Sea Breeze Events Research Articles

Coastal and synoptic recirculation affecting air pollutants dispersion: A numerical study

This study examines the spatial distribution of potential recirculation over the East Mediterranean Sea, and the combined effect of synoptic and meso-scale recirculations on plume dispersion in the region. For this purpose, three case studies are performed by the RAMS–HYPACT modeling system, each for a different synoptic scale flow pattern. Both a quantitative measure of the recirculation potential at each grid cell and particle dispersion are calculated. Although the recirculation index is an Eulerian quantity for the wind field and plume dispersion is a manifestation of the Lagrangian behavior of the wind, good correlation is found between the two. Several locations are identified as having high recirculation potential, including southern Cyprus, the coasts of Israel and Lebanon, the eastern slopes of the Judean Mountains and the Haifa Bay in particular. In the latter location, high recirculation potential could be explained by strong interaction between the land–sea surfaces, curvature of the bay and proximity of the Carmel ridge. It is shown that the synoptic and meso-scale recirculations may, under certain conditions, act together and at the same time in determining particle distribution. Under weak synoptic scale flows, particles are recirculated over the entire East Mediterranean Sea basin, returning onshore after a period of 2–3 days to join freshly emitted particles. At the same time, near-shore land–sea breeze effects cause particles to recirculate on smaller time scales of less then one day, sometimes passing as much as three times over the same airshed. A single elevated emission source is shown to have the potential to impair air quality at a coastal strip as long as 100–200 km upon returning onshore.

Viticultural terroirs in Stellenbosch, South Africa. I. The identification of natural terroir units

<p style="text-align: justify;"><strong>Aims</strong>: A natural terroir unit (NTU) can be defined as a unit of land that is characterized by relatively homogenous topography, climate, geological substrate and soil. The mapping of NTUs is the first stage of data acquisition in a terroir study. This study aimed to identify NTUs using a Geographic Information System and to characterize the Stellenbosch Wine of Origin District using existing digital information at the scale of a wine producing district.</p><p style="text-align: justify;"><strong>Methods and results</strong>: The study area is bordered by mountains, situated close to the Atlantic Ocean and bisected by the Eerste river valley, resulting in notable spatial variation of all climatic parameters. The geology is complex due to the high degree of tectonic movement and mixing of parent material. Terrain morphological units, altitude, aspect and soil type were used as primary keys/variables for the identification of NTUs. Each of the identified units was further described with respect to the extent of the expected sea breeze effect and, for certain of the soil types, the associated parent material. A total of 1389 NTUs were identified in the Stellenbosch Wine of Origin District.</p><p style="text-align: justify;"><strong>Conclusions</strong>: Many of the natural terroir units identified for the Stellenbosch Wine of Origin District are of a size that is not economically or practically viable.</p><p style="text-align: justify;"><strong>Significance and impact of the study</strong>: The natural terroir units should be grouped into larger, more manageable and thus more viable terroir units using data relating their viticultural and oenological potential. This task will be addressed in subsequent companion papers.</p>

Modeling and Simulation of Notional Future Radar in Non‐Standard Propagation Environments Facilitated by Mesoscale Numerical Weather Prediction Modeling

AbstractNormal near surface radio‐frequency (RF) propagation in the littorals across the land–sea boundary is rare due to the land–sea temperature difference, coastline shape, ground cover, urban density, coastal topography, and soil moisture content. The resulting frequent existence of coastal non‐standard vertical profiles of refractivity and the resulting RF propagation has a profound impact on the performance of Navy ship‐borne radars operating within 100 nm of the shore. In addition, these non‐standard RF propagation conditions are spatio‐temporally inhomogeneous. These spatial and time dependent propagation conditions and the resulting radar engineering implications cannot be revealed by a single vertical profile of refractivity taken near the ship borne radar. The results from single profile analysis techniques provide no spatiotemporal information and may lead to overly conservative radar design. Mesoscale numerical weather prediction (NWP) is a rapidly maturing technology with a strong operational Navy history that can provide a vertical profile of refractivity every 1 km in the battle space and every hour, up to 48 h, in the future. The Sensor Division at NSWCDD has applied mesoscale NWP for the last 2 years to better understand the performance of prototype radar in realistic four‐dimensional (4D) coastal environments. Modern RF parabolic equation models are designed to model specific radar designs and to employ 3D refractivity fields from mesoscale NWP models. This allows for a radar design to be tested in realistic littoral non‐standard atmospheres produced by stable internal boundary layers, sea breeze events, and the more rare sub‐refractive events. Mesoscale NWP is currently qualitative for this purpose, but a research and development program focused on sea testing of prototype radars is described with the purpose of developing a more quantitative mesoscale NWP technology to support radar acquisition, testing, and operations.

