Evaluation of tropical cloud regimes in observations and a general circulation model

Tropical cloud regimes defined by cluster analysis of International Satellite Cloud Climatology Project (ISCCP) cloud top pressure (CTP)–optical thickness distributions and ISCCP-like Goddard Institute for Space Studies (GISS) general circulation model (GCM) output are analyzed in this study. The observations are evaluated against radar–lidar cloud-top profiles from the atmospheric radiation measurement (ARM) Program active remote sensing of cloud layers (ARSCL) product at two tropical locations and by placing them in the dynamical context of the Madden–Julian oscillation (MJO). ARSCL highest cloud-top profiles indicate that differences among some of the six ISCCP regimes may not be as prominent as suggested by ISCCP at the ARM tropical sites. An experimental adjustment of the ISCCP CTPs to produce cloud-top height profiles consistent with ARSCL eliminates the independence between those regimes. Despite these ambiguities, the ISCCP regime evolution over different phases of the MJO is consistent with existing MJO mechanisms, but with a greater mix of cloud types in each phase than is usually envisioned. The GISS Model E GCM produces two disturbed and two suppressed regimes when vertical convective condensate transport is included in the model’s cumulus parameterization. The primary model deficiencies are the absence of an isolated cirrus regime, a lack of mid-level cloud relative to ARSCL, and a tendency for occurrences of specific parameterized processes such as deep and shallow convection and stratiform low cloud formation to not be associated preferentially with any single cloud regime.     

Calculations of river-runoff in the GISS GGM: impact of a new land-surface parameterization and runoff routing model on the hydrology of the Amazon River

This study examines the impact of a new land-surface parameterization and a river routing scheme on the hydrology of the Amazon basin, as depicted by the NASA/Goddard Institute of Space Studies (GISS) global climate model (GCM). The more physically realistic land surface scheme introduces a vegetation canopy resistance and a six-layer soil system. The new routing scheme allows runoff to travel from a river's headwater to its mouth according to topography and other channel characteristics and improves the timing of the peak flow. River runoff is examined near the mouth of the Amazon and for all of its sub-basins. With the new land-surface parameterization, river run-off increases significantly and is consistent with that observed in most basins and at the mouth. The representation of the river hydrology in small basins is not as satisfactory as in larger basins. One positive impact of the new land-surface parameterization is that it produces more realistic evaporation over the Amazon basin, which was too high in the previous version of the GCM. The realistic depiction of evaporation also affects the thermal regime in the lower atmosphere in the Amazon. In fact, the lower evaporation in some portions of the basin reduces the cloudiness, increases the solar radiation reaching the ground, increases the net radiation at the surface, and warms the surface as compared to observations. Further GCM improvement is needed to obtain a better representation of rainfall processes.     

The impact of vertical resolution upon GCM simulations of marine stratocumulus

 The impact of increased vertical resolution in the Hadley Centre Climate Model upon the simulation of stratocumulus is investigated in experiments using single column (SCM) and general circulation (GCM) model configurations. A threefold enhancement of vertical resolution in the boundary layer leads to improvements in the vertical structure of the cloud-topped boundary layer produced by the SCM and GCM in both well-mixed and decoupled situations. However, single and decoupled mixed layers in the marine stratocumulus subsidence regions are still too shallow and, despite increasing, layer cloud amounts remain generally too low. Moreover, closer examination of GCM data and SCM timeseries reveals an underlying sensitivity to vertical resolution in model interactions between boundary layer and convection processes which appears unrealistic. Stratocumulus simulation is thus unlikely to improve significantly as a result of enhanced resolution alone and further work is being undertaken to improve the Hadley Centre model’s boundary layer scheme and, in particular, its interaction with the convection scheme. Nevertheless, this study shows that the full benefit of an improved boundary layer scheme will not be realized if the boundary layer structure is constrained by the rather poor lower troposphere resolution of the standard 19-level climate model. Future Hadley Centre model versions will seek to combine the added flexibility of a better resolved structure with improvements to the subgrid boundary layer parametrizations. Received: 14 April 1998 / Accepted: 5 November 1998     

