自然地理学课件Dlx03atomospheremoving

1、tornado龙卷风年平均发生数龙卷风年平均发生数Hurricane (飓风）飓风）as seen from the space shuttle Satellite view of hurricane Floyd just before it made landfall in North Carolina, September 15, 1999Why the air movingnAir trends to move from high to low pressure until the air pressures are eaqualnImage or think of:lHow many

2、types of the air moving patterns there are in the sphere?Air trends to move from high to low temperature Formation of wind as a result of localized temperature differencesDevelopment of a closed atmospheric circulation cell because of surface heatingA AB B压力差压力差温度温度: 低低 高高第三章第三章 大气和气候大气和气候D DC C大气为什

3、么会运动？大气为什么会运动？ 压力差压力差nAir motions directionlhorizontal -called as Wind lvertical - not called winds, but as updrafts (上升气流上升气流)or downdraftslMixture- Cyclone (气旋气旋)nor anticycloneOther directions of air-movingnCyclone llow-pressure regions of ascending(上升上升)lcyclones rotate counterclockwise in the n

4、orthern hemisphereOther directions of air-movinglAnticyclone: n high-pressure spirals(螺旋螺旋) of descending or subsiding air.nclockwise spiral.高压高压压力梯度压力梯度风向风向Other directions of air-movingnDeflection of earth rotation（Coriolis effect)l be deflected away from its course. l right in the northern hemisp

5、here Some factors on air motion directionlthe pressure gradient thatnhigh to low presslthe Coriolis effect n turns to the sidel friction with the ground surfacenReduce speed, may change the direction. la result n will move toward low pressure but at an angle to the pressure gradient空空气运动气运动的影的影响响因素因

6、素nsolar radiationn the earths rotationn the ground surface characteristic and friction with the ground surfacen the air is formed three-dimensional motion of different scale.nWhy there is pressure gradientnunequal heating of the earths surfaceuproduces air of different temperatures. n warm air is le

7、ss dense than cool airuWarmer air will produce low pressureu colder air will produce high pressure.Pressure gradient force alone(只有压力只有压力梯度梯度)n水平气压梯度力（水平气压梯度力（G）l存在水平气压梯度时单位质量空气所受的存在水平气压梯度时单位质量空气所受的力力l表达式表达式nPnPG11(10-2N/g)gNcmcmNcmg/10/10/12223考虑考虑CoriolisCoriolisn The Coriolis Effect at wind l A =

8、 2sinn为地球角速度为地球角速度n为地理纬度为地理纬度n 为风速为风速Pressure gradient + Coriolis forceHigh and low press areas develop a rotary motion and wind flowing between highs and lows flows parallel to isobars n惯性离心力惯性离心力 （c）l空气曲线运动产生惯性离心力空气曲线运动产生惯性离心力l惯性离心力与空气运动方向相垂直惯性离心力与空气运动方向相垂直l大小与空气运动线速度大小与空气运动线速度v平方成正比，与曲平方成正比，与曲率半径

9、率半径 r 成反比：成反比：n惯性离心力通常很小惯性离心力通常很小C= v2 / rn摩擦力摩擦力-使气流速度发生改变使气流速度发生改变l内摩擦力内摩擦力n气层间的阻力气层间的阻力l外摩擦力外摩擦力n地面对气流运动的阻力地面对气流运动的阻力n近地面增大近地面增大n海拔愈高，作用愈弱海拔愈高，作用愈弱At surface of earth, theres friction too:Pressure + Coriolis + FrictionSurface friction adds a countering force to Coriolis. Surface winds cross isoba

10、rs at an angleMeasurement of Windsnwind speed nwind directionCyclone（气旋）气旋）lCyclone-低压中心低压中心lAnticyclones-高压中心高压中心n平面上呈等压线呈环状分布平面上呈等压线呈环状分布 lThe is a low pressure area that forms near the boundary between warm and cool air masses.n Cyclones l air spirals inwardl Low pressure at the center draws air

11、inward and carries it aloft. l Moist air rises, condensation or deposition can occurl Normally have dense, stratiform cloudsl often releasing rain or snowCyclones in northern hemisphereCyclones in southen hemisphereCyclonelThe cyclone grows in size and intensity as it draws on the energylThe energy

