西北太平洋热带气旋的闪电活动、雷达反射率和冰散射信号特征分析

利用热带测雨卫星(TRMM)携带的测雨雷达(PR)、闪电成像仪(LIS)和微波辐射计(TMI)的同步探测资料,选取1998-2008年登陆中国的46个热带气旋,分析了其不同强度阶段的闪电活动、雷达反射率和冰散射信号的分布特征,以及闪电的发生与雷达反射率和冰散射信号之间的关系.结果发现:强度较弱的热带气旋平均闪电次数相对较高;当强度达到强热带风暴阶段后,强度越强,闪电数量反而越少.热带气旋强度不同,闪电的空间分布也有差别,热带风暴、强台风和超强台风阶段眼壁区闪电密度最大,而其他阶段则在外雨带区密度最大.热带气旋大部分区域被层云和弱对流降水控制,0℃层以上雷达反射率迅速减小,冰散射信号也普遍较弱.虽然热带气旋的眼壁区对流活动最强.但相比于外面带却较不易发生闪电.在同等大小的雷达反射率下,闪电更易发生在台风和强热带风暴阶段,超强台风阶段发生闪电阈值最高.由于闪电的发生与软雹、冰晶和过冷水等微物理参量以及上升气流速度紧密相关,因此闪电资料可以提供关于热带气旋不同区域的微物理过程和动力过程信息.     

基于CloudSat云分类资料的华北地区云宏观特征分析

利用2007年1月至2008年12月的CloudSat 2B-CLDCLASS-LIDAR云分类资料对华北地区(36°~42°N,110°~120°E)各类云在单层及多层云中的出现频率、平均高度及平均厚度进行统计分析。结果表明:华北地区单层云和多层云出现频率存在明显的季节变化,夏季最大,春秋次之,冬季最小。单层云的出现频率远高于多层云,单层云出现频率在春、夏、秋、冬4个季节分别为44.3%、46.1%、37.8%和32.8%,而多层云中2层云所占比例最大。单层云和多层云各云层平均高度、平均厚度分析显示,3层云上层云顶云底高度最高,3层云下层云顶云底高度最低,单层云平均厚度明显大于多层云,云层数越多,各云层的平均厚度越小。对不同类型云出现频率分析显示,卷云主要出现在单层云及多层云中、上层,高层云和高积云在单层云和多层云各云层中均占有一定的比例,层云主要出现在多层云下层,层积云、积云、深对流云主要出现在单层云及多层云下层,雨层云主要出现在夏季单层云中。卷云、高层云、高积云的平均高度及厚度在不同云系统中存在显著的差异。     

Ice nuclei characteristics from M-PACE and their relation to ice formation in clouds

This paper presents airborne measurements of ice nuclei (IN) number concentration and elemental composition from the mixed-phase Arctic cloud experiment (M-PACE) in northern Alaska during October 2004. Although the project average IN concentration was low, less than 1 L⁻¹ STP, there was significant spatial and temporal variability, with local maximum concentrations of nearly 60 L⁻¹ STP. Immersion and/or condensation freezing appear to be the dominant freezing mechanisms, whereas mechanisms that occur below water saturation played a smaller role. The dominant particle types identified as IN were metal oxides/dust (39%), carbonaceous particles (35%) and mixtures of metal oxides/dust with either carbonaceous components or salts/sulphates (25%), although there was significant variability in elemental composition. Trajectory analysis suggests both local and remote sources, including biomass burning and volcanic ash. Seasonal variability of IN number concentrations based on this study and data from SHEBA/FIRE-ACE indicates that fall concentrations are depleted relative to spring by about a factor of five. Average IN number concentrations from both studies compare favorably with cloud ice number concentrations of cloud particles larger than 125 μm, for temperatures less than −10 °C. Cloud ice number concentrations also were enhanced in spring, by a factor of ∼2, but only over a limited temperature range.     

