Sea-breeze scaling from numerical model simulations,Part I: Pure sea breezes

Numerical model simulations of sea-breeze circulations under idealized conditions are subjected to dimensional analyses in order to resolve sea-breeze dynamical relations and unify previous results based on observations. The analysis is motivated by the fact that sea-breeze depth scaling and volume flux scaling are only partially understood. The analysis is based on nonlinear numerical modelling simulations in combination with recent observational scaling analyses. The analysis confirms scaling laws for sea-breeze strength dependence on governing variables and shows how the sea-breeze speed scale is controlled by surface heat flux. It also shows that the sea-breeze depth scale is controlled by stability. By combining sea-breeze speed and depth scales, the sea-breeze volume flux scale is determined by an equilibrium between the accumulated convergence of heat over land since sunrise and stable air advection from the sea surface.     

Scaling the Vertical Structure of Sea Breezes

This analysis presents a new set of scalings for sea-breeze circulations. The scales are based on surface-layer turbulent fluxes of sensible heat and momentum, thus avoiding the use of exchange coefficients. Nondimensionalization of the governing equations, using the new scales, results in four dimensionless governing parameters, two of which are new. A data set consisting of 36 profiles of atmospheric variables during pure sea-breeze circulations is presented. The data are used to generate scaling laws for dimensionless sea-breeze depth and strength in the form of products of powers of the governing dimensionless parameters. These scaling laws are used to nondimensionalize individual velocity profiles, which are composited to present a universal dimensionless sea-breeze velocity profile. The scaling laws, applied as a diagnostic scheme, are used to investigate the diurnal evolution of the depth and strength of sea breezes.     

Impacts of topography and land degradation on the sea breeze over eastern Spain

Summary A three-dimensional non-hydrostatic atmospheric model RAMS, version3b, is used to examine the impact of complex topography on the sea breeze under heterogeneous and degradation land use characteristics. In the study, it is shown that topography plays an important role in the sea-breeze circulation by aligning the sea breeze front to the coastline and locating the convergence zones close to the mountain range. When the sea breeze is coupled with the upslope wind, the sea-breeze circulation is strengthened by the topography.Sensitivity analyses are carried out to determine the influence of vegetation and soil moisture, i.e., land surface modifications, to this thermally driven flow. Land degradation results in an enhanced sea-breeze circulation which is characterized by a stronger onshore flow, a stronger return current, a larger updraft velocity associated with the sea-breeze front and further inland penetration. Other important features are a deeper sea-breeze depth, a larger downdraft velocity behind the sea-breeze front, and a longer offshore extent. The results also show how land changes modify the sea breeze temporal evolution resulting in an earlier onset and later end. The study stresses the convenience of using three-dimensional models with detailed land surface information to model the sea breeze in complex terrain where land use is rapidly modified.Received February 25, 2002; accepted October 7, 2002 Published online April 10, 2003     

Impact of the Rhône and Durance valleys on sea-breeze circulation in the Marseille area

Sea-breeze dynamics in the Marseille area, in the south of France, is investigated in the framework of the ESCOMPTE experiment conducted during summer 2001 in order to evaluate the role of thermal circulations on pollutant transport and ventilation. Under particular attention in this paper is the sea-breeze channelling by the broad Rhône valley and the narrow Durance valley, both oriented nearly-north–south, i.e., perpendicular to the coastline, and its possible impact on the sea-breeze penetration, intensity and depth, which are key information for air pollution issues. One situation of slight synoptic pressure gradient leading to a northerly flow in the Rhône valley (25 June 2001) and one situation of a weak onshore prevailing synoptic wind (26 June 2001) are compared. The impact of the Rhône and Durance valleys on the sea-breeze dynamics on these two typical days is generalized to the whole ESCOMPTE observing period.The present study shows by combining simple scaling analysis with wind data from meteorological surface stations and Doppler lidars that (i) the Durance valley always affects the sea breeze by accelerating the flow. A consequence is that the Durance valley contributes to weaken the temperature gradient along the valley and thus the sea-breeze circulation. In some cases, the acceleration of the channelled flow in the Durance valley suppresses the sea-breeze flow by temperature gradient inhibition; (ii) the Rhône valley does not generally affect the sea breeze significantly. However, if the sea breeze is combined with an onshore flow, it leads to further penetration inland and intensification of the low-level southerly flow. In this situation, lateral constriction may accelerate the sea breeze. Simple scaling analysis suggests that Saint Paul (44.35°N, about 100 km from the coastline) is the lower limit where sea breeze can be affected by the Rhône valley. These conclusions have implications in air quality topics as channelled sea breeze may advect far inland pollutants which may be incorporated into long-range transport, particularly in the Durance valley.     