12、is available from the temperature contrast between the two air masses lAfter a few days, most of the energy that was available to the cyclone is used up, and the cyclone slowly diesCyclonenCyclone has most likely movedl from low latitudes to higher latitudes. nCyclones accomplish lmuch of the heat t

13、ransfer from the tropics to the higher latitudesn An example of Hurricane in North Hemisphere Hurricane Andrew across Florida and into Louisiana from Sunday, August 23 through Thursday, August 27, 1992 (Credit: Nathan Gasser). cyclonic precipitation nPrecipitation caused by the activity of an atmosp

14、heric depression. n Anticyclonel air spirals outwardl high pressure at the center pushes surface air outwardl causing air to descend from abovel condensation does not occur and skies are fairl anticyclones are sometimes termed fair-weather systems高压高压压力梯度压力梯度风向风向The reasons for cyclone formingnAir i

15、n motion near the surface is subjected to three influencesn the pressure gradientn the Coriolis effect nthe frictionnAir moves toward low pressure at an angle to the pressure gradientThe process of cyclone forming nMaintain the general circulation of the atmosphere. lAs some of the warm air rises up

16、 over the cold air mass, land some of the cold air sinks land flows under the warm air massThe process of cyclone forming nMaintain the general circulation of the atmosphere. lthe cyclone deepens (the air pressure becomes lower) and the winds around the system increasenWind directionl can be determi

17、ned by a wind vane（风（风向标）向标）lwind vane keeps it facing into the wind. lWind direction is given as the direction from which the wind is coming. Winds are designated according to the compass point from which the wind comes. An east wind comes from the east, but the air is moving westwardMeteorological

18、 instruments used to measure wind speed and direction. nWind speed ( Units:m/s) lis measured by an anemometer（风速（风速计）计）lIt consists of three funnel-shaped cups mounted on the ends of spokes of a horizontal wheel. nWind speed and directionn1 Knot = 1.9 Kilometers Per Hour (KM/HR)中国的表示法n风向的风羽表示风向的风羽表示

19、l风羽标杆尖头方向是风的去向（风的吹向）风羽标杆尖头方向是风的去向（风的吹向）l有横线的一端表示来风的方向有横线的一端表示来风的方向l如如: “F”是北风是北风l上北，下南，左西，右东，顺时针旋转；上北，下南，左西，右东，顺时针旋转；中国的表示法n风速的风羽表示风速的风羽表示l风羽上的横线（矢羽）的一长横为米风羽上的横线（矢羽）的一长横为米秒秒l一短横为米秒一短横为米秒l一三角旗表示一三角旗表示20m/s。 n“F”就是北风就是北风5级级 风力等级表风风力力等等级级海面浪高海面浪高(米米)海面和渔船征象海面和渔船征象陆上地面物征象陆上地面物征象相当风速相当风速（米（米/秒）秒）一般一般最高最高

20、范围范围中中数数*0-平静平静静烟直上静烟直上0.00.2010.10.1有微波有微波烟能表示风向，树叶略烟能表示风向，树叶略有摇动有摇动0.31.5120.20.3有小波纹，渔船有小波纹，渔船摇动摇动人面感觉有风，树叶微人面感觉有风，树叶微响，旗子开始飘动，高响，旗子开始飘动，高草和庄稼开始摇动草和庄稼开始摇动1.63.3230.61.0有小浪，渔船渐有小浪，渔船渐觉簸动觉簸动树叶及小枝、高草摇动树叶及小枝、高草摇动不息，旗子展开不息，旗子展开3.45.4441.01.5浪顶有白色泡沫，浪顶有白色泡沫，渔船满帆时，船渔船满帆时，船身倾侧身倾侧吹起地面灰尘、纸张，吹起地面灰尘、纸张，树枝摇动，