Planetary radiation budget over North Africa from satellite data

Summary The large desert regions over North Africa are of particular importance to our climate and are therefore modelled numerically as part of sensitivity studies. The result of these models needs verification, but diagnostic studies of atmospheric energetics also require accurate values of the radiation budget at the upper boundary of the climate system.The radiation anomaly above Northern Africa is now established from various satellite data. However, it is suspected that there are serious errors caused in particular by angular and temporal sampling. A sample of NIMBUS-7 ERB—measurements (16.–30. June 1979) was therefore reanalysed, including the missing diurnal cycle which was reconstructed from the corresponding METEOSAT measurements. These more complete data on diurnal cycles change the results on outgoing thermal fluxes and net radiation by up to almost 60 Wm^–2, thus changes of the sign of net radiation also occur over several regions.

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Zusammenfassung Die ausgedehnten Wüstengebiete in Nordafrika sind von großer Wichtigkeit für unser Klima und daher Gegenstand zahlreicher numerischer Empfindlichkeitsstudien. Entsprechende Modellergebnisse können mit Hilfe von Messungen der Strahlungsbilanz am Oberrand der Atmosphäre verifiziert werden. Messungen dienen aber auch als Eingangsdaten für diagnostische Untersuchungen der Energietransporte in der Atmosphäre.Die Strahlungsanomalität über Nordafrika ist mittlerweile durch zahlreiche Satellitenmessungen bestätigt. Jedoch beinhalten ältere Studien z.T. Fehler auf Grund der Nichtberücksichtigung der speziellen Eigenschaften der Stichprobenentnahme durch das Satelliteninstrument. Aus diesem Grund wurde ein Datensatz des NIMBUS-7 ERB Experimentes (16.–30. Juni 1979) neu ausgewertet unter zusätzlicher Verwendung von METEOSAT-1-Messungen, um den Tagesgang der Strahlungsparameter berücksichtigen zu können. Diese zusätzlichen Daten bewirken Änderungen im kurz- und langwelligen Fluß sowie in dem daraus resultierenden Nettofluß von bis zu 60 Wm^–2, was für einige Gebiete eine Vorzeichenumkehr des Nettoflusses bedeutet.

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With 11 Figures     

The Characteristics of Atmospheric Ice Nuclei Measured at Different Altitudes in the Huangshan Mountains in Southeast China简

The concentration of ice nuclei （IN） and the relationship with aerosol particles were measured and analyzed using three 5-L mixing cloud chambers and a static diffusion cloud chamber at three altitudes in the Huangshan Mountains in Southeast China from May to September 2011.The results showed that the mean total number concentration of IN on the highest peak of the Huangshan Mountains at an activation temperature （Ta） of-20℃C was 16.6 L-1.When the supersaturation with respect to water （Sw） and with respect to ice （Si） were set to 5％,the average number concentrations of IN measured at an activation temperature of-20℃C by the static diffusion cloud chamber were 0.89 and 0.105 L-1,respectively.A comparison of the concentrations of IN at three different altitudes showed that the concentration of IN at the foot of the mountains was higher than at the peak.A further calculation of the correlation between IN and the concentrations of aerosol particles of different size ranges showed that the IN concentration was well correlated with the concentration of aerosol particles in the size range of 1.2-20 μtm.It was also found that the IN concentration varied with meteorological conditions,such as wind speed,with higher IN concentrations often observed on days with strong wind.An analysis of the backward trajectories of air masses showed that low IN concentrations were often related to air masses travelling along southwest pathways,while higher IN concentrations were usually related to those transported along northeast pathways.     

基于CloudSat资料的中国及周边地区各类云的宏观特征分析

利用2006年7月—2009年4月的CloudSat2B-CLDCLASS云分类资料,针对中国及周边地区(0°—60°N,70°—140°E)各类云量和垂直结构参数的地理分布及季节变化进行了统计分析,并根据气候特征的地域差异从该区域选出8个子区域,逐区统计了各类云的垂直结构特征。结果表明,各类云量的分布存在较明显的区域差异和季节变化;青藏高原和帕米尔高原地区卷云、高层云和高积云等中高云的高度和厚度相对较小,陆上深对流云的云底高度大于海上,而热带、副热带地区云顶高度大于中纬度地区;除积云、层积云和雨层云外,中国南方地区其他各类云的云层厚度均大于北方地区;除了层积云外,其他各类云的云顶高度在各区域都存在比较明显的季节变化,低云云底高度的季节变化和区域差异都很小,而中高云的云底高度除了在印度洋季风区、南海和西太平洋地区季节差异较小外,其他地区季节差异较明显,各个地区在任何季节内,深对流云厚度最大,层积云最小;各类云出现频率随高度的分布具有较明显的区域差异;卷云与高积云的相关性比较强,经常相伴出现,夏季更加明显,而雨层云和深对流云之间相互排斥,两者几乎不可能同时出现。此外,统计中国及周边地区各类云的水平均一性发现,中...     

