层状云微物理参数反演及其辐射效应的个例研究

利用毫米波云雷达、微波辐射计联合反演方法,对2015年11月11日安徽寿县的一次层状云过程的云参数进行了反演,将所得云参数加入到SBDART辐射传输模式中,进行辐射通量计算,并将计算的地面辐射通量与观测的地面辐射通量进行了对比分析。研究表明:1)利用毫米波雷达和微波辐射计数据联合反演的云参数比较可靠;2)利用SBDART模式并结合反演的云参数,可以准确实时地计算地面及其他高度层的长短波辐射通量;3)在反演的云参数中,光学厚度对地面各种辐射通量的影响是最大的,云层的光学厚度越大,到达地面的太阳短波辐射越小,地面反射短波辐射也越小。另外云底温度越高,云体向下发射的红外长波辐射越大。地面向上的长波辐射是地面温度的普朗克函数,随地面温度而变;4)云对地面的短波辐射强迫为负值,对地面有降温的作用。云对地面的长波辐射强迫是一个正值,对地面有一个增温的作用;5)云对地面的净辐射强迫随时间变化很大,它的正负与太阳高度角和云参数有关。     

RegCM4对中国东部区域气候模拟的辐射收支分析

利用卫星和再分析数据,评估了区域气候模式Reg CM4对中国东部地区辐射收支的基本模拟能力,重点关注地表净短波(SNS)、地表净长波(SNL)、大气顶净短波(TNS)、大气顶净长波(TNL)4个辐射分量。结果表明:1)短波辐射的误差值在夏季较大,而长波辐射的误差值在冬季较大。但各辐射分量模拟误差的空间分布在冬、夏季都有较好的一致性。2)对于地表辐射通量,SNS表现为正偏差(向下净短波偏多),在各分量中误差最大,区域平均误差值近50 W/m2;SNL表现为负偏差(向上净长波偏多);对于大气顶辐射通量,TNS和TNL分别表现为"北负南正"的误差分布和整体正偏差。3)利用空间相关和散点线性回归方法对4个辐射分量的模拟误差进行归因分析,发现在云量、地表反照率、地表温度三个直接影响因子中,云量模拟误差的贡献最大,中国东部地区云量模拟显著偏少。     

The disposition of radiative energy in the global climate system: GCM-calculated versus observational estimates

 A comprehensive dataset of direct observations is used to assess the representation of surface and atmospheric radiation budgets in general circulation models (GCMs). Based on combined measurements of surface and collocated top-of-the-atmosphere fluxes at more than 700 sites, a lack of absorption of solar radiation within the atmosphere is identified in the ECHAM3 GCM, indicating that the shortwave atmospheric absorption calculated in the current generation of GCMs, typically between 60 and 70 Wm^-2, is too low by 10–20 Wm^-2. The surface and atmospheric radiation budgets of a new version of the Max-Planck Institute GCM, the ECHAM4, differ considerably from other GCMs in both short- and longwave ranges. The amount of solar radiation absorbed in the atmosphere (90 Wm^-2) is substantially larger than typically found in current GCMs, resulting in a lower absorption at the surface (147 Wm^-2). It is shown that this revised disposition of solar energy within the climate system generally reduces the biases compared to the observational estimates of surface and atmospheric absorption. The enhanced shortwave absorption in the ECHAM4 atmosphere is due to an increase in both simulated clear-sky and cloud absorption compared to ECHAM3. The increased absorption in the cloud-free atmosphere is related to an enhanced absorption of water vapor, and is supported in stand-alone comparisons of the radiation scheme with synchronous observations. The increased cloud absorption, on the other hand, is shown to be predominantly spurious due to the coarse spectral resolution of the ECHAM4 radiation code, thus providing no physical explanation for the “anomalous cloud absorption” phenomenon. Quantitatively, however, an additional increase of atmospheric absorption due to clouds as in ECHAM4 is, at least at low latitudes, not in conflict with the observational estimates, though this does not rule out the possibility that other effects, such as highly absorbing aerosols, could equally contribute to close the gap between models and observations. At higher latitudes, however, the increased cloud absorption is not supported by the observational dataset. Overall, this study points out that not only the clouds, but also the cloud-free atmosphere might be responsible for the discrepancies between observational and simulated estimates of shortwave atmospheric absorption. The smaller absorption of solar radiation at the surface in ECHAM4 is compensated by an increased downward longwave flux (344 Wm^-2), which is larger than in other GCMs. The enhanced downward longwave flux is supported by surface measurements and by a stand-alone validation of the radiation scheme for clear-sky conditions. The enhanced flux also ensures that a sufficient amount of energy is available at the surface to maintain a realistic intensity of the global hydrological cycle. In contrast, a one-handed revision of only the shortwave radiation budget to account for the increased shortwave absorption in GCM atmospheres may induce a global hydrological cycle that is too weak. Received: 26 February 1998 / Accepted: 18 May 1998     