中国黄海西岸海陆风循环结构研究

陆海风是由于海陆表面之间的比热容不同而导致的昼夜热量分布差异,从而在海岸附近引发的大气中尺度循环系统.本文利用多普勒风激光雷达Windcube100s首次对黄海西海岸的海陆风的循环结构进行了观测研究.在2018年8月31日至9月28日观测期间发现,海陆风发展高度一般在700 m至1300 m.海陆风转化持续的时间为6小时至8小时.在425m高度,海风水平风速出现最大值,平均为5.6 m s-1.陆风最大水平风速出现在370m,约为4.5 m s-1.最大风切变指数在1300m处,为2.84;在陆风向海风转换过程中,最大风切变指数在700m处,为1.28.在同一高度上,风切变指数在海风盛行和陆风盛行时的差值范围为0.2-3.6,风切变能反映出海陆风的发展高度.     

Mesoscale model response to random,surface-based perturbations — A sea-breeze experiment

The introduction into a mesoscale model of random (in space) variations in roughness length, or random (in space and time) surface perturbations of temperature and friction velocity, produces a measurable, but barely significant, response in the simulated flow dynamics of the lower atmosphere. The perturbations are an attempt to include the effects of sub-grid variability into the ensemble-mean parameterization schemes used in many numerical models. Their magnitude is set in our experiments by appeal to real-world observations of the spatial variations in roughness length and daytime surface temperature over the land on horizontal scales of one to several tens of kilometers. With sea-breeze simulations, comparisons of a number of realizations forced by roughness-length and surface-temperature perturbations with the standard simulation reveal no significant change in ensemble mean statistics, and only small changes in the sea-breeze vertical velocity. Changes in the updraft velocity for individual runs, of up to several cms^-1 (compared to a mean of 14 cms^-1), are directly the result of prefrontal temperature changes of 0.1 to 0.2K, produced by the random surface forcing. The correlation and magnitude of the changes are entirely consistent with a gravity-current interpretation of the sea breeze.     

Sea-breeze scaling from numerical model simulations,part II: Interaction between the sea breeze and slope flows

Numerical model simulations of sea-breeze circulations in the presence of idealized topography are subjected to dimensional analysis in order to capture the dynamics of the sea-breeze circulation combined with an upslope-flow circulation. A secondary objective is to reconcile previous results based on observations. The analysis is based on a scaling analysis of sea-breeze speed, depth and volume flux. This study is motivated by the fact that the literature of sea breezes interacting with upslope flows is generally qualitative. Results show clear scaling regimes and strong interaction between the two thermally driven circulations. We distinguish three regimes, depending on slope length, slope angle, stability and surface heat flux. The first and third regimes obey the scaling laws of pure sea-breeze scaling. The second regime shows a significant decrease in the scaled volume flux relative to pure sea-breeze scaling. Dynamical relations in the second regime show a strong influence on the circulation of upslope stable air advection.     

Modelling Local Sea-Breeze Flow and Associated Dispersion Patterns Over a Coastal Area in North-East Spain: A Case Study

The structure and evolution of the sea breeze in the north-west part of the Mediterranean (Catalonia, north-east Spain) is studied both experimentally and, predominantly, using numerical models to increase understanding of sea-breeze structure and three-dimensional (3D) pollution distributions in coastal environments. Sea-breeze components are modelled and analyzed using the fifth-generation Pennsylvania State University–National Centre for Atmospheric Research Mesoscale Model (MM5). The results show that the growth and structure of the sea-breeze circulation is modulated by the synoptic flow and especially by the complex topography of the area. 3D pollution transport in a sea breeze is modelled by coupling the MM5 to the Community Multiscale Air Quality (CMAQ) model, with results indicating that topography and synoptic flow are the main factors modulating horizontal and vertical pollutant transport in sea-breeze episodes. In this way, horizontal dispersion is limited by the complex topography of the area, whilst the sea-breeze flow is intensified by anabatic upslope winds that contribute to vertical pollutant transport. The numerical model results also indicate that the sea-breeze circulation with a weak return flow at upper levels grows due to a synoptic onshore wind component. However, such a sea-breeze circulation is capable of transporting pollutants towards the coast.     

Seasonal Cycle of the Near-Surface Diurnal Wind Field Over the Bay of La Paz,Mexico