The Relationship between the Wintertime Blocking over Greenland and the Sea Ice Distribution over North Atlantic

The sea-ice concentration in the Northern Hemisphere, 500 hPa height, sea-level pressure and 1000-500 hPa thickness of monthly mean data are examined for the period 1953-1989, with emphasis on the winter season.Relationships between large-scale patterns of atmospheric variability and sea-ice variability are investigated, making use of the correlation method. The analysis is conducted for the Atlantic sectors. In agreement with earlier studies based upon monthly mean data on sea-ice concentration, the strongest sea-ice pattern is composed of a dipole with opposing centers of action in the Davis Straits / Labrador Sea region and the Greenland and Barents Seas. Its temporal variability is strongly coupled to the atmospheric North Atlantic Oscillation (NAO). The relationship between the two patterns is strongest with the atmosphere leading the ocean. The polarity of the NAO is associated with Greenland blocking episodes, during which the influence of the atmosphere is strong enough to temporarily halt the c     

An Evaluation of Tropical Cyclone Genesis Forecast over the Western North Pacificand the South China Sea from the CMA-TRAMS

Tropical cyclone (TC) genesis forecasting is essential for daily operational practices during the typhoon season.The updated version of the Tropical Regional Atmosphere Model for the South China Sea (CMA-TRAMS) offersforecasters reliable numerical weather prediction (NWP) products with improved configurations and fine resolution. Whiletraditional evaluation of typhoon forecasts has focused on track and intensity, the increasing accuracy of TC genesisforecasts calls for more comprehensive evaluation methods to assess the reliability of these predictions. This study aims toevaluate the effectiveness of the CMA-TRAMS for cyclogenesis forecasts over the western North Pacific and South ChinaSea. Based on previous research and typhoon observation data over five years, a set of localized, objective criteria has beenproposed. The analysis results indicate that the CMA-TRAMS demonstrated superiority in cyclogenesis forecasts, pre dicting 6 out of 22 TCs with a forecast lead time of up to 144 h. Additionally, over 80% of the total could be predicted 72 hin advance. The model also showed an average TC genesis position error of 218.3 km, comparable to the track errors ofoperational models according to the annual evaluation. The study also briefly investigated the forecast of Noul (2011). Theforecast field of the CMA-TRAMS depicted thermal and dynamical conditions that could trigger typhoon genesis, con sistent with the analysis field. The 96-hour forecast field of the CMA-TRAMS displayed a relatively organized three dimensional structure of the typhoon. These results can enhance understanding of the mechanism behind typhoon genesis,fine-tune model configurations and dynamical frameworks, and provide reliable forecasts for forecasters.     

Wind regime in the lower atmosphere over Moscow from the long-term acoustic sounding data

Presented are the results of the sounding of the lower atmospheric 500-meter layer for the period of 2004–2012 carried out at the Meteorological Observatory of the Moscow State University (MSU) with the MODOS Doppler acoustic radar (sodar) produced by METEK (Germany). Discussed is the methodological basis of the sodar wind data analysis. It is demonstrated that in the air layer up to 200 m the maximum values in the annual course of the wind speed are observed more often in autumn and winter, and the minimum values, in summer; this is associated with the fact that during the cold period of the year Moscow is often located in the zones of intense gradient currents. The diurnal course of the wind speed is characterized by the daytime maximum and night-time minimum in the layer up to 40–60 m from the surface; it is poorly pronounced and characterized by the minimum in the morning in the layer of 80–120 m; and the daytime minimum and night-time maximum are observed above 140–160 m. The layer from 80 to 120 m approximately corresponds to the height of the wind rotation. The amplitude of diurnal variations of the wind speed increases from 0.3 m/s at the height of 7 m and 0.6 m/s at the height of 15 m, to 4.5 m/s at the height of 400 m; however, its secondary minimum (0.5 m/s) associated with the rotation height is registered at the altitude of 80 m. The statistical relationship between the wind speed and surface air temperature is direct during the cold season, inverse during the warm season, and is absent in April and October. The average maximum wind speed over Moscow for ten minutes in the layer up to 500 m from the surface reaches 30–35 m/s in some cases if two conditions concur: the capital is located on the periphery of vast pressure formations (usually of deep cyclones) and the local low-level jet stream is present in the wind profile.     

