Sensitivity of transient eddies to climate change in the CCC general circulation model

Abstract

We use eddy life‐cycle simulations to evaluate the response of atmospheric transient eddies to a global warming caused by CO₂ doubling in the CCC general circulation model. In simulations using Northern Hemisphere winter conditions, transient waves attain larger kinetic energy and encompass a wider range of latitudes in the warmer climate. This behaviour contrasts with a previous investigation that used output from the NCAR and GFDL models. Our analysis indicates two primary factors for the difference between model responses: (1) a smaller change in the mid‐latitude temperature gradient in the CCC model, which allows (2) increased atmospheric water vapour in mid‐latitudes to catalyze a more rapidly evolving life‐cycle.     

Assessment of atmosphere-ocean general circulation model simulations of winter northern hemisphere atmospheric blocking

An assessment of six coupled Atmosphere-Ocean General Circulation Models (AOGCMs) is undertaken in order to evaluate their ability in simulating winter atmospheric blocking highs in the northern hemisphere. The poor representation of atmospheric blocking in climate models is a long-standing problem (e.g. D’Andrea et?al. in Clim Dyn 4:385–407, 1998), and despite considerable effort in model development, there is only a moderate improvement in blocking simulation. A modified version of the Tibaldi and Molteni (in Tellus A 42:343–365, 1990) blocking index is applied to daily averaged 500?hPa geopotential fields, from the ERA-40 reanalysis and as simulated by the climate models, during the winter periods from 1957 to 1999. The two preferred regions of blocking development, in the Euro-Atlantic and North Pacific, are relatively well captured by most of the models. However, the prominent error in blocking simulations consists of an underestimation of the total frequency of blocking episodes over both regions. A more detailed analysis revealed that this error was due to an insufficient number of medium spells and long-lasting episodes, and a shift in blocking lifetime distributions towards shorter blocks in the Euro-Atlantic sector. In the Pacific, results are more diverse; the models are equally likely to overestimate or underestimate the frequency at different spell lengths. Blocking spatial signatures are relatively well simulated in the Euro-Atlantic sector, while errors in the intensity and geographical location of the blocks emerge in the Pacific. The impact of models’ systematic errors on blocking simulation has also been analysed. The time-mean atmospheric circulation biases affect the frequency of blocking episodes, and the maximum event duration in the Euro-Atlantic region, while they sometimes cause geographical mislocations in the Pacific sector. The analysis of the systematic error in time-variability has revealed a negative relationship between the high-frequency variability of the transient eddies in the areas affected by blocking and blocking frequency. The blocking responses to errors in the low-frequency variability are different according to the region considered; the amplitude of the low-frequency variability is positively related to the blocking frequency and persistence in the Euro-Atlantic sector, while no such consistency is observed in the Pacific.     

北半球夏季西北太平洋热带地区西南季风强弱变化与南半球环流型的关系

本文分析了1978年夏季西北太平洋西南季风的强弱变化与南半球500mb环流形势的关系,发现当南半球出现经向环流型时,西南季风相应增强,反之,出现纬向环流型时,西南季风则减弱。 在南半球稳定的经向环流形势控制下,冷空气可以影响到低纬地带,高空长波槽后冷高压北侧的东南大风在其相对固定的通道上形成一股强而持久的越赤道气流,在北半球环流条件有利的情况下,这股越赤道气流可以在西北太平洋上转向成西南气流,导致该地区西南季风增强。由于南半球的长波槽容易在澳洲大陆东西两岸同时停滞加深,因此越赤道气流的路径则相对集中在这两     

关于夏季东亚大气环流的研究

东亚位于世界最大的欧亚大陆东部,具有世界最高的大高原——我国青藏高原,东、南毗连广大海洋——太平洋和印度洋,地理特征在全球范围内富有鲜明的特点,因此这一地区的大气环流及其相连系的天气过程也具有许多复杂的鲜明的特色。我国气象学研究工作者在五十年代就对东亚大气环流作了一系列研究,引起国内外的注意。东亚是世界上最著名的季风活动区域之一,夏季的大气环流及天气过程更为特殊和复杂,在天气预报上也更为重要,因此六十年代以来,对这方面的研究日益增多,为了纪念我们伟大的祖国建国30周年,本文回顾了有关东亚夏季大气环流的研究。     

