Aerosol-Cloud-Precipitation Interactions in WRF Model: Sensitivity to Autoconversion Parameterization

Cloud-to-rain autoconversion process is an important player in aerosol loading, cloud morphology, and precipitation variations because it can modulate cloud microphysical characteristics depending on the participation of aerosols, and affects the spatio-temporal distribution and total amount of precipitation. By applying the Kessler, the Khairoutdinov-Kogan(KK), and the Dispersion autoconversion parameterization schemes in a set of sensitivity experiments, the indirect effects of aerosols on clouds and precipitation are investigated for a deep convective cloud system in Beijing under various aerosol concentration backgrounds from 50 to 10000 cm-3. Numerical experiments show that aerosol-induced precipitation change is strongly dependent on autoconversion parameterization schemes. For the Kessler scheme, the average cumulative precipitation is enhanced slightly with increasing aerosols, whereas surface precipitation is reduced significantly with increasing aerosols for the KK scheme. Moreover, precipitation varies non-monotonically for the Dispersion scheme, increasing with aerosols at lower concentrations and decreasing at higher concentrations.These different trends of aerosol-induced precipitation change are mainly ascribed to differences in rain water content under these three autoconversion parameterization schemes. Therefore, this study suggests that accurate parameterization of cloud microphysical processes, particularly the cloud-to-rain autoconversion process, is needed for improving the scientific understanding of aerosol-cloud-precipitation interactions.     

东亚旱区气溶胶、云及其相互作用研究进展

东亚干旱半干旱区(简称为“东亚旱区”)是全球干旱带的重要组成部分,该区域水资源短缺,沙尘暴频发,沙尘气溶胶对大气辐射收支和云微物理过程的影响不可忽视。本文回顾了近年来东亚旱区气溶胶及云相关科学问题的研究进展,重点讨论了气溶胶、云特性以及气溶胶-云相互作用问题。东亚旱区大气中的气溶胶以沙尘为主,且春季多于其他季节;同时,该区域云水资源丰富,且以高云为主,夏季云量显著偏多。沙尘气溶胶可直接影响辐射收支对大气产生加热作用,并通过间接和半直接效应对云微物理过程和降水产生影响。由于云微物理观测资料稀缺,加之模式参数化方案的不准确,导致东亚旱区沙尘气溶胶-云相互作用仍存在较大的不确定,减小气溶胶、云所带来的不确定性是未来气候变化研究中亟需解决的科学问题。     

海洋层积云中的云滴谱宽度及其影响因子

云滴谱宽度对模式中云的光学厚度的参数化、气溶胶间接效应的评估以及降水形成过程的研究至关重要。本文利用美国POST（Physics of Stratocumulus Top）项目2008年7月19日的飞机观测资料，分析了微物理量和云滴谱的垂直分布及微物理过程。结果表明，该云系云滴谱宽度在云底附近较大，这是由低层核化过程导致的；中层凝结增长过程使得云滴谱宽度随高度增加逐渐减小；云顶附近夹卷混合过程导致云滴谱宽度增大。绝热云中垂直速度的增大会促进云凝结核的活化使云滴数浓度增大，促进凝结增长使云滴尺度增大、云滴谱宽度减小，云滴谱宽度与云滴数浓度、云滴尺度呈现负相关关系；云洞中受夹卷混合过程影响，垂直速度减小，云滴蒸发，云滴数浓度和云滴尺度减小、云滴谱宽度增大，且该效应随绝热程度减小而增强。建议云滴谱宽度的参数化将垂直速度、云滴数浓度、云滴尺度和绝热程度等考虑在内。     

气溶胶对云宏微观特性和降水影响的研究进展

气溶胶—云—降水相互作用是当今大气科学研究的热点和前沿问题.概述性地回顾了气溶胶对云宏微观特性和降水影响的研究进展,分别讨论了气溶胶对层状云、对流云等典型云系的动力和微物理过程的影响,总结了国内外研究关于气溶胶对云宏微观特性影响的可能的物理解释.回顾外场观测及数值研究表明,气溶胶对云液态水含量、地面降水及光学厚度的影响...     

