Numerical simulation of sea breezes over the Auckland region,New Zealand — Air quality implications

The air pollution meteorology of a typical sea breeze day is investigated using the Colorado State University Mcsoscale Model. Results are qualitatively compared with observations and reveal a complex wind field characterised by migratory sea breeze convergence zones. Associated with these features, the model predicts enhanced upward vertical velocities and doming of the planetary boundary layer (PBL). The diurnal variation in PBL depth is shown to vary markedly at different locations and is dependent on position in relation to the migratory convergence zones. These complex spatial and temporal variations in the wind and PBL depth have important implications for air quality in Auckland and confirm that simple Gaussian or box trajectory approaches are inappropriate for air quality assessment in such environments. The inclusion in the model of variable surface properties, a dynamic synoptic state and improved PBL parameterisations, as well as coupling with a Lagrangian particle model, are recommended if the model is to be used as a tool for further air quality studies in the Auckland area.     

Acoustic sounding of land and sea breezes

Sodar measurements have been made at La Spezia, Italy during land- and sea-breeze conditions. The backscatter returns are discussed qualitatively, including their relation to the vertical structure of the boundary layer as revealed by vertical soundings of wind and temperature. During inversion conditions, the sodar signals may be difficult to interpret especially when there is a land breeze flowing over irregular terrain.     

一次弱环境风切变下的强对流天气

本文对2012年7月15日发生在黑龙江省西北部一次弱环境风切变条件下的强对流天气进行了分析,在综合各种常规观测、卫星及多普勒雷达资料的情况下,详细讨论了此次强对流天气发生发展的环流背景场及物理量的变化,着重分析了垂直风切变较弱时仍能发生强风暴所需的条件.结果表明:在丰富的水汽条件、不稳定的层结和一定的触发机制等条件下,环境风切变较弱时也可产生强对流天气.     

Operating ranges of mesoscale numerical models and meteorological wind tunnels for the simulation of sea and land breezes

The operating ranges of mesoscale numerical models and meteorological wind tunnels for sea- and land-breeze simulations are defined in this paper based on a review of the theoretical and practical limitations of these two approaches. Numerical-model operating ranges are limited by the choice of governing equations, the numerical methods used to solve the governing equations, the scales of the surface or atmospheric forcing and the atmospheric response, the specified grid resolution and domain size, and the available computer resources. Wind-tunnel operating ranges are limited by the dimensions of the simulated circulations and of the tunnel itself, the tunnel flow speed and turbulence characteristics, the temperature gradients within the tunnel, the lack of Coriolis force and moist processes, and the characteristics of the measurement instrumentation. The operating ranges of these two simulation methods are shown to overlap. In this common range, results of simulations from both approaches can be compared so as to strengthen the validity of the results and to help in the development and improvement of parameterizations of physical processes in numerical models. In addition, the coupling of meteorological wind tunnels and mesoscale numerical models offers a larger range of operating conditions than can be achieved by either approach alone. Together, they can be used in a hybrid form to predict atmospheric conditions at the scale of a few meters for complex terrain (e.g., buildings, hills, etc.) within larger mesoscale atmospheric flow regimes. In the case of sea and land breezes, the sea-land transition zone and coastal internal boundary layer can be studied using both approaches.     

A study of atmospheric structures using sodar in relation to land and sea breezes

Simultaneous observations were made by an acoustic sounder and on a meteorological tower during the month of May 1978 at the Atomic Power Station Tarapur. The probing range of the acoustic sounder was 700 m. The meteorological tower could sense wind and temperature at various levels up to a height of 120 m.The site being close to the sea shore, the thermal environment of the lower atmosphere is controlled mostly by land and sea breeze circulations. Thermal convective structures were seen during the daytime and also at night. The frequency of plume formation and the height of the plumes were, however, low during the night. The convective boundary layer in the daytime ranged from 400–500 m while at night it was mostly under 200 m. The observation of thermals at night is explained by the presence of a naturally stable marine layer above 30 m at this site. In the morning hours, winds suddenly change their direction allowing advection of a land breeze which is responsible for the formation of surface-based shear echoes to a height of 200 m during the transition period and for the subsequent development of an elevated layer due to mixing of two different air masses. A marine layer was also seen over Tarapur for a few days during the early evening and night hours. Its height was mostly around 400 m. It may indicate the presence of a subsidence inversion at Tarapur. The need for collection of supporting meteorological data to a height of 500 m by tethered balloon or some other suitable in-situ technique is stressed.     

