Showing papers on "Sea breeze published in 2006"
TL;DR: In order to improve the outdoor comfort in Colombo, it is suggested to allow a more compact urban form with deeper street canyons and to provide additional shade through the use of trees, covered walkways, pedestrian arcades, etc.
Abstract: The outdoor environment is deteriorating in many tropical cities due to rapid urbanization. This leads to a number of problems related to health and well-being of humans and also negatively affects social and commercial outdoor activities. The creation of thermally comfortable microclimates in urban environments is therefore very important. This paper discusses the influence of street-canyon geometry on outdoor thermal comfort in Colombo, Sri Lanka. Five sites with different urban geometry, ground cover, and distance from the sea were studied during the warmest season. The environmental parameters affecting thermal comfort, viz. air temperature, humidity, wind speed, and solar radiation, were measured, and the thermal comfort was estimated by calculating the physiologically equivalent temperature (PET). The thermal comfort is far above the assumed comfort zone due to the combination of intense solar radiation, high temperatures, and low wind speeds, especially on clear days. The worst conditions were found in wide streets with low-rise buildings and no shade trees. The most comfortable conditions were found in narrow streets with tall buildings, especially if shade trees were present, as well as in areas near the coast where the sea breeze had a positive effect. In order to improve the outdoor comfort in Colombo, it is suggested to allow a more compact urban form with deeper street canyons and to provide additional shade through the use of trees, covered walkways, pedestrian arcades, etc. The opening up of the city's coastal strip would allow the sea breeze to penetrate further into the city.
352 citations
TL;DR: In this article, the influence of urban morphology and sea breeze on the microclimate of Colombo, Sri Lanka was examined by measuring air and surface temperatures, humidity and wind speed at 1 rural and 5 urban sites during the warmest season.
Abstract: Urbanisation leads to increased thermal stress in hot-humid climates due to increased surface and air temperatures and reduced wind speed We examined the influence of urban morphology and sea breeze on the microclimate of Colombo, Sri Lanka Air and surface temperatures, humidity and wind speed were measured at 1 rural and 5 urban sites during the warmest season The urban sites differed in their height to width (H/W) ratio, ground cover and distance to the sea Intra-urban air temperature differences were greatest during the daytime A maximum intra-urban difference of 7 K was recorded on clear days Maximum temperatures tended to decrease with increasing H/W ratio and proximity to the sea All urban sites experienced a nocturnal urban heat island (UHI) when the sky was clear or partly cloudy The temperature differences between sunlit and shaded urban surfaces reached 20 K, which shows the importance of shade in urban canyons (reducing long-wave radiation from surfaces) Within the urban areas, the vapour pressure was high (> 30 hPa) and showed little diurnal variation Wind speeds were low (< 2 m s(-1)) and tended to decrease with increasing H/W ratio Shading is proposed as the main strategy for lowering air and radiant temperatures; this can be achieved by deeper canyons, covered walkways and shade trees It is also suggested to open up wind corridors perpendicular to the sea to facilitate deeper sea breeze penetration (Less)
149 citations
TL;DR: In this article, in situ temperature records collected on six coral reefs in the Caribbean, Bahamas, and Florida Keys reveal significant variability across a range of temporal and spatial scales from minutes to seasons, across depths, and among sites.
Abstract: Analysis of in situ temperature records collected on six coral reefs in the Caribbean, Bahamas, and Florida Keys reveal significant variability across a range of temporal and spatial scales from minutes to seasons, across depths, and among sites. Subsurface variability occurring at daily and faster frequencies is prevalent across the region, likely driven by combinations of diurnal heating and cooling, wind driven advection, and internal waves at tidal and faster frequencies. This high frequency variability is not detected in records of remotely-sensed sea surface temperature alone. Diurnal variability likely caused by diurnal solar heating and cooling and possibly by advection associated with diurnal winds (daily sea breeze) was significant at all sites and showed greatest magnitude of variation at shallowest depths. Temperature fluctuations at tidal and faster frequencies were common at 5 out of the 6 sites. The magnitude of this variability is not well explained by measured vertical temperature stratification combined with oscillations of the water column associated with barotropic surface tides. Rather, the magnitude and nature of the temperature changes point to the presence of internal waves generated at tidal and faster frequencies. Power spectra calculated seasonally show greatest variability within both diurnal and semi-diurnal frequency bands in Spring and Summer at Florida, Bahamas, Jamaica, and St. Croix. Variability within the semi-diurnal frequency band at Belize and Bonaire was greatest in Winter. Warming in Summer estimated as degree-hours per day above 29.0°C increased with increasing latitude and varied significantly among sites and depths in a manner not predictable from remotely sensed SST data alone. Site latitude was directly related to the amplitude of the seasonal thermal variability, but was not tightly related to variability at daily and faster frequencies which was greatest at the highest and lowest latitude sites. The interactions of depth, site, and season across the study region are associated with distinct signals of thermal variability, and have significant implications for the physiology and ecology of corals and other reef organisms.