Satellite sub-pixel rainfall variability

Rain gauge networks are used to calibrate and validate quantitative precipitation estimation (QPE) methods based on remote sensing, which may be used as data sources for hydrologic models. The typical approach is to adjust (calibrate) or compare (validate) the rainfall in the QPE pixel with the rain gauge located within the pixel. The QPE result represents a mean rainfall over the pixel area, whereas the rainfall from the gauge represents a point, although it is normally assumed to represent some area. In most cases the QPE pixel area is millions of square meter in size. We hypothesize that some rain gauge networks in environments similar to this study (i.e., tropical coastal), which provide only one rain gauge per remote sensing pixel, may lead to error when used to calibrate/validate QPE methods, and that consequently these errors may be propagated throughout hydrologic models. The objective of this paper is to describe a ground-truth rain gauge network located in western Puerto Rico which will be available to test our hypothesis. In this paper we discuss observations from the rain gauge network, but do not present any QPE validation results. In addition to being valuable for validating satellite and radar QPE data, the rain gauge network is being used to test and calibrate atmospheric simulation models and to gain a better understanding of the sea breeze effect and its influence on rainfall. In this study, a large number of storms (> 60) were evaluated between August 2006 and August 2008. The area covered by the rain gauge network was limited to a single GOES-12 pixel (4 km × 4 km). Five-minute and total storm rainfall amounts were spatially variable at the sub-pixel scale. The average storm rainfall from 20% of the 120 possible rain gauge-pairs was found to be significantly different at the 5% of significance level, indicating significant rainfall variation at the sub-pixel scale. The average coefficient of determination (r2), describing the goodness of fit of a linear model relating rain gauge pairs, was 0.365, further suggesting a significant degree of variability at the satellite sub-pixel scale. Although there were several different storm types identified (localized, upper westerly trough, tropical easterly wave, tropical westerly trough, cold front and localized with cold front), there did not appear to be any relationship between storm type and the correlation patterns among the gauges.

A climatological study of the influence of synoptic-scale flows on sea breeze evolution in the Bay of Alicante (Spain)

The focus of this study is on sea breeze (SB) characteristics during May and August in the Bay of Alicante (south-eastern coast of the Iberian Peninsula, IP, Spain) for the period 2000-2005 in relation to dominating synoptic-scale winds. A dataset containing 292 SB events was objectively constructed to study the impact of the daily synoptic winds at 850 hPa on the main characteristics of SBs. The winds were used to designate three major synoptic-scale regimes: offshore, onshore, and coast-parallel flows. The SB features examined include mean lag of the SB passage, wind speed and direction at the time of onset, mean lag of SB cessation, mean duration of SB, mean maximum velocity, and inland propagation of SB. Some of the characteristics had not been previously considered in the literature. It is found that in comparison with onshore synoptic flows, offshore favors the delayed arrival and termination of SBs, resulting in a longer mean duration. Further, they produce the most intense passages, cause a more frequent southeasterly component, and result in a higher SB gust speed and shorter mean inland penetration. Results from coast-parallel flows are also presented. The strength of the large-scale flows plays a major role upon SB parameters, which essentially support other numerical modeling results.

STUDY ON THE EFFECTS OF SEA BREEZE FOR DECREASING URBAN AIR TEMPERATURES IN SUMMER

Recently, it has been desired to mitigate the Urban Heat Island Phenomena. So many studies have taken up the effects of sea breeze to mitigate the Urban Heat Island Phenomena. On the other hand, it is useful to clarify the effects of sea breeze for decreasing urban air temperature to consider the urban environmental design. In this paper, it is analyzed the effects of sea breeze based on the results of long-term multi-point measurements of air temperatures and observed wind conditions. As the results, the following were obtained.-The relations between sea breeze component velocity and air temperature at the measurement point near seashore were considered. As the results, it was clarified a rise of air temperature was decreased with increases of sea breeze component velocity.-The relations of distances from the near seashore, the arrival time of sea breeze on each point and sea breeze components velocity were analyzed. As the results, it was confirmed the relations between the arrival time of sea breeze on each point and sea breeze component velocity have high correlation.-The effects of sea breeze for decreasing urban air temperature were shown as a distribution map. As the results, the effects of sea breeze were clarified spatially and quantitatively.

