Showing papers on "Sea breeze published in 1990"

Numerical Study of the Influence of Environmental Conditions on Lake-Effect Snowstorms over Lake Michigan

Abstract: Numerical simulations are used to examine the influence of environmental parameters on the morphology of lake effect snowstorms over Lake Michigan. A series of model sensitivity studies are performed using the Colorado State University mesoscale model to examine the effects of lake–land temperature difference, surface roughness, atmospheric boundary layer stability, humidity, and wind speed and direction on the morphology of simulated storms. Four morphological types of lake effect snowstorms have been identified: (i) Broad area coverage, which may become organized into wind parallel bands or cellular convection; (ii) shoreline bands with a line of convection roughly parallel to the lee shore and a well developed land breeze on the lee shore; (iii) midlake band with low-level convergence centered over the lake; and (iv) mesoscale vortices with a well-developed cyclonic flow pattern in the boundary layer. The model is able to reproduce all four morphological types. Simulations varying environmenta...

Numerical studies on the inland penetration of sea breeze fronts at a coastline with tidally flooded mudflats

Abstract: Un modele numerique a moyenne echelle avec un maillage non uniforme d'au moins 1 km de cote est utilise pour etudier le developpement de la circulation et du front de brise marine en fonction de differentes caracteristiques cotieres et de la maree

Vertical Structure of the Sea Breeze Penetrating through a Large Urban Complex

Abstract: A series of observations of the three-dimensional wind and thermal structure of the boundary layer was carried out during each summer season from 1986 to 1988 over the western portion of the Kanto plain. The data obtained during five selected days were analyzed, focusing on the sea breeze system which advances north-westward from Tokyo Bay through the Tokyo metropolitan area. A distinct sea breeze front was found on three of the days examined, whereas no front was observed during the remaining two days. The difference in the synoptic weather conditions between the frontal and non-frontal days was small, although a definite difference was found in the convective-scale thermal structure. Temporal and spatial interpolation methods followed by an adjustment using a variational analysis technique were applied to analyze the three-dimensional wind distribution. Trajectories of air parcels wore examined, based on the interpolated wind held. As a result, it was found that, for the frontal case, the upwar...

An observational aircraft-based study of sea-breeze frontogenesis

Abstract: In the summer of 1988/89 flights were carried out in the Coorong coastal area of South Australia to investigate sea-breeze fronts. The flights yielded data sets of the structure of the fronts in the cross-frontal direction with a spatial resolution of approximately 3 m. The study is focused on the budgets of sensible and latent heat in the vicinity of the front and on frontogenesis/frontolysis processes which are closely related to budget considerations.

Sea breeze in Mallorca. A numerical study

Abstract: The Spanish island of Mallorca is located almost in the centre of the western Mediterranean. Very often from April to October, and almost every day during the summer, the sea breeze circulation develops. The shape and the topography of the island determine that the main characteristic feature of the sea breeze is the existence of a convergence line in the centre of the island. In this paper we describe the sea breeze circulation. A very simple non-eulerian numerical model allows us to simulate the evolution of the circulation during 24 hours.

Combination of Local Wind Systems under Light Gradient Wind Conditions and Its Contribution to the Long-Range Transport of Air Pollutants

Abstract: The meteorological structure and transport mechanism of long-range transport of air pollutants from the coastal region to the mountainous inland region were investigated using joint field observation data. The observations were conducted during 26–30 July 1983 over a wide area from the coastal region around Tokyo Bay to the mountainous region located in central Japan. Air, polluted around the Tokyo Bay area during the early morning remained there until noon, being transformed by photochemical reactions. It was then transported inland, at first by the extended sea breeze and thereafter by the large-scale wind system, toward the thermal low generated in the mountainous central region. At about 1600 Japan Standard Time (JST), polluted air penetrated into the mountainous region, and after sunset it drained down along the valley in the form of a gravity current. The path of the polluted air was in good agreement with the air trajectory started Tokyo at an altitude of 100 m, calculated from pilot-ballo...

Cloud and convection frequencies over the southeast United States as related to small-scale geographic features

Abstract: Based on relatively high spatial and temporal resolution satelite data collected at 0700 CST and at each hour from 1000 CST to 1700 CST during the summer of 1986, cloud and convection variations over the area from Mississippi east to Georgia and from the Gulf of Mexico north to Tennessee are discussed. The data analyses show an average maximum cloud frequency over the land areas at 1400 local time and a maximum of deep convection one hour later. Both cloudiness and deep convection are found to be at a maximum during the nocturnal hours over the Gulf of Mexico. Cloud frequency shows a strong relationship to small terrain features. Small fresh water bodies have cloud minima relative to the surroundings in the afternoon hours. Higher, steep terrain shows cloud maxima and the adjacent lower terrain exhibits afternoon cloud minima due to a divergence of mountain breeze caused by the valley.

