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1.
Radiative Processes in the Stable Boundary Layer: Part II. The Development of the Nocturnal Boundary Layer 总被引：2，自引：2，他引：0
J. M. Edwards 《Boundary-Layer Meteorology》2009,131(2):127-146
The interaction between radiation and turbulence in the stable boundary layer over land is explored using an idealized model,
with a focus on the surface layer after the evening transition. It is shown that finer vertical resolution is required in
transitional boundary layers than in developed ones. In very light winds radiative cooling determines the temperature profile,
even if similarity functions without a critical Richardson number are used; standard surface similarity theory applied over
thick layers then yields poor forecasts of near-surface air temperatures. These points are illustrated with field data. Simulations
of the developing nocturnal boundary layer are used to explore the wider role of radiation. Comparatively, radiation is less
significant within the developed stable boundary layer than during the transition; although, as previous studies have found,
it remains important towards the top of the stable layer and in the residual layer. Near the ground, reducing the surface
emissivity below one is found to yield modest relative radiative warming rather than intense cooling, which reduces the potential
importance of radiation in the developed surface layer. The profile of the radiative heating rate may be strongly dependent
on other processes, leading to quite varied behaviour. 相似文献
2.
Radiative destabilization of the nocturnal stable atmospheric boundary layer (NSABL) over homogeneous desert terrain is predicted by an analytical model based on a modified diffusion equation. The model applies late at night under calm, dry conditions when long-wave radiative transfer dominates the NSABL evolution. A three-layer structure for the NSABL is proposed: a shear sub-layer closest to the surface, a radiative sub-layer which contains the inversion top, and a coupling sub-layer which matches the NSABL with the residual layer aloft. A sub-sub-layer called the nocturnal internal boundary layer (NIBL) is nested within the radiative sub-layer and comprises the temperature maximum. The model can explain: (1) maximum cooling in the NIBL, (2) deepening of the NIBL, (3) radiative destabilization of the NSABL, and (4) possible surface warming before sunrise. An example from the Mohave Desert, USA is presented, and the observed temperature profile compares favorably with the model solution. 相似文献
3.
A one-dimensional model for the mean potential temperature within the nocturnal boundary layer (NBL) was used to assess the
sensitivity of three NBL properties (height, thermal stratification strength, and near-surface cooling) to three widely used
atmospheric emissivity formulations. The calculations revealed that the NBL height is robust to the choice of the emissivity
function, though this is not the case for NBL Richardson number and near-surface cooling rate. Rather than endorse one formulation,
our analysis highlights the importance of atmospheric emissivity in modelling the radiative properties of the NBL especially
for clear-sky conditions. 相似文献
4.
On calm clear nights, air at a height of a few decimetres above bare soil can be cooler than the surface by several degrees in what we shall call the Ramdas layer (Ramdas and Atmanathan, 1932). The authors have recently offered a logical explanation for such a lifted temperature minimum, together with a detailed numerical model. In this paper, we provide physical insight into the phenomenon by a detailed discussion of the energy budget in four typical cases, including one with a lifted minimum. It is shown that the net cooling rate near ground is the small difference between two dominant terms, representing respectively radiative upflux from the ground and from the air layers just above ground. The delicate energy balance that leads to the lifted minimum is upset by turbulent transport, by surface emissivity approaching unity, or by high ground cooling rates. The rapid variation of the flux emissivity of humid air is shown to dominate radiative transport near the ground. 相似文献
5.
Margreet C. Vanzanten 《Boundary-Layer Meteorology》2002,102(2):253-280
A mixing fraction determines the relative amount of above-cloud-top air that has been mixed into a cloudy air parcel. A method, based on the use of mixing fractions, to calculate the cooling effects due to mixing, longwave radiation and phase changes at cloud top is derived and discussed. We compute cooling effects for the whole range of mixing fraction for two observed cases of the stratocumulus-topped marine boundary layer. In both cases the total radiative cooling effect is found to be the most dominant contributor to the negative buoyancy excess found at cloud top. The largest radiative cooling rates are found for clear-air parcels immediately adjacent to cloud top rather than inside the cloud. With the help of a simple longwave radiation model, we show this to be caused by clear-air radiative cooling due to the temperature inversion at cloud top. Further we show that flux profiles in the entrainment zone can be computed from data obtained from a horizontal level run that is half the time in cloud and half the time out of cloud. 相似文献
6.