2017年西北太平洋和南海台风活动概述

2017年总计27个台风在西北太平洋和南海生成,其中8个在我国沿海登陆。台风生成时间集中于7—8月,生成源地较多年平均偏西5°,南海台风数（8个）较多年平均（4～7个）明显偏多,台风登陆点集中在广东沿海,气旋峰值强度（30.9 m·s-1）较多年平均（40.3 m·s-1）明显偏弱,登陆台风的平均登陆强度（29.0 m·s-1）较多年平均（32.8 m·s-1）偏弱。台风雨水情呈现降雨范围广、暴雨强度大,主要江河平稳、部分中小河流超警戒水位的特征。使用实时业务定位、定强及降水、大风、水文观测数据,针对2017年影响我国的10个台风个例的气象水文特征及社会经济影响做出详细分析。“天鸽”为2017年登陆中国最强的台风,导致灾损最为严重,其与“帕卡”在4 d内先后登陆经济发达、人口密集的珠三角地区,造成损失叠加。     

卫星遥感中国海域气溶胶直接辐射强迫

利用搭载在Terra卫星上的CERES和MODIS两颗传感器所提供的大气辐射通量和气溶胶数据,结合Fu-Liou辐射传输模式和SPRINTARS气溶胶模式,对中国海域气溶胶在大气顶的短波直接辐射强迫进行了研究.结果表明:(1)在中国海域,CERES的大气顶短波辐射通量与MODIS在550 nm处气溶胶光学厚度(AOT550)存在着非常好的线性相关关系,相关系数0.9左右,说明中国海域气溶胶对于大气顶的短波辐射通量作用是显著的;(2)利用这一线性相关关系,在中国海域,结合CERES和MODIS两颗传感器数据直接计算获取气溶胶瞬时短波直接辐射强迫(Fs).计算发现Fs具有明显的时间变化规律和空间分布特征:在时间上,Fs具有明显的季节变化,春季最大而夏季最小,秋、冬季介于两者之间.在空间上,Fs具有明显的区域分布特征,等值线沿着海岸线分布,随着离岸距离的增加而减小,这一特征说明陆源气溶胶是中国海域气溶胶的主要来源.同时,在数值上,AOT550与Fs在4个季节中都存在着相当好的负相关关系,说明气溶胶减少了进入大气顶的短波辐射,总体来说是"冷室作用";然后,利用Fu-Liou辐射传输模式计算获得修正因子,将卫星获得的Fs转化为日平均短波直接辐射强迫(Fd),得到中国海域的气溶胶日平均短波直接辐射强迫的分布;最后,利用SPRINTARS气溶胶模式的模拟结果,与上述卫星获得的日平均短波直接辐射强迫进行了比较,两者具有非常好的一致性.     

华北平原回流天气的结构特征

利用美国PSU／NCAR的MM5V3中尺度非静力模式，对发生在2002年12月22-23日华北平原的一次回流天气过程进行了数值试验。结果发现：来自东北平原的低层冷空气虽然经渤海侵入华北平原，但仍然保持干冷气团的特性，在降水中起“冷垫”作用。降水的起止时间与中高层暖湿气流和低层干冷空气的风向相关较好；降水强度的变化与风速的大小成正相关。伴随西南暖湿气流，华北回流降水的水汽来自南方。     

中国东部降水特征及其与印度、北美降水的关系

本文应用了10年平均的旬、候和日平均降水资料,研究了中国东部4—9月降水分布特点。结果指出,华南、华中4—9月候降水量高值中心区存在准一个月的振荡现象,东北、华北4—9月的日平均降水量低值中心区具有准一周的振荡现象。而在长江流域,4—9月的旬降水量高值中心区以不连续跳跃方式在东西方向上传播,高值中心区“重现”的准周期约为一个月左右。 同时,本文也应用了1957—1985年月平均降水资料,计算了中国东部和印度中部、北美西部同期降水相关系数。结果指出,华南、华中5—7月降水相关场的分布作反时针旋转。在6月梅雨季节,长江中下游地区是降水正相关区,而华南是负相关区。在6—8月,中国东部和北美西部的月平均降水量之间存在稳定的负相关关系。     

