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1.
In this study, the global energy cycle of five state-of-the-art climate models is evaluated in the wave number domain for all seasons. The energy cycle estimates are based on 30?years of 6-hourly data obtained at pressure levels of all models. The models energetics are compared to those obtained from three reanalysis datasets (ERA-40, JRA-25 and NCEP-R2). The results show that the distributions of the energetics integrands and the shape of the various wave number spectra are reasonably well simulated. Many important features can be found in most models, namely both the upscale and downscale energy cascade for the wave?Cwave interactions of kinetic energy, the downscale energy cascade for the wave?Cwave interactions of available potential energy and the downscale energy transfer for the zonal?Cwave interactions of kinetic energy. However, the magnitude in the integrands distributions is generally excessive, yielding too much energy and an overactive energy cycle in the models. Accordingly, this energy excess is also reflected in the various spectra, specially but not exclusively, at the synoptic scale wave numbers for the energy conversion/transfer rates. The well known cold pole bias and the too strong tropospheric jets, along with their dislocation in some cases, still persist in the climate models. These are some of the deficiencies in the models directly implicated in the energy cycle. Apparently, simply increasing the horizontal and vertical resolutions is not enough to eliminate these deficiencies due to somewhat opposite effects achieved by refining both spatial resolutions. Therefore, more accurate physics parameterisations as well as improved numerical schemes and resolution dependence of parameterisations seem to be essential for a significant improvement in the models energetics. Moreover, efforts should be made to improve the physical processes controlling the generation of zonal available potential energy and dissipation of eddy kinetic energy, in which the synoptic scale should be fundamental, as inferred from the excessive energy conversion/transfer rates in the models spectra. 相似文献
2.
Changes in the normal mode energetics of the general atmospheric circulation are assessed for the northern winter season (DJF) in a warmer climate, using the outputs of four climate models from the Coupled Model Intercomparison Project, Phase 3. The energetics changes are characterized by significant increases in both the zonal mean and eddy components for the barotropic and the deeper baroclinic modes, whereas for the shallower baroclinic modes both the zonal mean and eddy components decrease. Significant increases are predominant in the large-scale eddies, both barotropic and baroclinic, while the opposite is found in eddies of smaller scales. While the generation rate of zonal mean available potential energy has globally increased in the barotropic component, leading to an overall strengthening in the barotropic energetics terms, it has decreased in the baroclinic component, leading to a general weakening in the baroclinic energetics counterpart. These global changes, which indicate a strengthening of the energetics in the upper troposphere and lower stratosphere (UTLS), sustained by enhanced baroclinic eddies of large horizontal scales, and a weakening below, mostly driven by weaker baroclinic eddies of intermediate to small scales, appear together with an increased transfer rate of kinetic energy from the eddies to the zonal mean flow and a significant increase in the barotropic zonal mean kinetic energy. The conversion rates between available potential energy and kinetic energy, C, were further decomposed into the contributions by the rotational (Rossby) and divergent (gravity) components of the circulation field. The eddy component of C is due to the conversion of potential energy of the rotational adjusted mass field into kinetic energy by the work realized in the eddy divergent motion. The zonal mean component of C is accomplished by two terms which nearly cancel each other out. One is related to the Hadley cell and involves the divergent component of both wind and geopotential, while the other is associated to the Ferrel cell and incorporates the divergent wind with the rotationally adjusted mass field. Global magnitude increases were found in the zonal mean components of these two terms for the warmer climate, which could be the result of a strengthening and/or widening of both meridional cells. On the other hand, the results suggest a strengthening of these conversion rates in the UTLS and a weakening below, that is consistent with the rising of the tropopause in response to global warming. 相似文献
3.
