Showing papers on "Sea breeze published in 2002"
TL;DR: In this paper, numerical simulations for an anticyclonic summer episode in the Paris area have been performed at the meso-γ scale for a 48-hour period, and compared to observations from a dense operational observational network.
Abstract: Numerical simulations for an anticyclonic summer episode in the Paris area have been performed at the meso-γ scale for a 48-hour period, and compared to observations from a dense operational observational network The meteorological stations have been classified, according to the extent of urbanization of their surroundings, into four classes (central Paris, urban, suburban, and rural) The atmospheric model, coupled with an urban surface scheme, correctly reproduces the temperature (within 1 K from the observations) and humidity The intense urban heat island during the night is also well represented Following the validation, the model is used to quantify atmospheric effects of Paris on the bound- ary layer, through a comparison with a purely rural simulation At night, the model simulates a neutral or even slightly unstable boundary layer to a depth of 200 m over the city In contrast, a very stable layer formed in the countryside During the day, the boundary layer was more turbulent and 500 m deeper over Paris; vertical velocities of up to 1 m s −1 were created over the city This leads to an urban breeze with convergence at low levels (with winds around 5 to 7 m s −1 ), and divergence at the boundary-layer top (with similar wind speeds) The horizontal extent of the breeze reaches for more than 50 km from the city centre, and could have an important impact on pollutant diffusion in the area for calm days Finally, three other spring cases are presented briefly These show that an urban breeze develops if the synoptic wind is weak enough or disorganized; an urban plume develops otherwise
190 citations
TL;DR: Evaluated experimental evidence and complementary modelling results are evaluated to help in the interpretation of observed ozone cycles and to anticipate possible scenarios for anthropogenic nitrogen deposition in the region.
129 citations
TL;DR: In this paper, the authors investigated the origin of high and low PM episodes by correlating PM levels with the concentrations of gaseous pollutants, and making use of meteorological analysis and satellite observations.
128 citations
TL;DR: A set of criteria based on the diurnal reversal of wind direction, and the thermal gradient necessary to drive the circulation, is used to identify sea breeze days Statistics are presented that describe the occurrence, duration and strength of the sea breezes as discussed by the authors.
Abstract: Hourly wind speed and direction data from 12 coastline stations on Sardinia, Italy, are analysed in order to characterize sea breezes in the region A set of criteria based on the diurnal reversal of wind direction, and the thermal gradient necessary to drive the circulation, is used to identify sea breeze days Statistics are presented that describe the occurrence, duration, and strength of the sea breezes On a stationwide basis, sea breezes are most frequent in the summer months (May–August), when they appear on more than one-third of the days Sea breeze occurrence and duration are the greatest for the stations on the east coast of the island The all-station average sea breeze duration reaches a maximum of about 9 h in June The strength of the sea breezes is roughly 3 m s−1 during summer months on average over all stations in the sample
An analysis of mean daily hodographs for the stations in the sample shows clearly the onshore–offshore nature of the sea breeze circulation, and the response of the sea breezes to the local coastline Sea breezes are shown to develop simultaneously on all coasts of the island under appropriate synoptic conditions Copyright © 2002 Royal Meteorological Society
94 citations
TL;DR: In this article, an analysis of satellite images and data from long-term L-band boundary layer radar measurements carried out at Serpong (6.4°S, 106.7°E) was conducted to study the characteristics of sea-breeze circulation over the tropical site of Jakarta, Indonesia.
Abstract: Characteristics of sea-breeze circulation over the tropical site of Jakarta, Indonesia, have been documented based on analyses of satellite images and data from long-term L-band boundary layer radar measurements carried out at Serpong (6.4°S, 106.7°E). Inspection of satellite imagery reveals that a sea-breeze front develops well along the northern coastal plain of West Java and propagates inland until its structure is deformed over complex topography. It is found that the sea-breeze signal detected by the boundary layer radar is most well defined during the dry season months of July–October. In all of these months, radar observations indicate a late afternoon intensification of sea-breeze flow in the 0.5–0.8-km height range between 1700 and 1800 LT, which is not elucidated upon by surface measurements. The effect of weather conditions on the sea-breeze pattern is investigated by using a cloudiness index derived from data of incoming solar radiation. The results show that sea-breeze intrusion over...
