Showing papers on "Sea breeze published in 1989"

An Analytical Study of the Sea Breeze

Abstract: In this paper we present theoretical results concerning the sea breeze intensity and its inland penetration as a function of latitude and friction. We produce solutions for the spatial structure of the streamfunction and momentum components and for their Line behavior in the case of a step function forcing of finite duration, and in the case of periodic forcing. Results show that the sea breeze initially has an aspect ratio equal to unity and that earth rotation and friction aged its intensity but they are unimportant in determining its early geometry. The sea breeze has a characteristic time scale which is a combination of the inertial period and the e-folding time due to friction. For a time larger than this characteristic time scale, the inland penetration of the sea breeze is confined by a Rossby deformation radius, which includes a frictional effect. In fact, friction and inertia reduce, not only the intensity, but also the horizontal scale of motion; at the equator the controlling parameter...

Numerical modelling of the offshore extent of sea breezes

Abstract: Two- and three-dimensional versions of a nonlinear atmospheric model were used to investigate environmental controls on the offshore influence of sea-breeze circulations. The temperature of the water surface relative to the atmospheric temperature had a small effect when the water was colder than the overlying air, and a greater effect when the water temperature was high enough to create convective mixing in the planetary boundary layer over the water. Ambient thermal stratification, including elevated inversions with thermal stratification similar to trade wind inversions, had a small influence. The predicted offshore extent of the sea breeze was substantially affected by latitude. The effects of both ambient stratification and latitude were generally consistent with predictions of linear theory. Prevailing synoptic winds were also found to have a significant effect on the sea breeze offshore, with offshore influence greatly suppressed by onshore large-scale flow. Curvature of the coastline produces slightly stronger winds offshore for a concave coast than for a convex coast. The subsidence offshore also extends further over the water for a concave coast than for a convex coast. The model predictions were compared with previous investigations which used linear theory. It was found that the present results agreed with the linear theory of R. Rotunno with regard to the effects of latitude and ambient thermal stability. Linear theory is less suitable for explaining the effects of water temperature, owing to the simplified treatment of turbulent exchange necessary for a tractable linear model.

Inland penetration of the sea breeze over the suburban area of Tokyo

Abstract: Observational results of the structure of the sea breeze over the urban and suburban areas of Tokyo for four summer days are presented. On two of these days, the inland penetration of the sea breeze front could be clearly traced. In one case, the sea breeze was first observed along the shores of Tokyo Bay around 0900 JST, and propagated in three hours through the Tokyo City area, the width of which is about 20 km. It then advanced inland at a rate of 16 km h−1. Prior to the arrival of the sea breeze at the suburban site, the mixing height had remained at about 600 m for four hours. With the arrival of the sea breeze front, accompanied by an abrupt change in wind speed and direction, the mixing height increased sharply to 1700 m. It is suggested that this behavior and the structure of the front are intensified due to the urban effect, or the difference in the thermal characteristics between the urban and rural areas. On the days without a sea breeze front, the land breeze system during the early morning was less intense, allowing the sea breeze to develop simultaneously with the inland valley wind and easily form a large-scale local wind system during the morning hours. In both cases, the vertical motion accompanying the local wind system works as a feedback mechanism to control the local winds by modifying the thermal and pressure fields.

Numerical Simulation Of Sea Breezes with Vertical Wind Shear during Dry Season at Cape of Three Points, West Africa

Abstract: The airflow over Cape of Three Points (Gulf of Guinea: 4.5°N, 2°W) has been simulated using a three-dimensional mesoscale model in order to investigate the sea breeze developing in synoptic vertical wind shears during the 1979 dry season. Two different meteorological situations, characterized by two contrasted wind profiles between 500 and 2000 m have been studied, with two types of transitions between the lower circulation (SW monsoon) and the upper African easterly jet (AEJ). The first one is a veering case (6 January) and the second is a backing case (23 January). Calculations of CAPE (convective available potential energy) show that whereas instability is a maximum at both sides of the cape, the site of enhanced convection is determined by the wind shear in the 500–2000 m layer. Numerical results confirm satellite observations.