Summary Lower tropospheric (1000–500) hPa kinetic energy (KE), temporal variations of KE and nonlinear KE transfer of rotational and divergent flows and energy conversion between them, partitioning further into stationary and transient components in the Fourier spectral domain and the mechanism for the evolution of significant transient waves for the month July 1979 in the latitudinal belt 10° S–30° N are studied.Divergent zonal and eddy KE show their maxima at the lowest level 1000 hPa. Lower tropospheric monsoon motion provides a non-divergent level close to 850 hPa. The daily flow patterns bear little resemblence to the climatology over tropics at 500 hPa. Although the transient mode of synoptic scale waves is stronger than that of planetary scale waves they are comparable. Analysis of energetics over global tropics can get signature of transient activities embedded in the large scale system. Summer momentum flux in the lower troposphere is essentially associated with stationary planetary and transient synoptic scale waves. Waves 1, 3 and 6 are the most preferred transient waves. Divergent to rotational KE conversion is the most dominating mechanism for the maintenance of planetary and synoptic scale waves. All categories of waves contribute towards the maintenance of zonal flows. The primary source of energy for transient synoptic scale waves is the transient divergent rotational KE transfer whereas the interaction between zonal stationary and transient wave is likely to be secondary source. Transient KE and all transient interactions, stationary KE and all stationary interactions are found to be strongest at 500 hPa and 850 hPa respectively. Growth and decay of transient waves 1 and 3 are mainly controlled by divergent-rotational KE conversions whereas those of transient wave 6 are controlled by KE transfer due to zonal-wave interaction.With 13 Figures 相似文献
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5.
Dr. R. S. Ross 《Meteorology and Atmospheric Physics》1991,45(3-4):139-158
Summary The FSU Global Spectral Model including comprehensive physical parameterization and high resolution (T 106) is used to make predictions to 48 hours for two cases of African easterly wave disturbances which occurred during FGGE. Model output is compared with FGGE III-b analyses to qualitatively assess the model's performance. The results of energetics calculations for the two case studies are included in this study. These calculations are based on model output to 24 hours. The energetics results confirm that combined barotropic/baroclinic instability provides the primary energy source for the African waves. Such energetics results, based on individual case studies, also provide an interesting and valuable comparison with compositing studies on African waves. An aspect of this study deals with the definition of a double jet stream structure at 700 mb for the two cases under consideration. The energetics patierns in zones to the north and south of each of these jets are separately portrayed.With 15 Figures 相似文献
6.
The global energy cycle of stationary and transient atmospheric waves: Results from ECMWF analyses 总被引：3，自引：0，他引：3
Summary The role of stationary (monthly mean) and transient (departure from monthly mean) waves within the atmospheric energy cycle is examined using global analyses from the European Centre for Medium Range Weather Forecasts (ECMWF) for the period 1980–1987. Only January and July averages are considered.It is confirmed that planetary stationary waves are basically baroclinic. Their contribution to the globally averaged energy cycle of the atmosphere is comparable to that of the transient waves. In January they contribute about 40% to the baroclinic conversion (CA) from zonal mean to eddy available potential energy. Local values for the northern hemisphere even show a predominant role of the stationary wave conversions over those originating from transient waves. Part of the available potential energy of stationary waves (A
SE) is converted to kinetic energy by warm air rising and cold air sinking. Nonlinear energy conversion, which can be interpreted as destruction of stationary temperature waves by transients, is the second sink forA
SE. The order of magnitude of these two processes is similar.Barotropic nonlinear conversions, though negligible in the global average, reveal large conversion rates between the mean positions of the polar and the subtropical jets. Their orientation is suggestive of a tendency to increase stationary wave kinetic energyK
SE at its local minimum between the jets at the expense of the synoptic scale transients.While all terms of the energy cycle related to stationary waves reveal a predominance of the planetary scale (zonal wave numbers 1–3) transient waves are governed by synoptic scale waves (zonal wave numbers 4–9) only with respect to the baroclinic and barotropic conversions: a significant amount of transient wave energy (50% for the global average ofA
TE) is due to planetary scale waves.With 15 Figures 相似文献
7.
