A GCSS Boundary-Layer Cloud Model Intercomparison Study Of The First Astex Lagrangian Experiment

Three single-column models (all with an explicit liquid water budget and compara-tively high vertical resolution) and three two-dimensional eddy-resolving models (including one with bin-resolved microphysics) are compared with observations from the first ASTEX Lagrangian experiment. This intercomparison was a part of the second GCSS boundary-layer cloud modelling workshop in August 1995.In the air column tracked during the first ASTEX Lagrangian experiment, a shallow subtropical drizzling stratocumulus-capped marine boundary layer deepens after two days into a cumulus capped boundary layer with patchy stratocumulus. The models are forced with time varying boundary conditions at the sea-surface and the capping inversion to simulate the changing environment of the air column.The models all predict the observed deepening and decoupling of the boundary layer quite well, with cumulus cloud evolution and thinning of the overlying stratocumulus. Thus these models all appear capable of predicting transitions between cloud and boundary-layer types with some skill. The models also produce realistic drizzle rates, but there are substantial quantitative differences in the cloud cover and liquid water path between models. The differences between the eddy-resolving model results are nearly as large as between the single column model results. The eddy resolving models give a more detailed picture of the boundary-layer evolution than the single-column models, but are still sensitive to the choice of microphysical and radiative parameterizations, sub-grid-scale turbulence models, and probably model resolution and dimensionality. One important example of the differences seen in these parameterizations is the absorption of solar radiation in a specified cloud layer, which varied by a factor of four between the model radiation parameterizations.     

A Lagrangian Stochastic Model for Sea-Spray Evaporation in the Atmospheric Marine Boundary Layer

The dispersion of heavy particles subjected to a turbulent forcing is often simulated with Lagrangian stochastic models. Although these models have been employed successfully over land, the implementation of traditional LS models in the marine boundary layer is significantly more challenging. We present an adaptation of traditional Lagrangian stochastic models to the atmospheric marine boundary layer with a particular focus on the representation of the scalar turbulence for temperature and humidity. In this new model, the atmosphere can be stratified and the bottom boundary is represented by a realistic wavy surface that moves and deforms. Hence, the correlation function for the turbulent flow following a particle is extended to the inhomogenous, anisotropic case. The results reproduce behaviour for scalar Lagrangian turbulence in a stratified airflow that departs only slightly from the expected behaviour in isotropic turbulence. When solving for the surface temperature and the radius of evaporating heavy water droplets in the airflow, the modelled turbulent forcing on the particle also behaves remarkably well. We anticipate that this model will prove especially useful in the context of sea-spray dispersion and its associated sensible heat, latent heat, and gas fluxes between spray droplets and the atmosphere.     

A Lagrangian Stochastic Model for Heavy Particle Dispersion in the Atmospheric Marine Boundary Layer

The dispersion of heavy particles and pollutants is often simulated with Lagrangian stochastic (LS) models. Although these models have been employed successfully over land, the free surface at the air-sea interface complicates the implementation of traditional LS models. We present an adaptation of traditional LS models to the atmospheric marine boundary layer (MBL), where the bottom boundary is represented by a realistic wavy surface that moves and deforms. In addition, the correlation function for the turbulent flow following a particle is extended to the anisotropic, unsteady case. Our new model reproduces behaviour for Lagrangian turbulence in a stratified air flow that departs only slightly from the expected behaviour in isotropic turbulence. When solving for the trajectory of a heavy particle in the air flow, the modelled turbulent forcing on the particle also behaves remarkably well. For example, the spectrum of the turbulence at the particle location follows that of a massless particle for time scales approximately larger than the Stokes’ particle response time. We anticipate that this model will prove especially useful in the context of sea-spray dispersion and its associated momentum, sensible and latent heat, and gas fluxes between spray droplets and the atmosphere.     