Impacts of cumulus momentum transport on MJO simulation

Vertical cumulus momentum transport is an important physical process in the tropical atmosphere and plays a key role in the evolution of the tropical atmospheric system. This paper focuses on the impact of the vertical cumulus momentum transport on Madden-Julian Oscillation (MJO) simulation in two global climate models (GCMs). The Tiedtke cumulus parameterization scheme is applied to both GCMs [CAM2 and Spectral Atmospheric general circulation Model of LASG/IAP (SAMIL)]. It is found that the MJO simulation ability might be influenced by the vertical cumulus momentum transport through the cumulus parameterization scheme. However, the use of vertical momentum transport in different models provides different results. In order to improve model's MJO simulation ability, we must introduce vertical cumulus momentum transport in a more reasonable way into models. Furthermore, the coherence of the parameterization and the underlying model also need to be considered.     

The LMDZ4 general circulation model: climate performance and sensitivity to parametrized physics with emphasis on tropical convection

The LMDZ4 general circulation model is the atmospheric component of the IPSL–CM4 coupled model which has been used to perform climate change simulations for the 4th IPCC assessment report. The main aspects of the model climatology (forced by observed sea surface temperature) are documented here, as well as the major improvements with respect to the previous versions, which mainly come form the parametrization of tropical convection. A methodology is proposed to help analyse the sensitivity of the tropical Hadley–Walker circulation to the parametrization of cumulus convection and clouds. The tropical circulation is characterized using scalar potentials associated with the horizontal wind and horizontal transport of geopotential (the Laplacian of which is proportional to the total vertical momentum in the atmospheric column). The effect of parametrized physics is analysed in a regime sorted framework using the vertical velocity at 500 hPa as a proxy for large scale vertical motion. Compared to Tiedtke’s convection scheme, used in previous versions, the Emanuel’s scheme improves the representation of the Hadley–Walker circulation, with a relatively stronger and deeper large scale vertical ascent over tropical continents, and suppresses the marked patterns of concentrated rainfall over oceans. Thanks to the regime sorted analyses, these differences are attributed to intrinsic differences in the vertical distribution of convective heating, and to the lack of self-inhibition by precipitating downdraughts in Tiedtke’s parametrization. Both the convection and cloud schemes are shown to control the relative importance of large scale convection over land and ocean, an important point for the behaviour of the coupled model.     

Evaluation of NASA GISS Post-CMIP5 Single Column Model Simulated Clouds and Precipitation Using ARM Southern Great Plains Observations

The planetary boundary layer turbulence and moist convection parameterizations have been modified recently in the NASA Goddard Institute for Space Studies(GISS) Model E2 atmospheric general circulation model(GCM; post-CMIP5,hereafter P5). In this study, single column model(SCM P5) simulated cloud fractions(CFs), cloud liquid water paths(LWPs)and precipitation were compared with Atmospheric Radiation Measurement(ARM) Southern Great Plains(SGP) groundbased observations made during the period 2002–08. CMIP5 SCM simulations and GCM outputs over the ARM SGP region were also used in the comparison to identify whether the causes of cloud and precipitation biases resulted from either the physical parameterization or the dynamic scheme. The comparison showed that the CMIP5 SCM has difficulties in simulating the vertical structure and seasonal variation of low-level clouds. The new scheme implemented in the turbulence parameterization led to significantly improved cloud simulations in P5. It was found that the SCM is sensitive to the relaxation time scale. When the relaxation time increased from 3 to 24 h, SCM P5-simulated CFs and LWPs showed a moderate increase(10%–20%) but precipitation increased significantly(56%), which agreed better with observations despite the less accurate atmospheric state. Annual averages among the GCM and SCM simulations were almost the same, but their respective seasonal variations were out of phase. This suggests that the same physical cloud parameterization can generate similar statistical results over a long time period, but different dynamics drive the differences in seasonal variations. This study can potentially provide guidance for the further development of the GISS model.     

