共查询到20条相似文献，搜索用时 62 毫秒
1.
《Dynamics of Atmospheres and Oceans》1998,28(1):1-7
Mass and momentum conservation across an internal bore, together with an assumption that energy is dissipated in both fluid layers, yields a range of possible bore speeds. The upper speed limit is that given by Wood and Simpson [Wood, I.R., Simpson, J.E., 1984. Jumps in layered miscible fluids. J. Fluid Mech., 140: 215–231.] who assume no energy dissipation in the contracting layer, while the lower limit is that of Klemp et al. [Klemp, J.B., Rotunno, R., Skamarock, W.C., 1997. On the propagation of internal bores. J. Fluid Mech., 331: 81–106] who assume no energy dissipation in the expanding layer. The two bore speeds agree to within a few percent, except when the expanding layer is shallow upstream and the internal bore propagates as a gravity current. 相似文献
2.
Available potential energy in the atmosphere 总被引：2，自引：0，他引：2
Y. L. McHall 《Meteorology and Atmospheric Physics》1990,42(1):39-55
Summary The study of available potential energy is approached in a new way. According to the second law of thermodynamics, we may find, from among the states which can be attained through all the actual processes in an isolated atmosphere, the limit state, referred to as the lowest state, that is achieved by means of reversible processes and possesses the least total potential energy. Thus, the maximum available potential energy can be estimated by taking the lowest state as the reference state. The variations of the lowest state and maximum available potential energy with baroclinity and mean static stability are illustrated graphically as some examples in the text. This study gives a more fundamental understanding for the kinetic energy generation in the baroclinic atmosphere. Also, the extreme kinetic generation in irreversible processes is investigated. The obtained results may be adopted for the energetics of explosive systems in the atmosphere.With 10 Figures 相似文献
3.
Y. L. McHall 《Meteorology and Atmospheric Physics》1991,45(3-4):113-123
Summary The equivalent potential energy of the moist atmosphere is defined as the sum of its total potential energy and latent heat. The available equivalent potential energy is the amount of equivalent potential energy available for conversion into kinetic energy. For the isolated moist atmospheres, we may find the equivalent lowest state which is the limit of the states attained through all the actual processes involving water condensation and possesses the least equivalent potential energy. Thus, the maximum available equivalent potential energy with respect to the equivalent lowest state can be estimated for any provided initial state. This study may extend the understanding for the development of precipitation systems in the moist atmosphere.With 5 Figures 相似文献
4.
The surface energy budget components from two simulations of the regional climate model RegCM4.2 over the European/North African domain during the period 1989–2005 are analysed. The simulations differ in specified boundary forcings which were obtained from ERA-Interim reanalysis and the HadGEM2-ES Earth system model. Surface radiative and turbulent fluxes are compared against ERA-Interim. Errors in surface radiative fluxes are derived with respect to the Global Energy and Water Cycle Experiment/Surface Radiation Budget satellite-based products. In both space and time, we find a high degree of realism in the RegCM surface energy budget components, but some substantial errors and differences between the two simulations are also present. The most prominent error is an overestimation of the net surface shortwave radiation flux of more than 50 W/m2 over central and southeastern Europe during summer months. This error strongly correlates with errors in the representation of total cloud cover, and less strongly with errors in surface albedo. During other seasons, the amplitude of the surface energy budget components is more in line with reference datasets. The errors may limit the usefulness of RegCM simulations in applications (e.g. high-quality simulation-driven impact studies). However, by using a simple diagnostic model for error interpretation, we suggest potential sensitivity studies aiming to reduce the underestimation of cloud cover and overestimation of shortwave radiation flux. 相似文献
5.