The effect of sea breezes on atmospheric stability as observed with acoustic sounder

Acoustic sounder data obtained for a period of three years have been analysed to estimate the monthly mean percentage time of occurrences of sea breezes, thermal plumes, and nocturnal radiative inversion layers. The intrusion of marine air has been found to suppress daytime convection and also to inhibit the development of nocturnal inversions.     

盛夏杭州湾一次海风锋触发雷暴的数值模拟分析

利用常规气象观测资料、多普勒气象雷达资料、浙江省自动站加密资料、NCEP/FNL再分析资料,结合高分辨率中尺度数值模式WRF对杭州湾地区2016年7月28日一次海风锋触发雷暴天气的发生、发展演变特征进行数值模拟。结果表明:1)海风锋是此次强雷暴天气过程的主要触发系统。2)中尺度模式WRF较好地模拟出此次雷暴过程的降水和低层风场、温度场分布以及海风锋水平垂直结构。3)海风锋对局地比湿及涡度特征的加强有明显的促进作用,为雷暴的发生发展提供有利的水汽和动力条件。4)分析对流参数演变曲线的突变位置,对雷暴发生的时间有一定的指示和预报意义,杭州湾南侧单纯的海风锋也可以触发雷暴的发生发展。     

A study of the dynamics of hodograph rotation in the sea breezes of Attica,Greece

The diurnal evolution of the sea breeze hodograph over the Attic Peninsula has been studied using a three-dimensional numerical mesoscale model with fully nonlinear friction parameterization. The model results compare well with observed hodographs at three points in the modelling domain, and show that the balance of pressure gradient and terrain gradient forcing is dominant, and that this balance may result in either clockwise or anticlockwise rotation.     

青岛流亭机场海风特征分析及对飞行的影响

通过分析2008—2016年青岛流亭机场(简称青岛机场)各季节地面风向日变化规律,发现有两支海风环流影响青岛机场：一支是西支海风,风向210°～230°,一般上午影响机场,午后发展至最强,下午消失;另一支为南支海风,风向150°～170°,午后影响机场,下午取代西支海风,傍晚发展至最强,夜间逐渐减弱消失。两支海风夏季最为明显,南支海风强度季节性差异强于西支海风。海风对机场飞行的影响主要体现在两支海风引起的三种海风锋型低空风切变,分别为西支海风锋引起的侧风切变、两支海风环流相互作用引起的侧风切变以及南支海风引起的顺风切变,其季节及日变化规律为：夏季出现概率最大,春、秋季次之,冬季几乎不会发生;一天中最可能发生时段分别为08：00—11：00、12：00—15：00和15：00—17：00,具体时段在各季节略有差异。     

大尺度环境中中尺度对流系统生成的数值模拟试验

对1983年6月11日20时(北京时)实测资料进行低通滤波处理,取其大尺度部分作为初值,用七层原始方程模式对江淮气旋内中尺度对流系统的生成过程进行数值模拟试验.结果表明,从大尺度背景场出发,可以模拟出中尺度对流系统的生成.在西南低空急流十分潮湿的情况下,中尺度对流系统可以在江淮气旋暖区、低空急流大风速中心的前部、位势稳定度倾向维持负值的地区生成和发展.它的动力、热力结构,降水分布,以及发生、发展过程等,都与暖季(3—9月)在美国中部频繁出现的中尺度对流复合体(MCC)十分相似.     

NUMERICAL SIMULATION OF THE GENERATION OF MESOSCALE CONVECTTVE SYSTEMS IN LARGE－SCALE ENVIRONMENT

The generation of mesoscale convective systems is simulated by a 7-level primitive equation model. The large-scale parts of observed, data at 1200 Z June 11, 1983, which are obtained by low-pass filter, are used as the initial data. The results show that the generation of mesoscale convective systems can be simulated from fields of meteorological variables on the large-scale background. When the low-level south-west jet stream is very moist, mesoscale convective systems can develop ahead of the wind speed maximum in the warm sector of Jiang-Huai (Changjiang-Huaihe Rivers) cyclone, where the potential stability tends to remain negative. Furthermore, they are similar to the mesoscale convective complex (MCC), which appears frequently in the central part of the United States during the warm season (March to September), in dynamical and thermal structure, distribution of precipitation and the process of generation and development.     

