Showing papers on "Sea breeze published in 1999"

Application of lidar depolarization measurement in the atmospheric boundary layer: Effects of dust and sea‐salt particles

Abstract: We intensively observed the atmospheric boundary layer with a polarization lidar, a Sun photometer, and a high-volume sampler at a coastal area of Tokyo Bay. The purpose of the observation is to investigate a phenomenon discovered in the past summer: relatively high depolarization ratio events (≃ 10% at peak) in the lower atmosphere associated with sea breeze. From the chemical analyses of the simultaneously sampled aerosols, we found that the depolarization ratio might be related to crystallized sea salt and dust particles. A boundary structure was clearly revealed by the depolarization ratio in the lower atmosphere, which might correspond to the mixed layer (the internal boundary layer) or the sea breeze in which crystallized sea salt and/or dust particles were diffused. We also presented the first numerical calculation on the depolarization ratio of the cubic particles to apply crystallized sea-salt (NaCI) particles by the dipole discrete approximation (DDA) method: the calculation yields 8-22% of depolarization ratio for the effective size larger than 0.8 μm at the investigated wavelength (532 nm).

The dynamics of heat lows

Abstract: A numerical model is used to investigate dynamical aspects of the structure and evolution of a heat low in an idealized flow configuration with an area of land surrounded by sea. of particular interest is the evolution of the distributions of relative vorticity and potential vorticity. While the heat low has a minimum surface pressure in the late afternoon following strong solar heating of the land, the relative vorticity is strongest in the early morning hours following a prolonged period of low-level convergence. Thus the heat low is not approximately in quasi-geostrophic balance. the low-level convergence is associated with the sea-breeze and later with the nocturnal low-level jet. the effects of differing sea area, land area and Coriolis parameter on various aspects of the heat low are investigated. Although a cyclonic vortex, the heat low is characterized by an anticyclonic potential-vorticity anomaly relative to its environment throughout much of the lower troposphere on account of the greatly reduced static stability in the convectively well-mixed boundary layer; however, the surface temperature maximum over land corresponds with a cyclonic potential-vorticity anomaly at the surface. the reduced static stability in the mixed layer has the further consequence that the horizontal components of relative vorticity and horizontal potential-temperature gradient make a non-negligible contribution and of opposite sign to the potential vorticity in certain flow regions. Two processes associated with the flow evolution in the model appear to be fundamental to understanding a range of low-level atmospheric phenomena over the arid interior of Australia: these are the deep convective mixing over land during the daytime and the development of a nocturnal low-level jet, which leads to convergence in the trough. Such phenomena include the diurnal behaviour of dry cold fronts and the generation of nocturnal wind surges and bores. It is reasonable to assume that similar processes operate in other arid regions of the world where deep convective mixing over land produces local maxima of diabatic heating in the lower atmosphere.

Numerical Simulation of the Interaction between the Sea-Breeze Front and Horizontal Convective Rolls. Part I: Offshore Ambient Flow

Abstract: A three-dimensional, cloud-resolving model is used to investigate the interaction between the sea-breeze circulation and boundary layer roll convection. Horizontal convective rolls (HCRs) develop over land in response to strong daytime surface heating and tend to become aligned parallel to the vertical wind shear vector, whereas the land–sea heating contrast causes the formation of the sea-breeze front (SBF) along the coastline. The ability of HCRs to modulate the along-frontal structure of the SBF is examined, complementing and extending previous observational and numerical studies. Three simulations are discussed, the first two demonstrating that the model can produce both phenomena independently. The third is initialized with offshore mean flow and vertical shear perpendicular to the coastline, and results in a sharply defined, inland-propagating SBF that encounters HCRs aligned perpendicular to it. Before the interaction takes place, the SBF is nearly two-dimensional and devoid of along-front...