Yves Delage 《Boundary-Layer Meteorology》1988,43(4):365-381
Two formulations of the stable atmospheric boundary layer are proposed for use in weather forecasting or climate models. They feature the log-linear profile near the surface, but are free from the associated critical Richardson number. The diffusion coefficients in the Ekman layer are a natural extension of the surface layer. They are locally determined using wind shear in one case and turbulent kinetic energy in the other. The parameterizations are tested in a one-dimensional model simulating the evolution of the nocturnal boundary layer with and without radiative cooling. Both formulations give very similar results, except near the top of the boundary layer where the transition to the free atmosphere is smoother with the wind shear formulation. A distinctive feature of these schemes is that they retain their simulating skill when resolution is reduced. This is verified for a wide range of situations. In practice, this means that there is no need for a large-scale model to have a level below 50 m or so. 相似文献
7.
J. M. Edwards S. Basu F. C. Bosveld A. A. M. Holtslag 《Boundary-Layer Meteorology》2014,152(2):189-211
Large-eddy simulation in the GABLS3 intercomparison is concerned with the developed stable boundary layer (SBL) and the ensuing morning transition. The impact of radiative transfer on simulations of this case is assessed. By the time of the reversal of the surface buoyancy flux, a modest reduction of the lapse rate in the developed SBL is apparent in simulations that include longwave radiation. Subsequently, with radiation, the developing mixed layer grows significantly more quickly, so that four hours after the transition the mixed layer is roughly 40 % deeper; the resulting profiles of potential temperature and specific humidity are in better agreement with observations. The inclusion of radiation does not substantively alter the shape of turbulent spectra, but it does indirectly reduce the variance of temperature fluctuations in the mixed layer. The deepening of the mixed layer is interpreted as a response to the reduction of the strength of the capping inversion, resulting from cumulative radiative cooling in the residual layer and around the top of the former SBL. Sensitivity studies are performed to separate the two effects. Solar radiative heating of the atmosphere has a smaller impact on the development of the mixed layer than does longwave radiative cooling and slightly reduces its rate of growth, compared to simulations including longwave radiation alone. These simulations demonstrate that nocturnal radiative processes have an important effect on the morning transition and that they should be considered in future large-eddy simulations of the transition. 相似文献
8.
The structure of nocturnal inversions in the first 300 m of the atmosphere is analyzed using observational data from the Boulder Atmospheric Observatory (BAO) from March through June 1981. The temperature profiles show more than one inversion layer 41% of the time during the observational period. The vertical distributions of wind speed and moisture also show evidence of stratification during these multiple-layer events. The relation between the radiative cooling rate in time and height, including moisture, and the vertical structure of the multiple layers is calculated. The vertical distribution of eddy kinetic energy and the turbulent vertical fluxes of heat and momentum are also calculated. Turbulent structure in the elevated inversion layers is more complicated than that in the single-layer, stable nocturnal boundary layer. The total heat budget for a multiple-layer case is calculated, and turbulent cooling is found to be negligible relative to radiative cooling and to horizontal advection and/or horizontal divergence of heat flux. 相似文献
9.
Radiative Effects on Temperature in the Stable Surface Layer 总被引：2，自引：1，他引：1
Nelson Dias 《Boundary-Layer Meteorology》1998,89(1):141-159
The interaction between longwave radiation and temperature fluctuations plays a role in the dissipation of temperature variance. This interaction is most easily described by spectral models of atmospheric turbulence and a spectral radiative dissipation function which gives the intensity of the damping at each radiative wavelength and wavenumber k. We have used a Corrsin–Pao closure for the spectral budgets of turbulent kinetic energy and temperature to study the coupling of radiation to turbulence. The spectral radiative dissipation function and a related integral have been fitted by analytical approximations with the correct asymptotic behavior. This resulted in a simple analytical formula for the dimensionless temperature spectrum as a function of Monin-Obukhov stability, and a new dimensionless parameter describing the relative importance of radiation in the temperature spectral budget. The radiative effects both on the temperature spectrum and on the dimensionless temperature variance can then be calculated. Based on typical values of the radiative dimensionless parameters for the surface layer, we conclude that radiative dissipation is probably negligible there. 相似文献
10.
