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1.
S.J. Prinsenberg 《大气与海洋》2013,51(4):418-430
Abstract A one‐dimensional oceanic mixed‐layer model was used to simulate the annual surface layer properties of Hudson Bay. The model reproduces the sparse available data well and shows the equal importance of seasonal ice cover and run‐off on the pycnocline pattern. In spring, the large freshwater input from run‐off and local ice melt followed by summer heating slows the deepening of the pycnocline depth by wind mixing. As these stabilizing effects decrease and the wind strength increases, the pycnocline depth increases in the fall and continues to increase in the winter when the salt rejection effect during ice growth replaces the cooling effect. In the spring the salt rejection reduces and run‐off increases; the large pycnocline depth cannot be maintained and a shallow pycnocline is formed, starting a new seasonal cycle. When the run‐off cycle includes the effects of hydroelectric developments, the results indicate that a new shallow surface pycnocline is formed earlier in the spring. This causes a decrease in surface layer temperature and salinity, thus stimulating more ice growth. On the other hand, in the summer the surface layer salinity is higher and the temperature lower. This decreases the stability, thus further deepening the pycnocline and increasing the deviations from normal conditions. 相似文献
2.
The aquatic eco-environment is significantly affected by temporal and spatial variation of the mixed layer depth(MLD) in large shallow lakes.In the present study,we simulated the three-dimensional water temperature of Taihu Lake with an unstructured grid with a finite-volume coastal ocean model(FVCOM) using wind speed,wind direction,short-wave radiation and other meteorological data measured during 13-18 August 2008.The simulated results were consistent with the measurements.The temporal and spatial distribution of the MLD and the possible relevant mechanisms were analyzed on the basis of the water temperature profile data of Taihu Lake.The results indicated that diurnal stratification might be established through the combined effect of the hydrodynamic conditions induced by wind and the heat exchange between air and water.Compared with the net heat flux,the changes of the MLD were delayed approximately two hours.Furthermore,there were significant spatial differences of the MLD in Taihu Lake due to the combined impact of thermal and hydrodynamic forces.Briefly,diurnal stratification formed relatively easily in Gonghu Bay,Zhushan Bay,Xukou Bay and East Taihu Bay,and the surface mixed layer was thin.The center of the lake region had the deepest surface mixed layer due to the strong mixing process.In addition,Meiliang Bay showed a medium depth of the surface mixed layer.Our analysis indicated that the spatial difference in the hydrodynamic action was probably the major cause for the spatial variation of the MLD in Taihu Lake. 相似文献
3.
Study on Physical Mechanism of Influence on Atmospheric Boundary Layer Depth in the Arid Regions of Northwest China 总被引：1，自引：0，他引：1 
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下载免费PDF全文 Using the sounding data of wind, temperature, and humidity in the boundary layer and micrometeorological data on the earth's surface observed in the same period in Dunhuang arid region of Northwest China,this paper researches characteristics of potential temperature, wind, and humidity profiles, confirms the structure and depth of thermodynamic boundary layer in Dunhuang region, and analyzses the relationship of depth of thermodynamic boundary layer with surface radiation, buoyancy flux as well as wind speed and
wind direction shear in the boundary layer. The results show that the maximum depth of diurnal convective boundary layer is basically above 2000 m during the observational period, many times even in excess of 3000 m and sometimes up to 4000 m; the depth of nocturnal stable boundary layer basically maintains within a range of 1000-1500 m. As a whole, the depth of atmospheric boundary layer is obviously bigger than those results observed in other regions before. By analyzing, a preliminary judgement is that the depth
of atmospheric thermodynamic boundary layer in Dunhuang region may relate to local especial radiation characteristics, surface properties (soil moisture content and heat capacity) as well as wind velocity shear of boundary layer, and these properties have formed strong buoyancy flux and dynamic forcing in a local region which are fundamental causes for producing a super deep atmospheric boundary layer. 相似文献
4.