Urban shading—a design option for the tropics? A study in Colombo, Sri Lanka

AbstractRecent urban microclimate studies in Colombo, Sri Lanka, indicate that the maximum daily temperature within street canyons decreases with increasing height to width (H/W) ratio, but higher H/W ratio negatively affects street‐level wind flow. There is also evidence pointing to the cooling effect of sea breeze. The nocturnal heat island is small in contrast to daytime urban–rural differences. In this paper, we use the software ENVI‐met to simulate the effect of different urban design options on air and surface temperatures, as well as on outdoor thermal comfort. The latter is expressed as the physiologically equivalent temperature (PET), an index based on air and radiant temperatures as well as wind and humidity. It is found that high albedo at street level gives the lowest air temperature during daytime, although the reduction is only about 1 °C. The lowest daytime mean radiant temperatures result from high H/W ratios of streets. This has a positive effect on thermal comfort; the increase of H/W ratio from about 1 to 3 leads to a decrease in PET by about 10 °C. Differences in air and surface temperatures, as well as PET, are small during the night. The results show that strategies that lead to better air temperature mitigation may not necessarily lead to better thermal comfort. However, shade enhancement through increased H/W ratios is clearly capable of significant reductions in PET, and thus, improved outdoor thermal comfort. Consequently, a critical urban design task in the humid tropics will be to guide the rapid urban growth towards efficient ‘shade growth’. Copyright © 2007 Royal Meteorological Society

Regional transport and dilution during high‐pollution episodes in southern France: Summary of findings from the Field Experiment to Constraint Models of Atmospheric Pollution and Emissions Transport (ESCOMPTE)

In the French Mediterranean basin the large city of Marseille and its industrialized suburbs (oil plants in the Fos‐Berre area) are major pollutant sources that cause frequent and hazardous pollution episodes, especially in summer when intense solar heating enhances the photochemical activity and when the sea breeze circulation redistributes pollutants farther north in the countryside. This paper summarizes the findings of 5 years of research on the sea breeze in southern France and related mesoscale transport and dilution of pollutants within the Field Experiment to Constraint Models of Atmospheric Pollution and Emissions Transport (ESCOMPTE) program held in June and July 2001. This paper provides an overview of the experimental and numerical challenges identified before the ESCOMPTE field experiment and summarizes the key findings made in observation, simulation, and theory. We specifically address the role of large‐scale atmospheric circulation to local ozone vertical distribution and the mesoscale processes driving horizontal advection of pollutants and vertical transport and mixing via entrainment at the top of the sea breeze or at the front and venting along the sloped terrain. The crucial importance of the interactions between processes of various spatial and temporal scales is thus highlighted. The advances in numerical modeling and forecasting of sea breeze events and ozone pollution episodes in southern France are also underlined. Finally, we conclude and point out some open research questions needing further investigation.

Local diurnal upwelling driven by sea breezes in northern Monterey Bay

Sea breezes often have significant impacts on nearshore physical and biological processes. We document the effects of a diurnal sea breeze on the nearshore thermal structure and circulation of northern Monterey Bay, California, using an array of moorings during the summer upwelling season in 2006. Moorings were equipped with thermistors and Acoustic Doppler Current Profilers (ADCPs) to measure temperature and currents along the inner shelf in the bay. Temperature and current data were characteristic of traditional regional scale upwelling conditions along the central California coast during the study period. However, large diurnal fluctuations in temperature (up to 5 °C) were observed at all moorings inshore of the 60-m isobath. Examination of tidal, current, temperature, and wind records revealed that the observed temperature fluctuations were the result of local diurnal upwelling, and not a result of nearshore mixing events. Westerly diurnal sea breezes led to offshore Ekman transport of surface waters. Resulting currents in the upper mixed layer were up to 0.10 m s −1 directed offshore during the afternoon upwelling period. Surface water temperatures rapidly decreased in response to offshore advection of surface waters and upwelling of cold, subsurface water, despite occurring in the mid-afternoon during the period of highest solar heat flux. Surface waters then warmed again during the night and early morning as winds relaxed and the upwelling shadow moved back to shore due to an unbalanced onshore pressure gradient. Examination of season-long, moored time series showed that local diurnal upwelling is a common, persistent feature in this location. Local diurnal upwelling may supply nutrients to nearshore kelp beds, and transport larvae to nearshore habitats.