73 citations
TL;DR: In this paper, the authors analyzed an ozone episode recorded at the regional monitoring network of the Basque Country, located in northern Iberia, and investigated the origin of polluted air masses in the area and search for the transport/dispersion mechanisms that gave rise to such a severe O 3 episode.
72 citations
TL;DR: In this paper, four permanent surface stations were installed in the vicinity of the surface ozone monitoring station on the summit of the Cerro Tololo (2200 m MSL) in Chile at 30°S.
Abstract: In November of 1999, four permanent surface stations were installed in the vicinity of the surface ozone monitoring station on the summit of the Cerro Tololo (2200 m MSL) in Chile at 30°S. These stations were used to study the atmospheric flow conditions, which are important for the interpretation of the ozone measurements at Cerro Tololo. In addition, radiosonde ascents were performed in March of 2000 near the coast and about 60 km inland. Different wind regimes were distinguished. Above 4 km MSL, large-scale westerly winds prevailed, while northerly winds were observed in a band along the coastline between 2- and 4-km-MSL height. The upper boundary of the northerly wind regime corresponded to the mean height of the Andes mountain range. This wind regime resulted from the westerly winds being blocked and forced to flow in parallel to the Andes (when Froude number is less than 1). The phenomenon was also confirmed by model simulations. Seasonally varying, thermally induced valley winds and a sea ...
69 citations
TL;DR: In this paper, the authors measured the life cycle of the land and sea-breeze system at Monterey Bay, California, in 1987, during the Land-Sea Breeze Experiment (LASBEX).
Abstract: A NOAA/Environmental Technology Laboratory Doppler lidar measured the life cycle of the land- and sea-breeze system at Monterey Bay, California, in 1987, during the Land–Sea Breeze Experiment (LASBEX). On days with offshore synoptic flow, the transition to onshore flow (the sea breeze) was a distinct process easily detected by lidar. Finescale lidar measurements showed the reversal from offshore to onshore flow near the coast, its gradual vertical and horizontal expansion, and a dual structure to the sea-breeze flow in its early formative stages. Initially, a shallow (<500 m) sea breeze formed that later became embedded in a weaker onshore flow that was ∼1 km deep. Eventually these two flows blended together to form a mature sea breeze about 1 km deep. Regional Atmospheric Modeling System (RAMS) two-dimensional simulations successfully simulated this dual structure of the sea-breeze flow when both the coastal mountain range just east of Monterey Bay and the Sierra Nevada range, peaking 300 km eas...
55 citations
TL;DR: In this paper, the authors present analyses of flow characteristics in the near-shore and offshore environment using data from the Danish wind monitoring network and show that wind speeds at or above a height of 40m are not significantly higher than that from land masts.
50 citations
TL;DR: In this article, the horizontal distribution of ozone levels in the westcentral coastal plain of Taiwan was analyzed using 3-year data obtained from a network of air-pollution monitoring sites in the study area, while the vertical data came from two 2-day tethersonde experiments, measuring wind speed, direction, temperature and humidity, NO, NO2, NMHC and O3, conducted during August and November 1999.
50 citations
TL;DR: A strong lagged relationship between El Nino-Southern Oscillation (ENSO) and rainfall in the main rain season (October-January) on the leeward islands of Aruba, Curacao and Bonaire is found.
Abstract: A strong lagged relationship between El Nino–Southern Oscillation (ENSO) and rainfall in the main rain season (October–January) on the leeward islands of Aruba, Curacao and Bonaire is found. It can easily be used for skilful seasonal predictions, with an anomaly correlation coefficient r ≈ 0.6 at lag 4 months on historical data. The other two seasons, February–May and June–September, also show correlations with ENSO that can be exploited for predictions, r = 0.4 to 0.5. In the February–May dry season there is also a lagged correlation with sea-surface temperature (SST) in the Pacific Ocean off the Central American coast that can be used to increase the forecast skill. A June–September small rains season correlation to equatorial Atlantic Ocean SST is absent in earlier data. Most of these results are also applicable to other stations in northern South America. Regressions with the circulation show that the main intermediate factors are upper-level divergence and vorticity, and at lower levels a veering of the trade winds. This modifies the descending limb of the sea–continent breeze circulation that is responsible for the dry zone off the coast. Copyright © 2002 Royal Meteorological Society.
TL;DR: In this paper, a three-dimensional lake model driven by wind stress and heat flux fields derived from an atmospheric model is applied to Lake Kinneret, Israel, and the results are in good agreement with available observations.