This study deals with the variability of mixing height during daylight hours in the summer months for weak wind regimes. A two-dimensional model was employed using simulated input variables which are quite representative of conditions found over the midwestern United States in late summer and early fall. With the aid of this model and various analytical techniques, the dependence of the urban mixing height on such factors as horizontal advection, downward heat flux across the stable mixing-layer interface, lapse rate in the stable layer, etc., was delineated and compared with actual mixing height variations observed in St. Louis, Missouri during selected days for August, 1972.The experiment indicated the following: (1) A spatially symmetric surface heating profile over a city is accompanied by a similarly symmetric mixing-height profile in the absence of vertical wind shear; (2) When the same heating assumption is invoked and vertically variable wind profiles are introduced, the model-generated mixing-height contours become increasingly asymmetric with vertical wind shear; (3) The modelled mixing heights are more sensitive to temperature fluctuations than to those of wind over the range of speeds studied (wind speeds 4ms–1); (4) Present operational methods of predicting the time of erosion of an inversion (based upon forecast surface temperature ranges and adiabatic diagram considerations) underestimate breakup time by a factor which is proportional to the amount of available downward heat flux from the stable layer into the mixed layer below. 相似文献
5.
使用WRF中尺度数值模式, 分别选用两种不同的边界层参数化方案 (MYJ, YSU) 和3种陆面参数化方案 (SLAB, Noah, RUC), 对2004年7月1日08:00—7月4日20:00 (北京时) 北京地区夏季边界层结构进行1 km的高分辨模拟。对比分析了近地面层风场、温度场以及边界层的日变化特征, 结果发现:WRF模式基本模拟出了北京夏季边界层的日变化特征; 在边界层方案中, MYJ方案描述的边界层结构较YSU方案合理; Noah陆面模式较好地反映了城市的热岛效应; 无降水时, 风速及边界层高度对于陆面过程不敏感, 而降水发生后, 陆面过程对于边界层结构的影响增大; 各方案模拟的城区风速明显偏大, 这是因为没有充分考虑城市建筑物的阻力作用。 相似文献
6.
The authors investigate the relationship between bias in simulated sea surface temperature (SST) in the equatorial eastern Pacific cold tongue during the boreal spring as simulated by an oceanic general circulation model (OGCM) and minimal wind mixing (MWM) at the surface. The cold bias of simulated SST is greatest during the boreal spring, at approximately 3°C. A sensitivity experiment reducing MWM by one order of magnitude greatly alleviates cold biases, especially in March-April. The decrease in bias is primarily due to weakened vertical mixing, which preserves heat in the uppermost layer and results in warmer simulated SST. The reduction in vertical mixing also leads to a weak westward current in the upper layer, which further contributes to warmer SST estimates. These findings imply that there are large uncertainties about simple model parameters such as MWM at the oceanic surface. 相似文献
7.
Consideration of the dependence of various components of the sea-surface heat and momentum fluxes on sea surface temperature
(SST) leads to an explanation for the observed reduction in the horizontal temperature gradients in the uppermost layer of
the ocean (a few to 10 m in depth). Horizontal temperature gradients within the mixed layer can be masked by a near-surface
layer of warm water. This camouflage of horizontal temperature gradients has importance for the remote sensing of SST used
by the fishing industry, for the estimation of acoustic transmission, and for the forecasting of hurricane development, among
many uses of SST data. Diurnal warming conditions in the Straits of Florida are examined by a simulation calculation and by
analysis of observations obtained on moorings deployed on the south-east Florida shelf. When there is net heating (i.e., the
solar input is stronger than the combined latent, sensible and longwave radiative heat losses) the originally warmer water
experiences less heating than the colder water, leading to a weakening of the horizontal SST gradients as seen by surface
buoys or satellites. The warmer water also experiences more mixing and therefore less increase in temperature. The strongest
effect of the diurnal heating on wind stress occurs when the SST starts out cooler than the air temperature and the atmosphere
is stably stratified. Diurnal warming can then rapidly increase the SST above the air temperature because of reduced wind
stress and reduced upper-ocean mixing. After that the wind stress increases as convectively driven turbulence contributes
to the atmospheric exchange. 相似文献
8.
