Climate feedback efficiency and synergy

Earth’s climate sensitivity to radiative forcing induced by a doubling of the atmospheric CO₂ is determined by feedback mechanisms, including changes in atmospheric water vapor, clouds and surface albedo, that act to either amplify or dampen the response. The climate system is frequently interpreted in terms of a simple energy balance model, in which it is assumed that individual feedback mechanisms are additive and act independently. Here we test these assumptions by systematically controlling, or locking, the radiative feedbacks in a state-of-the-art climate model. The method is shown to yield a near-perfect decomposition of change into partial temperature contributions pertaining to forcing and each of the feedbacks. In the studied model water vapor feedback stands for about half the temperature change, CO₂-forcing about one third, while cloud and surface albedo feedback contributions are relatively small. We find a close correspondence between forcing, feedback and partial surface temperature response for the water vapor and surface albedo feedbacks, while the cloud feedback is inefficient in inducing surface temperature change. Analysis suggests that cloud-induced warming in the upper tropical troposphere, consistent with rising convective cloud anvils in a warming climate enhances the negative lapse-rate feedback, thereby offsetting some of the warming that would otherwise be attributable to this positive cloud feedback. By subsequently combining feedback mechanisms we find a positive synergy acting between the water vapor feedback and the cloud feedback; that is, the combined cloud and water vapor feedback is greater than the sum of its parts. Negative synergies surround the surface albedo feedback, as associated cloud and water vapor changes dampen the anticipated climate change induced by retreating snow and ice. Our results highlight the importance of treating the coupling between clouds, water vapor and temperature in a deepening troposphere.     

Greenhouse sensitivity experiments with penetrative cumulus convection and tropical cirrus albedo effects

Results are presented from two versions of a global R15 atmospheric general circulation model (GCM) coupled to a nondynamic, 50-m deep, slab ocean. Both versions include a penetrative convection scheme that has the effect of pumping more moisture higher into the troposphere. One also includes a simple prescribed functional dependence of cloud albedo in areas of high sea-surface temperature (SST) and deep convection. Previous analysis of observations has shown that in regions of high SST and deep convection, the upper-level cloud albedos increase as a result of the greater optical depth associated with increased moisture content. Based on these observations, we prescribe increased middle- and upper-level cloud albedos in regions of SST greater than 303 K where deep convection occurs. This crudely accounts for a type of cloud optical property feedback, but is well short of a computed cloud-optical property scheme. Since great uncertainty accompanies the formulation and tuning of such schemes, the prescribed albedo feedback is an intermediate step to examine basic feedbacks and sensitivities. We compare the two model versions (with earlier results from the same model with convective adjustment) to a model from the Canadian Climate Centre (CCC) having convective adjustment and a computed cloud optical properties feedback scheme and to several other GCMs. The addition of penetrative convection increases tropospheric moisture, cloud amount, and planetary albedo and decreases net solar input at the surface. However, the competing effect of increased downward infrared flux (from increased tropospheric moisture) causes a warmer surface and increased latent heat flux. Adding the prescribed cirrus albedo feedback decreases net solar input at the surface in the tropics, since the cloud albedos increase in regions of high SST and deep convection. Downward infrared radiation (from increased moisture) also increases, but this effect is overpowered by the reduced solar input in the tropics. Therefore, the surface is somewhat cooler in the tropics, latent heat flux decreases, and global average sensitivity to a doubling of CO₂ with regard to temperature and precipitation/evaporation feedback is reduced. Similar processes, evident in the CCC model with convective adjustment and a computed cloud optical properties feedback scheme, occur over a somewhat expanded latitudinal range. The addition of penetrative convection produces global effects, as does the prescribed cirrus albedo feedback, although the strongest local effects of the latter occur in the tropics.Portions of this study are supported by the Office of Health and Environmental Research of the U.S. Department of Energy as part of its Carbon Dioxide Research Program, and by the Electric Power Research Institute as part of its Model Evaluation Consortium for Climate Assessment ProjectThe National Center for Atmospheric Research is sponsored by the National Science Foundation     

Quantifying contributions of climate feedbacks to tropospheric warming in the NCAR CCSM3.0