Application of the NCAR regional climate model to eastern Africa: 1. Simulation of the short rains of 1988

Abstract: The National Center for Atmospheric Research (NCAR) Regional Climate Model (RegCM2) is employed to investigate the physical mechanisms that govern the October-December rains over eastern Africa. The model employs the Mercator conformai projection, with a domain of 5580 km × 5040 km centered at 31°E, 4°S, and a horizontal grid point spacing of 60 km. The simulation period is October-December 1988, and the model initial and lateral boundary conditions are taken from ECMWF reanalysis. A number of month-long simulations have been conducted to optimize various parameterizations of the model which include the following factors: cumulus convection, moisture parameterization, radiative transfer formulation, surface processes, boundary layer physics, and the lateral boundary conditions. The model was successfully customized over eastern Africa. The model simulates the large-scale circulation characteristics over the region as well as local features such as the dominant precipitation maxima, the Turkana low-level jet, and the diurnal reversal in the lake/land breeze circulation over Lake Victoria. Several model deficiencies are also identified. They include a negative rainfall bias over the western portions of the domain and the Kenya Highlands and a temperature bias over the tropical forest regions. Systematic analysis of surface water budget reveals that evapotranspiration is a major sink in the water budget over the regions where precipitation is moderate or small, while the role of runoff and drainage becomes important over the regions where precipitation is abundant. The model simulations also suggest that during the short-rains season, the large-scale circulation anomalies play the most important role in shaping the precipitation anomalies.

Observations and Modeling of the Sea Breeze with the Return Current

Abstract: Data from a wind profiler are used to investigate the vertical structure of the sea breeze with the accompanying return current at the North Sea coast in the Netherlands for three sea-breeze cases. In one of the cases, with a very weak and constant background flow, the return current mass flux approximately compensates for the sea-breeze mass flux. To study the sea breeze with the accompanying return current, a simple two-dimensional mesoscale model is constructed. It is found that the sea breeze as well as the return current of the three cases in this study are simulated well by the model. In the case mentioned above, the model indicates an overcompensation of the sea breeze by the return current. It is found that the latter is a function of the initial vertical temperature profile and the depth of the boundary layer, and that it can be as much as 30%. The overcompensation is balanced by a mass flow (in the sea-breeze direction) at a larger height (“return–return current”). As such, a three-laye...

The Temporal Behavior of the Atmospheric Boundary Layer in Israel

Abstract: Upper-air measurements collected for three consecutive years (1987‐89) from the Israel Meteorological Service permanent sounding site, in Beit-Dagan, Israel, enabled the temporal behavior of the atmospheric boundary layer over Israel to be characterized. Data analyzed consisted of the layer depth, the thermal gradient within the layer, and occurrence frequency of radiative and elevated inversions. To adequately represent the multiyear seasonal and diurnal behavior, the 3-yr databases were merged based on the tested hypothesis that the month sample in each individual year comes from the same population. The analysis shows that the depth of the radiative ground-based inversion, its frequency, as well as its thermal profile are maximal during spring and early summer. The upper-inversion layer is well defined during the summer, its lowest base (0.5‐1 km MSL) indicating a sharp interface layer formed between the marine turbulent boundary layer at the shallow layer of the atmosphere and the subsiding downward motion caused by the subtropical high pressure system. During the other three seasons a significant temporal variation of the upper-inversion base is observed as a result of the frequent larger-scale synoptic weather systems. The diurnal variation of the mixed-layer depth is most evident during the summer because it is mainly governed by heat fluxes and the daily sea-breeze cycle that are most intensive then. Henceforth, the layer minimal depth, along the coast, usually occurs during late afternoon hours when the wind speed of the cool sea breeze reaches its minimal rate and heat fluxes dissipate rapidly, leading to a decrease of the marine turbulent boundary layer.