激光测风雷达PPI扫描监测风切变的数值模拟

低空风切变严重威胁飞机起降安全,而激光测风雷达在晴空风切变监测方面具有显著优势,但其监测性能受到风场特点和监测算法的影响。由于无法对局地空间风场进行时空同步精细化探测,且风场具有阵性,导致风切变监测会出现虚警率、漏报等现象,只能通过数值模拟仿真的方式,对不同风场的监测性能进行分析评估。本文首先仿真构建了四种具有代表性的风场类型,然后模拟激光测风雷达平面—位置显示（Plane Position Indication,PPI）扫描方式获取不同仿真风场下的径向风速数据,最后利用八邻域系统算法对径向风速数据进行风切变监测,验证不同类型风场下激光测风雷达PPI扫描方式监测风切变算法的有效性。结果表明,激光测风雷达PPI扫描结果能够真实地反映风场情况;八邻域系统算法能够有效识别风切变;在进行风切变检测时,应尽可能地考虑到多个方位上的切变值,避免漏报。     

Observations and numerical modelling of Lake Ontario breezes

Abstract

Analysis of two years of land‐based data shows that the Lake Ontario breeze develops on 30% of the days during summer. It typically develops in mid‐morning and persists until the late evening when it is replaced by a well developed land‐breeze regime. Simulations of 4 cases with the Colorado State University mesoscale model show good agreement with observations and suggest that local lake breezes are strongly influenced by adjacent water bodies (e.g. Lake Erie), the elongated shape of the lake, and the large‐scale wind direction. With gradient flows across the long axis of the lake, a broad band of along‐lake flow develops during the afternoon (easterly winds during southerly gradient flows and westerly winds during northerly gradient flows). Furthermore, during west‐to‐northwesterly gradient flow a nocturnal cyclonic eddy is predicted at the western end of the lake. These results imply that wind‐field models applied in the vicinity of Lake Ontario should incorporate the entire lake in their modelling domain.     

风切变对积云发展影响的数值模拟研究

本文采用二维暖积云模式研究了风切变对积云发展和降水大小的影响。计算结果表阴:一般有风切变情况下积云的发展和降水量都明显减弱。这是由于水平气流的作用促进了云内外水汽和热量交换,减弱了积云发展的条件。计算还表明:在多种不同风速廓线和大气层结下风切变对云和降水发展均不利。 我们发现当云移行前方有高湿区时,在中等的风切变下可能有利于积云发展和降水形成。这是由于在水汽场和风场的配置下,云中得到充沛的水汽补充,促进了云和降水的发展,总降水量可增加2—3倍。     

Numerical simulation of a low-precipitation supercell thunderstorm

Summary Numerical simulations of thunderstorms using initial conditions from an Oklahoma storm event on 26 April 1984 have been carried out using the Klemp-Wilhelmson cloud model. Two thermodynamic and two horizontal wind profiles are mixed to create four initial storm environments. The two initial thermodynamic profiles are designated as moderately and highly unstable. Both hodographs have considerable vertical wind shear, with the extremely unstable profile having substantially stronger storm-relative curvature shear in the lowest few kilometers, as measured by the helicity of the environment. Storms are initialized with two different temperature-perturbation warm bubbles. A variety of storms, qualitatively covering the range observed on this day, are simulated. With a strongly sheared, moderate instability environment, the two different temperature-perturbation simulations differ qualitatively, unlike the other pairs of simulations.Of particular interest is the simulation carried out with the weaker temperature-perturbation. It displays many of the characteristics of observed low-precipitation (LP) supercell storms. Without artificially suppressing rainfall, this storm produces very little precipitation over the first 6000 s of its lifetime. During this time, there is no strong downdraft at the lowest model level and vorticity at that level is much less than the values aloft. We hypothesize that LP storms can be generated by smaller initial impulses than classic supercells in environments typically associated with a supercell storm, as speculated by Bluestein and Parks (1983), since they are more susceptible to turbulent entrainment in highly sheared environments.With 15 Figures     