Abstract: A three-dimensional lake model driven by wind stress and heat flux fields derived from an atmospheric model is applied to Lake Kinneret, Israel. The summer wind field over the lake has a strong diurnal and large spatial variation due to complex terrain surrounding the lake, the sharp temperature contrast between the arid land and the lake, and due to the penetration of the Mediterranean sea breeze (MSB) into the lake area. The daily mean wind curl field, which is predominantly determined by the penetration of the MSB, is responsible for the generation of three lake gyres. One of them dominates most of the lake and rotates counterclockwise. It is flanked to the north and to the south by two smaller ones that rotate clockwise. During the summer, the diurnal variation of the wind over the lake is repeated daily due to consistent forcing conditions during that season. Numerical tests show that the rectified flow induced by the diurnal winds plays a minor role in the lake circulation. The thermocline oscillation, which was believed to be the free propagation of internal Kelvin waves, mainly responds to the surface elevation set up by the time-dependent winds, and it appears that no systematic counterclockwise propagating waves with large thermocline displacements exist in the lake. The intense MSB over the lake in the late afternoon pushes the heated surface water toward the east, forcing the deep cooler water to be advected westward, and creating strong mixing over the shallow western shore. This results in higher temperature off the eastern shore and lower temperature off the western shore. However, a strong mean flow is constantly eliminating the temperature difference by counterclockwise transfer of the western cooler water eastward. The results are in good agreement with available observations.
TL;DR: In this paper, a simple analytical model, representing the dynamical balance of a homogeneous surface layer, predicts diurnal wind forcing, i.e., a sea-breeze, should drive diurnal currents whose amplitude will be particularly energetic close to 30° latitude, where the diurnal and inertial periods are similar.
TL;DR: A high-resolution air pollution numerical model system (APOPS) is applied to simulate the sea/land breeze and its impacts on the ozone distribution in northern Taiwan and can successfully simulate local flow patterns such as sea/ land breezes and mountain-valley wind.
Abstract: A high-resolution air pollution numerical model system (APOPS) is applied to simulate the sea/land breeze and its impacts on the ozone distribution in northern Taiwan. The system can successfully simulate local flow patterns such as sea/land breezes and mountain-valley wind. The predicted surface ozone concentrations also agree with observed surface ozone values ( Wang, Z., et al., Tellus, 52B, 2000, 1189 ). The sea/land breezes in northern Taiwan play a significant role in the distribution of ozone and transport of ozone from the urban to the coastal and mountain areas. The sea breeze is a weak system, extending vertically to a height of less than 1 km with the wind speed less than 4 ms-1. The land breeze can transport the photochemically produced ozone and its precursors over the sea. The accumulated ozone on the sea can return to the land in the daytime with the sea breeze. This kind of transport tends to contribute significantly to high-ozone episodes in clean coastal and mountain regions.
TL;DR: In this article, field data and modeling results from a three-dimensional atmospheric model are analyzed and compared to investigate the local boundary-layer dynamics on 28-31 December 1999. But, the model is not suitable for the analysis of large-scale data sets.
TL;DR: An experiment combining wind profiler and polarimetric radar analyses of intense, but shallow, tropical thunderstorms has been performed as mentioned in this paper, where all the storms sampled had a similar structure, with intense updrafts on the periphery of the cells producing significant-sized hail and downdrafts in the storm center.
Abstract: An experiment combining wind profiler and polarimetric radar analyses of intense, but shallow, tropical thunderstorms has been performed. These storms are important as they are very common along many tropical coasts and islands and are sometimes the precursors to large intense multicellular storms such as occur over the Tiwi Islands north of Darwin, Australia. All the storms sampled had a similar structure, with intense updrafts on the periphery of the cells producing significant-sized hail and downdrafts in the storm center. The hail concentrations are relatively small, but have a large effect on the radar reflectivity and polarimetric measurands because of the size (10–20 mm). It is this hail melting that produces characteristic ZDR columns in the polarimetric radar data.
TL;DR: In this article, ground level concentration and sky-shine dose due to radioactive emissions from a nuclear power plant at a coastal site have been estimated using the standard Gaussian Plume Model (GPM) and the modified GPM suggested by Misra (Atmospheric Environment 14 (1980) 397), which incorporates fumigation effect under sea breeze condition.
