Observation of a Self-Limiting,Shear-Induced Turbulent Inversion Layer Above Marine Stratocumulus

High-resolution measurements of thermodynamic, microphysical, and turbulence properties inside a turbulent inversion layer above a marine stratocumulus cloud layer are presented. The measurements are performed with the helicopter-towed measurement payload Airborne Cloud Turbulence Observation System (ACTOS), which allows for sampling with low true air speeds and steep profiles through cloud top. Vertical profiles show that the turbulent inversion layer consists of clear air above the cloud top, with nearly linear profiles of potential temperature, horizontal wind speed, absolute humidity, and concentration of interstitial aerosol. The layer is turbulent, with an energy dissipation rate nearly the same as that in the lower cloud, suggesting that the two are actively coupled, but with significant anisotropic turbulence at the large scales within the turbulent inversion layer. The turbulent inversion layer is traversed six times and the layer thickness is observed to vary between 37 and 85 m, whereas the potential temperature and horizontal wind speed differences at the top and bottom of the layer remain essentially constant. The Richardson number therefore increases with increasing layer thickness, from approximately 0.2 to 0.7, suggesting that the layer develops to the point where shear production of turbulence is sufficiently weak to be balanced by buoyancy suppression. This picture is consistent with prior numerical simulations of the evolution of turbulence in localized stratified shear layers. It is observed that the large eddy scale is suppressed by buoyancy and is on the order of the Ozmidov scale, much less than the thickness of the turbulent inversion layer, such that direct mixing between the cloud top and the free troposphere is inhibited, and the entrainment velocity tends to decrease with increasing turbulent inversion-layer thickness. Qualitatively, the turbulent inversion layer likely grows through nibbling rather than engulfment.     

Dynamic and thermodynamic features of low and middle clouds derived from atmospheric radiation measurement program mobile facility radiosonde data at Shouxian,China

By using the radiosonde measurements collected at Shouxian,China,we examined the dynamics and thermodynamics of single- and two-layer clouds formed at low and middle levels.The analyses indicated that the horizontal wind speed above the cloud layers was higher than those within and below cloud layers.The maximum balloon ascent speed(5.3 m s~(-1)) was located in the vicinity of the layer with the maximum cloud occurrence frequency(24.4%),indicating an upward motion(0.1-0.16 ms~(-1)).The average thickness,magnitude and gradient of the temperature inversion layer above single-layer clouds were117±94 m,1.3±1.3℃ and 1.4±1.5℃(100 m)~(-1),respectively.The average temperature inversion magnitude was the same(1.3℃) for single-low and single-middle clouds;however,a larger gradient[1.7±1.8℃(100 m)~(-1)]and smaller thickness(94±67 m) were detected above single-low clouds relative to those above single-middle clouds[0.9±0.7℃(100 m)~(-1) and157±120 m].For the two-layer cloud,the temperature inversion parameters were 106±59 m,1.0±0.9℃ and 1.0±1.0℃(100 m)~(-1) above the upper-layer cloud and 82 ± 60 m,0.6±0.9℃ and 0.7±0.6℃(100 m)~(-1) above the low-layer cloud.Absolute differences between the cloud-base height(cloud-top height) and the lifting condensation level(equilibrium level)were less than 0.5 km for 66.4%(36.8%) of the cases analyzed in summer.     

Parametric representation of heat and moisture fluxes in cloud-topped mixed layers

Aircraft measurements were made from the NCAR Electra in stratus and stratocumulus clouds off the coast of California in June 1976. Several types of cloud conditions were observed, including (1) a broken layer less than 100 m thick, capped by an inversion at ~1000 m, (2) a broken stratocumulus layer ~300 m thick with an inversion at ~500 m, and (3) a solid stratocumulus layer ~250 m thick with an inversion at ~500 m. Although these observations indicate that a variety of cloud conditions may exist in mixed layers, simple one-dimensional mixed-layer models implicitly assume a solid cloud layer with no unsaturated region within the cloud. In order to generalize these simple models, a parametric representation of the heat and moisture fluxes is considered. In this scheme, the fluxes are parameterized in terms of the product of a cloud mass flux and the characteristic difference between the thermodynamic properties of an updraft-downdraft circulation. This representation allows for an explicit representation of the buoyancy flux when the downdraft has no liquid water.Data collected during these flights were used to calculate heat and moisture fluxes and to obtain the mean difference in the thermodynamic properties of the updrafts and downdrafts at a given level. The mass flux was calculated using updraft-downdraft differences and the fluxes. The mass fluxes obtained using various thermodynamic quantities are examined for consistency. The vertical distribution of the mass flux is determined. These results indicate that a mass flux formulation could prove to be useful in modeling applications where cloud conditions may vary between solid and broken.     