Backcasting long-term climate data: evaluation of hypothesis

Most often than not, incomplete datasets or short-term recorded data in vast regions impedes reliable climate and water studies. Various methods, such as simple correlation with stations having long-term time series, are practiced to infill or extend the period of observation at stations with missing or short-term data. In the current paper and for the first time, the hypothesis on the feasibility of extending the downscaling concept to backcast local observation records using large-scale atmospheric predictors is examined. Backcasting is coined here to contrast forecasting/projection; the former is implied to reconstruct in the past, while the latter represents projection in the future. To assess our hypotheses, daily and monthly statistical downscaling models were employed to reconstruct past precipitation data and lengthen the data period. Urmia and Tabriz synoptic stations, located in northwestern Iran, constituted two case study stations. SDSM and data-mining downscaling model (DMDM) daily as well as the group method of data handling (GMDH) and model tree (Mp5) monthly downscaling models were trained with National Center for Environmental Prediction (NCEP) data. After training, reconstructed precipitation data of the past was validated against observed data. Then, the data was fully extended to the 1948 to 2009 period corresponding to available NCEP data period. The results showed that DMDM performed superior in generation of monthly average precipitation compared with the SDSM, Mp5, and GMDH models, although none of the models could preserve the monthly variance. This overall confirms practical value of the proposed approach in extension of the past historic data, particularly for long-term climatological and water budget studies.     

Cirrus Cloud Macrophysical and Optical Properties over North China from CALIOP Measurements

Two years of mid-latitude cirrus cloud macrophysical and optical properties over North China are described from Earth-orbiting Cloud-Aerosol Lidar with Orthogonal Polarization(CALIOP) satellite measurements. Global cloud climatological studies based on active remote sensing data sets benefit from more accurate resolution of vertical structure and more reliable detection of optically thin layers.The mean values for cirrus cases over North China are 0.19±0.18 for infrared emittance,0.41±0.68 for visible optical depth, 0.26±0.12 for integrated depolarization ratio,and 0.72±0.22 for integrated color ratio.When studied using reasonable assumptions for the relationship between extinction and ice crystal backscatter coefficients,our results show that most of the cirrus clouds profiled using the 0.532μm channel data stream correspond with an optical depth of less than 1.0.The dependence of cirrus cloud properties on cirrus cloud mid-cloud temperature and geometry thickness are generally similar to the results derived from the ground-based lidar, which are mainly impacted by the adiabatic process on the ice cloud content.However,the differences in macrophysical parameter variability indicate the limits of spaceborne-lidar and dissimilarities in regional climate variability and the nature and source of cloud nuclei in different geographical regions.     

Spatiotemporal long-term trends of extreme wind characteristics over the Black Sea

In this study, long-term change of wind characteristics on the Black Sea has been investigated using two widely used data sources, i.e., European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-Interim and National Centers for Environmental Prediction/Climate Forecast System Reanalysis (NCEP/CFSR), spanning 40 years between 1979 and 2018. Spatial and seasonal variability of climatic features such as the wind speed, direction, number and duration of storms, and wind power density are discussed. Wind climate is characterized by strong, durable and stable winds in the northern and western Black Sea, and relatively weak, short-lived and highly-variable winds in the eastern Black Sea. These long-term wind patterns indicate that the eastern part of the basin is likely to be subjected to the impacts of climate change. Long-term stable and strong wind conditions in the southwest part indicate reliable, persistent and sustainable wind energy potential. Long-term and seasonal variation of wind power density (WPD) at 110 m altitude over the Black Sea is investigated. There is a significant difference in WPD values between winter and summer seasons, with around 2.8 times larger WPD in winter than that in summer. In the western Black Sea, narrow confidence intervals observed in each season indicate a low level of variation during a season and ensures stable wind power conditions.     

