Analyzing the basic features of different complex terrain flows by means of a Doppler Sodar and a numerical model: Some implications for air pollution problems

The impact of sea breeze under different synoptic patterns on air pollution within Athens basin

Sea breezes are thermally-driven flows that develop on the mesoscale as a result of differential surface heating between the land and ocean surface. These wind circulations appear on coastal areas, influencing their thermal regime and comfort, the characteristics of the Atmospheric Boundary Layer (ABL), the diffusion of pollutants, transport and circulation of relevant gasses, offshore wind power production and convection onset. Moreover, an important part of the worldwide population lives near the coast and is thus affected by sea breezes, highlighting the importance of their study and understanding of the associated processes. The sea breeze on the coast of Malaga (southern Spain) is analysed in this study, an area where the sea breeze has not been studied yet. This region features complex topography and shoreline orientation, high density of buildings as well as enhanced variability of sea-surface temperatures (SST) due to frequent coastal upwelling events. These factors interact with sea breezes, adding complexity and interest to the study. The first objective of this work is to characterize sea breezes in Malaga, for which observational data from three synoptic stations during the summer months of 2022 are analysed. Despite being relatively close to each other (a few kilometers), the sites exhibit differences in the evolution of temperature and humidity on sea breeze days. The arrival of the sea-breeze front is particularly visible closer to the shoreline, where it contributes to a temperature decrease, which is not apparent on sites 2-5 km inland. The sea breeze also causes an increase in the specific humidity and wind speed. The analysis of the breeze events and the SST suggest that this variable has an impact on temperature close to the shoreline on sea breeze days. The second objective is to perform and analyse a numerical simulation with the Weather Research and Forecasting (WRF) model of a sea breeze event of particular interest, in which important temperature differences existed between the observational sites. Results from the numerical simulation show that complex wind circulations appear in the study area and may explain the observed temperature differences, highlighting the contribution of high-resolution numerical simulations to the understanding of the underlying physical mechanisms.

In this study the impact of land–sea breeze circulation and internal boundary layer (IBL) on the atmospheric dispersion of airborne effluent releases at the tropical coastal site Kalpakkam is simulated using mesoscale model WRF and Lagrangian particle dispersion model FLEXPART. Simulations with WRF are conducted for typical days in different seasons, i.e., 3 May 2011 (summer), 20 Sep 2010 and 20 Jun 2011 (southwest monsoon). Two K-based non-local turbulence closures (YSU, ACM) and two TKE-based local closures (MYNN, MYJ) in WRF are tested for simulating the sea breeze and IBL. Observations from a 50-m meteorological tower, GPS Sonde, and a Doppler SODAR are used for validation. Simulations indicate that the synoptic flow largely influences the characteristics of the sea breeze at the site. Results show that the sea breeze is more predominant with early onset and it is characterized by deep inland penetration, strong horizontal and vertical winds and is associated with formation of a deep IBL relative to monsoon with opposing large-scale flow. The YSU non-local diffusion scheme and the higher order local TKE closure (MYNN) simulated the sea breeze and IBL characteristics in good agreement with observations. Dispersion simulations with a hypothetical tracer release using FLEXPART showed relatively high ground-level concentrations during IBL formation in the daytime and during stable off-shore flow condition in the morning time. The coupled mesoscale dispersion model could simulate the plume trajectory and buildup of concentrations during sea-breeze time by realistically simulating the winds and mixed-layer characteristics at the coastal site.

