Sea-breeze Front Research Articles

The Impact of Urbanization on Current and Future Coastal Precipitation: A Case Study for Houston

The approach of this study was to determine, theoretically, what impact current and future urban land use in the coastal city of Houston, Texas has on the space and time evolution of precipitation on a ‘typical’ summer day. Regional model simulations of a case study for 25 July 2001 were applied to investigate possible effects of urban land cover on precipitation development. Simulations in which Houston urban land cover was included resolved rain cells associated with the sea breeze front and a possible urban circulation on the northwest fringe of the city. Simulations without urban land cover did not capture the initiation and full intensity of the ‘hypothesized’ urban-induced rain cell. The response is given the terminology the ‘urban rainfall effect’ or URE. An urban growth model (UrbanSim) was used to project the urban land-cover growth of Houston, Texas from 1992 to 2025. A regional atmospheric-land surface model was then run with the 2025 urban land-cover scenario. Though we used a somewhat theoretical treatment, our results show the sensitivity of the atmosphere to urban land cover and illustrate how atmosphere — land interactions can affect cloud and precipitation processes. Two urban-induced features, convergence zones along the inner fringe of the city and an urban low-pressure perturbation, appear to be important factors that lead to enhanced rain clouds independently or in conjunction with the sea breeze. Simulations without the city (NOURBAN) produced less cumulative rainfall in the west-northwest Houston area than simulations with the city represented (URBAN). Future urban land-cover growth projected by UrbanSim (URBAN2025) led to a more expansive area of rainfall, owing to the extended urban boundary and increased secondary outflow activity. This suggests that the future urban land cover might lead to temporal and spatial precipitation variability in coastal urban microclimates. It was beyond the scope of the analysis to conduct an extensive sensitivity analysis of cause — effect relationships, though the experiments provide some clues as to why the rainfall evolution differs. This research demonstrates a novel application of urban planning and weather — climate models. It also raises viable questions concerning future planning strategies in urban environments in consideration of hydroclimate changes.

THE TEMPORAL AND SPATIAL VARIATIONS OF EDDY DIFFUSIVITY ASSOCIATED WITH MOVING SEA BREEZE FRONT

THE TEMPORAL AND SPATIAL VARIATIONS OF EDDY DIFFUSIVITY ASSOCIATED WITH MOVING SEA BREEZE FRONT

The Atlantic inflow to the Saharan heat low: observations and modelling

AbstractThe inflow of relatively cold and stably stratified air from the Atlantic Ocean into western Mauritania and into the southwestern part of the Saharan heat low is studied using the mesoscale COSMO model. This model was used to provide operational forecasts for the GERBILS field campaign, which was conducted by the Met Office in West Africa in June 2007. The forecasts were validated against airborne measurements as well as satellite imagery and were found to represent the main synoptic features of the region accurately.A complex mesoscale feature in western Mauritania, which we call the Atlantic Inflow, was identified in the COSMO model output. The main component of the Atlantic Inflow is the sea breeze and associated front. The sea breeze interacts with larger‐scale, higher‐altitude fluctuations in the thermal and humidity advection. During the day the balance between horizontal advection of cool maritime air and turbulence in the convective boundary layer over land results in a stationary sea breeze front at the coast. Once turbulence dies down in the evening, the sea breeze front penetrates inland. Above the sea breeze layer, thermal advection in the Saharan Atmospheric Boundary Layer (SABL) also controls the structure of the Atlantic Inflow. A marked baroclinic zone was observed, in which the temperature and humidity made a relatively smooth transition from values typical of the Atlantic air to values characteristic of the SABL. Budget calculations showed that, through its cooling and occasional moistening at low levels, the Atlantic Inflow has an important impact on the regional heat and moisture budgets. Copyright © Royal Meteorological Society and Crown Copyright, 2009

Sea-Breeze Convergence Zones from AVHRR over the Iberian Mediterranean Area and the Isle of Mallorca, Spain

