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1.
Turbulence data collected over a total of 25 days during two summers are used to describe processes responsible for the nonstationarity
of turbulent sensible heat fluxes at Summit, Greenland. A stationarity test shows that about 40% of the data are classified
as nonstationary. Three main factors are explored to account for the large fraction of nonstationary runs: (1) intermittency
of turbulence in stable conditions, (2) changes in net all-wave radiation in response to cloud forcing, and (3) diurnal trends
in stability. A classification procedure that accounts for the intermittent nature of turbulence shows that during stable,
nonstationary conditions 50% of the total sensible heat flux is realized in 22% of the sampling time. Intermittency often
occurs at Summit during periods characterized by weak and irregular horizontal winds in combination with strong stability.
Rapid changes in net all-wave radiation in response to cloud forcing results in nonstationarity during unstable conditions.
Between 0930–1130 and 1900–1930 UTC turbulent heat fluxes are not only small in magnitude but also typically change sign,
with nonstationarity during these periods often as high as 65%. These results should help resolve some of the present uncertainties
in obtaining reliable fluxes at this site, in particular under stable atmospheric conditions. 相似文献
2.
一维辐射-对流模式对云辐射强迫的数值模拟研究 总被引：10，自引：9，他引：1
利用一维辐射－对流气候模式, 详细研究了云量、云光学厚度以及云高等要素的变化对大气顶和地面太阳短波辐射和红外长波辐射通量以及云的辐射强迫的影响, 给出了计算这些物理量的经验拟合公式。结果表明, 云具有极为重要的辐射－气候效应。云量、云光学厚度以及云高即使只有百分之几的变化, 所带来的辐射强迫也可以与大气二氧化碳浓度加倍所产生的辐射强迫（3.75 W/m2）相比拟。例如, 当分别给它们+3%的扰动时, 即取云量变化0.015, 云光学厚度变化0.27, 以及云高变化0.15 km时（在实际的地球大气中, 这种尺度的变化是完全可能发生的）, 那么,可以得到地气系统的太阳短波辐射强迫-3.10 W/m2以及红外长波辐射强迫-1.77 W/m2, 二者之和为-4.78 W/m2, 已经完全可以抵消大气二氧化碳浓度加倍所产生的辐射强迫。但是, 当云量、云光学厚度以及云高向相反方向产生类似扰动时, 所产生的辐射强迫可能极大地放大二氧化碳浓度增加所产生的增强温室效应。因此, 研究结果揭示出, 不管是为了解释过去的气候变化, 还是预测未来的气候变化, 亟待加强在一个变化了的气候环境（例如地面温度升高）下, 云将发生何种变化的研究。 相似文献
3.
获取准确的云高及其变化特征,对于揭示天气系统的演变以及改进气候模式具有重要作用。由于不同设备观测云高的不确定性,将锋区要素不连续变化理论引入云高分析中,将云底部、云顶部大气的交界过渡带区域视为云锋区,研究探空、毫米波雷达、风廓线雷达等不同类型设备观测要素在云锋区及云外环境大气的变化特征。对流云和层状云个例研究表明:在云锋区,温湿度及雷达反射率因子随高度的一阶、二阶导数均呈不连续现象(即一阶、二阶导数值在云内外和云锋区表现为不相等),风廓线雷达信噪比垂直梯度也出现突变,因此不同设备观测云高具有较好空间一致性,并得到云底和云顶高度的合理范围和相应判据;相对于层状云,对流云内外温度梯度差异以及云体内反射率因子二阶导数的脉动变化幅度均偏大,因此可作为区分二者的参考指标。 相似文献
4.
Quantifying the radiative forcing due to aerosol–cloud interactions especially through cirrus clouds remains challenging because of our limited understanding of aerosol and cloud processes. In this study, we investigate the anthropogenic aerosol indirect forcing (AIF) through cirrus clouds using the Community Atmosphere Model version 5 (CAM5) with a state-of-the-art treatment of ice nucleation. We adopt a new approach to isolate anthropogenic AIF through cirrus clouds in which ice nucleation parameterization is driven by prescribed pre-industrial (PI) and presentday (PD) aerosols, respectively. Sensitivities of anthropogenic ice AIF (i.e., anthropogenic AIF through cirrus clouds) to different ice nucleation parameterizations, homogeneous freezing occurrence, and uncertainties in the cloud microphysics scheme are investigated. Results of sensitivity experiments show that the change (PD minus PI) in global annual mean longwave cloud forcing (i.e., longwave anthropogenic ice AIF) ranges from 0.14 to 0.35 W m–2, the change in global annual mean shortwave cloud forcing (i.e., shortwave anthropogenic ice AIF) from–0.47 to–0.20 W m–2, and the change in net cloud forcing from–0.12 to 0.05 W m–2. Our results suggest that different ice nucleation parameterizations are an important factor for the large uncertainty of anthropogenic ice AIF. Furthermore, improved understanding of the spatial and temporal occurrence characteristics of homogeneous freezing events and the mean states of cirrus cloud properties are also important for constraining anthropogenic ice AIF. 相似文献
5.