一次暴雨过程数值模拟与诊断分析

利用NCEP/NCAR分辨率为1°×1°再分析资料和气象台实测降水资料及TRMM 3 h降水资料,采用WRF中尺度数值模式,对2010年7月22日发生在黄河流域中游南部的一次暴雨过程进行了数值模拟及诊断分析。结果表明：WRF模式能较为成功的模拟出本次暴雨过程。此次暴雨在大尺度环流形势上,是由于西太平洋副热带高压与河套低压槽的共同影响产生的;来自印度洋、中国南海的大量水汽输送为暴雨提供了充足的水汽来源。处于200 hPa的高空急流,由于地转调整激发出了中尺度重力波,使用散度场、云水分布,能够确定中尺度重力波的存在和移动方向。在利用模拟资料分析重力波对甘肃省东部地区暴雨产生的原因时得出：高空急流中产生的中尺度重力波与低层大气对中尺度重力波的吸收作用,共同导致了该地暴雨的发生。由高空急流风向和非线性平衡方程的数值分布情况,可以提前判断中尺度重力波发生的区域和移动方向,从而能够提前对暴雨可能发生的区域和时间作出预报。     

北京一次强降水过程的数值模拟

利用新一代中尺度数值预报模式WRF3.3和1°×1°的NCEP气象再分析资料,对2011年7月24日北京强降水天气过程进行数值模拟,并利用模式输出的高分辨率资料进行诊断分析。结果表明：WRF模式能较好地模拟出这次强降水过程。该过程不仅受到对流层中低层长波低槽和地面辐合区系统性的动力抬升作用,还受到对流层高层辐散的强迫作用。在这种配置下,中低层大尺度动力抬升与高层强辐散呈现出垂直耦合状态,有利于强降水区垂直环流和对流的发展。同时北京地区上空500 hPa以下相对湿度大于70 %,在降水区形成了深厚的高湿环境,为降水的产生、加强和维系提供了充沛的水汽条件。从大气稳定度方面看,北京市全境均处于K指数高值区,高峰值为42.5 ℃,反映了大气层结非常不稳定。从动力作用分析发现,高空辐散、低空辐合的流场特征促进了降水的产生,螺旋度低层正值、高层负值的耦合结构是触发并维持降水的动力机制。     

Doppler sounder observations of trade winds and sea breezes along the African west coast near 34 ° S, 19 ° E

Summer weather conditions along the west coast of Africa near 34 ° S, 18 ° E are investigated using doppler acoustic sounder profiles. Case studies were selected from a two-year record to form composite analyses over the diurnal cycle. The SE trade wind exhibited a low level jet at the level of the temperature inversion due to a sharp reversal in the thermal wind vector aloft. Mean wind speeds reached 14 m s^–1 just before midnight as the surface and upper inversions strengthened. Seabreezes were categorised by the supporting gradient wind and found to have mean depths of 400 m, speeds of over 6 m s^–1 at the 200 m level, and advance/retreat times of 09 hr and 16–20 hr. During seabreezes and weak on-shore gradient flow conditions, the thermal internal boundary layer (TIBL) was monitored with sounder transects in the first 12 km of the coastal zone. The growth height was observed to be 1:20 in the first 5 km and 1:50 farther inland. The sounder climatology, together with surface network and aerial survey results, illustrate the four-dimensional characteristics of trade winds and seabreezes near Cape Town.     

慕尼黑一次混合型雹暴的数值模拟与成雹机制

利用三维冰雹云模式,对2013年4月29日四川西昌的一次降雹过程进行了数值模拟。模拟结果显示：该例冰雹云存在过冷雨水累积带;霰是冰雹的主要胚胎,雹块主要通过撞冻云水增长,其次是撞冻霰增长;模拟区域内液态降水量和固态降水量分别占地面总降水量的52%和48%,冰雹占固态降水94%;通过对该例雹云中冰晶、雪、霰、冻滴的微物理过程分析发现,在雹云发展的不同阶段,冰雹的形成机制不同。

     

东北地区一次积层混合云过程的数值模拟

积层混合云是中国主要的降水云型之一,它的动力和热力特征比单一的层状云或对流云都要复杂。利用NCEP的 1°×1°再分析资料,通过WRF模式对东北地区一次典型积层混合云过程进行数值模拟,通过对模拟结果分析并结合实际资料,从热力和动力方面研究了积层混合云的形成过程。结果表明：从稳定性上分析,此次过程属于潜在不稳定型,在积云初始生成时,对流有效位能并不大,假相当位温随着高度递减,有利于对流的发展;在积云嵌入大片层状云的过程中,水汽高低空辐合辐散场的变化起了决定性作用,热力作用为积层混合云过程提供了条件,动力因素起主要作用。