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1.
Impact of the convection-wind-evaporation feedback on surface climate simulation in general circulation models 总被引：1，自引：0，他引：1
M. H. Zhang 《Climate Dynamics》1996,12(5):299-312
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. 相似文献
2.
Possible association of the western Tibetan Plateau snow cover with the decadal to interdecadal variations of northern China heatwave frequency 总被引：4，自引：0，他引：4
Zhiwei Wu Zhihong Jiang Jianping Li Shanshan Zhong Lijuan Wang 《Climate Dynamics》2012,39(9-10):2393-2402
Northern China has been subject to increased heatwave frequency (HWF) in recent decades, which deteriorates the local droughts and desertification. More than half a billion people face drinking water shortages and worsening ecological environment. In this study, the variability in the western Tibetan Plateau snow cover (TPSC) is observed to have an intimate linkage with the first empirical orthogonal function mode of the summer HWF across China. This distinct leading mode is dominated by the decadal to inter-decadal variability and features a mono-sign pattern with the extreme value center prevailing over northern China and high pressure anomalies at mid- and upper troposphere over Mongolia and the adjacent regions. A simplified general circulation model is utilized to examine the possible physical mechanism. A reduced TPSC anomaly can induce a positive geopotential height anomaly at the mid- and upper troposphere and subsequently enhance the climatological high pressure ridge over Mongolia and the adjacent regions. The subsidence associated with the high pressure anomalies tends to suppress the local cloud formation, which increases the net radiation budget, heats the surface, and favors more heatwaves. On the other hand, the surface heating can excite high pressure anomalies at mid- and upper troposphere. The latter further strengthens the upper troposphere high pressure anomalies over Mongolia and the adjacent regions. Through such positive feedback effect, the TPSC is tied to the interdecadal variations of the northern China HWF. 相似文献
3.
黄山地区不同高度云凝结核的观测分析 总被引：2，自引：0，他引：2
为研究华东高山地区云凝结核（Cloud Condensation Nuclei,CCN）沿山峰的垂直变化特征,2011年6月利用云凝结核计数器（Cloud Condensation Nuclei Counter,CCNC）在黄山三个不同高度处对CCN进行观测。观测结果表明,不同高度的CCN浓度随时间的变化趋势基本一致,CCN浓度随高度的升高而减小,过饱和度为0.8%时山顶、山腰、山底CCN浓度平均值分别为1105.62、1218.39和1777.78 cm-3,山底的高CCN浓度（大于1000 cm-3）出现频率大于山腰和山顶,表明山底受周边污染源的影响较山顶和山腰大。山顶和山底的日变化曲线均为双峰型,两个峰值分别出现在午前和午后,与大气边界层高度及山谷风变化有关。利用公式N=CSk拟合了山顶在不同天气条件下CCN活化谱,并分析了其变化特征。结果显示,晴天、雨天和雾天的C值分别为2798、384、765,小于一些污染城市,属于清洁大陆型核谱。本文结果有助于改进对华东背景地区云凝结核时空分布的认识,为该地区云雾核化在数值模式中的表达提供观测依据和参数化方案。 相似文献
4.
Quantifying contributions to polar warming amplification in an idealized coupled general circulation model 总被引：2，自引：1，他引：1
An idealized coupled general circulation model is used to demonstrate that the surface warming due to the doubling of CO2 can still be stronger in high latitudes than in low latitudes even without the negative evaporation feedback in low latitudes
and positive ice-albedo feedback in high latitudes, as well as without the poleward latent heat transport. The new climate
feedback analysis method formulated in Lu and Cai (Clim Dyn 32:873–885, 2009) is used to isolate contributions from both radiative and non-radiative feedback processes to the total temperature change
obtained with the coupled GCM. These partial temperature changes are additive and their sum is convergent to the total temperature
change. The radiative energy flux perturbations due to the doubling of CO2 and water vapor feedback lead to a stronger warming in low latitudes than in high latitudes at the surface and throughout
the entire troposphere. In the vertical, the temperature changes due to the doubling of CO2 and water vapor feedback are maximum near the surface and decrease with height at all latitudes. The simultaneous warming
reduction in low latitudes and amplification in high latitudes by the enhanced poleward dry static energy transport reverses
the poleward decreasing warming pattern at the surface and in the lower troposphere, but it is not able to do so in the upper
troposphere. The enhanced vertical moist convection in the tropics acts to amplify the warming in the upper troposphere at
an expense of reducing the warming in the lower troposphere and surface warming in the tropics. As a result, the final warming
pattern shows the co-existence of a reduction of the meridional temperature gradient at the surface and in the lower troposphere
with an increase of the meridional temperature gradient in the upper troposphere. In the tropics, the total warming in the
upper troposphere is stronger than the surface warming. 相似文献
5.