The Inland Penetration of Sea Breezes

Abstract: The inland penetration of sea breezes is studied with observations and a two-dimensional mesoscale model An anomalously high percentage of Northerly winds as compared to the average frequency distribution, is observed in the evening in the month of May, 1989, at a station about 100 km inland In more than 50% of the sea-breeze cases during this very dry and sunny month, the wind shifted to this Northerly direction around 21 UTC The model output of this month shows that this anomaly is caused by deep inland penetration of the sea breeze From sensitivity experiments with the model it is derived that the inland penetration distance is determined mostly by the forcing through the differential heating and the magnitude of the opposing large-scale flow With a linear combination of the scaled maximum sea-breeze strength and the opposing large-scale flow, the inland penetration of the sea breeze can be scaled

Circulation and mixing characteristics of a seasonally open tidal inlet : a field study

Abstract: Tidal inlets in microtidal, wave-dominated coastal environments tend to close to the ocean seasonally. This obstructs navigation and could cause degradation of water quality in the estuary/lagoon connected to the inlet. Hence, engineering solutions are often implemented to prevent inlet closure. However, a prior knowledge of circulation and mixing processes within the estuary is crucial for the sustainability of any engineering solution. This paper attempts to provide insight into circulation and mixing characteristics of seasonally open estuaries based on the results of a field study undertaken at Wilson Inlet, a typical seasonally open estuary, in south-western Australia. Results of the study indicate that this type of estuary may have two distinct behavioural patterns, in winter and in summer. During winter, solar heating causes density stratification during daytime, and convective cooling causes overnight de-stratification; a horizontal cyclonic gyre is established during winter by the combined action of the Coriolis force and streamflow. During summer, strong sea breezes (~10 m s–1 ) cause vertical mixing during daytime, and convective cooling vertically mixes the water column at night. When the inlet is open, sea water propagates into the estuary during flooding tides unless streamflows are very high.

Porewater nutrient fluxes in a shallow fetch-limited estuary

Abstract: The Swan River Estuary is a shallow meso-eutrophic system in SW Australia. The dominant summer wind pattern in the region includes a strong SW sea breeze each afternoon. We hypothesised that such a regular and significant wind event may be important in causing the release of sediment porewater with subsequent effects on water quality and nutrient dynamics. To test this, we conducted a multidisciplinary field experiment in 1996 during which we measured temperature microstructure profiles (to yield turbulence parameters), velocity profiles, light profiles and nutrient profiles. Bottom shear stresses were estimated via the viscous-dissipation method, which can be used in stratified and unstratified water bodies or during convective cooling, all of which are likely to affect sediment-water dynamics in shallow systems. We observed that, after the sea breeze began, there was a dramatic breakdown of temperature stratification, an increase in mean velocities and an increase in turbulence levels at the sediment-water interface. This coincided with a doubling of water column ammonium concentrations. However, this pulse of nutrients was shown to occur prior to conditions necessary for sediment resuspension. We therefore attribute the increased porewater fluxes to interactions between increasingly energetic hydrodynamics and the benthic environment. The technique used here to measure porewater fluxes as a function of hydrodynamic forcing is an excellent alternative to benthic chamber experiments, which isolate the sediments from the overlying hydrodynamics.

Aircraft observations of sea-breeze frontal structure

Abstract: Detailed aircraft observations of sea-breeze frontal structure and dynamics are presented for two cases of well defined sea-breeze fronts near the east coast of England. In the first case the sea-breeze was advancing into a well mixed convective boundary layer with strong turbulence and an offshore breeze of around 3 m s-1. In the second case the sea-breeze was penetrating into a convective boundary layer characterized by weaker turbulence and an offshore wind speed of 2-3 m s-1. Indeed, during the course of the measurements a stable internal boundary layer was forming in the early evening. Cross-sections of the frontal structure are derived from aircraft traverses at a range of heights along a fixed line normal to the coast. A typical head-like structure is observed in both cases, with a region of strong mixing immediately seawards of the head. an approximately exponential fall-off in dissipation rate with distance seaward of the leading edge of the front is found. Heat and momentum fluxes are used to derive turbulent kinetic energy (TKE) budgets for the mixing region and indicate that turbulence in this mixing region is maintained by TKE generated by strong shear at the top of the cold-air inflow. In the first case the shear production of TKE is almost twice that of the second case, suggesting that the presence of ambient turbulence in the convective boundary layer has a significant effect upon the frontal dynamics. In the second case, as the turbulence decayed, a curious wave-like structure appeared behind the leading edge of the front. the waves have wavelengths of 1-3 km and it is unlikely that they were caused by Kelvin-Helmholtz instability. It is suggested that the waves might be a solitary wave-train emerging as the sea-breeze interacts with a low-level stable layer forming in the early evening.

