Formation of cloud microstructure during hygroscopic seeding

The evolution of cloud microstructure initiated by hygroscopic seeding is studied on the basis of numerical simulation of cloud formation in the initial stage of condensation. The influence of both physicochemical properties of atmospheric aerosol and atmospheric conditions controlling the cloud type on the microstructure of a developing cloud (without hygroscopic seeding) is analyzed. It is shown that cloud seeding with additional particles whose sizes exceed the characteristic size of atmospheric condensation nuclei leads to a decrease in the concentration of cloud droplets and an increase in their sizes. This result of cloud seeding represents a positive effect for stimulation of precipitation from convective clouds. It is shown that this positive effect is achieved if there are some relationships between the parameters characterizing the hygroscopic particles and the atmospheric conditions. In particular, the maximum effect of action can be achieved at some optimal concentration of seeded particles. The decrease in the concentration of cloud droplets because of hygroscopic seeding is compared to the results of numerical simulations performed by other authors with allowance for coagulation processes in clouds. It is shown that this decrease can serve as an estimate for the effectiveness of hygroscopic seeding as a means for artificial intensification of precipitation from convective clouds.     

Experimental investigations of the effect of cloud-medium modification by salt powders

The results of experimental investigations into the action of polydispersion salt powders on model cloud media are presented. The results of experiments show a considerable positive effect of the modification of convective clouds by salt powders in order to obtain additional precipitation. The introduction of polydispersion salt powder into a forming cloud medium leads to the appearance of large cloud droplets and to the droplet-spectrum broadening. This result is a positive factor for the stimulation of coagulation processes and further precipitation formation. No “overseeding” phenomenon (when, instead of the enlargement of droplets, their sizes decrease and the concentration of cloud droplets increases) is observed at rather high mass concentrations of the introduced powder.     

Numerical simulation of the action on a warm convective cloud by hygroscopic particles

A one-dimensional numerical model of a warm convective cloud is presented. This model is used to study the effectiveness of the action on the cloud by hygroscopic particles with the aim of intensifying precipitation. The numerical simulation takes into account the processes of condensation, coagulation, and sedimentation of cloud droplets and makes it possible to obtain spatiotemporal characteristics of cloud development. A system of differential equations describing time variations in the temperature, pressure, and watervapor supersaturation during the adiabatic rise of a continuous air flow is solved. The evolution of the size distribution of cloud droplets is described by a kinetic equation. A continuous acting source of droplets with the size distribution calculated with consideration for condensation properties and dispersion characteristics of condensation nuclei (natural and additionally introduced during the action) is specified at the cloud-base level. The cloud top is formed owing to the evaporation of droplets in the barrier atmospheric layer over the cloud. The influence of changes in the barrier-layer height on the structure of cloud parameters and precipitation-formation processes is analyzed. The introduction of additional hygroscopic particles into a cloud is shown to act as a trigger mechanism initiating the processes of coagulation and sedimentation in the cloud medium. In this case, a positive effect of action by fine particles can be achieved if a certain reserve of sufficiently large droplets is present in the cloud. The results of calculating the dependence of the action effect on the height of the barrier layer, restricting cloud development, are presented.     

Study of the possibility of stimulating precipitation from warm convective clouds by hygroscopic particles from numerical simulation

We present the results of numerical simulation of the action of hygroscopic particles on a convective cloud for obtaining additional precipitation. The correspondence of vertical profiles of cloud parameters to those actually observed under natural atmospheric conditions is achieved within a one-dimensional numerical model by parametrization of the process of heat and moisture entrainment into the upward air flow forming the cloud. The model describes in detail microphysical processes in a cloud with the use of the kinetic equation for the size distribution of cloud droplets. The processes of forming precipitation in convective clouds with a vertical thickness of 3–4 km during their natural development and during the introduction of hygroscopic particles are analyzed using numerical calculations. It is shown that it is actually possible to obtain additional precipitation from convective clouds of continental type under the action of hygroscopic particles with sizes of 1–1.5 μm. The results of calculating the intensity and total amount of precipitation as functions of the vertical thickness of a cloud and the parameters of particles introduced into it are presented. The conditions necessary for obtaining the maximum positive effect are elucidated.     

