Numerical simulation of sea and bay breezes in a weak shear environment

Summary A numerical mesoscale model (COAMPS) is used to study some of the features associated with the evolution of the kinematic, thermodynamic, and physical structure of the Alabama sea and bay breeze circulations and convections in weak shear environments based on five cases from Medlin and Croft (1998). The general and expected features and evolution of sea and bay breeze circulations are captured by the model simulations, including horizontal and vertical wind shifts, thermal contrast between land and water surface, vertical stability over water and land, return currents and moisture increase. The relationship of the circulations to specific synoptic flow regimes and local physiographic features was investigated. The sea breeze triggered convective cells are confirmed to have a preferred location according to the flow regime and local conditions. This result can assist the forecasters in understanding the anticipated convective cell initiation and development on a given day as related to sea and bay breeze cells as well as improve the short-term forecast accuracy of the location of thunderstorm initiation based on routine observations and subsequent convective activity. If local NWS office model a selective subset of cases then they can better visualize and forecast those cases operationally.     

STATISTICAL CHARACTERISTICS AND NUMERICAL SIMULATION OF SEA LAND BREEZES IN HAINAN ISLAND

The sea-land breeze circulation （SLBC） occurs regularly at coastal locations and influences the local weather and climate significantly. In this study, based on the observed surface wind in 9 conventional meteorological stations of Hainan Island, the frequency of sea-land breeze （SLB） is studied to depict the diurnal and seasonal variations. The statistics indicated that there is a monthly average of 12.2 SLB days and an occurrence frequency of about 40%, with the maximum frequency （49%） in summer and the minimum frequency （29%） in autumn. SLB frequencies （41%） are comparable in winter and spring. A higher frequency of SLB is present in the southern and central mountains due to the enhancement effect of the mountain-valley breeze. Due to the synoptic wind the number of SLB days in the northern hilly area is less than in other areas. Moreover, the WRF model, adopted to simulate the SLBC over the island for all seasons, performs reasonably well reproducing the phenomenon, evolution and mechanism of SLBC. Chiefly affected by the difference of temperature between sea and land, the SLBC varies in coverage and intensity with the seasons and reaches the greatest intensity in summer. The typical depth is about 2.5 km for sea breeze circulation and about 1.5 km for land breeze circulation. A strong convergence zone with severe ascending motion appears on the line parallel to the major axis of the island, penetrating 60 to 100 km inland. This type of weak sea breeze convergence zone in winter is north-south oriented. The features of SLBC in spring are similar both to that in summer with southerly wind and to that in winter with easterly wind. The coverage and intensity of SLBC in autumn is the weakest and confined to the southwest edge of the central mountainous area. The land breeze is inherently very weak and easily affected by the topography and weather. The coverage and intensity of the land breeze convergence line is significantly less than those of the sea breeze. The orographic forcing of the cen     

湛江东海岛二月海陆风环流特征研究

利用2011年2月湛江东海岛风廓线雷达资料,系统分析了湛江东海岛2月平均风场特征及海陆风特征,结果表明:2月湛江东海岛150 m高度处以东偏北出现频率最大,在E、ENE和NE三个方位的风向出现频率之和为66.6%,偏西七个方位的风向出现频率之和仅为1%。以SSW方位为界,偏东风与偏西风的出现频率差异明显。各整点的月平均风速1:00—15:00变化较小,均在1 m/s左右波动;15:00—20:00风速及风速波动都较大,最大值出现在16:00时,为2.1 m/s。2011年2月中只有2日与14日两日符合海陆风日条件,两日共同海风时段为13:00—20:00,持续7 h;陆风时段为2:00—7:00,持续5 h。海风平均风速为2.1 m/s,陆风平均风速为0.8 m/s,海风平均风速明显大于陆风风速。海风与陆风环流垂直高度相差甚小,约1.2 km,风速随高度变化趋势均为先增后减;海风最大风速出现在750 m高度处,陆风出现在500 m高度处,500～750 m高度区间海风环流强度明显强于陆风环流。2 km之上为均匀一致的系统性西风环流。     

中国地区山谷风研究进展

随着城市化的发展,越来越多的城市建立在山区附近或山谷之中。受地理环境和气象条件等因素影响,各地山谷风特征各不相同。山谷风对局地风场、气候特征有着重要作用,与逆温和污染物浓度变化也具有良好相关。本文从山谷风研究的主要手段—观测、理论和数值模拟出发,重点回顾了国内山谷风研究成果,并讨论了与其他中尺度环流(海陆风、湖陆风、城市热岛、植被风、冰川风环流)的相互作用,以及包括山谷风在内的山地环流对大气污染的影响。最后对国内研究进展进行总结,并提出了一些还需深入研究和探讨的问题。     