In this study, a coupled atmosphere-surface “climate feedback-response analysis method” (CFRAM) was applied to the slab ocean model version of the NCAR CCSM3.0 to understand the tropospheric warming due to a doubling of CO₂ concentration through quantifying the contributions of each climate feedback process. It is shown that the tropospheric warming displays distinct meridional and vertical patterns that are in a good agreement with the multi-model mean projection from the IPCC AR4. In the tropics, the warming in the upper troposphere is stronger than in the lower troposphere, leading to a decrease in temperature lapse rate, whereas in high latitudes the opposite it true. In terms of meridional contrast, the lower tropospheric warming in the tropics is weaker than that in high latitudes, resulting in a weakened meridional temperature gradient. In the upper troposphere the meridional temperature gradient is enhanced due to much stronger warming in the tropics than in high latitudes. Using the CFRAM method, we analyzed both radiative feedbacks, which have been emphasized in previous climate feedback analysis, and non-radiative feedbacks. It is shown that non-radiative (radiative) feedbacks are the major contributors to the temperature lapse rate decrease (increase) in the tropical (polar) region. Atmospheric convection is the leading contributor to temperature lapse rate decrease in the tropics. The cloud feedback also has non-negligible contributions. In the polar region, water vapor feedback is the main contributor to the temperature lapse rate increase, followed by albedo feedback and CO₂ forcing. The decrease of meridional temperature gradient in the lower troposphere is mainly due to strong cooling from convection and cloud feedback in the tropics and the strong warming from albedo feedback in the polar region. The strengthening of meridional temperature gradient in the upper troposphere can be attributed to the warming associated with convection and cloud feedback in the tropics. Since convection is the leading contributor to the warming differences between tropical lower and upper troposphere, and between the tropical and polar regions, this study indicates that tropical convection plays a critical role in determining the climate sensitivity. In addition, the CFRAM analysis shows that convective process and water vapor feedback are the two major contributors to the tropical upper troposphere temperature change, indicating that the excessive upper tropospheric warming in the IPCC AR4 models may be due to overestimated warming from convective process or underestimated cooling due to water vapor feedback.     

Cloud albedo feedback and the super greenhouse effect in a global coupled GCM

Two competing cloud-radiative feedbacks identified in previous studies i.e., cloud albedo feedback and the super greenhouse effect, are examined in a sensitivity study with a global coupled ocean-atmosphere general circulation model. Cloud albedo feedback is strengthened in a sensitivity experiment by lowering the sea-surface temperature (SST) threshold in the specified cloud albedo feedback scheme. This simple parameterization requires coincident warm SSTs and deep convection for upper-level cloud albedos to increase. The enhanced cloud albedo feedback in the sensitivity experiment results in decreased maximum values of SST and cooler surface temperatures over most areas of the planet. There is also a cooling of the tropical troposphere with attendant global changes of atmospheric circulation reminiscent of those observed during La Niña or cold events in the Southern Oscillation. The strengthening of the cloud albedo feedback only occurs over warm tropical oceans (e.g., the western Pacific warm pool), where there is increased albedo, decreased absorbed solar radiation at the surface, stronger surface westerlies, enhanced westward currents, lower temperatures, and decreased precipitation and evaporation. However, the weakened convection over the tropical western Pacific Ocean alters the large-scale circulation in the tropics such that there is increased upper-level divergence over tropical land areas and the tropical Indian Ocean. This results in increased precipitation in those regions and intensified monsoonal regimes. The enhanced precipitation over tropical land areas produces increased clouds and albedo and wetter and cooler land surfaces. These additional contributions to decreased absorbed solar input at the surface combine with similar changes over the tropical oceans to produce the global cooling associated with the stronger cloud albedo feedback. Increased low-level moisture convergence and precipitation over the tropical Indian Ocean enhance slightly the super greenhouse effect there. But the stronger cloud albedo feedback is still the dominant effect, although cooling of SSTs in that region is less than in the tropical western Pacific Ocean. The sensitivity experiment demonstrates how a regional change of radiative forcing is quickly transmitted globally through a combination of radiative and dynamical processes in the coupled model. This study points to the uncertainties involved with the parameterization of cloud albedo and the major implications of such parameterizations concerning the maximum values of SST, global climate sensitivity, and climate change.Support is provided by the Office of Health and Environmental Research of the U.S. Department of Energy, as part of its Carbon Dioxide Research Program.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