TL;DR: In this paper, a new atmospheric model reanalysis product for the U.S. west coast from the Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS) implemented on a triply nested 81/27/9 km grid is presented.
Abstract: [1] This paper introduces and evaluates a new atmospheric model reanalysis product for the U.S. west coast from the Navy's operational Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS™) implemented on a triply nested 81/27/9 km grid. Wind measurements from Monterey Bay Aquarium Research Institute (MBARI) moorings are used to evaluate a two year time series of the model output from October 1998 to October 2000. The model accurately reproduced both the landward decrease in the large-scale wind field and the shoreward intensification of the diurnal cycle during the summer season. This new reanalysis product will be required for accurate high resolution (km) coastal (0–10 km) simulations of the U.S. west coast by ocean models.
TL;DR: A statistical study of the sea–land breeze in Mar del Plata (Argentina) to characterize the periods of the year when the breeze affects pollen transport, particularly the dispersion of airborne Poaceae pollen between urban and rural areas showed that breeze transport brings a regional component to pollen assemblage.
Abstract: This paper presents a statistical study of the sea-land breeze in Mar del Plata (Argentina) to characterize the periods of the year when the breeze affects pollen transport, particularly the dispersion of airborne Poaceae pollen between urban and rural areas. In order to analyse the sea breeze circulation, hourly data from coastal, urban and rural meteorological stations were used. The effect of the sea breeze on the particulate matter was analysed from syncronic hourly airborne pollen records from an urban and a rural area. A sea-land breeze appeared between spring and early autumn in the hours of greatest diurnal warming. Results showed that the surface wind direction most probably associated with this phenomenon is NE and E, the time of occurrence shifting to new directions following the counterclockwise rotation, according to theoretical models for the Southern Hemisphere. Poaceae emission takes place in the morning, during the hours of maximum insolation. However, after the occurrence of the breeze, a rise in pollen concentration between 2000 hours and 0200 hours is detected because of pollen reentrainment brought about by air recirculation. The results showed that breeze transport brings a regional component to pollen assemblage.
TL;DR: In this article, the authors measured the surface energy exchanges above the dominant surface types (savanna, grassland, forest and shallow tidal strait) during the monsoon transition period (October-December) using the Bowen ratio and the aerodynamic techniques.
Abstract: [1] Inputs of heat and moisture through surface energy exchanges are important in the evolution of diurnally modulated thunderstorms. As part of the Maritime Continent Thunderstorm Experiment (MCTEX) conducted on the Tiwi Islands, northern Australia, we measured the surface energy exchanges above the dominant surface types (savanna, grassland, forest and shallow tidal strait). Measurements were made during the monsoon transition period (October–December) using the Bowen ratio and the aerodynamic techniques. A full radiation balance was measured at the Savanna site, where the surface albedo was determined as 0.19. The surface energy exchanges showed broad similarities between the sites, with comparable high net radiation totals averaging 11.8 MJ.m−2.day−1 over the terrestrial sites. The substrate heat fluxes were large at the Tidal strait (4.21 MJ.m−2.day−1) due to the high rates of energy absorption into water. The partitioning of net radiation into sensible and latent heat fluxes was controlled primarily by surface characteristics such as soil moisture and vegetation cover, with Bowen ratios averaging 1.08, 0.65, 0.5 and 0.40 for grassland, forest, savanna and tidal strait sites, respectively. A higher Bowen ratio was recorded at the Grassland site as this was during an earlier period that was much drier. Strong relationships were observed between the total surface convective fluxes and boundary layer development (e.g., the lifting condensation level) and between the magnitude of the daytime surface sensible heat flux and the onset time of thunderstorm convection. Observed terrestrial surface fluxes of moisture (averaging 165–265 W.m−2) were deemed insufficient for observed thunderstorm initiation and suggest that sea breeze advection of moisture is necessary. Tiwi Island thunderstorms were shown to represent a dynamic system where surface fluxes are important in generating a boundary layer sufficient to initiate the thunderstorms but where feedbacks between thunderstorms and surface fluxes eventually help terminate the storms.
Journal Article•
TL;DR: In this article, the authors relate nearshore ripple behavior to cyclic changes in hydrodynamic conditions due to a sea breeze and propose that ripple migration direction is a function of the balance between onshore cross-shore velocity asymmetry and offshore mean flow.