The role of wintertime radiation in maintaining and destroying stable layers

Summary Strong stable layers are a common occurrence during western Colorado's winter. Analysis of radiosonde observations indicate wintertime boundary layer heights are near 500 m. The terrain in this region consists of mountains that rise approximately 1500–2000 m above the ground to the east, providing an effective blocking barrier. An experiment is described to observe upwelling and downwelling, longwave and shortwave radiative fluxes at two sites in western Colorado during January and February 1992, for combinations of clear, cloudy, snow covered, and bare ground periods. Analysis of the observations and the surface energy budget for typical Bowen ratios provides a better understanding of the role of radiation in maintaining and destroying stable layers.During the day, the surface received a net gain of energy from radiation, while at night there was a net loss. Over snow, the 24-hour net radiative flux was small and either positive or negative. Over bare soil, the 24-hour net radiative flux was positive but still small. There is little difference in the net radiative flux between clear and cloudy days; the reduction of the incident solar flux by clouds is nearly compensated by the hindering of the longwave cooling. The cumulative effects of the 24-hour net radiative flux were negative over snow early in the experiment. The 24-hour values shifted to near zero as the snow albedo decreased and were positive for bare ground.If the daytime net radiative flux is partitioned into sensible and latent heat flux using typical Bowen ratios, the daytime sensible heat available for destroying boundary layers is small for the low solar angles of the winter season. With a Bowen ratio of 0.5, the daytime sensible heat flux available is only 0.3 to 1.2 MJ m^–2 over a snow surface and 1.4 to 2.3 MJ m^–2 over soil. These heat fluxes will not build a deep enough boundary layer to break a typical wintertime inversion. The 24-hour sensible heat flux was negative at both sites for the entire experiment with this Bowen ratio.The radiation observations and the use of typical Bowen ratios lead to the conclusion that the net radiation will sustain or strengthen a stable atmosphere in the winter season in western Colorado. Analysis of the radiosonde observations confirm this result as the boundary layer depths were less than 500 m early in the experiment and grew to only 700 m later in the experiment.With 12 Figures     

Regional climate simulation with a high resolution GCM: surface hydrology

Aspects of the surface hydrology of high resolution (T106) versions of the ECHAM3 and ECHAM4 general circulation models are analysed over the European region and compared with available observations. The focus is on evaporation, and surface measurements are shown to be useful for the identification of systematic deficiencies in the regional-scale performance of climate models on an annual and seasonal basis, such as the excessive summer dryness over continents. The annual mean evaporation at the available European observation sites is overestimated by 4 mm/month by the ECHAM3 T106, quantitatively consistent with an overestimated surface net radiation of 4 Wm^–2 over Europe. In winter, ECHAM3 shows an overestimated evaporation which compensates for an overestimated downward sensible heat flux. This is primarily related to a too strong zonalisation of the large-scale flow and associated overestimated warm air advection and windspeed. Inaccurate local land surface parameters (e.g. leaf area index, roughness length) are minor contributors to the overestimation. In early summer, the excessive solar radiation at the surface calculated with the ECHAM3 radiation scheme generates a too large evaporation and an excessive depletion of the soil moisture reservoirs. This favours the subsequent excessive summer dryness over Europe with too low values of evaporation, convective precipitation and soil moisture content, leading to a too high surface temperature. In the ECHAM4 T106 simulation, the problem of the European summer dryness is largely reduced, and the simulated evaporation as well as convective precipitation, cloud amount and soil moisture content during summer are substantially improved. The new ECHAM4 radiation scheme appears to be an important factor for this improvement, since it calculates smaller insolation values in better agreement with observations and subsequently may avoid an excessive drying of the soil. Received: 20 September 1995 / Accepted: 10 May 1996     