Variation of sulfate aerosol concentrations over the western Pacific and their effect on clouds, radiation and precipitation

Under bilateral cooperation between the United States of America and the People's Republic of China, a series of research cruises were conducted over the western Pacific Ocean. It was found that a) the non-sea-salt sulfate aerosol particles are the major source of cloud condensation nuclei, b) the population of clouds and the total albedo are proportional to the concentration of condensation nuclei and consequently to the concentration of the non-sea-salt aerosol particles, and c) the amount of rainfall is inversely proportional to the concentration of non-sea-salt sulfate aerosol particles. It seems that anthropogenic sulfate aerosol particles affect the regional planetary albedo and climate and that the contribution from biogenically derived sulfate aerosol particles is of lesser importance.     

Investigation of the action of hygroscopic particles on a warm convective cloud from the results of numerical simulation

The results of a numerical simulation of the action of hygroscopic particles on a warm convective cloud with the purpose of obtaining additional precipitation are presented. The one-dimensional numerical model considered in this work describes the evolution of the cloud medium in the central part of an axisymmetric convective cloud at the specified height-variable velocity of the upward air flow which forms the cloud. Our model comprehensively describes microphysical processes in the cloud medium with the use of the kinetic equation for the size distribution of cloud droplets. This model makes it possible to obtain the spatiotemporal pattern of the cloud formation and development and to analyze regular features in the cloud evolution under the action of hygroscopic reagents. The cloud characteristics calculated with the use of this model correspond to the cloud parameters observed in natural conditions of the atmosphere. The process of precipitation stimulation by hygroscopic particles in convective clouds with vertical thicknesses of 2.5–4.5 km was analyzed on the basis of the results of numerical calculations. The results of calculations of the dependence of the intensity and total amount of precipitation on the vertical cloud thickness and parameters of particles introduced into the cloud are presented. It is shown that hygroscopic particles with root-mean-cube radii of 1–1.5 μm are the most effective for acting on warm convective clouds with the purpose of obtaining additional precipitation. In this case, the required reagent expenditure is 100–200 kg/km². The conditions necessary for obtaining the maximal positive effect of the action are elucidated.     

Parameterization of key optical and radiative characteristics of homogeneous layers of mixed phase clouds

Key optical characteristics of radiation scattering in clouds (mean cosine of the scattering phase function, averaged factors and indices of scattering efficiency, and single-scattering albedo) and integral characteristics of homogeneous cloud layers (cloud-layer albedo and transmission factor) have been calculated with the use of the earlier suggested model of the microstructure of mixed phase clouds, where ice crystals and water droplets are homogeneously mixed over the volume, for individual wavelengths in the range from 0.6 to 10.6 μm. An approach is elaborated for statistically valid parameterization of the above characteristics versus the mean temperature of a mixed layer only under the availability of reliable information about the temperature dependence of the characteristic sizes of particles of different fractions and their concentrations in the cloud.     

Electrization of aerosol wetted in bipolarly ionized air

We studied the influence of the characteristics of the atmospheric ionization and physical-chemical state of condensation nuclei on the electric state of convective cells. Based on the results of experiments in an adiabatic chamber with a volume of 3200 m³, we found that, with increase in relative air humidity H from 40 to 95% with an equivalent ascent rate of 100–400 cm/s, excessive charges in amounts of about 10³ or more elementary charges per cm3 may be accumulated on the nuclei. The sign of the charge depends on the chemical composition of the hygroscopic nuclei. For instance, media with insoluble nuclei (porous silica, etc.) typically have prevailing negative charges; those with soluble nuclei (sodium chloride, etc.) are dominated by positive charges. At H = 60−90%, the electrization of soluble nuclei can be interpreted in the diffusion-kinetic models of the ion charging of aerosols. Considerable negative volume charges, which appear on insoluble hygroscopic nuclei during a rise in humidity from 40 to 70%, are explained by the structuring of surface water films, which exhibit a resemblance to negative lightweight ions. At high values (H > 90%), it is necessary to take into account the resemblance of the wetted surfaces to positive lightweight ions. We showed for the first time that, at ion formation rates of 3 and 1010 ion pairs/(cm³ s), the differences in the volume charge and wetting rate of condensation nuclei are insignificant. It is concluded that, in many meteorological situations, the first stage of electrization of the convection-derived cloud media is the ion charging of the condensation nuclei.     