The climate of Madras during the eighteenth century

Abstract: Archives of a German–Danish missionary foundation, including two weather diaries for Madras covering the years 1732–1737 and 1789–1791 and annual reports and letters, are used to reconstruct aspects of the climate of the Madras region of SE India during the eighteenth century. Records of rainfall occurrence and diurnal variations in wind direction in the diaries are used to derive the number of raindays and wind direction frequencies at 08:00 and 17:00 h for each month of record. Modern data on rainfall per rainday are used to convert rainday data to estimates of monthly rainfall. Wind direction data at times of land breeze (08:00 h) and sea breeze (17:00 h) are used as indices of the strength of the NE monsoon (in the October–December rainy season) and summer SW monsoon, respectively. Results suggest that annual rainfall in the period 1732–1737 (and probably also the 1720s) was about 27% below the 1813–1991 average, with very low NE monsoon (−41%) but near-average SW monsoon rainfall. The wind direction data suggest that both the SW monsoon and NE monsoon were stronger than normal. In contrast, estimated annual rainfall in 1789–1791 was near-average, but with SW monsoon rain 54% below average and NE monsoon rain 22% above average. This appears to be linked to less strong NE and SW monsoon winds than in 1732–1737. The period 1740–1788 appears to have been considerably wetter than the 1720s and 1730s. Tropical cyclone frequency was low except in the 1740s and 1780s. The 1730s dry period coincided with a period of anomalously warm winters in Europe. Copyright © 1999 Royal Meteorological Society

The role of sound waves in sea-breeze initiation

Abstract: The dynamics of the pressure distribution associated with the sea-breeze circulation is investigated. Analysis of hourly observations of surface pressure reveals that, on a typical sea-breeze day, large surface-pressure falls are recorded very far inland. Using a linear numerical model we show that this can only be understood when sound waves are taken into account. Sound waves are excited when air in the boundary layer over land expands due to diabatic heating. the numerical study reveals that vertically travelling sound waves induce a pressure increase through the entire atmosphere above the heated layer within a few minutes, while horizontally travelling sound waves induce a surface-pressure decrease over land and a surface-pressure increase over sea, with the resulting horizontal surface-pressure gradient initiating the sea breeze. Because the signal travels inland at the speed of sound (about 300 m s-1), points at a distance of more than 1000 km from the coast experience a surface-pressure decrease within an hour after the initiation of diabatic heating over land. the pressure decrease near the earth's surface over land, as well as the pressure increase aloft, is in accord with the observations at mountain stations and the analyses of the observed daytime surface-pressure changes in summer over the continent and adjacent seas. the implications of these findings for hydrostatic modelling of sea breezes are investigated. It appears that after one hour the hydrostatic sea breeze is 10% stronger than the non-hydrostatic sea breeze, while the hydrostatic return current is about 20% weaker.

Helicopter Observations of the Sea Breeze over a Coastal Area

Abstract: Thermodynamical observations by a helicopter have been conducted to study the internal structure of the sea breeze blowing inland from Tosa Bay during three periods (September 1993, November 1994 and 1995). Inland-intrusion distances of the midday sea breeze observed at each flight leg were in the 10–25-km range, depending on the intensity of the ambient flow associated with the gradient wind, atmospheric stratification, and the geographical features of the observed area. The sea breeze observed over the sea had well-defined features, in particular a turbulent wake behind the head of the sea-breeze front and a closed sea-breeze circulation cell containing the subsidence of the return flow. In addition, a moist layer distributed around 15–20 km offshore forms because the land breeze moves in this region. Moreover, a calm condition exists from the coast to about 10 km offshore. Both phenomena are found before the onset of the sea breeze in the early morning. Such remarkable characteristics of the s...

