing Time, same below). NPF events particularly influenced the diurnal variations of aerosol number concentrations in different modes. The number concentrations of nucleation and Aitken modes increased rapidly while the accumulation mode increased slowly during 13:00 and 17:00 on NPF days. The peak particle number concentrations in the nucle-ation, Aitken and accumulation modes on NPF days were 5360.1 cm-3, 7185.6 cm-3 and 839.3 cm -3, respec-tively, which were 3.3, 1.8 and 1.7 times higher than those on non-NPF days during 13:00 and 17:00. The meteorological conditions of temperature higher than 20 degrees C, air pressure lower than 806 hPa, relative humidity (RH) lower than 40% and wind speed higher than 2.2 m s- 1 are favorable for the occurrence of NPF events. The NPF events at Mt.Tian can impact the mass concentration of PAHs. More Fluoride (FL) and Phenanthrene (PHE) were generated on NPF days. The mass concentrations of FL and PHE on NPF days were 0.002 & PLUSMN; 0.003 ng m- 3 and 0.020 & PLUSMN; 0.010 ng m- 3, which were 243.54% and 28.44% higher than those on non-NPF days, respectively. NPF events were conducive to increased CCN concentration at Mt.Tian. After the NPF events, the mean number concentrations of CCN at each supersaturation (SS) on NPF days was about 20%-50% higher than on non-NPF days. The contribution of NPF events to the CCN number concentrations was 35.75%, 28.56%, 44.15%, 42.11% and 29.12% at 0.1%, 0.2%, 0.4%, 0.6% and 0.8% SS, respectively.

Using the fog droplet spectrum and visibility data of two dense fog processes in 12-13 January2019 in Shouxian,Anhui Province,the microphysical characteristics（such as the size distribution,droplet number concentration,liquid water content,average diameter,spectral width,etc.） and the correlations among microphysical properties（number concentration,liquid water content,average diameter） in the different stages of fog are analyzed.The results show that both the fog processes were radiation fog.If the strong inversion structure close to the ground maintains,the water vapor can be restrained in the inversion layer,conducive to the long-term maintenance of dense fog.The formation time of the fog at 20 m was later than that on the surface.In the early stages of formation,development and maturity,the microphysical characteristics of the surface fog were all larger than that at 20 m.At the late stage of maturity,the release of latent heat by condensation and ground heating might increase the intensity of turbulent mixing in the fog,making the fog uniform in the vertical direction.The fog processes at two heights were dominated by nucleation and condensation growth,but the collision-coalescence process also played an important role in the fog on the surface.From the stages of formation,development to maturity,the collision-coalescence processes of the ground fog gradually strengthened.The correlation among the number concentration,water content,and average diameter generally changed from strong positive correlation to weak positive or negative correlation.From the early stage to the late stage of the mature stage,the relationship between average diameter and number concentration of the fog at 20 m height changed from a positive correlation to a negative correlation,which was likely to be related to the factors such as turbulent motion,entrainment mixing,etc.

一个地区良好的气候状况和空气质量状况是影响游客选择出游目的地的重要因素.文章从大气负氧离子浓度状况出发,分析了泾源县城和六盘山区大气负氧离子浓度分布特征及其与气象因子的关系.结果表明:泾源县城月平均负氧离子浓度在1184个/cm3～2301个/cm3之间,年平均负氧离子浓度为1784个/cm3,六盘山区月平均负氧离子浓度在1575个/cm3～2816个/cm3之间,年平均负氧离子浓度为2221个/cm3;泾源县城和六盘山区负氧离子浓度呈现明显的季节变化,最高为夏季,春、秋次之,冬季最低;泾源县大气负氧离子浓度从4月开始明显增加,至7月达到最大值,后又逐渐减小;泾源县城和六盘山区9:00—17:00平均负氧离子浓度分别为1890个/cm3和2573个/cm3,是一天中最适合有氧出游的时间;大气负氧离子浓度与气象因子的相关性因地域不同而有差异,泾源县城负氧离子浓度与气温、相对湿度和日照时数呈显著的正相关关系,六盘山区负氧离子浓度与气温、相对湿度呈正相关关系.