A pseudo-Lagrangian study of the sulfur budget in the remote Arctic marine boundary layer

The atmospheric sulfur cycle of the remote Arctic marine boundary layer is studied using trajectories and measurements of sulfur compounds from the International Arctic Ocean Expedition 1991, along with a pseudo-Lagrangian approach and an analytical model. The dimethyl sulfide [DMS(g)] turnover time was  h. Only  % of DMS(g) followed reaction paths to sulfur dioxide [SO₂(g)], sub-micrometre aerosol non-seasalt sulfate (nss-SO₄²⁻) or methane sulfonate (MSA). During the first 3 d of transport over the pack ice, fog deposition and drizzle resulted in short turnover times;  h for SO₂(g),  h for MSA and  h for nss-SO₄²⁻. Therefore, DMS(g) will, owing to its origin along or south of the ice edge and longer turnover time, survive the original sub-micrometre sulfur aerosol mass and gradually replace it with new biogenic sulfur aerosol mass. The advection of DMS(g) along with heat and moisture will influence the clouds and fogs over the Arctic pack ice through the formation of cloud condensation nuclei (CCN). If the pack ice cover were to decrease owing to a climate change, the total Arctic Ocean DMS production would change, and potentially there could be an ice–DMS–cloud–albedo climate feedback effect, but it would be accompanied by changes in the fog aerosol sink.     

CCN concentration in troposphere over China

CCN concentration in the middle-lower troposphere over northern China was observed using a cloud condensation nucleus counter, MEE-130, installed on an IL-14 aircraft in the summer of 1983 and 1984. More than 60 sets of data (each flight as one set) were collected. The main results are: (1) in northern China, CCN concentration is 10²-10⁴/ cm³ near ground, decreases with increasing height and follows exponential distribution; (2) the local CCN concentration and its distribution with altitude are influenced by some meteorological factors: such as inversion, cloud and precipitation, wind and land—sea breeze etc. The inversion makes CCN significantly accumulate just below the inversion level; CCN concentration is lower inside clouds than outside clouds at same level; wind plays an important role of transporting CCN horizontally; (3) the CCN concentration is higher above the land than above the sea at same level; CCN concentration is one order of magnitude lower over the coastal cities like Qingdao than over the continental cities like Zhengzhou; (4) all these suggest that CCN in northern China comes mainly from continental surface layer. Densely—populated areas and industrial areas may produce more CCN.     

Aerosol over the Southern Ocean

In a first attempt to assess a proposed climatic change feedback process involving cloud condensation nuclei (CCN) and cloud albedo, CCN concentrations N as a function of supersaturation S were measured on a voyage from latitude 43 to 65°S in October–November 1988. The usual relationship N=CS^k, with k=0.5 and C a constant was a fair apprraximation for S in the range 0.3–0.7% implying that CCN concentrations should largely determine cloud drop concentrations and hence albedo for clouds with S in that range. South of latitude 50°S and at smaller S,k was 1 or larger on average, which would lead to reduced dependence of albedo on CCN for the relevant clouds. N varied very widely for separations of the order of 100 km or 6 hours in time, particularly when the sea was partly ice-covered, suggesting strong local influences. During a large increase in N 60°S, unaccompanied by an increase in condensation nuclei (CN), cloud drops grew more rapidly than usual. In a subsidiary experiment particles were collected and examined by transmission electron microscopy. For particles less than 0.2 μm diameter, 80–90% appeared to consist of ammonium sulfate, the remainder being sea salt or an unknown substance which was more liquid and heat-resistant. Dialysis showed that the sulfate particles contained a few percent of insoluble material. Particles which formed cloud drops in vapours other water, were also studied. Comparison of these and water CCN and the rates of droplet suggested that the water insoluble portion of the particles was ethanol-soluble and surface-active. CN concentrations decreased by a factor of about 2 between 43 and 65°S, a change closely paralleled by ethanol CCN concentrations.     