Subseasonal reversal of haze pollution over the North China Plain

China has been frequently suffering from haze pollution in the past several decades. As one of the most emission-intensive regions, the North China Plain (NCP) features severe haze pollution with multiscale variations. Using more than 30 years of visibility measurements and PM_2.5 observations, a subseasonal seesaw phenomenon of haze in autumn and early winter over the NCP is revealed in this study. It is found that when September and October are less (more) polluted than the climatology, haze tends to be enhanced (reduced) in November and December. The abrupt turn of anomalous haze is found to be associated with the circulation reversal of regional and large-scale atmospheric circulations. Months with poor air quality exhibit higher relative humidity, lower boundary layer height, lower near-surface wind speed, and southerly anomalies of low-level winds, which are all unfavorable for the vertical and horizontal dispersion and transport of air pollutants, thus leading to enhanced haze pollution over the NCP region on the subseasonal scale. Further exploration indicates that the reversal of circulation patterns is closely connected to the propagation of midlatitude wave trains active on the subseasonal time scale, which is plausibly associated with the East Atlantic/West Russia teleconnection synchronizing with the transition of the North Atlantic SST. The seesaw relation discussed in this paper provides greater insight into the prediction of the multiscale variability of haze, as well as the possibility of efficient short-term mitigation of haze to meet annual air quality targets in North China.摘要中国近几十年来频受雾霾污染问题困扰, 其中华北平原作为排放最密集的区域之一, 常遭遇不同尺度的严重雾霾污染. 本文利用30余年的能见度和颗粒物 (PM_2.5) 观测数据, 发现了华北平原地区在秋季和早冬时雾霾污染在次季节尺度上“跷跷板式”反向变化的关系. 研究发现, 当9–10月污染较轻 (重) 时, 11–12月的污染倾向于加重 (减轻) . 这种突然的变化与局地和大尺度环流的反向变化有关. 污染较重的月份常伴随有更高的相对湿度, 更低的边界层高度和近地面风速以及低层的南风异常, 均不利于污染的垂直和水平扩散和传输, 从而导致了次季节尺度上霾污染的加重. 进一步的研究发现环流场的突然转向与在次季节尺度上活跃的中纬度波列的传播密切相关, 而此波列可能主要与大西洋海温转变及引起的EA/WR遥相关型有关. 这一次季节反向变化为霾污染多尺度变率预测提供了新的理解, 同时为华北地区年度空气质量达标的短期目标提供了具有可行性的参考方法.     

1999—2008年夏季华北冷涡的异常特征

利用1999—2008年5—8月中国160站月平均气温资料、每日2次的MICAPS资料及每日4次的NCEP 1°×1°资料,通过定义一个夏季华北冷涡强度指数(NCCVI),研究了夏季华北冷涡异常年西太平洋副高、东亚季风、高空急流及低层垂直运动的异常特征。结果表明：夏季NCCVI异常强年500 hPa上贝加尔湖地区有气旋性环流发展,从贝加尔湖至我国华北地区为一显著的高空槽所控制,冷空气较活跃并随槽后引导气流扩散南下影响华北地区。对流层各层偏暖湿,200 hPa上高空急流偏强,700 hPa上高纬冷涡后部偏北气流加强,低纬偏南气流加强,冷暖空气在华北交汇,华北和东北地区低层上升运动发展。同期副热带高压偏强,位置略偏南;东亚夏季风偏强, 加强了水汽输送。夏季NCCVI异常弱年相反。     

西北太平洋热带气旋强度资料的对比

在获取关岛联合台风警报中心(JTWC)以及中国气象局《台风年鉴》和《热带气旋年鉴》自1949—2004年西北太平洋热带气旋强度(近中心最大风力)资料的基础上,着重比较了两者在时间变化上的差异,结果显示:热带风暴以上近56 a所有样本的平均风速前者小于后者0.81 m.s-1,而这一差异主要的贡献是强台风以上样本。两资料集最显著的特征是热带风暴以上年平均风速随时间变化的差异上,自1970s中期到1990s中期,两者的走势趋向呈相反的态势,前者呈上升趋势,后者呈下降趋势,特别是强台风以上样本表现更为突出。利用资料相对稳定性原则,对JTWC和《台风年鉴》资料进行校正,1990s以来JTWC估计的热带气旋强度可能偏大,1970s之前《台风年鉴》估计的数值也可能偏大。