Showing papers on "Sea breeze published in 2012"

Influence of irrigated agriculture on diurnal surface energy and water fluxes, surface climate, and atmospheric circulation in California

Abstract: The impact of land use change on regional climate can be substantial but also is variable in space and time. Past observational and modeling work suggests that in a ‘Mediterranean’ climate such as in California’s Central Valley, the impact of irrigated agriculture can be large in the dry season but negligible in the wet season due to seasonal variation in surface energy partitioning. Here we report further analysis of regional climate model simulations showing that diurnal variation in the impact of irrigated agriculture on climate similarly reflects variation in surface energy partitioning, as well as smaller changes in net radiation. With conversion of natural vegetation to irrigated agriculture, statistically significant decreases of 4–8 K at 2 m occurred at midday June–September, and small decreases of ~1 K occurred in winter months only in relatively dry years. This corresponded to reduced sensible heat flux of 100–350 W m−2 and increased latent heat fluxes of 200–450 W m−2 at the same times and in the same months. We also observed decreases of up to 1,500 m in boundary layer height at midday in summer months, and marginally significant reductions in surface zonal wind speed in July and August at 19:00 PST. The large decrease in daytime temperature due to shifts in energy partitioning overwhelmed any temperature increase related to the reduced zonal sea breeze. Such changes in climate and atmospheric dynamics from conversion to (or away from) irrigated agriculture could have important implications for regional air quality in California’s Central Valley.

Evaluation of Global Onshore Wind Energy Potential and Generation Costs

Abstract: In this study, we develop an updated global estimate of onshore wind energy potential using reanalysis wind speed data, along with updated wind turbine technology performance, land suitability factors, cost assumptions, and explicit consideration of transmission distance in the calculation of transmission costs. We find that wind has the potential to supply a significant portion of the world energy needs, although this potential varies substantially by region and with assumptions such as on what types of land can be used to site wind farms. Total global economic wind potential under central assumptions, that is, intermediate between optimistic and pessimistic, is estimated to be approximately 119.5 petawatt hours per year (13.6 TW) at less than 9 cents/kWh. A sensitivity analysis of eight key parameters is presented. Wind potential is sensitive to a number of input parameters, particularly wind speed (varying by −70% to +450% at less than 9 cents/kWh), land suitability (by −55% to +25%), turbine density (...

Convective rain cells: Radar-derived spatiotemporal characteristics and synoptic patterns over the eastern Mediterranean

Abstract: [1] This paper examines the spatiotemporal characteristics of convective rain cells over the eastern Mediterranean (northern Israel) and their relationship to synoptic patterns. Information on rain cell features was extracted from high-resolution weather radar data. The radar-gauge adjustment, validation, cell segmentation and tracking techniques are discussed at length at the beginning of the paper. Convective rain cells were clustered into three synoptic types (two winter lows—deep Cyprus lows and shallow lows—and one tropical intrusion, Active Red Sea Trough) using several NCEP/NCAR parameters, and empirical distributions were computed for their spatial and temporal features. In the study region, it was found that the Active Red Sea Trough rain cells are larger, live for less time and possess lower rain intensities than the rain cells generated by the winter lows. The Cyprus low rain cells were found to be less intense and slightly larger on average than the shallow low rain cells. It was further discovered that the preferential orientation of the rain cells is associated with the direction and velocity of the wind. The effect of distance from the coastline was also examined. An increase in the number and area of the rain cells near the coastline was observed, presumably due to the sea breeze convection. The mean rainfall intensity was found to peak near the shore and decrease with distance inland. This information is of great importance for understanding rain patterns and can be further applied in exploring the hydrological responses of the basins in this region.

