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1.
Numerical model simulations of sea-breeze circulations in the presence of idealized topography are subjected to dimensional analysis in order to capture the dynamics of the sea-breeze circulation combined with an upslope-flow circulation. A secondary objective is to reconcile previous results based on observations. The analysis is based on a scaling analysis of sea-breeze speed, depth and volume flux. This study is motivated by the fact that the literature of sea breezes interacting with upslope flows is generally qualitative. Results show clear scaling regimes and strong interaction between the two thermally driven circulations. We distinguish three regimes, depending on slope length, slope angle, stability and surface heat flux. The first and third regimes obey the scaling laws of pure sea-breeze scaling. The second regime shows a significant decrease in the scaled volume flux relative to pure sea-breeze scaling. Dynamical relations in the second regime show a strong influence on the circulation of upslope stable air advection.  相似文献   

2.
A series of numerical sensitivity experiments is performed to quantify the impact of sea-surface temperature (SST) distribution on offshore surface fluxes and simulated sea-breeze dynamics. The SST simulations of two mid-latitude sea-breeze events over coastal New England are performed using a spatially-uniform SST, as well as spatially-varying SST datasets of 32- and 1-km horizontal resolutions. Offshore surface heat and buoyancy fluxes vary in response to the SST distribution. Local sea-breeze circulations are relatively insensitive, with minimal differences in vertical structure and propagation speed among the experiments. The largest thermal perturbations are confined to the lowest 10% of the sea-breeze column due to the relatively high stability of the mid-Atlantic marine atmospheric boundary layer (ABL) suppressing vertical mixing, resulting in the depth of the marine layer remaining unchanged. Minimal impacts on the column-averaged virtual potential temperature and sea-breeze depth translates to small changes in sea-breeze propagation speed. This indicates that the use of datasets with a fine-scale SST may not produce more accurate sea-breeze simulations in highly stable marine ABL regimes, though may prove more beneficial in less stable sub-tropical environments.  相似文献   

3.
This analysis presents a new set of scalings for sea-breeze circulations. The scales are based on surface-layer turbulent fluxes of sensible heat and momentum, thus avoiding the use of exchange coefficients. Nondimensionalization of the governing equations, using the new scales, results in four dimensionless governing parameters, two of which are new. A data set consisting of 36 profiles of atmospheric variables during pure sea-breeze circulations is presented. The data are used to generate scaling laws for dimensionless sea-breeze depth and strength in the form of products of powers of the governing dimensionless parameters. These scaling laws are used to nondimensionalize individual velocity profiles, which are composited to present a universal dimensionless sea-breeze velocity profile. The scaling laws, applied as a diagnostic scheme, are used to investigate the diurnal evolution of the depth and strength of sea breezes.  相似文献   

4.
利用船测近海层湍流热通量资料验证OAFlux数据集   总被引：1，自引：0，他引：1  
美国伍兹霍尔海洋研究所(Woods Hole Oceanographic Institution,WHOI)的客观分析海气通量(Objectively Analyzed air-sea Fluxes,OAFlux)数据集中的近海层湍流热通量数据被公认为最可信,并被广泛地用于气候模式模拟结果检验。利用NOAA ETL(Environmental Technology Laboratory)两个固定观测站点的科学试验的船测通量数据库(TOGA COARE试验观测资料和KAWJEX试验观测资料),对OAFlux的热通量进行验证。结果表明:OAFlux的潜热通量普遍高于船测值,并且风速较大时,两者差异较大。风速对潜热通量的变化趋势起主导作用,海表和大气湿度差影响甚微。低风条件下,OAFlux的潜热通量和船测值差异则很小。海面湍流感热交换很弱,通量值本身依然受到风速的主导作用,但由于感热通量值与观测仪器误差十分接近,导致比较分析异常困难。分析结果表明:在上述两个观测试验期内,由于海表空气湿度和大气的湿度差变化不显著,海气相互作用的强度主要取决于海面风速的变化。  相似文献   

5.
The sea-breeze scaling of Steynis extended by incorporating data fromtwo additional locations. This is done primarily to remove concerns that the original scaling laws contain featuresspecific to the Vancouver data upon which they were based. This new analysis also employs the integrated, ratherthan instantaneous, heat flux proposed by Tijm. The analysis results in well-defined scaling laws for allthree locations, and include explicit latitude dependence, which was not possible in the earlier study. The integratedheat flux reveals systematic diurnal behaviour that is shown to result in a separate scaling law for diurnalevolution of sea breezes at a single location.  相似文献   