Numerical simulation of sea breezes over the auckland region, new zealand - air quality implications

Abstract: The air pollution meteorology of a typical sea breeze day is investigated using the Colorado State University Mcsoscale Model. Results are qualitatively compared with observations and reveal a complex wind field characterised by migratory sea breeze convergence zones. Associated with these features, the model predicts enhanced upward vertical velocities and ‘doming’ of the planetary boundary layer (PBL). The diurnal variation in PBL depth is shown to vary markedly at different locations and is dependent on position in relation to the migratory convergence zones. These complex spatial and temporal variations in the wind and PBL depth have important implications for air quality in Auckland and confirm that simple Gaussian or box trajectory approaches are inappropriate for air quality assessment in such environments. The inclusion in the model of variable surface properties, a dynamic synoptic state and improved PBL parameterisations, as well as coupling with a Lagrangian particle model, are recommended if the model is to be used as a tool for further air quality studies in the Auckland area.

The Behavior of Dry Cold Fronts Traveling Along a Coastline

Abstract: Observations of intense, dry summertime cold fronts in southeast Australia provide evidence for frontal deformation (cold air surges) in the coastal region well to the west of the main mountain range. This compares with the severe deformation that occurs when such cold fronts, known as Southerly Busters, interact with the mountains to the east. Three-dimensional numerical simulations of unsteady gravity currents, in the absence of orography, provide some insight into the factors affecting the evolution of cold air surges, including differential friction between land and sea; boundary-layer heating over land and the magnitude of the large-scale offshore wind. The latter affects, in turn, the presence of an internal boundary layer of cool air in the prefrontal region over the sea and a sea breeze over land. Depending upon the magnitude of the offshore wind a preferred region of enhanced vertical motion occurs just ahead of the gravity-current front, and within about 200 km of the coastline. This ca...

Formulation of the thermal internal boundary layer in a mesoscale model

Abstract: Mesoscale models using a non-local K-scheme for parameterization of boundary-layer processes require an estimate of the planetary boundary layer (PBL) height z i at all times. In this paper, two-dimensional sea-breeze experiments are carried out to evaluate three different formulations for the advective contribution in the z i prognostic equation of Deardorff (1974). Poor representation of the thermal internal boundary layer in the sea breeze is obtained when z i is advected by the wind at level z i . However, significantly better results are produced if the mean PBL wind is used for the advecting velocity, or if z i is determined simply by checking for the first ‘sufficiently’ stable layer above the ground. A Lagrangian particle model is used to demonstrate the effect of each formulation on plume dispersion by the sea breeze.

Observed Structure of a Land Breeze Head in the Tokyo Metropolitan Area

Abstract: The penetration of a land breeze front and its turbulence structure was observed at the center of the Tokyo metropolitan area on 27–28 January 1983. A turbulence sonde, small tethersonde and an acoustic sounder were used for the experiment. The detailed shape of the land breeze head and its flow characteristics were analyzed. The penetration of the land breeze was detected at about 2130 JST, and the advance speed of the land breeze front was estimated to be about 2.4 m s−1. The shape of land breeze head was similar to that of a sea breeze head reported by Simpson et al. (1977). The top height of the land breeze head was 400 m and the depth of the land breeze layer proper was about 200 m. A closed circulation pattern was detected inside the land breeze head. Large velocity fluctuations were observed at the leading edge of the head and the boundary of the large turbulence zone showed a wavy pattern behind the land breeze head. These features coincided with the results of Simpson et al. (1977). A co...

Quasi-trajectory analysis of a sea-breeze front

Abstract: Observations from a parachute-borne omegasonde that executed a trajectory through, along, and up and over the head of a sea breeze are analysed. This sea-breeze head is shown to have similar characteristics to those of a gravity current. A deep lobe/cleft combination was observed at the front where continental air was entrained into the sea-breeze air. Observed vertical motion near the sea-breeze front exceeded 5 ms−1 and the sonde rose into a cloud that had formed in rising continental air over this front. An evaporatively cooled downdraught from this cloud was observed to be entrained through the turbulent wake region and deep into the sea-breeze head.

Numerical Simulation of Mesoscale Eddies over Melbourne

Abstract: A mesoscale wind field model is used to simulate a cyclonic nocturnal eddy which may form over Melbourne under stable conditions with light synoptic winds. Two types of eddy (Mel-I and Mel-II) are identified, with separate formation mechanisms. Mel-I is generated by vorticity shed from the upstream mountain ranges. Daytime anabatic effects enhance the strength of the eddy. When surface heat fluxes are suppressed, the numerical simulations are found to parallel previous to laboratory experiments, but with a somewhat relaxed Froude number formation criterion. The second type of eddy, Mel-II, is generated by interaction of the sea breeze front with the synoptic flow. The eddies are compared with the Kanto plain eddy modeled by Kimura.