中国地区夏季平均加热率的时空分布特征

The latitude-altitude distributions of radiative fluxes and heating rates are investigated by utilizing CloudSat satellite data over China during summer. The Tibetan Plateau causes the downward shortwave fluxes of the lower atmosphere over central China to be smaller than the fluxes over southern and northern China by generating more clouds. The existence of a larger quantity of clouds over central China reflects a greater amount of solar radiation back into space. The vertical gradients of upward shortwave radiative fluxes in the atmosphere below 8 km are greater than those above 8 km. The latitudinal-altitude distributions of downward longwave radiative fluxes show a slantwise decreasing trend from low latitudes to high latitudes that gradually weaken in the downward direction. The upward longwave radiative fluxes also weaken in the upward direction but with larger gradients. The maximum heating rates by solar radiation and cooling rates by longwave infrared radiation are located over 28-40°N at 7-8 km mean sea level (MSL), and they are larger than the rates in the northern and southern regions. The heating and cooling rates match well both vertically and geographically.     

Greenhouse effect and altitude gradients over the Alps – by surface longwave radiation measurements and model calculated LOR

Summary The greenhouse effect has been investigated predominantly with satellite measurements, but more than 90% of the greenhouse radiative flux affecting Earths surface temperature and humidity originates from a 1000 meter layer above the surface. Here we show that substantial improvements on surface longwave radiation measurements and very good agreement with radiative transfer model calculations allow the clear-sky greenhouse effect be determined with measured surface longwave radiation and calculated longwave outgoing radiation at the top of the atmosphere. The cloud radiative forcing is determined by measured net longwave fluxes and added to the clear-sky greenhouse effect to determine the all-sky greenhouse effect. Longwave radiation measurements at different altitudes were used to determine the clear-sky and all-sky annual and seasonal greenhouse effect and altitude gradients over the Alps. Linear altitude gradients are measured for clear-sky situations, whereas the all-sky greenhouse effect is strongly influenced by varying, cloud amounts at different altitudes. Large diurnal and seasonal variations show the importance of surface heating and cooling effects and demonstrate the strong coupling of the greenhouse effect to surface temperature and humidity.     

The effect of horizontal resolution on ocean surface heat fluxes in the ECMWF model

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.     

藏东南峡谷地区不同下垫面地表通量变化特征及其与降水的关系

利用藏东南峡谷地区排龙站、丹卡站、卡布站、墨脱站四个站点2018年11月至2019年10月的涡动协方差仪观测资料,分析藏东南峡谷地区不同位置入口、中段和末端地表通量变化的特征及其与局地降水的关系.研究表明:地表通量月平均日变化特征为夜间潜热通量大于感热通量,日间呈单峰变化特征.排龙站和丹卡站感热11月至次年4月较强,5...     