采用考虑化学气体传输过程的云模式模拟了2014年7月30日发生在安徽滁州境内一次深对流过程,研究深对流活动对不同高度示踪气体的输送及再分布作用。结果表明,在积云发展阶段,强上升气流使得云内源层示踪气体有效地向上输送,对流层中部强的夹卷过程及水平入流使得云外气体入云输送至主要对流区,并在垂直气流的作用下进一步影响各层示踪气体的分布。各层示踪气体均可向上输送至对流层上部,其中对流层中部示踪气体（2.1~4.5 km、4.5~7.5 km和7.5~10.8 km）的向上输送作用与近地层示踪气体（0~2.1 km）的贡献相当。例如,输送到11~13 km的示踪气体有4.9%来自近地层,6.3%来自2.1~7.5 km。此外,近地层示踪气体可在深对流的水平输送下向云侧边界扩散,将局地污染输送到云外周边地区。源层高度位于2.1~4.5 km的示踪气体可下沉输送至近地层,形成新的局地污染。随着源层高度的抬升,示踪气体向下输送作用减弱,其中对流层上层示踪物（10.8~15 km）无法输送到6 km以下。 相似文献
6.
BCC_AGCM2.1对中国东部地区云辐射特征模拟的偏差分析 总被引：2，自引：0，他引：2
通过与观测及再分析资料的对比,评估了中国国家气候中心大气环流模式BCC_AGCM 2.1对中国东部地区云辐射特征的模拟性能,并着重分析了模拟偏差的原因.在云辐射特征的基本气候态模拟方面,模式能大致再现中国东部中纬度层状云大值带,以及层状云冷季多、暖季少的季节特征,模拟的短波云辐射强迫也具有与观测相对应的季节变化特征.在云辐射强迫和地面温度相互影响过程的模拟方面,模式也能模拟出与观测相近的相互作用过程,即地面温度降低伴随着层状云云量增多以及负的净云辐射强迫加强,升温时层状云云量减少和净云辐射强迫减弱.但模式模拟的大陆层状云云量系统性偏少(尤其在冷季),使得模式在该处的短波云辐射强迫明显偏弱.初步分析表明,造成层状云模拟差异的主要原因是在中国西南地区对流层低层模式模拟的偏南气流明显偏弱以及陆-气潜热通量偏小.偏南气流偏弱导致低层散度和垂直运动条件不利于中层云的形成.同时偏南气流偏弱也不利于向西南地区的水汽输送,再加上模式模拟地表向上潜热通量偏小,这二者都使得模式模拟中国西南区域对流层低层的水汽含量严重偏少,相对湿度偏低,同样不利于层状云生成和发展.水汽偏少进一步导致在冷异常情况下青藏高原下游云辐射-地表温度反馈模拟偏弱,即呈现冷异常时,水汽条件偏弱限制了云量增加,弱化了进一步降低温度的反馈过程. 相似文献
7.