Operating ranges of mesoscale numerical models and meteorological wind tunnels for the simulation of sea and land breezes

Abstract: The operating ranges of mesoscale numerical models and meteorological wind tunnels for sea- and land-breeze simulations are defined in this paper based on a review of the theoretical and practical limitations of these two approaches. Numerical-model operating ranges are limited by the choice of governing equations, the numerical methods used to solve the governing equations, the scales of the surface or atmospheric forcing and the atmospheric response, the specified grid resolution and domain size, and the available computer resources. Wind-tunnel operating ranges are limited by the dimensions of the simulated circulations and of the tunnel itself, the tunnel flow speed and turbulence characteristics, the temperature gradients within the tunnel, the lack of Coriolis force and moist processes, and the characteristics of the measurement instrumentation. The operating ranges of these two simulation methods are shown to overlap. In this common range, results of simulations from both approaches can be compared so as to strengthen the validity of the results and to help in the development and improvement of parameterizations of physical processes in numerical models. In addition, the coupling of meteorological wind tunnels and mesoscale numerical models offers a larger range of operating conditions than can be achieved by either approach alone. Together, they can be used in a hybrid form to predict atmospheric conditions at the scale of a few meters for complex terrain (e.g., buildings, hills, etc.) within larger mesoscale atmospheric flow regimes. In the case of sea and land breezes, the sea-land transition zone and coastal internal boundary layer can be studied using both approaches.

Numerical Investigation of Mesoscale Circulations over the Los Angeles Basin. Part II: Synoptic Influences and Pollutant Transport

Abstract: This paper describes the influence of large-scale flows on mesoscale circulations and pollutant transport in the Los Angels Basin. National Meteorological Center (NMC) gridded data for twenty-six basin smog episodes were composited, and summer and winter synoptic-scale wind and temperature profiles were created. The 24-h evolution of the atmosphere in and around the basin was simulated, both with and without large-scale winds, using a three-dimensional mesoscale model. Light large-scale winds had little influence on the strong summertime mesoscale circulations, but stronger large-scale winds exerted considerable influence on the weak mesoscale wintertime circulations. During both seasons, daytime upslope flows near the mountains ventilate the basin, inducing basinwide airflow and augmenting the sea breeze. Air from the basin's planetary boundary layer (PBL) travels upslope and rises over the ridgetops, where it mixes convectively to great heights; winds aloft then transport the air from the regio...

Dynamics of the Cape Farewell upwelling plume, New Zealand

Abstract: Hydrological observations made in January 1984 in the region near Cape Farewell, New Zealand, are described and previously published observations reviewed. It is shown that upwelling depends on the existence of the intermittent Westland Current, and is intensified by an onshore wind. Such a wind induces a fall in sea level near Cape Farewell, and the resulting favourable sea surface slope accelerates deep water over the bathymetric rise inshore of Kahurangi Shoals. The hydraulic response of the thermocline, coupled with a coastal convergence of the bottom Ekman flow, produce a strong upwelling source near Kahurangi Point.

Boundary Layer and Mesoscale Structure over Lake Michigan during a Wintertime Cold Air Outbreak

Abstract: An investigation of a cloud-topped boundary layer during a wintertime cold air outbreak over Lake Michigan has been conducted based on research aircraft 1 and 20 Hz data for five vertically-stacked levels within the boundary layer. Mean east-west cross sections for this northerly flow event have been prepared for heat, moisture, and momentum fields along with spectral decomposition and turbulent flux statistics. Results have been interpreted on the basis of three generalized spatial domains: mesoscale ≥5 km, large eddies from 100 m to <5 km, and higher frequency turbulence <100 m. Mesoscale structures identified in the mean cross-sections include the lower Michigan land breeze, a strong offshore convergence snow band, cloud streets and precipitation bands over the lake, and entrainment spikes in the vicinity of the inversion layer. Analyses of particle concentrations, sizes, and liquid water content have also been presented in mean cross sections, which correspond well with all identifiable mesos...

Mesoscale model response to random, surface-based perturbations — A sea-breeze experiment

Abstract: The introduction into a mesoscale model of random (in space) variations in roughness length, or random (in space and time) surface perturbations of temperature and friction velocity, produces a measurable, but barely significant, response in the simulated flow dynamics of the lower atmosphere. The perturbations are an attempt to include the effects of sub-grid variability into the ensemble-mean parameterization schemes used in many numerical models. Their magnitude is set in our experiments by appeal to real-world observations of the spatial variations in roughness length and daytime surface temperature over the land on horizontal scales of one to several tens of kilometers. With sea-breeze simulations, comparisons of a number of realizations forced by roughness-length and surface-temperature perturbations with the standard simulation reveal no significant change in ensemble mean statistics, and only small changes in the sea-breeze vertical velocity. Changes in the updraft velocity for individual runs, of up to several cms-1 (compared to a mean of 14 cms-1), are directly the result of prefrontal temperature changes of 0.1 to 0.2K, produced by the random surface forcing. The correlation and magnitude of the changes are entirely consistent with a gravity-current interpretation of the sea breeze.