Interaction of the sea breeze with a river breeze in an area of complex coastal heating

A three-dimensional finite-element mesoscale model is used to study the interaction of two different but related mesoscale phenomena in an area having a complex pattern of surface heating. The model simulations have been compared with temperature and wind fields observed on a typical fall day during the Kennedy Space Center Atmospheric Boundary Layer Experiment on the east coast of Florida.Numerical results and observations both show that the meso- scale flow field is significantly modified from the conventional coastal-flow patterns by the smaller meso- scale irregular geographic features in this area. A local river breeze is observed to develop around the Indian River almost the same time as the Atlantic sea breeze. A comparison of the sea and the river breezes shows a large difference in their horizontal circulations but only slight differences in their vertical scales. The sea breeze intensifies more rapidly than the river breeze, so that a lag of 1 to 1.5 h exists between their most developed stages. The river breeze is relatively stationary, whereas the sea breeze propagates inland, with an eventual merger of the two circulations occurring about 6–8 h after their onset.Different synoptic wind regimes create different flow structures. Well-defined sea- and river-breeze circulations become established under calm, weak offshore, and weak alongshore synoptic-wind conditions. Maximum vertical velocities occur in the sea-breeze front (river-breeze front) in the cases of calm (offshore winds). The sea breeze and the river breeze are weaker when the synoptic winds are stronger.Finally, the results from numerical experiments designed to isolate the rivers' effect indicate that the convergence in the sea-breeze front is suppressed when it passes over the cooler surface of the rivers.Journal Paper No. J-14150 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa, Project No. 2779     

Influence of Changes in the Prevailing Synoptic Conditions on the Response of Aerosol Characteristics to Land- and Sea-Breeze Circulations at a Coastal Station

The changes in the response of near surfaceaerosol properties to land- and sea-breezecirculations, associated with the changes in the prevailing synoptic meteorological conditions, are examined for a tropical coastal station. Aerosol properties are nearly similar in both the breeze regimes (land and sea) during seasons of marine airmass while they are distinct during seasons of continental airmass. As the prevailing winds shift from continental to marine and the ambient weather changes from winter conditions to the humid monsoon season, the submicron mode, which dominated the aerosol mass-size distribution, is largely suppressed and the dominance of the super micron mode increases. During periods of continental air mass (winter), the aerosol loading is significantly higher in the land-breeze regime, (particularly in the submicron range) but as the winds shift to marine, the loading initially becomes insensitive to the breeze regimes and later becomes higher in the sea-breeze regime, particularly in the super micron range.     

香港地区海陆风的显式模拟研究

利用MM5模式对香港地区的海陆风进行了显式数值研究,模拟的风向、风速和温度与站点的观测值比较一致,较详细地分析了海陆风的日变化规律和三维结构特征,结果显示香港地区海风分布复杂,主要受偏西、偏南和偏东海风气流的影响,形成多个辐合带,海风锋最远可以深入内陆约90 km;陆风较简单,主要是偏北气流,陆风的风速和强度都比海风要弱,与山谷风、城市热岛环流等形成弱的辐合。香港是一个海岸曲折、多丘陵的地区,其中75%的面积是山区,为了研究这些丘陵地形对香港地区海陆风的影响,设计了保留海陆分布,去掉丘陵地形的敏感性试验,结果表明,由于丘陵地形的存在,在白天地形的热力作用是主要的,增强了海风的强度;而晚上动力阻挡作用比较明显,减弱了陆风的强度。     

Modeling of urban heat island and its impacts on thermal circulations in the Beijing–Tianjin–Hebei region,China

Through regulating the land–atmosphere energy balance, urbanization plays an important role in modifying local circulations and cross-border transport of air pollutants. The Beijing–Tianjin–Hebei (BTH) metropolitan area in northern China is frequently influenced by complex atmospheric thermal circulations due to its special topography and geographic position. In this study, the Weather Research and Forecasting (WRF) model combined with remote sensing is used to explore the urbanization impacts on local circulations in the BTH region. The urban heat island (UHI) effect generated around Beijing and Tianjin shows complex interactions with local thermal circulations. Due to the combined effects of UHI and topography, the UHI circulation around Beijing and valley breeze at the southern slopes of Yan Mountain are coupled together to reinforce each other. At the coastal cities, the increased land/sea temperature gradient considerably accelerates the sea breeze along Bohai Bay and moves the sea breeze front further inland to reach as far as Beijing. This study may lay a foundation for the better understanding of air pollutant dispersion on complex terrain.