Doppler sodar measurements were made at the tropical Indian station, i.e., Gadanki (13.5° N, 79. 2° E). According to wind climatologies, the wind pattern changes from month to month. In July and August, the predominant wind direction during the monsoon season was the southwest. In September, it was the northwest and south. While the winds in November came from the northeast, they came from the northwest and southwest in October. The winds in December were out of the southeast. The diurnal cycle of winds at 60-m above the ground was visible, with disturbed wind directions in September and October. This may be connected to the Indian subcontinent’s southeastern monsoon recession. To better understand the monsoon circulation on a monthly basis, the present work is innovative in that it uses high-resolution winds measured using the Doppler sodar at the atmospheric boundary layer. The convergence of a sea breeze and the background wind might result in a sudden change in wind direction, and forecasting such a chaotic atmospheric event is crucial in the aviation sector. As a result, the wind shear that is produced may pose a serious threat to airplanes that are landing. In the current study, we present a few cases of sea breeze intrusions. The physics underlying these intrusions may help modelers better understand these chaotic wind structures and use them as inputs in their models. Based on surface-based atmospheric characteristics, there have been two reports of deep sea breeze intrusions that we report in this research. The sea breeze days were marked by substantial (moderate) drops in temperature (dewpoint temperatures) and increased wind speed and relative humidity. The India Meteorological Department (IMD) rainfall data showed a rise in precipitation over this location on 23 July (4.8 mm) and 24 July (9.5 mm) when sea breeze intrusions over Gadanki were noticed. Sea breeze intrusions could have brought precipitation (intrusion-laden precipitation) to this area due to conducive meteorological conditions. A simple schematic model is proposed through a diagrammatic illustration that explains how a sea breeze triggers precipitation over adjacent locations to the seacoast. The skew-T log-P diagrams have been drawn using the balloon-borne radiosonde measured atmospheric data over Chennai (a nearby location to Gadanki) to examine the thermodynamic parameters to gain insights into the underlying mechanisms and meteorological conditions during sea breeze intrusion events. It is found that the convective available potential energy (CAPE), which is presented as a thermos diagram, was associated with large values on 23 July and 24 July (898 J/kg and 1250 J/kg), which could have triggered thunderstorms over Chennai.

Range height indicator (RHI) scans are performed routinely by the long-range Doppler Light Detection and Ranging (LIDAR) systems at the Hong Kong International Airport (HKIA). This paper presents some novel observations of the airflow in the airport region by RHI scans that have not been reported in the literature in the past—namely, areas of reverse flow and vortex shedding in east to southeasterly winds; severe windshear in the easterly; a converging southerly flow; a descending northeasterly jet; and the undercutting of the southwesterly flow by sea breeze. Many of these flow features are associated with low-level windshear, supported by pilot windshear reports, and thus their observations have practical applications. The technical feasibility of forecasting these airflow features is also studied in this paper, and it is found that large eddy simulations based on a mesoscale meteorology model manage to capture these wind features most of the time, but the simulated headwind change is generally slightly smaller than observed. The results in this paper have application value for windshear alerting and forecasting for an airport situated in an area of complex terrain, and they should be of interest for further studies of mountain meteorology.

The reasons for the relatively strong coastal afternoon surface winds observed along the Gulf of Finland were studied by using a high‐resolution two‐dimensional numerical model in typical summertime conditions. Sea breeze effects were included by defining a clear sky, whereas they were minimized by alternatively defining a thick cloud cover. The geostrophic wind was varied both in speed and direction. A case‐study was made with a three‐dimensional operational forecast model with results that agreed with the two‐dimensional experiments and observations.Strongish afternoon surface winds nearly parallel with the coastline were obtained in the overcast gulf experiments. In these cases, well‐mixed air entering the smooth sea slantwise from over land commenced an inertial oscillation downstream such that the emerging low‐level jet maximum was located just above the opposite coast, causing the strong winds there. If the sky was clear, sea breezes and strong convective mixing further enhanced the coastal surface winds to supergeostrophic speeds.In contrast, weak coastal winds occurred when the sea breeze and the basic flow were nearly opposite. Given the gulf geometry, the sea breeze cell from the opposite coast could be advected over the gulf in a suitable basic flow, which resulted in another minimum in the coastal wind speed as a function of geostrophic wind direction. Copyright © 2005 Royal Meteorological Society.

Regarding the actual conditions of the heat environment within urban city blocks, mobile meteorological observations in a residential area of Tokyo have pointed out the need to properly understand the dynamics of water vapor content on a city block scale due to significant WBGT fluctuations even within a few kilometers of observation routes. In this study, tracer flow analysis using LBM based on a detailed three-dimensional urban model assuming sea breeze inflow was conducted in order to understand the characteristics of water vapor distribution within a city block. As a result, it was found that the water vapor distribution in the city block is characterized by the distribution of water vapor inflow from the sea area due to sea breezes. The area with low water vapor was located on the leeward side of the high-rise buildings, where the sea breeze was blocked by the buildings and water vapor originating from the sea did not easily flow into the area. It was also found that the advection pattern of water vapor changed depending on the location of the main flow direction and the arrangement of the city block structures. Although we confirmed that the above distributions are generally consistent with the water vapor distributions measured by the mobile observations, there are also some difference from the observation result. This is expected to be evapo-transpiration from water bodies and vegetation which are not considered in the numerical model.