6.
Idealized large-eddy simulations of lake and sea breezes are conducted to determine the sensitivity of these thermally-driven circulations to variations in the land-surface sensible heat flux and initial atmospheric stability. The lake-breeze and sea-breeze metrics of horizontal wind speed, horizontal extent, and depth are assessed. Modelled asymmetries about the coastline in the horizontal extent of the low-level onshore flow are found to vary as a function of the heat flux and stability. Small lake breezes develop similarly to sea breezes in the morning, but have a significantly weaker horizontal wind-speed component and a smaller horizontal extent than sea breezes in the afternoon.  相似文献   

7.
A sea-breeze event in south-west Western Australia is simulated using the Regional Atmospheric Modelling System (RAMS) version 6.0. The model is evaluated against high resolution soundings as well as station observations and is shown to reproduce the qualitative features of the sea breeze well. Sensitivity tests are carried out to investigate the effects of historical land-cover change and changes in soil moisture on the dynamics of the sea breeze. It is found that land-cover change alone, i.e., a change from wooded grasslands to bare soil, with no change in soil moisture initialisation, does not significantly alter the overall structure of the sea breeze but results in higher surface winds due to the reduced vegetation roughness length, which leads to enhanced surface moisture advection inland. On the other hand, land-cover change in conjunction with increased soil moisture results in a considerably weaker, shallower, and less penetrative sea breeze, and delays its onset and duration. A sea-breeze scaling analysis highlights the impact of increasing soil moisture on reducing the sea-breeze volume flux scale.  相似文献   

8.
The lack of in situ observations and the uncertainties of the drag coefficient at high wind speeds result in limited understanding of heat flux through the air-sea interface and thus inaccurate estimation of typhoon intensity in numerical models. In this study, buoy observations and numerical simulations from an air-sea coupled model are used to assess the surface heat flux changes and impacts of the drag coefficient parameterization schemes on its simulations during the passage of Typhoon Kalmaegi (2014). Three drag coefficient schemes, which make the drag coefficient increase, level off, and decrease, respectively, are considered. The air-sea coupled model captured both trajectory and intensity changes better than the atmosphere-only model, though with relatively weaker sea surface cooling (SSC) compared to that captured by buoy observations, which led to relatively higher heat flux and thus a stronger typhoon. Different from previous studies, for a moderate typhoon, the coupled simulation with the increasing drag coefficient scheme outputted an intensity most consistent with the observation because of the strongest SSC, reasonable ratio of latent and sensible heat exchange coefficients, and an obvious reduction in the overestimated surface heat flux among all experiments. Results from sensitivity experiments showed that surface heat flux was significantly determined by the drag coefficient-induced SSC rather than the resulting wind speed changes. Only when SSC differs indistinctively (<0.4°C) between the coupled simulations, heat flux showed a weak positive correlation with the drag coefficient-impacted 10-m wind speed. The drag coefficient also played an important role in decreasing heat flux even a long time after the passage of Kalmaegi because of the continuous upwelling from deeper ocean layers driven by the impacted momentum flux through the air-sea interface.  相似文献   

9.
The structures of mean flow and turbulence in the atmospheric surface boundary layer have been extensively studied on Earth, and to a far less extent on Mars, where only the Viking missions and the Pathfinder mission have delivered in-situ data. Largely the behaviour of surface-layer turbulence and mean flow on Mars is found to obey the same scaling laws as on Earth. The largest micrometeorological differences between the two atmospheres are associated with the low air density of the Martian atmosphere. Together with the virtual absence of water vapour, it reduces the importance of the atmospheric heat flux in the surface energy budget. This increases the temperature variation of the surface forcing the near-surface temperature gradient and thereby the diabatic heat flux to higher values than are typical on the Earth, resulting in turn in a deeper daytime boundary layer. As wind speed is much like that of the Earth, this larger diabatic heat flux is carried mostly by larger maximal values of T*, the surface scale temperature. The higher kinematic viscosity yields a Kolmogorov scale of the order of ten times larger than on Earth, influencing the transition between rough and smooth flow for the same surface features.The scaling laws have been validated analysing the Martian surface-layer data for the relations between the power spectra of wind and temperature turbulence and the corresponding mean values of wind speed and temperature. Usual spectral formulations were used based on the scaling laws ruling the Earth atmospheric surface layer, whereby the Earth's atmosphere is used as a standard for the Martian atmosphere.  相似文献   

