Evolution Mechanism of a Severe Squall Line Triggered by the Coupling of a Sea Breeze Front and a Gust Front

In the present study, a severe squall line(SL) was analyzed by using intensive observational surface data and radar monitoring products. In this process, mesoscale convergence lines, such as the sea breeze front(SBF), gust front and dry line, served as the main triggering and strengthening factors. The transition from convection triggering to the formation of the initial shape was mainly affected by the convergence line of the SBF, which combined with thermal convection to form the main parts of the SL. In the later stage, the convergence line of the gust front merged with other convergence lines to form a series of strong convective cells. The SBF had good indicative significance in terms of severe convective weather warnings. The suitable conditions of heat, water vapor and vertical wind shear on the Shandong Peninsula were beneficial to the maintenance of the SL. Before SL occurrence, tropopause folding strengthened, which consequently enhanced the baroclinic property in the middle and upper troposphere. The high sensible heat flux at the surface easily produced a positive potential vorticity anomaly in the low layer, resulting in convective instability, which was conducive to the maintenance of these processes. In the system, when precipitation particles passed through the unsaturated air layer, they underwent strong evaporation, melting or sublimation, and the cooling effect formed negative buoyancy, which accelerated the sinking of the air and promoted the sustained development of the surface gale. Together with the development of lowlevel mesocyclones, the air pressure decreased rapidly, which was conducive to gale initiation.

Characteristics of Sea Breeze Front Development with Various Synoptic Conditions and Its Impact on Lower Troposphere Ozone Formation

To examine the correlation between the sizes of sea breeze fronts and pollutants under the influence of synoptic fields, a numerical simulation was conducted in the southeast coastal area of the Korean Peninsula, where relatively high concentrations of pollutants occur because of the presence of various kinds of industrial developments. Sea breeze and sea breeze front days during the period 2005 09 were identified using wind profiler data and, according to the results, the number of days were 72 and 53, respectively. When synoptic forcing was weak, sea breeze fronts moved fast both in horizontal fields and in terms of wind velocity, while in the case of strong synoptic forcing, sea breeze fronts remained at the coast or moved slowly due to strong opposing flows. In this case, the sea breeze front development function and horizontal potential temperature difference were larger than with weak synoptic forcing. The ozone concentration that moves together with sea breeze fronts was also formed along the frontal surfaces. Ozone advection and diffusion in the case of strong synoptic forcing was suppressed at the frontal surface and the concentration gradient was large. The vertical distribution of ozone was very low due to the Thermal Internal Boundary Layer （TIBL） being low.

Atypical Occlusion Process Caused by the Merger of a Sea-breeze Front and Gust Front

An atypical occlusion process that occurred in North China on 14 July 2011 is studied based on both observations and a real-data Weather Research and Forecasting （WRF） model simulation. The results show that this atypical occlusion process was significantly different from the traditional, synoptic-scale occlusion process that occurs within extratropical cyclones. It was caused by the merger of two cold-type mesoscale fronts. One of the fronts developed from the gust front of convective storms, while the other was a sea-breeze front. As the two fronts moved towards each other, the warm air between them was squeezed and separated from the surface. An atypical occluded front was formed when the two fronts merged, with the warm air forced aloft. This kind of occlusion is termed a ＂merger＂ process, different from the well-known ＂catch-up＂ and ＂wrap-up＂ processes. Moreover, local convection was found to be enhanced during the merger process, with severe convective weather produced in the merger area.

