Sea-Breeze Convergence Zones from AVHRR over the Iberian Mediterranean Area and the Isle of Mallorca, Spain

2009 ◽  
Vol 48 (10) ◽  
pp. 2069-2085 ◽  
Author(s):  
Cesar Azorin-Molina ◽  
Bernadette H. Connell ◽  
Rafael Baena-Calatrava
Keyword(s):  
Boundary Layer ◽  
High Resolution ◽  
Large Scale ◽  
Leading Edge ◽  
Sea Breeze ◽  
Heavy Rain ◽  
Detection Algorithm ◽  
Cloud Detection ◽  
Practical Applications ◽  
Convergence Zones

Abstract The aim of this study was to identify clear air boundaries and to obtain spatial distribution of convective areas associated with the sea breeze over the Iberian Mediterranean zone and the isle of Mallorca, both in Spain. Daytime Advanced Very High Resolution Radiometer (AVHRR) data from National Oceanic and Atmospheric Administration (NOAA) polar-orbiting satellites were collected for May–October 2004. A cloud detection algorithm was used to identify clouds to derive daytime sea-breeze cloud frequency composites over land. The high-resolution composites aided in identifying the location of five preferential sea-breeze convergence zones (SBCZ) in relation to the shape of coastline and orographic effects. Additionally, eight regimes were designated using mean boundary layer wind speed and direction to provide statistics about the effect of prevailing large-scale flows on sea-breeze convection over the five SBCZ. The offshore SW to W and the NW to N regimes were characterized by high cloud frequencies parallel to the coast. Small differences in mean cloud frequency values from morning to afternoon composites were detected with these regimes because sea-breeze fronts tended to form early and persist into the afternoon. Just the opposite occurred under the onshore NE to E and SE to S regimes. It was found that light to moderate (≤5.1 m s−1) winds aloft result in more clouds at the leading edge of sea breezes. In contrast, strong synoptic-scale (>5.1 m s−1) flows weaken boundary layer convergence. The results from this satellite meteorology study could have practical applications for many people including those that forecast the weather and those that use the forecast for making decisions related to energy use, fishing, recreation, or agriculture activities, as well as for estimating pollution or issuing warnings for heavy rain or flash flooding.

scholarly journals Performance of the WRF Model for Surface Wind Prediction around Qatar

2018 ◽  
Vol 35 (3) ◽  
pp. 575-592 ◽  
Author(s):  
B. S. Sandeepan ◽  
V. G. Panchang ◽  
S. Nayak ◽  
K. Krishna Kumar ◽  
J. M. Kaihatu
Keyword(s):  
Boundary Layer ◽  
Large Scale ◽  
Surface Wind ◽  
Wrf Model ◽  
Wave Model ◽  
Sea Breeze ◽  
Surface Winds ◽  
Model Errors ◽  
Sea Breezes ◽  
Practical Applications

AbstractThe performance of the Weather Research and Forecasting (WRF) Model is examined for the region around Qatar in the context of surface winds. The wind fields around this peninsula can be complicated owing to its small size, to a complex pattern of land and sea breezes influenced by the prevailing shamal winds, and to its dry and arid nature. Modeled winds are verified with data from 19 land stations and two offshore buoys. A comparison with these data shows that nonlocal planetary boundary layer (PBL) schemes generally perform better than local schemes over land stations during the daytime, when convective conditions prevail; at nighttime, over land and over water, both schemes yield similar results. Among other parameters, modifications to standard USGS land-use descriptors were necessary to reduce model errors. The RMSE values are comparable to those reported elsewhere. Simulated winds, when used with a wave model, result in wave heights comparable to buoy measurements. Furthermore, WRF results, confirmed by data, show that at times sea breezes develop from both coasts, leading to convergence in the middle of the country; at other times, the large-scale wind impedes the formation of sea breezes on one or both coasts. Simulations also indicate greater land/sea-breeze activity in the summer than in the winter. Differences in the diurnal evolution of surface winds over land and water are found to be related to differences in the boundary layer stability. Overall, the results indicate that the WRF Model as configured here yields reliable simulations and can be used for various practical applications.