Abstract The aim of this study was to identify clear air boundaries and to obtain spatial distribution of convective areas associated with the sea breeze over the Iberian Mediterranean zone and the isle of Mallorca, both in Spain. Daytime Advanced Very High Resolution Radiometer (AVHRR) data from National Oceanic and Atmospheric Administration (NOAA) polar-orbiting satellites were collected for May–October 2004. A cloud detection algorithm was used to identify clouds to derive daytime sea-breeze cloud frequency composites over land. The high-resolution composites aided in identifying the location of five preferential sea-breeze convergence zones (SBCZ) in relation to the shape of coastline and orographic effects. Additionally, eight regimes were designated using mean boundary layer wind speed and direction to provide statistics about the effect of prevailing large-scale flows on sea-breeze convection over the five SBCZ. The offshore SW to W and the NW to N regimes were characterized by high cloud frequencies parallel to the coast. Small differences in mean cloud frequency values from morning to afternoon composites were detected with these regimes because sea-breeze fronts tended to form early and persist into the afternoon. Just the opposite occurred under the onshore NE to E and SE to S regimes. It was found that light to moderate (≤5.1 m s−1) winds aloft result in more clouds at the leading edge of sea breezes. In contrast, strong synoptic-scale (>5.1 m s−1) flows weaken boundary layer convergence. The results from this satellite meteorology study could have practical applications for many people including those that forecast the weather and those that use the forecast for making decisions related to energy use, fishing, recreation, or agriculture activities, as well as for estimating pollution or issuing warnings for heavy rain or flash flooding.

Urban and ocean ensembles for improved meteorological and dispersion modelling of the coastal zone

A high-resolution (1.67 km) ensemble transform (ET)-based meso-scale modelling system utilizing urbanization and sea surface temperature (SST) perturbations is used to examine characteristics of sea breeze/heat island interactions and atmospheric transport and dispersion for Tokyo. The ensemble displays a positive spread—skill relationship, with the addition of urban perturbations enabling the ensemble variance to distinguish a larger range of forecast error variances. Two synoptic regimes are simulated. For a pre-frontal period (stronger synoptic flow), there is less variability among ensemble members in the strength of the urban heat island and its interaction with the sea breeze front. During the post-frontal time period, the sea breeze frontal position is very sensitive to the details of the urban representation, with horizontal frontal variation covering the width of the urban centre (∼30 km) and displaying significant impacts on the development and strength of the heat island. Moreover, the dosage values of a tracer released at offshore and urban sites have considerable variability among ensemble members in response to small-scale features such as coastally upwelled water, enhanced anthropogenic heating and variations in building heights. Realistic variations in SST (i.e. warm Tokyo Bay or local upwelling) produce subtle sea breeze variations that dramatically impact tracer distributions.

The Formation of Sharp Multi-Layered Wind Structure over Tokyo Associated with Sea-breeze Circulation

The front of a sea breeze originating from Sagami Bay passed over Tokyo between 1300 LST and 1400 LST on August 10, 2006. Field observations of wind distributions over Tokyo by the use of a ground-based coherent Doppler lidar developed at the National Institute of Information and Communications Technology showed that a sharp multi-layered structure of vertical wind fields was gradually formed after the sea-breeze front passed the observation site. Numerical simulations using the Weather Research and Forecasting (WRF) model demonstrated that the multi-layered wind structure consisted of 1) the sea breeze at an altitude below 0.8 km above mean sea level (AMSL), 2) a layer of weak winds at an altitude of 0.8-1 km AMSL, 3) a return flow of the sea breeze, and 4) a northerly synoptic wind at an altitude above 3 km AMSL. This is the first direct observation of the formation of sharp multi-layered wind structure over Tokyo associated with sea-breeze circulation.