Comparison of uncertainty sources for climate change impacts: flood frequency in England

This paper investigates the uncertainty in the impact of climate change on flood frequency in England, through the use of continuous simulation of river flows. Six different sources of uncertainty are discussed: future greenhouse gas emissions; Global Climate Model (GCM) structure; downscaling from GCMs (including Regional Climate Model structure); hydrological model structure; hydrological model parameters and the internal variability of the climate system (sampled by applying different GCM initial conditions). These sources of uncertainty are demonstrated (separately) for two example catchments in England, by propagation through to flood frequency impact. The results suggest that uncertainty from GCM structure is by far the largest source of uncertainty. However, this is due to the extremely large increases in winter rainfall predicted by one of the five GCMs used. Other sources of uncertainty become more significant if the results from this GCM are omitted, although uncertainty from sources relating to modelling of the future climate is generally still larger than that relating to emissions or hydrological modelling. It is also shown that understanding current and future natural variability is critical in assessing the importance of climate change impacts on hydrology.     

Interannual variation of the diurnal convection cycle in the western North Pacific

Summary As revealed from the interannual variation of outgoing longwave radiation in the western Pacific, deep cumulus convection along the Meiyü-Baiu front and ITCZ is modulated by the anomalous summer circulation in the following manner: when the sea surface temperatures on the eastern tropical Pacific are anomalously warm (cold), cumulus convection is enhanced (suppressed) along the equator east of 150° E and along the Meiyü-Baiu front, but is suppressed (enhanced) along the equator west of 150° E and along a longitudinal zone (10° N–30° N) extending from the northern section of the South China Sea to the International Dateline. Since tropical deep cumulus convection exhibits a pronounced diurnal variation, the diurnal convection cycle in the western Pacific may undergo an interannual variation coherent with that of deep tropical cumulus convection. This inference is substantiated by our analysis of the diurnal convection cycle for 1980–1993 with 3-hour equivalent black-body temperature observed by the Japanese Geostationary Meteorological Satellite (GMS). As expected, the diurnal convection cycle in the western Pacific is subjected to an interannual variation in accordance with deep cumulus convection along the Meiyü-Baiu front and ITCZ. Except along the equator east of 150° E, the diurnal convection cycle does not exhibit a drastic interannual change in phase.     

高分辨率有限区业务数值预报模式及降水预报试验

该文介绍了国家气象中心在原业务有限区模式基础上开发的一个新的高分辨率有限区模式（ＨＬＡＦＳ）．该模式除分辨率提高外，其主要改进表现在：（１）增加了地面土壤过程、地面辐射过程、地面摩擦及边界层垂直湍流输送；（２）积云对流参数化方案改用质量通量方案取代了原来的Ｋｕｏ方案．文章还对模式的准业务运行结果作了较全面地评述     

Sensitivity of the Simulated Tropical Intraseasonal Oscillation to Cumulus Parameterizations

The sensitivity of the simulated tropical intraseasonal oscillation or MJO (Madden and Julian oscilla tion)to different cumulus parameterizations is studied by using an atmospheric general circulation model (GCM)-SAMIL(Spectral Atmospheric Model of IAP LASG).Results show that performance of the model in simulating the MJO alters widely when using two different cumulus parameterization schemes-the moist convective adjustment scheme(MCA)and the Zhang-McFarlane(ZM)scheme.MJO simulated by the MCA scheme was found to be more realistic than that simulated by the ZM scheme.MJO produced by the ZM scheme is too weak and shows little propagation characteristics.Weak moisture convergence at low levels simulated by the ZM scheme is not enough to maintain the structure and the eastward propagation of the oscillation.These two cumulus schemes produced different vertical structures of the heating profile.The heating profile produced by the ZM scheme is nearly uniform with height and the heating is too weak compared to that produced by the MCA,which maybe contributes greatly to the failure of simulating a reasonable MJO.Comparing the simulated MJO by these two schemes indicate that the MJO simulated by the GCM is highly sensitive to cumulus parameterizations implanted in.The diabatic heating profile plays an important role in the performance of the GCM.Three sensitivity experiments with different heating profiles are designed in which modified heating profiles peak respectively in the upper troposphere(UH), middle troposphere(MH),and lower troposphere(LH).Both the LH run and the MH run produce eastward propagating signals on the intraseasonal timescale,while it is interesting that the intraseasonal timescale signals produced by the UH run propagate westward.It indicates that a realistic intraseasonal oscillation is more prone to be excited when the maximum heating concentrates in the middle-low levels,especially in the middle levels,while westward propagating disturbances axe more prone to be produced when the maximum heating appears very high.     