A low latitude general circulation model

Summary The primitive equations of motion are solved to find peak latitudes of families of trajectories of air moving from low latitudes towards the pole from a state of rest under the action of a constant meridional pressure gradient. The general case is discussed first and then calculations are applied to the 20° West meridian in January and July for the Northern Hemisphere.The resulting mass transposition indicates that a belt of convergence should occur at about 32° N in January; this agrees well with the latitude of the axis of the mean sub-tropical high pressure belt at that time of year.The nature of the climatological model in low latitudes suggested by the calculation is then discussed.

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Zusammenfassung Die vereinfachten Bewegungsgleichungen werden gelöst, um Scheitelbreiten für Trajektorienscharen der Luftbewegungen zu finden, die ausgehend von dem Ruhezustand unter Einwirkung eines konstanten meridionalen Druckgradienten polwärts gerichtet sind. Der allgemeine Fall wird diskutiert und es werden Berechnungen für den 20. westlichen Längengrad der Nordhemisphäre für Januar und Juli durchgeführt.Der resultierende Massentransport zeigt, daß im Januar in 32° N ein Konvergenzgürtel auftreten sollte. Dies stimmt gut überein mit der geographischen Breite der Achse des mittleren subtropischen Hochdruckgürtels zu dieser Jahreszeit.Schließlich wird die Form des klimatologischen Modells für niedere Breiten, das durch diese Berechnungen nahegelegt wird, diskutiert.

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Résumé Résolution des équations simpflifiées du mouvement pour déterminer l'origine des faisceaux de trajectoires des courants aériens qui, partant du repos, sont dirigés vers le pôle sous l'effet d'un gradient constant de pression méridien. Discussion du cas général; calcul pour le 20^e méridien Ouest de l'hémisphère Nord en janvier et en juillet.Le transport de masse résultant montre qu'il doit y avoir en janvier, a 32° de latitude Nord, une ceinture de convergence ce qui concorde bien avec la latitude de l'axe de la zone moyenne des hautes pressions subtropicales en cette saison.Forme du modèle climatologique aux basses latitudes suggéré par ces calculs.

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High-frequency patterns of the atmospheric circulation over the southern hemisphere and South America

Summary Daily 500-hPa geopotential height and 250-hPa meridional wind reanalyzed data obtained from the National Centers for Environmental Prediction are used to document austral winter (May to September) and summer (November to March) high-frequency variability in the Southern Hemisphere (SH) midlatitudes for the 1990–1994 period. Empirical orthogonal function (EOF) technique is used to determine the high-frequency patterns for these variables in selected areas. The high-frequency anomalous 500-hPa geopotential height patterns for two areas in the SH midlatitudes (the zonally global domain and the western hemisphere) and the high-frequency anomalous 250-hPa meridional wind patterns in the western hemisphere between 15° N and 70° S are discussed. The high-frequency winter and summer patterns for both variables feature a wavetrain structure in the SH midlatitudes which is related to synoptic-scale systems, such as cyclones and anticyclones associated with frontal zones. The dominant high-frequency patterns in the SH midlatitudes manifest in the eastern hemisphere while the secondary ones appear in the southeastern Pacific. Analysis of the western hemisphere data reveal that the wavetrain in the South American sector extends northeastward over the continent, thus affecting the regional weather conditions. An important result presented here concerns the preference of the intense synoptic systems in the eastern hemisphere and in the southeastern Pacific to occur in a sequential instead of an intermittent fashion. This result might have a potential for being used in weather monitoring.     