Changes in Arctic clouds during intervals of rapid sea ice loss 总被引：2，自引：0，他引：2
We investigate the behavior of clouds during rapid sea ice loss events (RILEs) in the Arctic, as simulated by multiple ensemble projections of the 21st century in the Community Climate System Model (CCSM3). Trends in cloud properties and sea ice coverage during RILEs are compared with their secular trends between 2000 and 2049 during summer, autumn, and winter. The results suggest that clouds promote abrupt Arctic climate change during RILEs through increased (decreased) cloudiness in autumn (summer) relative to the changes over the first half of the 21st century. The trends in cloud characteristics (cloud amount, water content, and radiative forcing) during RILEs are most strongly and consistently an amplifying effect during autumn, the season in which RILEs account for the majority of the secular trends. The total cloud trends in every season are primarily due to low clouds, which show a more robust response than middle and high clouds across RILEs. Lead-lag correlations of monthly sea ice concentration and cloud cover during autumn reveal that the relationship between less ice and more clouds is enhanced during RILEs, but there is no evidence that either variable is leading the other. Given that Arctic cloud projections in CCSM3 are similar to those from other state-of-the-art GCMs and that observations show increased autumn cloudiness associated with the extreme 2007 and 2008 sea ice minima, this study suggests that the rapidly declining Arctic sea ice will be accentuated by changes in polar clouds. 相似文献
6.
利用地基红外测云仪(WSIRCMS)在2011年11月北京观象台的连续观测数据,从总云量、云底高和天空类型3个方面初步分析其探测能力。结果表明:1该仪器能够不分昼夜同时实现云高、云量(高、中、低和总云量)和天空类型的连续自动探测;2与参考标准云量的差值在±10%以内的样本数占总样本数的72.5%,有霾存在时,对中高云的观测能力较弱,造成云量观测结果差异较大;3与激光云高仪的天顶方向的无云一致率达94.9%;在中低云情况下,云高观测结果一致性较好,高云时存在较大差异,WSIRCMS观测云高偏高;4与人工分类的天空类型一致的样本数占总样本数的82.63%,对波状云、积状云和混合云的识别能力稍低。 相似文献
7.
冬季青藏高原东部（22°N～32°N，102°E～118°E）层云区是唯一存在于副热带陆地的层云密集区，环流特征较为复杂，大多数耦合气候系统模式对该地区层云的模拟存在较大的偏差。对该地区层云模拟能力的系统分析评估是改进模式性能的重要基础。本文基于国际卫星云计划（ISCCP）卫星资料，评估了中国科学院大气物理研究所两个版本的气候系统模式FGOALS-s2和FGOALS-g2的大气环流模式试验（AMIP）对青藏高原东侧层云的模拟能力。通过分析云辐射强迫等相关特征、大气环流、稳定度、以及地表气温和云的关系，探讨了模式偏差的可能原因。结果表明，两个模式都不同程度地低估了青藏高原东侧的低层云量和云水含量。在垂直结构模拟方面，FGOALS-s2模式能较好地模拟出高原东侧低云主导的特征，其模拟的云顶高度与卫星资料更为接近；而FGOALS-g2模式则高估了该地区的平均云顶高度。分析表明，两个模式均低估了高原东侧的低层稳定度，同时不同程度地低估了该地区中低层水平水汽输送，导致层云云量的模拟偏少。此外，FGOALS-g2高估了高原东侧的上升运动和垂直水汽输送，使得模拟的低云偏少而云顶高度偏高。 相似文献
8.
9.
中国东部和印度季风区云辐射特性的比较 总被引：14，自引：0，他引：14
基于 ＩＳＣＣＰ和 ＥＱＢＥ资料,本文比较了中国东部和印度季风区的云和云辐射强迫的气候特征。虽然它们同属于亚洲季风区,并且有相似的降水季节特征,但它们各自的云和云辐射强迫特征差异很大。在印度区域,所有的云量有着相同的季节变化,最大云量分布都出现在夏季,且总云量中以高云量为主。而中国东部云量的季节变化都比较复杂,在总云量中以中、低云量为主,最大总云量出现在春季。冬季的总云量和中、低云量要大于夏季。在全球云量分布中,中国东部最典型的特征是：该地区为全球最大的雨层云覆盖区。与云的分布和变化相关,印度季风区最大的负短波云辐射强迫,最大的正的长波辐射强迫和最大的负的净云辐射强迫发生在夏季,而在中国东部,大的负的短波云辐射强迫发生在春夏之交。年平均的负的短波云辐射强迫在中国东部地区明显要大于在印度季风区。 相似文献
10.