On Thunderstorm Microphysics under Urban Heat Island, Sea Breeze, and Cold Front Effects in the Metropolitan Area of São Paulo, Brazil

This work discusses issues related to the impact of urbanization on the microphysical processes of precipitating systems associated with synoptic, mesoscale, and local scale systems. Among the issues addressed is the impact of urban heat island (UHI) in São Paulo city center and urban densification (UD) in the Metropolitan Area of São Paulo (MASP) on the microphysical, dynamic, and thermodynamic properties and distribution of precipitation and heavier rainfall from sea-breeze (SB) e cold-front (CF) combined during their space-time evolutions. For this purpose, it used four components: classification of hydrometeors with fuzzy logic, calculation of the raindrop diameters, an estimate of liquid water mass and ice mass from polarimetric-variables measured with dual-pola- rization X-band meteorological radar. The results indicated that urban densification (UD) and heat island (UHI) of the São Paulo city center impact the formation of precipitation, liquid water mass, and ice mass, depth, and duration of a thunderstorm. It was also observed the asymmetric configuration of the thunderstorm is induced by the strong convergence in the São Paulo city center, and this strong convergence is induced by the intense heat island (UHI) in the São Paulo city center. Was also observed that this event that is formed in the Metropolitan Area of São Paulo (MASP) depends on microphysical processes of mixed-phase of the cloud (water and ice) above the 0°C isotherm for the production of intense rain and cold pool at the surface. These important microphysical processes within long-lasting secondary convective cells over the São Paulo city center should be taken into account on convective parameterization schemes as well as the associated cold pool dynamics.

Sea Breeze Front Storm and Its Composite Analysis in Beibu Gulf

[Objective] The aim was to study the sea breeze front storm and its composite analysis in Beibu Gulf. [Method] By dint of routine observation data, ground automatic meteorology data and European numerical mode grid data, rainstorm caused by sea breeze in Guangxi during 1990 and 2007 and the strong convection triggered by sea breeze on June 5 in 2008 were expounded. The main characteristics of the configuration of circulation in the low and high latitude of breeze front of middle scale were summarized. [Result] Sea breeze front storm system was an important middle scale sea breeze front system that triggered storm in the Beibu Gulf. Sea breeze in Beibu Gulf occurred most easily during the southwest monsoon eruption period. Case study pointed out that after sunrise, the continental and island temperature in Beibu Gulf turned from warm-ocean-cold-island into warm-island-cold-ocean. The southerly airstream of high temperature and high humidity met with the relatively low temperature and dry northerly airstream in Beibu Gulf, and triggered vertical circulation and stimulated ground middle scale sea breeze front system. Composite analysis referred to the circulation characteristics of the ocean and continental temperature in Beibu Gulf. The upper air of south China was in strong divergence center. The air pressure was high in the east and low in the west. Beibu Gulf was in the southerly torrent belt in front of the trough and after the latitude in cyclonic circulation convergence area. The strata unstable structure of the divergence in the upper air and the convergence in the lower layer and the 'pumping effect' provided upward dynamics for the ocean circulation development. The southerly brought rich water vapor to the Beibu Gulf, which was conductive to the formation of strong convective cloud system in the lower layer and the generation of precipitation. [Conclusion] The research provided references for the study on the characteristics of middle scale convective system.

The Structure and Evolution of Sea Breezes During the Qingdao Olympics Sailing Test Event in 2006

Using data from automatic surface weather stations, buoys, lidar and Doppler, the diurnal variation and the three-dimensional structure of the sea breezes near the sailing sites of the Good Luck Beijing- 2006 Qingdao International Regatta from 18 to 31 August 2006 are analyzed. Results show that excluding rainy days and days affected by typhoon, the sea breezes occur nearly every day during this period. When Qingdao is located at the edge of the subtropical high at 500 hPa, the sea breeze is usually stronger, around 3-4 m s^-1. It starts at around 1100 to 1300 LST and lasts about 6 hours. The direction of the sea breeze tends to be southeasterly. When Qingdao is under the control of the subtropical high, the sea breeze is usually weaker, less than 2.5 m s^-1 throughout the day, and begins later, between 1300 and 1500 LST. In this case, the direction of the sea breeze is variable from easterly to southeasterly. Most sea breezes in Qingdao are very shallow, up to 300 meters deep. Strong sea breezes can reach 1.5 km in depth and can push as far as 100 km inland. If the Huanghai sea breeze moves inland and meets the sea breeze of the Jiaozhou Bay in the western part of Qingdao, the sea breeze will strengthen and form three boundaries due to the interaction of the two sea breezes.