Climate sensitivity of the NCAR Community Climate Model (CCM2) to horizontal resolution 总被引：3，自引：1，他引：3
The dependence on horizontal resolution of the climate simulated by the National Center for Atmospheric Research Community Climate Model (CCM2) is explored. Simulations employing R15, T21, T31, T42, T63, and T106 horizontal spectral truncations are compared. Parameters associated with the diagnostic cloud scheme are modified for each resolution to provide similar global average cloud radiative forcing at each resolution. Overall, as with earlier studies, there are large differences between the low resolution R15 and T21 simulations and the medium resolution T42 simulation. Many climate statistics show a monotonic signal with increasing resolution, with the largest variation occurring from low to medium resolution. Although the monotonic signal is often from the low resolution simulations toward atmospheric analyses, in some cases it continues beyond the analyses at the highest resolution. Where convergence occurs, it is not always to the atmospheric analyses, and the highest resolution simulations are not the best by all measures. Although many climate statistics converge, the processes that maintain the climate do not, especially when considered on a regional basis. The implication is that the finer scales are required to capture the nonlinear processes that force the medium scales. Overall, it appears that, at a minimum, T42 resolution is required, but higher resolution would be better. Applications at T42 should take into consideration how model errors indicated by these resolution signals might affect any findings.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
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9.
Based on the ECMWF data(1980-1983) and others, a further inquiry on the activities and the structure feature of 30-60 day oscillation in the tropical atmosphere has been completed. The following results are obtained:There is stronger perturbation kinetic energy of 30-60 day atmospheric oscillation(AO) in the equatorial eastern Pacific. This means the equatorial eastern Pacific is a stronger activity region of 30-60 day AO in the tropics. Analyses also show that the AO system with the time scale of 30-60 days might consist of various spatial scale disturbances. The zonal propagation of 30-60 day oscillation in the tropical atmosphere is not all eastward. Some differences are found for different spatial scales, and for propagations in upper and lower tropospheres. The meridional propagation of the oscillation is even more different in the various regions and might be related to the low-frequency wave train in the atmosphere. The stronger activities of 30-60 day AO in the equatorial middle-western Pacific are related to the El Nino events and the weaker ones are correspondent to the inverse El Nino phenomena. 相似文献
10.
The effect of barotropic shear on baroclinic instability has been investigated using both a linear quasi-geostrophic β-plane channel model and a multilevel primitive equation model on the sphere when a nonmodal disturbance is used as the initial perturbation condition. The analysis of the initial value problem has demonstrated the existence of a rapid transient growth phase of the most unstable mode. The inclusion of a linear barotropic shear reduces initial rapid transient growth, although at intermediate times the transient growth rates of the sheared cases can be larger than in the unsheared case owing to downgradient eddy momentum fluxes. Certain disturbances can amplify by factors of 4.5–60 times (for the L2 norm), or 3–30 times (for the perturbation amplitude maximum), as large as disturbances based on the linear normal modes. However, linear horizontal shear always reduces the amplification factors. The mechanism is that the shear confines the disturbance meriodionally and therefore limits the energy conversion from the zonal available potential energy to eddy energy. The effect of barotropic shear on the transient growth is not changed much in the presence of either thermal damping or Ekman pumping. Nonmodal integrations of baroclinic wave lifecycles show that the energy level reached by eddies is not very sensitive to the structure of the initial disturbance if the amplitude of the initial disturbance is small. Although in some cases the eddy kinetic energy level reached by the wave integrated from nonmodal disturbance can be 25–150% larger than the normal mode integrations, barotropic shear, characterized by large shear vorticity with small horizontal curvature, always reduces the eddy kinetic energy level reached by the wave, confirming the results of normal mode studies. 相似文献
11.