Impact of a sea breeze on the boundary-layer dynamics and the atmospheric stratification in a coastal area of the North Sea

In-situ sodar and lidar measurements were coupled with numerical simulations for studying a sea-breeze event in a flat coastal area of the North Sea. The study's aims included the recognition of the dynamics of a sea-breeze structure, and its effects on the lower troposphere stratification and the three-dimensional (3D) pollutant distribution. A sea breeze was observed with ground-based remote sensing instruments and analysed by means of numerical simulations using the 3D non-hydrostatic atmospheric model Meso-NH. The vertical structure of the lower troposphere was experimentally determined from the lidar and sodar measurements, while numerical simulations focused on the propagation of the sea breeze inland. The sea-breeze front, the headwind, the thermal internal boundary layer, the gravity current and the sea-breeze circulation were observed and analysed. The development of a late stratification was also observed by the lidar and simulated by the model, suggesting the formation of a stable multilayered structure. The transport of passive tracers inside the sea breeze and their redistribution above the gravity current was simulated too. Numerical modelling showed that local pollutants may travel backward to the sea above the gravity current at relatively low speed due to the shearing between the landward gravity current and the seaward synoptic wind. Such dynamic conditions may enhance an accumulation of pollutants above coastal industrial areas.

Impact of a sea breeze event on air pollution at the Eastern Tunisian Coast

In this paper, air pollutants concentrations are analyzed during two sea breeze days (18 July 2004 and 17 September 2005) at the Mediterranean sea, just in front of Sousse (35° 48′ N, 10° 38′ E), Tunisia. During these two cases, we found that Sousse and its suburbs have been contaminated by a nearby coastal power plant emissions of pollutants. On 18 July 2004, onshore synoptic wind was uniform (up to 4 m/s) and roughly perpendicular to the coast and made breeze occurrence easier. The observed wind breeze is about 2 m/s. No return flow was recorded, due to the onshore synoptic wind. During this breeze event, wind direction changed by about 30° to be aligned with power plant and Sousse sites. In these conditions O 3 and SO 2 concentrations were multiplied by a factors 1.5 and 3 respectively. On 17 September 2005, a similar sea breeze wind (2–3 m/s) took place at the region but without significant synoptic wind. Pollutant concentrations are also comparable to those of 18 July 2004. A calm synoptic conditions case (13 July 2004) is also studied and compared with the previous cases.

Investigation of a sea breeze front in an urban environment

AbstractThe dynamics of a sea breeze front interacting with the heavily urbanized New York City area are examined. In addition, we investigate the impact of the urban‐influenced sea breeze front on transport and diffusion of simulated passive tracer plumes. We employ the U. S. Navy's Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS®—a registered trademark of the Naval Research Laboratory) to perform a nested simulation with data assimilation for the sea breeze event of 9 August 2004. Available surface and upper‐air observations are used to validate the simulation. We also perform a sensitivity study in which the urban influence is removed (no‐urban).The sea breeze front has characteristics of a density current, including an elevated head at the leading edge. The density current moves slowly and unevenly across the city. Kelvin–Helmholtz billows form in the region of the density current head, and the results show evidence of the occurrence of Kelvin–Helmholtz instability (KHI). The density current head is greatly elevated owing to the enhanced surface drag of the urban area. This urban influence is further explored in the no‐urban simulation, in which the head of the density current is not elevated to the same degree and KHI does not occur.The sea breeze/density current has a large impact on transport and diffusion of simulated tracer plumes, not only changing the direction of plume motion due to the wind shift but also redistributing tracer material in the vertical so as to produce dramatic, rapid changes in near‐surface concentration as the front passes. In particular, large upward vertical velocity at the head of the density current advects tracer material to large elevations, greatly reducing near‐surface concentration. After passage of the front, tracer is released into the shallow density current and confined near the surface, enhancing near‐surface concentrations. KHI results in turbulent mixing at the upper surface of the plume, allowing for a small reduction in near‐surface concentration. Published in 2007 by John Wiley & Sons, Ltd.