Estimates from semiempirical models that characterize surface heat flux, mixing depth, and profiles of temperature, wind, and turbulence are compared with observations from atmospheric field studies conducted in Colorado, Illinois, Indiana, and Minnesota. Sodar observations are compared with tower measurements at the Colorado site, for wind and turbulence profiles. The median surface heat flux, as calculated using surface-layer flux-profile relationships and an energy budget model, was consistently overestimated by 20 to 80%. Several mixing-depth models were evaluated: (1) integration of the hourly surface heat flux and friction velocity, (2) solving for the time rate of change of profiles of virtual potential temperature, and (3) an interpolation scheme used by the U.S. Environmental Protection Agency in regulatory dispersion models. For the late afternoon, 80 to 90% of the estimates from the first and third models were within 40% of the observed values. For the morning hours after sunrise, all were less accurate. Temperature estimates from surface-layer flux-profile relationships compared well with observations within the mixed layer, but were too low for the inversion layer aloft. Wind profiles were derived using surface-layer flux-profile relationships, a windprofile power-law based on Pasquill stability category, and sodar measurements. The sodar measurements were superior to both types of model estimates. Turbulence profiles were derived from sodar measurements and from semiempirical similarity relationships based on mixing depth and Obukhov length. The scatter in the comparisons with the sodar observations is twice that seen in the comparisons with empirical profile relationships. Overall, it appears that uncertainty of as low as 20 to 30% in the characterization of the diffusion meteorology is the exception rather than the rule.On assignment from the National Oceanic and Atmospheric Administration, U. S. Department of Commerce.Disclaimer: Although the research described in this article has been supported by the United States Environmental Protection Agency, it has not been subjected to Agency review and therefore does not necessarily reflect the views of the Agency and no official endorsement should be inferred. Mention of trade names or commercial products does not constitute endorsement or recommendation for use. 相似文献
9.
In this study a coupled air–sea–wave model system, containing the model components of GRAPES-TCM, ECOM-si and WAVEWATCH III, is established based on an air–sea coupled model. The changes of wave state and the effects of sea spray are both considered. Using the complex air–sea–wave model, a set of idealized simulations was applied to investigate the effects of air–sea–wave interaction in the upper ocean. Results show that air–wave coupling can strengthen tropical cyclones while air–sea coupling can weaken them; and air–sea–wave coupling is comparable to that of air–sea coupling, as the intensity is almost unchanged with the wave model coupled to the air–sea coupled model. The mixing by vertical advection is strengthened if the wave effect is considered, and causes much more obvious sea surface temperature (SST) decreases in the upper ocean in the air–sea coupled model. Air–wave coupling strengthens the air–sea heat exchange, while the thermodynamic coupling between the atmosphere and ocean weakens the air–sea heat exchange: the air–sea–wave coupling is the result of their balance. The wave field distribution characteristic is determined by the wind field. Experiments are also conducted to simulate ocean responses to different mixed layer depths. With increasing depth of the initial mixed layer, the decrease of SST weakens, but the temperature decrease of deeper layers is enhanced and the loss of heat in the upper ocean is increased. The significant wave height is larger when the initial mixed layer depth increases. 相似文献
10.
利用WRF-Chem模式,采用3种边界层参数化方案 (YSU, MYJ和ACM2),针对1个晴空、静稳日 (2013年8月26日20:00—27日20:00(北京时)) 进行模拟,着重分析不同边界层参数化方案对夜间残留层形成及日出前后O3浓度垂直分布形式的模拟效果,并与固城站地面及垂直同步观测资料进行对比。结果表明:3种边界层参数化方案均能够模拟出温度及风速的区域分布形式以及风温垂直结构的变化特征;相比之下,MYJ方案模拟的夜间边界层高度较YSU方案和ACM2方案明显偏高,该对比结果可能是导致近地面污染物浓度模拟差异的重要原因;在夜间稳定层结至日出后稳定状态打破的边界层结构演变过程中,采用YSU方案和ACM2方案模拟的温度和风速垂直扩线形式与观测结果更为接近;同样采用非局地闭合的YSU方案和同时考虑局地和非局地闭合的ACM2方案,对于边界层高度内O3浓度垂直分布形式的模拟效果具有明显优势。 相似文献
11.