A Turbulent Boundary Layer Flow Over an Open Shallow Cavity

2016 ◽  
Author(s):  
Khaled J. Hammad
Keyword(s):  
Boundary Layer ◽  
Large Scale ◽  
Vector Fields ◽  
Turbulence Models ◽  
Leading Edge ◽  
Field Measurements ◽  
Recirculation Region ◽  
Mean Flow ◽  
Trailing Edge ◽  
Cavity Depth

Particle Image Velocimetry (PIV) was used to study the flow structure and turbulence, upstream, over, and downstream a shallow open cavity. Three sets of PIV measurements, corresponding to a turbulent incoming boundary layer and a cavity length-to-depth ratio of four, are reported. The cavity depth based Reynolds numbers were 21,000; 42,000; and 54,000. The selected flow configuration and well characterized inflow conditions allow for straightforward assessment of turbulence models and numerical schemes. All mean flow field measurements display a large flow recirculation region, spanning most of the cavity and a smaller, counter-rotating, secondary vortex, immediately downstream of the cavity leading edge. The Galilean decomposed instantaneous velocity vector fields, clearly demonstrate two distinct modes of interaction between the free shear and the cavity trailing edge. The first corresponds to a cascade of vortical structures emanating from the tip of the leading edge of the cavity that grow in size as they travel downstream and directly interact with the trailing edge, i.e., impinging vortices. The second represents vortices that travel above the trailing edge of the cavity, i.e., non-impinging vortices. In the case of impinging vortices, a strong, large scale region of recirculation forms inside the cavity and carries the flow disturbances, arising from the impingement of vortices on the trailing edge of the cavity, upstream in a manner that interacts with and influences the flow as it separates from the cavity leading edge.

scholarly journals The Impact of Secondary Flow Systems on Air Pollution in the Area of São Paulo

1998 ◽  
Vol 37 (3) ◽  
pp. 269-287 ◽  
Author(s):  
I. Bischoff-Gauß ◽  
N. Kalthoff ◽  
F. Fiedler
Keyword(s):  
Boundary Layer ◽  
Atlantic Ocean ◽  
Coastal Area ◽  
Air Pollutants ◽  
Large Scale ◽  
Sea Breeze ◽  
Sao Paulo ◽  
Steep Slope ◽  
São Paulo ◽  
Free Atmosphere

Abstract The area between the Atlantic Ocean and São Paulo is highly polluted due to high emission rates at Cubatão, a city situated 15 km inland at a steep slope. It was expected that secondary circulations would develop caused by the land–sea contrast and strong orographic changes, which influence the transport and diffusion of air pollutants. In 1994–95, surface stations were operated and radiosonde ascents were performed to analyze the characteristic features of the land–sea-breeze circulation. The stations make evident a land–sea-breeze system that arrived in the suburbs of São Paulo in the early afternoon. The upslope winds favor the propagation of the sea breeze at the steep slope. During the measurement period, large-scale northwesterly winds prevailed that advected warm air from the plateau to the coastal area in the afternoon and resulted in a limitation of the boundary layer growth. The data were used to initialize a three-dimensional mesoscale model for calculation of the transport and deposition of SO2 emitted at Cubatão. The boundary layer height was found to be a limitation for vertical mixing of the air pollutants. However, a step between the coastal boundary layer and the boundary layer over the plateau causes SO2 to be vented into the free atmosphere at the slope and then transported toward the Atlantic Ocean with the large-scale northwesterly winds. Thus, over the coastal area, the SO2 concentrations in the free atmosphere were even higher than within the mixed layer. The deposition, summed up over a day, was calculated and found to be strongest at the slope and over the Atlantic Ocean.