Using hourly precipitation data and reanalysis data from 2014 to 2018, the meteorological factors influencing wintertime precipitation in the Ili River Valley their statistical correlation with precipitation rate are analyzed. The results show that the vapor flux, which is positively correlated with the precipitation rate, is the major factor that controlling the precipitation in the Ili River Valley. All of the upstream wind speed, vapor flux, Froude number and precipitable water are found to have impacts on the precipitation over the downstream region, and these four parameters can be used to fit the precipitation rate by using a multiple regression in terms of vapor flux. Even though strong precipitation is usually observed in existence with low stability, no obvious statistical relationship between the static stability and precipitation rate is found. The local weather systems are classified into nine types by using T-modal oblique principal component analysis. The main feature of the weather types with higher precipitation occurrence is the large vapor flux, however, the spatial distribution of precipitation varies for different weather types. A relatively uniform distribution of precipitation can be seen if the local weather condition is controlled by low pressure and large vapor flux, and the intensity of precipitation will gradually increases towards the interior of the valley if the weather condition is controlled by strong wind and the relatively low vapor mixing ratio.

利用中尺度数值模式WRF4.0,对2020年8月14日南疆博斯腾湖地区的一次暴雨过程进行了数值模拟和敏感试验,研究分析了其中尺度结构特征.结果表明:(1)此次暴雨过程是由于受到伊朗高压系统推动,中亚槽东移,在天山中部与西西伯利亚槽合并加深形成了自北向南的中天山大槽的影响,博斯腾湖区位于该大槽的正中心位置,槽前西南气流强盛,受该大槽控制,博斯腾湖地区暴雨逐渐形成和发展.(2)强降水期间暴雨中心从低层到高层均出现了强烈的上升运动,暴雨过程的水汽来源于中亚槽前偏西向的气流输送,水汽通过该输送通道源源不断地被输送至降水区,为暴雨的形成提供了有利水汽条件.(3)大气上升运动、高低空涡度和散度的有利耦合形势、低空急流的存在以及大气中不稳定能量的释放,共同触发了此次暴雨过程的发生.(4)敏感性试验表明,库鲁克塔格山对于降水有显著影响,当模式中山脉高度降低后,模拟的雨量增多,降水范围增大.

新疆位于我国西北部,地处欧亚大陆腹地,远离海洋,气候不受季风系统的直接影响,新疆北部是阿尔泰山脉,南部是昆仑山脉,中部有横贯全境的天山山脉,三山环抱塔里木盆地和准噶尔盆地形成三山夹两盆的独特地形.研究发现,新疆西部和北部的气候主要受西风带系统的影响,在天山、帕米尔高原等地则出现多雨带,山区年降水量一般超过400 mm,个别地方超过500 mm,所以天山山地也被称为干旱区的"湿岛",是新疆重要的水资源来源.姚俊强等指出天山空中拥有丰富的云水资源,运用人工增雨(雪)技术来提高云水资源降水转化率,可以极大改善西北部干旱缺水的情况,增加河流径流量,增加山区积雪、冰川储水量.

雾对交通运输有不利影响,尤其是强浓雾.本文利用2019年1月上中旬在寿县国家气候观象台应用FM-100型雾滴谱仪测量的雾滴谱数据和常规气象观测数据,分析了不同强度雾的微物理特征,以及能见度与含水量、雾滴数浓度、相对湿度之间的关系,在此基础上建立了能见度参数化方案.结果表明:(1)随着雾的强度增强,雾中含水量显著增大,大雾、浓雾和强浓雾阶段含水量平均值分别为0.003 g m?3、0.01 g m?3和0.09 g m?3;当含水量大于0.02 g m?3,出现强浓雾的比例高达95％.(2)雾滴数浓度、雾滴尺度随着雾强度增强而增大,从大雾到浓雾,雾滴数浓度显著增加(增幅67％),而从浓雾到强浓雾,雾滴尺度显著增大,平均直径、平均有效半径分别增加62％、135％;当雾滴有效半径大于4.7μm,出现强浓雾的比例高达95％.(3)强浓雾、浓雾、大雾雾滴数浓度谱分布均为双峰结构,谱分布整体偏向小粒子一端,强浓雾谱型为Deirmendjian分布,浓雾、大雾均为Junge分布;强浓雾的雾水质量浓度谱呈现多峰特征,最大峰值出现在21.5μm处,浓雾雾水质量浓度谱为双峰分布,大雾为单峰型,最大峰值均出现在5μm处.(4)含水量、数浓度与能见度均呈反相关关系,含水量对能见度的影响最为显著;分别采用全样本和分段方式建立了四种能见度参数化方案,评估检验结果表明,基于含水量的能见度分段拟合方案对能见度的估算效果最好.