T. N. Krishnamurti M. C. Sinha Vasubandhu Misra O. P. Sharma 《Dynamics of Atmospheres and Oceans》1998,27(1-4)
Over the upper troposphere of the polar latitudes the zonal flows exhibit a large variance on the time scale of the Madden-Julian oscillation, i.e. roughly 30–50 days. The other prominent regions for these intraseasonal oscillations are the Asian and Australian monsoon belts. These two regions are separated by the so-called critical latitude, to the south of which easterlies generally prevail and westerlies are prevalent to the north. A perplexing issue is that of possible tropical-middle latitude interactions across the critical latitude. The notion of the critical latitude emerged from the linear theories for the wave energy flux which assume a constancy in time for the zonal flows. This same problem, viewed in its full non-linear context, can be cast in a frequency domain. Such a formulation does not assume a constancy of the zonal flows in time but does permit the intraseasonal variations of the zonal flows to be present. The computation of the wave energy flux, from the more complete non-linear system in the frequency domain, requires the handling of linear, quadratic and triple product terms via use of Hayashi's co-spectral method. These results of the present study, based on 6 years of daily global data sets, show that wave energy flux clearly passes from the latitudes of the monsoon to the polar latitudes. A strong convergence of wave energy flux in the polar latitudes suggests the tropical-middle latitude convergence interactions across the so-called critical latitude—when the problem is viewed in the frequency domain. 相似文献
6.
It is increasingly clear that averting ecological breakdown will require drastic changes to contemporary human society and the global economy embedded within it. On the other hand, the basic material needs of billions of people across the planet remain unmet. Here, we develop a simple, bottom-up model to estimate a practical minimal threshold for the final energy consumption required to provide decent material livings to the entire global population. We find that global final energy consumption in 2050 could be reduced to the levels of the 1960s, despite a population three times larger. However, such a world requires a massive rollout of advanced technologies across all sectors, as well as radical demand-side changes to reduce consumption – regardless of income – to levels of sufficiency. Sufficiency is, however, far more materially generous in our model than what those opposed to strong reductions in consumption often assume. 相似文献
7.
Observational analyses have demonstrated that the Hadley circulation has expanded poleward in recent decades. Important issues are what caused the widening of the Hadley circulation and whether the observed widening is related to anthropogenic forcing. In the present study, we use currently available simulations of the Coupled Model Intercomparison Project Phase-5 (CMIP5) to analyze changes in the width of the Hadley circulation. It is found that CMIP5 historical simulations with greenhouse gas (GHG) forcing generate a total widening of ～0.15o0.06o in latitude (10 yr)-1 for the period 1979--2005, and the widening in CMIP5 historical simulations with all forcings is ～0.17o0.06o per decade. Similar to that in CMIP3, the simulated poleward expansion in CMIP5 is much weaker than the observational reanalyses. In CMIP5 projection simulations for the 21st century, magnitudes of widening of the Hadley circulation increase with radiative forcing. For the extreme projected radiative forcing of RCP8.5, the total annual-mean widening of the Hadley circulation is ～0.27o0.04o(10 yr)-1 in the 21st century. Although CMIP5 underestimates observed poleward expansion of the Hadley circulation, the results of this study suggest that the observed trends in the width of the Hadley circulation are caused by anthropogenic forcing and that increasing GHGs play an important role in the observed poleward expansion of the Hadley circulation, in addition to other forcings emphasized in previous studies. 相似文献
8.
J. Bendtsen 《Climate Dynamics》2002,18(7):595-609
A simple coupled ocean, atmosphere and sea-ice model is presented. The idealised model consists of a zonally averaged land and ocean strip of constant angular width extending from pole to pole. The meridional energy transport in the ocean is modelled by contributions from the large scale thermohaline overturning cells and from horizontal diffusive fluxes. The atmospheric meridional energy transports are parametrised as diffusive fluxes in addition to advective transports in the Hadley domain. This parametrisation resolves the equatorward moisture transport as well as the poleward transport of potential energy in the upper branch of the Hadley circulation. The model reproduces the annual averaged meridional energy transports in the climate system with a small number of free model parameters. The basic feedbacks between the three climatic components are studied by investigating the model's sensitivity towards reductions in the solar insolation. It is found that the meridional energy transport in the ocean does not amplify the ice albedo feedback. This has important implications for modelling the climate sensitivity in atmosphere-only models, as these would exaggerate the sensitivity to changes in the solar insolation if their parametrisations of the meridional energy transport are constrained by surface temperatures. The role of the dependence of the atmospheric transports on the meridional temperature gradient is shown to have a significant influence on the sensitivity on the coupled model, and the inclusion of seasonal cycles greatly increase the models sensitivity. The Hadley circulation does significantly alter the strength of the ice-albedo feedback in the coupled model. The idealised configuration of the model makes it a useful tool for studying the feedbacks in the ocean-atmosphere-sea ice system in the context of the "Snowball Earth" hypothesis. 相似文献
9.
