Temporal and spatial variations of global deep cloud systems based on CloudSat and CALIPSO satellite observations

ABSTRACT The spatial and temporal global distribution of deep clouds was analyzed using a four-year dataset （2007-10） based on observations from CloudSat and CALIPSO. Results showed that in the Northern Hemisphere, the number of deep cloud systems （DCS） reached a maximum in summer and a minimum in winter. Seasonal variations in the number of DCS varied zonally in the Southern Hemisphere. DCS occurred most frequently over central Africa, the northern parts of South America and Australia, and Tibet. The mean cloud-top height of deep cloud cores （TDCC） decreased toward high latitudes in all seasons. DCS with the highest TDCC and deepest cores occurred over east and south Asian monsoon regions, west-central Africa and northern South America. The width of DCS （WDCS） increased toward high latitudes in all seasons. In general, DCS were more developed in the horizontal than in the vertical direction over high latitudes and vice versa over lower lat- itudes. Findings from this study show that different mechanisms are behind the development of DCS at different latitudes. Most DCS at low latitudes are deep convective clouds which are highly developed in the vertical direction but cover a rela tively small area in the horizontal direction; these DCS have the highest TDCC and smallest WDCS. The DCS at midlatitudes are more likely to be caused by cyclones, so they have less vertical development than DCS at low latitudes. DCS at high latitudes are mainly generated by large frontal systems, so they have the largest WDCS and the smallest TDCC.     

On the linkage between changes in cloud cover and precipitation extremes over Central India

In this study, linkage between changing characteristics of precipitation extremes and cloud covers over Central India is explored during summer monsoon period using Satellite data (1998–2015). This is a first attempt to relate the changes in cloud cover to the changes in precipitation extremes. Non-rainy cirrus clouds are excluded from this study. Results show that heavy rainfall (≥ 60 mm/day) is associated with cold cloud tops (Tb≤220 K) while moderate rainfall (<60 mm/day and ≥20 mm) occurs mostly with middle clouds (Tb>220 K and ≤245 K). Low level clouds (Tb> 245 K) are responsible for light rainfall (<20 mm/day). Increases in top 20%, 10%, 5% and 1% heavy precipitation relate well with the increases in very deep convective, deep convective and convective cloud cover. Among these relations, increase in top 5% heavy precipitation relates best with increase in very deep convective cloud cover. Decrease in bottom 30% low precipitation relates with decrease in low level cloud cover. The results reported in this study fit into the framework of how weather extremes respond to climate change.     

基于CloudSat探测的西南低涡对流云垂直结构特征

基于CloudSat卫星数据,结合多源常规和遥感等气象资料,研究分析了2013年8月6~7日的一次受西南低涡向西北方向移动发展影响的强降水天气过程中,对流云发展的三维结构和演变特征,结果表明:西南低涡发展有利于受其影响的对流云团发展为深厚对流云。西南低涡发展和成熟阶段低涡中心与强对流中心均不一致,强对流中心位于低涡中心以南。西南低涡不同发展阶段对流云团发展均符合“撒播-供水”机制。低涡发展成熟阶段对流云内部存在高温高湿中心。      

Characteristics of Pre-summer Daytime Cloud Regimes over Coastal South China from the Himawari-8 Satellite

Using the high spatiotemporal resolution (2 km-and-10 min) data from the Advanced Himawari Imager onboard the Himawari-8 satellite, this study documents the fine-scale characteristics of daytime cloud regimes (CRs) over coastal South China during the pre-summer rainy season (April–June). Six CRs (CR1–CR6) are identified based on the joint frequency distribution of cloud top brightness temperature and cloud optical thickness, namely, the optically thin-to-moderate cloud mixture, optically thin warm clouds with cirrus, optically thick warm clouds, weak convective cloud mixture, strong convective clouds, and extreme, deep convective clouds. The optically thick warm clouds are the major CR during April and May, with higher frequencies over land, especially along the urban agglomeration, rather than the offshore which may be an indicator of the higher aerosol concentrations being a contributing factor over the cities. The CRs with weak convective cloud mixtures and strong convective clouds appear more frequently over the land, while the two CRs with optically thinner clouds occur mainly offshore. Synoptic flow patterns (SPs) are objectively identified and examined focusing on those favoring the two major rain-producing CRs (CR5 and CR6) and the highly reflective CR with optically thick warm clouds (CR3). The two SPs favoring CR5 and CR6 are characterized by abundant moisture with low-level jets after monsoon onset, and a northwest high-southeast low pattern with strong dynamic convergence along the coastline, respectively. The non-convective CR3 with high reflectance is related to a SP that features the western North Pacific subtropical high extending more westward, leading to a moderate moisture supply and a wide range of convective available potential energy, but also, large convective inhibition.     