云凝结核对南京及周边地区夏季暴雨影响的数值模拟

利用WRF3.8.1模式,采用Thompson云微物理参数化方案,对南京2014年6月初的一次暴雨过程进行模拟;设置多组数值试验,从中选取清洁和严重污染两组试验,对比分析低、高云凝结核浓度对此次降水的影响。结果表明：1）Thompson方案对此次降水过程具有一定的再现能力,但对24 h累积降水量的模拟整体偏低,且随云凝结核浓度的上升,累积降水量增加。较高的云凝结核浓度有利于强降水中心强度增强、降水范围扩大,而对较弱降水中心则有相反的影响。2）云凝结核浓度的增加将抑制云滴向雨滴的转化,使更多云滴被输送到对流层中层,对流层低层的暖云过程被抑制。3）云凝结核浓度的增加使对流层中层的过冷云水增加,促进过冷云水向霰的转化,也促进雪的淞附过程,这有利于冷云过程的发展。4）云凝结核浓度的增加对暖云过程具有负反馈作用,对冷云过程具有正反馈作用。     

强对流天气对O3和CO的垂直输送作用

利用ACTIVE（aerosol and chemical transport in tropical convection）试验资料,取2006年1月20日澳大利亚北部达尔文岛附近发生的一次飑线强对流天气的AE17航次和2006年1月27日无对流天气的AE21航次飞行路径中的探测资料,对澳大利亚达尔文地区夏季风盛行期间发生的有无强对流发生时O₃和CO浓度垂直分布变化进行对比,考察强对流性天气发生对O₃和CO浓度垂直输送作用。深对流云内强烈的垂直上升运动将O₃和CO等化学气体携带输送至对流层上部并在对流层顶堆积,从而在对流层上部产生浓度峰值。当有强对流发生,飞机进入对流云上层时,O₃浓度和CO浓度升高,O₃和CO浓度变率增大,在对流层上部浓度出现峰值;当飞机飞出对流云时,O₃和CO浓度相对较低,在对流云外出现谷值。在无对流发生的条件下O₃和CO浓度相对较小,浓度变率也较小,无峰值产生。分析表明:O₃和CO浓度分布不仅与强对流的垂直输送作用关系密切,且与气象要素垂直和水平分布以及动力输送过程密切相关。     

Planetary albedo in strongly forced climate, as simulated by the CMIP3 models

In an ensemble of general circulation models, the global mean albedo significantly decreases in response to strong CO₂ forcing. In some of the models, the magnitude of this positive feedback is as large as the CO₂ forcing itself. The models agree well on the surface contribution to the trend, due to retreating snow and ice cover, but display large differences when it comes to the contribution from shortwave radiative effects of clouds. The ??cloud contribution?? defined as the difference between clear-sky and all-sky albedo anomalies and denoted as ??CC is correlated with equilibrium climate sensitivity in the models (correlation coefficient 0.76), indicating that in high sensitivity models the clouds to a greater extent act to enhance the negative clear-sky albedo trend, whereas in low sensitivity models the clouds rather counteract this trend. As a consequence, the total albedo trend is more negative in more sensitive models (correlation coefficient 0.73). This illustrates in a new way the importance of cloud response to global warming in determining climate sensitivity in models. The cloud contribution to the albedo trend can primarily be ascribed to changes in total cloud fraction, but changes in cloud albedo may also be of importance.     

Impact of the convection-wind-evaporation feedback on surface climate simulation in general circulation models

The wind-evaporation-convection feedback in the tropics is demonstrated to strongly affect the mean state of surface climate in atmospheric general circulation models. The feedback is shown to be very effective in channeling perturbations from one component of the climate system to other components, e.g., from evaporation to surface wind and from atmospheric convective activity to evaporation. It also provides an effective channel to pass on atmospheric perturbations in the middle and upper troposphere to the surface. As an illustration, it is shown that surface evaporation over tropical oceans is connected with cloud absorption of shortwave radiation through this feedback. Insufficient shortwave cloud absorption, causing excessive shortwave radiation at the surface as is common in most of the climate models, leads to excessive evaporation. Quantitatively, sensitivity of evaporation to short-wave cloud absorption, when averaged over the whole tropics, can be described by an approximate balance of variations in atmospheric radiative cooling and latent heating. This balance is achieved by the impact of radiation on convection, and then on the surface wind and evaporation. This mechanism calls for the need to include atmospheric processes far beyond the surface for improvements of the quality of surface climate simulation.     