21、高的草波浪树枝摇动，高的草波浪起伏起伏5.57.97n风速风速l口诀：口诀：“从一直到九，乘从一直到九，乘2各级有各级有”l从一级到九级风，各级分别乘从一级到九级风，各级分别乘2，大致可得，大致可得出该风的最大速度出该风的最大速度n如一级风的最大速度是每秒如一级风的最大速度是每秒2米米n2级风是每秒级风是每秒4米米n3级风是每秒级风是每秒6米米nn风力等级风力等级(歌谣表达歌谣表达)l零级无风炊烟上；一级软风烟稍斜；零级无风炊烟上；一级软风烟稍斜；l二级轻风树叶响；三级微风树枝晃；二级轻风树叶响；三级微风树枝晃；l四级和风灰尘起；五级清风水起波；四级和风灰尘起；五级清风水起波；l六级强风大树摇

22、；七级疾风步难行；六级强风大树摇；七级疾风步难行；l八级大风树枝折；九级烈风烟囱毁；八级大风树枝折；九级烈风烟囱毁；l十级狂风树根拔；十一级暴风陆罕见；十级狂风树根拔；十一级暴风陆罕见；l十二级飓风浪滔天。十二级飓风浪滔天。Mean January prevailing surface winds and centers of atmospheric pressure, 1959-1997Mean July prevailing surface winds and centers of atmospheric pressure, 1959-1997global barometric press

23、ures (Jan 1993) Air pressure and prevail surface wind in JanuaryGlobal pressure patterns Air pressure and prevail surface wind in Julyair pressure and prevail surface wind in January north and south hemisphere air pressure and prevail surface wind in July north and south hemisphere东东北北信信风风中中纬纬西西风风极地

24、东北风极地东北风东东南南信信风风中中纬纬西西风风极极 地地 东东 风风赤赤 道道 低低 压压 带带副热带高压带副热带高压带副热带高压带副热带高压带副极地低压带副极地低压带副极地低压带副极地低压带极地高压极地高压带带极地高压带极地高压带地球上的气压带和风带地球上的气压带和风带 极地高压带极地高压带极地高压带极地高压带赤道低压带赤道低压带副极地低压带副极地低压带副热带高压带副热带高压带副极地低压带副极地低压带副热带高压带副热带高压带Global pressure patterns( (理想理想). ). nThe distribution of surface air pressure (全球气压

25、带全球气压带)l赤道低压带（赤道低压带（Equatorial Trough)l 极地高压带极地高压带(Polar High)l副热带高压带副热带高压带(Subtropical Belt of High Pressure)l 副极地低压带副极地低压带(Subpolar of low Pressure)Primary High-Pressure and Low-Pressure AreasnEquatorial low-pressure troughnPolar high-pressure cellsnSubtropical high-pressure cellsnSubpolar low-pre

26、ssure cellsnEquatorial low-pressure troughlIntertropical convergence zone (ITCZ)lTrade windsnPolar high-pressure cellslPolar easterlieslAntarctic highnSubtropical high-pressure cellslWesterlieslBermuda highlAzores highlPacific highnSubpolar low-pressure cellslAleutian (阿留申群岛阿留申群岛)lowlIcelandic lowlP

27、olar frontnEquatorial Trough(赤道低压带赤道低压带)lthe sun is directly overhead, the equator will be heated lair rises over the equator, flows poleward, and descends at about a 30 latitude. lIs low press area in Equatorial TroughnSubtropical High Pressure Belt (副热带高副热带高压带压带)lair descends and surface pressures

28、 are highlcentered at about 30 latitude. n nSubpolar Belt of Low Pressure(副极地低压副极地低压带带)lis a zone of conflict (冲突冲突)between air bodies with different characteristics.n Masses of cool, dry air move into the regionn heading eastward and equatorwardl These form polar outbreaksl The border of the polar

29、outbreak is known as the polar front. 全球大气运动模式及机制全球大气运动模式及机制nPolar HighlAir is intensely cold. lHigh pressure occursnGlobe Surface Winds pattern lConsider wind on an ideal earthn without a complicated pattern of land and watern no seasonal changes.全球气压带分布的理想模式全球气压带分布的理想模式n地球表面均匀地球表面均匀n地表气压完全决定于纬度地表气

30、压完全决定于纬度n地表气温的纬度分布不均匀造成气压沿纬度地表气温的纬度分布不均匀造成气压沿纬度的分带规律的分带规律l“Hadley cells.” (哈德利圈）哈德利圈）nWhen air is heated, low pressure forms and air risesnEach Hadley cell in northern and southern hemispheres uair rises over the equatoru flows polewardudescends at about a 30 latitudeSimplified global three-cell sur