109 citations
TL;DR: In this article, a mesoscale atmospheric model (MM5) coupled with the Noah land surface model (LSM), which has bulk urban land use treatments along with a detailed Pearl River Delta land use map, is used to investigate the unique feature and mechanism of this landsea breeze effect and the temporal evolution.
Abstract: [1] Recent satellite observations show that a layer of haze perpetually hangs over the Pearl River Delta (PRD) region and surface observations show numerous violations of the Hong Kong Air Quality Objective. This layer of haze mostly concentrates in the Pearl River Estuary and a narrow (20 km wide) band along the shoreline, in particular during weak wind situations. Although researchers suspect the land-sea breeze (LSB) circulations “concentrate” or “trap” various pollutants in this region, the physical mechanism of the phenomenon has never been fully explained or quantified. In this paper, a mesoscale atmospheric model (MM5) coupled with the Noah land surface model (LSM), which has bulk urban land use treatments along with a detailed Pearl River Delta land use map, is used to investigate the unique feature and mechanism of this land-sea breeze effect and the temporal evolution. A three-dimensional particle trajectory model is used to understand its associated pollutant transport, trapping and accumulation. A conceptual model is then developed for the perpetual air pollution phenomenon in the region. Further sensitivity experiments are used to illustrate the impact of urbanization and large-scale winds on the pollution processes. Results show that urbanization enhances the pollutant trapping and therefore contributes to the overall poor air quality in the region.
107 citations
TL;DR: In this paper, the authors compare results from a field experiment in Puerto Rico with other long-term studies of the changes in surface fluxes after tropical deforestation, showing that tropical deforestation appears to have larger impacts on local, regional and global climate when it occurs under maritime conditions rather then under continental conditions.
82 citations
TL;DR: In this paper, the diurnal cycle of sea-breeze-related sea off the coast of Goa and write an equation for the energy of the seas as a function of the local wind.
Abstract: After withdrawal of the Indian Summer Monsoon and until onset of the next monsoon, i.e., roughly during November–May, winds in the coastal regions of India are dominated by sea breeze. It has an impact on the daily cycle of the sea state near the coast. The impact is quite significant when large scale winds are weak. During one such event, 1–15 April 1997, a Datawell directional waverider buoy was deployed in 23 m water depth off Goa, west coast of India. Twenty-minute averaged spectra, collected once every three hours, show that the spectrum of sea-breeze-related ‘wind-seas’ peaked at 0.23 ±0.05 Hz. These wind-seas were well separated from swells of frequencies less than 0.15 Hz. The TMA spectrum (Bouwset al 1985) matched the observed seas spectra very well when the sea-breeze was active and the fetch corresponding to equilibrium spectrum was found to be 77±43 km during such occasions. We emphasize on the diurnal cycle of sea-breeze-related sea off the coast of Goa and write an equation for the energy of the seas as a function of the local wind
82 citations
TL;DR: In this article, the effects of both the land-sea breeze and the orographic forcing on the diurnal evolution of precipitation during the rainy season (January-March) in the New Guinean region are studied on the basis of satellite observations from Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) measurements and regional atmospheric model simulations.
Abstract: [1] The diurnal cycle of precipitation in the New Guinean region is studied on the basis of satellite observations from Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) measurements and regional atmospheric model simulations. The study focuses on the effects of both the land-sea breeze and the orographic forcing on the diurnal evolution of precipitation during the rainy season (January–March) in the region. The 7-year TRMM PR data composite reveals several distinct features of the precipitation diurnal cycle in the region. Precipitation bands develop in the inland coastal region in the late morning to early afternoon and migrate inland from both northeast and southwest sides of the New Guinean Island following the inland penetration of the sea-breeze fronts. A separate convective rainband develops over the central mountain ridge in the early afternoon as a result of the development of the upslope winds due to the elevated surface warming over the mountain in the morning hours. This mountain ridge rainband intensifies and becomes the dominant rainband as the coastal rainbands associated with the sea-breeze fronts weaken during the late afternoon and the early evening. In the midnight to the early morning the rainband over the mountaintop weakens as downslope winds develop and splits into two rainbands, propagating away from the mountain ridge, one to the north and one to the south, and weakens over the lowland some distance away from the coasts. Meanwhile a coastal rainband develops offshore on each side of the island in the late evening to midnight and remains strong through early morning before it migrates offshore. As a result, the rainfall rate peaks in the late afternoon to early evening in most land areas except for in the lowland regions between the coastlines and the mountain where the rainfall rate peaks during the midnight, while the rainfall rate peaks in the late evening to early morning in most coastal regions offshore. The distribution of the diurnal amplitude shows two maxima: one over the mountains and the other in the coastal regions offshore. Convective rainfall rate peaks in the late afternoon while stratiform rainfall rate peaks in the midnight to early morning. The latter dominates the large diurnal amplitude over the mountain areas in the early morning. The above broad features are simulated reasonably well in a control experiment with a high-resolution regional atmospheric model. A sensitivity experiment with the terrain removed is conducted to elucidate the role of orographic forcing in the diurnal evolution of both the local circulation and rainfall patterns. The results show that the orographic forcing affects the diurnal precipitation through three major processes. First, the orography increases the moisture convergence at low levels by blocking and deflecting the mean flow. Second, the upslope winds help initiate convection in the afternoon at the mountaintop. Finally, the deep convection over the mountain acts as a source of propagating gravity waves, which help initiate rainbands in the coastal regions offshore in the late evening to early morning. Implication of the results is discussed.
