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1.
We discuss scalar similarities and dissimilarities based on analysis of the dissipation terms in the variance budget equations, considering the turbulent kinetic energy and the variances of temperature, specific humidity and specific CO\(_2\) content. For this purpose, 124 high-frequency sampled segments are selected from the Boundary Layer Late Afternoon and Sunset Turbulence experiment. The consequences of dissipation similarity in the variance transport are also discussed and quantified. The results show that, for the convective atmospheric surface layer, the non-dimensional dissipation terms can be expressed in the framework of Monin–Obukhov similarity theory and are independent of whether the variable is temperature or moisture. The scalar similarity in the dissipation term implies that the characteristic scales of the atmospheric surface layer can be estimated from the respective rate of variance dissipation, the characteristic scale of temperature, and the dissipation rate of temperature variance.  相似文献   

2.
The intertropical convergence zone (ITCZ) in atmospheric general circulation models (coupled to slab ocean) shift southwards in response to northern extratropical cooling. Previous studies have demonstrated the utility of diagnosing the atmospheric energy fluxes in interpreting this teleconnection. This study investigates the nature of global energy flux changes in response to North Atlantic high latitude cooling applied to the Community Atmosphere Model version 3 coupled to a slab ocean, focusing on key local and remote feedbacks that collectively act to alter the energy budget and atmospheric energy transport. We also investigate the relative roles of tropical sea surface temperature (SST) and energy flux changes in the ITCZ response to North Atlantic cooling. Using a radiative kernel technique, we quantify the effects of key feedbacks—temperature, cloud and water vapor, to the top-of-the-atmosphere radiative flux changes. The results show only partial local energy flux compensation to the initial perturbation in the high latitudes, originating from the negative temperature feedback and opposed by positive shortwave albedo and longwave water vapor feedbacks. Thus, an increase in the atmospheric energy transport to the Northern extratropics is required to close the energy budget. The additional energy flux providing this increase comes from top-of-the-atmosphere radiative flux increase over the southern tropics, primarily from cloud, temperature and longwave water vapor feedbacks, and largely as a consequence of increased deep convection. It has been previously argued that the role of tropical SST changes was secondary to the role played by the atmospheric energy flux requirements in controlling the ITCZ shifts, proposing that the SST response is a result of the surface energy budget and not a driver of the precipitation response. Using a set of idealized simulations with the fixed tropical SSTs, we demonstrate that the ITCZ shifts are not possible without the tropical SST changes and suggest that the tropical SSTs are a more suitable driver of tropical precipitation shifts compared to the atmospheric energy fluxes. In our simulations, the ITCZ shifts are influenced mainly by the local (tropical) SST forcing, apparently independent of the actual high latitude energy demand.  相似文献   

3.
Due to the chaotic and nonlinear nature of the atmospheric dynamics, it is known that small differences in the initial conditions (IC) of models can grow and affect the simulation evolution. In this study, we perform a quantitative diagnostic budget calculation of the various diabatic and dynamical contributions to the time evolution and spatial distribution of internal variability (IV) in simulations with the nested Canadian Regional Climate Model. We establish prognostic budget equations of the IV for the potential temperature and the relative vorticity fields. For both of these variables, the IV equations present similar terms, notably terms relating to the transport of IV by ensemble-mean flow and to the covariance of fluctuations acting on the gradient of the ensemble-mean state. We show the skill of these equations to diagnose the IV that took place in an ensemble of 20 3-month (summer season) simulations that differed only in their IC. Our study suggests that the dominant terms responsible for the large increase of IV are either the covariance term involving the potential temperature fluctuations and diabatic heating fluctuations, or the covariance of inter-member fluctuations acting upon ensemble-mean gradients. Our results also show that, on average, the third-order terms are negligible, but they can become important when the IV is large.  相似文献   