Inland Propagation of Sea Breeze under Opposing Offshore Wind

Abstract: According to past experience, the nearly stagnant conditions caused by the presumed equilibrium between the Saronikos Gulf sea breeze and an opposing synoptic flow is identified as the principal mechanism leading to high pollution episodes in Athens during the summer. However, previous experimental work has not examined in detail the interaction of the sea breeze flow with the opposing background flow. In this context, recent experimental work covering the basic key-locations of the Athens Basin focused on the inland propagation of the southerly sea breeze from the coast to the northern part of the basin mainly under moderate northerly background wind. During this campaign, a network of four meteorological stations established along the Athens Basin and a high range acoustic sounder at the centre of Athens operated over a two months time period in the summer of 1993. In addition, tethered balloon flights in the centre of Athens and on a sea vessel about 15 km offshore were employed during an experimental day with moderate opposing background wind. The results from this experimental campaign include the documentation of the sea breeze delay and its intensity as a function of a sea breeze index and features of the vertical structure of the sea breeze over land as well as over sea.

Vertical Interactions in a Nocturnal Multi-Scale Wind System Influenced by Atmospheric Stability in a Coastal Area

Abstract: The winter wind regime of Goteborg, located on the West coast of Sweden, is composed of three different wind systems besides the ambient wind; a nocturnal low level jet (NLLJ), a winter land breeze (WLB) and an urban heat island circulation (UHIC). An inversion divides the air column into two layers, one between 10 – 50 m and one between 50 – 100 m. The UHIC is located in the lower layer, the WLB in the top layer and the NLLJ above the top layer. The intensity of the interacting processes depends on the stability of each layer as calculated from the bulk Richardson number (BRilow and BRihigh) using continuous data collected during four years (1991 – 94) from two sites (one within and one outside the urban area) and sampled at three levels. In the evening the WLB develops from the ground level and increases in height until after midnight. At about the same time an UHIC develops in the urban area, below the WLB and causing an uplift of the latter. However, at both sites the WLB does not exceed the 100 m level. At this time BRi in both layers are below one resulting in continuous coupling between the WLB, the UHIC layers and the regional wind. Consequently, the exchange of momentum is still effective between all layers and this is highlighted by a change in the wind direction and a regulation of wind-speed to more constant levels. When BRihigh≥1, the layers become frictionally decoupled, as indicated by a return in the wind direction in the top level to the regional wind, and an acceleration of the top wind. The top level then becomes incorporated in to a nocturnal low-level jet (NLLJ) system. The normally acknowledged development of the NLLJ, with a start around sunset, is in this case delayed for several hours at the top level. The reason for this is that there are meso-scale/local wind systems present in layers beneath the jet causing an interaction between the layers. In the morning, when the layers are again coupled the top layer wind is once more influenced by the WLB and therefore changes direction and speed. The local and meso-scale wind systems thus delay the current nocturnal wind development.

Winter land breeze in a high latitude complex coastal area

Abstract: The winter land breeze (WLB) was studied in an area with complex topography on the Swedish West Coast (58°N). Methods used were mapping directions of smoke plumes, temperature soundings by tethered balloon and helicopter, three years of monitoring temperature and wind at three levels on a suspension bridge and on a mast, and meteorological observations from three stations located at different distances from the coast. To initiate the development of the WLB, the necessary temperature difference between sea and land was 5°C, but the magnitude of the difference appeared to have little influence. The direction of the typical WLB was at an oblique angle to the coast. The WLB started with a sudden wind shift as a result of frictional decoupling from the prevailing synoptic wind caused by increased stability. The flow, with a depth of about 100 m, developed within the nocturnal inversion at the level of the plateau-shaped mountains and overrode the cold air in the valleys and followed the uplifted inversion over...

