Showing papers on "Sea breeze published in 2007"

Interactions of an urban heat island and sea-breeze circulations during winter over the metropolitan area of São Paulo, Brazil

Abstract: The Town Energy Budget (TEB) model, a detailed urban parameterisa- tion using a generalised canyon geometry, coupled with the Regional Atmospheric Modelling System (RAMS) is used to simulate the wintertime local circulation in the megacityenvironmentofthemetropolitanareaofSaoPaulo(MASP)inBrazil.Model simulations are performed using actual topography and land-use fields. Comparison with a simple urban parameterisation based on the LEAF-2 scheme is also shown. Validation is based on comparison between model simulations and observations. Sen- sitivity tests with TEB reveal an important interaction between the sea breeze and the MASP heat island circulation. Even though topography is known to play an impor- tant role in the MASP region's weather, in these tests the simulations were performed without topography in order to unambiguously identify the interaction between the two local circulations. The urban heat island (UHI) forms a strong convergence zone in the centre of the city and thereby accelerates the sea-breeze front toward the centre of the city. The presence of the urban region increases the sea-breeze front propa- gation mean speed by about 0.32ms −1 when compared with the situation of no city. After its arrival in the urban region, the sea-breeze front stalls over the centre of the city for about 2h. Subsequently, the sea breeze progresses beyond the city when the heat island dissipates. Thereafter, the sea breeze propagates beyond the urban area at a decelerated rate compared to a simulation without an UHI.

Mesoscale covariance of transport and CO2 fluxes: Evidence from observations and simulations using the WRF‐VPRM coupled atmosphere‐biosphere model

Abstract: [1] We developed a modeling system which combines a mesoscale meteorological model, the Weather Research and Forecasting (WRF) model, with a diagnostic biospheric model, the Vegetation Photosynthesis and Respiration (VPRM). The WRF-VPRM modeling system was designed to realistically simulate high-resolution atmospheric CO2 concentration fields. In the system, WRF takes into account anthropogenic and biospheric CO2 fluxes and realistic initial and boundary conditions for CO2 from a global model. The system uses several “tagged” tracers for CO2 fields from different sources. VPRM uses meteorological fields from WRF and high-resolution satellite indices to simulate biospheric CO2 fluxes with realistic spatiotemporal patterns. Here we present results from the application of the model for interpretation of measurements made within the CarboEurope Regional Experiment Strategy (CERES). Simulated fields of meteorological variables and CO2 were compared against ground-based and airborne observations. In particular, the characterization by aircraft measurements turned out to be crucial for the model evaluation. The comparison revealed that the model is able to capture the main observed features in the CO2 distribution reasonably well. The simulations showed that daytime CO2 measurements made at coastal stations can be strongly affected by land breeze and subsequent sea breeze transport of CO2 respired from the vegetation during the previous night, which can lead to wrong estimates when such data are used in inverse studies. The results also show that WRF-VPRM is an effective modeling tool for addressing the near-field variability of CO2 fluxes and concentrations for observing stations around the globe.

Investigation of a sea breeze front in an urban environment

Abstract: The 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.

An Assimilation and Forecasting Experiment of the Nerima Heavy Rainfa11 with a Cloud-Resolving Nonhydrostatic 4-Dimensional Variational Data Assimilation System

Abstract: The Meteorological Research Institute of the Japan Meteorological Agency has developed a cloud-resolving nonhydrostatic 4-dimensional variational assimilation system (NHM-4DVAR), based on the Japan Meteorological Agency Nonhydrostatic Model (JMA-NHM), in order to investigate the mechanism of heavy rainfall events induced by mesoscale convective systems (MCSs). A horizontal resolution of the NHM-4DVAR is set to 2 km to resolve MCSs, and the length of the assimilation window is 1-hour. The control variables of the NHM-4DVAR are horizontal wind, vertical wind, nonhydrostatic pressure, potential temperature, surface pressure and pseudo relative humidity. Perturbations to the dynamical processes, and the advection of water vapor are considered, but these to the other physical processes are not taken into account.The NHM-4DVAR is applied to the heavy rainfall event observed at Nerima, central part of Tokyo metropolitan area, on 21 July 1999. Doppler radar's radial wind data, Global Positioning System's precipitable water vapor data, and surface temperature and wind data are assimilated as high temporal and spatial resolution data. The Nerima heavy rainfall is well reproduced in the assimilation and subsequent forecast, with respect to time sequence of 10-minute rainfall amount. The formation mechanism of the Nerima heavy rainfall is clarified from this study. A surface convergence line of horizontal winds was made of a southerly sea breeze and north-easterly winds over the Kanto plain around Nerima. Since the rise of temperature over the northern part of the Kanto plain was suppressed, due to a shield of clouds against sunshine, the difference of temperature between the convergence line and its northern side became large. Consequently, the wind convergence was enhanced around Nerima. An air with high equivalent potential temperature was lifted over this enhanced convergence line to generate cumulonimbi that caused the Nerima heavy rainfall.