2016/2017冬季在天津开展了平流雾微物理特征观测试验,结合距地66 m高度处雾滴谱和255 m气象塔大气边界层资料,借助突变和趋势一致性非参数检验方法对重度霾后接连发生的两次平流雾过程发展阶段进行客观划分,揭示雾体内部一定高度处雾滴微物理特征和尺度分布特征的观测事实,讨论其生消演变规律.结果 表明,伴随西南暖湿平流,饱和层首先在空中出现并向地面扩展,雾过程中成熟阶段观测高度范围内升温,雾层处于中性或弱不稳定层结状态.66 m高度处大雾滴持续存在,微物理特征与地面能见度准同步变化,数浓度高值出现在成熟阶段初期,而含水量、特征直径高值出现在成熟阶段后期,对应成熟阶段后期雾滴数浓度减少、地面能见度小幅跃升.消散阶段各尺度数浓度因雾滴蒸发同步减小.

Raindrop size distribution (DSD) characteristics at various altitudes in two landfalling typhoons in 2017 (Hato and Pakhar) were investigated by using laser-optical disdrometers mounted at four altitudes (10, 40, 160, and 320 m) of the Shenzhen 356-m meteorological tower. Significant differences of the DSD and derived parameters, mass-weighted mean diameter (Dm), normalized intercept parameter (NW), and standard deviation of the mass distribution σm, were observed at different altitudes for the two typhoons, while the rainwater content between the four altitudes had no statistically significant differences. The low-altitude DSDs had more midsize drops (1 < D < 3 mm), fewer large drops (D > 3 mm), and narrower distribution widths than the high-altitude ones, while the concentration of small drops varied nonlinearly with height. The value of NW decreased with height, while Dm and σm increased with height. The gamma distribution parameters N0, μ, and Λ are found to increase with decreasing height. Both the derived μ–Λ and Z–R relations were significantly varied in different altitudes.

利用WRF-Fire模式对2009年"5·21"蒙古国草原入境大火进行火场发展数值模拟研究,并通过敏感性试验分析了防火隔离带对火势的阻挡作用。结果表明,模式可以较准确地再现环境风场对本次大火蔓延过程的影响,模拟火场面积、蔓延方向与实况基本一致。第一阶段（21日12—22时,世界时,下同）在蒙古国境内起火点附近,地面为裸露地表,可燃物负载量小,近地面为东北风,火线向西南方缓慢蔓延;第二阶段（21日22时—22日11时）风向转为西北,火线经平缓均一草地向东南方发展,在到达中蒙边境前地面风速增大到8～10 m/s,且风向与坡向一致,火线迅速移向中蒙边境防火隔离带;第三阶段（22日11时—23日20时）隔离带和人工灭火有效阻止了火线继续向中国境内蔓延,此阶段风向转为南风,火线向北扩展;第四阶段（23日20时—24日12时）风速达到16 m/s以上且风向转为西北风。受东面隔离带和湖泊的阻碍,火线缓慢向南蔓延。当火线到达南面的隔离带后,受隔离带阻挡及人工扑火作业的共同作用,本次大火于26日08时结束。敏感性试验表明,若不存在隔离带,火线将在风场的驱动下继续向东南、东北方向蔓延,所经区域主要地面可燃物类型从草地过渡到针叶林,火场的蔓延将造成大面积的森林资源损失。

基于1960-2015年宁夏大雾逐日观测及大雾发生、结束时间资料,分析了宁夏四条主要高速公路大雾天气事件的时空分布特征.并运用层次分析法和模糊综合评价法,选取平均雾日数、平均持续时间、河网密度、道路密度等10个评价指标,构建宁夏高速公路大雾灾害评估模型,开展风险评价与区划.结果表明:宁夏高速公路9-11月是大雾发生最多的月份,一天中大雾事件高影响时段为02:00-08:00.大雾年平均雾日数特征为京藏高速由中间段向南北逐渐减少;定武高速西段多东段少;福银高速北段少南段多;青银高速北段多东段少.宁夏大雾天气有三个大雾灾害高风险区域中心,即京藏高速银川段、青铜峡段,定武高速中卫段,福银高速固原段.较高风险区域中心位于京藏高速平罗段,定武高速中宁段、盐池段,福银高速固原段附近,其他路段为中等到较低风险区域.

毫米波雷达在云探测方面比厘米波天气雷达和激光雷达具有显著优势,可获得更多的云粒子信息,是研究云特性的主要遥感探测设备.为了开展对毫米波雷达探测的云回波进行自动分类的研究,利用161次云回波的个例数据,统计得到了卷云、高层云、高积云、层云、层积云和积云6类云型的特征量和其他参量的数值范围,利用分级的多参数阈值判别方法,达到了自动分类的目标,通过与人工分类的初步验证,两种分类结果的一致性达到84％,其中,层云和积云的识别一致较低的原因在于样本数据有限,仅有6次层云和8次积云的个例样本数据.通过更多样本的处理,提取的特征参量更可靠,自动分类的准确率会得到提高,以便将基于毫米波雷达的云分类技术应用于将来的云观测自动化业务.