4.
The radiation budget in a regional climate model   总被引：3，自引：2，他引：1  
The long- and short-wave components of the radiation budget are among the most important quantities in climate modelling. In this study, we evaluated the radiation budget at the earth??s surface and at the top of atmosphere over Europe as simulated by the regional climate model CLM. This was done by comparisons with radiation budgets as computed by the GEWEX/SRB satellite-based product and as realised in the ECMWF re-analysis ERA40. Our comparisons show that CLM has a tendency to underestimate solar radiation at the surface and the energy loss by thermal emission. We found a clear statistical dependence of radiation budget imprecision on cloud cover and surface albedo uncertainties in the solar spectrum. In contrast to cloud fraction errors, surface temperature errors have a minor impact on radiation budget uncertainties in the long-wave spectrum. We also evaluated the impact of the number of atmospheric layers used in CLM simulations. CLM simulations with 32 layers perform better than do those with 20 layers in terms of the surface radiation budget components but not in terms of the outgoing long-wave radiation and of radiation divergence. Application of the evaluation approach to similar simulations with two additional regional climate models confirmed the results and showed the usefulness of the approach.  相似文献   

5.
Production, transport and dissipation terms in the temperature variance equation have been measured in the atmospheric surface layer. The transport term is, within the experimental uncertainty, negligible. The dissipation term, determined by assuming local isotropy, is approximately equal to production under near-neutral conditions. For moderately unstable conditions, the ratio of production to dissipation is 1.4. The resulting imbalance in the budget is attributed to the inequality between the three components of the dissipation term. The Kolmogorov constant for temperature is found to be about 0.8.  相似文献   

6.
Local Imbalance of Turbulent Kinetic Energy in the Surface Layer   总被引：1，自引：1，他引：0  
We utilize experimental data collected in 2002 over an open field in Hanford, Washington, USA, to investigate the turbulent kinetic energy (TKE) budget in the atmospheric surface layer. The von Kármán constant was determined from the near-neutral wind profiles to be 0.36 ± 0.02 rather than the classical value of 0.4. The TKE budget was normalized and all terms were parameterized as functions of a stability parameter z/L, where z is the distance from the ground and L is the Obukhov length. The shear production followed the Businger–Dyer relation for −2 < z/L < 1. Contrary to the traditional Monin–Obukhov similarity theory (MOST), the shear, buoyancy and dissipation terms were found to be imbalanced due to a non-zero vertical transport over all stabilities. Motivated by this local imbalance, modified parameterizations of the dissipation and the turbulent transport were attempted and generated good agreement with the experimental data. Assuming stationarity and horizontal homogeneity, the pressure transport was estimated from the residual of the TKE budget.  相似文献   

7.
The temperature biases of 28 CMIP5 AGCMs are evaluated over the Tibetan Plateau(TP) for the period 1979–2005. The results demonstrate that the majority of CMIP5 models underestimate annual and seasonal mean surface 2-m air temperatures(T_(as)) over the TP. In addition, the ensemble of the 28 AGCMs and half of the individual models underestimate annual mean skin temperatures(T_s) over the TP. The cold biases are larger in T_(as) than in T_s, and are larger over the western TP. By decomposing the T_s bias using the surface energy budget equation, we investigate the contributions to the cold surface temperature bias on the TP from various factors, including the surface albedo-induced bias, surface cloud radiative forcing, clear-sky shortwave radiation, clear-sky downward longwave radiation, surface sensible heat flux, latent heat flux,and heat storage. The results show a suite of physically interlinked processes contributing to the cold surface temperature bias.Strong negative surface albedo-induced bias associated with excessive snow cover and the surface heat fluxes are highly anticorrelated, and the cancelling out of these two terms leads to a relatively weak contribution to the cold bias. Smaller surface turbulent fluxes lead to colder lower-tropospheric temperature and lower water vapor content, which in turn cause negative clear-sky downward longwave radiation and cold bias. The results suggest that improvements in the parameterization of the area of snow cover, as well as the boundary layer, and hence surface turbulent fluxes, may help to reduce the cold bias over the TP in the models.  相似文献   