10.
Scaling of the Sea-Breeze Strength with Observations in the Netherlands   总被引：1，自引：1，他引：1  
In this study we evaluate recently proposed scaling relations for the sea-breeze strength using independent data for a relatively homogeneous area in The Netherlands. We show that several of the scaling relations in the literature incorporate hidden correlation. Furthermore, it appears that the estimate for the sea-breeze strength is better made on the basis of the time-integrated rather than of the instantaneous sensible heat flux. It also turns out that for similar forcing the sea breeze in The Netherlands is about twice as strong as the sea breeze in the Vancouver area of Canada.  相似文献   

11.
The role of a river of small dimensions in driving the surface exchange of sensible and latent heat fluxes at the bottom of a valley is investigated using large-eddy simulation (LES). Simulations were performed using different valley topographies, river widths and large-scale wind speed and direction. In all cases, the river acted as a sink of both sensible and latent heat during daytime. Despite the general agreement concerning the flux direction above the river surface, specific differences exist between the simulations. The topography enhances the wind divergence caused by the river, and the larger negative surface fluxes above the river occur when there are no slopes, a consequence of larger wind speeds above the river. For large-scale winds aligned with the valley axis, the surface fluxes depend on the large-scale wind speed, but this dependence is reduced if the large-scale wind is perpendicular to the valley axis. There is a minimum of temperature and a maximum of specific humidity above the river surface. The scalar budgets show that sensible heat flux converges above the river, being balanced by the warm air subsidence at the centre of the valley. Latent heat fluxes, on the other hand, converge above the river surface, and they are balanced by the horizontal advection of humidity towards the river margins.  相似文献   

12.
Abstract

Airborne measurements of mean wind velocity and turbulence in the atmospheric boundary layer under wintertime conditions of cold offshore advection suggest that at a height of 50 m the mean wind speed increases with offshore distance by roughly 20% over a horizontal scale of order 10 km. Similarly, the vertical gust velocity and turbulent kinetic energy decay on scales of order 3.5 km by factors of 1.5 and 3.2, respectively. The scale of cross‐shore variations in the vertical fluxes of heat and downwind momentum is also 10 km, and the momentum flux is found to be roughly constant to 300 m, whereas the heat flux decreases with height. The stability parameter, z/L (where z = 50 m and L is the local Monin‐Obukhov length), is generally small over land but may reach order one over the warm ocean. The magnitude and horizontal length scales associated with the offshore variations in wind speed and turbulence are reasonably consistent with model results for a simple roughness change, but a more sophisticated model is required to interpret the combined effects of surface roughness and heat flux contrasts between land and sea.

Comparisons between aircraft and profile‐adjusted surface measurements of wind speed indicate that Doppler biases of 1–2 m s?1 in the aircraft data caused by surface motions must be accounted for. In addition, the wind direction measurements of the Minimet anemometer buoy deployed in CASP are found to be in error by 25 ± 5°, possibly due to a misalignment of the anemometer vane. The vertical fluxes of heat and momentum show reasonably good agreement with surface estimates based on the Minimet data.  相似文献   

13.
Sea-breeze circulations in a stably stratified environment have been simulated in a water tank. The floor of the tank was divided into two halves representing land and sea; the land side was heated from the bottom of the tank, and the sea side was insulated by an underlying sponge slab. The temperature profiles over both land and sea sides, the land–sea temperature difference, and the horizontal temperature distributions were measured. Particle tracking velocimetry was applied to obtain the two-dimensional velocity field orthogonal to the coastline. It was shown that the overall flow consists of a closed circulation caused by the horizontal temperature difference between land and sea, and a strong updraft occurring at the sea-breeze front. The dimensionless governing parameters are calculated from the measurements and used to characterize the developing sea breezes. The analysis confirms the scaling laws for sea-breeze velocity and depth. The results indicate that the scaling characteristics of the sea-breeze translation speed during the developing period are different to those during the following maintaining period. A criterion for the onset of the sea breeze is proposed based on these results.  相似文献   