High-Resolution ASCAT Scatterometer Winds Near the Coast

Abstract: The European Organization for the Exploitation of Meteorological Satellites (EUMETSAT) Ocean and Sea Ice Satellite Application Facility delivers operational wind products from the Advanced Scatterometer (ASCAT) at 25 km and 12.5 km Wind Vector Cell (WVC) spacing. In these products, based on the backscatter processing performed at EUMETSAT, data closer than ~ 70 km (25 km products) or ~ 35 km (12.5 km products) to the coast are flagged because of land contamination. An alternative wind product is presented here which uses a different way of averaging the full resolution (FR) backscatter measurements from ASCAT. The FR backscatter measurements are screened for land contamination in the coastal zone, thus allowing the construction of WVCs that follow the coast line. The implied alternative spatial averaging allows good quality winds over sea as close as 15-20 km to the shore. The alternative (coastal) and nominal products are compared, and the resulting winds are validated with buoy winds, both in coastal and open sea regions. In regions far away from the coast, the ASCAT coastal and nominal products appear to be of identical quality, but fewer WVCs pass the quality control steps for the nominal product, indicating that the coastal product better resolves sub-WVC wind variability. In the coastal region, we anticipate enhanced wind variability due to katabatic and sea breeze effects, among others. However, the quality of the coastal winds in terms of buoy wind component difference standard deviation is almost as good as for the open sea winds.

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

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

The sea breeze/land breeze circulation in Los Angeles and its influence on nitryl chloride production in this region

Abstract: [1] The sea breeze/land breeze diurnal circulation within the Los Angeles Basin and adjacent waters transports marine air into the basin during the day and urban air to Santa Monica Bay during the night. Nitryl chloride, ClNO2 is a nocturnal trace gas formed from the heterogeneous reaction of dinitrogen pentaoxide (N2O5) with chloride containing aerosol. Its photolysis after sunrise produces atomic chlorine radicals and regenerates NO2, both of which may increase ozone production. Mixing of the chloride source from marine sea salt with the urban NOx source in Los Angeles provides conditions ideal for the production of ClNO2. This paper presents an analysis using a wind profiler on the coast and measurements of ClNO2 and its precursors made from both ship and aircraft to assess the prevailing meteorological conditions important for ClNO2 production in this region, with a particular focus on the production over water within the land breeze phase of the circulation. A box model is used to calculate an upper limit to the amount of ClNO2 capable of being produced strictly over Santa Monica Bay during the land breeze. On three out of the four nights of ClNO2 measurements in Santa Monica Bay, the ClNO2 exceeds the upper limit calculated using the box model and shows that the majority of the ClNO2 is produced over the city and transported to Santa Monica Bay by the land breeze. This ClNO2 transport suggests the sea breeze more efficiently transports aerosol chloride inland than land breeze transports NOx offshore.

Surface ozone at a coastal suburban site in 2009 and 2010: Relationships to chemical and meteorological processes

Abstract: [1] Air quality and meteorological measurements were conducted at the Chemistry and Physics of the Atmospheric Boundary Layer Experiment (CAPABLE) site during the summers of 2009 and 2010 in Hampton, Virginia. Significant differences in surface ozone mixing ratios were observed between the two years and are correlated with meteorological parameters such as temperature, humidity, and cloud cover. The number of exceedance days for ozone set by the U.S. Environmental Protection Agency within this region has been decreasing for the past decade, especially in urban areas. There were no exceedance days with respect to ozone in 2009, and there were four exceedance days in 2010. The four highest ozone daily maxima and the two exceedance days observed during the 2010 measurement period were coincident with sea breeze phenomena. In one case, surface ozone increased at a rate of 14.6 ppb h−1 with the passage of a sea breeze front. A comprehensive multilinear regression model as well as an operational forecast was unable to resolve the high ozone observed during sea breeze events. As the number of exceedance days per year within this region continues to decrease, accurately forecasting sea breezes may become more important for the forecasting of pollution events.