Improvement of Universal Dynamic Threshold Cloud Detection Algorithm and Its Application in High Resolution Satellite

2018 ◽  
Vol 38 (10) ◽  
pp. 1028002 ◽  
Author(s):  
王权 Wang Quan ◽  
孙林 Sun Lin ◽  
韦晶 Wei Jing ◽  
周雪莹 Zhou Xueying ◽  
陈婷婷 Chen Tingting ◽  
...  
Keyword(s):  
High Resolution ◽  
Detection Algorithm ◽  
Dynamic Threshold ◽  
Cloud Detection

scholarly journals Quantifying pollution inflow and outflow over East Asia in spring with regional and global models

2010 ◽  
Vol 10 (9) ◽  
pp. 4221-4239 ◽  
Author(s):  
M. Lin ◽  
T. Holloway ◽  
G. R. Carmichael ◽  
A. M. Fiore
Keyword(s):  
Boundary Layer ◽  
Air Pollution ◽  
High Resolution ◽  
Boundary Conditions ◽  
East Asia ◽  
Large Scale ◽  
Regional Model ◽  
Global Model ◽  
Global Models ◽  
High Resolution Models

Abstract. Understanding the exchange processes between the atmospheric boundary layer and the free troposphere is crucial for estimating hemispheric transport of air pollution. Most studies of hemispheric air pollution transport have taken a large-scale perspective using global chemical transport models with fairly coarse spatial and temporal resolutions. In support of United Nations Task Force on Hemispheric Transport of Air Pollution (TF HTAP; www.htap.org), this study employs two high-resolution atmospheric chemistry models (WRF-Chem and CMAQ; 36×36 km) driven with chemical boundary conditions from a global model (MOZART; 1.9×1.9°) to examine the role of fine-scale transport and chemistry processes in controlling pollution export and import over the Asian continent in spring (March 2001). Our analysis indicates the importance of rapid venting through deep convection that develops along the leading edge of frontal system convergence bands, which are not adequately resolved in either of two global models compared with TRACE-P aircraft observations during a frontal event. Both regional model simulations and observations show that frontal outflows of CO, O3 and PAN can extend to the upper troposphere (6–9 km). Pollution plumes in the global MOZART model are typically diluted and insufficiently lofted to higher altitudes where they can undergo more efficient transport in stronger winds. We use sensitivity simulations that perturb chemical boundary conditions in the CMAQ regional model to estimate that the O3 production over East Asia (EA) driven by PAN decomposition contributes 20% of the spatial averaged total O3 response to European (EU) emission perturbations in March, and occasionally contributes approximately 50% of the total O3 response in subsiding plumes at mountain observatories (at approximately 2 km altitude). The response to decomposing PAN of EU origin is strongly affected by the O3 formation chemical regimes, which vary with the model chemical mechanism and NOx/VOC emissions. Our high-resolution models demonstrate a large spatial variability (by up to a factor of 6) in the response of local O3 to 20% reductions in EU anthropogenic O3 precursor emissions. The response in the highly populated Asian megacities is 40–50% lower in our high-resolution models than the global model, suggesting that the source-receptor relationships inferred from the global coarse-resolution models likely overestimate health impacts associated with intercontinental O3 transport. Our results highlight the important roles of rapid convective transport, orographic forcing, urban photochemistry and heterogeneous boundary layer processes in controlling intercontinental transport; these processes may not be well resolved in the large-scale models.

scholarly journals Characteristics of shallow thermally driven flow in the complex topography of the south-eastern Adriatic

2010 ◽  
Vol 28 (10) ◽  
pp. 1905-1922 ◽  
Author(s):  
M. T. Prtenjak ◽  
I. Tomažić ◽  
I. Kavčič ◽  
S. Đivanović
Keyword(s):  
Large Scale ◽  
Sea Breeze ◽  
Small Scale ◽  
The South ◽  
Fine Grid ◽  
Easterly Wind ◽  
Sodar Data ◽  
South Eastern ◽  
The North ◽  
Convergence Zones