Thorsten Mauritsen Rune G. Graversen Daniel Klocke Peter L. Langen Bjorn Stevens Lorenzo Tomassini 《Climate Dynamics》2013,41(9-10):2539-2554
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. 相似文献
11.
利用2007-2013年新疆的十场强对流天气过程以及与之相应的FY-2D静止气象卫星数据,分析了强对流云红外一通道、红外二通道、水汽通道及通道差的光谱特征,提取强对流云团样本点,采用统计方法确定判识指标的阈值范围,构建多通道多阈值判识方法。利用三场天气过程的地面实测降水资料分别验证了单时次和整场天气过程强对流云判识的准确性,结果表明：单时次强对流云的识别区域与发生降雨台站一致的准确率为83%;在整个天气过程中,强对流频次分布与降水实况吻合度较高,说明随着对流云团的移动和发展,判识区域与地面降水区域保持一致,验证了判识方法有效,阈值选取合理,可以为监测暴雨天气系统的发生、发展提供支持。 相似文献
12.
云是天气与气候变化的重要影响因子,准确估量云顶高度和云量对分析云特性、降水及强天气预报、估算云辐射强迫等都具有重要意义。利用2006-2010年6-8月CloudSat卫星搭载的微波云廓线雷达（CPR,简称微波雷达）和CALIPSO卫星搭载的云-气溶胶偏振激光雷达（CALIOP,简称激光雷达）的探测资料,分析了全球云顶高度及云量的空间分布特征。结果表明,热带地区微波雷达探测云顶高度平均比激光雷达低约4 km,但均超过12 km;副热带洋面云顶高度在4 km以下,且两部雷达探测的云顶高度差异存在地域性。微波雷达对薄云、云砧及云顶高度低于2.5 km的低云存在漏判,对厚云的云顶高度偏低估;微波雷达探测的全球总云量均值为51.1%,比激光雷达少23.3%;两者给出的云量分布也存在显著的海-陆差异,其中洋面云量差异更大,如微波雷达测出局部洋面云量为80%,而激光雷达的探测结果却超过90%。由于激光雷达发射波长短,对云顶微小粒子比较敏感,而微波雷达波长较长,对相对较小粒子的探测存在局限性。因此,激光雷达对云顶高度的探测优于微波雷达。此结果不仅加强了对激光雷达和微波雷达探测原理的认识,而且进一步理解了云的气候特征。 相似文献
13.
The cloud variations under subtropical high(STH) conditions during summers over a ten-year period are studied using combined data from the International Satellite Cloud Climatology Project and the National Centers for Environmental Prediction.The results reveal that clouds mainly experience an isolated evolution in the STHs,which is designated in this study by the 1540 gpm geopotential lines at 850 hPa.In the STH domain throughout the Northern Hemisphere,the average amount of total clouds exceeds 30%.Low clouds dominate in the STH domain,contributing over 60%of total cloud amount within the Pacific subtropical high and over 40%within the Atlantic subtropical high.The prevalence of low clouds in above regions is determined by the circulation pattern around 150°-180°E and 850 hPa,which suppresses both the upward development of the cloud tops and the water vapor divergences near the surface.Furthermore,clouds present great geographical incoherence within the STH domain.In the eastern STHs,the amount of middle and low clouds increases to peak in the early morning and decreases to a trough in the afternoon,while the amount of high clouds remains stable throughout the day.Conversely,in the western STHs,the diurnal amplitude of low and middle clouds is less than three,while high clouds dramatically reach the maximum in the afternoon and drop to the minimum in the evening.Among the nine cloud categories,stratocumulus clouds with greater optical thickness account for the most under STH conditions,no matter their occurrence or amount,causing more shortwave cloud radiative forcing to cool the local atmosphere and surface as a consequence. 相似文献
14.