Signature of a southern hemisphere extratropical influence on the summer monsoon over India

The weakening relationship of El Nino with Indian summer monsoon reported in recent years is a major issue to be addressed. The altered relationships of Indian monsoon with various parameters excite to search for other dominant modes of variability that can influence the precipitation pattern. Since the Indian summer monsoon circulation originates in the oceanic region of the southern hemisphere, the present study investigates the association of southern extratropical influence on Indian summer monsoon using rainfall and reanalysis parameters. The effect of Southern Annular Mode (SAM) index during the month of June associated with the onset phase of Indian summer monsoon and that during July–August linked with the active phase of the monsoon were analysed separately for a period from 1951 to 2008. The extra-tropical influence over the monsoon is illustrated by using rainfall, specific humidity, vertical velocity, circulation and moisture transport. The June high SAM index enhances the lower level wind flow during the onset phase of monsoon over Indian sub-continent. The area of significant positive correlation between precipitation and SAM in June also shows enhancement in both ascending motion and specific humidity during the strong phase of June SAM. On the other hand, the June high SAM index adversely affects July–August monsoon over Indian subcontinent. The lower level wind flow weakens due to the high SAM. Enhancement of divergence and reduction in moisture transport results in the Indian monsoon region due to the activity of this high southern annular mode. The effect is more pronounced over the southwest region where the precipitation spell has high activity during the period. Significant correlation exists between SAM and ISMR, even after removing the effect of El Nino. It indicates that the signals of Indian summer monsoon characteristics can be envisaged to a certain extend using the June SAM index.     

A numerical world ocean general circulation model

This paper describes a numerical model of the world ocean based on the fully primitive equations. A “Standard” ocean state is introduced into the equations of the model and the perturbed thermodynamic variables are used in the modle’s calculations. Both a free upper surface and a bottom topography are included in the model and a sigma coordinate is used to normalize the model’s vertical component. The model has four unevenly-spaced layers and 4 × 5 horizontal resolution based on C-grid system. The finite-difference scheme of the model is designed to conserve the gross available energy in order to avoid fictitious energy generation or decay.The model has been tested in response to the annual mean surface wind stress, sea level air pressure and sea level air temperature as a preliminary step to its further improvement and its coupling with a global atmospheric general circulation model. Some of results, including currents, temperature and sea surface elevation simulated by the model are presented.     

一个灵活的海洋——大气耦合环流模式

Based on the National Center for Atmospheric Research (NCAR) Climate System Model version 1(CSM-1), a Flexible coupled General Circulation Model version 0 (FGCM-0) is developed in this study through replacing CSM-1＇s oceanic component model with IAP L30T63 global oceanic general circulation model and some necessary modifications of the other component models. After the coupled model FGCM--0 is spun up for dozens of years, it has been run for 60 years without flux correction. The model does not only show the reasonable long-term mean climatology, but also reproduce a lot of features of the interannual variability of climate, e.g. the ENSO-like events in the tropical Pacific Ocean and the dipole mode pattern in the tropical Indian Ocean. Comparing FGCM-0 with the NCAR CSM-1, some common features are found, e.g. the overestimation of sea ice in the North Pacific and the simulated double ITCZ etc.The further analyses suggest that they may be attributed to errors in the atmospheric model.     

Relationships between the global general circulation and the indian summer monsoon

The relationships between the global general circulation and the Indian monsoon during active and break phases are investigated with the help of FGGE IIIb data.It was found that the ultralong wave component positive and negative height anomalies over Tibet are associated with active and break monsoon phases respectively. This ultralong wave component has significant effect even upto 22oN over the Indian region which is the monsoon trough region. During a monsoon break, the general circulation was found to be more turbulent in the sense that more waves become energised.It was observed that during a break, blocking prevails over the Siberian region and cold air advection takes place toward Indian region from Siberian region depressing the temperatures over the Indian region by about 1oC. During the break, the Indian region gets connected with higher latitudes by the south winds blowing from polar Soviet re-gions to the Indian region. From active to break phase the zonal component weakens by about 25% from Indian ocean area right upto Alaskan region, along the east coast of Asia.     