Investigation of the atmospheric boundary layer dynamics during the ESCOMPTE campaign

Abstract. This paper presents some results about the behavior of the atmospheric boundary layer observed during the ESCOMPTE experiment. This campaign, which took place in south-eastern France during summer 2001, was aimed at improving our understanding of pollution episodes in relation to the dynamics of the lower troposphere. Using a large data set, as well as a simulation from the mesoscale non-hydrostatic model Meso-NH, we describe and analyze the atmospheric boundary layer (ABL) development during two specific meteorological conditions of the second Intensive Observation Period (IOP). The first situation (IOP2a, from 22 June to 23 June) corresponds to moderate, dry and cold northerly winds (end of Mistral event), coupled with a sea-breeze in the lower layer, whereas sea-breeze events with weak southerly winds occurred during the second part of the period (IOP2b, from 24 June to 26 June). In this study, we first focus on the validation of the model outputs with a thorough comparison of the Meso-NH simulations with fields measurements on three days of the IOP: 22 June, 23 June and 25 June. We also investigate the structure of the boundary layer on IOP2a when the Mistral is superimposed on a sea breeze. Then, we describe the spatial and diurnal variability of the ABL depths over the ESCOMPTE domain during the whole IOP. This step is essential if one wants to know the depth of the layer where the pollutants can be diluted or accumulated. Eventually, this study intends to describe the ABL variability in relation to local or mesoscale dynamics and/or induced topographic effects, in order to explain pollution transport processes in the low troposphere.

Diurnal Cycle of Water Vapor as Documented by a Dense GPS Network in a Coastal Area during ESCOMPTE IOP2

Abstract Global positioning system (GPS) data from a dense network have been used for the analysis of the diurnal cycle of water vapor over Marseille, France, during the second intensive observation period (IOP2; 21–26 June 2001) of the Expérience sur Sites pour Contraindre les Modèles de Pollution Atmosphérique et de Transport d’Emission (ESCOMPTE) field experiment. Both tomographic analyses and integrated water vapor (IWV) contents from GPS have been used, in addition to wind profiler data and surface observations. Tomographic analysis of data from the dense GPS network and radiosondes provided the continuous temporal evolution of the vertical distribution of water vapor over the city of Marseille. The city is located on the shore of the Mediterranean Sea in southeastern France and is often under the influence of sea-breeze effects. Two different layers of breeze circulation are identified: a shallow sea breeze, blowing perpendicular to the local coastline, and a deep sea breeze, induced by the regional temperature gradient between sea and land. The origin of water vapor is shown to be mainly due to the advection of marine moist air by these sea-breeze circulations. However, the diurnal cycle of water vapor over Marseille is strongly influenced by the synoptic situation, which changes during the IOP2 (between a northerly mistral in the early stage of the IOP and an easterly wind at the end). It is shown that vertical profiles from tomographic analyses (combined with wind profiler data) allow for a proper interpretation of the diurnal cycle observed in IWV. Two-dimensional maps of IWV are also shown to complement the description of the horizontal advection of moisture by the different circulation regimes.

THE EFFECT OF SEA BREEZE ON THERMAL ENVIRONMENTS IN FUKUOKA METROPOLITAN AREA

To understand the heat island structures of Fukuoka metropolitan area, 71 thermometers were set in the meteorological instrument shelters of elementary schools. In the present study, the data of air temperature obtained at the 71 sites in the summer seasons of 2003 and 2004 were analyzed to reveal the effect of sea breeze on the heat island structures. The classification of the occurrence of sea breeze and the non-occurrence were made based on the data of wind speed and wind direction at Fukuoka District Meteorological Observatory. In the case when the sea breeze was generated, the air temperature of the downtown area fell by about 4 °C at the maximum value. The wind speed of sea breeze and the fall of temperature are dependent on the amount of solar radiation for 1 hour after the intrusion of the sea breeze.

An observational and numerical study of the effects of the late sea breeze on ozone distributions in the Busan metropolitan area, Korea

The late sea breeze (LSB), defined as a sea breeze with an onset time later than 1200 LST, and its impact on O 3 concentration distributions have been investigated both observationally and numerically over the Busan metropolitan area in Korea. The observed LSB mostly occurred under weak offshore synoptic flows during mid-day, and was found with late but apparent transitions in wind direction along with lower wind speed. The observed O 3 concentrations associated with the LSB demonstrated more significant enhancement of maximum O 3 concentrations than those of the early sea breeze by a factor of approximately 1.5. The main meteorological feature associated with the LSB was also reproduced by MM5 for typical cases. The numerically derived backward trajectories suggested that the increase of O 3 at the coastal site is mainly due to recirculated polluted air mass. The numerical simulation of O 3 concentrations from MM5/UAM-V shows that offshore winds of northwesterly synoptic flow swept the precursors of O 3 that were emitted by the urban area toward the sea during the early morning. As the development of the LSB was suppressed by the synoptic flow, a large near-stagnant wind field formed over the sea with intense photochemical activity at mid-day. However, the subsequent LSB with low wind speed was simulated in order to slowly re-advect the photochemically produced air parcels toward the inland area, resulting in both a significant enhancement of O 3 concentrations and high concentrations over the coastal area lasting for relatively longer hours. This result implies that the LSB plays an important role in the recirculation/accumulation of O 3 concentrations over the Busan metropolitan area, Korea.