     

多云天气下海南岛地形对局地海风环流结构影响的数值模拟

采用WRF中尺度天气预报模式,针对海南岛多云天气条件下的一次典型海风个例,对局地海风环流结构进行数值模拟,分析海风环流的演变特征,并通过设计改变海南岛地形的敏感性试验,探究地形对海南岛局地海风环流结构以及云水分布的影响。结果表明:海岛西部陡峭的山区造成海风强迫抬升,偏南背景风使得海岛北部高空回流明显,海岛西部、北部的海风结构较为完整;地形高度越高,海岛南部山区的阻挡作用越强,西部地区的海风高空回流特征越显著,西部、西北部云水混合比的位置也越深入内陆;受南海季风的影响,与晴空天气相比,多云天气下海风强盛期全岛的最大风速稍大,海风在垂直方向上达到的高度更高;移平地形后,多云天气下全岛风速平均仅减少2~3 m·s^-1,而晴空天气下全岛风速则大大减弱,即多云天气下海风环流水平结构受地形的影响比晴空天气下弱。     

The Amazon river breeze and the local boundary layer: II. Linear analysis and modelling

Observed boundary-layer circulations close to the confluence of the Negro and Solimões rivers near Manaus in the Brazilian equatorial Amazon forest were presented in Part I. These are shown through linear analysis and second-order turbulence modelling to be aspects of a river breeze superimposed on the basic flow. Linear analysis is presented to estimate the spatial structure and intensity of a breeze induced by a river with width and thermal contrast similar to that observed in the central Amazon. It is found that observed thermal contrasts are sufficient to produce a river breeze that can be perceived more than 20 km inland daily. A one-dimensional second-order closure model is used to show that observed nocturnal low-level wind maxima and diurnal surface wind rotation are aspects of a river breeze interacting with the seasonally-varying mean flow. At night, partial decoupling of the surface from the lower atmosphere allows the land breeze to be expressed as a low-level wind maximum. During the day, convective mixing communicates upper level winds to the surface during rapid morning boundary-layer growth. Rotation of the surface wind follows as the river breeze circulation is then superimposed.     

Inland penetration of the sea breeze over the suburban area of Tokyo

Observational results of the structure of the sea breeze over the urban and suburban areas of Tokyo for four summer days are presented.On two of these days, the inland penetration of the sea breeze front could be clearly traced. In one case, the sea breeze was first observed along the shores of Tokyo Bay around 0900 JST, and propagated in three hours through the Tokyo City area, the width of which is about 20 km. It then advanced inland at a rate of 16 km h^–1. Prior to the arrival of the sea breeze at the suburban site, the mixing height had remained at about 600 m for four hours. With the arrival of the sea breeze front, accompanied by an abrupt change in wind speed and direction, the mixing height increased sharply to 1700 m. It is suggested that this behavior and the structure of the front are intensified due to the urban effect, or the difference in the thermal characteristics between the urban and rural areas.On the days without a sea breeze front, the land breeze system during the early morning was less intense, allowing the sea breeze to develop simultaneously with the inland valley wind and easily form a large-scale local wind system during the morning hours. In both cases, the vertical motion accompanying the local wind system works as a feedback mechanism to control the local winds by modifying the thermal and pressure fields.     

热力强迫对局地环流的扰动作用

用积分变换法求解了包含地面加热作用的二维不可压缩流体的Boussinesq方程组,得到一组描述地面加热作用激发的局地扰动流场的解析解,主要有垂直风、水平扰动风、扰动气压、扰动温度。进而用动力学分析的观点结合图形分析,定性讨论了热力强迫作用对局地环流的扰动作用,以及加热影响下各物理扰动场的空间分布及时间演变特征。     

Sea/land breeze climatological characteristics along the northern Croatian Adriatic coast