Estimation of Temporal Variation of Refractive Index Using C-band Doppler Radar Equipped with Magnetron Transmitter

An estimation method for temporal variation of refractive index (RI) using phase data observed by a C-band Doppler radar equipped with a magnetron transmitter is presented. Temporal variation of RI was estimated from phase increments that were caused by temporal atmospheric variations. Because the wavelength of the C-band radar is as short as 5.7 cm, phase wrapping frequently occurs. Thus, number of phase wrapping was counted by monitoring the phase increments at the interval of 30 seconds. Effect of frequency drift of the magnetron transmitter was removed by using phase increments of a reference target and atmospheric delay between the radar site and the reference target. The method was applied to a case study of daytime sea-breeze front in the Kanto plain. The estimated variation of RI, which has the information of water vapor, showed an agreement with the position of the cloud band that was generated in the surface convergence zone.

Urban effects of Chennai on sea breeze induced convection and precipitation

Doppler radar derived wind speed and direction profiles showed a well developed sea breeze circulation over the Chennai, India region on 28 June, 2003. Rainfall totals in excess of 100 mm resulted from convection along the sea breeze front. Inland propagation of the sea breeze front was observed in radar reflectivity imagery. High-resolution MM5 simulations were used to investigate the influence of Chennai urban land use on sea breeze initiated convection and precipitation. A comparison of observed and simulated 10m wind speed and direction over Chennai showed that the model was able to simulate the timing and strength of the sea breeze. Urban effects are shown to increase the near surface air temperature over Chennai by 3.0K during the early morning hours. The larger surface temperature gradient along the coast due to urban effects increased onshore flow by 4.0m s−1. Model sensitivity study revealed that precipitation totals were enhanced by 25mm over a large region 150 km west of Chennai due to urban effects. Deficiency in model physics related to night-time forecasts are addressed.

Sea breeze simulation over the Malay Peninsula in an intermonsoon period

This study presents a characteristic intermonsoon weather situation over the Malay Peninsula. The Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS) is used to investigate the mesoscale details of the simulated sea breeze circulations over the Malay Peninsula on 23 April 2002. The occurrence of sea breeze collisions occurring in the inland region of the southern Malay Peninsula is noted. On the peninsula‐scale, convection was first initiated along the low‐level convergence line that became established along the west coastal region of the Malay Peninsula in the early afternoon. Deep clouds that led to thunderstorms developed in the northwestern part of the Malay Peninsula after the sea breeze encountered the mountain wave induced under the ambient easterlies above the mountain ridge line. The convective activity was further enhanced over the central Malay Peninsula because of the interaction between sea breeze front and gap winds from the mountains. This case study suggests that the Malay Peninsula is a potentially fertile ground for many dynamically interesting case studies of land–sea breeze circulations.

The Influence of the City of Athens on the Evolution of the Sea-Breeze Front

In the present study, we examine the dynamics of a sea-breeze front and the urban heat island interacting with the heavily urbanized city of Athens. For this reason, simulations were performed with a modified version of the PSU/NCAR Mesoscale Model (MM5), whereby urban features are considered, and the model results were compared with surface routine meteorological data. An unrealistic run was also performed, where the city of Athens was replaced by dry cropland and pasture surface, as in the surrounding area. A delay in the sea-breeze front was found during daytime, together with frictional retardation concerning its penetration, as well as inland displacement of the heat island as the air moved over the city of Athens. During nighttime, the wind speed increased over the lower atmosphere in the city centre due to the enhanced urban heat island.