31、face and upper air circulation patternsHadley环流圈环流圈Ferrel环流圈环流圈极地环流圈极地环流圈Atmospheric circulationn大气环流大气环流l（1）信风环流圈，又称）信风环流圈，又称Hadley环流圈环流圈(Latitude:0-300)， l（2）中纬度环流圈，又称）中纬度环流圈，又称Ferrel环流圈环流圈(Latitude:30-600)；l（3）极地环流圈）极地环流圈(Latitude:60-900) 大气环流形成的原因大气环流形成的原因AB B地转偏向力C C太阳直射点的南北移动D海陆热力性质差异气压带断裂成块状，

32、形成季风气压带断裂成块状，形成季风气压带、风带南北移动气压带、风带南北移动单圈环流单圈环流三圈环流三圈环流气压带和风带气压带和风带n大气环流的作用大气环流的作用l高低纬度之间，海陆之间的热量和水汽得高低纬度之间，海陆之间的热量和水汽得到交换，促进了地球上的热量平衡和水平到交换，促进了地球上的热量平衡和水平衡；衡；l对天气和气候影响对天气和气候影响lAtmospheric circulation is controlled by the heat that has built up at the Equator.l The heated air expands, becomes less den

33、se and so rises.Atmospheric circulation Atmospheric circulationnThe air continues to rise and spreads further away from the Equator, this results in it being cooledn until it becomes more dense, descends and forms an area of high pressure close to the TropicsnOn descending, the air becomes drier and

34、 warmern Some returns to the Equator and replaces the air which had risen. nThe remaining tropical air moves away to join with colder polar air nAir is forced to rise again, creating low pressure and producing rainAtmospheric circulationnWind in Equatorial TroughnWind in Subtropical High Pressure Be

35、ltnWind in SubPolar of low PressurenWind in Equatorial Troughlair converges and moves aloft(向上）向上） llow pressure lAs air is generally rising, winds are light and variable. n Wind in Subtropical High Pressure Belt in the northern hemispherelTwo large anticyclones centered over oceanslEquatorwardlPole

36、ward Air pressure and prevail surface wind in Julythe Hawaiian High in the Pacificthe Azores (亚述尔亚述尔群群岛岛)High in the Atlantic.n Wind in Subtropical High Pressure Belt in the northern hemispherelTwo large anticyclones centered over oceansn the Hawaiian High in the Pacificn the Azores (亚述尔群岛亚述尔群岛)High

37、 in the Atlantic. lFrom January to July, these intensify and move northward. 一月一月七月七月高低纬间热量不均；地转偏向力；高低纬间热量不均；地转偏向力；太阳直射点位置的移动；太阳直射点位置的移动； 海陆热力性质差异海陆热力性质差异气压带断裂成单个的高低气压中心气压带断裂成单个的高低气压中心-60N30N亚亚 欧欧 大大 陆陆洋洋太太平平洋洋大大西西副副 极极 地地 低低 气气 压压 带带蒙古蒙古-西伯利亚高压西伯利亚高压阿留申阿留申低压低压冰岛冰岛低压低压副副 热热 带带 高高 气气 压压 带带亚洲（印度）低压亚洲（

38、印度）低压亚速尔亚速尔高压高压夏威夷夏威夷高压高压冬冬夏夏冬冬夏夏 lFrom this mapnTwo large high-pressure cells bounded by continentsnthe outspiraling circulation produces the trade winds inuthe tropicaluThe equatorial zonesu the westerlies in the subtropical zones and poleward. lIn the high-pressure cellsn air on the east side sub

39、sides (下下沉沉)more intensely n on the west side, subsidence is less strong. l This means that winds spiraling outward on the eastern side are drier and producing dry windslOn the western sidesn winds travel long distances across warm, tropical ocean surfaces before reaching land, n so are warm and moi

40、stWind in Subtropical High Pressure Beltlequatorward nThe winds moving equatorward are the strong nNorth of the equator, these are from the northeastnTo the south of the equator,they are from the southeastWind in Subtropical High Pressure BeltlPoleward (middle latitudes)n air spiraling outward nprod

