Showing papers on "Sea breeze published in 1993"

Effects of the Large-Scale Flow on Characteristic Features of the Sea Breeze

Abstract: A two-dimensional nonlinear numerical model has been used to examine the effects of the ambient wind on the development of characteristic features of the sea breeze. The specific features that were examined were the maximum shoreward velocity component (both total and as a perturbation from the large-scale flow) anywhere in the simulation domain, the inland penetration of the sea breeze, the depth of the inflow layer at the coastline, the maximum vertical velocity anywhere in the domain, the maximum potential-temperature gradient anywhere in the domain, and the surface heat flux. Thirty-one simulators were performed, with large-scale geostrophic winds ranging from onshore (i.e., supporting) flow of 15 m s−1 to offshore (i.e., opposing) flow of 15 m s−1, at 1 m s−1 intervals. The results indicated that the sea-breeze perturbation was suppressed for onshore large-scale flow of a few meters per second or more. In contrast, a sea breeze was produced for opposing large-scale flow as strong as 11 m s−1...

Evolution of the Monterey Bay Sea-Breeze Layer As Observed by Pulsed Doppler Lidar

Abstract: As part of the Land/Sea Breeze Experiment (LASBEX) to study the sea breeze at Monterey Bay, the pulsed Doppler lidar of the NOAA/ERL Wave Propagation Laboratory performed vertical and nearly horizontal scans of the developing sea breeze on 12 days. Analyses of Doppler velocity data from these scans revealed details on the growth of the sea-breeze layer and on the horizontal variability of the sea breeze resulting from inland topography. Two days were selected for study when the ambient flow was offshore, because the onshore flow of the sea breeze was easy to discern from the background flow. Sequences of vertical cross sections taken perpendicular to the coast showed the beginnings of the sea breeze beneath the land breeze at the coast and the subsequent growth of the sea-breeze layer horizontally and vertically. On one of the days a transient precursor—a “minor sea breeze”—appeared and disappeared before the main sea breeze began in midmorning. Other issues that the lidar was well suited to stud...

The Effects of Large-Scale Winds on the Sea–Land-Breeze Circulations in an Area of Complex Coastal Heating

Abstract: A three-dimensional mesoscale numerical model has been used to examine the effects of large-scale background winds on the characteristics of the sea–land-breeze circulations over an area with an irregular coastline and complex surface-heating patterns at Kennedy Space Center/Cape Canaveral in Florida. A series of numerical experiments was performed in which the large-scale winds were varied in both speed and direction. The surface heating was based on measured surface-temperature variation from the Kennedy Space Center Atmospheric Boundary Layer Experiment (KABLE) during the spring season when the land–sea temperature gradient reaches its maximum. The results from the simulations compared reasonably well with data available from KABLE. The results show that an onshore large-scale flow produces weaker sea-breeze perturbations compared to those generated by an offshore flow. However, the coastal rivers and lagoons create intense surface convergence with strong vertical motion on the seaward side of...

The Amazon river breeze and the local boundary layer: I. Observations

Abstract: Observations of the diurnal evolution of the planetary boundary layer over the Amazon rain forest, made at sites close to the confluence of the Solimoes and Negro rivers (approximately at 3°S, 60°W) near Manaus, Amazonas, Brazil, show the existence of a diurnal rotation of the wind near the surface and the frequent presence of low-level nocturnal wind maxima. These circulations are shown to be plausibly explained as elements of a river and land breeze circulation induced by the thermal contrast between the rivers and the adjacent forest.

The sea breeze and gravity‐current frontogenesis

Abstract: The development of a sea-breeze circulation into a sea-breeze front in often observed late in the afternoon. Measurements of horizontal temperature and humidity profiles in a number of sea-breeze circulation, made using an instrumented light aircraft, are presented. On each of the four days for which data are presented an initial weak horizontal temperature gradient, extending over a distance of 5 to 10 kilometres, developed later in the into a sharp front only a few hundred metres across. The data are discussed in terms of simple gravity-current frontogenesis models applied to the development of sharp sea-breeze front from an initial diffuse transition between the air over the land sea. Examination of the equations for frontogenesis, and the result of some previous laboratory experiments on gravity-current frontogenesis, lead to the proposal that, given sufficient contrast between land and sea temperatures, the formation of a sea-breeze front depends on the balance between convergent horizontal winds which act to generate a front, and turbulent convective mixing over the land which tends to prevent its formation. the differences in driving force, wind convergence and turbulent intensity are discussed for each day on which data are available and are shown to be consistent with the theory proposed.