Black carbon aerosols absorb solar radiation and decrease planetary albedo, and thus can contribute to climate warming. In this paper, the dependence of equilibrium climate response on the altitude of black carbon is explored using an atmospheric general circulation model coupled to a mixed layer ocean model. The simulations model aerosol direct and semi-direct effects, but not indirect effects. Aerosol concentrations are prescribed and not interactive. It is shown that climate response of black carbon is highly dependent on the altitude of the aerosol. As the altitude of black carbon increases, surface temperatures decrease; black carbon near the surface causes surface warming, whereas black carbon near the tropopause and in the stratosphere causes surface cooling. This cooling occurs despite increasing planetary absorption of sunlight (i.e. decreasing planetary albedo). We find that the trend in surface air temperature response versus the altitude of black carbon is consistent with our calculations of radiative forcing after the troposphere, stratosphere, and land surface have undergone rapid adjustment, calculated as “regressed” radiative forcing. The variation in climate response from black carbon at different altitudes occurs largely from different fast climate responses; temperature dependent feedbacks are not statistically distinguishable. Impacts of black carbon at various altitudes on the hydrological cycle are also discussed; black carbon in the lowest atmospheric layer increases precipitation despite reductions in solar radiation reaching the surface, whereas black carbon at higher altitudes decreases precipitation. 相似文献
8.
Tropical convective responses to microphysical and radiative processes: a sensitivity study with a 2-D cloud resolving model 总被引：1，自引：0，他引：1
Summary Prognostic cloud schemes are increasingly used in weather and climate models in order to better treat cloud-radiation processes.
Simplifications are often made in such schemes for computational efficiency, like the scheme being used in the National Centers
for Environment Prediction models that excludes some microphysical processes and precipitation-radiation interaction. In this
study, sensitivity tests with a 2-D cloud resolving model are carried out to examine effects of the excluded microphysical
processes and precipitation-radiation interaction on tropical thermodynamics and cloud properties. The model is integrated
for 10 days with the imposed vertical velocity derived from the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere
Response Experiment. The experiment excluding the depositional growth of snow from cloud ice shows anomalous growth of cloud
ice and more than 20% increase of fractional cloud cover, indicating that the lack of the depositional snow growth causes
unrealistically large mixing ratio of cloud ice. The experiment excluding the precipitation-radiation interaction displays
a significant cooling and drying bias. The analysis of heat and moisture budgets shows that the simulation without the interaction
produces more stable upper troposphere and more unstable mid and lower troposphere than does the simulation with the interaction.
Thus, the suppressed growth of ice clouds in upper troposphere and stronger radiative cooling in mid and lower troposphere
are responsible for the cooling bias, and less evaporation of rain associated with the large-scale subsidence induces the
drying in mid and lower troposphere. 相似文献
9.
使用二维云分辨模式研究冰晶增长过程(云水到冰晶的冻结增长和通过水汽凝华冰晶到雪的增长)对热量收支的影响。采用4种冰晶增长参数化方案模拟了热带到中纬度地区的4个降水个例。研究发现:(1)高冰核浓度的ZENG方案和SHEN方案引起对流层中上层辐射加热增多,这与它们模拟的冰晶在对流层中上层增多有关。(2)高冰核浓度的ZENG方案导致模拟区域—平均的局地温度变化在对流层上层出现异常减小值,这与它在热带个例中导致垂直热量通量辐合减少和在中纬度个例中导致潜热加热减少有关。(3)尽管高冰核浓度的ZENG方案引起质量加权平均的辐射加热增多,但是它在热带个例中引起地表感热通量减少和在中纬度个例中引起潜热加热减少,最终导致4种参数化方案计算的模拟区域—质量加权平均的局地温度变化基本一致。 相似文献
10.
L.M. Franois 《Atmospheric Research》1988,21(3-4)
A one-dimensional radiative-convective model extending from 0 to 70 km is used to study the sensitivity of surface temperature to perturbations in the ozone profile. Several simulations have been performed for 03 reductions in various altitude ranges. For each case, the resulting perturbation in the thermal structure is analysed. These calculations have been repeated for several types of cloud layers with different opacities and altitudes. It is shown that the sensitivity of the surface temperature to ozone changes is dependent on the cloudiness assumed. Ozone decreases in the lower atmosphere (0–30 km) cool the surface, since the greenhouse effect is dominant in this region, and the climate sensitivity is enhanced in the presence of a cloud layer. For higher-altitude 03 changes (30–70 km), the sign of the surface temperature variation depends on the cloud characteristics. In fact, the latter result is mostly the consequence of the different equilibrium temperature profiles corresponding to the various types of cloudiness. When high stratospheric ozone is reduced, positive and negative surface temperature changes of several tenths of degree are respectively associated with cold and warm climatic conditions. 相似文献
11.