Previous studies suggested that there are large discrepancies in the intensity trend of the zonally averaged Hadley circulation (ZAHC) among different reanalyses. As the land, ocean, and topography are not evenly distributed, the ZAHC may mask the regional variability. Changes in the regional HC have important implications for regional climate change. Here, we detect the long-term trend of the boreal spring regional Hadley circulation intensity over the western Pacific (WPHC) since 1979 in both hemispheres using six reanalysis datasets. Unlike the ZAHC, we find that the trend of the spring WPHC intensity is consistent among various reanalysis datasets. All reanalyses show pronounced strengthening trends for the WPHC in both the Northern and Southern Hemisphere, which may be partly attributable to the robust warming trends of sea surface temperature in the tropical western Pacific. The result could improve our understanding of Hadley circulation variability at the regional scale and has implications for regional climate changes. 相似文献
10.
We use the coupled atmosphere–ocean general circulation model ECHAM5/MPI-OM to investigate the transition from the present-day
climate to a modern Snowball Earth, defined as the Earth in modern geography with complete sea-ice cover. Starting from the
present-day climate and applying an abrupt decrease of total solar irradiance (TSI) we find that the critical TSI marking
the Snowball Earth bifurcation point is between 91 and 94% of the present-day TSI. The Snowball Earth bifurcation point as
well as the transition times are well reproduced by a zero-dimensional energy balance model of the mean ocean potential temperature.
During the transition, the asymmetric distribution of continents between the Northern and Southern Hemisphere causes heat
transports toward the more water-covered Southern Hemisphere. This is accompanied by an intensification of the southern Hadley
cell and the wind-driven subtropical ocean cells by a factor of 4. If we set back TSI to 100% shortly before the transition
to a modern Snowball Earth is completed, a narrow band of open equatorial water is sufficient for rapid melting. This implies
that for 100% TSI the point of unstoppable glaciation separating partial from complete sea-ice cover is much closer to complete
sea-ice cover than in classical energy balance models. Stable states can have no greater than 56.6% sea-ice cover implying
that ECHAM5/MPI-OM does not exhibit stable states with near-complete sea-ice cover but open equatorial waters. 相似文献
11.
CHARACTERISTICS OF THE NORTHERN HEMISPHERE SUB-TROPICAL HIGH SEASONAL SPLITTING OVER THE ASIAN
MONSOON SECTORS AND ITS POSSIBLE MECHANISM 总被引：1，自引：1，他引：1
The splitting of the Northern Hemisphere sub-tropical high (SH) during spring to summer and its possible mechanisms has been analyzed. Results indicate that the splitting of SH occurs over the Bay of Bengal to the Indo-China peninsula. However, remarkable contrast exists in the Hadley cell at the lower and upper levels over these sectors during March to May. The land surface sensitive/latent heating both play an important role, and decay the local Hadley cell over the Indo-China peni… 相似文献
12.
L. Haimberger B. Ahrens F. Hamelbeck M. Hantel 《Meteorology and Atmospheric Physics》2001,77(1-4):167-184
Summary Diagnostic time-mean budgets of energy and water are evaluated in many atmospheric process studies. The errors of budget-derived
quantities like sub-gridscale fluxes or diabatic heating are governed by the errors of the budgets. Here we consider 3D-budgets
on the meso-β scale over Europe. They are compiled from analyses of state quantities available from forecast centres.
