Impacts of Two Ice Parameterization Schemes on the Cloud Microphysical Processes and Precipitation of a Severe Storm in Northern China

A severe storm that occurred over Beijing in northern China on 23 June 2011 was simulated with two different ice crystal parameterization schemes(the DeMott scheme and Meyers scheme) by using the Regional Atmospheric Modeling System. Compared with the DeMott scheme, the simulation results with the Meyers scheme have the following characteristics:(1) Updrafts are stronger and more numerous;(2) The cloud is better organized and contains a greater peak of ice-phase hydrometeor mixing ratios;(3) Cloud water and hail mixing ratios increase while graupel mixing ratios decrease;(4) The surface precipitation is initially greater. However, at the end of the simulation, less precipitation is produced. In short, the differences between the two schemes are not obvious, but the De Mott scheme has a relatively more reasonable result.

Comparison of Aerosol Effects on Simulated Spring and Summer Hailstorm Clouds

Numerical simulations are carried out to investigate the effect of cloud condensation nuclei（CCN） concentrations on microphysical processes and precipitation characteristics of hailstorms. Two hailstorm cases are simulated, a spring case and a summer case, in a semiarid region of northern China, with the Regional Atmospheric Modeling System. The results are used to investigate the differences and similarities of the CCN effects between spring and summer hailstorms. The similarities are：（1） The total hydrometeor mixing ratio decreases, while the total ice-phase mixing ratio enhances, with increasing CCN concentration;（2） Enhancement of the CCN concentration results in the production of a greater amount of small-sized hydrometeor particles, but a lessening of large-sized hydrometeor particles;（3） As the CCN concentration increases, the supercooled cloud water and rainwater make a lesser contribution to hail, while the ice-phase hydrometeors take on active roles in the growth of hail;（4） When the CCN concentration increases, the amount of total precipitation lessens,while the role played by liquid-phase rainfall in the amount of total precipitation reduces, relatively, compared to that of icephase precipitation. The differences between the two storms include：（1） An increase in the CCN concentration tends to reduce pristine ice mixing ratios in the spring case but enhance them in the summer case;（2） Ice-phase hydrometeor particles contribute more to hail growth in the spring case, while liquid water contributes more in the summer case;（3） An increase in the CCN concentration has different effects on surface hail precipitation in different seasons.

Numerical investigations for the impacts of triple-moment and double-moment condensation schemes on the warm rain formation

在暖云发展过程中,云滴谱的凝结不仅为对流提供能量而且直接影响暖雨的形成和发展。目前国际上广泛使用的云滴谱凝结方案主要为双参数方案,此类方案模拟的云滴谱在凝结过程中呈不正常拓宽现象,三参数云滴谱方案有效解决了该问题。为了比较两种凝结方案对暖雨初始形成和发展强度的影响,本文采用WRF模式中的理想性大涡模拟个例在相同背景条件下,分别使用两种方案模拟了一个对流热泡中暖雨的形成、发展过程。模拟结果表明:在雨滴初始形成阶段,三参数方案因为克服了双参方案中的拓宽问题,推迟了暖雨形成的时间;在暖雨发展阶段,三参数凝结方案有效削弱了暖雨区的中心强度;但在暖雨发展后期,两个凝结方案模拟结果的差异逐渐缩小。

On the Variation of Divergent Flow： An Eddy-flux Form Equation Based on the Quasi-geostrophic Balance and Its Application

Based on basic equations in isobaric coordinates and the quasi-geostrophic balance,an eddy-flux form budget equation of the divergent wind has been derived. This newly derived budget equation has evident physical significance. It can show the intensity of a weather system,the variation of its flow pattern,and the feedback effects from smaller-scale systems(eddy flows). The usefulness of this new budget equation is examined by calculating budgets for the strong divergent-wind centers associated with the South Asian high,and the strong divergence centers over the Tibetan Plateau,during summer(June–August) 2010. The results indicate that the South Asian high significantly interacts with eddy flows. Compared with effects from the mean flow(background circulation),the eddy flows’ feedback influences are of greater importance in determining the flow pattern of the South Asian high. Although the positive divergence centers over the Tibetan Plateau intensify through different mechanisms,certain similarities are also obvious. First,the effects from mean flow are dominant in the rapid intensification process of the positive divergence center. Second,an intense offsetting mechanism exists between the effects associated with the eddy flows’ horizontal component and the effects related to the eddy flows’ convection activities,which weakens the total effects of the eddy flows significantly. Finally,compared with the effects associated with the convection activities of the mean flow,the accumulated effects of the eddy flows’ convection activities may be more favorable for the enhancement of the positive-divergence centers.

