Comparative energetics analysis of CCM2 with different horizontal resolutions

 Comprehensive global energetics analysis is carried out for the NCAR CCM2 with different horizontal resolutions of R15, T42, T63, and T106 to assess the effect of various model truncations on the global energetics characteristics in climate models. Both the energy levels and energy transformations are examined over the zonal wave number domain during a northern winter and summer. In addition to the simulated atmosphere, the ECMWF global analysis during 1986 to 1990 is analyzed for comparison using the same diagnostic scheme. Previous studies have revealed that zonal kinetic energy is supplied by synoptic disturbances in terms of the zonal-wave interactions of kinetic energy. According to our result, however, such an energy flow from eddies to zonal motions is valid only for zonal wave numbers up to about 30. We find that the zonal-wave interactions of kinetic energy change sign beyond wave number 30 where the energy is transformed from zonal to eddies for both the ECMWF and CCM2-T106. The large-scale zonal motions are diffusive against the short waves beyond wave number 30, which may well be parameterized by various forms of the diffusion schemes. We suggest from this result that the atmospheric disturbances with wave numbers lower than 30 are necessary to represent accurately the two-way interactions between zonal and eddy motions, because these waves can actively influence the behavior of the zonal motions. Based on this finding, we suggest that the model resolution of R15 is inadequate for climate studies from the energetics point of view, and that resolution of T42 is the minimum requirement to represent the general circulation adequately. Some other discrepancies are discussed in detail for the coarse resolution climate models. Received: 15 July 1996/Accepted: 3 January 1997     

Nonlinear kinetic energy interactions and their contributions to the growth and decay of atmospheric waves in the lower troposphere during summer monsoon, 1979

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     

Comparative energetics of ERA-40, JRA-25 and NCEP-R2 reanalysis, in the wave number domain

The European Centre for Medium-Range Weather Forecasts 40-year Reanalysis (ERA-40), the Japan Meteorological Agency and Central Research Institute of Electric Power Industry 25-year Reanalysis (JRA-25), and the National Centers for Environmental Prediction and Department of Energy AMIP-II Reanalysis (NCEP-R2) are intercompared through a global energetics analysis for all seasons.Overall, the Lorenz energy cycle is consistent among the three datasets. The flow of energy and the peaks and slopes in the spectra of the various components agree between the three reanalysis. Additionally, the temporal variability of the energy cycle terms shows consistency between the three reanalysis. Most differences between the three reanalysis are related to the magnitudes of energy forms and energy conversion/transfer rates at each wave number, generally following the relation ERA−40>JRA−25>NCEP−R2, and mainly located in the Southern Hemisphere. The best agreement between the three datasets is found for northern winter. Differences between the three datasets are greater for the other seasons, being greatest for northern summer. In general, these discrepancies are fairly modest, being likely due to the different model biases and resolutions, and the different data assimilation methods used by the respective reanalysis systems. The energetics of the three reanalysis become closer to each other in more recent years, which is likely due to the increase in the number of observations assimilated in the reanalysis.The NCEP-R2 reanalysis spectrum is smoother than those of ERA-40 and JRA-25, likely due to filtering and to its lower resolution model. The spectra show a rapid decrease for short waves in NCEP-R2 (n=36) and ERA-40 (n=63), as a consequence of filtering. The energy source in the nonlinear wave–wave interactions of kinetic energy, L(n), has a narrower spectral range in NCEP-R2 than in the other datasets. Energetics from the newer JRA-25 reanalysis is generally closer to that of ERA-40, with some exceptions as is the case of zonal–wave interactions of kinetic energy, M(n), for synoptic waves, or for eddy available potential energy, A_E, in the lower troposphere, for which JRA-25 is closer to NCEP-R2.     

How well do coupled models replicate ocean energetics relevant to ENSO?

Accurate replication of the processes associated with the energetics of the tropical ocean is necessary if coupled GCMs are to simulate the physics of ENSO correctly, including the transfer of energy from the winds to the ocean thermocline and energy dissipation during the ENSO cycle. Here, we analyze ocean energetics in coupled GCMs in terms of two integral parameters describing net energy loss in the system using the approach recently proposed by Brown and Fedorov (J Clim 23:1563?C1580, 2010a) and Fedorov (J Clim 20:1108?C1117, 2007). These parameters are (1) the efficiency ?? of the conversion of wind power into the buoyancy power that controls the rate of change of the available potential energy (APE) in the ocean and (2) the e-folding rate ?? that characterizes the damping of APE by turbulent diffusion and other processes. Estimating these two parameters for coupled models reveals potential deficiencies (and large differences) in how state-of-the-art coupled GCMs reproduce the ocean energetics as compared to ocean-only models and data assimilating models. The majority of the coupled models we analyzed show a lower efficiency (values of ?? in the range of 10?C50% versus 50?C60% for ocean-only simulations or reanalysis) and a relatively strong energy damping (values of ??^?1 in the range 0.4?C1?years versus 0.9?C1.2?years). These differences in the model energetics appear to reflect differences in the simulated thermal structure of the tropical ocean, the structure of ocean equatorial currents, and deficiencies in the way coupled models simulate ENSO.     

