Numerical Modelings of the Climatic Effects of the Land-Sea Distribution and Topography

The effects of the land-sea contrast and the topography on the climatic properties are simulated in this paper by use of a p- σ incorporated coordinate system model in a zonal domain. In this paper we firstly discuss the statistical features of the model and find that the capability of the model is stable, with the same land-sea distribution and to-pography seven monthly mean climate states are close to one another, their variance is even less than the initial one. Secondly, we focally discuss the effects of the land-sea contrast and the topography on the modeled climate fields, It is pointed out that the land-sea contrast and the topography influence the atmosphere mainly through the heating ef-fect and the former has larger influences on the simulated large scale climate fields than the latter.     

The climatic effects of the stratospheric volcanic ash

The climatic effects of the stratospheric volcanic ash are simulated. The model we used is a primitive equation model with the P-σ incorporated coordinate system. The model has 5 layers in the atmosphere and 2 layers in the soil. The volcanic ash is introduced to the first (highest) model layer with a fixed optical thickness of 0.1275. Two comparative numerical experiments with and without the volcanic ash are made. Results show that the effects of the stratospheric volcanic ash on the formations of the mean climatic fields are much smaller than those of the land-sea distribution and the large scale topography. However, it does have contributions to the anomalies of the basic climatic states. The direct effect of the volcanic ash is to increase the temperature in the stratosphere. It can also influence the temperature and the height fields of isobaric surfaces, horizontal and vertical motions, precipitation and the surface climate through dynamic and thermodynamic processes in the atmosphere.     

气候变化中下垫面作用的数值模拟

本文利用一个三维数值模式,对下垫面在气候变化中的作用进行了数值模拟.共做了两个均一土壤下垫面试验和一个非均一土壤下垫面试验.结果表明,东半球夏季季风气候区的基本气候特征,主要是由海陆分布和大地形的影响所产生.但是,细致的气候特征却受下垫面土壤物理性质和初始湿度的很大影响.而且,通过环流系统的相互作用,除对本地区天气气候产生影响外,还会影响周围地区.非洲撒哈拉大沙漠的形成很可能是长期受到海陆分布及高原地形所造成的基本气候场作用的结果.     

Numerical modellings of properties of the summer quasi-stationary circulation systems and their monthly variations

An ocean-atmosphere and land-air coupled numerical model system is used to study the basic properties and the monthly time variations of the summer quasi-stationary circulation systems. It is found that either at the upper or at the lower levels of the atmosphere, the circulation patterns have a two-wave structure in the zonal direction at the mid and high latitudes of the Northern Hemisphere. Such a structure of circulation is totally matchable to that of the land-sea distribution there. It is proved, hence, that the land-sea distributive pattern is the fundamental cause for the summer quasi-stationary circulation pattern. The topography in the globe is the secondary factor for circulation systems. The circulation centres of the quasi-stationary systems are always located in certain areas due to the thermodynamic contrast between land and sea.From the time evolutions of the circulation systems it is seen that the change is larger at the beginning period of the time integration, it is because of using t     

Conceptual understanding of climate change with a globally resolved energy balance model

The future climate change projections are essentially based on coupled general circulation model (CGCM) simulations, which give a distinct global warming pattern with arctic winter amplification, an equilibrium land-sea warming contrast and an inter-hemispheric warming gradient. While these simulations are the most important tool of the Intergovernmental Panel on Climate Change (IPCC) predictions, the conceptual understanding of these predicted structures of climate change and the causes of their uncertainties is very difficult to reach if only based on these highly complex CGCM simulations. In the study presented here we will introduce a very simple, globally resolved energy balance (GREB) model, which is capable of simulating the main characteristics of global warming. The model shall give a bridge between the strongly simplified energy balance models and the fully coupled 4-dimensional complex CGCMs. It provides a fast tool for the conceptual understanding and development of hypotheses for climate change studies, which shall build a basis or starting point for more detailed studies of observations and CGCM simulations. It is based on the surface energy balance by very simple representations of solar and thermal radiation, the atmospheric hydrological cycle, sensible turbulent heat flux, transport by the mean atmospheric circulation and heat exchange with the deeper ocean. Despite some limitations in the representations of the basic processes, the models climate sensitivity and the spatial structure of the warming pattern are within the uncertainties of the IPCC models simulations. It is capable of simulating aspects of the arctic winter amplification, the equilibrium land-sea warming contrast and the inter-hemispheric warming gradient with good agreement to the IPCC models in amplitude and structure. The results give some insight into the understanding of the land-sea contrast and the polar amplification. The GREB model suggests that the regional inhomogeneous distribution of atmospheric water vapor and the non-linear sensitivity of the downward thermal radiation to changes in the atmospheric water vapor concentration partly cause the land-sea contrast and may also contribute to the polar amplification. The combination of these characteristics causes, in general, dry and cold regions to warm more than other regions.     