The sea ice mass budget of the Arctic and its future change as simulated by coupled climate models

Arctic sea ice mass budgets for the twentieth century and projected changes through the twenty-first century are assessed from 14 coupled global climate models. Large inter-model scatter in contemporary mass budgets is strongly related to variations in absorbed solar radiation, due in large part to differences in the surface albedo simulation. Over the twenty-first century, all models simulate a decrease in ice volume resulting from increased annual net melt (melt minus growth), partially compensated by reduced transport to lower latitudes. Despite this general agreement, the models vary considerably regarding the magnitude of ice volume loss and the relative roles of changing melt and growth in driving it. Projected changes in sea ice mass budgets depend in part on the initial (mid twentieth century) ice conditions; models with thicker initial ice generally exhibit larger volume losses. Pointing to the importance of evolving surface albedo and cloud properties, inter-model scatter in changing net ice melt is significantly related to changes in downwelling longwave and absorbed shortwave radiation. These factors, along with the simulated mean and spatial distribution of ice thickness, contribute to a large inter-model scatter in the projected onset of seasonally ice-free conditions.     

Climate feedbacks in a general circulation model incorporating prognostic clouds

 This study performs a comprehensive feedback analysis on the Bureau of Meteorology Research Centre General Circulation Model, quantifying all important feedbacks operating under an increase in atmospheric CO₂. The individual feedbacks are analysed in detail, using an offline radiation perturbation method, looking at long- and shortwave components, latitudinal distributions, cloud impacts, non-linearities under 2xCO₂ and 4xCO₂ warmings and at interannual variability. The water vapour feedback is divided into terms due to moisture height and amount changes. The net cloud feedback is separated into terms due to cloud amount, height, water content, water phase, physical thickness and convective cloud fraction. Globally the most important feedbacks were found to be (from strongest positive to strongest negative) those due to water vapour, clouds, surface albedo, lapse rate and surface temperature. For the longwave (LW) response the most important term of the cloud ‘optical property’ feedbacks is due to the water content. In the shortwave (SW), both water content and water phase changes are important. Cloud amount and height terms are also important for both LW and SW. Feedbacks due to physical cloud thickness and convective cloud fraction are found to be relatively small. All cloud component feedbacks (other than height) produce conflicting LW/SW feedbacks in the model. Furthermore, the optical property and cloud fraction feedbacks are also of opposite sign. The result is that the net cloud feedback is the (relatively small) product of conflicting physical processes. Non-linearities in the feedbacks are found to be relatively small for all but the surface albedo response and some cloud component contributions. The cloud impact on non-cloud feedbacks is also discussed: greatest impact is on the surface albedo, but impact on water vapour feedback is also significant. The analysis method here proves to be a␣powerful tool for detailing the contributions from different model processes (and particularly those of the clouds) to the final climate model sensitivity. Received: 15 June 2000 / Accepted: 10 January 2001     

On the interpretation of inter-model spread in CMIP5 climate sensitivity estimates

This study diagnoses the climate sensitivity, radiative forcing and climate feedback estimates from eleven general circulation models participating in the Fifth Phase of the Coupled Model Intercomparison Project (CMIP5), and analyzes inter-model differences. This is done by taking into account the fact that the climate response to increased carbon dioxide (CO₂) is not necessarily only mediated by surface temperature changes, but can also result from fast land warming and tropospheric adjustments to the CO₂ radiative forcing. By considering tropospheric adjustments to CO₂ as part of the forcing rather than as feedbacks, and by using the radiative kernels approach, we decompose climate sensitivity estimates in terms of feedbacks and adjustments associated with water vapor, temperature lapse rate, surface albedo and clouds. Cloud adjustment to CO₂ is, with one exception, generally positive, and is associated with a reduced strength of the cloud feedback; the multi-model mean cloud feedback is about 33 % weaker. Non-cloud adjustments associated with temperature, water vapor and albedo seem, however, to be better understood as responses to land surface warming. Separating out the tropospheric adjustments does not significantly affect the spread in climate sensitivity estimates, which primarily results from differing climate feedbacks. About 70 % of the spread stems from the cloud feedback, which remains the major source of inter-model spread in climate sensitivity, with a large contribution from the tropics. Differences in tropical cloud feedbacks between low-sensitivity and high-sensitivity models occur over a large range of dynamical regimes, but primarily arise from the regimes associated with a predominance of shallow cumulus and stratocumulus clouds. The combined water vapor plus lapse rate feedback also contributes to the spread of climate sensitivity estimates, with inter-model differences arising primarily from the relative humidity responses throughout the troposphere. Finally, this study points to a substantial role of nonlinearities in the calculation of adjustments and feedbacks for the interpretation of inter-model spread in climate sensitivity estimates. We show that in climate model simulations with large forcing (e.g., 4 × CO₂), nonlinearities cannot be assumed minor nor neglected. Having said that, most results presented here are consistent with a number of previous feedback studies, despite the very different nature of the methodologies and all the uncertainties associated with them.     