79 citations
TL;DR: In this article, the UBL-ESCOMPTE program was used to document the vertical structure of the atmosphere above complex terrain, notably in Marseille, which is bordered by the Mediterranean sea and framed by numer- ous massifs.
Abstract: During the UBL-ESCOMPTE program (June-July 2001), intensive observations were performed in Marseille (France). In particular, a Doppler lidar, located in the north of the city, pro- vided radial velocity measurements on a 6-km radius area in the lowest 3 km of the troposphere. Thus, it is well adapted to document the vertical structure of the atmosphere above complex terrain, notably in Marseille, which is bordered by the Mediterranean sea and framed by numer- ous massifs. The present study focuses on the last day of the intensive observation period 2 (26 June 2001), which is characterized by a weak synoptic pressure gradient favouring the develop- ment of thermal circulations. Under such conditions, a complex stratification of the atmosphere is observed. Three-dimensional numerical simulations, with the M´ eso-NH atmospheric model including the town energy balance (TEB) urban parameterization, are conducted over south-east- ern France. A complete evaluation of the model outputs was already performed at both regional and city scales. Here, the 250-m resolution outputs describing the vertical structure of the atmo- sphere above the Marseille area are compared to the Doppler lidar data, for which the spatial res- olution is comparable. This joint analysis underscores the consistency between the atmospheric boundary layer (ABL) observed by the Doppler lidar and that modelled by MThe obser- vations and simulations reveal the presence of a shallow sea breeze (SSB) superimposed on a deep sea breeze (DSB) above Marseille during daytime. Because of the step-like shape of the Marseille coastline, the SSB is organized in two branches of different directions, which converge above the city centre. The analysis of the 250-m wind fields shows evidence of the role of the local topog- raphy on the local dynamics. Indeed, the topography tends to reinforce the SSB while it weakens the DSB. The ABL is directly affected by the different sea-breeze circulations, while the urban effects appear to be negligible.
66 citations
TL;DR: In this paper, the vertical profiles of O 3 revealed a depletion of ozone at altitudes lower than 100-300m during the night and early morning and a good vertical mixture during the day in the sea breeze boundary layer.
63 citations
TL;DR: In this paper, a new approach to the modeling of air quality in the northwestern Mediterranean basin (NWMB) has been adopted by combining the global climate-chemistry model ECHAM5/MESSy and the regional modeling system MM5-EMICAT2000-CMAQ to analyze the high levels of photochemical air pollution during a typical summertime episode.
Abstract: [1] The complex behavior of photochemical pollutants in the northwestern Mediterranean basin (NWMB) is conditioned by the superposition of circulations of different scale and the pattern of emissions. Therefore a new approach to the modeling of air quality in the NWMB has been adopted by combining the global climate-chemistry model ECHAM5/MESSy and the regional modeling system MM5-EMICAT2000-CMAQ to analyze the high levels of photochemical air pollution during a typical summertime episode. We show that this combination of models is well suited to address the range of scales involved. The complexity of the area requires the application of high spatial and temporal resolution (2 km and 1 hour) modeling to cover local to regional interactions. We address the local and large-scale processes controlling tropospheric ozone in the NWMB, notably emissions and photochemistry, convective and advective transport, deposition processes, and stratosphere-troposphere exchange. The simulation results indicate that the ozone buildup largely results from local photochemical production, which strongly exceeds the removal rates through transport and deposition. The contribution by advective transport is limited, associated with the stagnant meteorological conditions. In the lower troposphere, local recirculation systems are of key importance. The strength of the land-sea breeze circulation and thermally or mechanically driven convection over the complex orography of the eastern Iberian coast can induce vertical transport and the layering of air pollution.
60 citations
TL;DR: In this paper, two short biophysical surveys were carried out in order to assess how the decapod crustacean larvae vertical distribution and circulation patterns in an equatorward facing embayment (Gulf of Arauco, 37° S; 73° W) influenced larval transport into and out of the Gulf.
