Retrieval of effective cloud field parameters from radiometric data

Theoretical and Applied Climatology - This study presents evaluation of the ability of Rossby Centre Regional Climate Model (RCA4) driven by nine global circulation models (GCMs), to skilfully...     

红外高光谱资料模拟大气廓线反演对云的敏感性

用不同云顶高度和不同有效云量时的星载红外高光谱观测值,模拟大气温湿垂直廓线反演对云参数的敏感性。用特征向量统计反演法按照云顶高度和有效云量分类反演了大气温湿廓线,统计了不同云高（200,300,500,700和850hPa）及云高有50hPa误差时温度、水汽混合比反演的均方根误差随有效云量的变化。结果表明,随着有效云量的增大,云顶以下各高度层上的温度、水汽混合比反演误差都明显增大。云高有50hPa误差较准确已知而言,温度和水汽混合比的反演误差增大,但温度反演对云高误差的敏感性比水汽反演要高。     

基于星载云雷达资料的东亚大陆云垂直结构特征分析

利用近5年(2006年6月—2011年4月)的Cloudsat卫星资料分析了东亚大陆云垂直结构特征。结果表明:(1)降水(文中可降水是根据观测到的可降水粒子信息计算到达地面的降水,并不是指地面观测到的实际降水)云和非降水云的雷达反射率(回波)垂直分布存在一定差异,除降水云反射率通常接地外,降水云主要集中在8 km以下,反射率通常为-20—15dBz,非降水云主要集中在4—12 km,反射率为-28—0 dBz;降水云雷达反射率频数大值中心在2 4 km,对应的雷达反射率为0—10 dBz,而非降水云出现在8—10 km,且对应的雷达反射率为-26—-24 dBz;(2)从雷达反射率廓线来看,降水云中雷达反射率随高度的变化先增强后减弱,而非降水云几乎不变;(3)液态降水云、固态降水云和毛毛雨降水云反射率的垂直分布明显不同;(4)液态降水云自11至7 km雷达反射率迅速增强,表明此高度是粒子快速增长的优势空间;(5)固态降水云中-15℃温度频数分布与雷达反射率频数大值中心有很好的对应关系,表明在-15℃附近的条件下冰相粒子凝华-碰冻是粒子增长的优势过程;(6)云的垂直结构随着季节变更而变化,降水云春季、夏季和秋季的雷达反射率垂直分布变化不明显,而冬季主要在低层;固态降水云的垂直分布频数大值中心从春季至冬季呈"双-单"中心交替变化,且与云中-15℃频数分布变化一致;非降水云雷达反射率垂直分布没有明显的季节变化;(7)深对流云和雨层云是形成降水粒子的主要云型。     

Climate changes in atmospheric radiation parameters from the MSU meteorological observatory data

Variations in radiation fluxes and the factors that define them and their redistribution in the atmosphere are analyzed using the data of long-term ground-based measurements at the Meteorological Observatory of Lomonosov Moscow State University. It is demonstrated that since the middle of the 1990s trends in many atmospheric radiation parameters have changed as compared to the trends observed in the previous years. For some parameters the trends are significant, are kept for a long period of time, and. hence, can be considered as climate changes. The potential effects of these changes on the regional warming are assessed.     

On the vertical distribution of passive species in the atmospheric boundary layer

A similarity theory presented by Sorbjan (1986) is extended by taking into consideration diffusion of passive species (e.g., specific humidity) in the atmospheric boundary layer. Theoretical similarity functions are obtained for the convective and stable-continuous regimes.On leave from Institute of Environmental Engineering, Warsaw Technical University, Poland.     