采用基本气象站和区域气象站观测资料分析了2013年6月至2014年5月期间博斯腾湖的湖陆风日变化特征和季节特征,进而通过中尺度数值模拟分析博斯腾湖湖陆风的发展过程及其与天山山谷风的相互作用.结果 表明,博斯腾湖北侧湖风与中天山南侧谷风叠加效应造成局地环流增强,从湖岸到山体,叠加效应造成的局地环流最大振幅表现出增大、减小、再增大的特点;湖岸区域湖风开始时间与距离的关系不显著,当离岸距离增大到约20km以上,距离每增加约6km,湖风开始时间推迟1h;湖北侧湖风锋穿透内陆距离比受天山主体影响较小的湖南侧远约11km;随着湖北侧湖风锋向天山靠近,湖风与谷风耦合作用不断加强.

This paper extends the theoretical framework of universal forward and backward Monte Carlo radiative transfer modeling for passive and active polarization observation simulations. The framework is built upon newly derived forward and backward vector scattering order-dependent integral radiative transfer equations (IRTEs). The unified mathematical formalism not only establishes the design of object-oriented software architecture, but also speeds up software development via the reuse of developed scalar code. The polarization simulations are implemented with the addition of the Stokes vector and the Mueller matrix weight tracing schemes. To improve numerical performance order by order, the extension implementation of hybrid scattering order-dependent variance reduction techniques are given detailedly, with a focus on the formulation of scattering phase matrix truncation on the basis of remodeling vector IRTEs. To enrich polarization simulation features, not only scattering operators but also source vector function and detector response matrix function are formulated in unified mathematical forms for the hierarchies organization of various atmosphere, surface, source and detector classes. The framework was fully implemented in Multiple-Scaling-based Cloudy Atmospheric Radiative Transfer (MSCART) model. For passive simulation, it not only can handle all one-and three-dimensional (1D and 3D) test cases in the Phase A and B of the International Polarized Radiative Transfer (IPRT) intercomparison project by simulating area-averaged polarized radiance using forward and backward algorithm, but also can simulate polarized radiance in a specified direction at a specified position using backward algorithm; For active simulation, lidar backscatter range-resolved signals can be simulated using forward algorithm. (C) 2019 The Authors. Published by Elsevier Ltd.

2015年12月在南京市郊进行雾的外场综合试验,观测得到20-21日雨后两次强浓雾的爆发性增强过程.利用常规气象资料、边界层廓线、雾滴谱等,分析此次典型雾过程的天气背景和边界层结构特征,探讨雾爆发性增强的原因.结果 表明:雨后地表及近地层高湿环境为雾的形成提供了充足的水汽,南京冬季冷高压控制下稳定的天气层结,以及夜间的辐射冷却作用,极有利于辐射雾的产生.而雾的爆发性增强,主要和降温与增湿有关.晴天夜间地表向上长波辐射增强引起的强降温,日出后地面的强蒸发作用使得近地表水汽增多,都可直接引起雾的爆发性变浓.强的贴地逆温层的形成是雾爆发性增强的关键,易于近地面水汽的积累.而超低空急流的产生,有利于加速逆温层的贴地增强.

During the period of heavy haze in North China(September 30,2013),aerosol particle distribution and the vertical distribution characteristics of aerosol and cloud condensing nuclei(CCN)were analyzed by using observational datasets from the aircraft of Cheyenne ⅢA.The results show that the aerosol number concentration in both areas decreases with the increase of height, the effective radius of aerosol particles in both cities is close to each other,the range of aerosol effective radius in the accumulation mode and the coarse mode are 0.05~0.35 μm and 0.8~2.2 μm,respectively.Two inversion layers appear in and above the boundary layer, with a significant increase in the aerosol concentration below the inversion layers.The analysis of aerosol back trajectories indicates that the aerosol at the height of 3 000 m is mainly controlled by long transportation of the air mass,the aerosol at 1 500 m is mainly from the south side of the ground pollutant with a short transport distance, the aerosol at the height of 500 m is affected by the southern air mass with a high concentration of aerosol fine particles.The profiles of CCN shows that the number concentration of CCN decreases as the height increases,and the presence of inver-sion layer has a cumulative effect on CCN.Then the relationship between aerosol and CCN in both cities has been studied,the result shows that correlation coefficient of aerosol-CCN in both areas is above 0.95,while the correla-tion coefficient in clouds is just 0.83,and the number concentration of CCN in clouds is lower than outside,which indicates that the consumption of CCN in the activation of cloud droplets.The width of aerosol particles spectrum is narrow below cloud base,and is large in clouds or above cloud top height.