Intercomparison of precipitation simulated by regional climate models over East Asia in 1997 and 1998

Regional climate simulations in Asia from May 1997 to August 1998 were performed using the Seoul National University regional climate model （SNURCM） and Iowa State University regional climate model （ALT.MM5/LSM）, which were developed by coupling the NCAR/Land Surface Model （LSM） and the Mesoscale Model （MM5）. However, for physical processes of precipitation, the SNURCM used the Grell scheme for the convective parameterization scheme （CPS） and the simple ice scheme for the explicit moisture scheme （EMS）, while the ALT.MM5/LSM used the Betts-Miller scheme for CPS and the mixed phase scheme for EMS.
The simulated precipitation patterns and amounts over East Asia for the extreme climatic summer in 1997 （relative drought conditions） and 1998 （relative flood conditions） were especially focused upon. The ALT.MM5/LSM simulated more precipitation than was observed in 1997 due to more moisture and cloud water in the lower levels, despite weak upward motion. In the SNURCM, strong upward motion resulted in more precipitation than that was observed in 1998, with more moisture and cloud water in the middle levels. In the ALT.MM5/LSM, weak upward motion, unchanged moisture in the lower troposphere, and the decrease in latent heat flux at the surface increased convective precipitation only by 3% for the 1998 summer event. In the SNURCM, strong upward motion, the increase in moisture in the lower troposphere, and the increase in latent heat flux at the surface increased convective precipitation by 48% for the summer of 1998. The main differences between both simulations were moisture availability and horizontal momentum transport in the lower troposphere, which were also strongly influenced by large-scale forcing.     

Snow and cloud feedbacks modelled by an atmospheric general circulation model

One of the most important parametrizations in general circulation models used for climate change experiments is that of the surface albedo. The results of an albedo feedback experiment carried out under the auspices of the US Department of Energy are presented. An analysis of long and short wave components of the model response shows that short wave response dominates changes in fixed to variable albedo experiments, but that long wave response dominates in clear to cloudy sky changes. Cloud distribution changes are also discussed and are related to changes in global sensitivity. At the surface, the heat balance change for perturbed sea surface temperatures is dominated by changes in latent heat flux and downward long wave radiation. If albedo is freed up however, the major contrast lies in the change in surface reflected short wave radiation, amplified by changes in downward short wave radiation caused by cloud amount changes.     