用AMDAR资料分析两次强飞机积冰过程

利用常规气象资料和AMDAR(Aircraft Meteorological Data Relay,航空器气象资料中继)飞机气象资料,对2012年1月5日和23日贵阳机场飞机报告的两次强积冰个例过程进行了客观诊断分析.结果表明:“1·5”和“1·23”强积冰个例是静止锋形势下导致的,逆温层维持时间长,逆温层顶、逆温厚度基本不变且逆温强度有所增强;饱和冷云维持且冷云含水量不断加大,为强积冰的发生提供了有利的温度和水汽条件.AMDAR资料对于探空资料是有力的补充,能显示大气层结随时间细微的变化,为积冰预警预报服务提供参考.     

Stratiform Cloud—Inversion Characterization During the Arctic Melt Season

Data collected during July and August from the Arctic Ocean Experiment 2001 illustrated a common occurrence of specific-humidity (q) inversions, where moisture increases with height, coinciding with temperature inversions in the central Arctic boundary layer and lower troposphere. Low-level stratiform clouds and their relationship to temperature inversions are examined using radiosonde data and data from a suite of remote sensing instrumentation. Two low-level cloud regimes are identified: the canonical case of stratiform clouds, where the cloud tops are capped by the temperature inversion base (CCI—Clouds Capped by Inversion) and clouds where the cloud tops were found well inside the inversion (CII—Clouds Inside Inversion). The latter case was found to occur more than twice as frequently than the former. The characteristic of the temperature inversion is shown to have an influence on the cloud regime that was supported. Statistical analyses of the cloud regimes using remote sensing instruments suggest that CCI cases tend to be dominated by single-phase liquid cloud droplets; radiative cooling at the cloud top limits the vertical extent of such clouds to the inversion base height. The CII cases, on the other hand, display characteristics that can be divided into two situations—(1) clouds that only slightly penetrate the temperature inversion and exhibit a microphysical signal similar to CCI cases, or (2) clouds that extend higher into the inversion and show evidence of a mixed-phase cloud structure. An important interplay between the mixed-phase structure and an increased potential for turbulent mixing across the inversion base appears to support the lifetime of CII cases existing within the inversion layer.     

祁连山区一次非降水层状云的微物理结构探测分析

利用装载有粒子测量系统（PMS）的飞机对2007年8月15日甘肃省张掖市民乐县夏季非降水层状云进行了一次探测飞行,通过获取的资料分析了云层结构、云滴的垂直分布、液态含水量、谱特征等。结果表明：（1）此个例中云层结构明显,云中存在逆温层;（2）云中平均含水量为0．012g／m^3,含水层主要集中在4100～4200m与4700—5000m层之间;（3）此云系符合Bergeron提出的催化云一供水云相互作用导致降水的概念模型,可以在催化云中进行人工引晶来达到增加降水的目的。     

一次深厚浓雾过程的边界层特征和生消物理机制

2007年12月13-14日,南京出现一次厚度达600 m、持续近14 h的浓雾过程,其中强浓雾阶段维持4 h.通过系留气球边界层探测系统、涡动协方差测量系统、雾滴尺度分布和自动气象站等外场试验资料分析了此次深厚浓雾过程的边界层结构特征和生消物理机制.结果表明,此次雾过程首先由地面辐射冷却形成贴地雾层,而后因低空平流冷却形成低云.在发展阶段,伴随低云不断下伸,贴地雾层不断抬升.在贴地雾层受到地面弱冷空气平流降温影响下,雾中微物理过程迅速发展,雾滴数密度、含水量、平均直径、最大直径等微物理参数在15 min内跃增,雾体爆发性升高,最终导致地面雾和低云上下贯通形成深厚雾层,地面能见度骤降至15 m以下.雾体爆发性增强时,地面垂直动量通量和向下长波辐射通量密度增大,净辐射趋于零.整个雾过程中,由于贴地层持续弱冷平流降温和上层雾阻碍了下层雾的辐射降温,二者的共同作用使贴地强逆温结构始终维持.     

