Cloud radiative forcing of subtropical low level clouds in global models     

Johannes Karlsson  Gunilla Svensson  Henning Rodhe 《Climate Dynamics》2008,30(7-8):779-788

Simulations of subtropical marine low clouds and their radiative properties by nine coupled ocean-atmosphere climate models participating in the fourth assesment report (AR4) of the intergovernmental panel on climate change (IPCC) are analyzed. Satellite observations of cloudiness and radiative fluxes at the top of the atmosphere (TOA) are utilized for comparison. The analysis is confined to the marine subtropics in an attempt to isolate low cloudiness from tropical convective systems. All analyzed models have a negative bias in the low cloud fraction (model mean bias of −15%). On the other hand, the models show an excess of cloud radiative cooling in the region (model mean excess of 13 W m⁻²). The latter bias is shown to mainly originate from too much shortwave reflection by the models clouds rather than biases in the clear-sky fluxes. These results confirm earlier studies, thus no major progress in simulating the marine subtropical clouds is noted. As a consequence of the combination of these two biases, this study suggests that all investigated models are likely to overestimate the radiative response to changes in low level subtropical cloudiness.  相似文献   

强沙尘暴天气过程中的若干问题思考   总被引：4，自引：4，他引：0  

徐国昌 《干旱气象》2008,26(2):9-11

介绍沙尘暴反馈机制观念形成的经验过程,对沙尘暴反馈机制作了进一步讨论,以期引起对沙尘暴成因研究的重视。  相似文献   

年际时间尺度上全球植被与大气相互作用的诊断分析     

李伟平  季劲钧  董文杰 《大气科学》2008,32(1):75-89

利用NOAA AVHRR得到的19年（1982～2000）全球月平均的叶面积指数（LAI）与ERA40近地面气温和CMAP降水进行时滞相关分析,并研究了LAI的年际变化对后期温度、降水的反馈作用。结果表明,大部分地区LAI与同期气温的相关性更好,30°N以北（以南）基本上为正（负）相关。LAI滞后一个月时,北半球中低纬度和20°S以南大部地区LAI与降水的正相关更强;而在北半球中纬度大陆东部和南半球热带地区,LAI与前一个月温度的关系更密切。LAI与温度的相关性在春、秋季最明显,LAI与降水的关系在雨季最密切。LAI对气温比较显著的正反馈主要分布在北半球中高纬度地区;20°S以南大部地区为比较显著的负反馈。LAI对降水比较显著的正反馈分散在北美大陆西北部、东欧平原南部、欧亚大陆东北部和热带沿海地区。中高纬度（尤其是北半球）大部分地区LAI 对气温、降水反馈部分的解释方差达到总方差的20%以上。  相似文献   

春季我国东部海洋温度锋区对大气的强迫作用及其机制研究   总被引：6，自引：3，他引：3  

徐蜜蜜  徐海明  朱素行 《大气科学》2010,34(6):1071-1087

首先, 采用高分辨率的卫星资料研究了春季我国东部海区海洋锋区附近的海温与风场之间的关系, 资料分析表明海温与海表面风速之间存在明显的正相关关系, 特别是在海洋锋强的年份, 这种正相关关系更明显。资料分析还表明春季是黄海、 东海海洋锋最强的季节, 海温与海表面风速的对应关系在春季尤为明显。然后, 采用一个高分辨率和先进物理方案的中尺度模式探讨了海洋影响大气的机制。控制试验再现了海洋锋区附近海温与海表面风速之间的正相关关系。模拟的边界层垂直结构说明海温能够明显改变锋区两侧边界层大气的稳定度和垂直混合的强弱, 证明了垂直混合机制的存在。而另一方面, 对控制试验和平滑海温试验的水平动量方程中各收支项的比较分析发现, 由于海洋锋的存在而产生的气压梯度力对穿越锋区的空气的加速也有相当重要的贡献。综合观测和模拟结果说明春季我国东部海区海洋温度锋区的海洋—大气相互作用过程中海洋对大气的影响非常明显, 在海洋影响大气的机理方面, 海平面气压调整机制和垂直混合机制都在起作用。  相似文献   

Mechanisms and pathways of lateral flow on aspen‐forested,Luvisolic soils,Western Boreal Plains,Alberta, Canada     