西双版纳地区雾的数值模拟研究

建立了一个适用于复杂地形上的三维非定常雾模式,用于研究西双版纳地区雾的生消规律。模式详细考虑了湍流、长短波辐射、凝结、蒸发、重力沉降等影响因子,特别注意了植被和气溶胶辐射效应对雾的生消的影响。利用本模式对山谷风及雾的生消过程进行了实况模拟,结果表明,模式在一定程度上反映了实际情况。     

导线积冰的云雾特征观测研究

导线积冰在贵州山区是常见的气象灾害, 导线积冰增长率与气象云雾因子密切相关。研究选择贵州西部、北部、中部3个积冰区进行了专门外场观测, 观测项目有:云滴谱、含水量、气温、风向、风速、导线上积冰的长径、短径。观测分析表明:贵州云滴浓度、特征平均直径没有显著性地区差异; 云滴平均浓度140~312个/cm3, 云滴算术平均直径、均立方根直径、中值体积直径分别为7.5 μm, 11.3 μm和20 μm; 14 μm以上大云滴浓度平均占云滴总浓度的12.5%, 但对含水量的贡献高达78%, 大滴与导线碰撞效率高, 大滴是导线积冰的关键因子; 云雾含水量平均0.20 g/m3; 在0~-6 ℃之间, 含水量随温度的降低而降低; 南北向导线积冰比东西向的积冰多; 导线积冰增长率与含水量的大小成正比, 风速超过3 m/s时, 积冰增长率与风速有较明显的正比关系。     

重庆雾的二维非定常数值模拟

重庆是著名的“雾都”.本文建立了一个复杂地形下详细考虑长波辐射冷却、地表热量平衡、雾水沉降、水汽凝结和蒸发、湍流交换系数等的二维非定常雾模式,以实测资料为初始场,研究了一次重庆雾的形成和发展过程.对江河、热岛、辐射、地形和山城的影响,模式分别进行了数值试验.     

A Simple Parametrization for the Concentration Variance Dissipation in a Lagrangian Single-Particle Model

A new quasi-analytical mixed-layer model is formulated describing the evolution of the convective atmospheric boundary layer (ABL) during cold-air outbreaks (CAO) over polar oceans downstream of the marginal sea-ice zones. The new model is superior to previous ones since it predicts not only temperature and mixed-layer height but also the height-averaged horizontal wind components. Results of the mixed-layer model are compared with dropsonde and aircraft observations carried out during several CAOs over the Fram Strait and also with results of a 3D non-hydrostatic (NH3D) model. It is shown that the mixed-layer model reproduces well the observed ABL height, temperature, low-level baroclinicity and its influence on the ABL wind speed. The mixed-layer model underestimates the observed ABL temperature only by about 10 %, most likely due to the neglect of condensation and subsidence. The comparison of the mixed-layer and NH3D model results shows good agreement with respect to wind speed including the formation of wind-speed maxima close to the ice edge. It is concluded that baroclinicity within the ABL governs the structure of the wind field while the baroclinicity above the ABL is important in reproducing the wind speed. It is shown that the baroclinicity in the ABL is strongest close to the ice edge and slowly decays further downwind. Analytical solutions demonstrate that the \(\mathrm{e}\)-folding distance of this decay is the same as for the decay of the difference between the surface temperature of open water and of the mixed-layer temperature. This distance characterizing cold-air mass transformation ranges from 450 to 850 km for high-latitude CAOs.     

浅水湖沼—陆面地区平流辐射雾的数值模拟

建立了一个二维时变数值模式,模拟了浅水湖沼—陆面地区平流辐射雾形成、演变和消散的基本过程。结果表明,地面温度迅速下降是成雾前的一个重要特征;浅水湖沼地区充沛的水汽对平流辐射雾的形成极为有利;平流作用可使辐射雾呈爆发性发展;长短波辐射与湍流混合的共同作用是辐射雾生消的主要物理机制;成雾后在雾顶的稍下方有长波辐射冷却率的极大区,最大值为２１×１０－３ｏＣ／ｓ（７６ｏＣ／ｈ）。模拟结果与观测事实基本一致。     