广西南宁冬季层状暖云微物理特征的飞机观测分析

利用运十二飞机在2012年冬季广西南宁地区开展的12架次层状暖云微物理探测资料进行分析,统计和观测结果表明,层状暖云垂直方向分层显著。存在逆温是典型宏观特征,降水云基本都为多层逆温,逆温位置主要出现在云顶附近。云滴平均浓度为652±607个/cm3;无降水云比降水云云滴平均浓度略大,分别为678±348个/cm3和615±363个/cm3。平均液水含量为1.03±0.73 g/m3,其中降水云远大于无降水云,分别为1.3±0.9 g/m3和0.88±0.6 g/m3。平均有效直径为18.2±5.6 μm,降水云略大于无降水云,分别为19.4±5.0 μm和17.3±6.0 μm。垂直分布上,云滴数浓度在接近地面的下层云中最大,峰值区主要出现在云底,且随高度一般呈现递减趋势。云滴谱分布显示在6.5 μm出现次峰值。降水云中大云滴主要出现在接近地面的下层云中,而无降水云中几乎没有观测到大云滴。      

基于火箭探空资料的冰雹云内部结构个例分析

利用探空火箭、新一代天气雷达和气象探测资料对2015年7月17日延安宝塔区冰雹云进行了综合探测,结果表明:（1）当日08:00（北京时,下同）500 hPa河套低涡分裂东移,有较强冷平流且移动速度较快,地面14:00升温明显造成了这次降雹。（2）偏后位置的冰雹云内部温、湿条件以及对流指数（T_g）、整层比湿积分（IQ）、总指数（TT）均小于外部的自然大气;层结稳定度指数（K）、抬升指数（LI）、沙氏指数（SI）冰雹云内部比外部自然大气偏小;热力参数风暴强度指数（SSI）冰雹云内部低于外部自然大气;冰雹云内部能量参数（CAPE）明显低于自然大气;冰雹云内部0°C层高度低于冰雹云外部自然大气。（3）火箭探测的位置偏冰雹云后部,冰雹云由低层到高层风向呈逆时针变化,探空仪摆动明显,?20°C温度层偏高,气流较强,整层偏下沉气流。（4）冰雹云0°C附近,在温度区间?1.8～5.0°C、厚度1.0 km范围内有最大湿度区,湿度达80%以上,最大湿度87.1%,为冰雹的形成提供了水汽条件。（5）紧贴0°C下正温区,有最大水平风速为19 m s?1急流,厚度为0.022 km。在温度区间?4.8～5.0°C、厚度1.6 km范围内维持13 m s?1以上水平风速,为冰雹的形成提供了动力场条件。（6）在温度区间?8.7～?9.2°C、厚度0.2 km,有小于或等于2 m s?1弱风区;弱风区下方,在温度区间?4.6～?8.8°C、厚度0.889 km有上升气流,平均上升速度1.79 m s?1,最大上升速度4 m s?1,这种配置为冰雹的生长提供了环境场。     

热带西太平洋边界层的多层结构分析

本文主要利用第一次“中美热带西太平洋海气相互作用联合调查”所获得的海洋水文、气象及大气探测资料,分析了热带西太平洋暖水区边界层大气层结特征,指出热带西太平洋边界层大气具有多层结构和多层送温现象,边界层内各层厚度及气温、位温、混合比随高度的变化趋势如下:超绝热层位于地面以上50m左右,气温、位温、混合比迅速减小,系绝热不稳定层;第一层为混合层,平均厚度为351m,位温、混合比变化不明显;混合层上又是逆温层大多为30—100m厚,位温迅速增大,混合比迅速减小,系绝对稳定层;700—1000m为浅对流云活跃层,     

黄河源地区近地面逆温层特征及形成原因分析

利用黄河源地区达日国家基准气象站2008～2017a近10a的探空、地面观测资料,分析黄河源地区近地面逆温层特征及形成原因,结果表明:(1)黄河源地区逆温层的出现频率、厚度、强度在不同时次随季节有明显的变化;(2)云量的多少、低空风速的大小对逆温的产生及强弱直接有关,逆温层下常伴有露、霜、雾等天气现象出现,逆温层上下空气湿度存在着明显的差别;(3)黄河源地区的逆温是在气候背景、地理条件、天气条件共同影响下,地面辐射作用的结果。      

Stratocumulus-capped mixed layers derived from a three-dimensional model

Results of a three-dimensional numerical model are analysed in a study of turbulence and entrainment within mixed layers containing stratocumulus with or without parameterized cloud-top radiative cooling. The model eliminates most of the assumptions invoked in theories of cloud-capped mixed layers, but suffers disadvantages which include poor resolution and large truncation errors in and above the capping inversion.For relatively thick mixed layers with relatively thick capping inversions, the cloud-top radiative cooling is found to be lodged mostly within the capping inversion when the cooling is confined locally to the upper 50 m or less of the cloud. It does not then contribute substantially towards increased buoyancy flux and turbulence within the well mixed layer just below.The optimal means of correlating the entrainment rate, or mixed-layer growth rate, for mixed layers of variable amounts of stratocumulus is found to be through functional dependence upon an overall jump Richardson number, utilizing as scaling velocity the standard deviation of vertical velocity existing at the top of the mixed layer (near the center of the capping inversion). This velocity is found to be a fraction of the generalized convective velocity for the mixed layer as a whole which is greater for cloud-capped mixed layers than for clear mixed layers.     