The Land/Sea Breeze Experiment (LASBEX)

Abstract: The Land/Sea Breeze Experiment (LASBEX) was conducted at Moss Landing, California, 15–30 September 1987. The experiment was designed to study the vertical structure and mesoscale variation of the land/sea breeze. A Doppler lidar, a triangular array of three sodars, two sounding systems (one deployed from land and one from a ship), and six surface weather stations (one shipborne) were sited around the Moss Landing area. Measurements obtained included ten sea-breeze and four land-breeze events. This paper describes the objectives and design of the experiment, as well as the observing systems that were used. Some preliminary results and selected observations are presented, called from the data collected, as well as the ensuing analysis plans.

Sensitivity of Local Predictions to Initial Conditions

Abstract: A hydrostatic, anelastic mesoscale numerical model is used to study the predictability of a sea breeze type of circulation over La Plata River in South America. The experiments are designed to test the sensitivity of the predictions to uncertainties in the initial wind field. They consist in the comparison of control and perturbed forecasts which differ only in the initial specification of the wind held. In the case of small-domain prediction systematic uncertainties are probably more representative of actual initial uncertainties than are random, uncorrelated uncertainities. In order to study such cases we systematically add to or subtract from the control run at every grid point a constant value equal to the typical error in the measurement of the wind. We also perform other experiments on a larger domain covering most of South America. The results show that the predictions of the sea breeze type of circulation in the boundary layer around the La Plata River are sensitive to errors in the initi...

Winter Offshore/Onshore Wind Differences in Southeastern Hudson Bay, Canada

Abstract: Acquisition of two 38-day wind data sets collected over a fast-ice shelf and at a nearby coastal weather station (Kuujjuarapik) in Hudson Bay allowed the calculation for the first time of an offshore/onshore wind speed ratio for an ice-covered environment. Mean wind over the ice was 29% higher than at the coast, compared to values of 65% for open ocean locations. This reflects the effect of the higher drag coefficient of the sea ice that more strongly attenuates the wind than does the sea surface. The data set also allowed the evaluation of the change in the wind field by local topography. Thus, a strong orographic effect was found in the SW quadrant, as winds of less than 5 m/s were deflected toward the SE and NW.

Sea breeze: Induced mesoscale systems and severe weather

Abstract: Sea-breeze-deep convective interactions over the Florida peninsula were investigated using a cloud/mesoscale numerical model. The objective was to gain a better understanding of sea-breeze and deep convective interactions over the Florida peninsula using a high resolution convectively explicit model and to use these results to evaluate convective parameterization schemes. A 3-D numerical investigation of Florida convection was completed. The Kuo and Fritsch-Chappell parameterization schemes are summarized and evaluated.

Numerical analysis of dispersion over a near-mountain coast

Abstract: Local winds, of low or moderate intensity, such as sea and land breezes, have attracted the interest of many investigators, with respect to the air pollution problem. But, though in reality most coastal areas are surrounded by mountains or hill barriers, sea-land breezes and mountain-valley flows have mostly been investigated separately. On the other hand, few studies have attempted dispersion simulations in seaside regions with pronounced terrain features. The aim of the present analysis is to examine the effect of a quite high natural barrier near shore on sea breeze and pollutant transport characteristics, in case of a prevailing calm. For this purpose, a two-dimensional mountain range, 1000 m high, adjacent to a sea surface at one side is considered, with a point source located 40 km offshore. The domain represents an idealization of the greater Athens area.

Enhancement of Crosswind Pollutant Dispersion by Steadily Veering Winds in Sea Breezes

Abstract: An estimate is given of the relative importance of wind veering and turbulent diffusion in the mean horizontal spread of pollutant plumes in the atmosphere. Documented veering rates in sea breezes are used to illustrate the effect, and it is concluded that for typical sea breeze induced veering, the effect will be significant over much of the range of applicability of the Gaussian plume model.

Numerical analysis of characteristics of atmospheric dispersion around Tokai nuclear site for emergency plan.

Abstract: In order to make an effective countermeasure plan against an accidental release of radioactivity, it is important to grasp characteristics of atmospheric dispersion in objective areas beforehand. This paper describes the numerical analysis of characteristics of atmospheric dispersion and dose distribution in an emergency around the Tokai nuclear site, based on the analysis of observed meteorological data.Analysis of meteorological data at Tokai shows that steady flows from the northeast and land-sea breeze circulations characterize contamination of the land. Results obtained from simulations of atmospheric dispersion under such conditions are:1) The dose distribution can be represented approximately by Gaussian plume model, when radioactivity is discharged into the steady northeast wind.2) In the case of a short term release for the period of wind changing from the land to sea breeze, the dose distribution is formed in the shape of an unfolded fun with an angle of approximately 90°. The high contamination area is sometimes 1.5 times larger than that of the steady wind case.