14.
We have conducted large-eddy simulations (LES) of the atmospheric boundary layer with surface heat flux variations on a spatial scale comparable to the boundary layer depth.We first ran a simulation with a horizontally homogeneous heat flux. In general the results are similar to those of previous large-eddy simulations. The model simulates a field of convective eddies having approximately the correct velocity and spatial scales, and with the crucial property that kinetic energy is transported vigorously upwards through the middle levels. However, the resolved temperature variance is only about half what is observed in the laboratory or the atmosphere. This deficiency — which is shared by many other large-eddy simulations — has dynamic implications, particularly in the pressure/temperature interaction terms of the heat flux budget. Recent simulations by other workers at much higher resolution than ours appear to be more realistic in this respect.The surface heat flux perturbations were one-dimensional and sinusoidal with a wavelength equal to 1.3 times the boundary-layer depth. The mean wind was zero. Results were averaged over several simulations and over time. There is a mean circulation, with ascent over the heat flux maxima (vertical velocity ~0.1w *) and descent over the heat flux minima. Turbulence is consistently stronger over the heat flux maxima. The horizontal velocity variance components (calculated with respect to the horizontal average) become unequal, implying that convective eddies are elongated parallel to the surface heat flux perturbations.A consideration of the budgets for temperature and velocity suggests several simplifying concepts.The research reported in this paper was conducted while the first author was on study leave at Colorado State University.  相似文献   

15.
青藏高原作为世界第三极,其热力强迫作用不仅对亚洲季风系统的发展和维持十分重要,也会对大气环流场产生深远影响。利用欧洲中期天气预报中心（ECMWF）的ERA-Interim中1979-2016年3-10月青藏高原及其周边地区的地表热通量月平均再分析资料,通过分析得出以下结论:3-5月青藏高原主体由感热占据,感热强度快速上升且呈西高东低的分布态势,潜热强度较小但随时间而增强。季风爆发后的6-8月,青藏高原感热强度减弱,潜热强度迅速增强且呈东高西低的分布特征。季风消退后的9-10月,感热与潜热强度相当,但感热呈现出西高东低的分布特征。过去38年,青藏高原地表感热总体呈现微弱下降趋势,潜热呈较弱上升趋势。青藏高原西部地区感热呈微弱下降趋势,潜热呈上升趋势。东部感热呈较为明显的下降趋势且近年来变化趋势增强,东部潜热通量则呈现较为明显的上升趋势,分析结论与近期全球变暖条件下青藏高原气候变暖变湿这一变化状况一致,通过对青藏高原地表热通量的变化分析为下一步运用第三次青藏高原大气科学试验所获资料分析青藏高原上空大气热源的变化以及地表加热场如何影响大气环流奠定基础。   相似文献   

16.
Synthetic wind speed and air temperature profiles based on the sensible heat flux density and stress at the surface are averaged for the four possible ways in which the suface stress and heat flux density can vary maintaining the same average values. The analysis of the averaged wind and temperature profiles shows that, when the surface stress and/or heat flux density are time-variable, and wind speed and air temperature are averaged linearly, an erroneous estimate of surface roughness, surface stress, heat flux density and profile structure parameters will result.  相似文献   

17.
The present study compares seasonal and interdecadal variations in surface sensible heat flux over Northwest China between station observations and ERA-40 and NCEP-NCAR reanalysis data for the period 1960-2000.While the seasonal variation in sensible heat flux is found to be consistent between station observations and the two reanalysis datasets,both land-air temperatures difference and surface wind speed show remarkable systematic differences.The sensible heat flux displays obvious interdecadal variability that is season-dependent.In the ERA-40 data,the sensible heat flux in spring,fall,and winter shows interdecadal variations that are similar to observations.In the NCEP-NCAR reanalysis data,sensible heat flux variations are inconsistent with and sometimes even opposite to observations.While surface wind speeds from the NCEP-NCAR reanalysis data show interdecadal changes consistent with station observations,variations in land-air temperature difference differ greatly from the observed dataset.In terms of land-air temperature difference and surface wind speed,almost no consistency with observations can be identified in the ERA-40 data,apart from the land-air temperature difference in fall and winter.These inconsistencies pose a major obstacle to the application in climate studies of surface sensible heat flux derived from reanalysis data.  相似文献   