8.
We quantify the role of the convective buoyant structures and the remainder turbulence, here called background turbulence, in the convective atmospheric boundary layer in horizontally homogeneous, dry and barotropic conditions. Three filtering methods to separate the structures and the background turbulence are first evaluated. These are: short-time averaging, Fourier filtering and proper orthogonal decomposition. The Fourier method turns out to be the most appropriate for the present purpose. The decomposition is applied to two cases: one with no mean flow and another with moderate mean wind speed. It is shown that roughly 85 % of the vertical flux of the potential temperature and about 72 % of the kinetic energy is carried by the structures in the mixed layer in both cases. The corresponding percentage for the potential temperature variance is 81 % in the zero mean-wind case and 76 % in the moderate mean-wind case. The structures are responsible for as much as 94 % of the momentum flux in the mixed layer of the moderate mean-wind case. In the surface layer the background turbulence is generally more important than the structure contribution in both cases. The budget of the potential temperature flux is analyzed in detail and it is shown that its turbulent transport term is mostly built up by the structures but also the interaction between the structures and the background turbulence plays a significant role. The other important budget terms are shown to be dominated by the structures except for the pressure–temperature gradient covariance.  相似文献   

9.
Summary Convection, a sub-gridscale process, is coupled to the gridscale motions via the averaged budget equations. In this study atmospheric convection is represented by the vertical eddy flux of equivalent temperature, referred to asconvective flux. It is demonstrated with a thermodynamic diagnostic model for an atmospheric column (DIAMOD) that the convective flux can, with tolerable error, be diagnosed from daily global gridscale analyses. These yield the gridscale budget of equivalent temperature. The budget is the observable quantity, it is in balance with the unobservable convective flux. We reproduce the known result that in convectively active atmospheric columns the budget is negative in lower and positive in upper layers. The corresponding vertical mean slope of the budget controls the convective strength; the slope is strongly negative for deep convection.In the global mean column the convective flux converges upward throughout the entire atmosphere. In actual convective situations, however, the flux diverges in lower layers, reaches highest intensity somewhere between 700–500 hPa and converges in the upper atmosphere. We find maximum fluxes around 600 W/m2 in individual tropical columns and extreme fluxes exceeding 1000 W/m2 in midlatitude columns. In the monthly mean however, the convective flux is clearly larger in the tropics; it also reaches to significantly higher levels in the tropics than in midlatitudes. While these qualitative results are invariant against using both routine analysis and reanalysis data from different sources (ECMWF and NCEP) our results change quantitatively when changing the data sources. We attribute this effect to differences in the sub-gridscale parameterization implicit in the objective data assimilation of the weather centres which are not completely removed by the incoming observation data in the final analyses.With 12 Figures  相似文献   

10.
The deep ocean below 2000 m is a large water body with the sparsest data coverage, challenging the closure of the sea-level budget and the estimation of the Earth's energy imbalance. Whether the deep ocean below 2000 m is warming globally has been debated in the recent decade. However, as the regional signals are generally larger than the global average, it is intriguing to investigate the regional temperature changes. Here, we adopt an indirect method that combines altimetry, GRACE, and Argo data to examine the global and regional deep ocean temperature changes below 2000 m. The consistency between high-quality conductivity-temperature-depth (CTD) data from repeated hydrographic sections and our results confirms the validity of the indirect method. We find that the deep oceans are warming in the Middle East Indian Ocean, the subtropical North and Southwest Pacific, and the Northeast Atlantic, but cooling in the Northwest Atlantic and Southern oceans from 2005 to 2015.  相似文献   