Internal mechanism of metastable liquid water crystallization and its effects on intracloud processes

Specific features of an internal freezing (crystallization) mechanism for both ordinary supercooled water and amorphous water (A-water) are considered. Amorphous water plays the role of an intermediate phase in condensation ice formation and is capable of metastable existence in the form of cloud drops. It is demonstrated that, after passing the crystallization front, the ice phase takes the liquid-phase volume and the excessive water mass is detached from the front in the form of free molecules, which escape through the liquid into the gaseous medium. The released energy of the phase transition is removed with these molecules, so that the formed ice retains the initial temperature of the liquid. A high-rate vapor outflow from the freezing drop generates (around the drop) a zone of microscale turbulence, which accelerates the mass exchange between cloud particle and vapor. Since the freezing frequency of drops in a cloud increases with their size, the effects of their freezing develop initially in time. At the same time, these effects initiate such processes that end in a complete evaporation of supercooled water drops and in a sharp enlargement of A-water and ice particles, i.e., in cloud transition to such a phase-mixed state where the liquid disperse phase consists of A-water drops. A reduction in the duration of the initial (fine-dispersed) stage of the evolution of clouds with their temperature lowering can be explained only by the development of microscale disturbances as a result of the freezing of drops.     

台风“莫拉菲”潜热的数值模拟研究

WRF天气研究和预报模式是新一代中尺度数值预报模式,本文采用最细2公里的网格距对台风“莫拉菲”内核的宏观、微观以及潜热过程进行数值模拟。通过对台风路径、风速大小、降水形态以及内核热力和动力结构的验证,证实了单向六参数WSM6方案的合理性。本文通过计算台风过程中的潜热加热率,揭示了总潜热主要来源于0℃层以下的凝结潜热和0℃层以上的凝华潜热。证实了与霰有关的云微物理过程是对总潜热贡献最重要的因子。除此之外,在本次台风“莫拉菲”的模拟中,其他重要的潜热贡献因子分别是水汽凝结成云水、云冰的凝华增长、雪的凝华增长、云冰的初始化、霰的凝华增长、云水被雪和霰收集、云水和雨水的蒸发、雪的升华、霰的升华、霰的融化以及云冰的升华。总体而言,本文模拟的潜热加热率廓线和TRMM卫星的廓线基本一致,尽管具体数值略有不同。     

Experiment Study of the Evolution of Coral Sand Particle Clouds in Water

The motion of particle clouds (i.e., sediment clouds) usually can be found in engineering applications such as wastewater discharge, land reclamation, and marine bed capping. In this paper, a series of laboratory tests are conducted on coral sand to investigate the shape feature of the single particle and the mixing processes of the coral sand particle clouds. The shape of coral sand particle is measured and quantified. The experimental results demonstrate that the shape of coral sand particles tends to be spherical as the particle size decreases, and empirical equations were established to explain the variation of D₅₀ and f_S,50 of coral sand. Compared with the silica sand, the evolution of the coral sand particle cloud still experiences three stages, but the threshold for the Reynolds number of particle clouds entering the next stage changes. Further, the normalized axial distance of the coral sand particle clouds is 58% smaller. The frontal velocity exhibits similar varying tendency for the coral sand particle cloud. Considering the difference in shape between coral sand particles and silica sand particles, a semi-empirical formula was proposed based on the original silica sand prediction formula by adding the shape factor and the experimental data of 122 µm⩽D₅₀⩽842 µm. It can predict the frontal velocity of the coral sand particle clouds.

     

Absorption of infrasonic waves in a cloudy medium

We study the absorption of infrasonic waves when they are propagating in cloud media. In this case, the main mechanism of absorption is the relaxation processes associated with vapor-drop phase transitions caused by infrasonic waves. For frequencies comparable to the inverse relaxation time, the acoustic waves in a cloud medium were shown to have a noticeable dispersion. We derive an expression for the frequency-dependent effective adiabatic index linking the oscillations of pressure and density in the wave, the dispersion equation, and the expression for the absorption coefficient. For typical values of cloud parameters, the absorption coefficient was estimated to be around 0.1 km^?1. We discuss observation data which indirectly confirm that clouds can considerably absorb infrasonic waves.     