The Persian Gulf summertime low‐level jet over sloping terrain

Abstract: There are few observational and numerical studies of the summertime low-level jet (LLJ) over the Persian Gulf, known as the shamal. In this study, the Weather Research and Forecasting (WRF) model accurately simulates the LLJ's vertical structure, nocturnal features and strong diurnal variation of the wind. The case-study period is divided into a period during which the shamal is spatially extended (strong winds over the Gulf and Iraq) and a period during which it is less spatially extended (strong flow only over the Gulf). Orography, mountain slope and land/sea breeze are found to be key factors for the shamal diurnal variation of wind speed and wind direction; the Blackadar mechanism appears to be secondary to the heating in forcing the shamal. The Zagros Mountains not only channel the northwesterly winds but also provide a barrier for the easterly monsoon airflow, which maximizes the wind speed. Only during the less extensive period does the Zagros Mountains slope significantly affect the shamal wind intensity and direction. Both shallow and steep mountain slope sensitivity studies feature a jet-like flow over the Persian Gulf. The steep slopes cause larger wind speeds; however, the shallow slopes reveal a stronger diurnally varying wind direction due to larger heating and cooling of the sloping terrain. It is also shown that, during the less extensive period, the land breeze and the lower friction over the sea increase the intensity of the nocturnal jet over the Gulf. Copyright © 2011 Royal Meteorological Society

Topographic Effects on the Tropical Land and Sea Breeze

Abstract: The effect of an inland plateau on the tropical sea breeze is considered in terms of idealized numerical experiments, with a particular emphasis on offshore effects. The sea breeze is modeled as the response to an oscillating interior heat source over land. The parameter space for the calculations is defined by a nondimensional wind speed, a scaled plateau height, and the nondimensional heating amplitude.The experiments show that the inland plateau tends to significantly strengthen the land-breeze part of the circulation, as compared to the case without terrain. The strengthening of the land breeze is tied to blocking of the sea-breeze density current during the warm phase of the cycle. The blocked sea breeze produces a pool of relatively cold, stagnant air at the base of the plateau, which in turn produces a stronger land-breeze density current the following morning. Experiments show that the strength of the land breeze increases with the terrain height, at least for moderate values of the height...

Observations of Urban Heat Island Influence on Lake-Breeze Frontal Movement

Abstract: Predictions of lake and sea breezes are particularly important in large coastal population centers because of the circulations’ influence on heat-wave relief, energy use, precipitation, and dispersion of pollutants. While recent numerical modeling studies have suggested that sea or lake breezes should move more slowly through urban areas than in the surrounding suburbs because of urban heat island (UHI) circulations, there have been few quantitative observational studies to evaluate these results. This study utilizes high-resolution Weather Surveillance Radar-1988 Doppler (WSR-88D) observations to determine the effect of the UHI on lake-breeze frontal movement through Chicago, Illinois, and nearby suburban areas. A total of 44 lake-breeze cases from the April–September 2005 period were examined. The inland movement of the lake-breeze front (LBF) was calculated by tracking “fine lines” of radar reflectivity along several cross sections perpendicular to the Lake Michigan shoreline. The average inlan...

A case of offshore convective initiation by interacting land breezes near Darwin, Australia

Abstract: A case of offshore convective initiation by interacting land breezes near Darwin, Australia is investigated using convection-permitting model simulations, radar-derived precipitation observations, thermodynamic profiles from radiosonde soundings and surface measurements. These analyses elucidate the convergence of two land breezes in the Van Diemen Gulf, one originating from the Tiwi Islands and the other from mainland Australia; the convergence is sufficient to initiate a line of convection that forms parallel to the mainland coast in the early morning. While differing in small-scale features, the modeled system shows reasonably good agreement with the observed precipitation accumulations. However, using simulations with different initialization times and examining a second case, it is shown that the representation of the land-breeze system and subsequent convective initiation is very sensitive to the upstream wind and thermodynamic conditions, making correct simulation of these processes challenging.