L. Mahrt 《Boundary-Layer Meteorology》1981,21(1):3-19
A simple prognostic model of the depth of the stable boundary layer is developed which includes both the possibilities of growth due to entrainment and decreasing depth associated with turbulence decay. The model is designed to avoid requirement of surface fluxes and instead uses information on profiles of mean wind and temperature. Resulting coefficients for the model are estimated by comparisons with existing studies in the literature and comparison with Wangara data.On leave from the Dept of Atmospheric Sciences, Oregon State University, Corvallis, Oregon 97331, U.S.A. 相似文献
12.
13.
R. A. Treidl 《Boundary-Layer Meteorology》1970,1(2):155-168
When relatively warm, moist air moves over a snow surface, sensible heat and moisture are extracted from its lower layers and used to melt the snow. The depth of the cooled layer depends on horizontal wind speeds and the presence of high vertical wind shear. The mechanism for air mass modification appears to be turbulent mixing. 相似文献
14.
V. P. Yushkov 《Russian Meteorology and Hydrology》2013,38(12):818-827
The wind speed shear in the case of stable stratification in the linear part of the profile spreading high above the surface layer of constant flows is studied using the data of long-term sodar measurements in the atmospheric boundary layer. The wind speed shear in this part remains almost invariable during several hours at the significant change in parameters of the Monin-Obukhov theory. The length of this linear part can be associated with the layer of the critical Richardson number. In the case of the pronounced temperature inversion (with the positive gradient of more than 1°C per 100 m), the wind speed profile is close to the linear function in the most part of the nocturnal mixing layer. Proposed is a scale characterizing the height of the surface layer of constant flows. 相似文献
15.
This study conducted meteorological simulations in northern Colombia by analyzing different planetary boundary layer (PBL) schemes available in the numerical Weather Research and Forecasting (WRF) model. The study area included three nested domains with horizontal resolutions of 18 km, 6 km, and 2 km, with 38 vertical levels. The evolution and structure of the PBL were analyzed during the driest months (March, April, and May 2016) and in regions with the highest particulate matter concentrations. Sensitivity analysis of the WRF model was performed with two local and two non-local PBL schemes. The results were validated using observations of the surface air temperature, relative humidity, and surface wind speed collected from three meteorological stations in the area. The PBL heights were experimentally determined using radiosonde data provided by a station located in the center of the study area. Variations in PBL heights were estimated using linear regression methods and minimization of statistical errors for the bulk Richardson number, as well as analysis of vertical temperature and wind profiles. The WRF model reliably reproduced the daily values and diurnal cycles of temperature, relative humidity, and wind speed within the PBL and accounted for the influence of topography and sea breezes. Horizontal heat advection dominates the upwelling of air masses when sea breezes are active. The onshore wind direction starts to change from east to northwest, implying a decay in the land breeze regime. All schemes overestimate the mixing height and tend to underestimate surface air temperature values at night. All show wetter conditions and underestimate wind speed. Although the non-local Yonsei University (YSU) scheme shows the best performance, it also shows the largest sources of errors when determining the behavior of the surface layer during stable conditions. Relative humidity and wind speed estimates provided by the local Mellor‐Yamada‐Nakanishi‐Niino (MYNN) scheme were closer to those recorded at the meteorological stations. 相似文献
16.