18.
The spatio-temporal variation of surface sensible heat flux (SHF) in southern China (SC) is studied based on the data evaluated from conventional observational meteorological data. There exist prominent increasing trends in all seasonal surface sensible heat fluxes in the western SC and decreasing trends in the central-eastern part of southern China. The variations of surface sensible heat flux in all seasons are dominant on interannual time-scales. The land-air temperature difference and the near-surface wind speed are two key factors for the interannual variations of SHF, but the former is more important. The first two major anomalous patterns of SHF are presented as the region-wide in-phase anomalies and the east-west dipole anomalies, respectively, based on the EOF analysis results.  相似文献   

19.
ABSTRACT

Sea surface temperature (SST) from four Nucleus for European Modelling of the Ocean (NEMO) model simulations is analyzed to study the bulk flux parameterization to compute SST over the Hudson Bay Complex (HBC) for the summer months (August and September) from 2002 to 2009. The NEMO simulation was forced with two atmospheric forcing sets with different resolutions: the Coordinated Ocean-ice Reference Experiment, version 2 (COREv2), as the lower resolution and the Canadian Meteorological Centre’s Global Deterministic Prediction System Reforecasts (CGRF) as the higher resolution. The CGRF forcing is also implemented in the third and fourth runs using different runoff data and different NEMO resolutions (1/12° versus 1/4°). Results show that all four modelled SSTs followed observed SST patterns, with regional differences in SST bias between simulations with different atmospheric forcing. The SST differences are small between simulations forced with the same atmospheric forcing but with different model resolution or runoff. This implies that the model resolution and runoff have a small effect on the simulated SST in the HBC. Moreover, to better capture the effect of near-surface temperature (Tair) on simulated SST, we conducted three analyses using the Haney flux linearization formula. Results from these assessments did not indicate any direct influence on the model-simulated SSTs by Tair. Looking at the heat flux as a signature for SST showed that both averaged spatial distribution and time series of net heat flux produced by the three CGRF forcing simulations were higher than the net heat flux generated by the CORE 2 simulation. This was generally true for all four components of the total heat flux (sensible, latent, shortwave, and longwave) individually as well. Total heat flux in summer is governed by the shortwave heat flux, with values up to 120?W?m?2 in August, and the longwave heat flux is the main contributor to the total heat flux differences. These heat flux differences lead to corresponding colder model SSTs for the CGRF runs and warmer SSTs for the CORE 2 simulations.  相似文献   

20.
Sea-breeze dynamics in the Marseille area, in the south of France, is investigated in the framework of the ESCOMPTE experiment conducted during summer 2001 in order to evaluate the role of thermal circulations on pollutant transport and ventilation. Under particular attention in this paper is the sea-breeze channelling by the broad Rhône valley and the narrow Durance valley, both oriented nearly-north–south, i.e., perpendicular to the coastline, and its possible impact on the sea-breeze penetration, intensity and depth, which are key information for air pollution issues. One situation of slight synoptic pressure gradient leading to a northerly flow in the Rhône valley (25 June 2001) and one situation of a weak onshore prevailing synoptic wind (26 June 2001) are compared. The impact of the Rhône and Durance valleys on the sea-breeze dynamics on these two typical days is generalized to the whole ESCOMPTE observing period.The present study shows by combining simple scaling analysis with wind data from meteorological surface stations and Doppler lidars that (i) the Durance valley always affects the sea breeze by accelerating the flow. A consequence is that the Durance valley contributes to weaken the temperature gradient along the valley and thus the sea-breeze circulation. In some cases, the acceleration of the channelled flow in the Durance valley suppresses the sea-breeze flow by temperature gradient inhibition; (ii) the Rhône valley does not generally affect the sea breeze significantly. However, if the sea breeze is combined with an onshore flow, it leads to further penetration inland and intensification of the low-level southerly flow. In this situation, lateral constriction may accelerate the sea breeze. Simple scaling analysis suggests that Saint Paul (44.35°N, about 100 km from the coastline) is the lower limit where sea breeze can be affected by the Rhône valley. These conclusions have implications in air quality topics as channelled sea breeze may advect far inland pollutants which may be incorporated into long-range transport, particularly in the Durance valley.  相似文献   

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