Response of London's urban heat island to a marine air intrusion in an easterly wind regime

Abstract: Numerical simulations are conducted using the Weather Research and Forecast numerical model to examine the effects of a marine air intrusion (including a sea-breeze front), in an easterly wind regime on 7 May 2008, on the structure of London’s urban heat island (UHI). A sensitivity study is undertaken to assess how the representation of the urban area of London in the model, with a horizontal grid resolution of 1 km, affects its performance characteristics for the near-surface air temperature, dewpoint depression, and wind fields. No single simulation is found to provide the overall best or worst performance for all the near-surface fields considered. Using a multilayer (rather than single layer or bulk) urban canopy model does not clearly improve the prediction of the intensity of the UHI but it does improve the prediction of its spatial pattern. Providing surface-cover fractions leads to improved predictions of the UHI intensity. The advection of cooler air from the North Sea reduces the intensity of the UHI in the windward suburbs and displaces it several kilometres to the west, in good agreement with observations. Frontal advection across London effectively replaces the air in the urban area. Results indicate that there is a delicate balance between the effects of thermal advection and urbanization on near-surface fields, which depend, inter alia, on the parametrization of the urban canopy and the urban land-cover distribution.

Improving High-Resolution Numerical Weather Simulations by Assimilating Data from an Unmanned Aerial System

Abstract: In this study, it is demonstrated how temperature, humidity, and wind profile data from the lower troposphere obtained with a lightweight unmanned aerial system (UAS) can be used to improve high-resolution numerical weather simulations by four-dimensional data assimilation (FDDA). The combined UAS and FDDA system is applied to two case studies of northeasterly flow situations in southwest Iceland from the international Moso field campaign on 19 and 20 July 2009. Both situations were characterized by high diurnal boundary layer temperature variation leading to thermally driven flow, predominantly in the form of sea-breeze circulation along the coast. The data assimilation leads to an improvement in the simulation of the horizontal and vertical extension of the sea breeze as well as of the local background flow. Erroneously simulated fog over the Reykjanes peninsula on 19 July, which leads to a local temperature underestimation of 8 K, is also corrected by the data assimilation. Sensitivity experime...

California reanalysis downscaling at 10 km using an ocean-atmosphere coupled regional model system

Abstract: [1] A fully coupled regional downscaling system based on the Regional Spectral Model (RSM) for atmosphere and the Regional Ocean Modeling System (ROMS) for the ocean was developed for the purpose of downscaling observed analysis or global model outputs. The two models share the same grid and resolution with efficient parallelization through the use of dual message passing interfaces. Coupled downscaling was performed using historical Simple Ocean Data Assimilation (SODA) oceanic reanalysis and NCEP/DOE (R-2) atmospheric reanalysis in order to study the impact of coupling on the regional scale atmospheric analysis. The results were subsequently compared with the uncoupled downscaling forced by the prescribed observed sea surface temperature (SST). The coupled experiment yielded the SST and ocean current with realistic small-scale oceanic features that are almost absent in the oceanic reanalysis. Upwelling over the California coast is well resolved and comparable to findings obtained from high-resolution observations. The coupling impact on the atmospheric circulation mainly modulates the near surface atmospheric variables when compared to the simulation conducted without coupling. The duration of the Catalina Eddy detected in the coupled experiment increased by about 6.5% when compared to that in the uncoupled experiment. The offshore land breeze is enhanced by about 10%, whereas the change in the onshore sea breeze is very small during the summer.

Integration of Lidar Data into a Coupled Mesoscale–Land Surface Model: A Theoretical Assessment of Sensitivity of Urban–Coastal Mesoscale Circulations to Urban Canopy Parameters

Abstract: Urban–coastal circulations affect urban weather, dispersion and transport of pollutants and contaminants, and climate. Proper characterization and prediction of thermodynamic and dynamic processes in such environments are warranted. A new generation of observation and modeling systems is enabling unprecedented characterization of the three-dimensionality of the urban environment, including morphological parameters. Urban areas of Houston, Texas, are classified according to lidar-measured building heights and assigned typical urban land surface parameters appropriate to each classification. The lidar data were degraded from 1 m to the model resolution (1 km) with the goal of evaluating the impact of degraded resolution urban canopy parameters (UCPs) and three-dimensionality on the coastal–urban mesoscale circulations in comparison to typical two-dimensional urban slab approaches. The study revealed complex interactions between the sea breeze and urban heat island and offers a novel diagnostic tool,...