Sensitivity of the Simulated Tropical Intraseasonal Oscillation to Cumulus Parameterizations

The sensitivity of the simulated tropical intraseasonal oscillation or MJO （Madden and Julian oscillation） to different cumulus parameterizations is studied by using an atmospheric general circulation model （GCM）--SAMIL （Spectral Atmospheric Model of IAP LASG）. Results show that performance of the model in simulating the MJO alters widely when using two different cumulus parameterization schemes-the moist convective adjustment scheme （MCA） and the Zhang-McFarlane （ZM） scheme. MJO simulated by the MCA scheme was found to be more realistic than that simulated by the ZM scheme. MJO produced by the ZM scheme is too weak and shows little propagation characteristics. Weak moisture convergence at low levels simulated by the ZM scheme is not enough to maintain the structure and the eastward propagation of the oscillation. These two cumulus schemes produced different vertical structures of the heating profile. The heating profile produced by the ZM scheme is nearly uniform with height and the heating is too weak compared to that produced by the MCA, which maybe contributes greatly to the failure of simulating a reasonable MJO. Comparing the simulated MJO by these two schemes indicate that the MJO simulated by the GCM is highly sensitive to cumulus parameterizations implanted in. The diabatic heating profile plays an important role in the performance of the GCM. Three sensitivity experiments with different heating profiles are designed in which modified heating profiles peak respectively in the upper troposphere （UH）, middle troposphere （MH）, and lower troposphere （LH）. Both the LH run and the MH run produce eastward propagating signals on the intraseasonal timescale, while it is interesting that the intraseasonal timescale signals produced by the UH run propagate westward. It indicates that a realistic intraseasonal oscillation is more prone to be excited when the maximum heating concentrates in the middle-low levels, especially in the middle levels, while westward propagating disturbances     

The radiative influence of aerosol effects on liquid-phase cumulus and stratiform clouds based on sensitivity studies with two climate models

Aerosol effects on warm (liquid-phase) cumulus cloud systems may have a strong radiative influence via suppression of precipitation in convective systems. A consequence of this suppression of precipitation is increased liquid water available for large-scale stratiform clouds, through detrainment, that in turn affect their precipitation efficiency. The nature of this influence on radiation, however, is dependent on both the treatment of convective condensate and the aerosol distribution. Here, we examine these issues with two climate models—CSIRO and GISS, which treat detrained condensate differently. Aerosol–cloud interactions in warm stratiform and cumulus clouds (via cloud droplet formation and autoconversion) are treated similarly in both models. The influence of aerosol–cumulus cloud interactions on precipitation and radiation are examined via simulations with present-day and pre-industrial aerosol emissions. Sensitivity tests are also conducted to examine changes to climate due to changes in cumulus cloud droplet number (N _c); the main connection between aerosols and cumulus cloud microphysics. Results indicate that the CSIRO GCM is quite sensitive to changes in aerosol concentrations such that an increase in aerosols increases N _c, cloud cover, total liquid water path (LWP) and reduces total precipitation and net cloud radiative forcings. On the other hand, the radiative fluxes in the GISS GCM appear to have minimal changes despite an increase in aerosols and N _c. These differences between the two models—reduced total LWP in the GISS GCM for increased aerosols, opposite to that seen in CSIRO—appear to be more sensitive to the detrainment of convective condensate, rather than to changes in N _c. If aerosols suppress convective precipitation as noted in some observationally based studies (but not currently treated in most climate models), the consequence of this change in LWP suggests that: (1) the aerosol indirect effect (calculated as changes to net cloud radiative forcing from anthropogenic aerosols) may be higher than previously calculated or (2) lower than previously calculated. Observational constrains on these results are difficult to obtain and hence, until realistic cumulus-scale updrafts are implemented in models, the logic of detraining non-precipitating condensate at appropriate levels based on updrafts and its effects on radiation, will remain an uncertainty.     