湿过程对北半球夏季大气环流的作用

本文在Lorenz低谱湿模式中,引进温度和全露点温度垂直递减率随空间、时间的变化,积云对流调整和地形,设计与实施了十个时间积分大于90天的数值试验.结果指出:小尺度湿对流与大尺度环境场的相互作用,使对流上层增暖,下层变干,平均纬向风速极大值减小,非绝热加热场水平梯度加大,流型经向度及副热带高压强度增加. 从不同的初始场、不同的湿对流调整范围、不同的副热带高压强度演变方向所进行的试验均表明:湿过程与大尺度环境场的相互作用,使模拟的副热带高压加强.这意昧着湿过程在夏季副热带高压的形成、发展和维持方面,可能有着实质性的作用.     

A Nine-layer Atmospheric General Circulation Model and Its Performance

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Simulation of the summer Indian monsoon beginning during the experiments with the atmosphere general circulation model of Hydrometcenter of Russia

The influence of the Earth’s gravitational field on the simulation of the time of the beginning of monsoon circulation in Asia by the model is analyzed. The results of numerical experiments carried out with the circulation model of the Hydrometcenter of Russia during ten years (1979–1988) following the AMIP protocol are considered. Two standards were used during the analysis of results. The data of NCEP/NCAR (the United States) reanalysis were used for the comparison of circulation characteristics and the data of GPCP (Global Precipitation Climatology Project), for the precipitation analysis. Four different criteria of the monsoon beginning are analyzed: the occurrence of the negative divergence in the area under study, the beginning of heavy precipitation fall, the marked kinetic energy increase in the lower troposphere, and the origination of anticyclonic vorticity. The comparison of the data obtained during the numerical experiments with the chosen standards demonstrated that, in all cases, taking account of gravitation field variations results in the improvement of the simulation of the time of monsoon circulation beginning by the model.     

基于T106L26全球大气环流模式的夏季集合预报

使用国家气候中心新一代大气环流模式BCC_AGCM2.0(T106L26)进行22 a夏季(6-8月)、11个成员的集合回报试验;针对500 hPa高度场、降水和气温的预测能力进行交叉检验,并计算其均方根误差.结果表明:模式对热带地区、海洋和欧亚大陆部分地区500 hPa高度场的模拟较好;对我国长江中下游、华南大部分地区降水的模拟具有一定可信度;2m温度距平在我国北方大部分地区呈现正相关且相关系数通过90％的信度检验,在南方地区则有待改善.集合预报效果好于单样本预报.模式分辨率的提高在一定程度上有助于改进预报效果.     

A comparative study of the observations of high clouds and simulations by an atmospheric general circulation model

The importance of clouds in the upper troposphere (cirrus) for the sensitivity of the Earth's climate e.g., requires that these clouds be modeled accurately in general circulation model (GCM) studies of the atmosphere. Bearing in mind the lack of unambiguous quantitative information on the geographical distribution and properties of high clouds, the simulated distribution of upper tropospheric clouds in a spectral GCM is compared with several satellite-derived data-sets that pertain to high clouds only, for both winter and summer seasons. In the model, clouds are assumed to occupy an entire gridbox whenever the relative humidity exceeds 99%: otherwise the grid box is assumed to be free of cloud. Despite the simplicity of the cloud prediction scheme, the geographical distribution of the maxima in the model's upper tropospheric cloud cover coincides approximately with the regions of the observed maxima in the high cloud amount and their frequency of occurrence (e.g., intertropical convergence zone and the monsoon areas). These areas exhibit a minimum in the outgoing longwave radiation (OLR; Nimbus-7) and are also coincident with regions of heavy precipitation. The model, with its relatively simple cloud formation scheme, appears to capture the principal large-scale features of the tropical convective processes that are evident in the satellite and precipitation datasets, wherein the intense, upward motion is accompanied by condensation and the spreading of thick upper tropospheric layers of high relative humidity and cloudiness in the vicinity of the tropical rainbelt regions.This paper was presented at the International Conference on Modelling of Global Climate Change and Variability, held in Hamburg 11–15 September 1989 under the auspices of the Meteorological Institute of the University of Hamburg and the Max Planck Institute for Meteorology. Guest Editor for these papers is Dr. L. Dümenil     