Where is the ideal location for a US East Coast offshore grid

Abstract: This paper identifies the location of an “ideal” offshore wind energy (OWE) grid on the U.S. East Coast. The ideal location would provide the highest overall and peak-time summer capacity factor, use bottom-mounted turbine foundations (depth ≤50 m), connect regional transmissions grids from New England to the Mid-Atlantic, and finally, have a smoothed power output, reduced hourly ramp rates and hours of zero power. Hourly, high-resolution mesoscale weather model data from 2006–2010 were used to approximate wind farm output. The offshore grid was located in the waters from Long Island, New York to the Georges Bank, ≈450 km east. Twelve candidate 500 MW wind farms were located randomly throughout that region. Four wind farms (2000 MW total capacity) were selected for their synergistic meteorological characteristics that reduced offshore grid variability. Sites which were likely to have sea breezes helped increase the grid capacity factor during peak time in the spring and summer months. Sites far offshore, dominated by powerful synoptic-scale storms, were included for their generally higher but more variable power output. By interconnecting all 4 farms via an offshore grid versus 4 individual interconnections, power was smoothed, the no-power events were reduced from 9% to 4%, and the combined capacity factor was 48% (gross). By interconnecting offshore wind energy farms ≈450 km apart, in regions with offshore wind energy resources driven by both synoptic-scale storms and mesoscale sea breezes, substantial reductions in low/no-power hours and hourly ramp rates can be made.

The coupled Hudson River estuarine-plume response to variable wind and river forcings

Abstract: Observations of the Hudson River plume were taken in the spring of 2006 in conjunction with the Lagrangian Transport and Transformation Experiment using mooring arrays, shipboard observations, and satellite data. During this time period, the plume was subjected to a variety of wind, buoyant, and shelf forcings, which yield vastly different responses in plume structure including a downstream recirculating eddy. During weak and downwelling winds, the plume formed a narrow buoyant coastal current that propagated downstream near the internal wave speed. Freshwater transport during periods when the downwelling wind was closely aligned with the coast was near the river discharge values. During periods with a cross-shore component to the wind, freshwater transport in the coastal current estimated by the mooring array is less than the river discharge due to a widening of the plume that leads to the internal Rossby radius scaling for the plume width to be invalid. The offshore detachment of plume and formation of a downstream eddy that is observed surprisingly persisted for 2 weeks under a variety of wind forcing conditions. Comparison between mooring, shipboard, and satellite data reveal the downstream eddy is steady in time. Shipboard transects yield a freshwater content equal to the previous 3 days of river discharge. The feature itself was formed due to a large discharge following a strong onshore wind. The plume was then further modified by a brief upwelling wind and currents influenced by the Hudson Shelf Valley. The duration of the detachment and downstream eddy can be explained using a Wedderburn number which is largely consistent with the wind strength index described by Whitney and Garvine (J Geophys Res 110:C03014 1997).

Continuous detection and characterization of the Sea Breeze in clear sky conditions using Meteosat Second Generation

Abstract: . The sea breeze (SB) is a thermally induced boundary layer phenomenon that occurs at coastal locations throughout the world. Previous satellite remote sensing studies used low-level clouds formed over the sea-breeze convergence zones to identify the SB. In this study continuous thermal infrared data from a geostationary satellite (Meteosat Second Generation) and concurrent field measurements were used to detect and characterize the SB in clear sky conditions during the summer. Surface data (wind speed and direction) from 11 sites over Israel for ten summer days in July 2010 for three different synoptic circulation categories were selected. In order to assess the impact of the synoptic induced flow on the SB, we looked for the best agreement between surface and satellite SB timing. An independent classification of synoptic categories performed for the ten summer days revealed two distinct patterns of the SB. During weak horizontal pressure gradient (Weak Persian Trough and High to the West), which enables full development of the SB, the timing of the SB from satellite and field measurements were well correlated (R2 = 0.75), as compared to unfavorable atmospheric conditions (Deep Persian Trough) yielding lower value (R2 = 0.5). The SB was identified by surface measurements in an earlier time of the day, with respect to the satellite column integrated measurements. Visualizing timing of the SB retrieved from satellite data enabled distinction of SB behavior under different synoptic categories. Over desert regions the strong thermal contrast enables detection of the SB even under suppressing synoptic conditions (Deep Persian Trough). This method enables detection and timing of the SB over desert regions where clouds and field measurements are scarce, and is applicable worldwide.