Optimisation of simplified GCMs using circulation indices and maximum entropy production

Two kinds of objective functions for parameter optimisation in simplified general circulation models (SGCMs) are introduced and tested with an SGCM employing linear parameterisations for diabatic heating, surface friction and horizontal diffusion. (a) A set of circulation indices is introduced to characterise the zonal mean primary and secondary circulation and the global energetics. The objective function is then given by the distance between the modelled and a reference (e.g. observed) circulation in a state space spanned by these indices. (b) The global and time mean entropy production and kinetic energy dissipation are introduced as additional objective functions, following the maximum entropy production principle. It is found that both methods lead to optimal parameter values close to the standard configuration of the model, though the method of the second kind is restricted to those model parameters associated with internal processes such as heat and momentum fluxes.     

The global energy cycle of stationary and transient atmospheric waves: Results from ECMWF analyses

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     

Changes in the normal mode energetics of the general atmospheric circulation in a warmer climate

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.     

一次典型的平流层爆发性增温中的局地多尺度洛伦兹循环

利用一种新的工具,多尺度子空间变换(MWT),以及基于MWT的局地多尺度能量与涡度分析(MS-EVA)与Lorenz循环诊断方法,对2009年1月中下旬平流层发生的一次强爆发性增温(SSW)事件的内在动力学过程进行了研究。首先用MWT将各个场重构于三个尺度子空间,即平均尺度、爆发性增温尺度(或SSW尺度)和天气尺度子空间上。结果表明,极地迅速增长的温度主要是由于SSW尺度子空间上极区内的斜压不稳定引起的正则传输(有效位能从平均尺度子空间传输到SSW尺度子空间)造成的,显著增加的有效位能(APE)转换到了SSW尺度子空间的动能(KE)中,加之快速增温前极区内正压不稳定引起的正则传输(动能从平均尺度子空间传输到SSW尺度子空间)的作用,共同导致了极夜急流的反转。     

Some Aspects of the Characteristics of Monsoon Disturbances Using a Combined Barotropic－Baroclinic Model

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GOALS模式中大气能量循环的诊断分析与不同版本计算结果的比较研究

利用大气能量循环框图,对比分析中国科学院大气物理研究所大气科学与地球流体力学数值模拟国家重点实验室(LASG/IAP)全球海-陆-气耦合系统模式(GOALS)两个版本(GOALS-2和GOALS-4),以及观测的全球平均大气能量循环的主要特征,并从能量循环贮蓄和转换项的纬向平均贡献去解释全球积分值改善和转坏的原因,以及诊断分析参数化方案变化后产生的影响.结果表明:模式的两个版本基本上能正确地模拟出全球能量循环的主要特征.旧版本GOALS-2能较好模拟全球积分值,常常是不同符号局地误差的相互抵消结果.新版本GOALS-4中某种局地过程的改善在一些情况下导致了全球积分值的转坏.引入辐射日变化参数化方案可能对能量循环各参数的局地贡献有着明显的影响.如纬向平均有效位能向瞬变涡动有效位能的斜压转换率、瞬变涡动有效位能向瞬变涡动动能的斜压转换率以及定常涡动动能的局地贡献有明显改善.南极地区不合实际的上升运动,是模拟的纬向平均有效位能与纬向平均动能之间的转换项全球积分值为负数的主要原因.     