The simulation of Arctic clouds and their influence on the winter surface temperature in present-day climate in the CMIP3 multi-model dataset 总被引：1，自引：1，他引：0
We investigate the influence of clouds on the surface energy budget and surface temperature in the sea-ice covered parts of the ocean north of the Arctic circle in present-day climate in nine global climate models participating in the Coupled Model Intercomparison Project phase 3, CMIP3. Monthly mean simulated surface skin temperature, radiative fluxes and cloud parameters are evaluated using retrievals from the extended AVHHR Polar Pathfinder (APP-x) product. We analyzed the annual cycle but the main focus is on the winter, in which large parts of the region experience polar night. We find a smaller across-model spread as well as better agreement with observations during summer than during winter in the simulated climatological annual cycles of total cloudiness and surface skin temperature. The across-model spread in liquid and ice water paths is substantial during the whole year. These results qualitatively agree with earlier studies on the present-day Arctic climate in GCMs. The climatological ensemble model mean annual cycle of surface cloud forcing shows good agreement with observations in summer. However, during winter the insulating effect of clouds tends to be underestimated in models. During winter, most of the models as well as the observations show higher monthly mean total cloud fractions, associated with larger positive surface cloud forcing. Most models also show good correlation between the surface cloud forcing and the vertically integrated ice and liquid cloud condensate. The wintertime ensemble model mean total cloud fraction (69%) shows excellent agreement with observations. The across-model spread in the winter mean cloudiness is substantial (36?C94%) however and several models significantly underestimate the cloud liquid water content. If the two models not showing any relationship between cloudiness and surface cloud forcing are disregarded, a tentative across-model relation exists, in such a way that models that simulate large winter mean cloudiness also show larger surface cloud forcing. Even though the across-model spread in wintertime surface cloud forcing is large, no clear relation to the surface temperature is found. This indicates that other processes, not explicitly cloud related, are important for the simulated across-model spread in surface temperature. 相似文献
15.
南半球中高纬度区域不同类型云的辐射特性 总被引：1，自引：0，他引：1
利用CloudSat的2B-CLDCLASS-LIDAR云分类产品和2B-FLXHR-LIDAR辐射产品4 a（2007-2010年）的数据,定量分析了单层云（高云、中云、低云）和3种双层云（如:高云与中云共存、高云与低云共存以及中云与低云共存）在南半球中高纬度（40°-65°S）的云量、云辐射强迫和云辐射加热率。其中云辐射加热率定义为有云时的大气加热率廓线与晴空大气加热率廓线的差值。结果表明:研究区域盛行单层低云和单层中云,其云量分别为44.1%和10.3%。并且,中云重叠低云在双层云中云量也是最大（8.7%）。不同类型云的云量也显著影响着其云辐射强迫。单层低云在大气层顶、地表以及大气中的净云辐射强迫分别是-64.8、-56.5和-8.4 W/m2,其绝对值大于其他类型云。虽然单层的中云在大气层顶和地表的净辐射强迫也为负值,但其在大气中的净云辐射强迫为正值（2.3 W/m2）。最后,讨论了不同类型云对大气中辐射能量垂直分布的影响。所有类型云的短波（或长波）云辐射加热率都随高度升高表现为由负值转为正值（或由正值转为负值）。对于大部分云,其净云辐射加热率主要由长波云辐射加热率决定。这些研究结果旨在为模式中云重叠参数化方案在区域的适用性评估及改进提供观测依据。 相似文献
16.
低层暖平流强迫类强对流发生前,地面经常伴有低于日变化的3 h变压。结合常规地面观测资料,定义低于日变化的3 h变压异常（超过一个标准差定义为异常）指数PCR（Pressure Change Range）,讨论了中国中东部地区3 h变压标准差的气候分布特征;最后以3次强对流天气过程为例说明PCR指数的预报价值和时效。结果表明,与3 h变压均值相比,中国中东部地区的3 h变压标准差的日变化较小,PCR更适合作为变压异常程度的标准。东北、华北、华东-华中区域PCR冬春季节出现站次数偏多,夏秋季节偏少;华南区域除了冬春季外,夏季也偏多,秋季偏少。PCR主要集中在低级别强度上,但PCR级别越高,越有可能出现强对流天气。东北区域出现PCR的首要原因是受东北气旋的影响,且可能有TBB≤-52℃的云系相对应;华北、华东-华中、华南出现PCR的首要原因是冷高压变性或迅速东移,没有TBB≤-52℃的云系相对应;地面倒槽中出现的PCR全部有TBB≤-52℃的云系对应。3次强对流天气过程均发生在地面倒槽中;在发生前3 h左右,地面气压场上有较明显的负PCR中心出现,强对流天气中尺度云团有向负PCR中心移动的趋势。 相似文献
17.