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. 相似文献
12.
A moderate cold air outbreak from the Arctic ice over the warm West-Spitsbergen current on 15 and 16 May 1988 during the field experiment ARKTIS '88 is analysed using data from four aircraft and one research vessel.The downstream development of cloud coverage appears to depend sensitively on the moisture content above the inversion. The cloud amount determines the energy balance at the sea surface. Under daytime conditions and little cloud cover, energy is added to the ocean in spite of sensible and latent heat losses.The downstream temperature increase in the boundary layer is controlled by sensible heat flux and by longwave radiation cooling. The entrainment sensible heat flux is the dominating term in the region near the ice edge. The downstream moisture increase is controlled by surface evaporation. Condensation processes play no significant role.On 16 May 1988 cloud streets near the ice edge changed to closed cloud meanders in the downstream direction. The aspect ratio increased from 3 to around 10 over a distance of 200 km. In the cloud street region, the dynamical generation of turbulent kinetic energy due to wind shear at the tilted inversion was larger than the thermal generation.Cloud droplet concentration, mean droplet radius and liquid water content increased linearly with height. The maximum liquid water content was only 0.1 g/kg near the top of a 400 m thick closed cloud and clearly below the adiabatic value. The net longwave radiation flux decreased by 50 W/m2 at cloud top and increased by 13 W/m2 at cloud base. 相似文献
13.
海洋温带气旋爆发性发展数值试验 总被引：12，自引：5，他引：7
利用 Ｐ Ｓ Ｕ／ Ｎ Ｃ Ａ Ｒ Ｍ Ｍ ４ 对５ 个西北太平洋温带气旋的爆发性发展进行了一系列数值模拟和敏感性试验,并对重要的物理过程进行了分析和诊断。采用相同物理过程及边界条件的控制试验成功地模拟出了主要的爆发性气旋加深率,为海洋爆发性气旋的业务数值预报提供了可能。敏感性试验获得了湿物理过程、能量频散、 Ｓ Ｓ Ｔ 和海面能通量、日本岛地形及初、边值条件等影响气旋加深率的定量认识,分析表明水的微物理过程,特别是网格尺度的水汽凝结、未饱和层的云滴和雨滴蒸发,是气旋爆发性发展中最重要的物理过程;在高空 ２００～３００ｈ Ｐａ 层的云滴蒸发效应可能是形成相应层气旋中心非绝热冷却峰值的主要原因;由内在热力动力学过程所决定的潜热释放比对流参数化任意规定的加热分布更接近实际并能产生更好的模拟结果;没有能量频散效应时可减小模拟加深的 ３０％ ;海面能通量在初始时刻比在爆发性发展时更重要,不计初始时海面能通量将影响模拟加深约 ２５％ ,而不计爆发性发展时的海面能通量,这种影响不及前者的一半;爆发性发展时的海面能通量呈不均匀分布并能诱导反锋面热力环流在局部抑制气旋的加深;大气模式对海气边界层能通量交换的变化和海洋增暖产生了显著的热力学响 相似文献
14.
基于天山北坡西部温泉哈夏林区间隔100m海拔高度采集的雪岭云杉梯度样本的断面积生长量资料,分析该区域树木生态弹性变化。干旱事件是区域生态弹性最主要的干扰因子,高温事件也是干扰因子之一。干扰因子的强度会造成生态弹性梯度特征的变化。在极端干旱年份,哈夏林区梯度生长弹性特征最显著,即中高海拔为强抵抗力和弱恢复力,而低海拔则呈相反态势,并出现生长衰退现象。中旱事件时不同海拔均为强抵抗力和较强的恢复力。高温年份低海拔呈现弱抵抗力和弱恢复力。在发生持续干旱时,不同海拔高度的树木生长均受到遏制,但低海拔衰退强度大于高海拔区域,高海拔区域树木对干旱的适应能力要强于中低海拔。 相似文献
15.