In the present study we found that the mandatory 6 hours sampling interval between synoptic observations is the main error
source for routine time-mean budgets. The errors have been quantified (i) by first sampling forecast data of the German Europamodell every 5 minutes and averaging them over 12 hours (reference budget), and (ii) by sampling the same data only every 6 hours and averaging these also over 12 hours (routine budget). With this method we find that routine budgets in single atmospheric meso-β scale columns show relative random errors
of typically 200% and systematic errors of up to 20%, exclusively due to undersampling. Thus routine budgets, if applied to
specific days at individual locations, cannot be expected to yield useful results, except perhaps for cases with extremely
strong signal. Compositing over several hundreds of columns with similar weather reduces the random budget error down to about
50%; this seems to be the best one can achieve for routine budgets. The systematic error of some budget quantities is caused
by a correlation between the time of occurence of certain processes (mainly convection) and the sampling times. While this
error cannot be reduced through compositing, we find that it can be crudely estimated by using different time averaging methods.
As application for this method we determine sub-gridscale budget quantities over the BALTEX catchment (August-September 1995)
for an ensemble of convectively active and an ensemble of rain-active columns. For the ensemble mean profiles we find, in
terms of the diagnosed sub-gridscale test quantities diabatic heating and vertical moist enthalpy flux divergence, that their
accuracy is sufficient to detect statistically significant differences between both ensembles. The diabatic heating is about
the same for both ensembles, while the flux divergence in the convective ensemble is about three times as large as in the
rain ensemble.
Received November 7, 2001 Revised April 4, 2001 相似文献
13.
The major features of the westerly jets in boreal winter, consisting of the Middle East jet stream (MEJS), East Asian jet stream (EAJS) and North Atlantic jet stream (NAJS), simulated by a newly developed climate system model, were evaluated with an emphasis on the meridional location of the westerly jet axis (WJA). The model was found to exhibit fairly good performance in simulating the EAJS and NAJS, whereas the MEJS was much weaker and indistinguishable in the model. Compared with the intensity bias, the southward shift of the WJA seems to be a more remarkable deficiency. From the perspective of Ertel potential vorticity, the profiles along different westerly jet cores in the model were similar with those in the reanalysis but all shifted southward, indicating an equatorward displacement of the dynamic tropopause and associated climatology. Diagnosis of the thermodynamic equation revealed that the model produced an overall stronger heating source and the streamfunction quantifying the convection and overturning Hadley circulation shifted southward significantly in the middle and upper troposphere. The two maximum centers of eddy kinetic energy, corresponding to the EAJS and NAJS, were reproduced, whereas they all shifted southwards with a much reduced intensity. A lack of transient eddy activity will reduce the efficiency of poleward heat transport, which may partially contribute to the meridionally non-uniform cooling in the middle and upper troposphere. As the WJA is closely related to the location of the Hadley cell, tropopause and transient eddy activity, the accurate simulation of westerly jets will greatly improve the atmospheric general circulation and associated climatology in the model. 相似文献
14.
Tropical precipitation, SSTs and the surface energy budget: a zonally symmetric perspective 总被引：1，自引：1，他引：0
The relative importance of sea surface temperatures (SSTs) and the surface energy budget to tropical precipitation is examined by comparing models with zonally symmetric climates, both fixed SST and coupled to a slab mixed layer ocean. Two models are considered with differing surface flux formulations and in each case solutions that are symmetric about the equator are perturbed to create interhemispheric asymmetry. When SSTs are prescribed in the two models with different flux formulations, the magnitude of tropical precipitation response to identical SST anomalies is significantly different, but the differences can be understood in terms of the altered surface fluxes. In contrast, when the net surface energy fluxes are constrained to be identical in mixed layer simulations of the two different models, the response of tropical precipitation to perturbations in the surface energy balance is very similar. Both perspectives predict qualitatively the same precipitation response, but the energy budget better predicts the magnitude of the precipitation response. Thus, we argue that the atmospheric energy budget, controlled in these experiments primarily by the surface energy budget, is more fundamental to the control of tropical precipitation than the SSTs, in these simulations with axisymmetric climates. We touch briefly on a complication in the interpretation of the model results due to the fact that fixed SST and slab-ocean versions of the model can produce different Hadley cell strengths for the same SSTs. 相似文献
15.