Summary Climatological characteristics along the northern Croatian Adriatic coast have been examined for nine meteorological stations for the summertime sea/land breeze circulation. The stations considered are Pula-airport, Opatija, Rijeka, Senj, Malinska, Rijeka-airport, Mali Lošinj, Rab and Zadar. The hourly surface measurements at each station from June to September for the period 1991–2004 as well as the radiosoundings in Zadar (from 2002 to 2004) were used for the analysis. A dataset with the sea/land breeze days was formed according to the several criteria. The mean daily maxima of both air and sea surface temperatures were more influenced by the large scale disturbances toward north (e.g. in Rijeka or Opatija) compared to the values for e.g. Zadar. Furthermore, the influence of the large scale disturbances diminished toward the south concerning the sea–land temperature difference only at the stations placed at Rijeka Bay and Velebit channel. The strongest sea breeze was found at Pula-airport and the most frequent ones at Opatija and Zadar. At Senj the rarest, the weakest and the shortest sea breeze was observed. The climatological records of wind speed and air-sea temperature difference (ΔT) showed for Opatija, Malinska and Zadar that the maximum measured wind speed is around 4.5 °C confirming the nonlinear relationship between the sea breeze speeds and the ΔT during the day. At most stations, the clockwise rotation of the hodographs prevails which is typical for the Northern hemisphere due to Coriolis force, with the exception at Senj and Malinska. While the hodographs for Pula, Rijeka-airport and Mali Lošinj display a later onset of the prevailing sea breeze because of the interaction among several sea breeze circulations, the results for Opatija, Zadar and Senj show considerably distorted hodographs because of the nearby channeling of the air flow.     

多云天气下海南岛海风环流结构的数值模拟

利用WRF-Noah耦合中尺度模式对海南岛2012年7月5日的多云海风个例进行三维高分辨率数值模拟,重点分析多云天气条件下复杂地形区域的海风环流结构及其演变特征。通过观测资料与模拟结果的对比发现,WRF模式能够合理地模拟出岛屿四周的海风演变特征。与少云海风日相似,多云海风日中全岛海风于12时开始形成,15时海风发展最为强盛,影响范围最广,18时全岛海风的辐合程度最强,海风辐合区是主要的潜在降水区域。对比山区与平坦地区的海风环流发现,山区海风环流强盛期为13—18时,而平坦地区海风环流强盛期为15—18时。复杂的山地对海风环流结构有直接和间接的影响:一方面在山地地形动力阻挡和抬升作用下,海风环流变得更加清晰完整,间接延长了海风环流的维持时间;另一方面局地地形热力作用形成的谷风环流与海风几乎同时产生和消亡,两者汇合后,谷风的瞬间加强会引起海风锋锋消,瞬间减弱会引起海风锋锋生;两者同相叠加会使得海风环流结构更加完整。相比之下,平坦地区的海风受到的地形动力和热力作用小,海风水平分布比较规则,海风环流垂直结构的变化主要取决于不同方向海风之间的相互作用。     

The inland boundary layer at low latitudes: II Sea-breeze influences

Two-dimensional mesoscale model results support the claim of evening sea-breeze activity at Daly Waters, 280 km inland from the coast in northern Australia, the site of the Koorin boundary-layer experiment. The sea breeze occurs in conditions of strong onshore and alongshore geostrophic winds, not normally associated with such activity. It manifests itself at Daly Waters and in the model as a cooling in a layer 500–1000 m deep, as an associated surface pressure jump, as strong backing of the wind and, when an offshore low-level wind is present, as a collapse in the inland nocturnal jet.Both observational analysis and model results illustrate the rotational aspects of the deeply penetrating sea breeze; in our analysis this is represented in terms of a surge vector — the vector difference between the post- and pre-frontal low-level winds.There is further evidence to support earlier work that the sea breeze during the afternoon and well into the night — at least for these low-latitude experiments — behaves in many ways as an atmospheric gravity current, and that inland penetrations up to 500 km occur.     

Impacts of the Boreal Summer Intraseasonal Oscillation on the Warm-Season Rainfall over Hainan Island

This study investigates the roles of the boreal summer intraseasonal oscillation (BSISO) in the diurnal rainfall cycle over Hainan Island during the warm season (April-September) using 20-year satellite-based precipitation, ERA5 and the outgoing longwave radiation data with the phase composite analysis method. Results show that the spatial distributions of the hourly rainfall anomaly significantly change under the BSISO phases 1-8 while no clear variations are found on the daily and anomaly daily area-averaged rainfall over the island. During the BSISO phase 1, the rainfall anomaly distinctly increases in the morning over the southwest and late afternoon over the northeast of the island, while suppressed convection occurs in the early afternoon over the southwest area. Under this circumstance, strong low-level westerly winds bring abundant moisture into the island, which helps initiate the nocturnal-morning convection over the south coastal area, and drives the convergence region of sea breeze fronts to concentrate into the northwest. Opposite to Phase 1, an almost completely reversed diurnal cycle of rainfall anomaly is found in Phase 5, whereas a positive anomalous rainfall peak is observed in the early afternoon over the center while negative peaks are found in the morning and late afternoon over the southwest and northeast, owing to a strong low-level northeasterly anomaly flow, which causes relatively low moisture and enlarges a sea-breeze convergence area over the island. During Phase 8, strongest moisture is found over the island all through the day, which tends to produce highest rainfall in the afternoon with enhanced anomalous northerly. These results further indicate that multiscale interactions between the large-scale circulations and local land-sea breeze circulations play important roles in modulating diurnal precipitation cycles over the tropical island.     