基于CloudSat/CALIPSO资料的我国北方2个区域云垂直分布差异研究

选用2008年1月—2014年10月的Cloud Sat/CALIPSO卫星资料,对中国北方两个4°×4°区域云垂直结构及其微物理参量进行了对比研究,区域1(114~118°E,37.5~41.5°N)和区域2(110°E~114°E,37.5~41.5°N)纬度相同经度不同。结果表明:1)区域1(E1)和区域2(E2)暖云层、混合云层和冷云层的云出现概率(Cloud Occurrence Probability,COP)差别较大。E1暖云层COP春季最大,E2则在夏、秋季达到较大值;E1混合层COP最大值出现在冬季,E2则出现在春季;2个区域冷云层COP均在春季达到最大。2)2个区域的COP高值区厚度有明显的季节性差异,E1的COP高值主要出现在夏、冬季,E2则主要出现在春、夏季。E1秋、冬季云体雷达回波最大值强于E2,但春、夏季弱于区域1。3)E2在春、秋季的液水含量、冰水含量、云滴有效半径均高于E1。     

An atmospheric dispersion model with continuous vertical variation of dispersion parameters

Summary A dispersion model is proposed to predict the continuous vertical variation of the dispersion parameters _y and _z in case of hot pollutant release to the atmosphere. In such a case, the plume rises far above the ground and is subject to varying levels of turbulence. The framework in this paper can be divided into three approaches: (1) determination of the eddy diffusivitiesK _y (z, _y ) andK _z (z, _z ) as functions of height above ground and plume dimensions, (2) determination of both the plume rise and its vertical velocity using a modified version of Brigg's formula, and (3) numerical solution of actual problems with buoyant plumes at each time step. The model results have been applied to a case of pollutant release from fire destruction of a chemical storehouse roof.With 15 Figures     

A study of vertical cloud structure of the Indian summer monsoon using CloudSat data

Precise specification of the vertical distribution of cloud optical properties is important to reduce the uncertainty in quantifying the radiative impacts of clouds. The new global observations of vertical profiles of clouds from the CloudSat mission provide opportunities to describe cloud structures and to improve parameterization of clouds in the weather and climate prediction models. In this study, four years (2007–2010) of observations of vertical structure of clouds from the CloudSat cloud profiling radar have been used to document the mean vertical structure of clouds associated with the Indian summer monsoon (ISM) and its intra-seasonal variability. Active and break monsoon spells associated with the intra-seasonal variability of ISM have been identified by an objective criterion. For the present analysis, we considered CloudSat derived column integrated cloud liquid and ice water, and vertically profiles of cloud liquid and ice water content. Over the South Asian monsoon region, deep convective clouds with large vertical extent (up to 14 km) and large values of cloud water and ice content are observed over the north Bay of Bengal. Deep clouds with large ice water content are also observed over north Arabian Sea and adjoining northwest India, along the west coast of India and the south equatorial Indian Ocean. The active monsoon spells are characterized by enhanced deep convection over the Bay of Bengal, west coast of India and northeast Arabian Sea and suppressed convection over the equatorial Indian Ocean. Over the Bay of Bengal, cloud liquid water content and ice water content is enhanced by ~90 and ~200 % respectively during the active spells. An interesting feature associated with the active spell is the vertical tilting structure of positive CLWC and CIWC anomalies over the Arabian Sea and the Bay of Bengal, which suggests a pre-conditioning process for the northward propagation of the boreal summer intra-seasonal variability. It is also observed that during the break spells, clouds are not completely suppressed over central India. Instead, clouds with smaller vertical extent (3–5 km) are observed due to the presence of a heat low type of circulation. The present results will be useful for validating the vertical structure of clouds in weather and climate prediction models.     