Vertical Heat Fluxes Generated by Mesoscale Atmospheric Flow Induced by Thermal Inhomogeneities in the PBL

Abstract: An analytical evaluation of the vertical heat fluxes associated with the mesoscale flow generated by thermal inhomogeneities in the PBL in the absence of a synoptic wind is presented. Results show that the mesoscale fluxes are of the same order as the diabatic heat fluxes. In the sea-breeze case results show that in the lower layer of the atmosphere the heat flux is positive over the land and negative over the sea with an overall positive horizontal average. In the free atmosphere above the PBL the mesoscale vertical heat flux is negative over the land and over the sea; that is, the lower atmosphere becomes warmer while the free atmosphere above becomes cooler. As a result the mesoscale flow contributes to the weakening of the atmospheric stability within a region that extends a Rossby radius distance from the coastline, and up to an altitude larger than twice the depth of the convective PBL. The average momentum flux equals zero because the momentum removed over the sea is fed back into the atmo...

Diurnal Variation of Lee Vortices in Taiwan and the Surrounding Area

Abstract: Lee vortices have been frequently observed in the wake of mesoscale mountains under a low Froude number flow regime. During the Taiwan Area Mesoscale Experiment (TAMEX), a cyclonic vortex was observed to the Ice of Taiwan by a P-3 aircraft. In this paper a numerical simulation is carried out to study this event. It is shown that the numerical results are capable of recapturing the detailed features as observed by airplane and surface analysis. The simulated surface pressure, wind field, and Ice vortex are in good agreement with observations. The diurnal oscillation of cloudiness and precipitation in Taiwan is also consistent with the observations under undisturbed conditions during the TAMEX period. Under a prevailing southwesterly-to-westerly summer monsson flow, numerical results demonstrate that the observed cyclonic vortex initially develops to the southeast of Taiwan after sunset, then drifts northeastward. The diurnal forcing not only generates land/sea breezes but also controls the vortex ...

Sea-breeze front effects on boundary-layer aerosols at a tropical coastal station

Abstract: The effects of sea breeze on optical depth, size distribution, and columnar loading of aerosols at the tropical coastal station of Trivandrum are studied. It has been observed that sea-breeze front activity results in a significant and short-lived enhancement in aerosol optical depth and columnar loading in contrast to the effects seen on normal sea-breeze days. Examination of the changes in columnar aerosol size distribution associated with sea-breeze activity revealed an enhancement of small-particle (size less than 0.28 [mu]m) concentration. The aerosol size distribution deduced from optical depth measurements generally show a pronounced bimodal structure associated with the frontal activity. 22 refs., 12 figs., 1 tab.

A Study of the Influence of Terrain on Fog Development

Abstract: A general purpose mesoscale numerical weather prediction model is used to simulate the development of fog at Perth, Western Australia, on 27 April 1990. Using one-dimensional and two-dimensional model configurations, an attempt is made to identify the important processes involved. It is proposed that fog forms with an onshore wind when cold air drainage from the plateau to the east creates a stagnation point in the near surface flow on the coastal plain. A full model integration with time-dependent boundary conditions supports this but shows an along-coast variation associated with valleys that dissect the edge of the plateau. It is concluded that in uneven terrain the development of local nocturnal winds may frequently determine the location and timing of fog formation.

The turbulent characteristics in the lowest part of the sea breeze front in the atmospheric surface layer

Abstract: Tower measurements for the sea breeze front in the surface layer were carried out over the Kochi plain about 2 km inland from Tosa Bay in Shikoku, Japan during the period from August 1986 to October 1987. The study shows that the penetration time of the sea breeze has an annual variation, which is around 0830 JST in summer and 12 JST in winter, and that the width of the sea breeze front depends on the ratio of the sea breeze speed and the opposing flow speed. Moreover, the frontal width also shows a seasonal variation.

