Thermal internal boundary layer characteristics at a tropical coastal site as observed by a mini-SODAR under varying synoptic conditions

Atmospheric boundary layer observations are conducted at a coastal site during a transition phase from winter to summer season over the Indian peninsula. Thermal Internal Boundary Layer (TIBL) characteristics in presence of an off-shore and a weakly influenced on-shore synoptic wind are examined with the help of measurements carried out with a mini-SODAR (SOund Detection And Ranging), tethered balloon, and tower-based micrometeorological measurements. Influence of the changing synoptic scale conditions on turbulent characteristics of TIBL is discussed. Mini-SODAR data showed the development and decay of sea and land breeze. It is seen that the characteristics of TIBL over the coastal land after sea breeze onset are similar to that of a shallow convective boundary layer (CBL) commonly found over plain land. Inside the TIBL, a maximum wind speed was noted close to the surface due to the penetration of sea breeze. In the off-shore case, a distinct sea breeze circulation was observed unlike in the case of on-shore flow. In the presence of weak on-shore case, a ‘minor sea’ breeze is noted before the establishment of sea breeze and a reduction in the momentum fluxes gives rise to decrease in the turbulence intensity. Updraft in the sea breeze front was stronger during weak synoptic conditions. Influence of synoptic changes on the sea breeze-land breeze circulation such as onset, strength and duration of the sea-land breeze are also examined. This work was done while the first author was a visiting scientist at IGCAR, Kalpakkam, India.     

巢湖“5.21”降雹成因分析

利用常规气象资料和合肥多普勒雷达回波，分析了2004年5月21日巢湖市降雹的环流背景、回波发展演变过程。结果表明，炯炀至巢湖市沿湖一线短时间内连续两次遭受冰雹袭击可能与湖陆交界的特点有关，是湖陆风与天气系统叠加和共同作用的结果。     

A THREE-DIMENSIONAL ELASTIC NESTED-GRID MESO-(β-γ) SCALE ATMOSPHERIC MODEL——PART Ⅱ:MODEL VALIDATION

By using the model developed in Part Ⅰ of the sister papers,simulations of severe storm,winter airflow and snowfall over a mountain,as well as mountain-valley winds and sea breeze are performed.Different functions of the model are verified through the computation and special emphasis is put on some important properties of the meso-(β-γ) systems frequently occurring.The simulation results of the cases are agreeable to field observations,conceptual models,and previous numerical studies.It is shown that the model is applicable for the researches and prediction of various local and/or regional weather processes,and capable of describing their macro-and micro-structures,influences of orographic and underlying-surface forcing,and interaction between meso-β and meso-γ scales.In addition,the evolutional characteristics and mechanisms of the modeled processes are also analyzed.     

滇池区域性环流的数值模拟

为了开发云南省滇池地区的磷资源，对云南滇池湖畔的中尺度环流状况进行了三维数值模拟，模式比较详细地考虑了各种物理过程，模拟结果与实测资料较吻合；滇池区域湖南白天为冷中心，夜间为暖中心；白天的垂直环流比夜间大得多，湖风比陆风影响范围也大得多，系统风对湖风影响较大。     

Study of ozone distribution over the south-eastern France (ESCOMPTE campaign): discrimination between ozone tendencies due to chemistry and to transport

Ozone tendencies due to chemistry and transport are calculated by a mesoscale model using a fine horizontal resolution (3 km × 3 km), over South-Eastern France. Over that region where the anthropogenic emissions are very strong, ozone pollution is highlighted during two intensive observations periods of the ESCOMPTE campaign, when the sea breeze penetrates far into the Durance and Rhone valleys and the up-slope breezes are developed. From a fine analysis of time series of ozone concentration at different ground stations along these valleys and from numerical results, it is possible to discriminate the tendency due to chemistry from the tendency due to dynamical processes. We can distinguish both processes, either local chemical production/loss or dynamical increase/decrease (transport, deposition) on maps of ozone budget according to the meteorological conditions. In particular, we show that the variations due to transport can be have the same order of magnitude than those due to chemistry, reaching 20 ppbv h⁻¹, whereas those due to chemistry are around 30 ppbv h⁻¹.     