Abstract. Characteristics of thermally induced flow, namely the sea breeze, are investigated along the south-eastern Adriatic. The chosen period 24–25 April 2006 favoured sea breeze development and simultaneously allowed a comparison of the large-scale wind influence (north-westerly wind versus south-easterly wind) and the complex terrain on the local circulations. Particular attention is paid to the small-scale formation of the wind field, convergence zones (CZs), channelling flows and small scale eddies, especially in the vicinity of two airports in the central part of south-eastern Adriatic. The results are based on wind measurements (from meteorological surface stations, radiosoundings, satellite data and sodar data) and further supplemented by model data at fine grid spacing. This study shows the formation of numerous irregular daytime and nighttime CZs, which occurred along the coastline in the lee of mountains and over the larger, elongated islands. The results show that the above mentioned airports are surrounded by daytime CZ formations within the lowermost 1000 m and associated updrafts of 1 m s−1, especially if CZs are maintained by the north-westerly large-scale winds. Whereas the daytime CZ was generated due to merged sea breezes, the weaker and shallower nighttime CZs were formed by wind convergence of the seaward breezes, and significantly modified by the large-scale flow of the topography (e.g., accelerated flow in the sea channels and substantial swirled flows around the islands). The passes between the coastal mountain peaks changed the inflow penetration, provoking the increase in wind speed of the channelled flow. The strongest sea breeze channelling was observed above the valley of the Neretva River, where the onshore flow reached 40 km inland with a strength of 8 m s−1, and the highly asymmetric offshore part was confined within the sea channel.

Analysis of a server convective rainstorm in the weak background

2020 ◽  
Author(s):  
zhang yingxin ◽  
qin rui
Keyword(s):  
Boundary Layer ◽  
Cloud Model ◽  
Vertical Wind Shear ◽  
Sea Breeze ◽  
Heavy Rain ◽  
High Energy ◽  
Convective Cell ◽  
Visible Image ◽  
Convergence Line ◽  
Strong Winds

<p>Using conventional and unconventional meteorological observation dataes, RMAPS-NOW( RR4DVar cloud model), the severe convective rainstorm occurred over the Beijing-Tianjin-Hebei junction area on May 17, 2019 was analyzed. Taking the observation of  Tongzhou 101 farm rainstorm (17: 30-20h precipitation 179.1mm) as an example, the results showed that this server convective rainstorm took place under a weak background, (1) Boundary conditions : The Beijing-Tianjin-Hebei area had high temperature and high humidity. The θse energy front was located in the middle of Beijing-Tianjin-Hebei. The CAPE at Beijing Observatory reached 1113 J · Kg-1 at 08h, and correction value reached 2669 J · Kg-1 at 14h. Convection cloud streets appeared around 12 o'clock in the visible image of the Himawari-8 satellite; the southeast wind jet in the boundary layer provided sufficient water  for convection development; at 20 o'clock, sounding showed that the vertical wind shear of 0-6 km increased to 17.5 m · s-1. (2) Trigger conditions: The southeast wind at the rear of the offshore High merged with sea breeze and pushed inland, formed a local convergence line with the local southerly wind in the central part of Beijing, Tianjin, and Hebei, and convection occurred at the convergence line and the θse energy front. (3) Tongzhou heavy rain was caused by two convective cells. Cell 1 was generated at the convergence line and the θse front. It developed into a server storm within 1 hour, and the composite reflectivity was > 60dBz. Subsequently, at its downstream (northwest side, the leading airflow is the southeast airflow), Cell 2 developed rapidly, and the two Celles revolved, moved over Tongzhou successively, accompanied by heavy rainfall ,hail and strong winds. (4) RMAPS-NOW data can describe the refined process of cells formation and evolution, that is, the θse field in the Beijing-Tianjin-Hebei region is extremely uneven, even in the θse front area. In the boundary layer convergence line and θse high-energy region, the convective bubble stimulated the formation of cell 1, the airflow spined up, and the development of the convective cell was strengthened. Half an hour later, a single cell was gradually separated into two cells (cell 1 and cell 2) in the upper layer, and the updraft gradually separated from the center into two rotating oblique updrafts. Seen from the echo profile, the two cells were connected by a cloud bridge and rotated clockwise. The convergence line in the boundary connected the two cells and rotated organically.</p>