An analysis is made of the effects of topography on the summer atmospheric energetics of the Northern Hemisphere in a low-resolution global spectral model. The numerical model is a global, spectral, primitive equation model with five equally spaced sigma levels in the vertical and triangular truncation at wavenumber 10 in the horizontal. The model includes comparatively full physical processes.Each term of the energy budget equations is calculated in four specific latitudinal belts (81.11°S-11.53°S; 11.53°S-11.53°N; 11.53°N-46.24°N; 46.24°N-81.11°N) from a five-year simulation with mountains and a one-year simulation without mountains, respectively. Differences between them are compared and statistically tested. The results show that synoptical scale waves transport available potential energy and kinetic energy to long waves and increase conversion from available potential energy of the zonal flow to eddy’s and from the eddy kinetic energy to the zonal kinetic energy in region 3 (11.53°N-46.24°N) due to mountains; topography intensifies the atmospheric baroclinity in region 3, consequently the baroclinic conversion of atmosphere energy is increased. The seasonal characteristics associated with the summer atmospheric energy source in region 3 are caused by seasonal variation of the solar radiation and the land-ocean contrasts and independent of topographic effects. The mechanism of topographic effects on the increase of long wave kinetic energy is also discussed. 相似文献
12.
Impact of ocean model resolution on CCSM climate simulations 总被引：1，自引：1，他引：0
Ben P. Kirtman Cecilia Bitz Frank Bryan William Collins John Dennis Nathan Hearn James L. Kinter III Richard Loft Clement Rousset Leo Siqueira Cristiana Stan Robert Tomas Mariana Vertenstein 《Climate Dynamics》2012,39(6):1303-1328
The current literature provides compelling evidence suggesting that an eddy-resolving (as opposed to eddy-permitting or eddy-parameterized) ocean component model will significantly impact the simulation of the large-scale climate, although this has not been fully tested to date in multi-decadal global coupled climate simulations. The purpose of this paper is to examine how resolved ocean fronts and eddies impact the simulation of large-scale climate. The model used for this study is the NCAR Community Climate System Model version 3.5 (CCSM3.5)—the forerunner to CCSM4. Two experiments are reported here. The control experiment is a 155-year present-day climate simulation using a 0.5° atmosphere component (zonal resolution 0.625 meridional resolution 0.5°; land surface component at the same resolution) coupled to ocean and sea-ice components with zonal resolution of 1.2° and meridional resolution varying from 0.27° at the equator to 0.54° in the mid-latitudes. The second simulation uses the same atmospheric and land-surface models coupled to eddy-resolving 0.1° ocean and sea-ice component models. The simulations are compared in terms of how the representation of smaller scale features in the time mean ocean circulation and ocean eddies impact the mean and variable climate. In terms of the global mean surface temperature, the enhanced ocean resolution leads to a ubiquitous surface warming with a global mean surface temperature increase of about 0.2?°C relative to the control. The warming is largest in the Arctic and regions of strong ocean fronts and ocean eddy activity (i.e., Southern Ocean, western boundary currents). The Arctic warming is associated with significant losses of sea-ice in the high-resolution simulation. The sea surface temperature gradients in the North Atlantic, in particular, are better resolved in the high-resolution model leading to significantly sharper temperature gradients and associated large-scale shifts in the rainfall. In the extra-tropics, the interannual temperature variability is increased with the resolved eddies, and a notable increases in the amplitude of the El Ni?o and the Southern Oscillation is also detected. Changes in global temperature anomaly teleconnections and local air-sea feedbacks are also documented and show large changes in ocean–atmosphere coupling. In particular, local air-sea feedbacks are significantly modified by the increased ocean resolution. In the high-resolution simulation in the extra-tropics there is compelling evidence of stronger forcing of the atmosphere by SST variability arising from ocean dynamics. This coupling is very weak or absent in the low-resolution model. 相似文献
13.