Sea breeze climatology and nearshore processes along the perth metropolitan coastline, western australia

Abstract: The Perth metropolitan coastline is characterised by one of the strongest and most consistent sea breeze systems in the world. In contrast to the 'classic' sea breeze system, characterised by sea breezes blowing in the onshore direction, the sea breeze in Perth blows in a predominantly alongshore direction. Each year, around 200 sea breezes are experienced with an average wind speed of 5.7 m/s. Sea breezes in summer are stronger and more persistent than in winter. The importance of the sea breeze is clearly indicated by wind spectra showing significant spectral peaks at the diurnal frequency. The sea breeze system directly forces the incident wave field and induces a diurnal cycle of nearshore change by causing: (1) an increase in wave height; (2) a decrease in wave period; (3) an intensification of the nearshore currents; and (4) an increase in suspended sediment levels and suspended sediment transport. In addition, the seasonal variation in sea breeze activity, with frequent and strong sea breezes in summer and infrequent and weaker sea breezes in winter, is responsible for a seasonal change in the littoral drift direction. In summer, longshore sediment transport is towards the north and causes beaches located south of structures or headlands to widen considerably. In winter, when littoral drift is towards the south due to northwesterly storms, beaches located north of structures or headlands will become wider. It is further demonstrated that strong sea breeze activity is common along the entire Western Australian coastline, implying that the results obtained for the Perth metropolitan coastline can be applied to some extent to the entire state.

Urban Climatology Applied to the Deterioration of the Pisa Leaning Tower, Italy

Abstract: Among the peculiarities of the urban climatology, a relevant one concerns the interactions with monuments, which include stone weathering, deposition and removal of airborne pollutants. In order to know more about the case of the Pisa Leaning Tower, Italy, a field survey has been made for one year, measuring the microclimate interacting with the structure, the vertical temperature and humidity profiles, the Tower surface temperature at different locations and the concentration of particles in air. Also more general information was collected studying the meteorological parameters in the area of Pisa. The correlation between rainfalls and wind evidenced that the windborne droplets arrive from preferential directions, determined on the regional scale by the sea shore on the west (sea breeze) and the channelling operated by the valley of the Arno river on the west. The tilting of the Tower gives a natural shield to the southern part, which is hardly washed by rainfall. The complex balance between airborne particulate matter deposition, tower tilting, rainfall washout and surface runoff determines the pattern of the black crusts which disfigure the elegance of this historical building. The land and sea breezes transport air with different moisture content, and the urban heat island accentuates the mid day drop on relative humidity, determining condensation-evaporation cycles in the stone micropores. The urban climatology of Pisa and the interactions with the Leaning Tower are discussed in view of the conservation of this monument.

Studies of trace gases and Aitken Nuclei at inland and coastal stations - A part of INDOEX programme

Abstract: As a part of the Indian Ocean Experiment (INDOEX) programme, ground-based measurements of trace gases (SO2, NO2, NH3 and O3) and Aitken Nuclei (AN) were carried out at Pune during March-April 1998. Also, measurements of surface ozone and AN were made during 5-10 January 1998, the inter comparison campaign of various instruments at Thiruvananthapuram. The mean concentrations of SO2, NO2, NH3 and O3 at Pune were 3.75, 5.81, 3.21 and 57.8 I¼g/m3 respectively and that of O3 at Thiruvananthapuram was 44 I¼g/m3. The average concentration of AN was about five times higher at Pune (19,000/cm3) than that at Thiruvananthapuram (4,400/cm3), indicating more pollution at Pune than at Thiruvananthapuram. The diurnal variation of surface ozone showed high concentrations during the day and low concentrations during the night at both the locations. Diurnal variation of AN at Pune showed a daytime maximum and a night-time minimum. Whereas, at Thiruvananthapuram night-time values were higher than the daytime values which can be attributed to the influence of the land and sea breeze.

Effect of sea breeze on propagation characteristics over a LOS microwave link located in Indian south-east coast

Abstract: Studies on mi crowave signal propagation provide an opportunity to in vestigate the variab le nature of th e atmosphere. The present study deal s with the effect of sea breeze on the propagation characteristic s observed over a lin e-of-sight (LOS) microwave link operating at 6 GHz and situated in th e south- east coast of Indi a. It has been found that the amplitude of the received microwave sign al suffers appreciably during the onset of sea breeze. The correlatio n between th e cas es of on set of sea breeze observed from microwave amplitude measurements and those from meteorological observation s has been found to be good . The lar ge chan ge in refractivity has been observed during the onset of sea breeze. Such change in refrac ti vity profile causes fading in microwave radio signals .