This study investigated the drivers and physical processes for the abrupt decadal summer surface warming and increases in hot temperature extremes that occurred over Northeast Asia in the mid-1990 s. Observations indicate an abrupt increase in summer mean surface air temperature(SAT) over Northeast Asia since the mid-1990 s. Accompanying this abrupt surface warming, significant changes in some temperature extremes, characterized by increases in summer mean daily maximum temperature(Tmax), daily minimum temperature(Tmin), annual hottest day temperature(TXx), and annual warmest night temperature(TNx) were observed. There were also increases in the frequency of summer days(SU) and tropical nights(TR).Atmospheric general circulation model experiments forced by changes in sea surface temperature(SST)/ sea ice extent(SIE),anthropogenic greenhouse gas(GHG) concentrations, and anthropogenic aerosol(AA) forcing, relative to the period 1964–93, reproduced the general patterns of observed summer mean SAT changes and associated changes in temperature extremes,although the abrupt decrease in precipitation since the mid-1990 s was not simulated. Additional model experiments with different forcings indicated that changes in SST/SIE explained 76% of the area-averaged summer mean surface warming signal over Northeast Asia, while the direct impact of changes in GHG and AA explained the remaining 24% of the surface warming signal. Analysis of physical processes indicated that the direct impact of the changes in AA(through aerosol–radiation and aerosol–cloud interactions), mainly related to the reduction of AA precursor emissions over Europe, played a dominant role in the increase in TXx and a similarly important role as SST/SIE changes in the increase in the frequency of SU over Northeast Asia via AA-induced coupled atmosphere–land surface and cloud feedbacks, rather than through a direct impact of AA changes on cloud condensation nuclei. The modelling results also imply that the abrupt summer surface warming and increases in hot temperature extremes over Northeast Asia since the mid-1990 s will probably sustain in the next few decades as GHG concentrations continue to increase and AA precursor emissions over both North America and Europe continue to decrease. 相似文献
16.
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 相似文献
17.
Summary Cloud parameters and surface radiative fluxes predicted by regional atmospheric models are directly compared with observations
for a 10-day period in late summer 1995 characterized by predominantly large-scale synoptic conditions. Observations of total
cloud cover and vertical cloud structure are inferred from measurements with a ground-based network of Lidar ceilometers and
IR-radiometers and from satellite observations on a 100 kilometer scale. Ground-based observations show that at altitudes
below 3 km, implying liquid water clouds, there is a considerable portion of optically non-opaque clouds. Vertical distributions
of cloud temperatures simultaneously inferred from the ground-based infrared radiometer network and from satellite can only
be reconciled if the occurrence of optically thin cloud structures at mid- and high tropospheric levels is assumed to be frequent.
Results of three regional atmospheric models, i.e. the GKSS-REMO, SMHI-HIRLAM, and KNMI-RACMO, are quantitatively compared
with the observations. The main finding is that all models predict too much cloud amount at low altitude below 900 hPa, which
is then compensated by an underestimation of cloud amount around 800 hPa. This is likely to be related with the finding that
all models tend to underestimate the planetary boundary layer height. All models overpredict the high-level cloud amount albeit
it is difficult to quantify to what extent due to the frequent presence of optically thin clouds. Whereas reasonably alike
in cloud parameters, the models differ considerably in radiative fluxes. One model links a well matching incoming solar radiation
to a radiatively transparent atmosphere over a too cool surface, another model underpredicts incoming solar radiation at the
surface due to a too strong cloud feedback to radiation, the last model represents all surface radiative fluxes quite well
on average, but underestimates the sensitivity of atmospheric transmissivity to cloud amount.
Received August 31, 2000 Revised March 15, 2001 相似文献
18.