青藏高原那曲地区一次深对流云垂直结构的多源卫星和地基雷达观测对比分析

为了加强对青藏高原深对流云垂直结构的深入认识,利用TRMM、CloudSat和Aqua多源卫星观测资料及地基垂直指向雷达（C波段调频连续波雷达和KA波段毫米波云雷达）资料,对第三次青藏高原大气科学试验期间2014年7月9日13-16时（北京时）发生在那曲气象站附近的深厚强对流云和那曲气象站以西100 km左右的深厚弱对流云的垂直结构特征进行了分析,得到的结果如下:（1）深厚强对流云和深厚弱对流云的水平尺度均较小（10-20 km）,垂直发展高度较高（15-16 km,均指海拔高度）;深厚强对流云在0℃层以下雷达反射率因子递增非常快,表明对流云内固态降水粒子下落至0℃层以下后融化过程有很重要的作用;在对流减弱阶段有明显的0℃层亮带出现,亮带位于5.5 km左右（距地1 km）;（2）对比TRMM测雨雷达和C波段调频连续波雷达观测到的雷达反射率因子,发现TRMM测雨雷达在11 km以下存在高估;（3）深对流云主要为冰相云,云内10 km以上主要是丰富小冰粒子,而10 km以下是较少的大冰晶粒子;深厚强对流云和深厚弱对流云的微物理过程都主要包括混合相过程和冰化过程,混合相过程分为两种:一种是-25℃（深厚强对流云）或-29℃（深厚弱对流云）高度以下以凇附增长为主,另一种是该高度以上主要以冰晶聚合、凝华增长为主,该过程冰晶粒子有效半径增长较快。这些空基和地基的观测证据进一步揭示了青藏高原深对流云的垂直结构特征,为模式模拟青藏高原深对流云的检验提供了依据。      

东北地区嵌入对流过程的数值模拟分析

利用常规气象观测资料、NCEP FNL再分析资料以及中尺度WRF模式的数值模拟结果,对2010年7月1日发生在辽宁地区的一次嵌入对流云的形成、演变过程进行了分析,并对云中微物理特征进行了诊断。结果表明：WRF模式较理想地模拟出了此次对流过程。嵌入对流云是在大气上层分布有成片的层状云,低层有零星的对流泡生成的情况下,随着低层对流泡的不断发展壮大,当其伸展至层云的高度时镶嵌其中而成;嵌入的对流体在随层状云东移的过程中反复进行着并合、分裂过程,而且分裂过程中出现明显的右移性对流体的选择性加强;云系中不仅存在云水直接转化为雨水的暖云降水机制,也存在有播撒—供应的冷云降水机制,且成熟阶段冷、暖云降水机制均较为活跃;物理量场上,低层辐合高层辐散的强度在发展阶段最强,最有利云系的发展。     

基于CloudSat–CALIPSO资料的全球不同类型云的水平和垂直分布特征

基于Cloud Sat-CALIPSO(Cloud Sat–Cloud Aerosol Lidar and Infrared Pathfinder Satellite Observations)卫星观测资料,分析了全球总云量和8类云的云量、云底高、云顶高、云厚度的水平和垂直分布。分析结果表明,全球平均总云量为66.7%,其中卷云(Ci)和层积云(Sc)云量之和与其他6类云量总和相当,是全球云量最多的两类云。积状云云量呈现从赤道向极地递减的特征,层状云则相反,反映了二者不同的生成环境,同时下垫面地形和天气系统也严重影响云的分布。8类云的高度及厚度特征有显著差异。Ci的云底高度和云顶高度都较高,厚度则较薄;高层云(As)和高积云(Ac)的云底高度和云顶高度都位于大气中层,但As比Ac出现的高度高且厚度大;层云(St)、层积云和积云(Cu)的云底高度和云顶高度都很低,属于薄的低云;雨层云(Ns)和深对流云(DC)云底较低但云顶伸展很高,归属于厚云类。总体而言,海洋上云底高度较陆地低;赤道等大气不稳定地区,云底较高,云厚度较大;高原地区则表现出"高云不高,低云不低,云厚较薄"的特征。     