毫米波雷达与无线电探空对云垂直结构探测的一致性分析

在众多种针对云垂直结构的探测中,毫米波雷达可获取云底、云顶、云厚等完整的云垂直结构信息,并可以连续监测云的垂直剖面变化,是有力的探测手段之一。而无线电探空因其直接的测量优势,能直观、确切地描述大气湿度垂直结构,可将其进一步处理生成云垂直结构信息,并作为一种数据源用于与毫米波雷达云垂直结构探测结果进行比对,以评估毫米波雷达针对云宏观垂直结构的探测性能,为毫米波雷达更好地应用于云探测提供参考。通过获取位于北京南郊观象台的毫米波雷达2014年10月28日至2015年2月17日长达113天连续观测的反射率因子以及探空温、压、湿数据,设计或选取合适的方法对二者进行云边界的计算,并进行云高（包括云底高和云顶高）以及云层数的一致性比对分析。结果认为,除对于高层云的云顶高度毫米波雷达由于探测限制不能探测到10 km以上的云顶,某些时刻与探空产生较大差异外,在云底高度以及中低云的云顶高度上可以与探空观测取得很好的匹配效果,对于云的垂直分层上二者也有较强的一致性。该毫米波雷达具有较为准确并连续刻画10 km以下云垂直结构的能力。     

Sensitivity of retrieved atmospheric profiles from infrared radiances to physical and statistical parameters of the data assimilation system

Abstract

The direct assimilation of satellite radiances is now operational in a few forecast centres, providing global temperature (T) and moisture (Q) information. The critical parameters which influence the quality of the resulting analysis are mainly the selection of channels, the respective errors of the background field and radiance observations, and the quality of the radiative transfer model. These various aspects are studied from sensitivity experiments based on 1‐D variational assimilations using the ensemble of 19 infrared channels (HIRS) of the NOAA‐14 satellite.

It is shown that significant improvements in the retrievals would be obtained if the radiance observation error (measurement plus radiative transfer), currently estimated to be about equal to that of the background (in radiance units), were decreased. This could in principle be achieved by improving the forward radiative transfer model (RTM). Two RTMs suitable for radiance assimilation are compared in terms of analyzed increments, Jacobians, brightness temperature and equivalent background error. Important differences are noted for all of these interrelated measures. The existence of air‐mass dependent biases of fast radiative transfer models of the order of 1.5 K is confirmed in several channels from additional comparison with a line‐by‐line model. The importance of correctly specifying surface emissivity and the effective angle for downward calculations is demonstrated.

The paper also evaluates, in some detail, the impact of uncertainties on the background error covariance matrix. The uncertainty on the skin temperature (TJ error affects mostly the retrieval of that parameter; it has a modest impact on the T and Q profiles in the low troposphere. The uncertainty on the Q‐Q elements has more impact than that on the T‐T elements. Off‐diagonal elements of the background error covariance matrix are very important as they impose smoothness and level‐to‐level consistency, especially for Q retrievals. Finally, T_s‐T correlations, often ignored, could result in significant improvements in the retrieval of temperature at low levels. Research issues are discussed in the conclusion.     

On the vertical extent of atmospheric feedbacks

This study addresses the question: what vertical regions contribute the most to water vapor, surface temperature, lapse rate and cloud fraction feedback strengths in a general circulation model? Multi-level offline radiation perturbation calculations are used to diagnose the feedback contribution from each model level. As a first step, to locate regions of maximum radiative sensitivity to climate changes, the top of atmosphere radiative impact for each feedback is explored for each process by means of idealized parameter perturbations on top of a control (1?×?CO₂) model climate. As a second step, the actual feedbacks themselves are calculated using the changes modelled from a 2?×?CO₂ experiment. The impact of clouds on water vapor and lapse rate feedbacks is also isolated using `clear sky' calculations. Considering the idealized changes, it is found that the radiative sensitivity to water vapor changes is a maximum in the tropical lower troposphere. The sensitivity to temperature changes has both upper and lower tropospheric maxima. The sensitivity to idealized cloud changes is positive (warming) for upper level cloud increases but negative (cooling) for lower level increases, due to competing long and shortwave effects. Considering the actual feedbacks, it is found that water vapor feedback is a maximum in the tropical upper troposphere, due to the large relative increases in specific humidity which occur there. The actual lapse rate feedback changes sign with latitude and is a maximum (negative) again in the tropical upper troposphere. Cloud feedbacks reflect the general decrease in low- to mid-level low-latitude cloud, with an increase in the very highest cloud. This produces a net positive (negative) shortwave (longwave) cloud feedback. The role of clouds in the strength of the water vapor and lapse rate feedbacks is also discussed.     