Abstract Using GATE A/B‐scale U.S.S.R. ship data, heat and moisture budget analyses have been carried out for the three‐day period: 0000 GMT, 7 September to 2400 GMT, 9 September, 1974. The period has been subdivided into an undisturbed period (0000 GMT, 7 September ‐1800 GMT, 8 September) and a disturbed period (1800 GMT, 8 September ‐ 2400 GMT, 9 September) based on surface precipitation and satellite cloud observations. During the undisturbed period, precipitation was very light (1–3 mm day‐1). On the other hand, the precipitation rate became well over 10 mm day‐1 during the disturbed period. A/B‐scale heat and moisture budget results for both periods are presented. It is found that during the undisturbed period, cumulus clouds have heating and moistening effects in the lower troposphere below 700 mb, and cooling and moistening effects in the upper troposphere above 600mb. In the disturbed period, clouds have strong heating and drying effects throughout the entire cloud layer. Using the diagnostic scheme developed by Cho (1977), the collective properties of cumulus clouds for both the undisturbed and the disturbed periods are also determined. During the undisturbed period, some clouds reached as high as the 300‐mb level, however, little precipitation was produced. The total cloud mass flux is found to be negative in the upper troposphere and can be attributed to downdrafts induced by the evaporation of cloud liquid water. On the other hand, total cloud mass flux for the disturbed period is positive throughout the entire troposphere. 相似文献
19.
夏季我国干旱、半干旱区陆面过程能量平衡及其局地大气环流 总被引：28，自引：10，他引：18
利用NCEP资料分析得出,夏季我国干旱,半干旱区在整个欧亚大陆上是陆面感热通量最强的地方,与此对应的陆面潜热通量则最弱.陆面所接收的太阳短波辐射主要以感热和长波辐射的能量形式释放.该区降水量很少,降水量的年际变率也很弱;因此,该区的陆面热量通量都显出很弱的年际变率;然而,这些通量的年代际变率信号则比较显著.我国干旱、半干旱区大气环流的热力过程与其陆面过程特征密切相关.该区对流层大气的辐射冷却很强,达-3 K d-1.由于缺乏水汽和上升运动,大尺度凝结加热率、深对流加热率、浅对流加热率都非常弱.因此,600hPa以上的大气以绝热下沉加热来平衡辐射冷却;600hPa以下,陆面感热引起的垂直扩散加热率非常强,多达8 K d-1,它除了平衡辐射冷却以外还制造对流层低层的对流运动,以绝热上升冷却来平衡多余的垂直扩散加热.总之,我国干旱、半干旱区的陆面过程特征决定了该区大气运动的特殊垂直结构,即对流层低层对流上升运动及其上层的下沉运动.我国干旱、半干旱区陆面能量平衡及其局地大气环流的年代际变率,是全球气候系统年代际变率的必然结果. 相似文献
20.
Global simulations with the Bureau of Meteorology Research Centre climate model coupled to the CHAmeleon Surface Model (CHASM) are used to explore the sensitivity of simulated changes in evaporation, precipitation, air temperature and soil moisture resulting from a doubling of carbon dioxide in the atmosphere. Five simulations, using prescribed sea surface temperatures, are conducted which are identical except in the level of complexity used to represent the surface energy balance. The simulation of air temperature, precipitation, evaporation and soil moisture at 1 2 CO2 and at 2 2 CO2 are generally sensitive at statistically significant levels to the complexity of the surface energy balance representation (i.e. the level of complexity used to represent these processes affects the simulated climate). However, changes in mean quantities, resulting from a doubling of atmospheric CO2, are generally insensitive to the surface energy balance complexity. Conversely, changes in the spatial and temporal variance of evaporation and soil moisture are sensitive to the surface energy balance complexity. The addition of explicit canopy interception to the simplest model examined here enables that model to capture the change in the variance of evaporation simulated by the more complex models. In order to simulate changes in the variability of soil moisture, an explicit parameterization of bare soil evaporation is required. Overall, our results increase confidence that the simulation by climate models of the mean impact of increasing CO2 on climate are reliable. Changes in the variability resulting from increased CO2 on air temperature, precipitation or evaporation are also likely to be reliable since climate models typically use sufficiently complex land surface schemes. However, if the impact of increased CO2 on soil moisture is required, then a more complex surface energy balance representation may be needed in order to capture changes in variability. Overall, our results imply that the level of complexity used by most climate models to represent the surface energy balance is appropriate and does not contribute significant uncertainty in the simulation of changes resulting from increasing CO2. Our results only relate to surface energy balance complexity, and major uncertainties remain in how to model the surface hydrology and changes in the physiology, structural characteristics and distribution of vegetation. Future developments of land surface models should therefore focus on improving the representation of these processes. 相似文献