塔克拉玛干沙漠腹地春季一次沙尘暴沙尘气溶胶的辐射特征   总被引：3，自引：2，他引：1  

孔丹  何清  张瑞军  黄向春 《干旱气象》2008,26(2):36-41

利用塔中气象站地面辐射等气象资料结合PNIO（空气动力学当量≤10um的悬浮颗粒）质量浓度资料,以2007年4月15日晴天辐射特征为背景对4月22日塔克拉玛干沙漠腹地发生的沙尘暴天气进行局地辐射特征和沙尘气溶胶与净辐射作相关分析。结果表明白天沙尘的辐射强迫对地表有冷却作用,夜间起保温作用。观测期间,总辐射日峰值减少量为507W／m^2,地面长波日峰值增加量为185w／m^2,地面净辐射能量收支表现为白天的日峰值减少量为198w／m^2,夜间的日峰值增加量为40W／m^2。  相似文献   

Equivalent forcing depth in tropical oceans     

Takeshi Doi  Tomoki Tozuka  Toshio Yamagata 《Dynamics of Atmospheres and Oceans》2010,50(3):415-423

The forcing efficiency for the first and the second baroclinic modes by the wind stress in tropical oceans has been discussed by calculating equivalent forcing depth from annual mean, seasonal, and pentadal density profiles of the observational data. In the annual mean field, the first mode is forced preferentially in the western Pacific and the Indian Ocean, whereas the second mode is more strongly excited in the Atlantic and the eastern Pacific. This difference is mostly due to the pycnocline depth; the second mode is more dominantly forced where the pycnocline depth is shallower. We also revealed large seasonal variations of the second mode's equivalent forcing depth in the western Indian Ocean. The first mode is more dominantly forced during boreal spring and fall in the western Indian Ocean, while the second mode becomes more dominantly forced during boreal summer and winter. Those are due to seasonal variations of both the zonal wind and the pycnocline depth. Moreover, we show that the excitation of the second mode in the western Pacific increases after the late 1970s, which is associated with the decreasing trend of the zonal pycnocline gradient. Revealing the variation of the equivalent forcing depth will be useful for understanding the oceanic response to winds in tropical oceans and the improvement in the predictability of air-sea coupled climate variability in the tropics.  相似文献   

冬季北太平洋风暴轴的年代际变化特征及其可能影响机制   总被引：12，自引：0，他引：12  

朱伟军  李莹 《气象学报》2010,68(4):477-486

利用1958-2002年的ERA-40再分析资料,用谐波变换和EOF方法分析了冬季北太平洋风暴轴在年代际时间尺度上的变化特征,并通过回归分析的方法初步探讨了风暴轴年代际变化的可能影响机制.结果表明,在年代际时间尺度上,北太平洋风暴轴有两种主要模态,第1模态是风暴轴在其气候平均位置增强或减弱的主体一致变化型,其年代际变化受到上游涡旋强迫的影响,北大西洋强(弱)的涡旋活动,使得冬季北太平洋西风急流减弱(增强)、变宽(窄)、北抬(南压),同期北太平洋风暴轴活动偏强(弱),黑潮延续体区海表温度有偏暖(冷)的响应;第2模态是风暴轴中东部在气候平均位置南北两侧振荡的经向异常型,与太平洋年代际振荡(PDO)循环的暖(冷)位相相联系,下垫面海温非绝热加热的作用,激发加强(减弱)大气中类太平洋/北美遥相关型(PNA)的响应,引起大气斜压性异常偏南(北),使得风暴轴整体南压(北抬),且中东部向东南(北)方向移动.因此,冬季北太平洋风暴轴的年代际变化不仅是局地波-流相互作用的结果,还应考虑上游涡旋活动和海温热力强迫的作用.  相似文献   

Aerosol optical properties and its radiative forcing over Yulin,China in 2001 and 2002     

车慧正  张小曳  赵剑琦 《大气科学进展》2009,26(3):564-576

The aerosol optical properties and direct radiative forcing over the Mu Us desert of northern China, acquired through a CE318 sunphotometer of the ground-based Aerosol Robotic Network (AERONET), are analyzed. The seasonal variations in the aerosol optical properties are examined. The effect of meteorological elements (pressure, temperature, water vapor pressure, relative humidity and wind speed) on the aerosol optical properties is also studied. Then, the sources and optical properties under two different cases, a dust event and a pollution event, are compared. The results show that the high aerosol optical depth (AOD) found in Yulin was mostly attributed to the occurrence of dust events in spring from the Mu Us desert and deserts of West China and Mongolia, as well as the impacts of anthropogenic pollutant particles from the middle part of China in the other seasons. The seasonal variation and the probability distribution of the radiative forcing and the radiative forcing efficiency at the surface and the top of the atmosphere are analyzed and regressed using the linear and Gaussian regression methods.  相似文献   

A model study of the Little Ice Age and beyond: changes in ocean heat content,hydrography and circulation since 1500   总被引：1，自引：1，他引：0  