Abstract: Two short biophysical surveys were carried out in order to assess how the decapod crustacean larvae vertical distribution and circulation patterns in an equatorward facing embayment (Gulf of Arauco, 37° S; 73° W) influenced larval transport into and out of the Gulf. The embayment is located at the upwelling area of south central Chile and features a deep (∼60 m) and a shallow (∼25 m) pathway of communication with the adjacent coastal ocean. Profiles of zooplankton, temperature, salinity, dissolved oxygen and current velocity were measured during a 22-h period at the shallow entrance to the gulf. In addition, three zooplankton profiles were carried out at the deep entrance to the gulf on the basis of observed changes in hydrographic structure. At the shallow entrance to the gulf, current velocities showed a clear semidiurnal tidal signal, with stronger ebb than flood at the surface and stronger flood at depth. Decapod larval abundances showed a bimodal distribution through time, with a maximum during night-time ebb, and a smaller, second peak at day-time ebb. Larval transport in and out of the Gulf depended on larval vertical distribution and the timing of higher densities. Export was reduced when larvae deepened during ebbing tides or when larvae remained deeper throughout the day. Export was enhanced when larger numbers of individuals occupied ebbing surface waters. At the deep entrance, two groups of crustacean larvae were found associated with two different water types: a surface high oxygen water and a deeper suboxic equatorial subsurface water. A group of larvae that originates in the shelf area appeared entering the Gulf in the deeper waters of this entrance but was absent from the shallower one. Larval vertical distribution in the two layer circulation at the embayment entrances can enhance or preclude retention within the bay. The motion of these layers was determined remotely by upwelling dynamics and modified by local wind (sea breeze) and tides. Overall, high frequency processes (semidiurnal tides, diurnal fluctuations) superimposed onto others of lower frequency (3-8 d period of winddriven upwelling), may contribute significantly to variations in the transport of individuals from bays in upwelling areas.
01 Nov 2006
TL;DR: In this article, the authors used a numerical model (RAMS) at 1 km horizontal grid intervals over the Sydney Basin to assess the impact of land cover change on storms and found that synoptically forced storms (e.g., those triggered by cold fronts) were unresponsive to a changed land surface, while local convective storms were highly sensitive to the triggering mechanism associated with land surface influences.
Abstract: This study has used a numerical model (RAMS) at 1 km horizontal grid intervals over the Sydney Basin to assess the impact of land cover change on storms. Multiple storms using the National Center for Environmental Prediction (NCEP) reanalysis data were simulated with pre-European settlement land cover then re-simulated with land cover representing Sydney's current land use pattern. While all simulated storms did not respond to the change in land cover consistently, storms of similar types responded in comparable ways. All simulated synoptically forced storms (e.g. those triggered by cold fronts) were unresponsive to a changed land surface, while local convective storms were highly sensitive to the triggering mechanism associated with land surface influences. Storms travelling over the smoother agricultural land in the south-west of the Sydney Basin experienced an increase in velocity, and in a special case, the dense urban surface of Sydney's city core appears to trigger an intense convective storm. It is shown that the dynamical setting predominantly triggers storm outbreaks. This is seen most clearly in the isolated convective storm category where the sea breeze front often dictates the location of storm cell initiation.
TL;DR: In this article, a high-resolution version of the RAMS model was run to simulate the campaign and characterize the diurnal patterns of the flow regime: night-time katabatic drainage, morning sea-breeze development and its subsequent coupling with mountain up-slopes, and evening flow-veering under larger-scale interactions.
Abstract: . We collected ground-based and aircraft vertical profile measurements of meteorological parameters during a 2-week intensive campaign over the Valencia basin, in order to understand how mesoscale circulations develop over complex terrain and affect the atmospheric transport of tracers. A high-resolution version of the RAMS model was run to simulate the campaign and characterize the diurnal patterns of the flow regime: night-time katabatic drainage, morning sea-breeze development and its subsequent coupling with mountain up-slopes, and evening flow-veering under larger-scale interactions. An application of this mesoscale model to the transport of CO2 is given in a companion paper. A careful evaluation of the model performances against diverse meteorological observations is carried out. Despite the complexity of the processes interacting with each other, and the uncertainties on modeled soil moisture boundary conditions and turbulence parameterizations, we show that it is possible to simulate faithfully the contrasted flow regimes during the course of one day, especially the inland progression and organization of the sea breeze. This gives confidence with respect to future applicability of mesoscale models to establish a reliable link between surface sources of tracers and their atmospheric concentration signals over complex terrain.
TL;DR: The late sea breeze (LSB), defined as a sea breeze with an onset time later than 1200 LST, and its impact on O3 concentration distributions have been investigated both observationally and numerically over the Busan metropolitan area in Korea as discussed by the authors.
TL;DR: In this paper, a simulation study of the sea breeze circulation and thermal internal boundary layer (TIBL) characteristics has been carried out at the tropical site Kalpakkam on the east coast of India, for operational atmospheric dispersion prediction.
Abstract: A simulation study of the sea breeze circulation and thermal internal boundary layer (TIBL) characteristics has been carried out at the tropical site Kalpakkam on the east coast of India, for operational atmospheric dispersion prediction. The community based PSU/NCAR MM5 Meso-scale meteorological model is used for the study. Three cases on typical days in summer (24 May 2003), southwest (SW) monsoon (1 July 2001) winter season (2 February 2003) with different large-scale flow pattern are studied. The MM5 model is used with 3 nested domains with horizontal grid resolutions 18 km, 6 km and 2 km and 26 vertical levels. The model is integrated for 24 hours in the above cases with initial and boundary conditions taken from NCEP-FNL analyses data. Observations of 10 meteorological stations and coastal boundary layer experiments conducted at Kalpakkam are used for comparison and validation of the simulation. The characteristics of simulated sea breeze and TIBL at Kalpakkam are seen to vary in the above cases according to the prevailing large-scale winds and surface fluxes. The sea breeze circulation is seen to develop early with larger strength and inland propagation in the summer case under the influence of moderate synoptic wind and strong heating conditions than in the SW monsoon and winter cases. The horizontal and vertical extents of TIBL are found to be larger in the summer case than in other cases. Although model parameters agree in general with observations, all the fine features are not clearly captured and some slowness in model sea breeze development is also seen. The results indicate the need to improve i) the initial conditions by assimilation of available surface/upper air observations to reduce model bias and ii) surface net radiation parameterisation. The model could predict the essential features of the local circulation and further improvement is expected with better initial condition data and incorporation of more realistic surface data.