Decadal-scale climate variability in the tropical and North Pacific during the 1970s and 1980s: observations and model results

An abrupt change in the large-scale boreal winter circulation pattern over the North Pacific was observed during the mid-1970s. Most notably, this change was marked by a southward shift and intensification of the Aleutian Low and prevailing westerlies over the mid-latitude central and eastern Pacific. Associated changes in diverse North Pacific climatological, hydrological, and biological variables have been noted by numerous researchers. Intriguingly, the timing of these changes in the extra-tropical circulation was coincident with a shift in the background state of the coupled ocean-atmosphere system over the tropical Pacific. These changes include increases in SST over broad regions of the central and eastern tropical Pacific and an eastward displacement of the region of persistent convection in the western Pacific. This paper presents a variety of observed data and model results to describe the climate shift, and to understand some of the links within the coupled climate system that produced it. Five main findings are emphasized: (1) evidence of abrupt, simultaneous, and apparently related changes can be found in many fields and in many model results; the climate shift is not an artifact, (2) over the tropical Pacific the climate change represents a shift in the state of the coupled ocean-atmosphere system, some aspects of which resemble features associated with El Niño episodes. However, the shift in state is not well characterized as due to a change in the frequency of intensity of El Ni~no episodes; it is better described as a change in background mean state, (3) when forced with observed SSTs, both a very simple atmospheric model and a full general circulation model (GCM) qualitatively simulate aspects of the decadal-scale shift over the tropical Pacific, (4) when forced with observed surface wind stress, two ocean models of the tropical Pacific, in which surface heat fluxes are parameterized as Newtonian damping, reproduce some aspects of the near-equatorial decadal SST signal. However, the models do not reproduce the large changes in SST observed at higher latitudes of the tropical Pacific, suggesting that altered surface heat fluxes dominated in producing these changes, and (5) an important new finding of this study is the success of a GCM in reproducing important aspects of the observed mid-1970s shift in winter northern hemisphere circulation. Comparative analyses of the observed and GCM simulated circulation suggest the altered patterns of tropical Pacific SST and convection were important in forcing the changes in the mid-latitude circulation, a finding corroborated by recent GCM experiments.     

A Gcm Study of the Impact of Greenhouse Gas Increase on the Frequency of Occurrence of Tropical Cyclones

In order to make inferences on the possible future changes of tropical cyclogenesis frequency, we apply the diagnostic computation of the Yearly Genesis Parameter (YGP) proposed by Gray (1975) to the large-scale fields simulated by a GCM. The YGP is an empirical diagnostic of the frequency of Tropical Cyclones (TCs) based on six physical parameters computed from seasonal means of atmospheric and oceanic variables. In this paper, we apply the YGP diagnostic to the results of three climate simulations performed with the atmospheric General Circulation Model (GCM) of Météo-France: ARPEGE-Climat. In a control simulation of the current climate, it is shown that the model has a realistic tropical climatology and that the computed YGP reproduces the geographical distribution of the tropical cyclogenesis frequency. The YGP is then applied to two simulations corresponding to two scenarios of doubled carbon dioxide concentration. The two experiments differ by the sea surface temperatures (SSTs) used as a lower boundary condition. In both simulations the YGP gives a large increase of total cyclogenesis frequency, but without extension of the area of possible cyclone genesis. The increase in YGP is due essentially to the contribution of the ocean thermal energy factor in the thermodynamical potential. The dynamical parameters, on the contrary, limit the cyclogenesis increase and are a major explanation of the difference between the two experiments. This is in agreement with the results of the previous similar study of Ryan et al. (1992) concerning the importance of large-scale atmospheric circulation modifications on tropical cyclone climatology. After discussing the observed relationships between ocean surface temperature and large-scale convection, and questioning the use of a fixed temperature threshold in the diagnosis of tropical cyclone frequency, we propose a modification to the YGP consisting in replacing the thermodynamical potential by a term proportional to the convective precipitation computed by the GCM. For the simulation of the present climate this modification affects only marginally the geographical distribution of tropical cyclone genesis, but for the doubled CO₂ case, the modified YGP diagnoses a more limited increase in TC genesis in the Northern Hemisphere and a small reduction in the Southern Hemisphere, which seems in better agreement with other recent modelling studies with high resolution climate models (Bengtsson et al., 1996). We conclude that the modified YGP based on convective precipitation could serve as a useful diagnostic of tropical cyclone genesis, and should be tested in simulations with other GCMs.     

