Characteristics of clouds,precipitation, and latent heat in midlatitude frontal system mixed with dust storm from GPM satellite observations and WRF simulations

A heavy dust storm originating in Mongolia and Inner Mongolia traveled to Northeast China and met a midlatitude frontal system on May 3, 2017. The potential ice nuclei (IN) effects of mineral dust aerosols on the vertical structure of clouds, precipitation, and latent heat (LH) were studied using Global Precipitation Mission (GPM) satellite observations and Weather Research and Forecasting (WRF) model simulations. The WRF simulations correctly captured the main features of the system, and the surface rain rate distribution was positively correlated with data retrieved from the GPM Microwave Imager. Moreover, the correlation coefficient increased from 0.31 to 0.54 with increasing moving average window size. The WRF-simulated rainfall vertical profiles are generally comparable to the GPM Dual-Frequency Precipitation Radar (DPR) observations, particularly in low layers. The joint probability distribution functions of the rain rate at different altitudes from the WRF simulation and GPM observations show high positive correlation coefficients of ~0.80, indicating that the assumptions regarding the raindrop size distribution in the WRF model and DPR retrieval were consistent. Atmospheric circulation analysis and aerosol optical depth observations from the Himawari-8 satellite indicated that the dust storm entered only a narrow strip of the northwest edge of the frontal precipitation system. The WRF simulations showed that in carefully selected areas of heavy dust, dust can enhance the heterogeneous ice nucleation process and increase the cloud ice, snowfall, high-altitude precipitation rate, and LH rate in the upper layers. This effect is significant at temperatures of ?15 °C to ?38 °C and requires dust number concentrations exceeding 106 m?3. It is important to accurately classify the dusty region in this type of case study. In the selected vertical cross section, the WRF-simulated and DPR-retrieved LH have comparable vertical shapes and amplitudes. Both results reflect the structure of the tilted frontal surface, with positive LH above it and negative LH below it. The simulated area-averaged LH profiles show positive heating in the entire column, which is a convective-dominated region, and this feature is not significantly affected by dust. DPR-based LH profiles show stratiform-dominated or convective-dominated shapes, depending on the DPR retrieval product.     

特殊地形下对WRF模式积云参数化的研究应用

以发生在地形复杂的四川地区2012年07月03日暴雨为个例,从环流形势、水汽通量和云微物理量3方面具体研究WRFV3.3版本模式7种积云方案对暴雨模拟的效果,结果表明:BMJ方案和KF方案模拟降水效果好于GD和G3D方案,TS评分表明BMJ方案和KF方案得分要远远高于其它方案,GD和G3d方案得分最低.云水混合比与雨水混合比的含量高低直接影响模式预报降水量强度,高层大气模拟值的大小对降水量预报起着主要作用.除KF方案以外,其它积云方案模拟的云水混合比发展要早于雨水混合比,随后两者几乎同步发展,云水混合比和雨水混合比值迅速增长后,降水落区和降水范围迅速扩大.最终结果表明在四川地区利用WRF模拟暴雨,积云参数化方案考虑使用KF和BMJ方案,不使用GD和G3d方案.     

Deep convective clouds with sustained supercooled liquid water down to -37.5 degrees C

In cirrus and orographic wave clouds, highly supercooled water has been observed in small quantities (less than 0.15 g m(-3)). This high degree of supercooling was attributed to the small droplet size and the lack of ice nuclei at the heights of these clouds. For deep convective clouds, which have much larger droplets near their tops and which take in aerosols from near the ground, no such measurements have hitherto been reported. However, satellite data suggest that highly supercooled water (down to -38 degrees C) frequently occurs in vigorous continental convective storms. Here we report in situ measurements in deep convective clouds from an aircraft, showing that most of the condensed water remains liquid down to -37.5 degrees C. The droplets reach a median volume diameter of 17 microm and amount to 1.8 gm(-3), one order of magnitude more than previously reported. At slightly colder temperatures only ice was found, suggesting homogeneous freezing. Because of the poor knowledge of mixed-phase cloud processes, the simulation of clouds using numerical models is difficult at present. Our observations will help to understand these cloud processes, such as rainfall, hail, and cloud electrification, together with their implications for the climate system.     