Spatial pattern of ozone injury in aleppo pine and air pollution dynamics in the Mediterranean

Abstract: Interdisciplinary studies, combining the evaluation of ozone effects with the meso-meteorological interpretation of the ozone data have been carried out in eastern Spain since 1994. Mesoscale circulations are very important from the point of view of how and where forest ecosystems are affected by point sources and regional air pollution in the Mediterranean Area. First results of these field surveys show that during 1994, 95 and 96, ozone visual injury (chlorotic mottle) in Pinus halepensis Mill. was well correlated with the penetration of the sea breeze in coastal valleys of Castellon. Patterns of ozone injury, chlorotic mottle, have been positively correlated with needle-age classes looking at tree level.

A four-year summertime microburst climatology and relationship between microbursts and cloud-to ground lightning flash rate for the NASA Kennedy Space Center, Florida: 1995-1998

Abstract: : In order to ameliorate the forecasting of microbursts, the first summertime microburst climatology in the United States was produced. This climatology was based on a four year wind data base during the summer months (May - September) of 1995-1998 for 50 mesonet wind towers that encompasses the KSC. An investigation into the microburst characteristics of frequency, diurnal variation, spatial variation, speed frequency distribution, and the wind direction was accomplished. Finally, an examination into the relationship between microbursts and lightning was conducted. A total of 282 microbursts were observed during this four-year period. There were 114 microburst days with 59 of these days having more than one microburst. The most prominent months of microbursts are June, July, and August with July being the most dominant. Several important characteristics of wind speed and direction were found. The median wind speed was 34 knots. The majority of microburst wind speeds fell within 25 and 44 knots. As the wind increases above 43 knots, the frequency decreases exponentially, reaching virtually zero at 65 knots. The predominant wind direction of the microbursts is from southeast through the west-northwest with a maximum from the southwest. The spatial variation of the microbursts revealed an interesting pattern. Some areas received a substantial amount of microbursts, while others received few, if any. It is hypothesized that this difference is due to the sea breeze interacting with the abundant river breezes causing the formation of convection over the same areas on a daily basis. The investigation into the relationship between lightning and microbursts revealed that in most cases there was an evident increase in the CG flash rate up to 25 minutes prior to the microburst. Moreover, a clear peak often occurred 5-10 minutes before the microburst. Thus, CG lightning may also improve microburst forecasting.

Analytic study of sea-land breezes

Abstract: An analytic study of the structure of sea-land breezes is presented, with special attention paid to the dependence on the model parameters. In this linearized model, the wind speed of the sea-land breezes is directly proportional to the difference of sea and land heating rates. For the same differential heating, the sea-land breeze is more prominent if the stratification is weakly stable, or if the frictional force is small. The horizontal penetration from the coast is also investigated, and found to be asymmetric between the land and the sea. The above results are in agreement with observation.

Cooling effects of a river and sea breeze on the thermal environment: a case of Kuala Terengganu, Terengganu, Malaysia