11.
Results from two air quality models (LOTOS, EURAD) have been used toanalyse the contribution of the different terms in the continuity equationto the budget of ozone, NOx and PAN. Both models cover largeparts of Europe and describe the processes relevant for troposphericchemistry and dynamics. One of the models is designed to simulate episodesin the order of 1–2 weeks (EURAD), the other is focussing on theseasonal scale (LOTOS). Based on EURAD simulations it is found that theatmospheric boundary layer (ABL) in Central Europe during a summer-smogepisode in 1990 acts as a source of ozone, which is partly exported from theproduction region in Central Europe. About 40% of the ozone producedchemically in the ABL is lost from Central Europe due to net transport(large-scale and turbulent), 40% are deposited within the domain. Vertical mass exchange of ozone is dominated by the prevailing subsidenceand averaged vertical mass fluxes are directed downward. Averaged massfluxes of PAN, which has no stratospheric source, are upward in the upperpart of the ABL. The results from LOTOS are discussed for the same episodeand for a two month period (July/August 1990). The budget calculation showlarger chemical production for the LOTOS model compared to EURAD. Therelative importance of deposition and net transport, however, is in the sameorder. Differences between the two-month calculation and the one weekepisode are only important for Western Europe where the chemical production is enhanced by 30% during the summer-smog episode. The dependence ofthe results on initial and boundary values is discussed for ozone on thebasis of a simple sensitivity study with EURAD where ozone in the FT is setto 10 ppb initially. This leads to a reversal in the direction of averagedozone mass fluxes in the upper part of the ABL.  相似文献   

12.
We compute the interannual fluctuations of the surface heat budget of the North Atlantic using the trimmed monthly summaries of the Comprehensive Ocean-Atmosphere DataSet (COADS) for the period 1950–1979. The presence of long-period trends in the heat budget imply large variations of the northward cross-equatorial heat transport over the years. To assess the reliability of these variations, we compare the COADS climate signal to that derived from the ocean weather stations (OWSs) of the North Atlantic. The sea surface temperature, air temperature and sea level pressure show good correlation between the anomaly time series derived from the merchant ship monthly summaries of COADS, and those derived from OWS monthly summaries, except for northernmost locations during winter. In contrast, the sensible and latent heat parameters, which require simultaneous measurements of various variables, have merchant ships and ocean weather stations anomaly time series that are poorly correlated. Only in heavily travelled latitudes and during winter, when the air-sea heat exchange anomalies are large, are the merchant ship measurements able to reproduce the interannual fluctuations of the heat fluxes. The long-period trends in the surface heat budget of North Atlantic equatorward of 40° N implied by COADS thus appear unrepresentative of true climate trends. The COADS trends result from a gradual increase in the magnitude of the reported winds over the years due probably to variations in the ratio of measured to estimated winds, as well as from long period fluctuations in the near surface vertical temperature and humidity gradients. Offprint requests to: R Michaud  相似文献   

13.
Summary The maximum entropy production (MEP) principle used in Part J has been extended to separate the two-dimensional required energy transports determined from Nimbus 7 satellite net radiation measurements into atmospheric and oceanic components. In terms of the meridional component of the ocean transport vectors, results show northward ocean transports throughout the entire Atlantic ocean from southern hemisphere high latitudes to northern hemisphere polar regions, southward transports throughout the entire Indian Ocean, and poleward transports separated at approximately 10°S in the Pacific Ocean. The ocean transport patterns are consistent with well-known features concerning heat transport within the three ocean basins. However, uncertainty remains in the magnitudes of the transports. Because of the large remaining discrepancies between published estimates based on direct measurements and indirect estimates derived from energy budget methods, assessing the accuracy of the magnitudes is difficult, although there is evidence that the limited model resolution leads to synergistic biases in the North Atlantic and North Pacific. In terms of the crossmeridional energy transport component, results suggest that most of the net energy transfer in the tropics takes place within the ocean. In the southern hemisphere high latitudes, the Pacific and Indian Oceans export heat cross-meridionally to the Atlantic Ocean through the passages below Cape Horn and the Cape of Good Hope, although the magnitudes of these inter-ocean heat exchanges are small. Another important aspect of the southern hemisphere results is that poleward transports are dominated by the atmospheric component with strong zonal asymmetry. By contrast, in the northern hemisphere, atmospheric transports over the ocean are generally weaker than the corresponding southern hemisphere terms, indicating that the northern hemisphere oceans are relatively more effective in transferring heat poleward. Finally, poleward atmospheric transports over the continental areas exceed those over the ocean at equivalent latitudes as a result of the generally greater energy deficits over the land areas.With 7 Figures  相似文献   