基于激光雷达资料的气溶胶辐射效应研究 总被引：2，自引：0，他引：2
利用新型激光雷达气溶胶探测资料及综合数值模式,以地形复杂的兰州市及周边地区冬季典型天气形势下的大气边界层为研究对象,通过理想试验模拟研究了城市气溶胶辐射效应与大气边界层的相互作用。结果表明:夜间,低空(50~600 m)气溶胶所在气层冷却效应明显,温度降低0.13~0.18℃,600 m高度以上,气溶胶浓度较低,其冷却效应较小,温度降低不足0.1℃;白天,受气溶胶短波辐射效应影响,边界层内增温明显,增温最大值位于低层脱地逆温层顶300 m高度附近,600 m以上由于气溶胶浓度减小,加热率亦降低,增温由0.2℃减至0.1℃。此外,气溶胶的存在使得所在层的风速降低。可见,激光雷达探测资料在边界层模式中有很好的应用价值,对于研究气溶胶辐射效应的大气边界层响应有重要意义。 相似文献
11.
我国西北大气沙尘气溶胶的辐射效应 总被引：21，自引：3，他引：18
利用HEIFE地面辐射平衡观测资料和同期NOAA-11/AVHRR卫星遥感资料定量估算春季我国西北大气沙尘的辐射效应。大气沙尘减小地面净辐射冷却地面,对地-气系统和大气的辐射效应均与地表反照率有关,严重浑浊的沙尘大气在沙漠为短波加热和长波冷却,在绿洲则相反,但净效应都是加热。文中给出了4月大气浑浊度系数约由0.1增大到0.6,在沙漠和绿洲上空沙尘层（850～600 hPa）内大气的附加短波、长波和净加热/冷却率。 相似文献
12.
复杂地形城市冬季边界层对气溶胶辐射效应的响应 总被引：9，自引：3，他引：6
作者着眼于城市气溶胶辐射效应与大气边界层的相互作用问题,针对地形复杂的兰州市及周边地区,开发应用了WRF(Weather Research and Forecasting,天气研究和预报)模式,使之与包含了大气气溶胶辐射效应和气溶胶粒子扩散的综合大气边界层数值模式嵌套起来.通过个例分析,揭示了冬季气溶胶辐射效应对边界层结构的定量影响.主要特征为夜间气溶胶的长波辐射效应使地面附近的气温增高,增温幅度为0.1～0.3 K/h,使低空(25～300 m)大气层冷却,降温幅度为0.08～0.15 K/h,风速在150 m以下减小;白天气溶胶的短波辐射效应使地面层内明显增温,1 h内升温约0.5 K,增温最大值在混合层顶500～600 m高度.受增温影响,垂直风场和水平风场随之调整,风速在450 m以下增大约0.1 m/s左右,而在450 m以上风速减小0.1 m/s左右. 相似文献
13.
A case study was performed in Beijing in 2000 to observe concentrations of SO2 and NOx in the atmosphere and to evaluate their radiative impact. It was found that the concentrations of these gases are usually high in the morning due to a temperature inversion in the boundary layer. The average concentrations obtained from the observations are much higher than those used in the McClatchey reference atmosphere. The radiative impacts of these gases are calculated using a line-by-line radiative transfer model. The results show that the radiative forcing at the surface due to SO2 is 0.0576 W m-2 and that due to NOx is 0.0032 W m-2. These figures are almost compatible with that due to CFC11. 相似文献
14.