The results of numerical simulations of the troposphere over the Bay of La Paz, calculated for the months of January, April, July and October during the period 2006–2010 with the Weather Research and Forecast (WRF v3.5) regional model, are used to describe the seasonal features of the diurnal cycle of planetary boundary-layer winds. Two distinct near-surface diurnal flows with strong seasonal variability were identified: (1) a nocturnal and matutinal breeze directed from the subtropical Pacific Ocean, over the Baja California peninsula and the Bay of La Paz, into the Gulf of California that is associated with the regional sea-surface temperature difference between those two major water bodies; and (2) a mid to late afternoon onshore sea-breeze related to the peninsula’s daily cycle of insolation heating that evolves with counter-clockwise rotation over the Bay of La Paz. The model results reveal the interaction over Baja California of opposing afternoon sea-breeze fronts that originate from the subtropical Pacific Ocean and the Gulf of California, with a convergence line forming over the peaks of the peninsula’s topography and the associated presence of a closed vertical circulation cell over the Bay of La Paz and the adjacent Gulf. The collision of the opposing sea-breeze fronts over the narrow peninsula drives convection that is relatively weak due to the reduced heat source and only appears to produce precipitation sporadically. The spatial structure of the sea-breeze fronts over the Bay of La Paz region is complex due to shoreline curvature and nearby topographic features. A comparison of the numerical results with available meteorological near-surface observations indicates that the modelling methodology adequately reproduced the observed features of the seasonal variability of the local planetary boundary-layer diurnal wind cycle and confirms that the low-level atmospheric circulation over the Bay of La Paz is dominated by kinetic energy in the diurnal band. The strongest (weakest) diurnal flows occur during the summer (winter) in response to the seasonally varying magnitudes of the daily land–sea thermal contrast and the regional subtropical Pacific Ocean–Gulf of California sea-surface temperature difference.     

Investigation on the fine structure of sea-breeze during ESCOMPTE experiment

Surface and remote-sensing instruments deployed during ESCOMPTE experiment over the Marseille area, along the Mediterranean coast, were used to investigate the fine structure of the atmospheric boundary layer (ABL) during sea-breeze circulation in relation to pollutant transport and diffusion. Six sea-breeze events are analyzed with a particular focus on 25 June 2001.Advection of cool and humid marine air over land has a profound influence on the daytime ABL characteristics. This impact decreases rapidly with the inland distance from the sea. Nearby the coast (3 km inland), the mixing height Zi rises up to 750 m and falls down after 15:00 (UT) when the breeze flow reaches its maximum intensity. A more classical evolution of the ABL is observed at only 11-km inland where Zi culminates in the morning and stabilizes in the afternoon at about 1000 m height.Fine inspection of the data revealed an oscillation of the sea-breeze with a period about 2 h 47 min. This feature, clearly discernable for 3 days at least, is present in several atmospheric variables such as wind, temperature, not only at the ground but also aloft in the ABL as observed by sodar/RASS and UHF wind profilers. In particular, the mixing height Zi deduced from UHF profilers observations is affected also by the same periodicity. This pulsated sea-breeze is observed principally above Marseille and, at the northern and eastern shores of the Berre pond.In summary, the periodic intrusion over land of cool marine air modifies the structure of the ABL in the vicinity of the coast from the point of view of stability, turbulent motions and pollutants concentration. An explanation of the source of this pulsated sea-breeze is suggested.     

Numerical Simulations of the Impacts of Land-Cover Change on a Southern Sea Breeze in South-West Western Australia

A sea-breeze event in south-west Western Australia is simulated using the Regional Atmospheric Modelling System (RAMS) version 6.0. The model is evaluated against high resolution soundings as well as station observations and is shown to reproduce the qualitative features of the sea breeze well. Sensitivity tests are carried out to investigate the effects of historical land-cover change and changes in soil moisture on the dynamics of the sea breeze. It is found that land-cover change alone, i.e., a change from wooded grasslands to bare soil, with no change in soil moisture initialisation, does not significantly alter the overall structure of the sea breeze but results in higher surface winds due to the reduced vegetation roughness length, which leads to enhanced surface moisture advection inland. On the other hand, land-cover change in conjunction with increased soil moisture results in a considerably weaker, shallower, and less penetrative sea breeze, and delays its onset and duration. A sea-breeze scaling analysis highlights the impact of increasing soil moisture on reducing the sea-breeze volume flux scale.     

两种反映东亚夏季风异常的指数的比较研究

本文利用文献^ [4]提出的一种新的反映东亚夏季风异常的海陆温差指数分析了夏季风异常时我国气温、降水异常以及东亚环流状况，通过分析指出，东亚夏季风偏强，则中国东部夏季气温偏高，江淮干旱，华北多雨；夏季风偏弱则夏季气温偏低，江淮多雨，易涝，华北少雨。通过两种夏季风指数的对比，海陆温差指数能更好地反映东亚夏季环流及天气气候异常。文中还指出，海陆温差指数能更好的反映夏季风异常的原因是它的定义方法更科学，更全面的反映东亚海陆热力差异，既包含了东亚纬向海陆热力差异的影响，又考虑了东亚经向海陆热力差异的因素，并用地表气温和海表温度差来表示海陆热力差，好于以往用海平面气压差来反映海陆热力差。     

Scaling of the Sea-Breeze Strength with Observations in the Netherlands

In this study we evaluate recently proposed scaling relations for the sea-breeze strength using independent data for a relatively homogeneous area in The Netherlands. We show that several of the scaling relations in the literature incorporate hidden correlation. Furthermore, it appears that the estimate for the sea-breeze strength is better made on the basis of the time-integrated rather than of the instantaneous sensible heat flux. It also turns out that for similar forcing the sea breeze in The Netherlands is about twice as strong as the sea breeze in the Vancouver area of Canada.     