Cloud Microphysical Processes and Atmospheric Water Budget during the 20 July 2021 Extreme Precipitation Event in Zhengzhou,China

This study investigated the cloud microphysical processes and atmospheric water budget during the extreme precipitation event on 20 July 2021 in Zhengzhou of Henan Province,China,based on observations,reanalysis data,and the results from the high-resolution large-eddy simulation nested in the Weather Research and Forecasting(WRF)model with assimilation of satellite and radar observations.The results show that the abundant and persistent southeasterly supply of water vapor,induced by Typhoons In-Fa and Cempaka,under a particular synoptic pattern featured with abnormal northwestward displacement of the western Pacific subtropical high,was conducive to warm rain processes through a high vapor condensation rate of cloud water and an efficient collision–coalescence process of cloud water to rainwater.Such conditions were favorable for the formation and maintenance of the quasi-stationary warmsector heavy rainfall.Precipitation formation through the collision–coalescence process of cloud water to rainwater accounted for approximately 70%of the total,while the melting of snow and graupel accounted for only approximately 30%,indicating that warm cloud processes played a dominant role in this extreme rainfall event.However,enhancement of cold cloud processes promoted by latent heat release also exerted positive effect on rainfall during the period of most intense hourly rainfall.It was also found that rainwater advection from outside of Zhengzhou City played an important role in maintaining the extreme precipitation event.

Characteristics for the sources and sinks of gravity waves in an orographic heavy snowfall event

The characteristics of the mesoscale gravity waves during a snowfall event on November 30,2018 over the Ili Valley and the northern slope of the Tianshan Mountains are analyzed based on the Weather Research and Forecasting model simulation.The vertical distribution of Ro is similar to that of the residual of the nonlinear balance equation(△NBE),with their high-value areas located over the leeward slope and the fluctuations extending upwardly with time,indicating the characteristics of strong ageostrophy and non-equilibrium of atmospheric motions.In addition,the Ro and(△NBE)are first developed in the lower layers over the leeward slope,revealing that the generation of the gravity waves is closely related to the topography.Thus,the topographic uplifting greatly affects this snowfall,and the ageostrophic motion in the whole troposphere and the lower stratosphere,as well as the unbalanced motions between convergence and divergence over the peak and the leeward slope are conductive to the development of the inertia-gravity waves.In terms of the horizontal scale of the gravity waves,the Barnes’bandpass filter is applied to separate the mesoscale waves and the synoptic-scale basic flow.The vertical distributions of the vorticity and divergence perturbations have a phase difference ofπ/2,indicating the polarization state of gravity waves.The analyses on the sources and sinks of gravity waves by the non-hydrostatic wave equation show that the main forcing term for orographic gravity waves is the second-order nonlinear term,whose magnitude mainly depends on the nonlinear thermal forcing.This term is mainly related to the vertical transport of potential temperature perturbations.During the snowfall,the potential temperature perturbations are mainly caused by the topographic relief and the release of condensation latent heat.Therefore,the gravity waves in this snowfall are caused by the topographic forcing and condensation latent heating.

西北太平洋上一次极端强度爆发气旋对流层低层风速迅速增强的能量特征分析

2011年一月中旬,西北太平洋上发生了一次罕见的双子气旋事件。该双子气旋中的一个气旋(简称气旋A)迅速发展成为一个强度堪比台风的极端强度爆发气旋。本文采用旋转风,辐散风动能收支分析来研究造成该极端强度爆发气旋风速迅速增强的原因。研究发现,在气旋A的最快发展期,对流层低层,气旋的总动能迅速增大,风速增大最迅速的象限是气旋的东南象限,而西北象限的增速最慢。旋转风动能的增长显著,对应了总动能的增大,而辐散风的动能显著小于旋转风动能并且主要表现出减少的趋势。旋转风动能的增大与气旋A在水平和垂直方向上的伸展过程相一致,非正交风动能在旋转风动能大值区增强总动能,这促使了对流层低层最大风速的形成,然而,在辐散风动能较强的区域,非正交风动能主要减弱总动能。向北的总动能输送以及气压梯度力对旋转风动能的做功是气旋A风速迅速增大的主导因子,尤其是在其东南象限。然而,从旋转风向辐散风动能的转换在一定程度上延缓了气旋风速的增强过程。

Progress in Severe Convective Weather Forecasting in China since the 1950s

Located in the Asian monsoon region, China frequently experiences severe convective weather(SCW), such as short-duration heavy rainfall(SDHR), thunderstorm high winds, hails, and occasional tornadoes. Progress in SCW forecasting in China is closely related to the construction and development of meteorological observation networks,especially weather radar and meteorological satellite networks. In the late 1950 s, some county-level meteorological bureaus began to conduct empirical hail forecasting based on observations of clouds and surface meteorological variables. It took over half a century to develop a modern comprehensive operational monitoring and warning system for SCW forecast nationwide since the setup of the first weather radar in 1959. The operational SCW forecasting, including real-time monitoring, warnings valid for tens of minutes, watches valid for several hours, and outlooks covering lead times of up to three days, was established in 2009. Operational monitoring and forecasting of thunderstorms,SDHR, thunderstorm high winds, and hails have been carried out. The performance of operational SCW forecasting will be continually improved in the future with the development of convection-resolving numerical models(CRNMs), the upgrade of weather radar networks, the launch of new-generation meteorological satellites, better understanding of meso-γ and microscale SCW systems, and further application of artificial intelligence technology and CRNM predictions.