热带大气中的准双周（10—20天）振荡 总被引：10，自引：3，他引：10
基于欧洲中期天气预报中心（ECMWF）的资料（1981—1988），本文对全球热带大气中的10—20天（准双周）振荡进行了比较系统的研究，包括其动能的分布及演变。扰动的结构和传播特征等。资料分析充分表明，热带大气10—20天振荡是热带大气中另一重要低频系统，其动能比30—60天振荡还要大，而其结构和活动又同30—60天振荡很不一样。例如热带大气10—20天振荡主要表现为纬向波数2—4；垂直结构以正压特征更显著；主要表现为向西传播；其经向风分量与纬向风分量同等重要。因此，对热带大气10—20天振荡值得更多注 相似文献
14.
利用ECMWF格点资料,分析研究了大气季节内(30—60天)振荡的全球特征。30—60天振荡动能的分布表明高纬度地区要比赤道地区大得多。说明那里有较突出的30—60天振荡。中高纬度地区的30—60天振荡与热带有明显不同,垂直结构为正压模态,以纬向2—4波为主,多为向酉传播。30—60天振荡存在明显的低频遥相关,北半球主要为欧亚—太平洋(EAP)型和PNA型,南半球主要有澳洲—南非(ASA)型和环南美(RSA)型,并且在全球范围构成南北半球相互衔接的低频波列,即EAP-ASA波列和PNA-RSA波列。南北半球30—60天大气振荡有明显的相互影响,本文研究了南北半球30—60天振荡相互影响的3种主要过程。 相似文献
15.
An analysis of 3 years' (1967–70) radiosonde wind data on the windward (Salt Lake City, Utah) and lee (Denver, Colorado) sides of mountains indicates that at these two stations: (1) the distributions of the kinetic energy of the mean and turbulent motions are similar above the mountain top; (2) below the mountain top, on the windward side, mountains tend to divert the component of the mean motion normal to the mountains to that parallel to the mountains; (3) the meridional eddy transport of westerly momentum is affected by the presence of the mountains to a higher level to the lee of the mountains than upwind of them; (4) the production of turbulent energy is higher below the mountain top in the vicinity of mountains than it is for the zonal average; (5) high frequencies of the motion show a more pronounced contribution in the meridional motion in the windward side, but in the zonal motion in the lee of the mountains; (6) disturbances of 1–2 day periods can be maintained deep into the valley, whereas disturbances of longer periods reduce their amplitudes rapidly with decreasing height from the mountain top; (7) the cospectra of the wind velocities show that the southward/northward transport of westerly momentum results from a southward/northward contribution from most frequencies. The main contributions come from eddies with periods longer than two days. 相似文献
16.
An analysis is made of the effects of topography on the summer atmospheric energetics of the Northern Hemisphere in a low-resolution
global spectral model. The numerical mode! is a global, spectral, primitive equation model with five equally spaced sigma
levels in the vertical and triangular truncation at wavenumber 10 in the horizontal. The model includes comparatively full
physical processes.
Each term of the energy budget equations is calculated in four specific latitudinal belts (81.11°S–11.53°S; 11.53°S–11.53°N;
11.53°N–46.24°N; 46.24°N–81.11°N) from a five-year simulation with mountains and a one-year simulation without mountains,
respectively. Differences between them are compared and statistically tested. The results show that synoptical scale waves
transport available potential energy and kinetic energy to long waves and increase conversion from available potential energy
of the zonal flow to eddy's and from the eddy kinetic energy to the zonal kinetic energy in region 3 (11.53°N-46.24°N) due
to mountains; topography intensifies the atmospheric baroclinity in region 3, consequently the baroclinic conversion of atmosphere
energy is increased. The seasonal characteristics associated with the summer atmospheric energy source in region 3 are caused
by seasonal variation of the solar radiation and the land-ocean contrasts and independent of topographic effects. The mechanism
of topographic effects on the increase of long wave kinetic energy is also discussed. 相似文献
17.