基于CloudSat卫星资料分析青藏高原东部夏季云的垂直结构

本文利用CloudSat卫星资料,对青藏高原东部2006~2010年6~8月云垂直结构的空间分布进行分析,结果表明:(1)夏季青藏高原东部云发展可达到平流层,且高原东部云在5km以下以水云存在,5~10km以液相和固相共存的混态存在,在垂直高度10km以上以冰云存在。由于CloudSat卫星资料云相的反演问题,可能会造成水云和混态云的发展上限偏低,冰云的发展下限抬升。(2)研究区整层水汽输送和云水平均路径空间分布存在一定的差异性,云水含量纬向分布表现为在26.5°~30.5°N附近存在一个明显的峰值区,经向分布表现为95°E以西云水含量低于以东。(3)研究区以单云层为主,尤其在青藏高原主体。单云层平均云层厚度4182 m,云顶高度、云厚限于水汽的输送,表现为由南向北波动下降。多层云发生频率在27°N以北明显减少,说明强烈的对流运动更容易激发多层云的产生。     

干湿地表的湍流特征及其对深对流影响的大涡模拟

利用大涡模式模拟了对流边界层结构演变以及深对流触发过程。通过改变鲍恩比的敏感性试验研究不同大气初始状况下湿润和干旱下垫面湍流特征及其对深对流触发过程的影响。结果表明:干旱下垫面的混合层干而暖,厚度较大;湿润下垫面相反。由于地表感热通量对热力湍流形成的作用更大,干旱下垫面上湍流混合和夹卷作用更强,使得水汽和相当位温在边界层内分布更均一,而在边界层顶有较大的负扰动;干旱下垫面上对流强度较湿润下垫面大,但均表现为泡状对流,水平方向上呈网状结构。不同下垫面上深对流的发生与大气初始状况有关,当初始时刻1—3 km的逆温强度较弱时（0.15 K/（100 m））,边界层内湍流迅速发展,深对流首先在干旱下垫面发生,但因对流有效位能较小,云层厚度小于湿润下垫面。当1—3 km的逆温强度增加到0.55 K/（100 m）时,云层形成时间较晚,云层厚度明显减小,仅当边界层顶的比湿较大时,有深对流发生,但仍首先发生在干旱下垫面,考虑贯穿对流在边界层顶引起的较强冷却作用,云层厚度大于湿润下垫面。      

A numerical investigation of the JASIN atmospheric boundary layer

A numerical model of the cloudy marine boundary layer is described and used to investigate the role of entrainment instability on the developing boundary layer. In general, previous studies have been limited to boundary layers capped by convectively stable inversions or have described only cumulus fields. Here we extend a stratus-capped boundary-layer model to consider the transition to a convectively unstable cloud layer capped by an inversion across which there is a rapid decrease in wet-bulb or equivalent potential temperature. In this case, the inversion is very active and the entrainment rate is determined by the active instability at the interface, in contrast to the mean turbulent motion within the boundary layer.The model is used to interpret the observed boundary layer from the JASIN experiment. Cool, dry air is modified by prolonged passage over increasingly warmer ocean which leads to the development of a convectively unstable cloud layer.     

河北冬季一次冷锋降雪云系微物理演变特征综合观测分析研究

利用河北省中南部地区皇寺国家观测站布设的毫米波云雷达、微雨雷达结合飞机等联合观测数据，对2019年2 月14日河北中南部地区一次冷锋降雪云系微物理演变特征进行分析，探讨雷达回波与冰雪晶粒子微结构的关系，以便更好地认识该地区自然降雪的宏微观结构特征。研究结果表明：降雪初生阶段表现为双层云结构，中云云顶高约4100 m，云底高约3600 m，低云云顶高约3100 m，云底高约200 m，中间存在一干层，3000 m以下高度粒子增长以凇附过程为主。降雪发展阶段上下两层云相接，雷达回波强度较强的时段地面降水量也较大，该时段降雪过程主要以凝华〖CD*2〗聚并增长为主。降雪后期回波强度最大值减小，云顶高降低，3000 m以下高度范围内回波强度、多普勒速度、谱宽随高度降低呈增大趋势；飞机观测结果显示，降雪消散阶段逆温层底部由于水云云层较薄，催化潜力较小,冰雪晶粒子主要位于云的中上部，随着高度降低，冰雪晶粒子在下落过程中增大，与雷达观测结果一致，毫米波云雷达和微雨雷达反射率因子随高度变化与降水粒子有效粒径之间相关系数分别为0.89和0.83, 雷达反射率因子主要受冰雪晶等大尺度粒子主导。     