Possible Impacts of Global Warming on the Hydrology of the Ogallala Aquifer Region

The Ogallala or High Plains aquifer provides water for about 20% of the irrigated land in the United States. About 20 km³ (16.6 million acre-feet) of water are withdrawn annually from this aquifer. In general, recharge has not compensated for withdrawals since major irrigation development began in this region in the 1940s. The mining of the Ogallala has been pictured as an analogue to climate change in that many GCMs predict a warmer and drier future for this region. In this paper we attempt to anticipate the possible impacts of climate change on the sustainability of the aquifer as a source of water for irrigation and other purposes in the region. We have applied HUMUS, the Hydrologic Unit Model of the U.S. to the Missouri and Arkansas-White-Red water resource regions that overlie the Ogallala. We have imposed three general circulation model (GISS, UKTR and BMRC) projections of future climate change on this region and simulated the changes that may be induced in water yields (runoff plus lateral flow) and ground water recharge. Each GCM was applied to HUMUS at three levels of global mean temperature (GMT) to represent increasing severity of climate change (a surrogate for time). HUMUS was also run at three levels of atmospheric CO₂ concentration (hereafter denoted by [CO₂]) in order to estimate the impacts of direct CO₂ effects on photosynthesis and evapotranspiration. Since the UKTR and GISS GCMs project increased precipitation in the Missouri basin, water yields increase there. The BMRC GCM predicts sharply decreased precipitation and, hence, reduced water yields. Precipitation reductions are even greater in the Arkansas basin under BMRC as are the consequent water yield losses. GISS and UKTR climates lead to only moderate yield losses in the Arkansas. CO₂-fertilization reverses these losses and yields increase slightly. CO₂ fertilization increases recharge in the base (no climate change) case in both basins. Recharge is reduced under all three GCMs and severities of climate change.     

The flexible global ocean-atmosphere-land system model, Grid-point Version 2: FGOALS-g2

This study mainly introduces the development of the Flexible Global Ocean-Atmosphere-Land System Model: Grid-point Version 2 (FGOALS-g2) and the preliminary evaluations of its performances based on results from the pre-industrial control run and four members of historical runs according to the fifth phase of the Coupled Model Intercomparison Project (CMIP5) experiment design. The results suggest that many obvious improvements have been achieved by the FGOALS-g2 compared with the previous version,FGOALS-g1, including its climatological mean states, climate variability, and 20th century surface temperature evolution. For example,FGOALS-g2 better simulates the frequency of tropical land precipitation, East Asian Monsoon precipitation and its seasonal cycle, MJO and ENSO, which are closely related to the updated cumulus parameterization scheme, as well as the alleviation of uncertainties in some key parameters in shallow and deep convection schemes, cloud fraction, cloud macro/microphysical processes and the boundary layer scheme in its atmospheric model. The annual cycle of sea surface temperature along the equator in the Pacific is significantly improved in the new version. The sea ice salinity simulation is one of the unique characteristics of FGOALS-g2, although it is somehow inconsistent with empirical observations in the Antarctic.     

Impacts of Shallow Convection Processes on a Simulated Boreal Summer Climatology in a Global Atmospheric Model

This study investigates the impacts of shallow convection schemes on a simulated seasonal climatology in the Global and Regional Integrated Model system (GRIMs). The eddy-diffusivity scheme of Tiedtke (TDK) is evaluated, focusing on the dependency upon deep convection schemes. Drying and warming near the top of the planetary boundary layer (PBL) and opposing effects above are observed. The height of PBL is reduced due to the increase of thermal stability near the PBL top. The weakened PBL turbulence is partly compensated with the increased downward solar radiation due to the reduction of low clouds. These effects are pronounced over the oceans, which leads to the modulation of tropical precipitation. It is found that the original TDK scheme shows similar behavior regardless of the choice of deep convection schemes. A revised TDK scheme that explicitly couples the PBL and shallow convection processes is proposed and evaluated. The proposed scheme generally improves the simulated climatology over the results with the original TDK scheme, along with further improvement in the case of the revised deep convection scheme. Our results indicate that the role of the shallow convection scheme needs to be carefully examined to improve the performance of atmospheric models, with a focus on modulated PBL and deep convection processes.     