Two numerical simulations of forced local Hadley circulation are carried out based on a linear diagnostic equation to provide
an insight into the mechanisms of monsoon evolution in different monsoon regions. One simulation is for the zonal mean Hadley
circulation over East Asia (from 95°E to 122.5°E), another over India (from 70°E to 85°E).
With the NCEP/ NCAR re-analysis data re—processed by Chinese Academy of Science in Beijing, the former simulation displays
a dominant anti—Hadley circulation pattern over East Asia at 1200 UTC May 1, 1994. The simulated circulation pattern is consistent
well enough with the circulation pattern plotted directly from the data for lack of the radiation information at each level.
Although the simulation over India is not as good as that over East Asia, a dominant Hadley circulation pattern is obvious
as data show. Further analysis shows that the defective simulation over India is due to the presence of statically unstable
condition at some grid points in the lower troposphere. This circumstance slightly violates the hydrodynamic stability criterion
required by the elliptic diagnostic equation for the forced circulation.
Since the simulations are reliable enough compared with the given data, the linear equation facilitates a systematic assessment
of relative importance of each internally forcing process. The assessment shows that among the internal processes, the horizontal
temperature advections account obviously for the Hadley (anti—Hadley) circulation over India (East Asia) at 1200 UTC May 1,
1994 in addition to the process associated with the latent heat releasing. The calculation of latent heat energy is a little
bit unreliable due to the unclear cloud physics in the convection processes and the less accurate humidity data. These preliminary
results are consistent with the results of previous studies which show that the feature of the seasonal warming in the upper
troposphere and the corresponding processes are part of key processes closely related to the evolution of the summer monsoon
over East Asia and India.
This work was supported by the “ National key programme of China for developing basic science” G 1998040900 part 1, NSFC 49675264
and NSFC 49875021. 相似文献
16.
A Comparison between Numerical Simulations of Forced Local Hadley (Anti-Hadley) Circulation in East Asian and Indian Monsoon Regions 总被引：4，自引：0，他引：4
1. IntroductionIt is well known that one of the distinguishable differences between the summer monsoonand the winter monsoon is the reversal of lower--layer winds with southwesterly during theNorthern summer and northeasterly during the Northern winter. Previous studies (e.g. Chenet al., 1991 ) show that on the one hand. this seasonal alternation of the lower--layer winds isassociated with thermal contrast between continents and their adjacent oceans due todifferential heating including radia… 相似文献
17.
18.
Janelle Knox-Hayes Marilyn A. Brown Benjamin K. Sovacool Yu Wang 《Global Environmental Change》2013,23(3):609-622
Energy security is embedded in a complex system encompassing factors that constitute the social environment in which individuals are immersed. Everything from education, to access to resources to policy and cultural values of particular places affects perceptions and experiences of energy security. This article examines the types of energy security challenges that nations face and characterizes the policy responses that are often used to address these challenges. Drawing from a survey of energy consumers in Brazil, China, Germany, India, Kazakhstan, Japan, Papua New Guinea, Saudi Arabia, Singapore, and the United States, we conduct a cross-national comparison of energy security attitudes as well as analyze each country's energy resources, consumption characteristics and energy policies. Through multivariate regression analysis and case studies we find that socio-demographic and regional characteristics affect attitudes towards energy security. Specifically, we find a strong relationship between level of reliance on oil imports and level of concern for a variety of energy security characteristics including availability, affordability and equity. Our results reaffirm the importance of gender and age in shaping perceptions of security, but also extend existing literature by elucidating the impacts of country energy portfolios and policies in shaping climate and security perceptions. Level of development, reliance on oil, and strong energy efficiency policies all affect individuals’ sense of energy security. In sum, we find that energy security is a highly context-dependent condition that is best understood from a nuanced and multi-dimensional perspective. 相似文献
19.