Signature of large-scale motions on turbulent/non-turbulent interface in boundary layers

2017 ◽  
Vol 819 ◽  
pp. 165-187 ◽  
Author(s):  
Jin Lee ◽  
Hyung Jin Sung ◽  
Tamer A. Zaki
Keyword(s):  
Boundary Layer ◽  
High Speed ◽  
Large Scale ◽  
Streamwise Velocity ◽  
Detection Algorithm ◽  
Turbulence Statistics ◽  
Low Speed ◽  
Point Correlation ◽  
Average Variation ◽  
Correlation And Spectral Analysis

The effect of large-scale motions (LSMs) on the turbulent/non-turbulent (T/NT) interface is examined in a turbulent boundary layer. Using flow fields from direct numerical simulation, the shape of the interface and near-interface statistics are evaluated conditional on the position of the LSM. The T/NT interface is identified using the vorticity magnitude and a streak detection algorithm is adopted to identify and track the LSMs. Two-point correlation and spectral analysis of variations in the interface height show that the spatial undulation of the interface is longer in streamwise wavelength than the boundary-layer thickness, and grows with the Reynolds number in a similar manner to the LSMs. The average variation in the interface height was evaluated conditional on the position of the LSMs. The result provides statistical evidence that the interface is locally modulated by the LSMs in both the streamwise and spanwise directions. The modulation is different when the coherent structure is high- versus low-speed motion: high-speed structures lead to a wedge-shaped deformation of the T/NT interface, which causes an anti-correlation between the angles of the interface and the internal shear layer. On the other hand, low-speed structures are correlated with crests in the interface. Finally, the sudden changes in turbulence statistics across the interface are in line with the changes in the population of low-speed structures, which consist of slower mean streamwise velocity and stronger turbulence than the high-speed counterparts.

The Impact of High-Resolution Sea Surface Temperatures on the Simulated Nocturnal Florida Marine Boundary Layer

2008 ◽  
Vol 136 (4) ◽  
pp. 1349-1372 ◽  
Author(s):  
Katherine M. LaCasse ◽  
Michael E. Splitt ◽  
Steven M. Lazarus ◽  
William M. Lapenta
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Large Scale ◽  
Flow Direction ◽  
Thermal Structure ◽  
Sea Surface ◽  
Scale Model ◽  
Florida Current ◽  
Convergence Zones ◽  
The Impact

Abstract High- and low-resolution sea surface temperature (SST) analysis products are used to initialize the Weather Research and Forecasting (WRF) Model for May 2004 for short-term forecasts over Florida and surrounding waters. Initial and boundary conditions for the simulations were provided by a combination of observations, large-scale model output, and analysis products. The impact of using a 1-km Moderate Resolution Imaging Spectroradiometer (MODIS) SST composite on subsequent evolution of the marine atmospheric boundary layer (MABL) is assessed through simulation comparisons and limited validation. Model results are presented for individual simulations, as well as for aggregates of easterly- and westerly-dominated low-level flows. The simulation comparisons show that the use of MODIS SST composites results in enhanced convergence zones, earlier and more intense horizontal convective rolls, and an increase in precipitation as well as a change in precipitation location. Validation of 10-m winds with buoys shows a slight improvement in wind speed. The most significant results of this study are that 1) vertical wind stress divergence and pressure gradient accelerations across the Florida Current region vary in importance as a function of flow direction and stability and 2) the warmer Florida Current in the MODIS product transports heat vertically and downwind of this heat source, modifying the thermal structure and the MABL wind field primarily through pressure gradient adjustments.

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