华北中部夏季气溶胶和云分布特征

气溶胶与云的垂直分布特征是气溶胶间接气候效应关注的重点。基于2018年7—8月华北中部6架次飞机观测数据,研究气溶胶和云滴的垂直和水平分布特征。结果表明:华北中部780~5687 m高度内气溶胶数浓度( Na )平均值为821.36 cm-3,最大量级可达到104 cm-3,云中气溶胶数浓度(Nacc)占总颗粒浓度的80%以上,表明细颗粒占大多数,气溶胶粒子算术平均直径( Dm )平均值为0.12~0.52 μm;大气层结对气溶胶垂直分布影响较大,逆温阻挡气溶胶垂直输送,高空(高度2000 m以上) Dm 的垂直分布受到相对湿度影响较大; Na 和 Dm 在垂直方向波动较大,水平方向波动较小;低层云中云滴数浓度(Nc)较大、液态水含量(L)较小,而中层和高层云中Nc较小、L较大,Nc和云滴有效半径(Re)的概率密度函数均为双峰型分布,L的概率密度函数为单峰型分布;气溶胶数浓度谱基本呈现多峰型分布,而云滴数浓度谱多呈现单峰型分布。     

中国北方沙尘气溶胶对云和降水影响的数值模拟研究

已有的研究表明中国北方千旱半干旱地区是对流层沙尘气溶胶的主要来源之一,对当地乃至全球气候都有重要的意义.利用数值模拟研究方法探讨不同干燥程度的大气背景环境下,沙尘气溶胶数浓度对混合云形成和发展的可能影响,并采用析因试验讨论了主次影响因素.结果表明:沙尘气溶胶的增加导致降水减少、延长了云在空中存在的时间,改变了云的空间结构和微观结构.析因分析表明干旱半干旱气候背景条件下,混合云的累计降水量对沙尘气溶胶数浓度变化的敏感性要高于对大气环境湿度的敏感性;沙尘气溶胶数浓度增加导致云累计降水量的减少;沙尘气溶胶数浓度和大气环境湿度对云的累计降水量的影响是复杂的,研究结果可以用于指导降水预报业务.     

晴空云凝结核垂直探测个例分析

利用机载DMT云凝结核计数器观测了2009年10月13日陕西关中西部晴空云凝结核（CCN）的垂直分布。分析结果显示：关中西部晴天地面CCN平均浓度在过饱和度为0.2%时大于10000个/cm3,大雾天气下地面CCN浓度明显高于晴天。CCN浓度随高度增加而递减,1500 m以下为高值区,1000 m、1550 m、4100 m、5500 m高度的CCN平均浓度在过饱和度为0.4%时分别为8827个/cm3、4439个/cm3、456个/cm3、504个/cm3。     

AGCM中云的不均匀性作用的初步研究

利用ISCCP的云不均匀性资料,探讨了云不均匀性在AGCM中的作用,分别考查了不均匀云光学厚度的贡献、单次散射反照率和不对称因子的贡献,以及3个因子的总贡献.研究表明,考虑云不均匀性效应后,AGCM模拟的气候场有着较为明显的变化.由于不均匀云光学厚度对短波辐射场的贡献与不均匀云单次散射反照率和不对称因子这两个因子对短波辐射场的作用基本上是相反的,从而造成同时考虑3个因子作用时,云的不均匀性效应对辐射场的直接作用很小,但可通过云水场的改变来间接影响辐射场.研究清楚地显示了云-辐射相互作用的复杂性,云的全面正确处理对模式模拟能力的提高非常重要.       

北京地区对流层中上部云和气溶胶的激光雷达探测

介绍了近年来研制的一台多波长激光雷达及其探测对流层高云和气溶胶的实验,并依据探测结果重点分析了北京2000年1月至4月对流层上部云和气溶胶在532 nm波长的消光系数分布特征.结果表明:从6 km至11 km的气溶胶光学厚度值在0.0152至0.0284之间变化,均值为0.0192.从6 km至11 km的云光学厚度值在0.014至0.23之间变化.观测到的单层高云的厚度最大为6 km.4月6日,近年来最强的一次沙尘暴袭击北京.4月7日北京地区无可见云,激光雷达探测结果表明,从4 km至10 km高度范围内,存在一层厚度约为6 km的气溶胶粒子层,消光系数峰值处于8 km附近,比晴天无云时的消光系数值约大一个数量级.估计这是一层沙尘气溶胶,系由远距离输送至北京形成的.     