TL;DR: The structure and evolution of the sea breeze in southern France on 25 June 2001 is investigated experimentally and numerically in this article, and the analysis of the front propagation and the associated turbulent kinetic energy budget allows four distinct stages of sea-breeze front evolution to be identified.
Abstract: The structure and evolution of the sea breeze in southern France on 25 June 2001 is investigated experimentally and numerically. This study shows how interactions between the sea breeze, the synoptic flow and the complex terrain affect the sea-breeze structure, and quantifies and discusses the air-mass transport associated with the sea-breeze circulation. The analysis of the front propagation and the associated turbulent kinetic energy budget allows four distinct stages of sea-breeze front evolution to be identified. Quantification of the horizontal and vertical air-mass fluxes is related to these four stages: the horizontal advection is directly linked to the intensity of the sea-breeze flow. Two main mechanisms contribute to the vertical export within the free troposphere: anabatic upslope winds which are intensified by the sea-breeze flow and frontogenesis at the sea-breeze front which generates turbulence and mixing and upward motion. Copyright © 2006 Royal Meteorological Society
TL;DR: The Regional Atmospheric Modeling System (RAMS) was run at a 1-km grid spacing over the Sydney basin in Australia to assess the impact of land cover change on a simulated storm event as discussed by the authors.
Abstract: The Regional Atmospheric Modeling System (RAMS) was run at a 1-km grid spacing over the Sydney basin in Australia to assess the impact of land cover change on a simulated storm event. The simulated storm used NCEP–NCAR reanalysis data, first with natural (i.e., pre-European settlement in 1788) land cover and then with satellite-derived land cover representing Sydney's current land use pattern. An intense convective storm develops in the model in close proximity to Sydney's dense urban central business district under current land cover. The storm is absent under natural land cover conditions. A detailed investigation of why the change in land cover generates a storm was performed using factorial analysis, which revealed the storm to be sensitive to the presence of agricultural land in the southwest of the domain. This area interacts with the sea breeze and affects the horizontal divergence and moisture convergence—the triggering mechanisms of the storm. The existence of the storm over the dense ur...
TL;DR: In this paper, two models were used to assess the effects of coastal characteristics on radar propagation in ducting conditions in the Persian Gulf, and the output from this model was input to the AREPS propagation model to produce radar coverage over coastal areas.
Abstract: Two models were used to assess the effects of coastal characteristics on radar propagation in ducting conditions in the Persian Gulf. The NCAR/Penn State MM5 model simulated atmospheric conditions at a 5-km horizontal spatial and hourly temporal resolution on a day on which observations of ducts existed. The output from this model was input to the AREPS propagation model to produce radar coverage over coastal areas. Four factors influenced radar propagation: the sea breeze; coastal configuration; orography; and ambient wind. The sea breeze alone allowed propagation to extend about 100 km inland in a layer 200 m deep. When the breeze was aided by a following ambient wind the propagation layer extended for 150 km and was 400 m deep. A coastal indentation caused differences in depth and intensity of propagation over a distance of about 30 km parallel to the coast in which the indentation occurred. Steep near-coastal orography blocked radar propagation. Copyright © 2006 Royal Meteorological Society.
TL;DR: In this article, the authors used an airborne Doppler lidar, a meteorological surface station network and radiosoundings 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.
Abstract: . Sea-breeze dynamics in southern France is investigated using an airborne Doppler lidar, a meteorological surface station network and radiosoundings, 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. The airborne Doppler lidar WIND contributed to three-dimensional (3-D) mapping of the sea breeze circulation in an unprecedented way. The data allow access to the onshore and offshore sea breeze extents (xsb), and to the sea breeze depth (zsb) and intensity (usb). They also show that the return flow of the sea breeze circulation is very seldom seen in this area due to (i) the presence of a systematic non zero background wind, and (ii) the 3-D structure of the sea breeze caused by the complex coastline shape and topography. A thorough analysis is conducted on the impact of the two main valleys (Rhone and Durance valleys) affecting the sea breeze circulation in the area. Finally, this dataset also allows an evaluation of the existing scaling laws used to derive the sea breeze intensity, depth and horizontal extent. The main results of this study are that (i) latitude, cumulative heating and surface friction are key parameters of the sea breeze dynamics; (ii) in presence of strong synoptic flow, all scaling laws fail in predicting the sea breeze characteristics (the sea breeze depth, however being the most accurately predicted); and (iii) the ratio zsb/usb is approximately constant in the sea breeze flow.