14.
东亚季风湿润区水分收支的气候特征   总被引：1，自引：1，他引：0       下载免费PDF全文
采用1958-2007年NCEP/NCAR月平均再分析资料,分别从水汽通量、水汽通量散度以及区域内降水量与蒸发量差计算东亚季风湿润区的水分收支,分析其差异特征,结果表明:用不同方法计算的水分收支距平年际变化的相关系数分别为0.91,0.71和0.81,误差ε百分率分别为17.4%,44.1%和44%,其中利用水汽通量和散度计算得到的季风湿润区水分收支结果很接近。总体上看,整个区域全年表现为水分收入,春季和夏季的水分收入贡献最大,秋季和冬季贡献较小。在水汽经向输送中,南边界为主要的水汽输入区。从水汽输送计算的水分收支垂直分布来看,多年平均气候态下整个区域除850 hPa存在水分支出外,其余各层均为水分收入,3种方法计算的水分收支在4个季节的年际变化明显。  相似文献   

15.
Both water vapor and heat processes play key roles in producing surface rainfall.While the water vapor effects of sea surface temperature and cloud radiative and microphysical processes on surface rainfall have been investigated in previous studies,the thermal effects on rainfall are analyzed in this study using a series of two-dimensional equilibrium cloud-resolving model experiments forced by zonally-uniform,constant,large-scale zonal wind and zero large-scale vertical velocity.The analysis of thermally-related surface rainfall budget reveals that the model domain mean surface rain rate is primarily associated with the mean infrared cooling rate.Convective rainfall and transport of hydrometeor concentration from convective regions to raining stratiform regions corresponds to the heat divergence over convective regions,whereas stratiform rainfall corresponds to the transport of hydrometeor concentration from convective regions and heat divergence over raining stratiform regions.The heat divergence over convective regions is mainly balanced by the heat convergence over rainfall-free regions,which is,in turn,offset by the radiative cooling over rainfall-free regions.The sensitivity experiments of rainfall to the effects of sea surface temperature and cloud radiative and microphysical processes show that the sea surface temperature and cloud processes affect convective rainfall through the changes in infrared cooling rate over rainfall-free regions and transport rate of heat from convective regions to rainfall-free regions.  相似文献   

16.
This study builds upon two prior papers, which examine Arctic region bias of CAM3 (NCAR Community Atmosphere Model version 3) simulations during winter. CAM3 output is compared with ECMWF (European Centre for Medium-Range Weather Forecasts) 40?year reanalysis (ERA-40) data. Our prior papers considered the temperature and the vorticity equation terms and demonstrated that diabatic, transient, and linear terms dominate nonlinear bias terms over most areas of interest. Accordingly, this paper uses a linearized form of the model??s dynamical core equations to study aspects of the forcing that lead to the CAM3 biases. We treat the model??s long term winter bias as a solution to a linear stationary wave model (LSWM). Key features of the bias in the vorticity, temperature, and ln of surface pressure (=q) fields are shown at medium resolution. The important features found at medium resolution are captured at the much lower LSWM resolution. The Arctic q bias has two key features: excess q over the Barents Sea and a missing Beaufort High (negative maximum q bias) to the north of Alaska and eastern Siberia. The forcing fields are calculated by the LSWM. Horizontal advection tends to create multi-polar combinations of negative and positive extrema in the forcing. The positive and negative areas of forcing approximately match corresponding areas in the bias. There is a broad relation between cold bias with elevated q bias, as expected from classical theory. Forcing in related quantities: near surface vorticity and surface pressure combine to produce the sea level pressure bias.  相似文献   

17.
Summary The annual and inter-annual variability of the water budget over the Baltic Sea area has been studied using the global climate model ECHAM4/T106 and the regional climate model REMO for three experiments covering a time period of 10 years each. To address the capability of REMO to simulate realistically the water budget over the Baltic Sea re-analyses data (so-called perfect boundaries) were applied as lateral boundary conditions. The validation against observations shows that the results agree rather well. However not all components of the hydrological cycle are observed, therefore only some of them could be compared to the simulation results. A clear dependence of the annual cycle of precipitation from the horizontal resolution was found in the experiments. Until now it is still unclear which processes are responsible for this. Further research will help to identify the sensitive physical processes involved in the water budget and their interactions. Received September 8, 2000 Revised April 3, 2001  相似文献   