北疆地区云系的讨论

利用1998－2000年3a的GMST5静止气象卫星红外云图资料和北疆地面观测站6h降水资料，对北疆地区出现的275次云系进行分类，探讨了各类云系的生命史，出现频率，给出云型和TBB与北疆地区降水之间的关系。     

不同吸湿性的气溶胶对云和降水影响研究进展

气溶胶、云、降水相互关系是现今大气科学的前沿领域。本文总体概括了气溶胶作为云凝结核和冰核,对云宏微观物理特性及降水的影响原理研究的主要成果。并根据气溶胶自身化学性质的吸湿性,从吸湿性气溶胶和非吸湿性气溶胶两方面,重点探讨了模拟研究中,硫酸盐、海盐、沙尘、黑碳气溶胶对于云和降水的影响,以及各类气溶胶与其它类型气溶胶相比,作用于云降水的不同方式。提出之前研究工作的不足,以期为今后该方向的研究提供一些思路。      

LASG Global AGCM with a Two-moment Cloud Microphysics Scheme:Energy Balance and Cloud Radiative Forcing Characteristics

Cloud dominates influence factors of atmospheric radiation, while aerosol–cloud interactions are of vital importance in its spatiotemporal distribution. In this study, a two-moment(mass and number) cloud microphysics scheme, which significantly improved the treatment of the coupled processes of aerosols and clouds, was incorporated into version 1.1 of the IAP/LASG global Finite-volume Atmospheric Model(FAMIL1.1). For illustrative purposes, the characteristics of the energy balance and cloud radiative forcing(CRF) in an AMIP-type simulation with prescribed aerosols were compared with those in observational/reanalysis data. Even within the constraints of the prescribed aerosol mass, the model simulated global mean energy balance at the top of the atmosphere(TOA) and at the Earth's surface, as well as their seasonal variation, are in good agreement with the observational data. The maximum deviation terms lie in the surface downwelling longwave radiation and surface latent heat flux, which are 3.5 W m-2(1%) and 3 W m-2(3.5%), individually. The spatial correlations of the annual TOA net radiation flux and the net CRF between simulation and observation were around 0.97 and 0.90, respectively. A major weakness is that FAMIL1.1 predicts more liquid water content and less ice water content over most oceans. Detailed comparisons are presented for a number of regions, with a focus on the Asian monsoon region(AMR). The results indicate that FAMIL1.1 well reproduces the summer–winter contrast for both the geographical distribution of the longwave CRF and shortwave CRF over the AMR. Finally, the model bias and possible solutions, as well as further works to develop FAMIL1.1 are discussed.     

Aerosol Microphysical and Radiative Effects on Continental Cloud Ensembles

Aerosol–cloud–radiation interactions represent one of the largest uncertainties in the current climate assessment. Much of the complexity arises from the non-monotonic responses of clouds, precipitation and radiative fluxes to aerosol perturbations under various meteorological conditions. In this study, an aerosol-aware WRF model is used to investigate the microphysical and radiative effects of aerosols in three weather systems during the March 2000 Cloud Intensive Observational Period campaign at the US Southern Great Plains. Three simulated cloud ensembles include a low-pressure deep convective cloud system, a collection of less-precipitating stratus and shallow cumulus, and a cold frontal passage. The WRF simulations are evaluated by several ground-based measurements. The microphysical properties of cloud hydrometeors, such as their mass and number concentrations, generally show monotonic trends as a function of cloud condensation nuclei concentrations.Aerosol radiative effects do not influence the trends of cloud microphysics, except for the stratus and shallow cumulus cases where aerosol semi-direct effects are identified. The precipitation changes by aerosols vary with the cloud types and their evolving stages, with a prominent aerosol invigoration effect and associated enhanced precipitation from the convective sources. The simulated aerosol direct effect suppresses precipitation in all three cases but does not overturn the aerosol indirect effect. Cloud fraction exhibits much smaller sensitivity(typically less than 2%) to aerosol perturbations, and the responses vary with aerosol concentrations and cloud regimes. The surface shortwave radiation shows a monotonic decrease by increasing aerosols, while the magnitude of the decrease depends on the cloud type.     