A Numerical Study of Nocturnal Sea Breezes: Prefrontal Gravity Waves in the Compensating Flow and Inland Penetration of the Sea-Breeze Cutoff Vortex

Abstract: It is demonstrated in this numerical study that prefrontal perturbations may be triggered by a penetrating sea-breeze head into an existing nocturnal temperature inversion. The perturbations consist of the lower-layer wavelike perturbation and the upper-wave motion, both of which are manifested as rotor streaming. However, these prefrontal gravity waves take the form of the weak transient waves of a depression trapped in the ambient compensating flow field. The sea-breeze head dissipates as it penetrates inland into the nocturnal temperature inversion. At midnight, a horizontal vortex is completely detached from the feeder flow of the sea breeze. This isolated horizontal vortex is identified as the sea-breeze cutoff vortex. It is shown that the sea-breeze cutoff vortex may be evolved from a dissipating sea-breeze head. After the sea-breeze cutoff vortex is formed, it propagates farther inland as an isolated wave-type disturbance. Examination of the force balance suggests that the inertia and radi...

On the spectral behaviour of atmospheric boundary‐layer parameters at Thumba, India

Abstract: The features of the spectra of meteorological fields of wind velocity and temperature observed at Thumba, a site on the western coast of India, are discussed. Data utilized for the study are mostly from an instrumented tower, sodar and long-period temperature data available for the site. The influence of local circulations like the sea breeze is manifested also in the general spectral characteristics of horizontal wind, as with the spectral gap in the mesoscale region between the synoptic-scale region and the turbulent-scale region of the spectra. The width of the spectral gap observed between the wave-active region and the microscale region in the wind velocity spectra is seen to be dependent on the stability of the medium, and the gap is found to shift to the high-frequency side with increasing stability. The composite spectrum of temperature also reveals a prominent gap at about an hour. It is seen that with the advection of a sea breeze over the land, a shallow thermal internal boundary layer is formed and regions above one tenth of this depth obey mixed-layer similarity.

A numerical model for estimation of the diurnal fluctuation of the inversion height due to a sea breeze

Abstract: Vertical profiles of temperature, measured over the sea in the summer near the Eastern coast of the Mediterranean, show significant diurnal fluctuation in the height of the marine inversion. During the day, the inversion moved down and during the night it moved up. The fluctuation was about 250 m. Numerical simulations of the daily fluctuation in the height of the inversion during the summer day shows the following: Over the sea, during daytime, the inversion base sinks by 250 m, and during the night, it rises back to its original height. The developing sea breeze during the day causes the air over the sea to move downward adiabatically. At night, the inversion rises mainly due to advection of cool stratified air (including an inversion at 480 m) from a long distance over the sea. Such diurnal fluctuations are observed 100 km off shore. This scale is determined by the scale of the sea breeze. Comparison of some of the model vertical profiles with the temperature profiles measured over the sea show a similar diurnal oscillation. The amplitude of the oscillation is the same.

Characterization of tidal currents in Monterey Bay from remote and in-situ measurements

Abstract: : A first order description of tidal heights and currents in Monterey Bay is provided. Analysis of sea level records indicate that a mixed, predominantly semidiurnal tide nearly co-oscillates within the bay. Analysis of month-long moored ADCP records obtained in the winter and summer of 1992 reveals that tidal-band currents account for approximately 50 percent of the total current variance in the upper ocean (20-200 m). A relatively strong (7 cm/s) fortnightly tide (MSf) is present in both seasons. Considerable rotation of the semidiurnal ellipse orientations occurs with depth during both seasons. A month- long record of surface current measurements obtained with CODAR, an HF radar system, during September 1992 reveals that the Monterey Submarine Canyon clearly influences the strength and direction of semidiurnal (M2) tidal currents. Good agreement exists between the strength and orientation of ADCP- and CODAR-derived tidal ellipses, with the exception of the constituent K1. Large, spatially uniform K1 surface currents (20-30 cm/s) appear to be the result of diurnal sea breeze forcing.

Effects of onshore and offshore topography on sea breeze circulation: An observational study at eastern Attica, Greece

Abstract: Field measurements of wind, air temperature and humidity were taken at the eastern part of the Attika district in June 1991, to examine the topographic influences exerted on the local sea breezes. These influences are due either to the elongated Evia island, faced by the northern half of Attica coastline some tens of kilometers offshore, or to the coast-parallel range of Hymettos mountain, rising steeply 12 km onshore. The instrumentation consisted mainly of three tethered meteorological balloons released at characteristic sires (i.e., the coast, a location between shoreline and mountain foot and the mountain top) and three autographic ground-based anemometers operating at selected locations. Data from the ground-based and upper air stations of the Hellenic National Meteorological Service, as well as the diurnal weather maps were also obtained and analyzed. Observations were made under different synoptic wind and the latter was found to determine remarkably the significance of the topographic effects. A preliminary two-dimensional numerical approach was also made concerning the sea breeze capability to reach the Hymettos mountain top in the case of a weak opposing geostrophic flow.

