气象专业英语5.ppt

1、Unit Five:The General circulation of the atmosphere第五课第五课 大气环流大气环流 New words:Vector:向量Zonal 纬向的 latitude 纬度Meridional:经向的 longitude:经度Subpolar:副极地的 subgridJetstream 急流Reversal 颠倒，反转Westerly 西风 easterly 东风Westerlies 西风带 easterlies 东风带Retreat:复原，恢复；撤退 withdraw Equator 赤道 ribbon 带状物，strip;beltCoriolis

2、科里奥利力Oceanographic 海洋学的 kinetic 运动的 大气环流：一般是指具有世界规模的、大范围大气环流：一般是指具有世界规模的、大范围的大气运行现象，既包括平均状态，也包括瞬的大气运行现象，既包括平均状态，也包括瞬时现象，其水平尺度在数千公里以上，垂直尺时现象，其水平尺度在数千公里以上，垂直尺度在度在10km以上，时间尺度在数天以上。以上，时间尺度在数天以上。大气大范围运动的状态。大气大范围运动的状态。某一大范围的地区（如欧亚地区、半球、全球）某一大范围的地区（如欧亚地区、半球、全球），某一大气层次（如对流层、平流层、中层、，某一大气层次（如对流层、平流层、中层、整个大气圈）

3、在一个长时期（如月、季、年、整个大气圈）在一个长时期（如月、季、年、多年）的大气运动的平均状态或某一个时段多年）的大气运动的平均状态或某一个时段（如一周、梅雨期间）的大气运动的变化过程（如一周、梅雨期间）的大气运动的变化过程都可以称为大气环流。都可以称为大气环流。大气环流通常包含平均纬向环流、平均水平环流和平均经圈环流3部分。平均纬向环流。指大气盛行的以极地为中心并绕其旋转的纬向气流，这是大气环流的最基本的状态，就对流层平均纬向环流而言，低纬度地区盛行东风，称为东风带（由于地球的旋转，北半球多为东北信风，南半球多为东南信风，故又称为信风带）；中高纬度地区盛行西风，称为西风带（其强度随高度增大，

4、在对流层顶附近达到极大值，称为西风急流）；极地还有浅薄的弱东风，称为极地东风带。平均水平环流。指在中高纬度的水平面上盛行的叠加在平均纬向环流上的波状气流（又称平均槽脊），通常北半球冬季为3个波，夏季为4个波，三波与四波之间的转换表征季节变化。平均经圈环流。指在南北-垂直方向的剖面上，由大气经向运动和垂直运动所构成的运动状态。通常，对流层的径圈环流存在3个圈：低纬度是正环流或直接环流（气流在赤道上升，高空向北，中低纬下沉，低空向南），又称为哈得来环流；中纬度是反环流或间接环流（中低纬气流下沉，低空向北，中高纬上升，高空向南），又称为费雷尔环流；极地是弱的正环流（极地下沉，低空向南，高纬上升，高空

5、向北）。控制大气环流状态的基本因子 大气本身的特殊尺度（准水平）太阳辐射随纬度分布的不均匀性（三圈环流）地球自转（准地转）地球表面的不均匀性（海陆分布、陆地起伏）地面摩擦（东西风维持）赤道无风带是指赤道附近南、北纬赤道无风带是指赤道附近南、北纬5之间的地带。之间的地带。这里太阳终年近乎直射，是地表年平均气温最高地这里太阳终年近乎直射，是地表年平均气温最高地带。由于温度的水平分布比较均匀，水平气压梯度带。由于温度的水平分布比较均匀，水平气压梯度很小，气流以辐合上升为主，风速微弱，故称为赤很小，气流以辐合上升为主，风速微弱，故称为赤道无风带。它控制下的天气特点是气压低、湿度大、道无风带。它控制下的

6、天气特点是气压低、湿度大、多云、多雷暴，是海上航行时要避开的区域。多云、多雷暴，是海上航行时要避开的区域。abfellP1:The general circulation comprises the movements of the atmosphere on a worldwide scale.Since it is usually studied by means of data averaged over several days,so that minor,local or day-to-day irregularities are smoothed out,any model of

7、the general circulation must be generalized,and cannot include very many short-lived features of importance for local weather.The general circulation is the overall pattern that must obviously affect local weather at sometime or another,directly or indirectly,and is in this sense the greatest single

8、 terrestrial cause of climate and weather.P2:Technically,the general circulation may be defined as the mean three-dimensional pattern of the meteorological elements,plus the“turbulence”,the oscillation or perturbations of the mean pattern,provided by changing,day-to-day synoptic weather patterns.Its

9、 basic features may be described in terms of global,seasonal vector mean winds as a function of height,or they may be derived by applying the geostrophic wind relation to means pressure-contour charts.P3:The three-dimensional aspects of the general circulation as actually observed must be particular

10、ly emphasized.For comparative purposes,it is convenient to separate the zonal(east-west)and meridional(north-south)components of the mean motion for the northern hemisphere.The mean meridional circulation is about a meter per second in the lower and middle latitudes throughout a substantial depth of

11、 the atmosphere:this is a much weaker circulation than the zonal one,but can nevertheless create or destroy momentum at the rate of 10 m per sec.P4:The simplest model that incorporates the main features of the observed mean meridional is given in the figures(omitted).The three kinds of cells are in

12、the troposphere in each hemisphere:the Hadley cells in the tropics,the Ferrel cells in middle latitudes,and the weak subpolar cells beyond these.Angular momentum is injected into the Ferrel cells as indicated by the arrows,and is later carried downward by small convective eddies.Convection is most i

13、ntense in low latitudes and thus for equilibrium to occur the Hadley cells must rotate faster than the Ferrel cells.全球大气环流示意全球大气环流示意P5:The model devised by Palmen takes into account the existence of jetstreams,which are the dominant features of the actual circulation.Observation shows that the Hadle

14、y cells,which are directly driven by heat,are the most important single elements of mean tropospheric circulation,but the Ferrel cells,driven by friction with the Hadley cells,probe to be more significant than Palmen envisaged.P6:An independent circulation is generated by heating and cooling in the

15、stratosphere,down to about 10 mb.Stratospheric winds reveal remarkable reversals in direction.A stratospheric monsoon occurs in the northern hemisphere:westerlies change to easterlies in April above 10 mb,the reversal proceeding downward and southward from the polar regions,reaching 100 mb in late M

16、ay.Easterlies prevail above 100 mb from May to August.In late August and early September,these easterlies revert back to westerlies.P7:Over North America in April,stratospheric polar easterlies are separated by the middle-latitude westerlies from the tropical easterlies of the lower atmosphere,which move northward in the month.By July,easterlies prevail down to at least 15 km in low latitudes,to 20 km in middle latitudes and to 15-17 km in polar latitudes.By September,the polar and tropical east