Application of high resolution land use and land cover data for atmospheric modeling in the Houston–Galveston metropolitan area, Part I: Meteorological simulation results

To predict atmospheric conditions in an urban environment, the land surface processes must be accurately described through the use of detailed land use (LU) and land cover (LC) data. Use of the U.S. Geological Survey (USGS) 25-category data, currently in the Fifth-generation Mesoscale Model (MM5), with the Noah land surface model (LSM) and MRF (medium-range forecast) planetary boundary layer (PBL) schemes resulted in the over-prediction of daytime temperatures in the Houston downtown area due to the inaccurate representation as a completely impervious surface. This bias could be corrected with the addition of canopy water in the urban areas from the evapotranspiration effects of urban vegetation. A more fundamental approach would be to utilize an LULC dataset that represents land surface features accurately. The Texas Forest Service (TFS) LULC dataset established with the LANDSAT satellite imagery correctly represents the Houston–Galveston–Brazoria (HGB) area as mixtures of urban, residential, grass, and forest LULC types. This paper describes how the Noah LSM and PBL schemes in the MM5 were modified to accommodate the TFS-LULC data. Comparisons with various meteorological measurements show that the MM5 simulation made with the high resolution LULC data improves the boundary layer mixing conditions and local wind patterns in the Houston Ship Channel, which is a critically important anthropogenic emission area affecting the HGB air pollution problems. In particular, when the synoptic flows are weak, the improved LULC data simulates the asymmetrically elongated Houston heat island convergence zone influencing the location of the afternoon Gulf of Mexico sea-breeze front and the Galveston Bay breeze flows. This paper is part I of a two-part study and focuses on the meteorological simulation. In part II, effects of using the different meteorological inputs on air quality simulations are discussed.

A SIMULATION OF SEA BREEZE OVER FUKUOKA METROPOLITAN AREA

A numerical simulation was carried out to investigate the characteristics of sea breeze intrusion on the Fukuoka Metropolitan area by using ARPS and the results were compared with the field data of sea breeze obtained in August 2, 2003. The sea breeze front runs parallel to the costal line at the beginning of the sea breeze intrusion, but as it goes into the inland, the two-dimensional front becomes wavy and breaks. The sea breeze consists of the tail of about 600 m thickness and the head 1000 m and above high. The head is accompanied with a pair of upward and downward currents that reach to about 2000 m height.

Numerical Simulations on the Effect of Sea–Land Breezes on Atmospheric Haze over the Pearl River Delta Region

The atmospheric haze over the Pearl River Delta (PRD) was investigated by using the Models-3 Community Multi-scale Air Quality modeling system with meteorological fields simulated by the Fifth-generation National Center for Atmospheric Research/Penn State University Mesoscale Model (MM5) from September 26th to September 30th, 2004. The model-simulated meteorological elements and particulate matter with aerodynamic diameter less than 10 μm (PM10) were compared with observations at four air quality-monitoring stations. The results showed that MM5 successfully reproduced the diurnal variations of temperature, wind speed, and wind directions at these stations. The temporal variations of the simulated values were consistent with those of the observed (such as temperature, wind speed, and wind direction). The correlation coefficient was 0.91 for temperature and 0.56 for wind speed. The modeling results show that the spatial distributions of simulated PM10 were closely related to the source emissions indicating three maxima of PM10 over the PRD. The sea–land breezes diurnal cycle played a significant role in the redistribution and transport of PM10. Nighttime land breeze could transport PM10 to the coast and the sea, while daytime sea breeze (SB) could carry the accumulated PM10 offshore back to the inland cities. PM10 could also be transported vertically to a height of up to about 1000 m because of strong turbulence in the SB front. Process analyses indicated that the emission sources and the vertical diffusion were the major processes to influence the concentrations of particulate matter with aerodynamic diameter less than 2.5 μm (PM2.5).

Identification and Interpretation of Representative Ozone Distributions in Association with the Sea Breeze from Different Synoptic Winds over the Coastal Urban Area in Korea