High-resolution seasonal snowfall simulation over Northeast China

Performance of the Weather Research and Forecasting (WRF) model in simulating seasonal snowfall over Northeast China was examined. The influences of horizontal resolution and physics parameterization schemes were also investigated. The results indicate that WRF can reasonably reproduce the main features of temperature and precipitation. The simulated spatial and temporal distribution of snowfall compared well with observations. Higher resolution simulations achieved better results, and WRF was found to be more sensitive to the choice of land surface and microphysics scheme than convective cumulus parameterization scheme.     

The impact of humidity above stratiform clouds on indirect aerosol climate forcing

Some of the global warming from anthropogenic greenhouse gases is offset by increased reflection of solar radiation by clouds with smaller droplets that form in air polluted with aerosol particles that serve as cloud condensation nuclei. The resulting cooling tendency, termed the indirect aerosol forcing, is thought to be comparable in magnitude to the forcing by anthropogenic CO2, but it is difficult to estimate because the physical processes that determine global aerosol and cloud populations are poorly understood. Smaller cloud droplets not only reflect sunlight more effectively, but also inhibit precipitation, which is expected to result in increased cloud water. Such an increase in cloud water would result in even more reflective clouds, further increasing the indirect forcing. Marine boundary-layer clouds polluted by aerosol particles, however, are not generally observed to hold more water. Here we simulate stratocumulus clouds with a fluid dynamics model that includes detailed treatments of cloud microphysics and radiative transfer. Our simulations show that the response of cloud water to suppression of precipitation from increased droplet concentrations is determined by a competition between moistening from decreased surface precipitation and drying from increased entrainment of overlying air. Only when the overlying air is humid or droplet concentrations are very low does sufficient precipitation reach the surface to allow cloud water to increase with droplet concentrations. Otherwise, the response of cloud water to aerosol-induced suppression of precipitation is dominated by enhanced entrainment of overlying dry air. In this scenario, cloud water is reduced as droplet concentrations increase, which diminishes the indirect climate forcing.     

Numerical simulation of topography effects on the "00.7" severe rainfall in Beijing

In an effort to study the severe rainfall event of 4-5th July 2000 in Beijing (with 24h accumulated precipitation of 240 mm), we perform numerical simulations to investigate this event using the MM5v3.6 model. The model is initialized with the MM5/WRF 3DVAR analysis, which incorporates the ground-based GPS precipitable water vapor, automatic and conventional meteorological observations in its assimilation step. For 24 h accumulated precipitation forecast, the threat scores are 0.72, 0.76, 0.67 and 0.63, for thresholds of 1, 5, 10, and 20 mm, respectively. Holding other factors unchanged, sensitivity experiments were conducted with different topographic resolutions of 110, 50 and 3.7 km to investigate the topographic effects on precipitation over the Beijing area. In these sensitivity experiments, we attempt to preserve the realistic orographic distribution in the model topography under the condition of keeping the dynamic-thermodynamic consistency of the initial model atmosphere to the extent possible. Results indicate that the unique topographic distribution and variations in the Beijing area play an important role in determining the location, distribution and intensity of heavy precipitation.     

Numerical simulation of topography effects on the “00.7” severe rainfall in Beijing

In an effort to study the severe rainfall event of 4?5th July 2000 in Beijing (with 24h accumulated precipitation of 240 mm), we perform numerical simulations to investigate this event using the MM5v3.6 model. The model is initialized with the MM5/WRF 3DVAR analysis, which incorporates the ground-based GPS precipitable water vapor, automatic and conventional meteorological observations in its assimilation step. For 24 h accumulated precipitation forecast, the threat scores are 0.72, 0.76, 0.67 and 0.63, for thresholds of 1, 5, 10, and 20 mm, respectively. Holding other factors unchanged, sensitivity experiments were conducted with different topographic resolutions of 110, 50 and 3.7 km to investigate the topographic effects on precipitation over the Beijing area. In these sensitivity experiments, we attempt to preserve the realistic orographic distribution in the model topography under the condition of keeping the dynamic-thermodynamic consistency of the initial model atmosphere to the extent possible. Results indicate that the unique topographic distribution and variations in the Beijing area play an important role in determining the location, distribution and intensity of heavy precipitation.     