Energy Paths that Sustain the Warm-Sector Torrential Rainfall over South China and Their Contrasts to the Frontal Rainfall: A Case Study

Predicting warm-sector torrential rainfall over South China, which is famous for its destructive power, is one of the most challenging issues of the current numerical forecast field. Insufficient understanding of the key mechanisms underlying this type of event is the root cause. Since understanding the energetics is crucial to understanding the evolutions of various types of weather systems, a general methodology for investigating energetics of torrential rainfall is provided in this study. By applying this methodology to a persistent torrential rainfall event which had concurrent frontal and warm-sector precipitation, the first physical image on the energetics of the warm-sector torrential rainfall is established. This clarifies the energy sources for producing the warm-sector rainfall during this event. For the first time, fundamental similarities and differences between the warm-sector and frontal torrential rainfall are shown in terms of energetics. It is found that these two types of rainfall mainly differed from each other in the lower-tropospheric dynamical features, and their key differences lay in energy sources. Scale interactions (mainly through downscale energy cascade and transport) were a dominant factor for the warm-sector torrential rainfall during this event, whereas, for the frontal torrential rainfall, they were only of secondary importance. Three typical signals in the background environment are found to have supplied energy to the warm-sector torrential rainfall, with the quasi-biweekly oscillation having contributed the most.     

一次暴雨过程中天气尺度与次天气尺度系统的相互作用

文章利用动能方程计算天气尺度与次天气尺度系统动能以及非线性动能的作用，以分析强降水系统中主要动力过程。结果表明:在暴雨系统中，存在着天气尺度和次天气尺度系统间的相互作用，次天气尺度运动增加天气尺度动能，使暴雨系统得以维持。     

Diagnostic Study of Global Energy Cycle of the GRAPES Global Model in the Mixed Space-Time Domain

Some important diagnostic characteristics for a model’s physical background are reflected in the model’s energy transport, conversion, and cycle. Diagnosing the atmospheric energy cycle is a suitable way towards understanding and improving numerical models. In this study, formulations of the “Mixed Space-Time Domain”energy cycle are calculated and the roles of stationary and transient waves within the atmospheric energy cycle of the Global-Regional Assimilation and Prediction System （GRAPES） model are diagnosed and compared with the NCEP analysis data for July 2011. Contributions of the zonal-mean components of the energy cycle are investigated to explain the performance of numerical models. The results show that the GRAPES model has the capability to reproduce the main features of the global energy cycle as compared with the NCEP analysis. Zonal available potential energy （AZ） is converted into stationary eddy available potential energy （ASE） and transient eddy available potential energy （ATE）, and ASE and ATE have similar values. The nonlinear conversion between the two eddy energy terms is directed from the stationary to the transient. AZ becomes larger with increased forecast lead time, reflecting an enhancement of the meridional temperature gradient, which strengthens the zonal baroclinic processes and makes the conversion from AZ to eddy potential energy larger, especially for CAT （conversion from AZ to ATE）. The zonal kinetic energy （KZ） has a similar value to the sum of the stationary and transient eddy kinetic energy. Barotropic conversions are directed from eddy to zonal kinetic energy. The zonal conversion from AZ to KZ in GRAPES is around 1.5 times larger than in the NCEP analysis. The contributions of zonal energy cycle components show that transient eddy kinetic energy （KTE） is associated with the Southern Hemisphere subtropical jet and the conversion from KZ to KTE reduces in the upper tropopause near 30？S. The nonlinear barotropic conversion between stationary     

The energy cycle in atmospheric models

The energy cycle characterizes basic aspects of the physical behaviour of the climate system. Terms in the energy cycle involve first and second order climate statistics (means, variances, covariances) and the intercomparison of energetic quantities offers physically motivated “second order” insight into model and system behaviour. The energy cycle components of 12 models participating in AMIP2 are calculated, intercompared and assessed against results based on NCEP and ERA reanalyses. In general, models simulate a modestly too vigorous energy cycle and the contributions to and reasons for this are investigated. The results suggest that excessive generation of zonal available potential energy is an important driver of the overactive energy cycle through “generation push” while excessive dissipation of eddy kinetic energy in models is implicated through “dissipation pull‘’. The study shows that “ensemble model” results are best or among the best in the comparison of energy cycle quantities with reanalysis-based values. Thus ensemble approaches are apparently “best” not only for the simulation of 1st order climate statistics as in Lambert and Boer (Clim Dyn 17:83–106, 2001) but also for the higher order climate quantities entering the energy cycle.     