民勤干旱区冬季浓雾形成的边界层条件分析

利用民勤县气象站过程地面小时观测资料、逐日08时和20时每隔50 m探空资料和NECP再分析资料,对2015年11月9—13日出现在干旱区民勤县的一次罕见浓雾天气过程进行了研究分析。结果表明:前期降水后地面相对湿度增大,为大雾形成提供了必要的水汽条件,稳定的高低层环流配置提供了大雾形成的稳定层结和弱风条件。雾层的厚度和强度与近地面逆温层的强度和厚度、边界层高度、水汽垂直运动以及夜间地气温差绝对值密切相关,边界层高度越高,逆温层越厚,雾层越厚;逆温层越强,夜间地气温差绝对值越小,雾层越强。高空环流形势稳定少动,近地层强逆温层、稳定等温层以及饱和湿层长时间维持,导致此次大雾强度和持续时间异常罕见。     

气溶胶激光雷达和无线电探空观测边界层高度的对比分析

利用北京地区2017年11月至2018年1月连续3个月的激光雷达资料和无线电探空数据,按照清洁天、污染天和多云天3种天气条件,对大气边界层高度的计算方法和结果进行对比分析。结果表明,基于激光雷达消光系数的梯度法、标准差法和小波法都能够较好地提取边界层高度。清洁天标准差法计算的边界层高度高于梯度法和小波法,08:00（当地时间,下同）和20:00由无线电探空得到的清洁天边界层高度平均值分别为1176 m和1224 m。污染天标准差法的计算结果要低于梯度法和小波法,污染天无线电探空得到的边界层高度平均值约为956 m,和清洁天相比降低了两百多米,重污染时最低降低至562 m,逆温层高度和PM2.5浓度具有明显的反相关关系。有云时,梯度法和小波法确定的边界层高度和云高非常接近,标准差法计算的结果略低。总体而言,气溶胶激光雷达计算的边界层高度随着污染等级的提高没有明显的降低趋势,相反在重度污染情况下反而有所增加,这可能是由于污染物的不断堆积导致的。梯度法确定的边界层高度易受到污染物传输过程的影响,略高于逆温层高度。另外,激光雷达确定的边界层高度受到残留层影响时,也会高于逆温层。     

Measurements Of Fine-Scale Structure At The Top Of Marine Stratocumulus

During the Dynamics and Chemistry of the MarineStratocumulus (DYCOMS) experiment in July–August 1985, the NCAR Electra aircraft flew a series of flight legs just at the top of the marinestratocumulus cloud decks that cap the mixed layer off the coast of southernCalifornia. Because of the corrugated structure of the cloud-top, the aircraft, which was flown at a nearly constant level and adjusted only to maintain its altitude at the average cloud-top height, was alternately within and above the clouds – roughly half the time in each domain. These legs were used to examine the structure of the cloud-top by compositing the segments on either side of the cloud/clear-air interface, which was identified by the transitions of liquid water measured by the Forward Scattering Spectrometer Probe (either increasing or decreasing) through a threshold of 0.04 × 10^-3 kg m^-3.An equivalent vertical distance (EVD) from the cloud-top was obtained from the horizontal flight legs by estimating the average slope of the cloud-top from the cloud-top radiation temperature. The results show that a near discontinuity occurs in variables across cloud top over an EVD of 0.3 m, but that above this, the air has already been modified by boundary-layer air. Thus, cloud-top is not the limit of mixing of boundary-layer air. This mixing may extend to tens of metres or more. The bulk Richardson number in the vicinity of cloud-top increases from near zero within the cloud to about 1.2 at an EVD of 3–6 m above cloud. Fluctuations of the three velocity components within cloud are nearly equal; above cloud the vertical component structure function is about half the horizontal components. The scalar structure functions are about an order of magnitude higher above cloud than in cloud. The structure parameters of temperature and humidity measured just below cloud-top agree reasonably well with predicted values based on a previously-developed model for the clear convective boundary layer. Above cloud, the scalar structure parameters are much larger, but their interpretation is questionable, since this region does notcontain isotropic turbulence.