FORMATION MECHANISM AND PROPAGATION CHARACTERISTICS OF THE EQUATORIAL THERMALLY-FORCED SHORT-TERM CLIMATIC OSCILLATION DURING THE NORTHERN SUMMER 
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下载免费PDF全文 In this study, in order to investigate the global climatic oscillations forced by sea surface temperature (SST) anomalies over equatorial central-eastern Pacific, two numerical schemes with different SST distri-butions (normal and anomalous cases) are tested by using a nine-layer global spectral model. Experiment results show that (i) in northern summer, a wave train that is similar to the teleconnection pattern suggested by Nitta (1987) and Huang (1987) in the Northern Hemisphere and another one in the Southern Hemisphere are reproduced; (ii) simulated results suggest that the response of atmosphere in middle-high latitudes of both hemispheres to an anomalous heating source is more sensitive in tropical western Pacific than in equatorial central-eastern Pacific; and (iii) in northern summer, the formation of low-frequency oscillations on monthly (seasonal) time scale results from energy dispersion as well as interactions between eddies and zonal flow; and between eddies. 相似文献
18.
热带大气季节内振荡的进一步分析 总被引：2，自引：1，他引：1
利用ＥＣＭＷＦ的格点资料对热带大气季节内振荡作了进一步分析研究,表明热带大气季节内振荡既有Ｋｅｌｖｉｎ波型扰动,也有Ｒｏｓｓｂｙ波型扰动;影响热带大气季节内振荡移动的主要因素有扰动波型和积云对流活动的异常;伴随ＥｌＮｉｎｏ事件的发生,热带大气季节内振荡的动能急剧减小,而准定常扰动动能急剧增大,既反映了热带大气季节内振荡对ＥｌＮｉｎｏ的激发作用,也说明了在ＥｌＮｉｎｏ期间热带大气季节内振荡偏弱的原因。 相似文献
19.
Annual mean ocean surface heat fluxes have been studied as a function of horizontal resolution in the ECMWF model (cycle 33) and compared with Oberhuber's COADS (1959–1979) based empirical estimates. The model has been run at resolutions of T21, T42, T63 and T106 for 15 months with prescribed monthly varying climatological SST and sea ice. The T42 simulation was extended to 2 years, which enabled us to determine that many differences between the resolution runs were significant and could not be explained by the fact that individual realizations of an ensemble of years can be expected to give different estimates of the annual mean climate state. In addition to systematic differences between the modeled and the observed fluxes, the simulated fields of surface shortwave and longwave radiation showed much more spatial variability than the observed estimates. In the case of the longwave radiation this may be attributable more to deficiencies in the observations than to errors in the model. The modeled latent and sensible heat fields were in better agreement with observations. The primary conclusion concerning the dependence of ocean surface fluxes on resolution is that the T21 simulation differed significantly from the higher resolution runs, especially in the tropics. Although the differences among the three higher resolution simulations were generally small over most of the world ocean, there were local areas with large differences. It appears, therefore, that in relation to ocean surface heat fluxes, a resolution greater than T42 may not be justified for climate model simulations, although the locally large differences found between the higher resolution runs suggest that convergence has not been achieved everywhere even at T106. 相似文献
20.
Wind component fluctuations have been decomposed into contributions of large and small-scale eddies to study turbulence structures in the atmospheric surface layer over snow-covered pack ice for a case with snow drift and another without. It was found that on average, the large eddies contribute little to the covariance, but significantly to the variance of the horizontal wind components. The turbulent kinetic energy and the friction velocity show clearly expressed energy and flux variations. The time series of turbulent statistics, calculated on the basis of large eddies only, show the same behavior. However, the time variations of the turbulent kinetic energy and the friction velocity, determined by the small eddies, are suppressed when there is drifting snow.The occurrence of different types of motions (ejections, sweeps and interactions) was detected by the quadrant-technique. It was found that events with strong drag reduction during snow drift correspond to a strong increase of contributions from the first and third quadrant. However, strong drag reduction events in the case without snow drift are caused by a general decrease of contributions from all four quadrants. It was also found that interactions are significantly less correlated with ejections and sweeps in the case with snow drift than in the case without. 相似文献