Near the vicinity of 30° latitude, the coincidence of the period of sea breeze and the inertial period of the ocean leads to a maximum near-inertial ocean response to sea breeze. This produces a propagating inertial internal (Poincare) wave response that transfers energy laterally away from the coast and provides significant vertical mixing. In this paper, the latitudinal dependence of this wave propagation and its associated vertical mixing are investigated primarily using a nonlinear numerical ocean model. Three-dimensional idealized simulations show that the coastal oceanic response to sea breeze is trapped poleward of 30° latitude; however, it can propagate offshore as Poincare waves equatorward of 30° latitude. Near 30° latitude, the maximum oceanic response to sea breeze moves offshore slowly because of the near-zero group speed of Poincare waves at this latitude. The lateral energy flux convergence plus the energy input from the wind is maximum near the critical latitude, leading to increased local dissipation by vertical mixing. This local dissipation is greatly reduced at other latitudes. The implications of these results for the Gulf of Mexico (GOM) at ∼30°N is considered. Simulations with realistic bathymetry of the GOM confirm that a basinwide ocean response to coastal sea-breeze forcing is established in form of Poincare waves. Enhanced vertical mixing by the sea breeze is shown on the model northern shelf, consistent with observations on the Texas–Louisiana shelf. Comparison of the three-dimensional and one-dimensional models shows some significant limitations of one-dimensional simplified models for sea-breeze simulations near the critical latitude.

Topographical influences on the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) rain retrievals over the terrain area of the Korean peninsula were examined using a training dataset constructed from numerical mesoscale model simulations in conjunction with radiative transfer calculations. By relating numerical model outputs to rain retrievals from simulated brightness temperatures, a positive relationship between topographically forced vertical motion and rain retrievals in the upstream region over the mountainous area was found. Based on the relationship obtained, three topographical correction methods were developed by incorporating slope-forced vertical motion and its associated upward vapor flux, and vapor flux convergence in the surface boundary layer into a scattering-based TMI rain retrieval algorithm. The developed correction methods were then applied for the rain retrievals from simulated TMI brightness temperatures with model outputs and measured TMI brightness temperatures. Results showed that orographic influences on the rain formation can be included in the TMI rainfall algorithms, which tend to underestimate rainfall over the complex terrain area. It was shown that topographical corrections surely improve the rain retrieval when a strong rain event is present over the upslope region. Among various elements, moisture convergence in the boundary layer appears to be an important factor needed in the topographical correction. Overall topography-corrected estimates of rainfall showed a better agreement with ground measurements than those without correction, suggesting that satellite rain retrieval over the terrain area can be improved when accurate numerical forecast outputs are incorporated into the rain retrieval algorithm.

The vertical structures of nocturnal drainage winds that blow onto the Fukuoka Plains from mountains behind were examined on the basis of echo intensity and wind velocity obtained by using a Doppler sodar. Air and soil surface temperatures, wind velocity and net radiation near the ground surface were also measured to estimate the heat budget between the air and the ground. Though the nocturnal drainage winds have the depth of 250 m to 300 m, the shape of the fronts varies with the sea breeze and the surrounding flow. Twice in the nighttime, the occurrence of the horizontal wind with the maximum speed of 4 to 6 ms-1 was observed at the height about 150 m above the ground surface. Though the ascending currents with the speed of 0.2 to 0.4 ms-1 were also seen twice with the occurrence, the second current ascended higher than the first one. These phenomena may be due to the intermitted supply of cold air mass from a basin being in the upstream side. After the first occurrence, the air temperature near the ground surface reaches to the air temperature at a height of 30m. This reason is that the cold air near the ground surface formed by the radiational cooling is replaced with the upper warm air by the advection of the drainage winds. After then, the decreasing rate of the air temperature becomes smaller because the heat fluxes from the air toward the ground suppress the radiational cooling.

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.

Within the numerical mesoscale model described by McNider and Pielke (1981) the eddy exchange coefficients are estimated from either a local or nonlocal scheme. Switching between these is dependent on the sign of the surface heat flux. In inhomogeneous regions this switching is shown to be sensitive to the height of the stable planetary boundary layer. By defining the boundary layer height as the height to which turbulence generated by the wind shear falls to zero, a more realistic estimate can be obtained and the model is able to simulate observed potential temperature fields.