城市气溶胶对边界层热量收支的影响

本文利用长、短波辐射模式和地面能量平衡模式，计算了烟雾层状况下的边界层和地面热量收支情况，计算表明，烟地务层的全天辐射效应使低层大气上部辐射能量收入为正，中下部辐射能量收入为负，总的结果是使低层大气稍稍冷却并使稳定增加，计算还表明，烟雾层造成的地面接收短波辐射能量的减少量可由大气逆辐射的增加量来补偿，烟雾层使得地面温度振幅变小。     

Assessment of GCM simulated snow albedo using direct observations

 Annual cycles of monthly albedos simulated with a general circulation model (GCM) are compared with surface observations. The data observed at 35 stations are retrieved from the Global Energy Balance Archive (GEBA) and drawn from the soil moisture and meteorological observations in the former Soviet Union. The model data are obtained with the ECHAM4 GCM in a ten-year simulation of the present-day climate at T106 resolution. The model calculated albedo values are modified before they are compared with the surface observations: They are interpolated to the stations and adjusted to account for altitude differences and fractional forest area. During the snow-free period, the model underestimates the albedo by up to 0.05 at the stations (with values between 0.2 and 0.25 measured over short grass) because the albedo for grassland is too low in the model. During the period with seasonal snow cover, the model underestimates the albedo by up to 0.2 at stations in Russia, Scandinavia and Canada, which experience severe winters. This underestimation is due to an oversimplified parameterization of the snow covered grid fraction and an inadequate linear relation between snow albedo and temperature. The derivative of albedo with respect to the forest fraction implemented in ECHAM is in line with the observations, although a small overestimation of the model’s gradient has been detected. Received: 3 July 1998 / Accepted: 24 December 1998     

Influences of Two Convective Schemes on the Radiative Energy Budget in GAMIL1.0

The Grid-point Atmospheric Model of IAP LASG version 1.0 (GAMIL1.0) is used to investigate the impacts of different convective schemes on the radiative energy budget.The two convective schemes are Zhang and McFarlance (1995)/Hack (1994) (ZM) and Tiedtke (1989)/Nordeng (1994) (TN).Two simulations are performed:one with the ZM scheme (EX_ZM) and the other with the TN scheme (EX_TN).The results indicate that during the convective process,more water vapor consumption and temperature increment are found in the EX_ZM,especially in the lower model layer,its environment is therefore very dry.In contrast,there is a moister atmosphere in the EX_TN,which favors low cloud formation and large-scale condensation,and hence more low cloud fraction,higher cloud water mixing ratio,and deeper cloud extinction optical depth are simulated,reflecting more solar radiative flux in the EX_TN.This explains why the TN scheme underestimates the net shortwave radiative flux at the top of the atmosphere and at surface.In addition,convection influences longwave radiation,surface sensible and latent heat fluxes through changes in cloud emissivity and precipitation.     

Contrasting characteristics of the surface energy balance between the urban and rural areas of Beijing

A direct comparison of urban and rural surface energy balances, as well as a variety of other variables including incoming shortwave/longwave radiation and aerosol optical depth, is conducted for the Beijing metropolitan area. The results indicate that, overall, the urban area receives a smaller amount of incoming shortwave radiation but a larger amount of incoming longwave radiation. However, comparisons in the aerosol optical depth and cloud fraction at the two locations suggest that neither aerosol optical depth nor cloud fraction alone can explain the difference in the incoming shortwave radiation. The urban–rural differences in the incoming longwave radiation are unlikely to be caused by the presence of more abundant greenhouse gases over the urban area, as suggested by some previous studies, given that water vapor is the most dominant greenhouse gas and precipitable water is found to be less in urban areas. The higher incoming longwave radiation observed over the urban area is mostly likely due to the higher temperatures of the ambient air. The urban area is also found to always produce higher sensible heat fluxes and lower latent heat fluxes in the growing season. Furthermore, the urban area is associated with a larger amount of available energy(the sum of sensible and latent heat fluxes) than the rural area, except in May and October when evapotranspiration in the rural area significantly exceeds that in the urban area. This study provides observational evidence of urban–rural contrasts in relevant energy-balance components that plausibly arise from urban–rural differences in atmospheric and land-surface conditions.     