Sea breezes drive currents on the inner continental shelf off southwest Western Australia

Abstract: In southwest Western Australia, strong and persistent sea breezes are common between September and February. We hypothesized that on the inner continental shelf, in the absence of tidal forcing, the depth, magnitude, and lag times of the current speed and direction responses to sea breezes would vary though the water column as a function of the sea breeze intensity. To test this hypothesis, field data were used from four sites were that were in water depths of up to 13 m. Sites were located on the inner continental shelf and were on the open coast and in a semi-enclosed coastal embayment. The dominant spectral peak in currents at all sites indicated that the majority of the spectral energy contained in the currents was due to forcing by sea breezes. Currents were aligned with the local orientation of the shoreline. On a daily basis, the sea breezes resulted in increased current speeds and also changed the current directions through the water column. The correlation between wind–current speeds and directions with depth, and the lag time between the onset of the sea breeze and the response of currents, were dependent on the intensity of the sea breezes. A higher correlation between wind and current speeds occurred during strong sea breezes and was associated with shorter lag times for the response of the bottom currents. The lag times were validated with estimates of the vertical eddy viscosity. Solar heating caused the water column to stratify in summer and the sea breezes overcame this stratification. Sea breezes caused the mixed layer to deepen and the intensity of the stratification was correlated to the strength of the sea breezes. Weak sea breezes of 14 m s−1 caused only slight thermal stratification up to 0.5°C. Apart from these effects on the vertical structure of water column, the sea breezes also influenced transport and mixing in the horizontal dimension. The sea breezes in southwest Western Australia rotated in an anticlockwise direction each day and this rotation was translated into the currents. This current rotation was more prominent in surface currents and in the coastal embayment compared to the open coast.

The Effect of Variable Sea Surface Temperature on Forecasting Sea Fog and Sea Breezes: A Case Study

Abstract: A preliminary study of the effect of sea surface temperature (SST) temporal and spatial variability on regional coastal weather forecasts is described. A high-resolution numerical weather forecast model from the Met Office is run for the U.K. region with hourly updates of SST data obtained from a shelf sea model. When compared with a control run in which SST is maintained with Operational Sea Surface Temperature and Sea Ice Analysis (OSTIA) data, it is found that there are significant differences in the coastal-region forecasts for sea breezes and fog formation. The control run underestimates surface temperature and the strength of the sea breeze when compared with the run with hourly SST updates.

A Linear Theory of Three-Dimensional Land–Sea Breezes

Abstract: Land–sea breezes (LSBs) induced by diurnal differential heating are examined using a three-dimensional linear model employing fast Fourier transform with emphasis on the complex coastline shape and geometry, the earth’s rotation, and background wind effects. It has been demonstrated that the low-level vertical motion associated with LSB can be significantly enhanced over a bay (peninsula) because of convergence of perturbations induced by differential heating along a seaward concave (convex) coastline. The dependence of surface winds and vertical motion patterns and their evolutions on the coastline geometries such as the width and the aspect ratio of the bay, the earth’s rotation, and the background winds are investigated.The LSB induced by an isolated tropical island is characterized by onshore flow and ascent over the island in the afternoon to early evening, with a reversal of direction from midnight to early morning. The diurnal heating–induced vertical motion is greatly enhanced over the isl...