Variability in annual mean circulation in southern high latitudes

 Using a hierarchy of climate models together with observations from gridded analyses, I examine the atmosphere-only and coupled ocean-atmosphere variability in the general circulation for the region south of 40 °S. The variability in mean sea level pressure (MSLP) is well simulated by the coupled models. A complication is that the difference between the two analyses used for verification is comparable to the analysis-model differences. An increase in variability is seen within the hierarchy of model runs although even a model without interannual variations in sea surface temperatures (SSTs) captures most of the observed variability. The temporal variation in MSLP in southern high latitudes has a white spectrum consistent with “random” forcing by weather events and a decoupling from oceanic “integration”. In contrast, the spatial pattern of MSLP variability shows large-scale structure that is consistent between observations and various models, even without interannual variation in SSTs. This shows that the models are sufficiently skillful to reproduce the pattern of observed variability and suggests that the pattern of variability is a characteristic of the land-sea distribution and topography. Received: 18 December 1996/Accepted: 23 May 1997     

夏季季风区气候的模拟特征

用一个由大气模式、土壤模式和水域模式三个子模式组成的模式模拟了夏季风区的气候特征。模拟得到的平均气候特征,如温度场、风场、降水和蒸发场均与实际观测场接近;模式模拟出季风区的地面气候特征,表明其与大气状态和下垫面性质关系密切;对加热场的模拟则表明,积云对流凝结潜热加热对总加热率的贡献最大.     

Comparison of regional climate model and statistical downscaling simulations of different winter precipitation change scenarios over Romania

Summary Regional climate model and statistical downscaling procedures are used to generate winter precipitation changes over Romania for the period 2071–2100 (compared to 1961–1990), under the IPCC A2 and B2 emission scenarios. For this purpose, the ICTP regional climate model RegCM is nested within the Hadley Centre global atmospheric model HadAM3H. The statistical downscaling method is based on the use of canonical correlation analysis (CCA) to construct climate change scenarios for winter precipitation over Romania from two predictors, sea level pressure and specific humidity (either used individually or together). A technique to select the most skillful model separately for each station is proposed to optimise the statistical downscaling signal. Climate fields from the A2 and B2 scenario simulations with the HadAM3H and RegCM models are used as input to the statistical downscaling model. First, the capability of the climate models to reproduce the observed link between winter precipitation over Romania and atmospheric circulation at the European scale is analysed, showing that the RegCM is more accurate than HadAM3H in the simulation of Romanian precipitation variability and its connection with large-scale circulations. Both models overestimate winter precipitation in the eastern regions of Romania due to an overestimation of the intensity and frequency of cyclonic systems over Europe. Climate changes derived directly from the RegCM and HadAM3H show an increase of precipitation during the 2071–2100 period compared to 1961–1990, especially over northwest and northeast Romania. Similar climate change patterns are obtained through the statistical downscaling method when the technique of optimum model selected separately for each station is used. This adds confidence to the simulated climate change signal over this region. The uncertainty of results is higher for the eastern and southeastern regions of Romania due to the lower HadAM3H and RegCM performance in simulating winter precipitation variability there as well as the reduced skill of the statistical downscaling model.     

NUMERICAL SIMULATION EXPERIMENTS OF THE IMPACTS OF LOCAL LAND-SEA THERMODYNAMIC CONTRASTS ON THE SCS SUMMER MONSOON ONSET

1INTRODUCTIONAmongdrivingfactorsfortheEastAsianmonsoonareplanetary-scaleland-seathermodynamiccontrast(e.g.betweentheEurasiancontinentandthePacificOcean)andsub-planetary-scaleone(e.g.betweentheIndochinaandtheSouthChinaSea).ItisovertheSouthChinaSea(SCS)andadjoiningareasthattheEastAsiansummermonsoonfirstbreaksout.ItthenadvancestotheregionsofEastAsiaandSouthAsia.ItisthereforenaturaltofindlocalgeographicandtopographiceffectsoftheSCSregionevidentlyshownontheonsetoftheSCSsummermonsoon…     

High-resolution simulations of global climate, part 2: effects of increased greenhouse cases

We report results from the highest-resolution simulations of global warming yet performed with an atmospheric general circulation model. We compare the climatic response to increased greenhouse gases of the National Center for Atmospheric Research (NCAR) climate model, CCM3, at T42 and T170 resolutions (horizontal grid spacing of 300 and 75 km respectively). All simulations use prescribed sea surface temperatures (SST). Simulations of the climate of 2100 ad use SSTs based on those from NCAR coupled model, Climate System Model (CSM). We find that the global climate sensitivity and large-scale patterns of climate change are similar at T42 and T170. However, there are important regional scale differences that arise due to better representation of topography and other factors at high resolution. Caution should be exercised in interpreting specific features in our results both because we have performed climate simulations using a single atmospheric general circulation model and because we used with prescribed sea surface temperatures rather than interactive ocean and sea-ice models.