Nocturnal meso-beta basin and katabatic flows on a midlatitude island

Abstract: A mesoscale simulation for the island of Majorca, Spain, in the western Mediterranean Sea is used to study the nocturnal system of winds under weak synoptic pressure gradients. A very high vertical resolution is used in the first 500 m above ground level to characterize with large detail the thin circulations close to ground, namely, basin and katabatic flows. It is found that the island, the basin, and the slope scales interact strongly, especially when a quasi-steady state is reached in the second part of the night. A high mountain range creates a high pressure area upwind where local winds can develop. Katabatic flows converge to the valleys where they interact with a cold pool, which is advected slowly to sea by the land–sea night-breeze effect combined with a topographic forcing. The katabatic flows experience small entrainment at the top and have well-defined characteristics. The results are partially confirmed by the observations and some satellite images.

Large-Eddy Simulation of the Onset of the Sea Breeze

Abstract: This paper describes results from a large-eddy simulation (LES) model used in an idealized setting to simulate the onset of the sea breeze. As the LES is capable of simulating boundary layer–scale, threedimensional turbulence along with the mesoscale sea-breeze circulation, a parameterization of the planetary boundary layer was unnecessary. The basic experimental design considers a rotating, uniformly stratified, resting atmosphere that is suddenly heated at the surface over the “land” half of the domain. To focus on the simplest nontrivial problem, the diurnal cycle, effects of moisture, interactions with large-scale winds, and coastline curvature were all neglected in this study. The assumption of a straight coastline allows the use of a rectangular computational domain that extends to 50 km on either side of the coast, but only 5 km along the coast, with 100-m grid intervals so that the small-scale turbulent convective eddies together with the mesoscale sea breeze may be accurately computed. Through dimensional analysis of the simulation results, the length and velocity scales characterizing the simulated sea breeze as functions of the externally specified parameters are identified.

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

Abstract: 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.

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 Experience sur Sites pour Contraindre les Modeles de Pollution Atmospherique 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.

Atmospheric CO2 modeling at the regional scale: Application to the CarboEurope Regional Experiment

Abstract: [1] The CarboEurope Regional Experiment Strategy (CERES) experiment took place in May and June 2005 in France and offers a comprehensive database on atmospheric CO2 and boundary layer processes at the regional scale. One “golden” day of CERES is interpreted with the mesoscale atmospheric model Meso-NH coupled on-line with the Interactions between Soil, Biosphere and Atmosphere, CO2-reactive (ISBA-A-gs) surface scheme, allowing a full interaction of CO2 between the surface and the atmosphere. The rapid diurnal cycle of carbon coupled with water and energy fluxes is parameterized including, e.g., plant assimilation, respiration, anthropogenic emissions, and sea fluxes. During the analyzed day, frequent vertical profiles and aircraft transects revealed high spatial and temporal variabilities of CO2 concentrations within the boundary layer at the regional scale: a 10-ppm gradient of CO2-mixing ratio is observed during the day by the aircraft measurements. The Meso-NH model proved able to simulate very well the CO2 concentration variability as well as the spatial and temporal evolution of the surface fluxes and the boundary layer in the domain. The model is used to explain the CO2 variability as a result of two complementary processes: (1) the regional heterogeneity of CO2 surface fluxes related to the land cover (e.g., winter crops versus a pine forest) and (2) the variability of mesoscale circulation across the boundary layer: development of the sea breeze in the western part of the domain and dominating wind flow in the eastern part of the domain.