Seasonality of the Interaction between Convection over the Western Pacific and General Circulation in the Northern Hemisphere

The seasonality of the interaction between convection over the western Pacific and general circulation in the Northern Hemisphere (NH) is analyzed in the present paper with singular value decomposition (SVD) and empirical orthogonal function (EOF) analysis approaches, based on 500 hPa monthly mean geopotential height data and high-cloud amount data. The analyses demonstrate that coupled dominant patterns in the interaction between the convection over the western Pacific and the general circulation in NH are different in various seasons. In spring, the convection over the western Pacific is closely related with the western Atlantic (WA) and North Pacific (NP) like patterns of the general circulation in NH, and some associations between the WA and NP like pat?terns and the El Ni?o / Southern Oscillation (ENSO) cycle are also existed. The Pacific Japan (PJ) pattern is the dom?inant pattern in the interaction between the interannual variabilities of the convection over the western Pacific and the general circulation in NH summer. The WA like pattern and 3-4 year period oscillation are also relatively obvious for the summer case. In autumn, the convection over the western Pacific is closely linked with the Eurasian (EU) like pattern and the Atlantic oscillation in the general circulation in NH, it is suggested that in autumn the vitiation of convective activity over the western Pacific is largely affected by the general circulation anomaly (cold air from high latitudes) through EU like teleconnection pattern. Abrupt change happened by the end of 1980’s in the autumn interaction. The strong interaction between the western Pacific (WP) and EU like patterns in the general circulation in NH and the convection over the western Pacific and a linear trend of increasing of this interaction are also suggested in winter. It is also demonstrated that the interaction in summer and winter is stronger than in the transition seasons (spring and autumn).     

A global ocean biogeochemistry general circulation model and its simulations

An ocean biogeochemistry model was developed and incorporated into a global ocean general circulation model (LICOM) to form an ocean biogeochemistry general circulation model (OBGCM). The model was used to study the natural carbon cycle and the uptake and storage of anthropogenic CO2 in the ocean. A global export production of 12.5 Pg C yr-1 was obtained. The model estimated that in the pre-industrial era the global equatorial region within 15o of the equator released 0.97 Pg C yr-1 to the atmosphere, which was balanced by the gain of CO2 in other regions. The post-industrial air-sea CO2 flux indicated the oceanic uptake of CO2 emitted by human activities. An increase of 20－50 mol kg-1 for surface dissolved inorganic carbon (DIC) concentrations in the 1990s relative to pre-industrial times was obtained in the simulation, which was consistent with data-based estimates. The model generated a total anthropogenic carbon inventory of 105 Pg C as of 1994, which was within the range of estimates by other researchers. Various transports of both natural and anthropogenic DIC as well as labile dissolved organic carbon (LDOC) were estimated from the simulation. It was realized that the Southern Ocean and the high-latitude region of the North Pacific are important export regions where accumulative air-sea CO2 fluxes are larger than the DIC inventory, whereas the subtropical regions are acceptance regions. The interhemispheric transport of total natural carbon (DIC+LDOC) was found to be northward (0.11 Pg C yr-1), which was just balanced by the gain of carbon from the atmosphere in the Southern Hemisphere.     

Winter season stratospheric circulation in the SAMIL/LASG general circulation model

In this paper, we examine the performance of the 26-level version of the SAMIL/LASG GCM (R42/L26) in simulating the seasonal cycle and perpetual winter mean stratospheric circulation as well as its variability by comparing them with the NCEP/NCAR reanalysis. The results show that the model is capable of reproducing many key features of the climatology and seasonal variation of the stratospheric circulation despite that the model’s mean polar vortex is stronger and more zonally symmetric compared to the obse...