Sea Breeze Characteristics Research Articles

Near-Resonant Ocean Response to Sea Breeze on a Stratified Continental Shelf

Abstract The spatial structure and temporal characteristics of sea breeze and the associated coastal ocean response in the northwest Gulf of Mexico are investigated using moored instruments, hydrographic stations, and wind measurements. Near the study area of 30°N, motions in the diurnal–inertial band (DIB) may be significantly enhanced by a near-resonant condition between local inertial and diurnal forcing frequencies. Wavelet analysis is used to quantify the results. Results indicate that diurnal sea-breeze variability peaks in summer and extends at least 300 km offshore with continuous seaward phase propagation. The maximum DIB oceanic response occurs in June when there is a shallow mixed layer, strong stratification, and an approximately 10-day period of continuous sea-breeze forcing. DIB current variance decreases in July and August as the consequence of the deepening of the mixed layer and a more variable phase relationship between the wind and current. River discharge varies interannually and can significantly alter the oceanic response during summer. The “great flood” of the Mississippi River in 1993 deepened the summer mixed layer and reduced the sea-breeze response during that year. Vertically, DIB currents are surface intensified, with a first baroclinic modal structure. The significance of these DIB motions on the shelf is that they can provide considerable vertical mixing in summer, as seen by the suppression of the bulk Richardson number (by a factor of 30) during strong DIB events. This provides a potential mechanism to ventilate seasonally occurring near-bottom hypoxic waters of the coastal ocean.

Impacts of boundary layer turbulence and land surface process parameterizations on simulated sea breeze characteristics

Abstract. This paper investigates the sensitivity of sea breeze (SB) simulations to combinations of boundary-layer turbulence and land-surface process parameterizations implemented in the MM5 mesoscale meteorological mode for an observed SB case over the Swedish west coast. Various combinations from four different planetary boundary layer (PBL) schemes [Blackadar, Gayno-Seaman (GS), Eta, MRF], and two land surface model (LSM) schemes (SLAB, Noah) with different complexity are designed to simulate a typical SB case over the Swedish west coast. The simulations are conducted using two-way interactively nested grids. Simulated 10-m winds are compared against observed near-surface wind data from the GÖTE2001 campaign to examine the diurnal cycle of wind direction and speed for SB timing. The SB (vertical) circulation is also compared in the different experiments. The results show that the different combinations of PBL and LSM parameterization schemes result in different SB timing and vertical circulation characteristics. All experiments predict a delayed SB. The vertical component of the SB circulation varies in the experiments, among which the GS PBL scheme produces the strongest SB circulation. Evident differences between the SLAB and Noah LSMs are also found, especially in maximum of updraft and downdraft velocities of the SB vertical circulation. The results have significant implications for convective initiation, air quality studies and other environmental problems in coastal areas.

Impact of sea breeze air masses laden with ozone on inland surface ozone concentrations: A case study of the northern coast of Taiwan

This work examines how ozone‐laden sea breeze air masses contribute to inland surface ozone concentrations. The vertical distributions of ozone in sea breeze air masses and the characteristics of sea breezes are investigated using tethered ozonesondes and meteorological radiosondes, respectively, at a measurement site near the northern coast of Taiwan during 24–30 August 2003. The investigations reveal that, initially, sea breeze air masses are stable with relatively high concentrations of ozone distributed in the upper portions of the air masses. Elevated ozone layers with concentrations of 60–100 ppb were frequently observed at 500–1600 m. The growth of a thermal internal boundary layer (TIBL) inland that can bring ozone‐rich air aloft in a sea breeze air mass into the growing TIBL subsequently increases the surface ozone concentrations farther inland. Accordingly, the surface ozone concentrations increase with distance inland, regardless of the photochemical production of ozone inland. A new conceptual model was presented to depict this pollution feature. According to a simple Lagrangian analysis, ozone‐rich sea breeze air masses under the observed conditions generated a difference of as much as a 30 ppb between the surface ozone concentration at a near‐coast location and that at a far inland location. TIBL development at a near‐coast area can protect the area from fumigation of elevated ozone layers because the depth of the TIBL is limited there, such that the ozone in the elevated ozone layers cannot be brought to the ground.

Variability of three-dimensional sea breeze structure in southern France: observations and evaluation of empirical scaling laws

Abstract. Sea-breeze dynamics in southern France is investigated using an airborne Doppler lidar, a meteorological surface station network and radiosoundings, in the framework of the ESCOMPTE experiment conducted during summer 2001 in order to evaluate the role of thermal circulations on pollutant transport and ventilation. The airborne Doppler lidar WIND contributed to three-dimensional (3-D) mapping of the sea breeze circulation in an unprecedented way. The data allow access to the onshore and offshore sea breeze extents (xsb), and to the sea breeze depth (zsb) and intensity (usb). They also show that the return flow of the sea breeze circulation is very seldom seen in this area due to (i) the presence of a systematic non zero background wind, and (ii) the 3-D structure of the sea breeze caused by the complex coastline shape and topography. A thorough analysis is conducted on the impact of the two main valleys (Rhône and Durance valleys) affecting the sea breeze circulation in the area. Finally, this dataset also allows an evaluation of the existing scaling laws used to derive the sea breeze intensity, depth and horizontal extent. The main results of this study are that (i) latitude, cumulative heating and surface friction are key parameters of the sea breeze dynamics; (ii) in presence of strong synoptic flow, all scaling laws fail in predicting the sea breeze characteristics (the sea breeze depth, however being the most accurately predicted); and (iii) the ratio zsb/usb is approximately constant in the sea breeze flow.