Rory O. R. Y. Thompson 《Boundary-Layer Meteorology》1974,6(3-4):515-518
A Simple slab model of the planetary boundary layer is extended to include vertical shear of the geostrophic wind. The layer depth is assumed to be determined by a Richardson number criterion. The cross-isobar angle for the surface wind is given in terms of the drag coefficient, the Froude number of the layer, and the angle between the thermal wind and the surface isobars. The theoretical results resemble the observations rather well. 相似文献
17.
Analysis of three-dimensional wind profiles recorded by an acoustic sounder near Cape Town has indicated that extreme subsidence (-35 cm s-1) is a mean feature throughout the atmospheric boundary layer (50–1000m) during summertime southerly winds. Over the SW Cape coast, the atmospheric subsidence translates into a N-S gradient of the mean summer water deficit (-20 to -32 cm month-1). The rapid drying out of the air mass along a northward trajectory is linked to a number of factors including synoptic-scale divergence of the surface wind and the effects of the local orography which produce a hydraulic jump of the southerly wind. The along-coast reduction in sea surface temperature provides a major constraint on the height of the moist marine layer. As the depth of the marine air mass shrinks, its potential for inland penetration becomes limited. In addition, dry air is entrained towards the surface as evidenced by aerial survey data. A model is formulated which indicates the importance of the surface heat fluxes in reducing the depth of the Agulhas air mass as it passes northward over the SW tip of Africa during summer. 相似文献
18.
We propose a dynamical interpretation of the inverse relationship between the tropical eastern Pacific annual-cycle (AC) amplitude and the El Niño-Southern Oscillation (ENSO) amplitude, based on a pre-industrial simulation of Geophysical Fluid Dynamics Laboratory Couple climate model 2.0 with a fixed concentration of greenhouse gases spanning approximately 500 years. The slowly varying background conditions over more than a decade alternately provided favorable conditions for two opposite regimes, namely the ‘strong AC—weak ENSO regime’ and the ‘weak AC—strong ENSO regime’. For the weak AC—strong ENSO regime, the tropical eastern Pacific shows meridional-asymmetric surface warming with an emphasis on the southern part, leading to weakening of both the zonal trade wind and the cross equatorial southerly wind, as well as deepening of both the thermocline and mixed layer. The deeper mixed layer, weaker southerly wind, and reduced zonal gradient of the mean sea surface temperature due to tropical eastern Pacific warming all acts to reduce the AC. Conversely, the ENSO was intensified by the deeper mixed layer and deeper thermocline depth (thermocline feedback), but suppressed by the deeper thermocline depth (Ekman feedback) and the reduced zonal temperature gradient. We also computed the coupling strengths of the ENSO and AC, defined as the linear regression coefficients of the zonal and meridional wind stresses against the eastern Pacific SST, respectively. The coupling strengths of both the AC and ENSO are larger when they are intensified, and vice versa. All processes for the weak AC—strong ENSO regime operate in the opposite manner for the strong AC—weak ENSO regime. 相似文献
19.
1.IntroductionItiswellknownthattheecosystemcangreatlyinfluencebothlocalclimateandgeneralcirculation.Onthenumericalstudyoftheturbulenceinandaboveforestcanopies,alotofsignificantstudieshavebeendone.Inallthesestudies,modelsaregenerallydividedintotwotypes:oneis'K--theory'type(Waggoner,1975;Gross,1987;Gross,1988,Jietal.,1989;Schilling,I991;Dickinsonetal.,1993;Wang,1996),theotherappliesthehigher--orderclosuremethod(Wilsonetal.,1977,Yamada,1982;Yinetal.,1989)ortheLagrangianmethod(Rampach,1987;R… 相似文献
20.
Air pollution sources such as oil platforms and ships are sometimes located near coastlines where the plumes can impact population centers. Models of overwater dispersion must account for the stability of the overwater boundary layer. An overwater dispersion model based on the standard Gaussian formula is described which uses measurements of the air-sea temperature difference, the wind speed, and the mixing depth to predict concentration patterns at the coastline. Internal boundary layers and complex terrain at the coastline are accounted for. This new model is evaluated using the results of three tracer experiments in United States coastal zones. 相似文献