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。     

北京及周边地区2003年夏秋季气溶胶和云滴分布特征

对2003年夏秋季利用机载PMS在北京及周边地区进行的不同天气状况下6次气溶胶粒子探测资料进行了分析.结果表明,北京及周边地区气溶胶粒子的分布,在不同天气背景时有较大差别.粒子平均浓度的最大值为3.46×102cm-3,最大粒子浓度为5.26×103cm-3,相差一个量级;粒子平均最大直径为1.392μm,最大直径为2.75μm.粒子平均浓度的最小值为25.7cm-3.在有雾的天气条件下,气溶胶粒子浓度在近地层基本随高度的增加而减小,粒子尺度变化较为复杂.在阴雨天气情况下,气溶胶粒子浓度和尺度都有增加的现象.另外,逆温层底存在明显的气溶胶粒子累积.0℃层以下气溶胶粒子呈单峰分布,0℃层以上气溶胶出现双峰结构.小云粒子一直是多峰结构,峰值直径分别在3.5μm、12.5μm、23.5μm处.     

Compensating Errors in Cloud Radiative and Physical Properties over the Southern Ocean in the CMIP6 Climate Models

The Southern Ocean is covered by a large amount of clouds with high cloud albedo. However, as reported by previous climate model intercomparison projects, underestimated cloudiness and overestimated absorption of solar radiation (ASR) over the Southern Ocean lead to substantial biases in climate sensitivity. The present study revisits this long-standing issue and explores the uncertainty sources in the latest CMIP6 models. We employ 10-year satellite observations to evaluate cloud radiative effect (CRE) and cloud physical properties in five CMIP6 models that provide comprehensive output of cloud, radiation, and aerosol. The simulated longwave, shortwave, and net CRE at the top of atmosphere in CMIP6 are comparable with the CERES satellite observations. Total cloud fraction (CF) is also reasonably simulated in CMIP6, but the comparison of liquid cloud fraction (LCF) reveals marked biases in spatial pattern and seasonal variations. The discrepancies between the CMIP6 models and the MODIS satellite observations become even larger in other cloud macro- and micro-physical properties, including liquid water path (LWP), cloud optical depth (COD), and cloud effective radius, as well as aerosol optical depth (AOD). However, the large underestimation of both LWP and cloud effective radius (regional means ~20% and 11%, respectively) results in relatively smaller bias in COD, and the impacts of the biases in COD and LCF also cancel out with each other, leaving CRE and ASR reasonably predicted in CMIP6. An error estimation framework is employed, and the different signs of the sensitivity errors and biases from CF and LWP corroborate the notions that there are compensating errors in the modeled shortwave CRE. Further correlation analyses of the geospatial patterns reveal that CF is the most relevant factor in determining CRE in observations, while the modeled CRE is too sensitive to LWP and COD. The relationships between cloud effective radius, LWP, and COD are also analyzed to explore the possible uncertainty sources in different models. Our study calls for more rigorous calibration of detailed cloud physical properties for future climate model development and climate projection.     

长水机场低云低能见度天气过程714KaDP型云雾雷达释用

714KaDP型云雾雷达具备30km内的低云和雾监测和预警能力,是专门针对影响机场运行的低云低能见度(两低)天气研制的国内首部毫米波脉冲多普勒雷达。昆明长水机场的试验验证表明,通过提供的云雾基本产品和二次产品,实现了机场两低天气生消演变的有效探测,显著提升了对严重影响空管正常运行的两低天气的监测预警能力。雷达探测发现,714KaDP型云雾雷达对机场及周边低云和雾的生消、演变、移动有着非常敏锐的捕捉能力,特别适合具有明显平流特征的低云和雾(锋面雾、低云平流、辐射雾平流等)的监测和预警,本文介绍了雷达特性、安装位置以及对锋面雾、平流低云和辐射平流混合雾过程的雷达产品分析方法,为提前预警、实时跟踪和云消雾散二次放行决策提供支撑提供了参考。     