A Case Modeling of Sea-Land Breeze in Macao and Its Neighborhood

PSU / NCAR MM5 was utilized to simulate the sea-land breeze circulation in Macao and the three-dimensional flow around the Pearl River estuary. Four two-way nested grids having resolution of 1, 3, 9, and 27 km were included in the simulation. It was initialized with conventional observational data, and a 30 h simulation and analysis of one sea-land breeze case were performed. It was shown, that the model with a finer resolution (1 km) captures the sea breeze and land breeze in Macao with reasonable skill. The sea breeze front and the thermal internal boundary layer (TIBL) were also obviously revealed. However, the coarser horizontal resolution (3 km) could capture the sea breeze but not the land breeze.

Numerical Simulations of a Florida Sea Breeze and Its Interactions with Associated Convection:Effects of Geophysical Representation and Model Resolution

The Florida peninsula in the USA has a frequent occurrence of sea breeze(SB)thunderstorms.In this study,the numerical simulation of a Florida SB and its associated convective initiation(CI)is simulated using the mesoscale community Weather Research and Forecasting(WRF)model in one-way nested domains at different horizontal resolutions.Results are compared with observations to examine the accuracy of model-simulated SB convection and factors that influence SB CI within the simulation.It is found that the WRF model can realistically reproduce the observed SB CI.Differences are found in the timing,location,and intensity of the convective cells at different domains with various spatial resolutions.With increasing spatial resolution,the simulation improvements are manifested mainly in the timing of CI and the orientation of the convection after the sea breeze front(SBF)merger into the squall line over the peninsula.Diagnoses indicate that accurate representation of geophysical variables(e.g.,coastline and bay shape,small lakes measuring 10-30 km2),better resolved by the high resolution,play a significant role in improving the simulations.The geophysical variables,together with the high resolution,impact the location and timing of SB CI due to changes in low-level atmospheric convergence and surface sensible heating.More importantly,they enable Florida lakes(30 km2 and larger)to produce noticeable lake breezes(LBs)that collide with the SBFs to produce CI.Furthermore,they also help the model reproduce a stronger convective squall line caused by merging SBs,leading to more accurate locations of postfrontal convective systems.

NUMERICAL EXPERIMENTS ON THE TIBL PROFILES AND THE LOCAL SEA BREEZE CIRCULATION IN COASTAL AREAS

A two-dimensional nonlinear PBL numerical model using an energy closure (E-ε)method has been employed to study the sea breeze circulation and TIBL in coastal areas. The main characteristics of sea breeze obtained from numerical experiments agree with those from general observation facts. The depth of sea breeze ranges from 300 to 900 meters, maximum velocity from 1,5 m/s to 4 m/s, and its height from 100 m to 300 m. The agreement between comparisons reveals that the performance of the model is good, and the selected experiment conditions are reasonable. This paper refits the function of TIBL profiles using the Weisman’s formula and the exponent value is considered to change with the different states of sea breeze. Numerical experiment results indicate that the exponent of the TIBL profile, ranging from 0.4 to 1. 1, is related to the strength and depth of the sea breeze. The exponent of 0.5 is suitable only when sea breeze is fully developed. This paper also gives various exponents under different sea breezes.