Observations of the diurnal oscillation of the inversion over the Israeli coast

Abstract: Vertical profiles of temperature and humidity were measured over the sea in two series of 48 hours each, during the summer near the Israeli coast of the Mediterranean. A prominent inversion was observed in the temperature profiles. In the first series the average height of the inversion base was 350m and in the second, 600m. In the inversion a very sharp decrease of the absolute humidity was found. Below the inversion down to the sea surface the atmosphere was well mixed. A significant diurnal oscillation was observed at the height of the inversion base. During the day the inversion moved up and during the night it moved down. This movement was 250m in the first series and 450m in the second. The movement of the inversion base was almost adiabatic. It is suggested that the fluctuation in the height of the inversion base is mainly due to the developing breeze.

Time-space model of summer ozone distribution around Ravenna

Abstract: The time-space distribution of photochemical ozone during the summer along the western coast of the upper Adriatic Sea is strongly influenced by small-scale transport phenomena, especially land and sea breezes (Giovanelli et al., 1985). When these events involve the movement of air masses rich in primary and secondary pollutants across one or more lines of physical discontinuities, such as that between land and sea or across the inshore strip (flat, predominantly farmland) lying between seaboard and city, they can determine irregular, varying ozone distribution patterns at ground level in areas only a few kilometers apart. An empirical model was developed to characterize these local differences in ozone distribution over the entire area. The method makes it possible to compare the data recorded at the various sites and times by “standardizing” parameters for meteorological and local-diffusion conditions as well as for source emission values by processing the data from a series of measurements taken at several coastal sites, both inshore and offshore, during the summers 1980–1985. The resulting space-time models show, despite the limited number of monitor stations, “local” differences in the processes of production, transport, and spread of photochemical ozone in the area studied. The final distribution of the mean daily evolution (MDE) of ozone throughout the greater Ravenna area is reported and discussed.

Evolution of diurnal surface winds and surface currents for Monterey Bay

Abstract: : The diurnal-period fluctuations of winds and surface currents are analyzed for September 1992 in and around Monterey Bay Wind records are compared for three coastal stations and two mooring sites Remotely-sensed surface current observations from two CODAR (HF radar) sites are used to explore the ocean's response to diurnal-period forcing An average diurnal cycle is formed at each wind station and at all CODAR bins The earliest sea breeze response is seen at the coastal wind stations where morning winds accelerate toward the coastal mountain ranges A few hours later, the coastal winds accelerate to the southeast down the Salinas Valley Offshore afternoon winds rotate from their normal alongshore orientation to also become aligned with the valley The CODAR-derived surface currents respond in less than the two-hour sampling rate to the onset of the diurnal onshore winds Currents accelerate in the direction of the Salinas Valley As the day progresses, the more offshore currents rotate clockwise out from under the winds in a possible Ekman or inertial adjustment that continues throughout the night and spreads onshore In the afternoon, a complicated eddy pattern develops near shore in a possible response to the coastal boundary

Pollutant Transport in Buoyancy Driven Atmospheric Flows.

Abstract: Due to the complexity of some buoyancy driven atmospheric flows, it is sometimes not possible to accurately predict pollutant transport on the basis of sparse wind field measurements. A possible solution is mathematical modelling of both the flow and pollutant transport. In order to overcome shortcomings of the conventional Ee model such as defining proportionality coefficients (cm, ch) and to develop a more general model of stratified environmental flows, a modified E-e model was proposed through use of the algebraic stress model including wall proximity effects. The resulting model was compared herein to data and higher order simulations in stable, neutral and convective atmospheric boundary layers (ABL). The modified E-e model reproduced well the observed behaviors. The modified E-e model with full nonhydrostatic equations was applied to a sea breeze circulation. The key characteristics of the sea breeze, such as development of a daytime onshore flow, deep inland penetration of the breeze in late afternoon, frontal development in late evening, thermal internal boundary layer (TIBL) and fumigation in the TIBL were reproduced. The residual plume over the sea showed great impacts on the ground level concentration during the following day sea breeze and it should be considered in the estimation of pollutants near the coastal xvi region. All the plume emitted from an elevated line source during the nighttime offshore flow also returned back to the land with the subsequent afternoon sea breeze. The modified E-e model was also used to estimate the dispersion of pollutants by a "thermal fence" under neutral and stable conditions. A line of heaters or a thermal fence has been proposed as a means of reducing ground level concentrations near area source such as a landfill under nighttime stable condition. It was proved that the thermal fence with the relatively small heating rate enhanced the dispersion of the pollutants behind it by increasing the vertical mixing under the neutral and stable conditions.