TL;DR: In this paper, the meso-NH atmospheric model including the Town Energy Balance urban parameterization was used for simulation of the south-east of France and the city of Marseille in the framework of the ESCOMPTE-UBL program.
Abstract: 3D numerical simulations with the Meso-NH atmospheric model including the Town Energy Balance urban parameterization, are conducted over the south-east of France and the one million inhabitants city of Marseille in the frameworks of the ESCOMPTE-UBL program. The geographic situation of the area is relatively complex, because of the proximity of the Mediterranean Sea and the presence of numerous massifs, inducing complex meteorological flows. The present work is focused on six days of the campaign, characterized by the development of strong summer sea-breeze circulations. A complete evaluation of the model is initially realized at both regional- and city-scales, by using the large available database. The regional evaluation shows a good behavior of the model, during the six days of simulation, either for the parameters near the surface or for the vertical profiles describing the structure of the atmosphere. The urban-scale evaluation indicates that the fine structure of the horizontal fields of air temperature above the city is correctly simulated by the model. A specific attention is then pointed to the 250-m horizontal resolution outputs, focused on the Marseille area, for two days of the campaign. From the study of the vertical structure of the Urban Boundary Layer and the thermodynamic fields near the surface, one underscores the important differences due to the regional and local flows, and the complex interactions that occur between the urban effects and the effects of sea breezes.
TL;DR: In this article, the authors analyzed the mechanisms leading to lofting and largescale advection of aerosols over the Indian Ocean region due to interaction of the sea breeze with the northeast monsoon winds along the west coast of India.
Abstract: [1] This work was carried out to understand the mechanisms leading to lofting and largescale advection of aerosols over the Indian Ocean region due to interaction of the sea breeze with the northeast monsoon winds along the west coast of India. European Centre for Medium-Range Weather Forecasts (ECMWF) wind fields for the months of February and March 1999 were analyzed at various times of day. Intense sea breeze activity was observed at 1200 UT (1730 local time) along the west coast of India with average intensity larger in March than in February. The sea breeze was seen to extend inland deeper in March than in February. Lofting of air observed as high as 800 hPa (approximately 2 km above sea level) could lead to entrainment of aerosols into the free troposphere and long-range transport. Upward motion of air was observed everywhere along the west coast of India (from 8� to 20� N), on average higher in March than in February, because of convergence between the sea breeze and the synoptic-scale flow. A region of intense lofting of air and well-defined convergence was observed along the coast of the Karnataka region (12� –16� N). A simulation with a general circulation model nudged with ECMWF data indicated that the intrusion of marine air masses with low concentrations of organic matter is seen as deep as 64 km inland in the evening (1500 UT). Intrusion of the sea-salt plume is seen to a maximum distance of around 200 km from 1500 until 2300 UT. A well-developed lofted layer of aerosols as high as 3 km was also simulated during sea breeze activity along the west coast of India. The general circulation model simulation shows a clear diurnal evolution of the vertical profile of the aerosol extinction coefficient at Goa but fails to reproduce several features of the lidar observations, for example, the marked diurnal variability of the upper layers between 1 and 3 km. However, the model simulates a diurnal cycle at the surface (0–0.7 km) that is not apparent in lidar measurements. The model simulates long-range transport and captures the lofted plume downwind of the west coast of India. However, there was a 1–2 day delay in the model transport of lofted aerosols at higher layers to Hulule, 700 km downwind of India, when compared to lidar observations.
TL;DR: The three-dimensional structure and dynamics of the combination of the sea breeze and the mistral at the Rhone Valley exit, in southeastern France, have been investigated experimentally and numerically on 22 June 2001 as discussed by the authors.
Abstract: The three-dimensional structure and dynamics of the combination of the sea breeze and the mistral at the Rhone Valley exit, in southeastern France, have been investigated experimentally and numerically on 22 June 2001. The mistral refers to a severe northerly wind that develops along the Rhone Valley. The exit of this valley is located near the Mediterranean Sea where sea-breeze circulation often develops. The sea breeze and the mistral coexist this day because of the weakness of this mistral event. The event was documented in the framework of the Experience sur Site pour Contraindre les Modeles de Pollution Atmospherique et de Transport d'Emissions (ESCOMPTE) field experiment. Several important data sources are used (airborne Doppler lidar, UHF wind profilers, radiosoundings, and surface stations) as well as nonhydrostatic mesoscale simulations. This paper examines the various mechanisms that drive the time and spatial variability of the mistral and the sea breeze in various regions of the Rhone Valley. In the morning, the sea breeze penetrates inland near the western side of the Rhone Valley then moves back because of the reinforcement of the mistral flow caused by the deepening of the leeward surface low due to convection at noon. At midday, the sea breeze penetrates inland in the middle of the Rhone Valley only. In contrast to pure sea-breeze episodes when the sea breeze can extend inland over a horizontal range of more than 150 km, the presence of the mistral prevents the sea breeze from penetrating more than 40 km onshore. In the late afternoon, the sea breeze reaches the eastern side of the Rhone Valley but over a smaller horizontal range because of higher local topography and because the mistral is more intense in this part of the Rhone Valley. The situations of sea-breeze–mistral interactions can have a severe impact on regional air quality. Indeed, the southerly sea breeze, which advects toward the countryside the pollutants emitted from the large coastal city of Marseille, France, and its industrialized suburbs, cannot penetrate far inland because of the mistral blowing in the opposite direction. This leads to the stagnation of the pollutants near the area of emission that is also the most densely inhabited area of the region (over one million inhabitants).