Abstract: This paper relates nearshore ripple behaviour to cyclic changes in hydrodynamic conditions due to a sea breeze. Simultaneous time series measurements of waves, currents, sediment suspension and ripple crest positions were obtained from the nearshore of a micro-tidal low energy beach in southwestern Australia during two diurnal sea breeze cycles. Large parallel ripples with wavelengths of 0.3m-1.2m and heights of 0.05m-0.15m were present in coarse sand for the duration of observations. Mean ripple wavelengths and migration rates were measured at half hour intervals. During the sea breeze, wave height increased and wave period decreased with the addition of locally generated, short period wind waves on the incident swell waves. As a result, mean offshore flow (undertow) increased and cross-shore asymmetry decreased. Ripple wavelength increased during the sea breeze in proportion to the nearbed orbital diameter. Ripple wavelength remained relatively constant, except for a slight decreasing trend, with respect to the varying near-bed orbital diameter during the swell-dominated periods before and after the sea breeze suggesting the presence of suborbital ripples. Ripples migrated onshore during the swell-dominated period find offshore during the sea breeze. It is proposed that the ripple migration direction is a function of the balance between onshore cross-shore velocity asymmetry and offshore mean flow. Increased sediment suspension concentration during the sea breeze resulted in an increase in the amount of sand available for transport by the larger mean offshore flow providing a mechanism for the offshore migration of ripples.
TL;DR: In this paper, a statistical analysis of wind speed and direction data for five selected meteorological stations at the Cyprus coast, is carried out in order to evaluate wind energy applications, mainly along the southeastern coastline.
Abstract: ¶A statistical analysis of wind speed and direction data for five selected meteorological stations at the Cyprus coast, is carried out in this study. Daily, monthly and annual variations of wind speed are established. The Weibull distribution statistics of the sites are also determined. In addition, an attempt is made to find the sea-breeze circulation effects in the same wind data. The wind statistics obtained are expected to serve as a validation test for wind energy applications, mainly along the southeastern coastline.
TL;DR: In this article, conditions of airflow in the wind tunnel were determined so as to satisfy the similarity rule for the bulk Richardson number, by controlling temperature profiles and wind velocity of the thermally stratified wind tunnel.
TL;DR: Strong sea breeze and cold winters reduced the survival ratio of buds and further resulted in reduction of female flowering, which suggests that acorn crop was decreased by cool conditions in the flowering period.
Abstract: We modeled the annual acorn crops of Kashiwa oak (Quercus dentata Thunb.) in a coastal forest in Hokkaido, northern Japan. Shoots of Kashiwa oak withered away during winter because of sea breeze and cold, and succeeding production of female inflorescences were strongly affected by mortality of buds. Thus, strong sea breeze and cold winters reduced the survival ratio of buds and further resulted in reduction of female flowering. Number of female flowers was related with current acorn crops, however, survival of female flowers after pollination was strongly influenced by warmth in the flowering period. Regression analysis of the annual acorn crop versus weather conditions suggests that acorn crop was decreased by cool conditions in the flowering period. A model equation was constructed to estimate the annual acorn crops by three weather variables: cumulative velocity of sea breeze and mean monthly temperature in winter (DecemberMarch) and maximum monthly temperature in current flowering period (June). This...
01 May 2002
TL;DR: In this paper, a three-dimensional non-hydrostatic prognostic mesoscale model is used to simulate the circulation around Rome, Italy, on a cloudless summer day with weak synoptic winds, with the aim of characterising the local circulation on such days.
Abstract: A three-dimensional non-hydrostatic prognostic mesoscale model is used to simulate the circulation around Rome, Italy, on a cloudless summer day with weak synoptic winds, with the aim of characterising the local circulation on such days. The simulation shows that the sea breeze and slope flows play roles of comparable importance. At night the circulation is dominated by katabatic flow. During the late morning/early afternoon there is a sea breeze with a front curving pincer-like around Rome, and well-developed anabatic flows on all slopes. In the late afternoon, sea breeze and slope flows coalesce into a single circulation reaching hundreds of kilometers inland, with an offshore return flow aloft. Comparison with observations is favourable, particularly during the day.
01 Jan 2002
TL;DR: In this article, load combinations of wind forces and earthquake forces for wind energy power units are investigated from a probabilistic point of view when large-scale earthquake events are taken into consideration in structural design, wind forces at the mean wind velocity during service life can be added to the earthquake forces.