台湾地形对1998年6月7—8日中尺度对流系统降雨的影响

利用中尺度模式MM5研究了台湾地形对中尺度对流系统所引起的降雨的影响。通过一系列不同模式分辨率和不同精确度地形高度的敏感性实验, 发现模式的分辨率对降水的预报起决定作用,同时,地形的精确度也可以改变降水的分布和强度。为了得到合理的模拟,6km 的模式分辨率和18km 的地形精确度是必须的。去掉台湾地形的敏感性实验表明,台湾中央山脉对降水的影响可以分为两类,即“强迫”和“修正”效应。在对流层低层,中央山脉对中α尺度低压有阻挡作用,并强迫局地中β尺度的低压。中β尺度的低压和中α尺度低压相互作用,在台湾北部“强迫”出暴雨;而在台湾中部,中尺度对流系统登陆的地方,中央山脉对降雨的落区和强度都给予了“修正”。     

Entrainment-mixing parameterization in shallow cumuli and effects of secondary mixing events

Parameterization of entrainment-mixing pro- cesses in cumulus clouds is critical to improve cloud parameterization in models, but is still at its infancy. For this purpose, we have lately developed a formulation to represent a microphysical measure defined as homoge- neous mixing degree in terms of a dynamical measure defined as transition scale numbers, and demonstrated the formulation with measurements from stratocumulus clouds. Here, we extend the previous work by examining data from observed cumulus clouds and find positive cor- relations between the homogeneous mixing degree and transition scale numbers. These results are similar to those in the stratocumulus clouds, but proved valid for the first time in observed cumulus clouds. The empiricalrelationships can be used to parameterize entrainment- mixing processes in two-moment microphysical schemes. Further examined are the effects of secondary mixing events on the relationships between homogeneous mixing degree and transition scale numbers with the explicit mixing parcel model. The secondary mixing events are found to be at least partially responsible for the larger scatter in the above positive correlations based on obser- vations than that in the previous results based on numerical simulations without considering secondary mixing events.     

Heterogeneous chemistry in the atmosphere of Mars

Hydrogen radicals are produced in the martian atmosphere by the photolysis of water vapour and subsequently initiate catalytic cycles that recycle carbon dioxide from its photolysis product carbon monoxide. These processes provide a qualitative explanation for the stability of the atmosphere of Mars, which contains 95 per cent carbon dioxide. Balancing carbon dioxide production and loss based on our current understanding of the gas-phase chemistry in the martian atmosphere has, however, proven to be difficult. Interactions between gaseous chemical species and ice cloud particles have been shown to be key factors in the loss of polar ozone observed in the Earth's stratosphere, and may significantly perturb the chemistry of the Earth's upper troposphere. Water-ice clouds are also commonly observed in the atmosphere of Mars and it has been suggested previously that heterogeneous chemistry could have an important impact on the composition of the martian atmosphere. Here we use a state-of-the-art general circulation model together with new observations of the martian ozone layer to show that model simulations that include chemical reactions occurring on ice clouds lead to much improved quantitative agreement with observed martian ozone levels in comparison with model simulations based on gas-phase chemistry alone. Ozone is readily destroyed by hydrogen radicals and is therefore a sensitive tracer of the chemistry that regulates the atmosphere of Mars. Our results suggest that heterogeneous chemistry on ice clouds plays an important role in controlling the stability and composition of the martian atmosphere.     