一次东北冷涡发展过程中的能量学研究

对一次典型的东北冷涡过程做了能量学分析。结果表明,东北冷涡活动具有鲜明的阶段性能量学特征。东北冷涡发展之前,各种能量之间的转换很小,边界通量也处于正负相间的振荡状态。早期发展阶段,扰动动能边界通量作用是至关重要的。随着非绝热加热制造扰动有效位能和扰动有效位能向扰动动能转换的大幅度增长,以及外界扰动动能的大量输送和纬向平均动能向扰动动能转换的明显加强,导致了东北冷涡的强烈发展,即这一时期区域内部的能量过程也同样十分重要。东北冷涡的减弱是从有大量扰动动能转换成纬向平均动能开始的,随后加上扰动有效位能向扰动动能转换以及边界通量作用的减弱,使得冷涡逐渐衰亡。     

Maintenance and oscillation mechanisms of summer tropical upper-tropospheric easterlies

The mechanisms of the maintenance and oscillation of 1982 summer tropical 200-hPa mean easterly flow and extra-long waves are investigated in terms of the energy equations in wavenumber-frequency space. Calculation results show that the difference in heating between land and sea and the boundary effect serve as the main source of energy; frictional dissipation as the sink; the conversion of available potential energy into kinetic takes place dominantly in the waves of number 1–2 such transformation is accomplished in just a small amount in zonal mean flow and therefore can be ignored because of the value. In the interaction between wave and zonal mean flow, the latter loses its available potential and gains kinetic energy. The tropical easterly belt over 20°N-5°S is found barotropically stable and that over 10°-5°S, unstable. The waves of number 2 and 1 manifest themselves a primary source and sink of kinetic energy, respectively, in the interplay between waves and between zonal mean flow and wave. It is found that zonal mean flow and the waves of number 1-2 have a roughly 40-and 20-day oscillational period of kinetic energy, respectively, whose primary mechanism is the transfer of barotropic energy, the conversion of baroclinic energy, and the boundary effect.     

MAINTENANCE AND OSCILLATION MECHANISMS OF SUM-MER TROPICAL UPPER-TROPOSPHERIC EASTERLIES

The mechanisms of the maintenance and oscillation of 1982 summer tropical 200-hPa mean easterly flow and extra-long waves are investigated in terms of the energy equations in wavenumber-frequency space. Calculation results show that the difference in heating between land and sea and the boundary effect serve as the main source of energy; frictional dissipation as the sink; the conversion of available potential energy into kinetic takes place dominantly in the waves of number 1-2; such transformation is accomplished in just a small amount in zonal mean flow and therefore can be ignored because of the value.In the interaction between wave and zonal mean flow, the latter loses its available potential and gains kinetic energy. The tropical easterly belt over 20oN-5oS is found barotropically stable and that over 10oN-5oS, unstable. The waves of number 2 and 1 manifest themselves a primary source and sink of kinetic energy, respectively, in the interplay between waves and between zonal mean flow and wave.It is found that zonal mean flow and the waves of number 1-2 have a roughly 40-and 20-day oscillational period of kinetic energy, respectively, whose primary mechanism is the transfer of barotropic energy, the conversion of baroclinic energy, and the boundary effect.     

“96.8”暴雨过程中不同尺度系统的相互作用

利用动能方程计算了天气尺度,次天气尺度的动能以及非线性相互作用的动能,分析了“９６．８”暴雨过程强降水时段的主要动力过程,结果表明：在暴雨系统中,存在着天气尺度和次天气尺度系统间的相互作用,天气尺度动能减小,次天气尺度动能增加,即对于次天气尺度系统而言,天气尺度系统是一个动能源,通过非线性相互作用,天气尺度系统把动能传递给次天气尺度系统,使暴雨系统得以发展。     

Nonlinear energy and enstrophy transfers in a realistically stratified ocean

We discuss the nonlinear transfers possible in a quasigeostrophic fluid with a basic stratification taken from oceanic data. The energy and enstrophy conservation laws imply a cascade of energy to larger total scale (including both the horizontal scale, defined as wavelength/2π, and the deformation radius of the vertical mode). The triplet interactions among components with various horizontal scales and vertical structures, represented by the vertical mode numbers, are considered in detail for exchanges involving the barotropic and first three baroclinic modes. The initial transfer rates from one component into the other two are estimated and the most rapid transfers described as a function of the initial scale and mode number. These results suggest that barotropic motions will cascade to larger-scale barotropic motions, first baroclinic small-scale motions will transfer to first baroclinic larger scales, and first baroclinic large-scale motions will cascade to barotropic and first baroclinic motions at the deformation scale. Second and third mode motions prefer to transfer energy into small-scale (second or third mode deformation radius) first and third baroclinic mode motions.We also show the relationship of these triplet interactions to Rossby wave instabilities and resonant triads. For the latter motions, the weakness of the nonlinearity adds additional constraints which impty that the motions will tend to become zonal.