CloudSat/CALIPSO卫星资料分析云的全球分布及其季节变化特征

全球气候模式（GCM）中云的参数化方案具有不确定性,了解云的时、空变化能为参数化方案提供有效参考。利用搭载在属于A-Train卫星序列的CloudSat和CALIPSO上的94 GHz云廓线雷达（CPR）以及正交极化云-气溶胶激光雷达（CALIOP）联合的2级云分类产品,分析了2007年3月-2010年2月8种云类及三相态的云量地理分布、纬向垂直分布的季节变化特征以及云层分布概率。结果发现,卷云的分布体系与深对流云相似,主要集中在西太平洋暖池、全球各季风区及赤道辐合带,分布格局与气压带、风带季节性移动一致。层云与层积云主要分布在中低纬度非季风区以及中高纬度的洋面上。高积云与高层云的分布形成明显的海陆差异,雨层云与积云的分布形成明显的纬度差异。冰云分布与卷云相似,云高随纬度递增而递减;水云分布与层积云相似,平均分布于2 km高度;混合云集中于高纬度地区及赤道辐合带,中纬度地区随纬度变化集中于海拔0-10 km的弧形带。层状云多以多层云形式出现,积状云多以单、双层云的形式出现,层状云的云重叠现象比积状云更显著。积状和层状云的分布特征与积云和层云降水的分布特征基本一致,验证了不同类型降水的卫星观测结果,同时为气候模式的云量诊断方案提供对比验证的数据。      

青藏高原、东亚季风区、西北太平洋地区云系结构及相联加热机制的对比分析

应用7年(2006年5月18日—2013年5月18日)的CloudSat卫星观测资料,对比分析了青藏高原、东亚季风区、西北太平洋地区云发生频率的特征,并利用欧洲中心再分析资料,计算了三个地区的视热源、视水汽汇Q₁、Q₂,分析探讨了三个地区与云发生频率相联系的加热机制。结果表明:青藏高原、东亚季风区、西北太平洋地区云的发生频率分别为35%、22%、27%,其中:青藏高原和东亚季风区的低云频率最大,中云次之;西北太平洋地区的高云和低云的频率大,分别为19%和16%。具体云型来看,青藏高原多高层云、雨层云;东亚季风区多高层云和卷云,夏季深对流云频率增大明显;西北太平洋地区多卷云、深对流云和高层云。三个地区视水汽汇Q₂的垂直分布特征及季节变化与云发生频率对应较好,青藏高原的低云(雨层云)、中云(高层云)形成过程中,凝结释放潜热,加热大气;东亚季风区低云(深对流云)、中云(高层云)对加热大气贡献大;西北太平洋地区大气的主要加热机制是深对流云形成过程中凝结释放潜热以及湿静能涡旋垂直输送。      

A process oriented characterization of tropical oceanic clouds for climate model evaluation, based on a statistical analysis of daytime A-train observations

This paper aims at characterizing how different key cloud properties (cloud fraction, cloud vertical distribution, cloud reflectance, a surrogate of the cloud optical depth) vary as a function of the others over the tropical oceans. The correlations between the different cloud properties are built from 2?years of collocated A-train observations (CALIPSO-GOCCP and MODIS) at a scale close to cloud processes; it results in a characterization of the physical processes in tropical clouds, that can be used to better understand cloud behaviors, and constitute a powerful tool to develop and evaluate cloud parameterizations in climate models. First, we examine a case study of shallow cumulus cloud observed simultaneously by the two sensors (CALIPSO, MODIS), and develop a methodology that allows to build global scale statistics by keeping the separation between clear and cloudy areas at the pixel level (250, 330?m). Then we build statistical instantaneous relationships between the cloud cover, the cloud vertical distribution and the cloud reflectance. The vertical cloud distribution indicates that the optically thin clouds (optical thickness <1.5) dominate the boundary layer over the trade wind regions. Optically thick clouds (optical thickness >3.4) are composed of high and mid-level clouds associated with deep convection along the ITCZ and SPCZ and over the warm pool, and by stratocumulus low level clouds located along the East coast of tropical oceans. The cloud properties are analyzed as a function of the large scale circulation regime. Optically thick high clouds are dominant in convective regions (CF?>?80?%), while low level clouds with low optical thickness (<3.5) are present in regimes of subsidence but in convective regimes as well, associated principally to low cloud fractions (CF?<?50?%). A focus on low-level clouds allows us to quantify how the cloud optical depth increases with cloud top altitude and with cloud fraction.     