The sea/land breeze in the northern coastal area of Shandong Peninsula

In this paper the seasonal variation and structural characteristics of the sea/ land breeze in the northern coastal area of' Shandong Peninsula are studied in two ways: one is the analysis of the observed wind data, and the other is numerical simulation and experiments. Firstly, the hour to hour wind data through the year 1984 at Longkou Meteorological Station and Yantai Oceanographic Station are analysed through energy spectra and hodograph. It is revealed from the analysed results that the effects of the sea/ land breeze in the area are notable in spring, summer and fall, especially in May. However, in winter the effects of sea / land breeze are not obvious. because the cold noitherly is prevailing. Secondly, a two-dimensional non- linear model of primitive equations is used to study the sea / land breeze circulation in May in the area. The results of numerical simulation consist basically with the analysed results of the observed sea / land breeze. A reasonable theoretical structure of the sea / land breeze circulation is displayed, and a new undeerslanding of the developmental mechanism of land breeze circulation in that area is obtained. Lastly, numerical experiments about the effects of large scale wind and temperature fields upon the sea / land breeze circulation are performed.

Analytic Study of Sea-Land Breezes

An analytic study of the structure of sea-land breezes is presented, with special attention paid to the dependence on the model parameters. In this linearized model, the wind speed of the sea-land breezes is directly proportional to the difference of sea and land heating rates. For the same differential heating, the sea-land breeze is more prominent if the stratification is weakly stable, or if the frictional force is small. The horizontal penetration from the coast is also investigated, and found to be asymmetric between the land and the sea. The above results are in agreement with observation.

Seasonal Behavior of Aerosol Vertical Concentration in Dakar and Role Played by the Sea-Breeze

The Westward transport of mineral dust from the North Africa continent to Atlantic Ocean can produce poor air quality, low visibilities, and negatively impacting respiratory and cardiac health due to the optical and physical properties of aerosols. The dynamical impact of the sea-breeze on the dust vertical distribution in West Africa remains unknown. To investigate this issue, we have used in-situ measurements from lidar. We have focused on the attenuated backscatter of aerosols to study the effect of the local circulation on the vertical profile of mineral dust at land-sea transition. The results highlight a strong diurnal cycle of mineral dust associated with the nocturnal low-level jet (NLLJ). The jet is located between 500 m and 1000 m and crucially affected by the dynamic of the sea-breeze circulation.

Method for Evaluating the Influence of Obstruction of Sea Breeze by Clusters of High-Rise Buildings on the Urban Heat Island Effect

This study aims to propose a method for quantitatively evaluating the influence which the obstruction of sea breezes by clusters of high-rise buildings has on the urban heat island effect using a weather simulation model and Geographic Information Systems (GIS). Specifically, a method of evaluating the influence of the obstruction of sea breeze by high-rise buildings on the urban heat island effect was proposed. In the method, two scenarios that imagine urban forms which differ with regard to whether or not they contain high-rise buildings are created and weather simulation is conducted, and the results of the simulations are comparatively analyzed focusing on temperature and wind speed. Evaluation was conducted in two stages, and Shiodome of Minato City in the Tokyo Metropolis was selected as the region for evaluation. In two stages of evaluation, a rise in temperature of approximately 0.3 K and a reduction in wind speed of approximately 1 m/s were observed in a region approximately five to ten kilometers square downwind of high-rise buildings in the period 6 PM to 9 PM, and a higher temperature caused by the obstruction of sea breeze by high-rise buildings was identified. The fact that such a higher temperature was confirmed in the time period from 6 PM onwards, in which the temperature decreases, reveals that obstruction of sea breeze by high-rise buildings dulls the decrease in temperature which occurs from evening onwards, and influences nighttime urban heat island formation.

Land-sea breeze circulation structure on the west coast of the Yellow Sea,China

Land-sea breeze(LSB)is an atmospheric mesoscale circulation that occurs in the vicinity of the coast and is caused by uneven heating resulting from the difference in specific heat capacity between the sea and land surfaces.The circulation structure of LSB was quantitatively investigated with a Doppler wind lidar Windcube100s on the west coast of the Yellow Sea for the first time.The time of observation was 31 August to 28 September 2018.It was found that the height of LSB development was 700 m to 1300 m.The duration of conversion of LSB was between 6 h and 8 h.The biggest average horizontal sea-breeze wind speed at 425 m was 5.6 m s^(-1),and at 375 m it was 4.5 m s^(-1).During the conversion process from sea breeze to land breeze,the maximum wind shear exponent was 2.84 at 1300 m altitude.During the conversion process from land breeze to sea breeze,the maximum wind shear exponent was 1.28 at 700 m altitude.The differences in wind shear exponents between sea-breeze and landbreeze systems were between 0.2 and 3.6 at the same altitude.The maximum value of the wind shear exponent can reflect the height of LSB development.