To aid the studies of long-term impact assessment of cumulative ozone (O3) exposures, the representative 8-hr O3 pollution patterns have been identified over the Greater Seoul Area (GSA) in Korea. Principal component analysis and two-stage clustering techniques were used to identify the representative O3 patterns, and numerical and observational analyses were also used to interpret the identified horizontal distribution patterns. The results yielded three major O3 distribution patterns, and each of the three patterns was found to have strong correlations with local and synoptic meteorological conditions over the GSA. For example, pattern 1, accounting for 46% of O3 concentration distributions, mostly occurred under relatively weak westerly synoptic winds. The predominant features of this pattern were infrequent high O3 levels but a distinct gradient of O3 concentration from the western coastal area to the eastern inland area that was mainly induced by the local sea breeze. Pattern 2, accounting for 31% of O3 concentration distributions, was found with higher O3 levels in the western coastal area but lower in the eastern inland area. This is due to the modified sea breeze under the relatively stronger easterly opposing synoptic wind, affecting the high O3 occurrence in the western coastal area only. However, pattern 3, accounting for 21% of O3 concentration distributions, showed significantly higher O3 concentrations over the whole GSA mainly due to the retarded and slow-moving sea-breeze front under the weak opposing synoptic flow. Modeling study also indicated that local and synoptic meteorological processes play a major role in determining the high O3 concentration distribution patterns over the GSA.

Sea breeze signatures on line‐of‐sight microwave links in tropical coastal areas

The unusual fast fading observed around middays on line‐of‐sight microwave links in a tropical coastal area is described. Fading was as deep as 20–30 dB with fade rates double the normal rates. The fading is attributed to multipath propagation produced under sea breeze circulations. Sea breeze circulations modify the boundary layer and cause the formation of a low level super‐refractive layer associated with a temperature inversion above the ground. At the same time, an elevated layer of high refractivity variance is formed at the boundary of the cool and humid marine air flowing on‐shore and the relatively dry and hot air flowing offshore. However, when there is a strong vertical heat transfer from the ground, a modified convective boundary layer with a height of about 100–150 m above the ground with a capping elevated layer at the upper boundary of the sea breeze front is formed. In both cases, specular reflections and scattering of radio signals from the layered structures, along with multiple refractive paths are expected to be the cause of the observed fast daytime fading, which is conspicuously absent on inland paths.

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

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.

Idealized Numerical Simulations of the Interactions between Buoyant Plumes and Density Currents

Idealized numerical experiments using a large-eddy simulation (LES) model are performed to examine the fundamental dynamical processes associated with the interactions between buoyant plumes and density currents. The aim of these simulations is to provide insight into the rapid changes in the structure of plumes that may be observed during the passage of density current phenomena such as thunderstorm outflows, sea-breeze fronts, or intense cold fronts. The LES model results indicate that when the ambient winds are calm the vertical velocity in the plume decreases with the passage of the density current, but that when the ambient winds oppose the motion of the density current a significant increase in vertical velocity in the plume may occur temporarily. In the latter case, the pressure perturbation and the associated region of horizontal convergence that lead the head of the density current interact with the tilted plume, causing the base of the plume to become vertical and resulting in a dramatic increase in vertical velocity within the plume. This basic dynamical behavior occurs over a relatively broad range of parameters, provided the characteristic velocity in the density current (taken as the densimetric speed) exceeds the ambient wind speed. When this is the case, the interaction is dominated by the effect of the density current on the buoyant plume such that the plume is essentially advected as a passive tracer by the flow due to the density current, and the increase in vertical velocity depends on the inverse of the convective Froude number of the buoyant plume.

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

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

Investigation of a sea breeze front in an urban environment

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

Evaluation of Vertical Ozone Profiles Simulated by WRF/Chem Using Lidar-Observed Data

molec. m �3 (～100 ppbv below 1.5 km above sea level ASL) observed on 28 July and 20 August, and the low concentrations on the other days below 1.5 km ASL, as well as day-to-day variations above 1.5 km ASL. The formation mechanism of the observed O3 layer in the typical northward transport case on 28 July was also examined by the model. The O3 plumes entered the free troposphere through vertical transport and mixing near the sea breeze front and southward transport by the return flow in the afternoon. In the evening, the O3 layer formed at 0.7�1.5 km ASL possibly because of less transport between the sea breeze and return flow and longer photochemical lifetime than at the surface.