A Radar-Based Investigation of Lake Breezes in Southern Manitoba,Canada

Lake breezes are thermally direct circulations that form as a result of the differential heating of land and water and are important in modifying local climate and triggering convection; they have also been linked to tornadogenesis. Although lake breezes are generally well understood, studies of smaller lakes have been relatively scarce, and none have examined lake-breeze circulations in southern Manitoba even though they are seemingly apparent on weather radar. The objectives of this paper are to provide a radar-based analysis of lake-breeze frequency and characteristics in southern Manitoba, determine the detectability of lake-breeze fronts using the radar analysis with data collected in 2013, assess the types of lake-breeze circulations that occur, and examine the meteorological conditions in which they occur. Between 2008 and 2013, lake-breeze fronts were noted on 205 days using radar over the summer months, accounting for 37% of study days, with an average of 11–12 days with lake-breeze fronts each month. These findings agree fairly well with, and are only slightly less than, frequencies reported for Lake Michigan but are lower than the most recent findings for southern Ontario. In an effort to validate the results, a broad comparison between the radar analysis and a more complete analysis using satellite and surface stations is provided for 2013 demonstrating that radar is more useful for detecting lake breezes around Lake Manitoba than around Lake Winnipeg. Lake-breeze circulations originating on Lake Manitoba and the Shoal lakes were classified into three types. The distribution of types for the Shoal lakes was similar to previous findings by other authors with “moderate deformation” circulations being the most frequent. Finally, a brief meteorological analysis was completed for each month of this study. The results of the analysis were inconclusive with no single meteorological factor being consistently well correlated to higher or lower lake-breeze frequency.     

福建沿岸一次飑线过程发生发展机理分析

利用常规观测资料、NCEP/NCAR(1°×1°)的逐6h再分析资料结合ARW-WRF中尺度数值模式模拟结果对2018年6月20日发生在福建沿岸的一次飑线过程的发生发展机理进行了分析,结果表明:①本次飑线过程属于槽前型,对流层低层存在发展的低涡切变,切变南侧有冷空气南下,低空西南急流不明显,但有持续的暖湿气流输送至福建中北部地区,飑线生成于低涡南侧的沿岸附近。②飑线发展期间系统南侧低层风速不断增大且维持高的水汽输送和不稳定能量;前期对流的触发因子包括锋面对流系统的冷出流、地形的抬升以及海风锋造成的冷堆强迫抬升;后期冷出流边界与海风锋边界碰撞合并,加强了低层辐合促进了对流的发展,是飑线形成的主要原因。③飑线成熟时期地面存在中高压和尾流低压,高压后部为强烈的辐散区,风速较大;成熟时期内部存在两支气流,前向入流为低层暖湿气流在飑线前方流入并在对流云区被抬升,后向入流为中层干冷空气在飑线后方流入,在低层形成下沉运动,是地面大风形成的重要原因之一。     

中国地区城市热岛环流研究进展

城市热岛环流是由城市热岛激发的、存在于边界层的局地环流。这一环流常影响城市区域污染物的扩散及城市降水,是城市气象学的重点研究对象。在过去30多年间,中国城市热岛环流的研究不断取得突破,研究成果丰富。为了今后更有效地开展相关研究,本文从观测分析、理论与数值模拟研究两方面,回顾并总结了我国在热岛环流研究方面取得的成果,包括热岛环流的时空特征、产生机制,以及热岛环流与其他局地环流的相互作用。此外,本文总结了热岛环流对城市及其周边地区污染物水平和垂直分布的影响。     

2017年漳州海陆风特征与冬春季污染物浓度关系

利用2017年福建漳州和南部海岛气象观测资料,通过统计分析和人工订正判识海陆风日,再结合天气形势和污染物浓度资料分析海陆风日的天气特征及其与污染物浓度的关系。结果表明：漳州海陆风日是海岛站的2.2倍,春夏季是海陆风的高发季节,秋冬季相对较少。冬季海陆风日主导天气形势为变性冷高压、高压后部、锋前暖区等,气象要素场配置为气压梯度小、气温高、风速小、日照时间长、湿度低、云量少,气象条件不利于污染物的稀释、扩散;海陆风影响下除了O₃,其他5种污染物浓度均高于系统风日2—3倍,其中颗粒物浓度明显偏高。与冬季不同,春季海陆风不仅对颗粒物浓度升高有利,对O₃浓度升高贡献更加明显,主导天气形势、气象要素场配置与冬季类似;海陆风影响下所有污染浓度均高于系统风日1—2倍,且易出现O₃超标现象。研究显示,漳州的海陆风全年发生频率虽然不到30%,但其特有的日变化规律和局地环流结构对污染物累积、输送具有重要的影响。     

海陆风及沿海风速廓线在风电场风速预报中的应用

为了建立沿海风功率预报系统,本文探讨了中国沿海风电场风速预报问题,并利用数值模式RAMS对海陆风进行了模拟研究.发现海陆风发生时,海风和陆风阶段风速廓线存在较大差异,海风阶段风速的垂直切变明显小于陆风阶段.海陆风发生时,风速会呈现有规律的变化,即海风和陆风分别有两个时段：风速增加时段和风速减少时段.在为沿海风电场提供风速预报时,当模式预报到海陆风发生时,可以利用海陆风的这种特点,使用统计方法对预报出的风速进行有效的订正.并发现即使没有海陆风发生,当风向为海洋吹向陆地时,风速随高度的垂直切变同样小于陆地吹向海洋的时段.利用统计方法根据不同风向时风速廓线的特性,把数值模式计算高度上的预报结果,精确地插值到风机涡轮高度,会很大程度上减少风速预报的误差及风功率预报环节的误差.