Todd Redding  Kevin Devito 《水文研究》2010,24(21):2995-3010

Rainfall simulation experiments by Redding and Devito ( 2008 , Hydrological Processes 23: 4287–4300) on two adjacent plots of contrasting antecedent soil moisture storage on an aspen‐forested hillslope on the Boreal Plain showed that lateral flow generation occurred only once large soil storage capacity was saturated combined with a minimum event precipitation of 15–20 mm. This paper extends the results of Redding and Devito ( 2008 , Hydrological Processes 23: 4287–4300) with detailed analysis of pore pressure, soil moisture and tracer data from the rainfall simulation experiments, which is used to identify lateral flow generation mechanisms and flow pathways. Lateral flow was not generated until soils were wet into the fine textured C horizon. Lateral flow occurred dominantly through the clay‐rich Bt horizon by way of root channels. Lateral flow during the largest event was dominated by event water, and precipitation intensity was critical in lateral flow generation. Lateral flow was initiated as preferential flow near the soil surface into root channels, followed by development of a perched water table at depth, which also interacted with preferential flow pathways to move water laterally by the transmissivity feedback mechanism. The results indicate that lateral flow generated by rainfall on these hillslopes is uncommon because of the generally high available soil moisture storage capacity and the low probability of rainfall events of sufficient magnitude and intensity. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

绝对加速度反馈主动控制     

刘晖  唐家祥 《世界地震工程》2001,17(1):36-39

利用绝对加速度测量简单、可靠的特点，提出了一种新的反馈控制方法，即基于绝对加速度的反馈控制算法。同时，考虑到驱动器的时滞，发展了考虑察动器时滞的结构状态方程。实例研究表明，该方法改善了时滞的影响，具有良好的控制效果。  相似文献   

隧道工程地质预报方法探讨   总被引：32，自引：1，他引：32  

丁恩保  马继平 《工程地质学报》1995,3(1):28-34

本文从一些隧道工程事故实例出发，讨论了引起坍方和涌水灾害的工程、水文地质条件，不同工程阶段的预报方法以及预报研究的重大经济效益。最后提出五点提高预报符合率的原则和方法。  相似文献   

夏季副热带中——中间尺度系统发展的一种机制     

陈忠明 《大气科学》1993,17(6):756-761

本文研究了夏季副热带中—中间尺度天气系统的发展问题,结果表明,在潮湿不稳定大气中,扰动与凝结释热之间的正反馈过程是系统初期发展的一种机制,非线性作用将抑制系统的无限发展,使之发展到一定强度后即处于稳定状态。  相似文献   

具有门限的一种非线性随机-动力模式   总被引：3，自引：0，他引：3       下载免费PDF全文

丁裕国  江志红 《热带气象学报》1993,9(2):97-104

提出一种附加门限控制的具有非线性反馈作用的随机-动力模式,从而对具有线性反馈的随机-动力气候模式加以改进。从理论上说,这种具有门限的随机气候模式可使气候系统内部反馈机制中的非线性特征更为明显,以便更加客观地模拟和预报短期的气候变化。  相似文献   

THE MEANDER OF KUROSHIO AND OSCILLATION IN A COUPLED OCEAN-ATMOSPHERE MODEL^*          下载免费PDF全文

Liu Qinyu  Xu Qichun  Wang Zhilian  Qin Zenghao 《Acta Meteorologica Sinica》1993,7(3):338-346

A numerical experiment of an asynchronous coupled ocean-atmosphere model has been described in this paper.A two-layer global atmosphere general circulation model(OSU/IAP-AGCM)and a two-layer North Pacific Ocean general circulation model(NPOGCM) developed by Liu et al.(1992)are used in numerical experiment.The sea surface temperature anomaly(SSTA) corresponding to the meander of the Kuroshio is treated as the initial perturbation in the Pacific Ocean and the abnormal phenomena caused by the disturbance and the interaction between atmosphere and ocean,have been studied.The numerical experiment showed that the SST anomaly in the North Pacific could induce a new 30-60 day osciltation through the coupling between atmosphere and ocean and the interaction between the meander of the Kuroshio and atmosphere circulation is a positive feedback process.  相似文献