Numerical simulation of sea breeze characteristics observed at tropical coastal site, Kalpakkam

Sea breeze characteristics around Kalpakkam tropical coastal site are studied using an Advanced Regional Prediction System (ARPS) mesoscale model, which is non-hydrostatic, compressible atmospheric prediction model following the terrain coordinate system. Various options such as surface physics, atmospheric radiation physics, Coriolis force, microphysics, cumulus parameterization and 1.5 level TKE closure scheme for diffusion are included in the model. A joint meteorological field experiment was carried out by IITM-Pune and IGCAR at Kalpakkam by deploying state-of-the-art sensors and tether balloon systems for observing the height profiles of meteorological parameters. The data obtained from the field experiment are used here to compare the results from numerical simulations. From the simulated results, it is seen that duration of the sea breeze is 6 hours which agrees well with the observations. The height of the Thermal Internal Boundary Layer (TIBL) is also simulated from the vertical profiles of potential temperature. Simulated wind speed and wind directions are compared with the 50 m tower data and potential temperature profiles are compared with the kytoon data. Results are in good agreement with the observed values except during night time wherein a small difference is seen in the wind speed.

A model‐aided investigation of winter thermally driven circulation on the Italian Tyrrhenian coast: A case study

Data collected during a campaign carried out in and around Rome in February 1996 using sodars, tethered balloon, and surface data suggest the development of a winter sea breeze that could not be detected by conventional data and analyses. A model‐aided study is performed to verify the development of thermally driven local circulation and to prove the onset of a winter sea breeze regime, propagating inland and interacting with the urban heat island (UHI). The area of interest for the study is the central part of Italy (latitude 41°–43°N, longitude 10°–16°E). The MM5 mesoscale model was used at high resolution: three nested domains with up to 3 km of grid resolution were used in the area where the sea breeze was observed. To highlight the effect of the sea breeze, a simulation with a thick cloud layer in the innermost domain was performed. By removing the cloud layer the diurnal evolution of the horizontal temperature gradient led to the development of the sea breeze and the UHI circulation, in agreement with the data. Sensitivity tests were carried out to evaluate the effect of land use resolution and of satellite‐retrieved/climatological sea surface temperature on the simulation results. Doppler‐sodar data recorded at three sites, tethersonde profiles, and surface data were used to verify the results. As expected, using high‐resolution land use and the daily sea surface temperature retrieved by satellite observations led to improvements in the local circulation produced by the model. However, the model falls short in reproducing some of the sea breeze characteristics. It finds that the sea breeze starts too early and lasts for a shorter time than the observed one does, and the wind direction shows a too strong northerly component. Also, it slightly underestimates the daily temperature pattern. The interaction of the urban heat islands of Rome and Ostia with the sea breeze flow is analyzed to explain the causes of these discrepancies.

Idealised numerical simulations of diurnal sea breeze characteristics over a step change in roughness

A two-dimensional hydrostatic meso-scale model is used to study possible effects of a step change in roughness on the daytime sea breeze (SB). Two approaches are employed for the calm synoptic condition with a clear sky. First, idealised numerical simulations are made with the length of aerodynamical roughness (z0) ranging from 0.05m to 0.6 m and by an increase of 0.05 m. The magnitudes are changed in all ground surface grid points. The specific features examined are the maxima of the wind velocity field, the turbulent fluxes and the turbulent kinetic energy (TKE), the height of the mixed layer, the inland penetration of the SB and the slope of the SB front. Two z0 effects are pointed out: an increase in the turbulent mixing and a reduction in the wind speeds in the surface layer. Results show that a relationship between these two effects is crucial for the SB inland penetration. A moderate z0 change increases both turbulence intensity and a vertical extent of the boundary layer. An increase of both heights and magnitudes of the SB circulation, caused by a vertical extension of the turbulent field, what followed by a faster inland penetration of the SB. For larger z0 change, the effect of dissipation overcomes the effect of the SB strengthening and the inland penetration is slower. Second, an urban area is simulated only by a locally increased z0. The rough area intensifies both TKE and the SB during its growing stage. An increase of z0 also reduces the wind speed in the vicinity of the urban area and it augments the slope of the SB front.

Influence of the Synoptic-Scale Flow on Sea Breezes Observed during CaPE

Mean sea-breeze characteristics were determined by analyzing a number of sea-breeze events during offshore, parallel, and onshore flow regimes during the Convection and Precipitation/Electrification Experiment (CaPE). It was observed that offshore flow cases exhibited the widest, and relatively strongest, radar-detected thin lines. The thin-line reflectivity values steadily increased during the day. In contrast, a thin line was detected only during late afternoon on parallel flow days while no easily identifiable thin line was observed during onshore flow days. The gradients of temperature and moisture, as measured by a surface meteorological station during sea-breeze passage, were strongest and weakest during offshore and onshore flow days, respectively. In addition, the moisture and temperature gradients across the leading edge of the sea breeze steadily increased during the day and were strongest during late afternoon. Using dual-Doppler techniques, the detailed kinematic structure of the sea-breeze circulation for offshore and onshore flow regimes is presented. In particular, detailed measurements of the sea-breeze return flow at upper levels are presented for both offshore and onshore flow events for the first time. The observed inland propagation speed for offshore and parallel flow events is consistent with calculated values for density currents. Onshore flow events, however, are observed to move inland at a rate that is slower than what is expected for a density current.

Characteristics of sea breezes blowing over the Lake Kasumigaura, I baragi prefecture

Characteristics of sea breeze are investigated by field research and laboratory experiments. Field research was conducted at the Lake Kasumigaura where a sea-breeze front shows its plane figure through water surface ripples. Experiments were carried out using water tank with heating device below the inland part. Both front structures observed at the field and laboratory water tank are closely similar to each other.