A study of the Merritt Island, Florida sea breeze flow regimes and their effect on surface heat and moisture fluxes

Abstract: Data collected during the Convective and Precipitation/Electrification Experiment were analyzed as part of an investigation of the sea breeze in the vicinity of Merritt Island, Florida. Analysis of near-surface divergence fields shows that the classical 24-hour oscillation in divergence over the island due to the direct sea breeze circulation is frequently disrupted and exhibits two distinct modes: the classical sea breeze pattern and deviations from that pattern. A comparison of clear day surface energy fluxes with fluxes on other days indicates that changes in magnitudes were dominated by the presence or absence of clouds. Non-classical sea breeze days tended to lose more available energy in the morning than classical sea breeze days due to earlier development of small cumulus over the island. A composite storm of surface winds, surface energy fluxes, rainfall, and satellite visible data was constructed. A spectral transmittance over the visible wavelengths for the cloud cover resulting from the composite storm was calculated. It is shown that pre-storm transmittances of 0.8 fall to values near 0.1 as the downdraft moves directly over the site. It is also found that under post-composite storm conditions of continuous clear sky days, 3.5 days are required to evaporate back into the atmosphere the latent heat energy lost to the surface by rainfall.

野外実測で得られたカルデラ湖の内部波特性―北海道・倶多楽湖

Abstract: The dynamics of internal waves in a small caldera lake, Lake Kuttara, Hokkaido was examined for the period of September-October 1989, by means of the FFT spectral analysis of time series of water level, water temperature, flow velocity and meteorological conditions. The lake during that period was thermally stratified, but the epilimnion decreased water temperature due to convective cooling. Spectral analysis of water level, water temperature and flow velocity revealed that a lake-current system below the thermocline is characterized by periodic free motions due to rotational internal waves. Meanwhile, a wind system over the lake consisted of daily land-sea breezes and some episodic events due to cyclone lows. The former is characteristic of the lake near the Pacific Ocean. It was oberved that an internal wave rotating counterclockwise or clockwise with periods of 3.1-3.3 hr is induced by both relatively strong sea breezes and episodic eastern-wind events, whereas in the episodic events, an internal wave rotating clockwise with a period of 2.7 hr simultaneously prevails.

Charactaristic of suburban heat island with an example of northern part of Tokyo

Abstract: Hot air is transported form the center to the nothern suburbs of Tokyo by the diurnal sea breeze and the southeast monsoon. This causes severe heat island phenomenon in this area. First, the structure is discussed with the observed temperature distribution. Then the phenonenon was simulated with a turbulent closure model.

Flux aggregation at large scales: On the limits of validity of the concept of blending height

Abstract: The concept of blending height is known to be applicable to estimate areally averaged surface heat and momentum fluxes over heterogeneous terrain with horizontal scales of surface variations much smaller than 10 km. Here, the performance of this concept is explored beyond this limit of validity. This is accomplished by analysing a three-dimensional meso-scale simulation of land-sea breeze systems which originate at large-scale temperature differences between water and land surfaces and by employing a one-dimensional version of the meso-scale model as a vertical column of a hypothesized macro-scale model. It appears that areally averaged surface fluxes can be reproduced reasonably well. This is valid for area-averaged fluxes obtained by the average of surface fluxes on each land type, i.e. for so-called flux aggregation, and for a combination of flux aggregation and so-called parameter aggregation where similar land types are combined into an aggregated land surface. The weak dependence of averaged surface fluxes on secondary, meso-scale motions agrees with earlier theoretical considerations.