A review of satellite-based microwave observations of sea surface temperatures

Satellite-based microwave radiometers can measure sea surface temperature (SST) over wide areas, even under cloud cover, owing to the weak absorption of microwaves by cloud droplets. This advantage is not available in the case of infrared observations, hence SST data derived from microwave radiometers have been widely used for operational and research purposes in recent years. This paper reviews the significant algorithms, validations, and applications related to microwave observation of SST. The history and specifications of past and present microwave radiometers are also documented. Various physical properties, including sea surface salinity, sea surface wind, molecules in the atmosphere, and clouds, affect the accuracy of SST data estimated by satellite-based microwave radiometers. Estimation algorithms are designed to correct these effects by using microwave measurements in several frequency channels and by using data of ancillary geophysical parameters. Validation studies have shown that microwave radiometer SST data have high accuracy that is comparable to the accuracy of data obtained from infrared measurements. However, certain persistent problems, such as sea-surface wind correction, remain to be solved.     

Observation of clouds and solar radiation over the Pacific Ocean as relation to global climate

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卫星遥感业务系统海表温度误差控制方法

提高卫星遥感海表温度的反演精度是各种反演模型追求的目标,也是遥感系统业务化应用的关键.据相关文献报道,在晴空无云的条件下遥感海表温度的精度达到了0.5℃,但考虑到影响海表温度反演精度的多种因素,在遥感业务系统真正实现SST精度在1℃以内是非常困难的.在北太平洋渔场速报制作系统中,对遥感海表温度与船测温度误差统计显示均方根误差达到5.71℃,匹配点误差分布显示存在大量较大的负误差值,最大的为-17.2℃,遥感温度图也反映出存在片状温度低值区,这些区域很可能被错误地当作冷涡或冷锋区,严重干扰渔情分析,这些异常的温度误差很难通过海表温度反演模式和云检测技术来消除.采用一种标准海表温度参考图用于温度误差控制技术,可有效地检测温度反演异常值,将均方根值从5.71℃降低到1.75℃,如果采用2℃阈值控制计算均方根值,则海表温度精度达到0.785℃.该方法基本消除了遥感海表温度的低值现象,明显提高了遥感海表温度的精度,并已成功地应用于北太平洋渔区的海况速报产品制作中.     

2001—2017年北极秋季低云变化及其可能原因

本文通过对2001—2017年秋季北极低云的多源数据的分析,展示了本世纪以来北极秋季低云的变化,并为其变化提供了一个新的可能的解释。卫星和再分析数据表明,秋季北极有冰海面低云存在减少的趋势,且在北极边缘海区表现为950 hPa(约500 m)以下近地面云显著减少。本文研究表明,在有冰海面上,低云减少的趋势与背景大气增暖导致的大气相对湿度降低有关,这一关系在80°N以北的北极中央区更明显。而在北极边缘海区,气旋活动对云的影响更重要。在有冰海面,气旋与低云的长期变化趋势相反,两者的年际变化呈负相关关系。利用自组织映射(SOM,Self-Organizing Map)对所有气旋日垂直运动和云分布进行了初步分析,结果表明:在无冰海面和有冰海面由于气旋垂直运动及背景(无气旋日)云分布的差异,气旋对云的影响存在差异。气旋在有冰海面导致低云减少为主,而在无冰海面导致低云增加为主。     