声波对气溶胶和云雾粒子聚并影响研究进展

声波对气溶胶和云雾粒子聚并的作用和影响是当今云雾物理和人工影响天气领域研究的前沿科学问题。已有研究表明：声聚并机制主要包括同向团聚机制、流体力学机制（包括共辐射压效应、共散射效应和声波尾流效应）和声致湍流机制等;气溶胶粒子在声场中的聚并现象是在多种声聚并机制共同作用下出现的;低频强声波在声聚并机制作用下会增加云雾滴粒子之间的相对运动,促进粒子间的碰并过程,对云雾滴生长和降水过程有显著的影响。但由于声波聚并过程的复杂性、实验条件的多样性和理论的局限性,使声聚并效率最高的最佳实验条件和参数配置依然具有很大的不确定性,需要进行大量实验与数值模拟的综合研究。今后应加强声聚并对云雾滴作用的云室和数值模拟研究,并开展声波对云雾过程和降水影响的野外综合观测试验评估,这对发展人工影响天气（如人工消雾、增雨等）新技术有重要的科学意义。     

北京一次对流云人工催化作业效果检验

利用北京SA波段天气雷达每6 min一次的体扫数据和FY-2气象卫星云图,以2015年8月22日北京平谷地区一次人工影响天气作业为例,分析作业单元和与之条件相似的对比单元两者雷达回波参数的变化,并运用非参数检验方法进行显著性检验,对冷涡后局地新生的强对流风暴群的人工催化效果进行检验。结果表明,第一次地面作业后,在作业点位置的回波明显减弱,第二次地面作业后,作业点位置的回波持续减弱,组合反射率大于30 dBz的回波逐渐减弱消失,同时作业点东北方的回波不断增强合并,并向东边移动。此次作业所在区域的对流发展强烈,组合反射率大于45 dBz的回波直径为5—20km,组合反射率大于50 dBz的持续时间较长。显著性检验表明,作业回波与对比回波的最大组合反射率和平均组合反射率的衰减率通过了信度为0.15的显著性检验,存在显著差异;回波面积衰减速率通过了信度为0.3的显著性检验;且作业回波的各物理量的衰减率均小于中值和平均值,表明催化作业对维持云系发展起到积极作用。     

冻滴微物理过程的分档数值模拟试验研究

霰和冻滴是深对流降水的主要来源。由于二者密度差异造成的不同下落末速度必然会导致云微物理过程的变化以及降水时空分布的改变。我们在以色列特拉维夫大学二维轴对称对流云全分档模式的基础上,将水成物粒子从34档增加到40档,修改了霰和雪的密度,加入冻滴分档处理的微物理过程,发展了一个包括液滴、冰晶、雪、霰和冻滴更为详细的云微物理分档模式。利用改进后的模式模拟了一次理想的强对流天气过程,分析了改进模式与原模式模拟的云微物理量场以及水成物粒子的时空分布特征,模拟结果表明:（1）由于冻滴的产生,较大的下落末速度导致在云内-3℃至-8℃较早地出现了冻滴,并造成了大量的冰晶繁生。（2）冻滴形成前期,液态水中心区域位于垂直上升速度大值中心上方,形成液态水累积区;冻滴形成期,液态水累积区位于0℃层以上,雨滴冻结生成冻滴,霰与半径大于100 μm的液滴碰并生成冻滴;冻滴增长期,在垂直上升气流的支撑下,冻滴碰并过冷水增长,导致冻滴含量增大,液态水含量减小。因此,改进模式能较好的模拟冻滴的形成过程,可以将该分档处理的微物理方案耦合到三维WRF（Weather Research and Forecasting model）模式中,更深入地研究强雷暴风切变在冰雹生成过程中的作用。     

江西区域性大雾出现前期云图云场特征分析

主要介绍江西省区域性大雾中几种主要类型雾的前期云场特征,并介绍雾区已形成时的云场特征及多数连续性大雾天气的卫星云图云场特征。     

层状云数值模式与实际观测研究

改进了一维层状云雨滴分档模式,利用雨滴分档模式在计算雨滴粒子谱型及数浓度自然演变方面中的优势,对吉林省长春市6月21日3个不同时刻的降雨进行了模拟,并与实测资料进行了比较。结果表明,改进后的模式计算稳定,可以模拟出与实际降水谱型相接近的雨滴谱;对于层状云中上升气流速度难以直接测量的问题,通过选用不同的上升气流速度方案,并将计算所得的雷达回波反射率廓线与实际地面雷达观测值相拟和的方法,从而为实现通过雷达回波与模式计算相比较来测量定量降水提供一个新的思路;与实际观测结果比较可知,暖区碰并过程对本次降水的贡献在10%左右,与上升气流的速度有关。     