Abstract: Load combinations of wind forces and earthquake forces for wind energy power units are investigated from a probabilistic point of view When large-scale earthquake events are taken into consideration in structural design, wind forces at the mean wind velocity during service life can be added to the earthquake forces. Dynamic response analysis is carried out to estimate sectional forces at the wind energy power units. It is made clear that the tower has fairly large seismic capacity when the tower is designed by wind force at strong wind velocities due to typhoons.
TL;DR: In this article, 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) on the calm synoptic condition with a clear sky.
Abstract: 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.
TL;DR: In this article, a numerical mesoscale model is used to make a high-resolution simulation of the marine boundary layer in the Persian Gulf, during conditions of offshore flow from Saudi Arabia.
Abstract: A numerical mesoscale model is used to make a high-resolution simulation of the marine boundary layer in the Persian Gulf, during conditions of offshore flow from Saudi Arabia. A marine internal boundary layer (MIBL) and a sea-breeze circulation (SBC) are found to co-exist. The sea breeze develops in the mid-afternoon, at which time its front is displaced several tens of kilometres offshore. Between the coast and the sea-breeze system, the MIBL that occurs is consistent with a picture described in the existing literature. However, the MIBL is perturbed by the SBC, the boundary layer deepening significantly seaward of the sea-breeze front. Our analysis suggests that this strong, localized deepening is not a direct consequence of frontal uplift, but rather that the immediate cause is the retardation of the prevailing, low-level offshore wind by the SBC. The simulated boundary-layer development can be accounted for by using a simple 1D Lagrangian model of growth driven by the surface heat flux. This model is obtained as a straightforward modification of an established MIBL analytic growth model.
TL;DR: In this article, the characteristics and the formation mechanism of the weak-wind region were investigated, using a 2D mesoscale atmospheric model, and it was shown that the weakwind region is created by the development of the heat-island circulation over the urban area; the heat island circulation weakens the inlandward ambient wind during the morning hours.
Abstract: A weak-wind region, whose horizontal scale is comparable to that of an urban area, is occasionally formed ahead of the sea-breeze front, over a large coastal urban area (Yoshikado and Kondo 1989; Yoshikado 1990; Ohashi and Kida 2001). In this study, the characteristics and the formation mechanism of the weak-wind region were investigated, using a 2D mesoscale atmospheric model. The following results were obtained: The weak-wind region is created by the development of the heat-island circulation over the urban area; the heat-island circulation (i.e., the urbanward pressure-gradient-force) weakens the inlandward ambient wind during the morning hours. At that time, the sea-breeze circulation is inessential in creating this weak-wind region. The weak-wind region cannot be created under the influence of the seaward ambient wind. Subsequently, the weak-wind region is persistently formed ahead of the sea-breeze front, and gradually moves inlandward. A long-term balance between the urbanward pressure-gradient-force, and the turbulent mixing, causes such a phenomenon. Thus, interactions among the sea-breeze circulation, heat-island circulation, and inlandward ambient wind play an important role in the above processes. The spatial scale of the weak-wind region strongly depends on the urban size (width), i.e., the spatial scale of the heat-island circulation developing over the urban area, during the daytime hours.
TL;DR: In this article, the vertical wind profiles determined by Doppler sodar and the water vapourmixing ratio profiles obtained by Raman lidar are used to estimate the atmosphericwater vapour flux profiles in the nocturnal urban boundary layer under unstable conditions.
Abstract: The vertical wind profiles determined by Doppler sodar and the water vapourmixing ratio profiles obtained by Raman lidar are used to estimate the atmosphericwater vapour flux profiles in the nocturnal urban boundary layer under unstableconditions. The experiment was conducted for several nights in the central areaof Rome under a variety of moisture conditions and different urban boundary-layerflow regimes. Despite some scatter in the profiles, the latent heat flux is found tobe positive throughout the depth of the nocturnal urban boundary-layer. Thelayer-averaged flux shows a variation between -4 to +40 W m-2, whileindividual values of flux in excess of +150 W m-2 pertain to a case offree convection during cold air advection caused by the sea breeze. The qualityof flux estimates is found to be highly limited by the low sampling rates employedin the experiment resulting in errors to the order of 60%. Therefore, the results mustbe viewed as estimates rather than precise measurements. The skewness profiles ofthe turbulent fluctuations of vertical velocity and water vapour mixing ratio are alsopositive.