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

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

Ozone differences between near-coastal and offshore sites in New England: Role of meteorology

Abstract: [1] Time series from two ozone monitoring stations are evaluated, one on an island several km off the New England coast, the other several km inland in New Hampshire. In the summer of 2002, during the New England Air Quality Study 2002 (NEAQS-2002), ozone measurements at the island station, Appledore Island (ADI), were consistently higher than at the inland station, Thompson Farm (TF). We hypothesized that the differences in ozone concentrations were due to transport differences driven by mesoscale meteorology, since neither site was in a source region. We found that the Appalachian Trough, coastal cold fronts and coastal stationary fronts at times caused TF to have westerly component flow while ADI had southerly component flow. In these situations, the southwesterly flow along the New England coast brought ozone and precursors to ADI from metropolitan areas to the southwest (e.g., Boston). Conversely, the air transported to TF from the west was contaminated by fewer upstream sources, and therefore the ozone was lower at TF. The sea breeze was also a factor, which tended to have the contrasting effect of nearly equalizing the ozone concentrations at the two sites by transporting ozone-rich air already impacting ADI inland to TF. Enhanced measurements from the NEAQS-2002 study were used in the analysis, including radar wind profilers, Doppler and ozone profiling lidars, and radiosondes launched from a ship. We also assessed model performance for two models, WRF/Chem and MM5/Chem, for four key days.

Local diurnal upwelling driven by sea breezes in northern

Abstract: 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 51C) 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 midafternoon 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.

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)

Abstract: 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.

Spatial and temporal variability of diurnal wind forcing in the coastal ocean

Abstract: [1] Spatial and temporal variability of diurnal wind forcing and the coastal response is characterized for the New York Bight from February through May, 2005. This analysis demonstrates that diurnal wind forced motions are significant in the coastal ocean during the spring and summer months, near shore and as far as 100 km offshore. A doubling of diurnal current amplitudes is common in the spring compared to the winter months, associated with an increase in sea/land breeze days. Diurnal fluid motions due to sea/land breeze events can account for up 50% of the total kinetic energy during the spring.

Dynamical controls on the diurnal cycle of temperature in complex topography

Abstract: We examine the climatological diurnal cycle of surface air temperature in a 6 km resolution atmospheric simulation of Southern California from 1995 to the present. We find its amplitude and phase both have significant geographical structure. This is most likely due to diurnally- varying flows back and forth across the coastline and ele- vation isolines resulting from the large daily warming and cooling over land. Because the region's atmosphere is generally stably stratified, these flow patterns result in air of lower (higher) potential temperature being advected upslope (downslope) during daytime (nighttime). This suppresses the temperature diurnal cycle amplitude at mountaintops where diurnal flows converge (diverge) during the day (night). The nighttime land breeze also advects air of higher potential temperature downslope to- ward the coast. This raises minimum temperatures in land areas adjacent to the coast in a manner analogous to the daytime suppression of maximum temperature by the cool sea breeze in these same areas. Because stratification is greater in the coastal zone than in the desert interior, these thermal effects of the diurnal winds are not uniform, gen- erating spatial structures in the phase and shape of the temperature diurnal cycle as well as its amplitude. We confirm that the simulated characteristics of the tempera- ture diurnal cycle as well as those of the associated diurnal winds are also found in a network of 30 observation sta- tions in the region. This gives confidence in the simula- tion's realism and our study's findings. Diurnal flows are probably mainly responsible for the geographical structures in the temperature diurnal cycle in other regions of

Impact of turbulence, land surface, and radiation parameterizations on simulated boundary layer properties in a coastal environment

Abstract: [1] The impact of planetary boundary layer (PBL) turbulence, land surface, and radiation parameterizations on mesoscale simulations of boundary layer properties in a coastal environment are examined using observations from different platforms and numerical simulations using the mesoscale model MM5 during a 10-day period in July 2004. The parameterization schemes examined are the MRF and Eta PBL schemes, the simple soil model and the more sophisticated NOAH land surface model, and the Dudhia and RRTM longwave radiation parameterizations. Comparisons are made between simulated and observed near surface mean variables, radiation, turbulence fluxes, mixed layer heights and morning inversion strengths, low-level jets, and land-sea breeze circulations. The comparisons indicate that for the Gulf Coast environment and typical summertime conditions, the Eta PBL scheme clearly outperforms the MRF PBL scheme in nearly all aspects. The results reveal that the popular Dudhia radiation scheme tends to overpredict the downward longwave radiation, which consequently results in a warm bias at night and a weaker nocturnal low level jet. Although the NOAH land surface model is much more sophisticated than the simple soil model, it failed to deliver significantly improved simulations of boundary layer properties for the conditions considered in this study.