A Basic Study on Utilization of the Cooling Effect of Sea Breeze in Waterfront Areas along Tokyo Bay

abstract″Priority Urban Redevelopment Areas″ in Tokyo, Japan, are currently undergoing large-scale urban renewal. However, the heat island phenomenon has become a serious problem in large cities in Japan.We surveyed the temperature and wind conditions in two adjacent areas: a new skyscraper district on the coast (A district) and a typical inland urban district (B district). Our observations indicated local temperature increases and unstable wind with weak velocity in B district.It is possible that differences in the wind environment influence the local temperature. We analyzed the relationship between undulations in ground level and the wind environment by wind tunnel experiments. The results confirmed that there was a weak wind area in B district located behind A district from the direction of the coastline.Our findings indicate that it is important to consider the heat island phenomenon in urban planning in order to make best use of the cooling effect of the breeze from the sea at waterfront areas.

Temperature And Wind Velocity Oscillations Along a Gentle Slope During Sea-Breeze Events

The flow structure on a gentle slope at Vallon d’Ol in the northern suburbs of Marseille in southern France has been documented by means of surface wind and temperature measurements collected from 7 June to 14 July 2001 during the ESCOMPTE experiment. The analysis of the time series reveals temperature and wind speed oscillations during several nights (about 60--90 min oscillation period) and several days (about 120–180 min oscillation period) during the whole observing period. Oscillating katabatic winds have been reported in the literature from theoretical, experimental and numerical studies. In the present study, the dynamics of the observed oscillating katabatic winds are in good agreement with the theory.In contrast to katabatic winds, no daytime observations of oscillating anabatic upslope flows have ever been published to our knowledge, probably because of temperature inversion break-up that inhibits upslope winds. The present paper shows that cold air advection by a sea breeze generates a mesoscale horizontal temperature gradient, and hence baroclinicity in the atmosphere, which then allows low-frequency oscillations, similar to a katabatic flow. An expression for the oscillation period is derived that accounts for the contribution of the sea-breeze induced mesoscale horizontal temperature gradient. The theoretical prediction of the oscillation period is compared to the measurements, and good agreement is found. The statistical analysis of the wind flow at Vallon d’Ol shows a dominant north-easterly to easterly flow pattern for nighttime oscillations and a dominant south-westerly flow pattern for daytime oscillations. These results are consistent with published numerical simulation results that show that the air drains off the mountain along the maximum slope direction, which in the studied case is oriented south-west to north-east.

Coastal winds and low‐level jets: Simulations for sea gulfs

AbstractThe reasons for the relatively strong coastal afternoon surface winds observed along the Gulf of Finland were studied by using a high‐resolution two‐dimensional numerical model in typical summertime conditions. Sea breeze effects were included by defining a clear sky, whereas they were minimized by alternatively defining a thick cloud cover. The geostrophic wind was varied both in speed and direction. A case‐study was made with a three‐dimensional operational forecast model with results that agreed with the two‐dimensional experiments and observations.Strongish afternoon surface winds nearly parallel with the coastline were obtained in the overcast gulf experiments. In these cases, well‐mixed air entering the smooth sea slantwise from over land commenced an inertial oscillation downstream such that the emerging low‐level jet maximum was located just above the opposite coast, causing the strong winds there. If the sky was clear, sea breezes and strong convective mixing further enhanced the coastal surface winds to supergeostrophic speeds.In contrast, weak coastal winds occurred when the sea breeze and the basic flow were nearly opposite. Given the gulf geometry, the sea breeze cell from the opposite coast could be advected over the gulf in a suitable basic flow, which resulted in another minimum in the coastal wind speed as a function of geostrophic wind direction. Copyright © 2005 Royal Meteorological Society.

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.