When the temperature difference between land and sea surface along coastline is large enough, thermally induced circulation is likely developed in the coastal region, called as Sea/Land (S/L) breeze. It has been an important issue in coastal region because of its significant role for the transport, dispersion of air pollutants generated in coastal regions. Meso-scale modeling was carried out using the commercial modeling tool ‘A2C flow / A2C t&d (A2C represents the Atmospheric to Computational fluid dynamics and t&d represents the transport and diffusion)’ to characterize the meso-scale circulation of pure breeze in the study region (125.22E, 36.32N to 127.95E, 38.39N) in late July for typical summer conditions of Korea. Maximum potential temperature differences were approximately 5K and 14K in early morning and mid day, respectively in the study domain. Strong land breeze was observed around 6AM and it was neutralized to transition stage between 9AM ~ 10AM then the sea breeze started. Maximum speed of sea breeze, approximately 2.5m/s was found around 3PM which is about double of land breeze (1.5m/s). With the declination of sun energy with the passing of time, sea breeze lost its momentum and reached to transition stage between (9PM ~ 10PM). The penetration lengths of sea breeze and land breeze are approximately 25km~30km and 20km~25km, respectively while the suction lengths of sea breeze and land breeze are approximately 15km~20km each. In addition, the maximum depths of the S/L breeze are approximately 400m and 1200m, respectively in early morning and sometimes in mid day along the coastal area. DOI: http://dx.doi.org/10.3126/jie.v8i3.5936 JIE 2011; 8(3): 94-104

Kaiga, located on the west coast of Karnataka, India is a complex terrain region with dense forest cover often influenced by land-sea breeze flows during warm summer season. In this study, dispersion of tritium released from Kaiga Nuclear Power Plant (NPP) under the influence of land-sea breeze circulations is simulated using FLEXPART-WRF models. Sensitivity experiments with Weather Research and Forecasting (WRF) are conducted with two Land Surface Models (LSMs), Noah and Noah-Multi Physics (Noah-MP) to study their impact on the wind flow and meteorological characteristics. Mini Boundary Layer Masts (MBLMs) and Doppler SODAR observations are used for evaluating the model performance. WRF simulations showed large sensitivity of simulated sea breeze characteristics to the model land surface physics. It has been found that the Noah-MP better represented the onset time, inland extent, intensity and duration of the sea breeze circulation over the Kaiga complex terrain region with lesser error statistics compared to Noah. The improvements with Noah-MP over Noah are due to the better representation of vegetation and soil hydrological processes over the dense forest region, realistic simulation of surface energy and momentum fluxes and reduction in the land-sea temperature contrast by including a separate canopy physics. FLEXPART simulation of tritium releases from the Kaiga NPPs using WRF predicted meteorological fields showed large diurnal variability in the dispersion pattern and air concentrations around the Kaiga valley. Tritium plume is transported to the northwest sector during early morning and morning time by the land-breeze and to the east-southeast sector by the sea breeze during daytime. Predicted tritium concentrations are found to be higher during the morning under stable atmospheric conditions and lower during sea breeze hours due to stronger winds and deep mixed layers. FLEXPART predicted tritium activity concentrations at different measurement locations using WRF-Noah-MP meteorological data are in better agreement with measurements with higher correlation coefficient and index of agreement. • Tritium dispersion over a coastal complex terrain site is modeled by using the coupled WRF-FLEXPART model. • Dispersion of tritium released from a Nuclear Power Plant under mesoscale sea breeze and land breeze circulations is presented. • Sensitivity of Land Surface Models, Noah and Noah-MP in WRF on the simulation of sea breeze characteristics and tritium dispersion are assessed. • Explicit treatment of forest canopy in the Noah-MP LSM over a model domain with dense forest improved the model results.

A simulation with the Méso-NH model over the island of Mallorca, Spain, has been made in a case of synoptic high pressure (5 June 2010) that allowed the development of sea breezes (SB) in the three main basins of the island. The results compare well to the available observations and are qualitatively very close to a previous idealized study with no synoptic forcing made by Ramis and Romero in 1995. The temporal and spatial structure of the SB in the southeastern basin is analyzed with the use of the momentum, temperature, and turbulence kinetic energy budgets provided by the numerical model. Five stages of evolution from before dawn to after sunset are discussed, identifying the main physical mechanisms at play. The morning land heating warms the land and the air over it until an air temperature gradient is created and a marine flow accelerates inland, dragged by turbulence in the low layers. The upper part of the inland current and the layers just above are dominated by compensatory motions, which oppose the corresponding pressure gradient at these levels. These mechanisms last while the SB is active, with significant effects from the local topography, and they decrease in intensity as sunset approaches. This relatively simple case has been used to check the goodness of two analytical models of the SB that perform relatively well because they use turbulence as a surrogate for the missing advection terms in the layers above 200 m. These models are formulated here in a more consistent manner in the turbulence parameterization than were the original propositions.