Cloud and Radiation Processes Simulated by a Coupled Atmosphere-Ocean Model

Using NCC/IAP T63 coupled atmosphere-ocean general circulation model (AOGCM),two 20-yr integra- tions were processed,and their ability to simulate cloud and radiation was analysed in detail.The results show that the model can simulate the basic distribution of cloud cover,and however,obvious differences still exist compared with ISCCP satellite data and ERA reanalysis data.The simulated cloud cover is less in general,especially the abnormal low values in some regions of ocean.By improving the cloud cover scheme, simulated cloud cover in the eastern Pacific and Atlantic,summer hemisphere's oceans from subtropical to mid-latitude is considerably improved.But in the tropical Indian Ocean and West Pacific the cloud cover difference is still evident,mainly due to the deficiency of high cloud simulation in these regions resulting from deep cumulus convection.In terms of the analysis on radiation and cloud radiative forcing,we find that simulation on long wave radiation is better than short wave radiation.The simulation error of short wave radiation is caused mostly by the simulation difference in short wave radiative forcing,sea ice,and snow cover,and also by not involving aerosol's effect.The simulation error of long wave radiation is mainly resulting from deficiency in simulating cloud cover and underlying surface temperature.Corresponding to improvement of cloud cover,the simulated radiation (especially short wave radiation) in eastern oceans, summer hemisphere's oceans from subtropical to mid-latitude is remarkably improved.This also brings obvious improvement to net radiation in these regions.     

华北地区气溶胶垂直分布特征的观测与分析

利用2006 2013年CALIOP激光雷达Level 1B数据的气溶胶衰减后向散射系数、退偏比和色比观测,分析了华北地区大气气溶胶光学特性的垂直分布特征。统计结果显示:2010-2013年,华北地区4-8 km高度范围内衰减后向散射系数均值呈减小的趋势,而0-4 km高度范围内衰减后向散射系数均值呈增长趋势。说明2010年以后近地面层(0-2 km)气溶胶散射作用逐渐增强,高层(4-8 km)气溶胶散射作用逐渐降低,这与近年华北地区霾天气(颗粒物主要聚集在近地层)日趋增加、沙尘天气(沙尘气溶胶层经常存在于4-8 km的范围)有所减少相吻合。20062013年,华北地区冬季0-4 km高度范围内衰减后向散射系数均值最大,近地面层气溶胶散射作用最大,这与该地区冬季取暖燃烧排放增加有关。春、秋两季4-8 km高度范围内衰减后向散射系数均值较大,夏季0-8 km各高度范围内衰减后向散射系数均最小,说明春、秋季节的气溶胶散射贡献主要来自4-8 km的对流层上部大气。春季对流层上部的高后向散射系数与华北地区春季频发的沙尘天气有关,秋季对流层上部的高后向散射系数与华北收获季节的生物质燃烧有关。2008年以后,华北地区2-8 km范围内各高度层的退偏比均值逐年减小,这说明规则的球形气溶胶粒子在近几年有所增加。0-4 km范围的低层大气,2009年后色比均值缓慢增加。而6-8 km范围内的色比均值从2008年后一直都是减小的,说明2008年后对流层上部大气(4-8 km)气溶胶粒子的尺度在减小,这也与近几年沙尘天气减少、霾天数增加的现象是一致的。0-8 km各个高度范围内的退偏比和色比均值春季最大,且退偏比随着高度的增加而增加,再次证明春季华北受沙尘天气影响,不规则的粗粒子气溶胶最多。夏、冬季节近地面层(0-2km)退偏比和色比均值略大于2-4 km高度层的,夏、冬两季近地面主要以人为活动排放的气溶胶为主,冬季除了汽车尾气排放和工业排放外,还有取暖增加的排放。近地面层易受人为活动影响混合一些不规则气溶胶。     

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。