The Anatomy of the South Carolina U.S.A. Coastal Sea Breeze 2019-2020

The study presented herein is the analysis of Sodar based instrument measurements of air temperature, dew point, and vertical wind speed and direction, recorded at two South Carolina sites, Waties Island in North Myrtle Beach and in Sumter, and at three atmospheric ground stations. Two of the ground stations are National Weather Service stations near the Sodars and one is a Coastal Carolina University Sea-Econet, as a part of the National Oceanic & Atmospheric Administration, MESO program, weather-sensor site on the Coastal Carolina University campus in Conway South Carolina. Objectives of this study are to establish specific values of winds, land and sea temperatures, precipitation and dew points associated with the changes induced by passages of the Sea Breeze Front, and to examine differences in the station-to-station incarnation of the Sea Breeze circulation. Variability from station to station in the nature and timing of Sea Breeze Front passage is found to be a function of relative proximity to the coast with Sea Breeze Front passage occurring earliest at the North Myrtle Beach site (the station at the coast), then at Sumter (~100 km inland) and finally Aiken at >100 km inland. Satellite based estimates of the percentages of onshore penetration distances from the coast are depicted. Wind vectors and air temperatures associated with onsets and passages of the Sea Breeze display robust wind fields directed onshore perpendicular to the coastline. Kinematical descriptors of the Sea Breeze wind particle motions are presented and display coherent stable elliptical motions during the late summer to early fall but are absent during the winter.

The research of sea-land breeze (SLB) on the west coast of Bohai Bay based on field observation

Four automatic meteorological stations were set up in a line from beach to inland perpendicular to the west coast of Bohai Bay. Wind direction and velocity at altitudes of 2 m, 4 m and 12 m were surveyed with 10 minute intervals. On ＂Sea-Land Breeze＂ （SLB） days, the transition from sea breeze to land breeze was very evident in the study area. Direction of sea breeze was basically perpendicular to the coast and mainly from the ENE and E. Duration of sea breeze varied by the stations＇ distance to the coastline, and the near-coast wind velocity was larger than that of the inland and decreases as it reaches inland. There was increased development of SLB on sunny days than on overcast days. The term ＂Climatic Coastal Zone＂ can be defined for the area influenced by SLB, which reaches more than 74 km inland on a typical SLB day but less than 10 km on a non-typical SLB day.

海南岛土地覆盖变化对海风锋结构演变影响的数值模拟

本文利用WRF-Noah陆气耦合中尺度模式,针对海南岛一次典型的海风锋事件进行了高分辨率的数值模拟,研究了海南岛土地覆盖(下垫面)变化对海风锋结构演变的影响及其机制。结果表明,海南岛土地覆盖变化对海风锋的作用是通过多种地表和植被属性的综合影响决定的。森林化试验中动力和热力作用分别抑制和促进海风锋的发展,对海风锋的影响是两者共同作用的结果;反照率的减小引起净辐射的增大,从而使感热通量小幅增加,使低层大气增温而增加海陆温度梯度,这在一定程度上增强了海风驱动力,但地表粗糙度的增大减弱了海风风速,进一步减弱了海风锋传播距离和上升速度。然而,由于海南岛森林覆盖面积较大,导致森林化试验与控制试验中海风锋的整体差异较小。相比之下,荒漠化试验中热力和动力作用均有利于海风锋的发展;反照率的增大和叶面积指数的降低,改变了地表能量分配,造成潜热通量显著减小,感热通量先减少后增大,对低层大气的增温效应非常明显,从而加大了海陆温度梯度。另一方面,地表粗糙度显著减小,下垫面对海风的阻挡作用减弱,海风风速增大。因此,荒漠化试验海风锋传播距离、上升速度以及海风厚度都显著增大。