Simulations of late 20th and 21st century Arctic cloud amount from 20 global climate models (GCMs) in the Coupled Model Intercomparison Project phase 3 (CMIP3) dataset are synthesized and assessed. Under recent climatic conditions, GCMs realistically simulate the spatial distribution of Arctic clouds, the magnitude of cloudiness during the warmest seasons (summer–autumn), and the prevalence of low clouds as the predominant type. The greatest intermodel spread and most pronounced model error of excessive cloudiness coincides with the coldest seasons (winter–spring) and locations (perennial ice pack, Greenland, and the Canadian Archipelago). Under greenhouse forcing (SRES A1B emissions scenario) the Arctic is expected to become cloudier, especially during autumn and over sea ice, in tandem with cloud decreases in middle latitudes. Projected cloud changes for the late 21st century depend strongly on the simulated modern (late 20th century) annual cycle of Arctic cloud amount: GCMs that correctly simulate more clouds during summer than winter at present also tend to simulate more clouds in the future. The simulated Arctic cloud changes display a tripole structure aloft, with largest increases concentrated at low levels (below 700 hPa) and high levels (above 400 hPa) but little change in the middle troposphere. The changes in cloud radiative forcing suggest that the cloud changes are a positive feedback annually but negative during summer. Of potential explanations for the simulated Arctic cloud response, local evaporation is the leading candidate based on its high correlation with the cloud changes. The polar cloud changes are also significantly correlated with model resolution: GCMs with higher spatial resolution tend to produce larger future cloud increases. 相似文献
18.
Values of downward and upward flux densities of solar and terrestrial radiation were continuously recorded between 1 December 2001 and 30 November 2002 using a four-components radiometer at S. Pietro Capofiume (SPC) in northern Italy (44°39′N, 11°37′E, alt. 11 m a.m.s.l.), which is characterized by a weakly-reflective surface. The aim of the study was to investigate the effects of clouds on surface radiation balance (SRB); the cloud fraction (N) has been retrieved through the inverted form of the parameterization proposed by Kasten and Czeplak [Solar Energy 24 (1980) 177] and cloud types estimated following the methodology of Duchon and O'Malley [J. Appl. Meteorol. 38 (1999) 132]. The cloud radiative forcing (CRF) was evaluated through the Bintanja and Van den Broeke [Int. J. Climatol. 16 (1996) 1281] formula and then associated with cloud type. Experimental results showed that during the measuring period the net shortwave (Sw) balance always decreased with increasing N, whereas the net longwave (Lw) balance increased in all seasons. The net radiation available at the surface decreased with increasing N in all seasons except in winter, where no significant dependency was detected.The analysis of the cloud radiative forcing indicates that all seasons were characterized by a net cooling of the surface except winter, where clouds seem to have no effects on the surface warming or cooling. Taking into account the dependence on solar radiation cycle, an intercomparison between the retrieved cloud types seems to indicate that the effect of stratus was a slight cooling whereas that of cumulus clouds was a stronger cooling of the surface. On the contrary, cirrus clouds seem to have slight warming effect on the surface.The annual trends of mean monthly values of shortwave and longwave radiation balances confirmed that the measurement site is characterized by a temperate climate. Moreover, in spite of the cooling effect of clouds, a monthly radiative energy surplus is available all year long for surface–atmosphere energy exchanges. The analysis is also instrumental for the detection of SRB variations. 相似文献
19.
C. E. Coulman 《Boundary-Layer Meteorology》1980,19(1):31-50
Observations of temperature, humidity and velocity structure beneath fields of cumulus clouds are analysed with the needs of cloud modelling and cloud field parameterization in mind. Sub-cloud fluxes of sensible and latent heat and their diurnal variations are determined from layer-mean profiles and from eddy-correlation measurements; the latter are especially sensitive to sampling on cloud-sized scales. The characteristic fluctuations in velocity temperature and humidity beneath clouds have time scales like the lifetime typical of small cumulus clouds; there is no evidence that such fluctuations occur only as brief pulses at cloud initiation. The magnitudes of these fluctuations exhibit well-marked diurnal patterns of change. 相似文献
20.
N. Šinik 《Theoretical and Applied Climatology》1992,46(2-3):135-142
Summary Filtered secular series of temperature at Zagreb (Croatia) are negatively correlated with simultaneous series of solar radiation and positively correlated with cloudiness.The local balance of radiative fluxes, with cloudiness interference included, provides a basis for the evaluation of a local deterministic model, which can describe both the positive and negative impacts of cloud radiative forcing upon surface temperature. A theoretical temperature series, generated by the model simulation, proves a prevailing greenhouse effect of clouds upon recent climatic variations of temperature at Zagreb.With 5 Figures 相似文献