我国西北大气沙尘气溶胶的辐射效应

利用HEIFE地面辐射平衡观测资料和同期NOAA-11/AVHRR卫星遥感资料定量估算春季我国西北大气沙尘的辐射效应。大气沙尘减小地面净辐射冷却地面,对地-气系统和大气的辐射效应均与地表反照率有关,严重浑浊的沙尘大气在沙漠为短波加热和长波冷却,在绿洲则相反,但净效应都是加热。文中给出了4月大气浑浊度系数约由0.1增大到0.6,在沙漠和绿洲上空沙尘层（850～600 hPa）内大气的附加短波、长波和净加热/冷却率。     

On the vertical profile of surface radiative fluxes in southwest Germany

Summary Vertical profile of surface radiative fluxes in an area of heterogeneous terrain in south-west Germany is presented. Main data sets utilized for the study were recorded during the REgio KLIma Projekt (REKLIP). Supporting observational data were provided by the German weather service and German geophysical consultant service. Elevation of the study sites ranged from 212 m a.s.l. to 1489 m a.s.l. From May to September, monthly mean albedo was generally low at the study sites, ranging from 19% to 24%. For the other months, monthly mean albedo lie between 22% and 25% at the lowland site but extended between 27% and 71% at the highly elevated mountain site. Following the altitudinal increase in surface albedo, net radiative flux and radiation efficiency declined with elevation at an annual mean of 1.15 Wm⁻²/100 m and 0.008/100 m respectively. Absorbed shortwave radiation and effective terrestrial radiation showed mean decline of 1.54 Wm⁻²/100 m and 0.34 Wm⁻²/100 m, respectively, with the mean sky-to-earth radiation deficit amounting to about 52 Wm⁻² for the lowland site and 73 Wm⁻² for the highest elevated site. Some empirical models which express shortwave and longwave radiative fluxes in terms of meteorological variables have been validated for the lowland and mountain sites. Monthly mean daily total estimates of solar radiation obtained from ?ngst?m-Prescott relation were quite consistent with observed values. Parameterisation of downward atmospheric radiation under all sky condition was achieved by extending Brutsaert clear sky atmospheric model. Relationship between outgoing longwave radiation and screen temperature at the study sites was best described by an exponential function unlike the linear relationship proposed by Monteith and Unsworth. Net radiative flux for the lowland and mountain sites has been expressed in terms of absorbed shortwave radiation, cloud amount and screen temperature. Received March 5, 2001 Revised October 29, 2001     

不同形状冰晶权重假定对冰云光学和辐射特性的影响

在BCC_RAD辐射传输模式和包含多形状冰晶粒子的冰云光学性质参数化方案的基础上,详细分析了不同冰晶粒子权重选取对冰云光学和辐射特性的影响。结果显示,不同形状冰晶粒子权重的选取对长波带平均消光系数、单次散射比、不对称因子和短波带平均不对称因子均有较大的影响。冰晶粒子权重选取对长波辐射通量有很大影响:对长波向下辐射通量,权重选择不同可在云底处造成高达10.50 W/m2的差别;对长波向上辐射通量,权重选择不同可在云顶处造成高达15.05 W/m2的差别。冰晶粒子权重选择对短波辐射通量也存在较大影响:对短波向下辐射通量,权重选择不同可在云底处造成高达12.48 W/m2的差别;对短波向上辐射通量,权重选择不同可在云顶处造成高达10.23 W/m2的差别。冰晶粒子权重选择对长波加热率影响较大,在云顶处和云底处分别可达1.31和-2.06 K/d。研究表明,不同形状冰晶粒子权重的选取对冰云光学性质和辐射计算均有较大的影响,在长波区间尤其明显。      

TropFlux: air-sea fluxes for the global tropical oceans—description and evaluation