弱天气背景下天津三次局地突发暴雨中尺度特征及触发机制

利用ERA5再分析(0.25°×0.25°)、加密自动气象站、多普勒天气雷达和变分多普勒天气雷达分析系统等高时空分辨率资料,对比分析了2018年7月22日、2019年7月18日、2021年8月23日天津中心城区三次局地突发性暴雨过程的中尺度特征及其触发机制。结果表明:三次局地突发性强降雨均无明显天气尺度系统主导,但环境大气具备较高的对流不稳定能量和较小的对流抑制能量,抬升凝结高度仅0.2~0.4 km,且低层均存在一定的湿层。局地突发性暴雨的发生与城市热岛及海陆下垫面特征差异造成的中小尺度系统有关,暴雨发生前天津中心城区与沿海地区之间的温差和气压差增大,中心城区附近温压场具有明显的非均匀分布特性,中尺度暖低压及其东侧的高温度梯度为局地对流发生提供了有利的中尺度环境条件。此外,暴雨发生前沿海地区均出现了明显的海风加强,城市热岛暖低压辐合与海风风速辐合共同作用使得中尺度辐合强度明显加强,是局地突发性暴雨发生的主要原因,初生的γ中尺度对流单体均位于地面强辐合中心边缘上空。

海南岛沿海城镇化对海风锋推进影响的数值模拟

本文利用中尺度模式WRF-ARW(Weather Research and Forecasting Model-Advanced Research WRF)(Version 4.0)对海南岛不同天气条件下的典型海风锋个例进行了高分辨率数值模拟,通过设计局地城镇化的敏感性试验,重点分析了海南岛沿海城镇化对海风锋推进的影响及其可能机制。研究结果表明:海南岛沿海城镇化造成的海风锋结构差异是热力作用和动力作用共同影响的结果;城镇下垫面的摩擦效应与城市热岛的增强阻碍海风向内陆推进,减弱了海风锋途经地区的降温增湿效应,造成海风锋位置相对滞后;而城镇化所引起的高海陆热力差异增强了海风风速及海风辐合,同时导致海风锋前的垂直上升气流和海风环流厚度也明显增强。海风锋发展不同时期,城镇化对海风锋的推进影响有所不同。海风锋发展初期,海陆热力差异引起的推动作用与摩擦效应的阻碍作用相抵消,导致海风锋的推进无明显影响;海风锋发展强盛阶段,城镇化条件下内陆城市与非城市之间的热力差异有所增强,阻碍了海风锋向内陆推进,导致海风锋内陆渗透距离减小。不同天气条件下城市化对海风锋推进的影响有所不同,相比于晴空天气,多云天气下城市与非城市的热力差异稍强,加强了城市热岛效应对海风推进的阻碍作用,导致海风锋滞后距离稍远。此外,当土地利用类型更换为城镇后,净辐射与陆气间交换能量减少,导致其潜热通量显著减小,感热通量值变大,从而升高了下垫面温度,增强了海风的垂直上升运动,进而造成边界层高度的升高。

渤海湾海陆风环流及臭氧特征分析

利用2023年夏季在乐亭县开展的观测实验数据和相关气象数据及环境数据,分析渤海湾地区海陆风环流及其对臭氧污染的影响。结果表明,海陆风环流可以影响臭氧在海陆间输送,可能导致渤海湾上空及沿海地区臭氧污染。HYSPLIT后向轨迹模拟解析共有5条主要气团轨迹影响到实验观测地区,其中有2条偏南方向气团通过短距离输送进入实验地区,对该区域的臭氧污染贡献率高达65%。