Analysis of Airborne Doppler Lidar Measurements of the Extended California Sea Breeze

Abstract: Airborne Doppler lidar data obtained by NASA near the top of the PBL in the central valley of California are analyzed. The experimental conditions and quality of the data are described. Wind vectors are produced on a geographic grid divided into 1-km square cells. The resulting wind field has features similar to those seen in ground level wind observations. It is suggested that, although the analysis is labor intensive and cumbersome, it produces a previously unattainable high-resolution depiction of air flow over a broad region.

Evaluation of a Simple Numerical Model as a Mesoscale Weather Forecasting Tool

Abstract: During the America's Cup race series of 1986–1987, a numerical sea breeze model was used to assist offshore forecasts. The exercise has provided a detailed insight into the extent to which such a model may assist the forecasting process the parameterizations necessary, and the factors that limit its accuracy. It also has demonstrated some of the factors controlling the behavior of the Western Australian sea breeze.

The Surface Sea Breeze: Applicability of Haurwitz-Type Theory

Abstract: The Haurwitz sea-breeze theory, and modifications by Kusuda and Alpert, are not generally applicable to observed winds in coastal regions, in part because they make no allowance for spatial evolution of wind hodographs. This is demonstrated by integrating the Haurwitz equations of motion to find trajectories of air reaching the shoreline at various times of day through the action of a large-scale pressure gradient force. Hodographs and momentum advection are computed from the trajectories. Hodograph size, shape, and orientation depend on distance from the shoreline, friction, spatial distribution of the time-varying part of the geostrophic wind (that parallel to the shore), and other factors. Differences between the hodographs found here and those found by Haurwitz, or by Kusuda and Alpert are largely related to nonlinearity.

Performance Examination of Atmospheric Model at Seacoast Region

Abstract: A three-dimensional numerical atmospheric model (PHYSIC) was developed to apply it to atmospheric transport and diffusion evaluation The main frame of PHYSIC is made up of momentum equations with the hydrostatic and Boussinesq approximation, the second-order turbulence closure model level 2.5 and other basic equations of physical process in the atmosphere. A terrain following z* coordinate system is used. The calculation results at a coastal plain were examined using meteorological data observed during atmospheric diffusion experiments at Tokai in 1983. The present model successfully predicts the temporal change of wind field within 20 h from evening to next noon and the occurrence and structure of sea breeze are simulated satisfactorily. The model performance concerning the structure of sea breeze and the distribution of eddy diffusivities is thought to be reasonable, although the direct comparison between calculation and observation is restricted to wind and temperature profiles by limited observation d...

Conclusions and Summary of Results

Abstract: The aim of this study has been to analyse the structure of a particular time series of wind speeds and directions Special techniques were developed to divide the series into the following four components, as mentioned in the introduction: (i) a geostrophic component, (ii) a land and sea breeze cycle, (iii) a storm component, and (iv) a residual series of short-term fluctuations

Buoyant Subrange Observed in the Stably Stratified Atmospheric Surface layer

Abstract: The vertical wind component (w) and air temperature fluctuations (θ) observed at a height of 11.25 m by sonic anemometer-thermometers on 12 December 1986 at Kochi, Japan AMM to give experimental support for the existence of a buoyant subrange following the breakdown of wave motions that occur normally in the Stably stratified atmospheric surface layer after sunset. An important favors the occurrence of the buoyant subrange in the present observation is the downdraft formed ahead of the land breeze front during the slow transition from the sea breeze to the land breeze. The downdraft triggers the breaking of the wave. Examination of the fine records of w suggest that the disturbance induced into the wave are suppressed by the negative buoyancy related to the formation of the buoyant subrange during breaking. The wave feeds part of its energy into turbulence, however, which ultimately is enhanced and increases because of nonlinear interaction with w-fluctuation.

Low level remote sensing: The Doppler Radar wind profiler

Abstract: Mesoscale phenomena such as thunderstorm and sea breeze frontal circulations are being investigated using a 50 MHz Doppler wind profiler at the Kennedy Space Center. The profiler installation will begin October 1, 1988 and will be completed by February 17, 1989. The focus of current research and plans for next year include: examination of vertical velocities associated with local thunderstorm activity and sea breeze frontal circulations and compare the vertical velocities to conceptual mesoscale models; implementation of space-time conversion analysis techniques to blend profiler data with National Meteorological Center's model output and other wind data such as jimsphere, windsonde and rawinsonde for mesoscale analysis; development of suggestions for use of wind profiler data in mesoscale analysis and forecasting at Kennedy Space Center; and problems detection in the quality of the profiler data during this research project. Researchers will work closely with MSFC to identify and solve the data quality problems.