In this paper, we evaluate several timely, daily air-sea heat flux products (NCEP, NCEP2, ERA-Interim and OAFlux/ISCCP) against observations and present the newly developed TropFlux product. This new product uses bias-corrected ERA-interim and ISCCP data as input parameters to compute air-sea fluxes from the COARE v3.0 algorithm. Wind speed is corrected for mesoscale gustiness. Surface net shortwave radiation is based on corrected ISCCP data. We extend the shortwave radiation time series by using “near real-time” SWR estimated from outgoing longwave radiation. All products reproduce consistent intraseasonal surface net heat flux variations associated with the Madden-Julian Oscillation in the Indian Ocean, but display more disparate interannual heat flux variations associated with El Ni?o in the eastern Pacific. They also exhibit marked differences in mean values and seasonal cycle. Comparison with global tropical moored buoy array data, I-COADS and fully independent mooring data sets shows that the two NCEP products display lowest correlation to mooring turbulent fluxes and significant biases. ERA-interim data captures well temporal variability, but with significant biases. OAFlux and TropFlux perform best. All products have issues in reproducing observed longwave radiation. Shortwave flux is much better captured by ISCCP data than by any of the re-analyses. Our “near real-time” shortwave radiation performs better than most re-analyses, but tends to underestimate variability over the cold tongues of the Atlantic and Pacific. Compared to independent mooring data, NCEP and NCEP2 net heat fluxes display ~0.78 correlation and >65?W?m^?2 rms-difference, ERA-I performs better (~0.86 correlation and ~48?W?m^?2) while OAFlux and TropFlux perform best (~0.9 correlation and ~43?W?m^?2). TropFlux hence provides a useful option for studying flux variability associated with ocean–atmosphere interactions, oceanic heat budgets and climate fluctuations in the tropics.     

Current problems in the stratocumulus-topped atmospheric boundary layer

Extended sheets of stratocumulus (Sc) in the upper part of the atmospheric boundary layer (ABL) often occur under appropriate meteorological conditions. These cloud decks are important both in climate studies and in weather forecasting. We review the current knowledge of the turbulent structure of the ABL capped by a cloud deck, in the light of recent observations and model studies. The most important physical processes determining this structure are longwave radiative cooling at cloud top, shortwave radiative wanning by absorption in the cloud, surface buoyancy flux, and wind shear in the ABL. As a result, turbulence can cause entrainment against the buoyancy jump at cloud top. In cases where only longwave radiative fluxes and surface buoyancy fluxes are important, the turbulent structure is relatively well understood. When shortwave radiative fluxes and/or wind shear are also important, the resulting turbulent structure may change considerably. A decoupling of the cloud from the sub-cloud layer or of the top of the cloud from the rest of the ABL is then regularly observed. In no cases are the details of the entrainment at cloud top understood well enough to derive a relatively simple formulation that is consistent with observations. Cloud-top entrainment instability may lead to the break-up of a cloud deck (but also to cloud deepening). The role of mesoscale circulations in determining fractional cloudiness is not yet well understood.     

The impact of boundary forcing on RegCM4.2 surface energy budget

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.     

A parameterization of radiative fluxes suitable for use in a statistical-dynamical model

Summary A parameterization of shortwave and longwave radiation fluxes derived from detailed radiative transfer models is included in a global primitive equation statistical-dynamical model (SDM) with two bulk atmospheric layers. The model is validated comparing the model simulations with the observed mean annual and seasonal zonally averaged climate. The results show that the simulation of the shortwave and longwave radiation fluxes matches well with the observations. The SDM variables such as surface and 500 hPa temperatures, zonal winds at 250 hPa and 750 hPa, vertical velocity at 500 hPa and precipitation are also in good agreement with the observations. A comparison between the results obtained with the present SDM and those with the previous version of the model indicates that the model results improved when the parameterization of the radiative fluxes based on detailed radiative transfer models are included into the SDM.The SDM is used to investigate its response to the greenhouse effect. Sensitivity experiments regarding the doubling of CO₂ and the changing of the cloud amount and height are performed. In the case 2×CO₂ the model results are consistent with those obtained from GCMs, showing a warming of the climate system. An enhancement of the greenhouse effect is also noted when the cloud layer is higher. However, an increase of the cloud amount in all the latitude belts provokes an increase of the surface temperature near poles and a decrease in all the other regions. This suggests that the greenhouse effect overcomes the albedo effect in the polar latitudes and the opposite occurs in other regions. In all the experiments the changes in the surface temperature are larger near poles, mainly in the Southern Hemisphere.With 8 Figures