用区域气候模式对1951——2000年我国夏季降水的模拟

为了检验区域气候模式对我国夏季降水的模拟能力,利用高分辨率区域气候模式RegCM3对1951?2000年的夏季中国区域降水进行了数值模拟。初始值及边界值取自美国国家环境预测中心(NCEP)和国家大气中心(NCAR)的全球再分析资料。每年的模拟积分时段从5月1日开始到9月1日结束, 但是每年降水量的分析只使用6?8月的模拟结果。主要结论如下: (1) 从全国平均总降水量看,该区域模式的模拟结果与观测比较接近,明显好于NCEP的降水资料,但模拟的降水量空间分布不理想; (2) 从降水量距平的空间分布来看,该区域模式对我国的东北夏季降水的模拟结果明显好于全国其他地区,黄河中下游最差; (3) 从时间分布上看,该模式模拟能力呈现出明显的年代际变化,20世纪60年代及90年代模拟较好,也比较稳定,70年代及80年代的模拟能力呈大起大落不稳定状态; (4) 模式未能模拟出70—80年代我国降水偏少的观测事实,说明模式对我国夏季降水年代际变率的模拟能力不足。     

土壤湿度对中国西北地区夏季气候年际变率模拟效果的影响

利用耦合陆面过程模式CLM3的全球大气环流模式NCAR CAM3进行2组1979～2000年5～8月的集合试验,研究了表层土壤湿度对中国西北地区夏季气候年际变率模拟的影响。结果表明:在相同海温强迫条件下,采用年际变化的表层土壤湿度(ISSM)时,CAM3模式对于夏季西北地区气温和降水年际变率的模拟能力明显好于采用气候态的表层土壤湿度(CSSM)。计算表明,1979～2000年CSSM试验和ISSM试验模拟的西北地区夏季气温距平与ERA40资料的相关系数分别为0.60和0.65; CSSM试验模拟的西北地区夏季降水距平与CMAP资料的相关系数仅为0.29,而ISSM试验模拟结果与CMAP资料的相关系数为0.48。在相同海温强迫条件下,ISSM试验比CSSM试验能更好地模拟出中国西北地区夏季降水年际变率。     

bin和bulk微物理方案在我国飑线模拟中的敏感性研究

分别利用weather research and forecasting(WRF)中尺度模式中的bulk和bin微物理参数化方案,对2014年7月12日发生在华东地区的一次飑线过程进行了数值模拟。结果表明:bulk方案基本模拟出了飑线初生、发展、成熟和消亡的生命史,但与实况存在1~2 h的延迟,且强度偏弱;而bin方案模拟的雷达回波结构松散,组织化程度较低,更类似于现状对流。从模拟的地面降水看,bin方案模拟的雨带偏窄,且强降水区偏北;而bulk方案则基本模拟出了强降水区的位置。在此基础上进一步分析了两种方案模拟的各水凝物的垂直分布,结果表明bulk方案在高层产生了大量云冰,而bin方案中雪和霰粒子数量较多。     

LAPS同化MTSAT-2水汽资料在一次中尺度大暴雨模拟中的应用

中尺度分析系统LAPS(local analysis and prediction system)在国内已业务化多年,可以融合多种国内观测资料;但是针对卫星资料的融合应用研究还不够充分。为此,实现了LAPS融合MTSAT-2卫星资料的接口;并结合WRF模式,选取2014年7月24~25日发生在江苏及附近地区的一次强降水过程进行模拟。通过对比LAPS系统融合MTSAT-2卫星资料前后的物理量场的差异,以及经WRF模式预报的降水量差异,分析基于LAPS系统同化MTSAT-2资料对暴雨预报的作用。结果表明,LAPS融合MTSAT-2卫星资料后对地面相对湿度场和降水区域分布均有明显改善作用。利用多种评分方法对24 h累计降水进行检验,发现同化MTSAT-2资料对大雨及以上量级降水的预报改善作用明显,特别是对大暴雨级别的降水预报效果改善最为显著。     

MCloudSim： modeling and simulating distributed clouds

Many distributed clouds which try to integrate the advantages of centralized clouds and distributed systems have been studied in recent years. Traditional cloud simulators focus on large scale data centers with virtualized servers, and cannot meet the needs of distributed cloud simulations. This paper introduces a generalized and extensible simulation framework, named MCloudSim, which is used for modeling and simulating distributed clouds. MCloudSim has the following characteristics： （ 1 ） the overlay protocol in MCloudSim can be freely replaced without affecting the function of other modules; （2） a Petri net workflow theory based task model is proposed to simulate distributed tasks; （3） a distributed cloud can be easily built by assembling and expanding the basic resource entities provided by MCloudSim. Finally, simulation results of scenarios with a 3-tier central-controlled distributed cloud and a P2P based cloud prove that MCloudSim has high efficiency and satisfies performance in supporting large scale experiments and different distributed clouds.     