An evaluation of the Arctic clouds and surface radiative fluxes in CMIP6 models

To assess the performances of state-of-the-art global climate models on simulating the Arctic clouds and surface radiation balance, the 2001–2014 Arctic Basin surface radiation budget, clouds, and the cloud radiative effects(CREs) in 22 coupled model intercomparison project 6(CMIP6) models are evaluated against satellite observations. For the results from CMIP6 multi-model mean, cloud fraction(CF) peaks in autumn and is lowest in winter and spring, consistent with that from three satellite observation products(Cloud Sat-CALIPSO, CERESMODIS, and APP-x). Simulated CF also shows consistent spatial patterns with those in observations. However,almost all models overestimate the CF amount throughout the year when compared to CERES-MODIS and APP-x.On average, clouds warm the surface of the Arctic Basin mainly via the longwave(LW) radiation cloud warming effect in winter. Simulated surface energy loss of LW is less than that in CERES-EBAF observation, while the net surface shortwave(SW) flux is underestimated. The biases may result from the stronger cloud LW warming effect and SW cooling effect from the overestimated CF by the models. These two biases compensate each other,yielding similar net surface radiation flux between model output(3.0 W/m~2) and CERES-EBAF observation(6.1 W/m~2). During 2001–2014, significant increasing trend of spring CF is found in the multi-model mean,consistent with previous studies based on surface and satellite observations. Although most of the 22 CMIP6 models show common seasonal cycles of CF and liquid water path/ice water path(LWP/IWP), large inter-model spreads exist in the amounts of CF and LWP/IWP throughout the year, indicating the influences of different cloud parameterization schemes used in different models. Cloud Feedback Model Intercomparison Project(CFMIP)observation simulator package(COSP) is a great tool to accurately assess the performance of climate models on simulating clouds. More intuitive and credible evaluation results can be obtained based on the COSP model output. In the future, with the release of more COSP output of CMIP6 models, it is expected that those inter-model spreads and the model-observation biases can be substantially reduced. Longer term active satellite observations are also necessary to evaluate models' cloud simulations and to further explore the role of clouds in the rapid Arctic climate changes.     

改进的ICP点云配准算法

三维激光点云配准是点云三维建模的关键问题之一。经典的ICP算法对点云初始位置要求较高且配准效率较低,提出了一种改进的ICP点云配准算法。该算法首先利用主成分分析法实现点云的初始配准,获得较好的点云初始位置,然后在经典ICP算法的基础上,采用k-d tree结构实现加速搜索,并利用方向向量夹角阈值去除错误点对,提高算法的效率。实验表明,本算法流程在保证配准精度的前提下,显著提高了配准效率。     

Convective cloud fields in the Atlantic sector of the Arctic: Satellite and ground-based observations

Convective cloudiness in the Atlantic sector of the Arctic is considered as an atmospheric spatially self-organized convective field. Convective cloud development is usually studied as a local process reflecting the convective instability of the turbulent planetary boundary layer over a heated surface. The convective cloudiness has a different dynamical structure in high latitudes. Cloud development follows cold-air outbreaks into the areas with a relatively warm surface. As a result, the physical and morphological characteristics of clouds, such as the type of convective cloud, and their geographical localization are interrelated. It has been shown that marginal sea ice and coastal zones are the most frequently occupied by Cu hum, Cu med convective clouds, which are organized in convective rolls. Simultaneously, the open water marine areas are occupied by Cu cong, Cb, which are organized in convective cells. An intercomparison of cloud statistics using satellite data ISCCP and ground-based observations has revealed an inconsistency in the cloudiness trends in these data sources: convective cloudiness decreases in ISCCP data and increases in the groundbased observation data. In general, according to the stated hypothesis, the retreat of the sea-ice boundary may lead to an increase in the amount of convective clouds.     

基于CALIPSO卫星数据的吕宋海峡云时空特征统计分析

基于2006年6月—2021年10月期间CALIPSO星载激光雷达观测数据,对吕宋海峡低云和深对流等影响飞行的云时空分布特征进行统计学分析。结果表明,在南海季风、太阳辐射和季风槽的共同影响下:(1)低云覆盖率在8月左右最小,为2.9% ,在1月左右最大,为67.4%;低云平均云底高在7月左右最低,为756.1 m,在1月左右最高,为1 259.4 m;低云平均厚度在7月最小,为714.1 m,在12月最大,为1 039.4 m。(2)深对流发生概率在10月左右最小,为1.9%,12月最大,为18.7%;深对流顶高在10月最大,平均顶高为16 056.2 m,在4月最小,平均顶高为14 164.0 m。