A Two-Dimensional Lagrangian Stochastic Dispersion Model for Convective Boundary Layers with Wind Shear

Rotach, Gryning and Tassone constructed a two-dimensional Lagrangian stochastic model to describe the dispersion of passive tracers in turbulent boundary layers with stabilities ranging from ideally-neutral (w_* = 0) to fully-convective (u_* = 0). They found that the value of the Kolmogorov constant, C₀, as determined by optimizing model agreement with the measured spread of passive tracers, was dependent upon stability. Here, it is shown that the non-uniqueness, associated with satisfaction of the well-mixed condition, can be exploited to construct an alternative version of the model of Rotach et al. for which C₀ = 3 is universally applicable over the entire range of stabilities under consideration. This alternative model is shown to be in very close agreement with predictions, obtained in large-eddy simulations, for the dispersion of passive tracers in turbulent boundary layers with stabilities ranging from ideally-neutral to fully-convective.     

华东地区一次持续大雾过程及其与空气污染相互作用分析

2008年1月7～11日期间,华东地区自北向南出现了一次持续大雾过程,分别影响到山东、江苏、安徽、上海、浙江、福建等地,并伴随有轻至中度空气污染,对当地生活、生产、运输造成严重影响。利用地面探测和探空资料、NCEP/NCAR再分析资料及MM5数值模拟结果等资料,分别从天气形势分析、水汽条件、动力因子、温度层结、空气质量变化等多方面入手,对此次大雾过程的成雾条件及空气污染对持续大雾的贡献进行诊断分析。分析指出,近地面层水汽通量散度、垂直速度以及500hPa与1000hPa散度差与能见度无显著相关,近地面相对湿度(Rh)与能见度呈明显反相关,近地面温度递减率(γ)与能见度呈明显正相关,可以把Rh≥85%、γ0.2℃.(100m)-1作为大雾形成的必要条件。另外,选取与空气污染指数(API)相同时间段(前一日04时至当日03时,协调世界时)上海虹桥机场的航空能见度最低值与API对比发现,航空能见度最低值与API呈强烈的反相关,空气污染对大雾形成或维持具有显著的促进作用,可以把"API上升达到150"作为上海虹桥机场出现大雾的一个重要的判断条件。     

宁波近海雾预报的研究

本文用日本FSAS地面24小时数值预报输出图,建立了逐日格点最佳相似和各级雾平均气压场相似两种方案,作宁波地区近海24小时雾的分级预报,并对1987年独立样本资料进行试报,1988年投入业务检验。     

大气模式中云量诊断的系统性误差研究

对云量的诊断方案作了深入的分析,证明了无论云量与其他变量的关系是离散型还是连续型,只要云量与其他变量的关系是由凸函数描述的,则云量会系统性地偏少;反之,如果云量与其他变量的关系是由凹函数来描述的,则云量会系统性地偏大。故Slingo型云量方案中,大尺度云量会系统性偏少,而积云对流所对应的云量会系统性地偏大。同时还证明了如果其他气象变量是高频振荡型的,则云量与该气象变量的关系在局地相关较好,而长期时间平均后则相关程度急剧下降;如果其他气象变量是稳定型变量,则云量与该气象变量的关系在局地相关长期平均好,但就短时间而言相关较差。故云量方案(含Slingo型)存在系统性误差,应被新的物理上更合理的方案所代替。     

中国古诗词中的云雾雨雪

从云雾降水物理学的角度学习和分析了一些中国古诗词。内容有:1）分析和统计了唐诗300首和毛泽东诗词中用到云雾雨雪等字的百分比,其分别占总首数的45%和66%;2）列举和分析了描述自然过程、大气过程有云雨雪等字的诗(词)句;3）从现代科学观出发,分析了在一些古诗词中有关云、雨、霜、露等的理解,并作了一些评述;4）对古诗词中直接描述云、雾、雨、雪的内容进行了评论。