Flow and transport modeling in the sea-breeze part II: Flow model application and pollutant transport

A modifiedE- non-hydrostatic model with non-equilibrium level 2.5 closure was applied to the flow and pollutant dynamics in the sea-breeze. The model predicts key observed characteristics of the sea-breeze, such as midday slowing of inland penetration, fast and deep inland penetration in late afternoon, and detachment of the sea-breeze from the feeding flow in early evening. In late evening when the turbulent mixing over the land subsides due to the surface cooling, a frontal density current is formed and the predicted structure is in good agreement with observations and laboratory experiments of density currents. Turbulent mixing over the land is a key parameter that controls midday slowing and late afternoon frontal development.The calculated thermal internal boundary layer and fumigation of an elevated line source show good agreement with observations and similarity theory. Calculations suggest that the residual plume aloft over the sea returns onshore at ground level during the afternoon sea-breeze and has a large impact on ground-level concentrations during the following day.     

A complete sea-breeze circulation cell derived from aircraft observations

Using an instrumented aircraft, a complete sea-breeze circulation cell was sampled from its offshore end to the sea-breeze front over land and up to a height of approximately 1000 m AMSL. Many of its typical features can be resolved in detail mainly by cross-sectional analysis. These are: the diverging onshore flow in the lower layers over the sea the convergence over land at the seabreeze front and the connected cross-frontal circulation, a distinct return flow in the upper layers, the propagation of the seaward end of the cell over water, as well as the propagation of the front over land, the baroclinicity as a driving mechanism of the cell and also budget and frontogenesis terms.     

Idealized Large-Eddy Simulations of Sea and Lake Breezes: Sensitivity to Lake Diameter, Heat Flux and Stability

Idealized large-eddy simulations of lake and sea breezes are conducted to determine the sensitivity of these thermally-driven circulations to variations in the land-surface sensible heat flux and initial atmospheric stability. The lake-breeze and sea-breeze metrics of horizontal wind speed, horizontal extent, and depth are assessed. Modelled asymmetries about the coastline in the horizontal extent of the low-level onshore flow are found to vary as a function of the heat flux and stability. Small lake breezes develop similarly to sea breezes in the morning, but have a significantly weaker horizontal wind-speed component and a smaller horizontal extent than sea breezes in the afternoon.     

Scaling the Vertical Structure of Sea Breezes Revisited

The sea-breeze scaling of Steynis extended by incorporating data fromtwo additional locations. This is done primarily to remove concerns that the original scaling laws contain featuresspecific to the Vancouver data upon which they were based. This new analysis also employs the integrated, ratherthan instantaneous, heat flux proposed by Tijm. The analysis results in well-defined scaling laws for allthree locations, and include explicit latitude dependence, which was not possible in the earlier study. The integratedheat flux reveals systematic diurnal behaviour that is shown to result in a separate scaling law for diurnalevolution of sea breezes at a single location.     

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     

南海及其邻近地区夏季风爆发的特征及其机制的初步研究

利用ＯＬＲ和ＴＢＢ资料,提出一个指标,确定了１９７５～１９９３年间南海夏季风爆发日期,发现与风向转变的日期比较一致。在此基础上,讨论了南海夏季风爆发的过程。随后,还讨论了南海夏季风爆发与海温异常、高原热状况和海陆温差变化的关系,发现它与４月份南海、东太平洋赤道以及３０～４０°ＮＳＳＴＡ有关,与海陆温差由冬季的冷陆暖海转变到热陆冷海有关。     

Convective characteristics of the nocturnal urban boundary layer as observed with Doppler sodar and Raman lidar

Convective plume patterns, characteristic of clear sky and light wind daytime boundary layers over land, were observed for two nights with a tri-axial Doppler sodar operated in the central area of Rome during the summer of 1994. An urban heat island effect, combined with a continuation of a breeze from the sea late into night during both days, is believed to be responsible for the observed nocturnal convection. Estimates of the surface heat flux and the vertical velocity scaling parameter are obtained from profiles of vertical velocity variance, and the Raman lidar water vapor measurements are used to obtain the humidity scaling parameter. Convective scaling results for vertical wind and humidity fairly agree with the results of other experiments and models. On the basis of available measurements, it appears that mixed-layer similarity formulations used to characterize the daytime convective boundary layer over horizontally homogeneous surfaces can also be applied to the nocturnal urban boundary layer during periods of reasonable convective activity.