层状云人工催化物理效应的数值模拟

对于自然云催化过程的数值模拟可以再现人工催化后云的宏微观物理响应特征,有助于提高对人工催化机理的科学认识、优化人工催化方案。本文在WRF（Weather Research and Forecasting Model）模式Thompson微物理方案中加入碘化银人工催化过程,对2018年河北省一次层状云催化过程开展数值研究。数值模拟结果表明,采用与实际催化过程相似的催化剂量,层状云降水个例催化后冰晶含水量、数浓度及地面降水显著增加。该次降水个例自然云中冰相粒子较少,自然云中冰相过程不活跃,数值模拟结果再现了降水个例催化后从过冷却到冰、雪晶含量明显增加的转变。相同催化剂量下,催化层厚度的减少提高了播撒率,进一步优化了催化效果,可见,应该在云中过冷水含量丰富的云区开展冷云催化作业。人工催化过程增加的冰晶通过凝华过程增长并自动转化为雪晶,雪晶增长下落过程中以凇附过冷云水增长为主。本次催化过程导致地面降雪显著增加。     

基于纹理特征的地基云分类识别研究

云是一种重要的天气现象,云观测对当时天气系统的观测具有很强的指导意义,同时云的变化趋势也是预测未来天气的一项重要指标?目前对遥感卫星云图的研究取得了较丰富的成果,但地基云图分类识别研究取得的成果则比较有限,地基云图的研究一直是模式识别中的难点?采用标准气象站地基云图数据,选取了浓积云?积雨云?雨层云等5类常见的云类,并将Gabor小波变换应用于地基云图的纹理特征数据提取,运用实验法选取了Gabor小波变换的最优参数?将地基云图纹理特征数据运用到最短距离和包含BP神经网络的陀螺分类器构造成的地基云图分类系统,从而实现了对地基云图的分类?实验结果表明,该方案不仅能够有效地运用于地基云图分类,而且分类效果也是比较理想的?     

一次层状云人工增雨过程的数值模拟研究

模拟分析了河南南阳一次层状云人工增雨过程的自然云和催化云的微物理过程.结果表明自然云内冰晶含量很少,冰相过程不活跃,消耗水汽较少,大滴形成较为困难,降水效率低,降水强度出现过2次峰值.通过对自然云的模拟分析可以得出合适的催化部位,一般在过冷水含量较大,温度较低,云稳定维持阶段(模拟第52分)开始播撒,催化位置为(18 ...     

高速碰撞下二次破片光滑粒子流体力学法数值模拟

采用AUTODYN-2D无网格光滑粒子流体力学方法(SPH)数值技术,对遭遇速度为1.5～2.5 km/s下圆柱钨弹丸垂直碰撞装甲靶板产生的二次破片云分布特征进行了数值模拟,获得了不同碰撞速度下靶板穿孔直径及破片云前端运动速度、侧向膨胀速度和最大飞散角等分布特征.在此基础上,建立了二次破片云质量及空间分布预测模型.结果表明,数值模拟和模型预测均与实验结果相吻合.     

青藏高原上空对流云特征的初步分析

利用常规地面观测资料、高空资料以及卫星云图资料,通过2010年7月与2011年7月的云图对青藏高原及周边地区对流云和中尺度对流系统的活动进行初步研究,分析了青藏高原上空对流云的特征.结果表明:①青藏高原上的对流过程是在特定的环流背景下受西风带500 hPa低槽、700 hPa切变线、850 hPa低涡以及地面图上中尺度低涡和地面静止锋的共同影响造成的;②对流云产生不仅与水汽条件有关,还与不稳定层结条件和抬升力条件即触发机制有关;③对流云的发生发展具有明显的日变化.