A method of cloud detection from satellite data

The main results of the development and testing of the cloud detection method are presented. The main purpose of the method is the identification and classification of clouds in satellite images with the subsequent retrieval of quantitative characteristics. The method provides digital datasets in the form of maps of cloud classes, cloud top height, and cloud top temperature. The consecutive stages of cloud detection are considered, and the conditions and basic results of the method testing are presented.     

Specifying the atmospheric pollutant distribution forecast using the mathematical modeling and measurement data

Considered is a possibility of specifying the forecast of volcanic aerosol distribution in the atmosphere using the data of ground-based actinometric measurements. To simulate the aerosol distribution, the FlexPart software (Norwegian Institute for Air Research) was used. Using the FlexGraph software (Planeta Research Center for Space Hydrometeorology), the visualization and interactive analysis were carried out of aerosol concentration fields at different time moments. The prognostic concentration of volcanic ash from Grímsvötn volcano (May 2011) is bound to the results of measurements of aerosol optical depth in Hamburg at one of the points of AERONET global network. The comparison of the corrected aerosol concentration with the measurements at other AERONET points demonstrated the competence of the proposed approach. To specify the aerosol cloud distribution forecast on the territory of Russia, the Roshydromet actinometric network data can be used.     

关于中性层结大气边界层湍流参量铅直分布的计算分析

根据大气边界层平均风速廓线实测资料,参照Lettau方法计算了湍流参数——动量交换系数k_m,摩擦速度u_*,湍流切应x和混合长l随高度的分布.并与国外研究结果进行比较,基本规律一致,某些参数有所修正.     

The impact of the PBL scheme and the vertical distribution of model layers on simulations of Alpine foehn

Summary This paper investigates the influence of the planetary boundary-layer (PBL) parameterization and the vertical distribution of model layers on simulations of an Alpine foehn case that was observed during the Mesoscale Alpine Programme (MAP) in autumn 1999. The study is based on the PSU/NCAR MM5 modelling system and combines five different PBL schemes with three model layer settings, which mainly differ in the height above ground of the lowest model level (z ₁). Specifically, z ₁ takes values of about 7 m, 22 m and 36 m, and the experiments with z ₁ = 7 m are set up such that the second model level is located at z = 36 m. To assess if the different model setups have a systematic impact on the model performance, the simulation results are compared against wind lidar, radiosonde and surface measurements gathered along the Austrian Wipp Valley. Moreover, the dependence of the simulated wind and temperature fields at a given height (36 m above ground) on z ₁ is examined for several different regions. Our validation results show that at least over the Wipp Valley, the dependence of the model skill on z ₁ tends to be larger and more systematic than the impact of the PBL scheme. The agreement of the simulated wind field with observations tends to benefit from moving the lowest model layer closer to the ground, which appears to be related to the dependence of lee-side flow separation on z ₁. However, the simulated 2 m-temperatures are closest to observations for the intermediate z ₁ of 22 m. This is mainly related to the fact that the simulated low-level temperatures decrease systematically with decreasing z ₁ for all PBL schemes, turning a positive bias at z ₁ = 36 m into a negative bias at z ₁ = 7 m. The systematic z ₁-dependence is also observed for the temperatures at a fixed height of 36 m, indicating a deficiency in the self-consistency of the model results that is not related to a specific PBL formulation. Possible reasons for this deficiency are discussed in the paper. On the other hand, a systematic z ₁-dependence of the 36-m wind speed is encountered only for one out of the five PBL schemes. This turns out to be related to an unrealistic profile of the vertical mixing coefficient. Correspondence: Günther Z?ngl, Meteorologisches Institut der Universitat München, 80333 München, Germany     

Evaluation of cloud vertical structure simulated by recent BCC_AGCM versions through comparison with CALIPSO-GOCCP data