宁夏三类降水云的时空分布及环流特征分析

利用宁夏24个测站1971—2000年常规地面观测中云状、总云量、低云量、天气现象、降水量等资料,对宁夏30年中层状云、对流云及混合云降水的时空变化特征进行了分析。同时,利用NCEP/NCAR(1971—2000年)全球再分析资料,对宁夏三类降水云的环流特征进行了诊断分析。结果表明:30年中层状云降水次数明显多于对流云和混合云降水次数,是宁夏降水的主要类型,而混合云降水是宁夏大雨以上降水的主要类型;宁夏南部地区以层状云降水为主,北部地区对流云和混合云降水次数相对较多;三类降水云的月、年际和年代际变化特征及所对应的环流背景和影响系统具有明显的差异。     

新疆降雹云团的特征分析

普查1998－2001年4－8月的资料，得到全疆438个降雹云团。2000年降雹云团出现最多，按尺度大小将降雹云团分为雷暴云、对流云、中尺度对流系统、冷云核、系统云系云区有云团边缘6类。强以流云团是冰雹云的主体。新疆降雹云团尺度小、形状不规则、云顶温度较高。     

南海季风爆发期间中尺度对流云带演变特征与持续性加强的机理研究

南海季风爆发与随后爆发的东亚季风,与夏季东亚地区旱涝关系密切,而相伴的南海对流活动与季风爆发的维持和发展存在何种相互关系,是需要探究的.为此,利用热带测雨卫星(Tropical Rainfall Measuring Mission,TRMM)的雷达(Precipitation Radar,PR)、微波成像仪(TRMM ...     

Using Satellite Data to Analyze the Initiation and Evolution of Deep Convective Clouds

In this study, two deep convective cloud cases were analyzed in detail to study their initiation and evolution. In both cases, all deep convective clouds were positioned at the rear of the cold front cloud bands and propagated backward. Satellite data showed that prior to initiation of the deep convective clouds, thermodynamic and moist conditions were favorable for their formation. In the morning, a deep convective cloud at the rear of cold front cloud band propagated backward, the outflow boundary of which created favorable conditions for initiation. An additional deep convective cloud cluster moved in from the west and interacted with the outflow boundary to develop a mesoscale convective system（MCS） with large, ellipse-shaped deep convective clouds that brought strong rainfall. The initiation and evolution of these clouds are shown clearly in satellite data and provide significant information for nowcasting and short-term forecasting.     

华北两次副高边缘暴雨过程卫星云图释用

利用实况探空资料与FY 2C、2E卫星探测资料,对2005年8月16日、2010年8月20—21日两次西太副高与西风槽共同作用下出现的华北暴雨过程进行分析,将两次过程卫星云图与各种物理要素场的配置进行对比,得到以下结果。两次过程云系均表现为典型的锋面云系特征,靠近冷空气一侧云带边界光滑整齐。从结构上看,锋面云带主要由多层云系组成。整个云系位于高空槽前580 dagpm线与副高外围588 dagpm线之间;降水云带由对流云团、稳定性降水云带及混合性降水云带3部分组成,对流云团集中发展在云带靠近副高边缘晴空区一侧,通常位于在584 dagpm线与588 dagpm线之间靠近副高一侧;稳定性降水集中高空槽前,即云带后部,580 dagpm线与584 dagpm线之间;混合性降水位于两个云系之间,多产生于584 dagpm线附近。云系的分布与各层的垂直速度场、涡度场、散度场,以及中高层的涡度平流场有很好的对应关系。比湿通量、比湿通量散度与假相当位温等温湿参量的分布特征,清楚的解释了锋面云带的移动、发展和分布特征。     

台风利奇马(1909)与台风摩羯(1814)云特征对比

利用FY-2H,Aqua,CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation)和GPM(Global Preciptation Measurement)卫星产品,对比同在浙江温岭沿海登陆且路径相似的台风利奇马(1909)和...     