Based on data of radiation fog events in Xuanen, Hubei province, 2010, this paper analyzes the microphysical process and evolution characteristics of radiation fogs with complicated substrate in the upper and middle reaches of the Yangtze River, and compares them with findings in other areas. Results are as follows: radiation fog in Xuanen is evidently weaker in droplet number concentration and liquid water content than land fogs in other areas. Its liquid water content fluctuates obviously, 0.01g/m3 with visibility of 1,000 meters, which is quite different from that in urban areas, but similar to the Nanling Mountains. Bi-modal droplet distribution is likely to occur in Xuanen mountain radiation fog (MRF) events. Statistical analysis shows that the observed droplet size distribution can be piecewise described well by the Gamma distribution. There is a positive correlation between liquid water content, fog droplet concentration and mean radius, especially in the development and dissipation stage. Condensation growth and droplet evaporation are major processes of Xuanen MRF. The dissipation time coincided with the time when the grass temperature reached the peak value, which indicated that dew evaporation is a key role in maintaining Xuanen MRF. In the early stage of dense fog's growth, droplets with diameter of over 20 micrometers can be observed with visibility of 800-1,000m, which might be caused by the transportation of low cloud droplets to earth's surface by turbulence. Big droplets in the initial stage correspond to higher water content, leading to the higher observed value of water content of Xuanen MRF.

The Taihang Mountains are located between the Shanxi Plateau and the North China Plain,and extend over 400 km from north to south.Since the range rises steeply from the North China Plain to an elevation of approximately 1 000 to 1 200 m,hail is much more common along the eastward slope of the mountains.It was found that the upper level observations at 00 UTC on May 25th,2011 showed that the 500 hPa synoptic pattern in North China was dominated by a northwesterly flow,with a cold advection behind the pressure trough.A cyclonic wind shear was located at 850 hPa,with a southwesterly warm/moist conveyor belt to the east of the shear line.It was determined that,from 17:00 to 21:00 (BST),convective precipitation occurred in Xingtai,at the eastern foot of the Taihang Mountains,with amounts of up to 29.3 mm observed.Also,hail of up to 5 cm in diameter was observed in the steep eastward-facing slope.A Weather Research and Forecasting(WRF) model was utilized in an attempt to determine if the dynamical and physical impacts of the Taihang Mountains and its surrounding terrain may have contributed to the triggering and development of the severe convection.The impact of the resolution effects of the terrain data of the topographic height on the precipitation simulation in this special scenario were evaluated by a comparison between resolution of the 5-minute and 30-second terrain resolution with the model's horizontal grid space of 1.67 km.It was observed in this study that the finer representation of the complex terrain improved the precipitation simulation.The simulated results indicated that the easterly warm moist air flow on the north side of the Huanghai low was blocked by the Taihang Mountains,and joined the southwesterly warm moist air flow from the southeast side of low level shear line.This led to a high value in the water vapor mixing ratio at the eastern side of the Taihang Mountains.The upward heat flux at the eastern slope of the Taihang Mountains was apparently higher than that of the North China Plain,due to the larger daily shortwave radiation warming on the slope surface.This resulted in the pseudo-equivalent potential temperature gradient reaching 0.2 K · km-1 at the 850 hPa level between the mountain slope and the air over the plain.Also,the vertical gradient of the pseudoequivalent potential temperature reached 4 K · km-1 between the 850 and 600 hPa levels during the afternoon.The high thermal gradients of the pseudo-equivalent potential temperature increased the horizontal and vertical pressure gradient forces in such a way as to drive the wind in an upslope direction.The resulting upslope winds led to a strong ascending velocity (above 1 m · s-1),and created dynamic conditions for the convection development on the eastern slope of the Taihang Mountains.The dry and cold westerly flow passed over the warm moist air layer on the eastern side of Taihang Mountains,which resulted in a strong static instability.The occurrence and intensification of the local convection on the eastern side of the Taihang Mountains were caused by a combination of the strong instability,high values of the water vapor mixing ratio,and upslope winds.Due to the local small-scale orographic uplift and gravity wave which were generated by the Luliang Mountains,weak convection cells appeared at the Taiyuan Basin.Then,a weak convection cell developed when it moved to the western slope of the Taihang Mountains due to the uplift caused by the blocking.When the eastward moving convection cell passed the Taihang Mountains,it combined with a local strong convection on the eastern side of the Taihang Mountains,which resulted in the intense development of a combined convection.