The Grid-point Atmospheric Model of IAP LASG version 1.0 (GAMIL1.0) is used to investigate the impacts of different convective schemes on the radiative energy budget.The two convective schemes are Zhang and McFarlance (1995)/Hack (1994) (ZM) and Tiedtke (1989)/Nordeng (1994) (TN).Two simulations are performed:one with the ZM scheme (EX_ZM) and the other with the TN scheme (EX_TN).The results indicate that during the convective process,more water vapor consumption and temperature increment are found in the EX_ZM,especially in the lower model layer,its environment is therefore very dry.In contrast,there is a moister atmosphere in the EX_TN,which favors low cloud formation and large-scale condensation,and hence more low cloud fraction,higher cloud water mixing ratio,and deeper cloud extinction optical depth are simulated,reflecting more solar radiative flux in the EX_TN.This explains why the TN scheme underestimates the net shortwave radiative flux at the top of the atmosphere and at surface.In addition,convection influences longwave radiation,surface sensible and latent heat fluxes through changes in cloud emissivity and precipitation. 相似文献
15.
Eun-Hee Lee Eunjung Lee Raeseol Park Young Cheol Kwon Song-You Hong 《Asia-Pacific Journal of Atmospheric Sciences》2018,54(1):371-384
The impact of enhanced turbulent mixing induced by radiative cooling at the top of the stratocumulus-topped boundary layer (STBL) on numerical weather prediction is examined. An additional term involving top-down turbulent mixing via in-cloud radiative cooling is applied to the Yonsei University (YSU) planetary boundary layer (PBL) parameterization scheme using a top-down diffusivity profile and cloud-top entrainment. The modified scheme is evaluated in an advection fog case over the Yellow Sea of Korea using the Weather Research and Forecasting (WRF) model and in global medium-range forecasts using the Global/Regional Integrated Model system (GRIMs). In the fog case simulation, consideration of the additional top-down mixing parameterization in the YSU PBL simulates less formation and more rapid dispersion of the fog. As a result, the modified scheme simulates a drier and warmer boundary layer and a moister and cooler layer above the PBL. The modified algorithm also improves surface temperature prediction over the Yellow Sea accompanying early dissipation of the fog. In the global medium-range forecast experiment, the modified scheme simulates overall enhanced PBL mixing over the STBL in the tropics and subtropical ocean, showing drier and warmer regions near the surface and moister and cooler regions above the PBL, resulting in prediction of reduced low level cloud amount and increased downward shortwave radiation at the surface. The modified scheme appears to improve systematic bias in temperature and humidity in the lower troposphere compared to the control simulation. 相似文献
16.
Turbulence, Radiation and fog in Dutch Stable Boundary Layers 总被引：5，自引：1，他引：4
Peter G. Duynkerke 《Boundary-Layer Meteorology》1999,90(3):447-477
The effect of longwave radiation on the structure the clear stable boundary layer (SBL) is examined. Special emphasis is given to radiative cooling near the surface and the top of the boundary layer and its impact on the heat flux profile. Further, the formation, growth and dissipation of fog in the SBL are studied both from observations and from a one-dimensional ensemble averaged turbulence closure model. The model is compared with detailed observations that were made for both a shallow (about 30 m) radiation fog and a deep (about 200 m) fog layer at the 200-m tower at Cabauw in the Netherlands. The model describes adequately the most important mechanisms occurring during the fog evolution. In this study special attention is given to the parameterization of the vegetation, which is important for a good representation of the (minimum) air temperature. The influence of turbulence transport, longwave radiative cooling and gravitational droplet settling on the fog evolution is described. The study demonstrates the need for more accurate measurements of turbulence quantities, especially the master length scale, in a variety of SBLs. 相似文献
17.