中国夏季云和降水的定量关系及其成因分析

云的形成是产生降雨的必要条件,云和降水之间存在着极为密切而复杂的联系。利用常规站点数据和ISCCP卫星数据等资料分析了夏季中国地区云的多种特征参数的变化与降水变化在时空分布上的联系。站点数据结果表明总云量、低云量与降水的距平在全国范围内表现出显著的正相关关系;在通过0.05水平显著性检验的站点上,云量和降水距平百分率之间的线性关系较明显,总云量每增加1.00%降水增加2.23%,低云量每增加1.00%降水增加0.46%。ISCCP数据结果显示总云云量、光学厚度和云水路径以及高云中的卷层云和深对流云云量与降水距平呈非常好的正相关关系。采用K-means聚类分析方法并参考中国地理气候分布特点,将中国分为9个气候区,以小波相干分析和交叉小波分析对各个气候区夏季云量和降水距平百分率序列在时频域内多尺度特征的关系做了进一步研究。结果显示9个气候区夏季白天总云量和低云量与降水变化在2~4年(a)和5~8a的尺度周期都具有较强的相干性与共振周期,且处于正相关位相。在时空分布和时频域上,中国地区夏季云和降水的变化之间都存在非常显著的正相关关系,尤其是低云量。云和降水变化之间具有强相干性与共振周期是两者之间正相关联系的原因。     

厄尔尼诺次年夏季中国地区云的变化特征及其与降水的关系

基于1961—2010年中国地面台站和卫星观测等多种数据,对不同类型厄尔尼诺事件次年夏季中国地区云的变化特征和不同类型降水的变化特征进行了分析,探讨云的变化特征与总降水异常的复杂联系。结果表明:站点数据中,厄尔尼诺事件次年夏季总云量和低云量的异常与降水异常分布形势大致相同;积雨云、雨层云和层积云等低云的出现频率有所增加。云量与降水异常在全国范围内表现出显著的正相关;通过显著性检验的正相关站点,云量与降水异常的线性关系也通过了显著性检验,总云量和低云量与降水的增加比例分别接近1:3和1:1。卫星观测数据中,厄尔尼诺事件次年夏季高云量、深对流云量、光学厚度和云水路径的变化与站点降水异常基本呈正相关;黄河以南地区总降水的变化主要来源于对流降水的异常,其贡献比例高达80%。中国东部地区低云对降水具有很好的指示作用;厄尔尼诺事件次年夏季南方地区总降水的异常主要来自对流降水的变化;对流降水异常增加与深对流云的异常增多有关。厄尔尼诺事件的发生使得次年夏季中国季风区对流活动增强,对流云云量增多,云层增厚,云顶向上发展,故而对流降水增加,异常雨带形成。      

A study on radiative properties of Indian summer monsoon clouds

Possible causes behind the unusual cooling by summer monsoon clouds over India are investigated. Results suggest that the causes behind the cooling over the Bay of Bengal, India (BBI) and Arabian Sea (AS) within the Indian monsoon region are different. Over the BBI, clouds are tall. A unique upper tropospheric easterly jet stream exists over India during the summer monsoon season, which horizontally spreads the vertically growing deep convective clouds and thereby increases the cloud cover. Hence, more incoming solar radiation is reflected back to space, which leads to cooling. A radiative transfer study employing the Santa Barbara DISORT Atmospheric Radiative Transfer model supports this view. Over the Arabian Sea, clouds are shallow, and hence the upper tropospheric jet cannot affect them. Due to their proximity to the ground, Arabian Sea clouds exert less warming effect, but they exert a considerable cooling effect, which arises because of the high reflectivity of the clouds. Over the Equatorial Indian Ocean (EIO), where the monsoon clouds originate and propagate towards the monsoon trough region, both cooling and warming effects are nearly canceled out. The upper tropospheric jet is located hundreds of kilometers north of the EIO, and hence it does not disturb the deep convective clouds of the EIO. Therefore, they behave similarly to other deep convective clouds in the tropical belt.     

低压倒槽影响下积层混合云形成过程模拟研究

利用多普勒雷达资料和中尺度天气预报模式wRF（Weather Research and Forecasting）模拟结果,对2009年5月9—10日发生在太原及其周边地区的一次积层混合云降水形成过程进行分析。结果表明,在积层混合云的形成初期,局地对流云得到发展,随着其强度不断增强,与周围云发生并合过程（包括局地单体对流的并合、积云团的并合和积层混合云内强中心的并合）,形成范围较大的积层混合云云系。局地单体对流和积云团的并合可带来云体的爆发性增长,霰含量、雨水含量大幅增加。积层混合云内强中心的并合对降水强度影响不大,但有利于降水面积扩大。低压倒槽和弱冷锋是此次积层混合云形成和维持的主要影响因素。低压倒槽有利于低层大范围不稳定能量的积累,风向切变有利于近距离云团的发展和并合,山地动力和热力作用有利于局地对流单体、积层混合云内强中心的形成和加强。