We present a comparison of the zonal mean meridional circulations derived from monthly in situ data (i.e. radiosondes and
ship reports) and from the NCEP/NCAR reanalysis product. To facilitate the interpretation of the results, a third estimate
of the mean meridional circulation is produced by subsampling the reanalysis at the locations where radiosonde and surface
ship data are available for the in situ calculation. This third estimate, known as the subsampled estimate, is compared to
the complete reanalysis estimate to assess biases in conventional, in situ estimates of the Hadley circulation associated
with the sparseness of the data sources (i.e., radiosonde network). The subsampled estimate is also compared to the in situ
estimate to assess the biases introduced into the reanalysis product by the numerical model, initialization process and/or
indirect data sources such as satellite retrievals. The comparisons suggest that a number of qualitative differences between
the in situ and reanalysis estimates are mainly associated with the sparse sampling and simplified interpolation schemes associated
with in situ estimates. These differences include: (1) a southern Hadley cell that consistently extends up to 200 hPa in the
reanalysis, whereas the bulk of the circulation for the in situ and subsampled estimates tends to be confined to the lower
half of the troposphere, (2) more well-defined and consistent poleward limits of the Hadley cells in the reanalysis compared
to the in-situ and subsampled estimates, and (3) considerably less variability in magnitude and latitudinal extent of the
Ferrel cells and southern polar cell exhibited in the reanalysis estimate compared to the in situ and subsampled estimates.
Quantitative comparison shows that the subsampled estimate, relative to the reanalysis estimate, produces a stronger northern
Hadley cell (∼20%), a weaker southern Hadley cell (∼20–60%), and weaker Ferrel cells in both hemispheres. These differences
stem from poorly measured oceanic regions which necessitate significant interpolation over broad regions. Moreover, they help
to pinpoint specific shortcomings in the present and previous in situ estimates of the Hadley circulation. Comparisons between
the subsampled and in situ estimates suggest that the subsampled estimate produces a slightly stronger Hadley circulation
in both hemispheres, with the relative differences in some seasons as large as 20–30%. 6These differences suggest that the
mean meridional circulation associated with the NCEP/NCAR reanalysis is more energetic than observations suggest. Examination
of ENSO-related changes to the Hadley circulation suggest that the in situ and subsampled estimates significantly overestimate
the effects of ENSO on the Hadley circulation due to the reliance on sparsely distributed data. While all three estimates
capture the large-scale region of low-level equatorial convergence near the dateline that occurs during El Nino, the in situ
and subsampled estimates fail to effectively reproduce the large-scale areas of equatorial mass divergence to the west and
east of this convergence area, leading to an overestimate of the effects of ENSO on the zonal mean circulation.
Received: 16 September 1998 / Accepted: 22 April 1999 相似文献
20.
分析了热带太平洋El Nino事件和热带印度洋海盆一致的暖海温异常事件（记为暖海盆模态）与东亚Hadley环流的关系及海温异常对东亚Hadley环流的影响。结果表明：（1）东亚Hadley环流与El Nino循环的关系密切,El Nino事件从开始到消亡的不同位相期,东亚地区表现为随位相变化的异常经向垂直环流,在El Nino成熟期由异常顺时针经向环流圈转换为异常逆时针经向环流圈,意味着东亚Hadley环流圈的显著减弱。（2）冬季Nino3指数、赤道印度洋海盆一致型模态指数（IOBMI）与东亚Hadley环流指数间呈负相关关系,相关系数分别为-0.42、-0.39,远超过0.01信度的显著性检验,表明当El Nino事件和印度洋暖海盆模事件发生时,东亚Hadley环流减弱。模拟结果与诊断分析结果一致。（3）鉴于印度洋海盆模态和太平洋El Nino事件的密切联系,在考虑冬季东亚Hadley环流变化时,应考虑El Nino事件和印度洋海盆一致型海温异常事件的共同作用。数值试验结果表明两大洋的共同作用会产生更强的东亚异常逆时针经向垂直环流,使得东亚Hadley环流显著减弱。 相似文献