Abstract: A series of sea breeze observations have been carried out along the Terengganu river in the state of Terengganu on the east coast of the Peninsular of Malaysia. These observations were carried out during the north-east monsoon months ofNovember and December, 1993. Wind and temperature data were measured at the height of about I.S m above the ground along the three traverses on both sides of the river which is approximately 10 km long that perpendicular to the coast and then the results were presented in a horizontal cross-section. Generally, the formation of sea breeze of the speed of ~ 4.1 ms-1 was observed capable in reducing the ambient air temperature of about 2.0° to 4.0°C. Although the effect of sea breeze can be traced further inland along the river, its cooling effects, however, were well marked at the estuary of the Terengganu river than at the 7th km interior area of Kuala Terengganu. The difference in the temperature decrease was observed in the order of 1.7° and 2.4°C from the inland to the coastal areas, respectively. During the sea breeze episode, most of the coastal field stations indicated a slower temperature increase than the field stations located in the interior area. Furthermore, the effect of sea breeze in reducing ambient air temperature was well marked above the river (stations on bridges) than stations on both sides of the river. Simultaneously, an overall time-lag increase in relative humidity was observed during the fall of ambient air temperature, owing to the effect of sea breeze. In general, the establishment of sea breeze cooling effect was significantly felt about 3 to 6 hours period i.e., between 14.00 and 20.00 (Malaysian Local Time) which was varied between stations; longer period was experienced by stations located at or near the coastal area than stations further inland.

Sea breeze generated waves and coastal morphology

Abstract: For the determination of the stability of coastlines, coastal erosion and the design of erosion protection studies, the “local” wave climate is the most important input parameter. For morphology, “local” means just outside the breaker line. On relatively calm days the local wave climate is strongly influenced by the effect of sea breeze. On the basis of the sea breeze model of HAURWITZ [1947] and HSU [1988] an operational method has been developed for the determination of sea breeze and the effect on coastal morphology. Examples are presented from Cartagena, Colombia, and from the Bulgarian Black Sea coastline.

Local Climate Change Related with Land Use Change since the Near Modern

Abstract: LUIS (Land Use Information System) is a digital land use data set covering all Japan with 2 km grid. The land use on each grid point in circa 1850, circa 1900, circa 1955 and circa 1985 were compiled in LUIS. By the numerical simulations with a mesoscale model referring to LUIS, the author attempted to pick up the influence on near surface air temperature by regional warming related with land use change during around 135 years.During 4 periods, the area showing the regional warming related with land use change has expanded. This feature was significant around Tokyo and Osaka. The maximum difference between circa 1850 and circa 1985 emerged at 9PM and the minimum emerged at 6AM. The former was 1.8 Celsius degrees in Tokyo (Otemachi).Urbanization during 4 periods weakened the daytime penetration of sea breeze in south Kanto and it brought a regional warming. The warming area moved to north with expanding on the Kanto Plain by sea breeze since daytime to mid-night. But an effect of recovery of forest in the mountainous area in central Japan was not clear. In Osaka Plain the movement of warming area by sea breeze was smaller than in Kanto Plain.

Mesoscale Simulations of a Florida Sea Breeze Using the PLACE Land Surface Model Coupled to a 1.5-Order Turbulence Parameterization

Abstract: A sophisticated land-surface model, PLACE, the Parameterization for Land Atmospheric Convective Exchange, has been coupled to a 1.5-order turbulent kinetic energy (TKE) turbulence sub-model. Both have been incorporated into the Penn State/National Center for Atmospheric Research (PSU/NCAR) mesoscale model MM5. Such model improvements should have their greatest effect in conditions where surface contrasts dominate over dynamic processes, such as the simulation of warm-season, convective events. A validation study used the newly coupled model, MM5 TKE-PLACE, to simulate the evolution of Florida sea-breeze moist convection during the Convection and Precipitation Electrification Experiment (CaPE). Overall, eight simulations tested the sensitivity of the MM5 model to combinations of the new and default model physics, and initialization of soil moisture and temperature. The TKE-PLACE model produced more realistic surface sensible heat flux, lower biases for surface variables, more realistic rainfall, and cloud cover than the default model. Of the 8 simulations with different factors (i.e., model physics or initialization), TKE-PLACE compared very well when each simulation was ranked in terms of biases of the surface variables and rainfall, and percent and root mean square of cloud cover. A factor separation analysis showed that a successful simulation required the inclusion of a multi-layered, land surface soil vegetation model, realistic initial soil moisture, and higher order closure of the planetary boundary layer (PBL). These were needed to realistically model the effect of individual, joint, and synergistic contributions from the land surface and PBL on the CAPE sea-breeze, Lake Okeechobee lake breeze, and moist convection.