TL;DR: In this article, the Coupled Ocean-Atmosphere Mesoscale Prediction System (COAMPS) is used to examine the atmospheric boundary layer processes involved in pollutant transport.
Abstract: Concentrations of ozone exceeding regulatory standards are regularly observed along the coasts of New Hampshire and Maine in summer. These events are primarily caused by the transport of pollutants from urban areas in Massachusetts and farther south and west. Pollutant transport is most efficient over the ocean. The coastline makes transport processes complex because it makes the structure of the atmospheric boundary layer complex. During pollution episodes, the air over land in daytime is warmer than the sea surface, so air transported from land over water becomes statically stable and the formerly well-mixed boundary layer separates into possibly several layers, each transported in a different direction. This study examines several of the atmospheric boundary layer processes involved in pollutant transport. A three-dimensional model [the Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS)] run on grids of 2.5 and 7.5 km is used to examine the winds, thermodynamic structure, and struct...
01 Jan 2006
TL;DR: The three-dimensional structure and dynamics of the combination of the sea breeze and the mistral at the Rhone Valley exit, in southeastern France, have been investigated experimentally and numerically on 22 June 2001 as mentioned in this paper.
Abstract: The three-dimensional structure and dynamics of the combination of the sea breeze and the mistral at the Rhone Valley exit, in southeastern France, have been investigated experimentally and numerically on 22 June 2001. The mistral refers to a severe northerly wind that develops along the Rhone Valley. The exit of this valley is located near the Mediterranean Sea where sea-breeze circulation often develops. The sea breeze and the mistral coexist this day because of the weakness of this mistral event. The event was documented in the framework of the Experience sur Site pour Contraindre les Modeles de Pollution Atmospherique et de Transport d’Emissions (ESCOMPTE) field experiment. Several important data sources are used (airborne Doppler lidar, UHF wind profilers, radiosoundings, and surface stations) as well as nonhydrostatic mesoscale simulations. This paper examines the various mechanisms that drive the time and spatial variability of the mistral and the sea breeze in various regions of the Rhone Valley. In the morning, the sea breeze penetrates inland near the western side of the Rhone Valley then moves back because of the reinforcement of the mistral flow caused by the deepening of the leeward surface low due to convection at noon. At midday, the sea breeze penetrates inland in the middle of the Rhone Valley only. In contrast to pure sea-breeze episodes when the sea breeze can extend inland over a horizontal range of more than 150 km, the presence of the mistral prevents the sea breeze from penetrating more than 40 km onshore. In the late afternoon, the sea breeze reaches the eastern side of the Rhone Valley but over a smaller horizontal range because of higher local topography and because the mistral is more intense in this part of the Rhone Valley. The situations of sea-breeze–mistral interactions can have a severe impact on regional air quality. Indeed, the southerly sea breeze, which advects toward the countryside the pollutants emitted from the large coastal city of Marseille, France, and its industrialized suburbs, cannot penetrate far inland because of the mistral blowing in the opposite direction. This leads to the stagnation of the pollutants near the area of emission that is also the most densely inhabited area of the region (over one million inhabitants).
TL;DR: In this article, a methodology developed to optimize a network of 20 stations measuring air temperature and moisture over the city of Marseille is presented, based on the analysis of a numerical simulation, performed with the non-hydrostatic, mesoscale Meso-NH model, run with four nested-grids down to a horizontal resolution of 250 m over a city and including a specific parametrization for the urban surface energy balance.
Abstract: Within the framework of ESCOMPTE, a French experiment performed in June and July 2001 in the south-east of France to study the photo-oxidant pollution at the regional scale, the urban boundary layer (UBL) program focused on the study of the urban atmosphere over the coastal city of Marseille. A methodology developed to optimize a network of 20 stations measuring air temperature and moisture over the city is presented. It is based on the analysis of a numerical simulation, performed with the non-hydrostatic, mesoscale Meso-NH model, run with four nested-grids down to a horizontal resolution of 250 m over the city and including a specific parametrization for the urban surface energy balance. A three-day period was modelled and evaluated against data collected during the preparatory phase for the project in summer 2000. The simulated thermodynamic surface fields were analysed using an empirical orthogonal function (EOF) decomposition in order to determine the optimal network configuration designed to capture the dominant characteristics of the fields. It is the first attempt of application of this kind of methodology to the field of urban meteorology. The network, of 20 temperature and moisture sensors, was implemented during the UBL-ESCOMPTE experiment and continuously recorded data from 12 June to 14 July 2001. The measurements were analysed in order to assess the urban thermodynamic island spatio-temporal structure, also using EOF decomposition. During nighttime, the influence of urbanization on temperature is clear the field is characterized by concentric thermo-pleths around the old core of the city, which is the warmest area of the domain. The moisture field is more influenced by proximity to the sea and airflow patterns. During the day, the sea breeze often moves from west or south-west and consequently the spatial pattern for both parameters is characterized by a gradient perpendicular to the shoreline. Finally, in order to assess the methodology adopted, the spatial structures extracted from the simulation of the 2000 preparatory campaign and observations gathered in 2001 have been compared. They are highly correlated, which is a relevant validation of the methodology proposed. The relations between these spatial structures and geographical characteristics of the site have also been studied. High correlations between temperature spatial structure during nighttime and urban cover fraction or street aspect ratio are observed and simulated. For temperature during daytime or moisture during both daytime and nighttime these geographical factors are not correlated with thermodynamic fields spatial structures.