ABSTRACT The abilities of BCC-AGCM2.1 and BCC_AGCM2.2 to simulate the annual-mean cloud vertical structure （CVS） were evaluated through comparison with GCM-Oriented CALIPSO Cloud Product （CALIPSO-GOCCP） data. BCC-AGCM2.2 has a dynamical core and physical processes that are consistent with BCC-AGCM2.1, but has a higher horizontal resolution. Results showed that both BCC-AGCM versions underestimated the global-mean total cloud cover （TCC）, middle cloud cover （MCC） and low cloud cover （LCC）, and that BCC_AGCM2.2 underestimated the global-mean high cloud cover （HCC）. The global-mean cloud cover shows a systematic decrease from BCCA-GCM2.1 to BCC_AGCM2.2, especially for HCC. Geographically, HCC is significantly overestimated in the tropics, particularly by BCC_AGCM2,1, while LCC is generally overestimated over extra-tropical lands, but significantly underestimated over most of the oceans, especially for subtropical marine stratocumulus clouds. The leading EOF modes of CVS were extracted. The BCC_AGCMs perform well in reproducing EOF1, but with a larger variance explained. The two models also capture the basic features of EOF3, except an obvious deficiency in eigen- vector peaks. EOF2 has the largest simulation biases in both position and strength of eigenvector peaks. Furthermore, we investigated the effects of CVS on relative shortwave and longwave cloud radiative forcing （RSCRF and RLCRF）. Both BCC_AGCM versions successfully reproduce the sign of regression coefficients, except for RLCRF in PC1. However, the RSCRF relative contributions from PC1 and PC2 are overestimated, while the relative contribution from PC3 is underes timated in both BCC_AGCM versions. The RLCRF relative contribution is underestimated for PC2 and overestimated for PC3.     

边界层大气水平风速低频谱的垂直分布特征

本文根据320米气象塔上水平风速的观测资料,分析了不同天气条件下边界层大气中湍流的宽谱特性及其垂直分布结构. 结果表明,大气边界层水平风速低频谱的垂直分布是很复杂的,在不同的天气条件下,这种垂直分布特征具有明显的差异.边界层温度和风速的垂直结构也会影响到水平风速低频谱的垂直分布. 在水平风速低频谱中,除了与天气过程有关的4天周期峰值和反映气象要素日变化频率的峰值外,在十几分钟到几十分钟频率范围内还存在着几个峰值,而且有时在不同的高度上,峰值频率有所不同.这可能反映了一些中尺度系统的特征,也可能是这些中尺度系统与局地地形的综合作用所引起的.     

Effects of atmospheric boundary layer mixing representations on vertical distribution of passive and reactive tracers

Summary A one-dimensional chemistry-boundary layer model was used to study the effects of differing representations of atmospheric boundary layer (ABL) processes on simulated concentrations of passive and chemically reactive tracers. Two local- and two nonlocal-closure ABL schemes were used to perform numerical simulations during convective conditions in the ABL. Observational data from the First International Statellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE) were used to provide initial meteorological conditions while representative chemical concentrations and surface and elevated emission rates were used to provide initial chemical conditions and chemical sources to the one-dimensional model. Two sets of numerical simulations were performed using the four ABL schemes. The first set simulated bottom-to-top mixing characteristics, and the second set simulated top-to-bottom mixing characteristics. Model simulations were performed for 12h starting from 0700LT 11 July 1987.Our analysis indicate that the simulated concentrations of both passive and reactive chemical species were sensitive to the type of ABL scheme used to represent turbulent mixing processes. Characteristic features associated with each scheme (e.g., growth and intensity of mixing in the ABL) contributed to the differences among the simulated species concentrations. For some of the chemical species these differences were large, particularly in the surface layer and in the interfacial layers of the ABL. In turn, differences caused by the differing mixing representations resulted in different chemical production/destruction rates. As a consequence, the simulated species concentrations differed among the simulations. We also found that chemical species concentrations were more sensitive to the type of ABL scheme in the bottom-to-top mixing simulations than in the top-to-bottom simulations.With 10 Figures