To investigate the processes of development and maintenance of low-level clouds during major synoptic events, the cloudy boundary
layer under stormy conditions during the summertime Arctic has been studied using observations from the Surface Heat Budget
of the Arctic Ocean (SHEBA) experiment and large-eddy simulations (LES). On 29 July 1998, a stable Arctic cloudy boundary-layer
event was observed after the passage of a synoptic low pressure system. The local dynamic and thermodynamic structure of the
boundary layer was determined from aircraft measurements including the analysis of turbulence, cloud microphysics and radiative
properties. After the upper cloud layer advected over the existing cloud layer, the turbulent kinetic energy (TKE) budget
indicated that the cloud layer below 200 m was maintained predominantly by shear production. Observations of longwave radiation
showed that cloud-top cooling at the lower cloud top has been suppressed by radiative effects of the upper cloud layer. Our
LES results demonstrate the importance of the combination of shear mixing near the surface and radiative cooling at the cloud
top in the storm-driven cloudy boundary layer. Once the low-level cloud reaches a certain height, depending on the amount
of cloud-top cooling, the two sources of TKE production begin to separate in space under continuous stormy conditions, suggesting
one possible mechanism for the cloud layering. The sensitivity tests suggest that the storm-driven cloudy boundary layer is
possibly switched to the shear-driven system due to the advection of upper clouds or to the buoyantly driven system due to
the lack of wind shear. A comparison is made of this storm-driven boundary layer with the buoyantly driven boundary layer
previously described in the literature. 相似文献
18.
Observations obtained mainly from a research aircraft are presented of the mean and turbulent structure of the stably stratified internal boundary layer (IBL) over the sea formed by warm air advection from land to sea. The potential temperature and humidity fields reveal the vertical extent of the IBL, for fetches out to several hundred of kilometres, geostrophic winds of 20–25 m s–1, and potential temperature differences between undisturbed continental air and the sea surface of 7 to 17 K. The dependence of IBL depth on these external parameters is discussed in the context of the numerical results of Garratt (1987), and some discrepancies are noted.Wind observations show the development of a low-level wind maximum (wind component normal to the coast) and rotation of the wind to smaller cross-isobar flow angles. Potential temperature () profiles within the IBL reveal quite a different structure to that found in the nocturnal boundary layer (NBL) over land. Over the sea, profiles have large positive curvature with vertical gradients increasing monotonically with height; this reflects the dominance of turbulent cooling within the layer. The behaviour is consistent with known behaviour in the NBL over land where curvature becomes negative (vertical gradients of decreasing with height) as radiative cooling becomes dominant.Turbulent properties are discussed in terms of non-dimensional quantities, normalised by the surface friction velocity, as functions of normalised height using the IBL depth. Vertical profiles of these and the normalised wavelength of the spectral maximum agree well with known results for the stable boundary layer over land (Caughey et al., 1979). 相似文献
19.
W. H. Moores 《Boundary-Layer Meteorology》1982,22(3):283-294
Results derived from simultaneous measurements of turbulent heat flux and radiation convergence in the daytime convective boundary layer are presented. It is found that the effects of long-wave radiation result in a warming near the surface and cooling at higher levels, in good agreement with infra-red radiative transfer models. Heating rates, roughly 30% of those produced by turbulence, are observed as a result of the absorption of short-wave radiation in the lowest 1000 m of the atmosphere. 相似文献
20.
Freezing of rainwater on a surface is often caused by nocturnal clearing after precipitation, which goes along with radiative cooling. Forecasting cloudiness, and especially the risk of clearing, on a scale of 1 to 3 h is of interest in the domains of road weather, agriculture, or water management.Cloud amount and the difference between air and surface temperature are important parameters of the radiation balance. In this contribution, we show the relationship between them, proved at several stations all over Switzerland. We found a correlation coefficient of 0.88 and improved it considering other meteorological parameters like wind speed. We conclude that temperature difference is a signature for nocturnal cloudiness.We investigated nocturnal cloudiness for a case from winter 2001/02 in northern Switzerland. An ultra-dense combination of two networks with 70 stations in total is operated, measuring air and surface temperature, wind and other parameters. With the aid of our equations, these measurements where converted into cloud maps, including also precipitation seen by radar. We identified a frontal precipitation area, postfrontal clearing, freezing, and the first clouds of a following frontal passage.All these findings will contribute to a better observation and predictability of surface state and other risks connected with radiative cooling. 相似文献