18.
The output of a large-eddy simulation was used to study the terms ofthe turbulent kinetic energy (TKE) budget for the air layers above andwithin a forest. The computation created a three-dimensional,time-dependent simulation of the airflow, in which the lowest third ofthe domain was occupied by drag elements and heat sources to representthe forest. Shear production was a principal source of TKE in theupper canopy, diminishing gradually above tree-top height and moresharply with depth in the canopy. The transfer of energy to subgridscales (dissipation) was the main sink in the upper part of the domainbut diminished rapidly with depth in the canopy. Removal ofresolved-scale TKE due to canopy drag was extremely important,occurring primarily in the upper half of the forest where the foliagedensity was large. Turbulent transport showed a loss at the canopytop and a gain within the canopy. These general features have beenfound elsewhere but uncertainty remains concerning the effects ofpressure transport. In the present work, pressure was calculateddirectly, allowing us to compute the pressure diffusion term. Wellabove the canopy, pressure transport was smaller than, and opposite insign to, the turbulent transport term. Near the canopy top andbelow, pressure transport acted in concert with turbulent transport toexport TKE from the region immediately above and within the uppercrown, and to provide turbulent energy for the lower parts of theforest. In combination, the transport terms accounted for over half ofthe TKE loss near the canopy top, and in the lowest two-thirds of thecanopy the transport terms were the dominant source terms in thebudget. Moreover, the pressure transport was the largest source ofturbulent kinetic energy in the lowest levels of the canopy, beingparticularly strong under convective conditions. These resultsindicate that pressure transport is important in the plant canopyturbulent kinetic energy budget, especially in the lowest portion ofthe stand, where it acts as the major driving force for turbulentmotions.  相似文献   

19.
Data from a convective internal boundary layer (IBL) are analyzed by focusing on the instantaneousstructure of the top of the IBL instead of the time-average structure.A conditional averaging technique is developed todiscriminate between air from above the IBL and air from below the IBL , which alternately invade some instrument levels due tosubstantial variation of the top of the convective IBL.Sensitivity to the conditional sampling criteria is examined.Inside the IBL , buoyant and mechanicalproduction and dissipation dominate the turbulent kinetic energy budget.The horizontal advection and turbulent transport terms are smaller, but not negligible. The inferred pressure correlation term is negligible.Above the IBL , buoyant production and dissipation, although weak,dominate the turbulent kinetic energy budget. Shear generation andturbulent transport are smaller but significant.  相似文献   

20.
Four aircraft measurement sets made in late May 1989 within low level jets over the Baltic Sea have been analyzed to estimate the turbulence energy budget. It is concluded that the jets had the same origin as found in an earlier study from the same general area: inertial oscillation caused by frictional decoupling when relatively warm air flows out over much colder water.In order to combine budget estimates from the four flights to form a representative average, self-preservation similarity was assumed. When the terms were made nondimensional with the proper scale combination, the largest terms in all four runs were of order one, indicating that the scaling is physically sound.Three terms were found to dominate the turbulence energy budget: shear production, dissipation and pressure transport. The latter was obtained as remainder term, since local time rate of change and advection terms were found to be of negligible magnitude. Shear production was found in a narrow layer above the jet core and in a much deeper layer below it. The pressure transport term was a gain in this layer as well, helping to keep the layer below the jet well mixed. This is in agreement with results from aircraft measurements in the low level jet and monsoon boundary layer over the Arabian Sea.It is concluded that development of the inertial jet downwind of a coastline is of fundamental importance for exchange of momentum at the sea surface in conditions when relatively warm air is advected over cold water. The jet produces turbulence that promotes mixing in the lower layers, which sharpens the shear below the jet core, so that mixing becomes even more effective. Turbulence brought down to the surface by the pressure transport term is likely to be of the inactive type, which does not produce shear stress. Through the above-mentioned process it is, however, instrumental in promoting the mechanism that eventually produces active turbulence, the carrier of momentum.  相似文献   

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