Sea breeze Initiated Rainfall over the east Coast of India during the Indian Southwest Monsoon

Abstract: Sea-breeze-initiated convection and precipitation have been investigated along the east coast of India during the Indian southwest monsoon season. Sea-breeze circulation was observed on approximately 70–80% of days during the summer months (June–August) along the Chennai coast. Average sea-breeze wind speeds are greater at rural locations than in the urban region of Chennai. Sea-breeze circulation was shown to be the dominant mechanism initiating rainfall during the Indian southwest monsoon season. Approximately 80% of the total rainfall observed during the southwest monsoon over Chennai is directly related to convection initiated by sea-breeze circulation.

Formulation of an Index for Sea Breezes in Opposing Winds

Abstract: A scaling analysis is conducted to explore the dependence of sea-breeze speed and inland occurrence in the presence of opposing winds on a set of dynamical parameters. The overall aim of the analysis is to develop an index for sea-breeze occurrence in the face of opposing winds, similar to the Biggs and Graves lake-breeze index. Most studies separate sea-breeze speed and sea-breeze inland occurrence or, at best, link the two in linear analyses. This work analyzes the output of a nonlinear numerical mesoscale model ( in idealized simulations) using scaling methods commonly applied in observational studies. It is found that the scaled sea-breeze speed, in response to increasing magnitude of opposing wind, shows two distinct phases: a phase of increasing speed while the sea breeze progresses inland and a phase of sharply decreasing speed when the sea breeze is no longer detected inland. The analysis also allows the development of an index for sea-breeze inland occurrence. This index is an improvement over existing analyses through the use of nonlinear scaling and the use of surface heat flux as opposed to simpler land-sea temperature contrasts.

Dynamics of the Coastal Boundary Layer off Perth, Western Australia

Abstract: Field measurements were used to investigate circulation, mixing processes, and variations in temperature and salinity in the coastal boundary layer off Perth, Western Australia. This region is characterized by a low amplitude diurnal tidal regime, a strong southwesterly summer sea breeze, and a topography dominated by submerged barrier reefs. Subinertial current dynamics were analyzed using a simplified depth-averaged alongshore momentum equation. Offshore of the reefs, the results showed a balance between wind stress, alongshore pressure gradient, and bottom friction and acceleration forces. The alongshore pressure gradient contributed to accelerating the water body, but wind was the dominant driving force for a majority of the time. Onshore of the reefs (lagoonal waters), the alongshore dynamic balance was mainly between wind stress and bottom friction. The temperature variability in Perth coastal waters was in agreement with the seasonal variations in the net air–sea heat flux. The exchange ra...

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

Abstract: 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.

Divergence of turbulent fluxes in the surface layer: case of a coastal city

Abstract: This study quantifies the processes that take place in the layer between the mean building height and the measurement level of an energy balance micrometeo- rological tower located in the dense old core of a coastal European city. The contribu- tions of storage, vertical advection, horizontal advection and radiative divergence for heat are evaluated with the available measurements and with a three-dimensional, high-resolution meteorological simulation that had been evaluated against observa- tions. The study focused on a summer period characterized by sea-breeze flows that affect the city. In this specific configuration, it appears that the horizontal advec- tion is the dominant term. During the afternoon when the sea breeze is well estab- lished, correction of the sensible heat flux with horizontal heat advection increases the measured sensible heat flux up to 100Wm −2 . For latent heat flux, the horizontal moisture advection converted to equivalent latent heat flux suggests a decrease of 50Wm −2 . The simulation reproduces well the temporal evolution and magnitude of