TL;DR: In this article, a TSI nano-SMPSP was installed in a lab at Bodega Bay, about 50 m from the coastline and 5 m above sea level.
Abstract: [1] A TSI nano-SMPS was installed in a lab at Bodega Bay, about 50 m from the coastline and 5 m above sea level. On the basis of measurements conducted from June to December 2001 and from January to June 2003, we have observed two kinds of nucleation events, i.e., long-term (a few hours) and short-term (a few minutes) particle bursts. The long-term events mostly occur during daytime in the summer, lasting from 0.5 to 8 hours. Narrow spikes (short-term events) that occur year-round, both day and night, last only a few minutes to a half hour but contain particle number concentrations comparable to some of the long-term events. Wind direction and speed affect the occurrence and intensity of the particle burst. Nucleation mostly takes place during northwesterly onshore wind for both long- and short-term events, and the probability of nucleation occurrence is higher at higher wind speed. However, in contrast to what has been observed at Mace Head, Ireland, nucleation at Bodega Bay does not correlate with tidal height. Instead, the seasonal and interannual variations of ultrafine particle number concentration N3–10nm appear to correlate with ocean upwelling, a characteristic of currents along the west coast of the United States that brings up nutrients from subsurface waters, promoting plant productivity. Simultaneous measurements of nucleation at the coast and 1.6 km out suggest that nucleation is a coastal phenomenon, supporting the contention that it is related to direct or biogenic emission of precursor gases from the coastal area during the sea upwelling periods.
TL;DR: In this paper, a high-resolution mesoscale model was used to evaluate the impact of limiting assumptions in the eddy-covariance (EC) method as well as the effectiveness of tower flux data time-filtering for the main tower site of the Fluxnet-Canada British Columbia flux station.
TL;DR: In this article, the authors investigate the fine structure of the sea-breeze circulation and its relationship with the pollutant concentrations in the Mediterranean coast of France and show that these dynamical characteristics have profound influences on the atmospheric boundary layer (ABL) development and on pollutant concentration.
Abstract: . The international ESCOMPTE campaign, which took place in summer 2001 in the most highly polluted French region, was devoted to validate air pollution prediction models. Surface and remote sensing instruments (Lidar, Radar and Sodar) were deployed over the Marseille area, along the Mediterranean coast, in order to investigate the fine structure of the sea-breeze circulation and its relationship with the pollutant concentrations. The geographical situation of the Marseille region combines a complex coastline and relief which both lead to a peculiar behaviour of the sea-breeze circulation. Several local sea breezes, perpendicular to the nearest coastline, settled in during the morning. In the afternoons, when the thermal gradient between the continental and marine surface grows up, a southerly or a westerly sea breeze may dominate. Their respective importance is then a function of time, space and altitude. Furthermore, an oscillation of the westerly sea breeze with a period of about 3 h is also highlighted. We show that these dynamical characteristics have profound influences on the atmospheric boundary-layer (ABL) development and on pollutant concentrations. In fact, the direction and intensity of the sea-breeze determine the route and the transit time of the stable marine air flow over the continental surface. Thus, the ABL depth may exhibit several collapses correlated with the westerly sea-breeze pulsation. The ozone and aerosol concentrations are also related to the dynamical features. In the suburbs and parts of the city under pulsed sea breezes, a higher ABL depth and higher ozone concentrations are observed. In the city centre, this relationship between pulsed sea-breeze intensity and ozone concentration is different, emphasising the importance of the transit time and also the build-up of pollutants in the marine air mass along the route. Finally, the variations of aerosol concentration are also described according to the breeze direction.
TL;DR: In this article, a method of identifying sea-breeze fronts by remote sensing (visible and infrared data from the GOES-8 satellite) was applied to north-eastern Brazil.
Abstract: A method of identifying sea-breeze fronts by remote sensing (visible and infrared data from the GOES-8 satellite) was applied to north-eastern Brazil. The aim of the study was to estimate the frequency of observed sea-breeze fronts and the average distance they penetrate inland at 1800 UTC. During the dry season (between September and December) in 2000, the highest frequency of sea-breeze fronts was recorded on the northern fringe of the study area. The sea-breeze fronts penetrated furthest inland between September and November, with a maximum distance from the coast at Ceara of 100 km. Copyright © 2006 John Wiley & Sons, Ltd.