Observations of Cloud Condensation Nuclei in North China

Using a DMT （Droplet Measurement Technologies） continuous flow streamwise thermal gradient cloud condensation nuclei （CCN） counter mounted on a Cheyenne IIIA aircraft, about 20 flights for aircraft mea- surements of CCN over North China were conducted in the autumn of 2005 and spring of 2006. According to the design for aircraft observation, the method of spiral ascent or descent in the troposphere was used for the vertical measurement of CCN, and some certain levels were chosen for horizontal measurement. The vertical distributions of CCN concentrations show that most CCN particles are concentrated in the low level of troposphere and CCN concentration decreased with height increasing. It suggests that the main source of CCN is from the surface. This result is consistent with former studies during 1983-1985 in China with a static thermal gradient CCN counter. The comparison of vertical observations between polluted rural area near Shijiazhuang and non-polluted rural area near Zhangjiakou shows that there is about five times difference in CCN concentration. But over two polluted cities, Shijiazhuang and Handan, there is no notable difference in CCN concentration. The horizontal flight measurements for penetrating the cumulus clouds experiment show the apparent decrease of CCN in clouds. It confirms that cloud has a definite consumptive effect on CCN particles because some CCN particles can form cloud droplets. The surface measurements of CCN in Shijiazhuang City were made during June-August 2005. The statistical CCN data show the great difference in concentration at the same supersaturation （S） in Shijiazhuang summertime. The minimum CCN concentrations were 584, 808, and 2431 cm-3, and the maximum concentrations were 9495, 16332, and 21812 cm-3 at S=0.1%, 0.3%, and 0.5%, respectively. CCN has a diurnal variation cycle. From 0600 BT, the concentration began to increase and reached the maximum at about noon. Then it generally decreased throughout the afternoon. The reason maybe is related to the onset o     

硫酸盐气溶胶间接效应对中国东部冬季气候的影响

气溶胶间接效应通过对云的作用来影响气候,其过程复杂且不确定性较大。本研究利用美国国家大气研究中心（NCAR）的公共大气模式CAM5.1,通过改变模式中硫酸盐气溶胶转化为云凝结核数浓度的数量,设计了硫酸盐气溶胶间接效应的敏感性试验,通过与控制试验对比来研究其间接效应对中国东部地区冬季云、降水和季风强度的影响。结果表明：在东亚地区云凝结核形成过程中,硫酸盐气溶胶占绝对的主导地位。硫酸盐气溶胶间接效应导致中国东部地区冬季云凝结核和云滴数浓度显著增加,海洋和陆地低层的云滴有效半径减小和总云液水路径的增加,导致了云反照率的增加。引起的负辐射强迫使地表和大气降温,海平面气压升高,增加的海陆气压梯度导致中国南方地区东亚冬季风增强,总降水率减少。硫酸盐气溶胶间接效应可能不是东亚冬季风在20世纪80年代中期年际变率减弱的原因。     

人为气溶胶对中国东部冬季风影响的模拟研究

采用美国国家大气研究中心(NCAR)的公共大气模式CAM5.1研究了人为气溶胶排放增加对中国东部冬季风的影响,同时通过对比中国东部地区不同人为气溶胶排放源的敏感性试验结果,探讨了人为硫酸盐、黑碳及总人为气溶胶(硫酸盐+黑碳)增加对东亚冬季风的影响。结果表明:冬季硫酸盐气溶胶排放增加的直接和第一间接效应减少了到达地表的短波辐射通量,引起了陆地地表和对流层低层降温,海平面气压升高,增加了海陆间气压梯度,使得东亚冬季风增强。其第二间接效应导致中国南部大尺度降水率减少;黑碳气溶胶排放增加导致到达地表的短波辐射通量减少和大气中短波辐射通量增加,其半直接效应部分抵消了直接效应,故地表温度变化微小且不显著。加热的对流层低层导致中国南部对流活动和对流降水率增加;总人为气溶胶排放增加导致的大气温度变化表现为弱的降温作用,引起中国北部对流和大尺度降水率减少,而南部对流降水率增加。总人为气溶胶和黑碳气溶胶排放增加是导致中国北(南)部的东亚冬季风增强(减弱)的重要因素。     

CCN Concentration in Troposphere over China

CCN concentration in the middle-lower troposphere over northern China was observed using a cloud condensation nucleus counter, MEE-130, installed on an IL-14 aircraft in the summer of 1983 and 1984. More than 60 sets of data (each flight as one set) were collected.The main results are: (1) in northern China, CCN concentration is 102-104/ cm3 near ground, decreases with increasing height and follows exponential distribution; (2) the local CCN concentration and its distribution with altitude are influenced by some meteorological factors: such as inversion, cloud and precipitation, wind and land-sea brce/.e etc. The inversion makes CCN significantly accumulate just below the inversion level; CCN concentration is lower inside clouds than outside clouds at same level; wind plays an important role of transporting CCN horizontally; (3) the CCN concentration is higher above the land than above the sea at same level; CCN concentration is one order of magnitude lower over the coastal cities like Qingdao than over