物理过程参数化方案对中尺度暴雨数值模拟影响的研究

利用中尺度非静力MM 5模式和中国 2 0 0 1年 8月的 4个暴雨个例 ,研究了非绝热物理过程对中国暴雨动力和热力场预报的影响 ,深入分析了对流参数化方案在中尺度暴雨预报中的作用 ,讨论了利用模式扰动方法开展中国暴雨集合预报的可行性。结果表明 ,在短期数值预报中 ,非绝热物理过程对高度场预报影响较小 ,但边界层方案和对流参数化方案对产生暴雨的 3个基本条件即水汽通量散度、垂直速度、不稳定层结的影响很明显。不同对流参数化方案所预报的中尺度热力、动力场离差的结构特征与所预报降水的离差特征相似 ,且主要是在模式积分初期迅速增加 ,其后即趋于稳定。对中国热力场较均匀的暴雨过程 ,可以通过扰动模式的边界层和对流参数化方案 ,构造集合预报模式     

Evaluation of grid-point atmospheric model of IAP LASG version 2 (GAMIL2)

The Grid-point Atmospheric Model of IAP LASG version 2 (GAMIL2) has been developed through upgrading the deep convection parameterization, cumulus cloud fraction and two-moment cloud microphysical scheme, as well as changing some of the large uncertain parameters. In this paper, its performance is evaluated, and the results suggest that there are some significant improvements in GAMIL2 compared to the previous version GAMIL1, for example, the components of the energy budget at the top of atmosphere (TOA) and surface; the geographic distribution of shortwave cloud radiative forcing (SWCF); the ratio of stratiform versus total rainfall; the response of atmospheric circulation to the tropical ocean; and the eastward propagation and spatiotemporal structures of the Madden Julian Oscillation (MJO). Furthermore, the indirect aerosols effect (IAE) is -0.94 W m-2, within the range of 0 to -2 W m-2 given by the IPCC 4th Assessment Report (2007). The influence of uncertain parameters on the MJO and radiation fluxes is also discussed.     

Continental vegetation as a dynamic component of a global climate model: a preliminary assessment

A simplified vegetation distribution prediction scheme is used in combination with the Biosphere-Atmosphere Transfer Scheme (BATS) and coupled to a version of the NCAR Community Climate Model (CCM1) which includes a mixed-layer ocean. Employed in an off-line mode as a diagnostic tool, the scheme predicts a slightly darker and slightly rougher continental surface than when BATS' prescribed vegetation classes are used. The impact of tropical deforestation on regional climates, and hence on diagnosed vegetation, differs between South America and S.E. Asia. In the Amazon, the climatic effects of removing all the tropical forest are so marked that in only one of the 18 deforested grid elements could the new climate sustain tropical forest vegetation whereas in S.E. Asia in seven of the 9 deforested elements the climate could continue to support tropical forest. Following these off-line tests, the simple vegetation scheme has been coupled to the GCM as an interactive (or two-way) submodel for a test integration lasting 5.6 yr. It is found to be a stable component of the global climate system, producing only ~ 3% (absolute) interannual changes in the predicted percentages of continental vegetation, together with globally-averaged continental temperature increases of up to + 1.5 °C and evaporation increases of 0 to 5 W m^–2 and no discernible trends over the 67 months of integration. On the other hand, this interactive land biosphere causes regional-scale temperature differences of ± 10 °C and commensurate disturbances in other climatic parameters. Tuning, similar to the q-flux schemes used for ocean models, could improve the simulation of the present-day surface climate but, in the longer term, it will be important to focus on predicting the characteristics of the continental surface rather than simple vegetation classes. The coupling scheme will also have to allow for vegetation responses occurring over longer timescales so that the coupled system is buffered from sudden shocks.