A case study of boundary layer ventilation by convection and coastal processes

Abstract: It is often assumed that ventilation of the atmospheric boundary layer is weak in the absence of fronts, but is this always true? In this paper we investigate the processes responsible for ventilation of the atmospheric boundary layer during a nonfrontal day that occurred on 9 May 2005 using the UK Met Office Unified Model. Pollution sources are represented by the constant emission of a passive tracer everywhere over land. The ventilation processes observed include shallow convection, turbulent mixing followed by large-scale ascent, a sea breeze circulation and coastal outflow. Vertical distributions of tracer are validated qualitatively with AMPEP (Aircraft Measurement of chemical Processing Export fluxes of Pollutants over the UK) CO aircraft measurements and are shown to agree impressively well. Budget calculations of tracers are performed in order to determine the relative importance of these ventilation processes. Coastal outflow and the sea breeze circulation were found to ventilate 26% of the boundary layer tracer by sunset of which 2% was above 2 km. A combination of coastal outflow, the sea breeze circulation, turbulent mixing and large-scale ascent ventilated 46% of the boundary layer tracer, of which 10% was above 2 km. Finally, coastal outflow, the sea breeze circulation, turbulent mixing, large-scale ascent and shallow convection together ventilated 52% of the tracer into the free troposphere, of which 26% was above 2 km. Hence this study shows that significant ventilation of the boundary layer can occur in the absence of fronts (and thus during high-pressure events). Turbulent mixing and convection processes can double the amount of pollution ventilated from the boundary layer.

Blowing in the wind

Abstract: Part of the answer to rising energy needs and costs may literally be blowing in the wind. Among sustainable sources of electricity, only wind energy has the capacity and technology needed to compete in the open marketplace. The largest onshore wind farm in Europe is being built in Scotland, the largest in the USA is planned for southern California, and the biggest offshore wind farm production in the world is slated for the Thames Estuary. But wind is intermittent. Marc Genton and Amanda Hering explain how advanced statistical techniques will enable wind energy to be more efficiently incorporated into the electrical grid.

Diurnal Cycle of Surface Flows during 2004 NAME and Comparison to Model Reanalysis

Abstract: During the North American Monsoon Experiment (NAME), an unprecedented surface dataset was collected over the core monsoon region. Observations from 157 surface sites in this region along with twice-daily Quick Scatterometer (QuikSCAT) oceanic winds were quality controlled and processed into a gridded dataset covering the domain (15°–40°N, 90°–120°W) at 1-h, 0.25° resolution for the period from 1 July to 15 August. Using this dataset, the mean, temporal variability, and diurnal characteristics of the monsoon surface flow are documented with detail not previously possible. Being independent of model data over land, these objectively analyzed surface products are compared to similar analyses from a special North American Regional Reanlysis for NAME (NARR_NAME) that was produced for the same period. Observed surface fields indicate that a robust land–sea breeze circulation is present over most of the Gulf of California (GoC) region in response to the strong diurnal heating of landmasses on both sides...

Observation of Sea Breeze Front and its Induced Convection over Chennai in Southern Peninsular India Using Doppler Weather Radar

Abstract: Sea breeze, the onshore wind over a coastal belt during daytime, is a welcoming weather phenomenon as it modulates the weather condition by moderating the scorching temperature and acts as a favourable mechanism to trigger convection and induce precipitation over coastal and interior locations. Sea breeze aids dispersal of pollutants as well. Observational studies about its onset, depth of circulation and induced precipitation have been carried out in this paper for the period April to September, 2004–2005 using a S-band Doppler Weather Radar functioning at Cyclone Detection Radar Station, India Meteorological Department, Chennai, India. The onset of sea breeze has been observed to be between 0900 and 1000 UTC with the earliest onset at 0508 UTC and late onset at 1138 UTC. The frequency is greater during the southwest monsoon season, viz., June – September and the frequency of initial onset is greater in north Chennai. The modal length of sea breeze is between 20 and 50 km with extreme length as high as 100 km also having been observed. Though the inland penetration is on average 10 to 20 km, penetration reaching 100 km was also observed on a number of cases. The induced convection could be seen in the range 50–100 km in more than 53% of the cases. The mean depth of sea breeze circulation is 300–600 m but may go well beyond 1000 m on conducive atmospheric conditions.