CHARACTERISTICS OF BOUNDARY LAYER AND ITS EFFECTS ON ATMOSPHERIC AEROSOL CONCENTRATIONS IN DONGGUAN, GUANGDONG

The structure of atmospheric boundary layer determines the ability of atmospheric dispersion and has an essential impact on airborne aerosols. In this paper, the data of a radio sounding experiment held in Dongguan National Meteorological Observation Station, which is in a coastal city in Pearl River Delta, as well as the data of atmospheric aerosols, were utilized in order to analyze the characteristics of atmospheric boundary layer and its effects on surface aerosol concentrations. The results are showed at follows: the local circulations, associated with dominant winds, made complex structures of atmospheric layers, as the cold air and systematic winds weakened in the end of a cold air event. Weakened wind shears and inversion layers, especially a strong near-surface inversion layer, remarkably diminished the atmospheric diffusion abilities and facilitated an especially high concentration of surface aerosols. The convergence line or weak shear line of sea breeze in the ground level helps weaken the atmospheric diffusion abilities and results in atmospheric aerosols accumulation.     

珠江三角洲秋季大气边界层温度和风廓线观测研究

根据2004年10月珠江三角洲3个代表性观测点大气边界层观测资料, 分析了珠江三角洲秋季大气边界层温度和风廓线特征。结果表明:珠江三角洲秋季气温递减率较低, 逆温出现频率较高, 强度较弱, 海风使珠江口贴地逆温的出现时间推迟、低空逆温的出现频率增加。珠江三角洲秋季受多种局地环流影响, 边界层内风廓线比较复杂, 晚上城市群与非城市群地区风向有明显差别; 城市群和珠江口多次分别观测到城市热岛环流和海风环流。     

一次冷锋过境后的海风三维结构数值模拟

为研究大尺度系统风对海风的影响以及海风三维结构特征,利用山东省123个地面自动站资料、青岛地区三十多个内陆及沿海、海岛观测站以及奥帆赛场3个浮标站资料,对2006年8月21日青岛一次海风个例进行了分析,并利用美国俄克拉荷马大学风暴分析预测中心开发的ARPS(the Advanced Regional Prediction System)模式,对海风过程进行了数值模拟研究。结果发现:在较强的离岸风背景下,当内陆气温高于海面气温2℃左右时,海风也可以发生。海风首先在海岸线附近的海上开始,发展的同时向内陆及远海地区推进。海风低层环流很浅,主要位于500 m以下。在较强的偏北离岸风下,海风向内陆推进的距离很短。偏北的大尺度系统风由于渤海冷下垫面的影响,不利于青岛海风的维持。海风开始时,在1500～2500 m高度处同时有反环流出现,但直到傍晚前后,海风的垂直环流圈才发展得比较清晰,其高度也更接近地面。海风消亡后,高层的垂直环流圈及反环流维持3 h左右才逐渐消亡。     

连云港沿海近地层湍流强度特征

在对连云港沿海15个各类气象观测站2000—2009年8级以上强风样本统计分析基础之上,利用6座沿海梯度测风塔2005—2007年测风资料,探讨了连云港沿海近地层风湍流强度的时空分布规律及特点,并重点对不同类型天气系统引起的强风湍流演变特征及其对风电场影响进行剖析。研究结果表明:①风湍流强度具有很强的季节性,冬季小、夏季大,随高度增加而减小;②海面动力粗糙度对海上强湍流变化的影响有别于无强风及下垫面是陆地时;③在热带气旋影响区域,同一时段内可能会出现风速和湍流强度瞬时骤变现象;④海上强湍流出现在30m以上高度,陆地出现在底层,这一现象在不同天气系统引起的强风湍流变化中都有发现;⑤风机轮毂高度处有2.1%～3.8%的湍流强度特征值超过目前风机最大抗湍流强度设计标准,建议华东中、北部沿海地区风机抗湍流强度参数调整为0.31～0.41。