Jan Sedláček  Lawrence A. Mysak 《Climate Dynamics》2009,33(4):461-475

The Earth System Climate Model from the University of Victoria is used to investigate changes in ocean properties such as heat content, temperature, salinity, density and circulation during 1500 to 2000, the time period which includes the Little Ice Age (LIA) (1500–1850) and the industrial era (1850–2000). We force the model with two different wind-stress fields which take into account the North Atlantic Oscillation. Furthermore, temporally varying radiative forcings due to volcanic activity, insolation changes and greenhouse gas changes are also implemented. We find that changes in the upper ocean (0–300 m) heat content are mainly driven by changes in radiative forcing, except in the polar regions where the varying wind-stress induces changes in ocean heat content. In the full ocean (0–3,000 m) the wind-driven effects tend to reduce, prior to 1700, the downward trend in the ocean heat content caused by the radiative forcing. Afterwards no dynamical effect is visible. The colder ocean temperatures in the top 600 m during the LIA are caused by changes in radiative forcing, while the cooling at the bottom is wind-driven. The changes in salinity are small except in the Arctic Ocean. The reduced salinity content in the subsurface Arctic Ocean during the LIA is a result from reduced wind-driven inflow of saline water from the North Atlantic. At the surface of the Arctic Ocean the changes in salinity are caused by changes in sea–ice thickness. The changes in density are a composite picture of the temperature and salinity changes. Furthermore, changes in the meridional overturning circulation (MOC) are caused mainly by a varying wind-stress forcing; the additional buoyancy driven changes due to the radiative forcings are small. The simulated MOC is reduced during the LIA as compared to the industrial era. On the other hand, the ventilation rate in the Southern Ocean is increased during the LIA.  相似文献   

Identifying Nonstationarity in Turbulence Series   总被引：1，自引：1，他引：0  

Edgar L Andreas  Cathleen A. Geiger  George Treviño  Kerry J. Claffey 《Boundary-Layer Meteorology》2008,127(1):37-56

Because of rapid forcing by varying cloud and sky conditions, turbulence time series collected in the atmospheric surface layer over land may often be nonstationary. The meteorological community, however, has no consensus definition of what nonstationarity is and, thus, no consensus method for how to identify it. This study, therefore, adopts definitions for first-order and second-order stationarity taken from the time series analysis literature and implements new analysis techniques and probabilistic tests to quantify first-order and second-order nonstationarity. First-order nonstationarity manifests as a change in the series mean; second-order nonstationarity, as a change in the variance. The analysis identifies nonstationarity in surface-level turbulent temperature and water vapour series collected during two sample days with solar forcing influenced by cirrus and cirrostratus clouds, but that nonstationarity is not as severe as expected despite the rapid thermal forcing by these clouds. On the other hand, even with negligible cloud forcing, both sample days exhibited severe nonstationarity at night.  相似文献   

一次西南低涡特大暴雨过程的中尺度特征分析   总被引：5，自引：0，他引：5  

顾清源  周春花  青泉  张驹 《气象》2008,34(4):39-47

针对西南低涡诱发的2007年7月9日川南特大暴雨个例,采用Barnes带通滤波和非平衡动力强迫的中尺度特征分析方法,对特大暴雨过程中西南低涡内的中尺度系统活动特征进行分析.结果得出:特大暴雨过程中西南低涡内存在着一个向西南倾斜的、深厚的中-β尺度低涡,具有低层辐合、高层辐散的暴雨典型垂直结构.在特大暴雨天气过程中对流层中低层中尺度辐合和高层中尺度辐散呈现出一种先逐渐加强然后逐渐减弱的演变规律,并且特大暴雨区逐渐向中尺度低涡中心靠近.在特大暴雨发生的初始阶段,西南低涡内的大气运动已处于较强的非平衡状态,且越临近特大暴雨发生,低层U相似文献   

山东半岛一次强降雪过程的中尺度特征   总被引：16，自引：2，他引：14  

张勇  寿绍文  王咏青  周军  陆汉城 《南京气象学院学报》2008,31(1):51-60

利用非静力平衡模式MM5V3．6对2005年12月3日影响山东半岛的一次强降雪过程进行数值模拟,对其中中尺度重力波（MGW）的特征进行分析。并且通过非线性平衡方程（NBE）对高分辨率模式数据进行诊断分析,较详细地说明了非平衡流的出现而引起的地转适应过程以及地形强迫对重力波产生和发展的作用,和它们对强降雪过程的影响。研究表明：这次强降雪过程中的中尺度重力波波长约为100km。相速约20m／s;在有利的大尺度环流形势下,太行山的地形强迫与非平衡流是其产生的首要机制,而冬季海陆热力差异形成的海洋的热力作用也是造成区域性强降雪的一个重要原因。非线性平衡方程（NBE）对于非平衡流的诊断在确定波动产生区域方面有比较好的指示作用;通过对波动的结构以及维持机制的分析,这次过程中的中尺度重力波符合波导条件和Wave-CISK理论框架,波动能够从环境场中得到足够的能量从而维持相当长时间,从而造成这次罕见的连续性强降雪过程。  相似文献   

RESPONSE OF THE OCEAN UPPER MIXED LAYER TO ATMOSPHERIC FORCING   总被引：1，自引：0，他引：1  

刘秦玉 《中国海洋湖沼学报》1994,12(3):280-283

Using a one-dimension Turbulence Kinetic Energy(TKE)mixed layer model based on a simple eddyKinetic energy parameterization of the ocean upper mixed layer,some numerical examinations are intro- duced in this paper.These examination results show that the TKE ocean mixed layer model can respondwell to the effect of atmospheric forcing on the ocean upper mixed layer.The joint effect of wind stressand heat exchange on the ocean upper layer has nonlinear characteristics.The adjustment time of the re-sponse of the ocean upper mixed layer to the atmospheric forcing is about 12 hours in this model.  相似文献   

全型涡度方程和经典涡度方程比较   总被引：15，自引：4，他引：15  

吴国雄 《气象学报》2001,59(4):385-392

在简要回顾经典涡度方程和全型涡度方程推导的基础上 ,比较了两种涡度方程的异同。集中讨论全型涡度方程新的物理内涵 ,证明了与稳定度和斜压性变化 (锋生、锋消过程 )相联系的内部强迫以及与摩擦耗散和非绝热加热相联系的外部强迫所诱发的涡度发展的机制。最后 ,指出了全型涡度方程的天气和气候应用前景。  相似文献