41、uces southwesterly winds in the northern hemispherennorthwesterly winds in the southern hemisphere.nWind in SubPolar of low Pressure lWind pattern becomes more complex. l winds can be quite variable lThe reasonnThere are polar outbreaksWind in SubPolar of low PressurenRossby Waves（罗斯贝波）（罗斯贝波）lThe sm

42、ooth westward flow of the upper-air westerlies(西风带西风带) frequently forms undulations（波动）（波动）lThe waves arise in a zone of contact between cold polar air and warm tropical air（热带气团）（热带气团） Rossby WavesWind in SubPolar of low PressurelAn undulation develops, and warm air pushes poleward while a tongue o

43、f cold air is brought to the south. lEventually, the tongue is pinched off, leaving a pool of cold air at a latitude far south of its normal location. lThis cold pool may persist for some days or weeks, slowly warming with timeWind in Pole HighnWind in Pole High lOutspiraling of winds around a polar

44、lanticyclone create surface winds from a generally easterly directionlPolar easterlies(极地东风带）极地东风带）Simplified global three-cell surface and upper air circulation patternsHadley环流圈环流圈Ferrel环流圈环流圈极地环流圈极地环流圈Wind in Pole HighlIn wintern the strong Siberian High is in Asia, and a weaker cousin, the Canad

45、ian High, is in North America.n From these high-pressure centers, air spirals outward, bringing cold air to the southWind in Pole HighlIn summern the pattern reversesn The continents show generally low pressuren while high pressure builds over the oceans. 风的类型风的类型l阵风阵风l海陆风海陆风 l山谷风山谷风l焚风焚风l干热风干热风l旋风旋

46、风l龙卷风龙卷风l台风台风l季风季风l.The types of windnMonsoonlPrevailing winds vary distinctly with seasons in a large range between winter and summer.n Simplified global three-cell surface and upper air circulation patternsHadley环流圈环流圈Ferrel环流圈环流圈极地环流圈极地环流圈Monsoons formingnMonsoons forminglThe ITCZ and the Monsoon

47、 Circulationlthe Hadley cell circulation and subtropical high-pressure belts-will shift with the seasonsl ITCZ-Intertropical Convergence Zone Air pressure and prevail surface wind in JanuaryGlobal pressure patternsITCZMonsoons forminglITCZ shift is moderate in the western hemispherenThe ITC moves a

48、few degrees north from January to July over the oceans. lITCZ is a huge shift strong ( 40 degrees of latitude) in the eastern hemisphere nIn January, the ITCZ runs south at a latitude of about 15 Sn In July, it swings north at a latitude of about 25 N. Air pressure and prevail surface wind in JulyIT

49、CZ ITCZ ITCZJanuaryJulyMonsoons forminglWhy there is huge shiftnin winteru temperatures in northern Asia are very colduso this high-pressure is to be expected to southumake the ITCZ forward southn Monsoons forminglWhy there is huge shiftnIn July,u this high-pressure center is absent,u replaced inste

50、ad by a low centered over the Middle Eastern desertu make the ITCZ forward NorthlThe most famous monsoon is the Indian summer monsoonnit affects a large portion of Asia. nIn May and June of each yearn the dry northerly wind flow over India changes directionMonsoonnwarm humid air from the Indian Ocea

51、n flows from the southnwarm humid air gradually overspreading the Indian subcontinent.n Widespread torrential rainsn来自北方的北风与来自南方的洋流相互作用，来自北方的北风与来自南方的洋流相互作用，在印度次大陆上形成温暖潮湿的空气在印度次大陆上形成温暖潮湿的空气The types of windnLocal windslsea and land breezeslPlateau monsoonlMountain and valley breezeslFoehnThe types of

52、 windnLocal windslPlateau monsoonnthermal differentia between the plateau and surrounding free airn causes reversed prevailing wind systems between winter and summer.l The types of windnLocal windslMountain and valley breezesnThey are local winds that alternate in direction from day to night. The ty

53、pes of windlMountain winds and valley winds nDuring the dayu mountain hill slopes are heated by the sun, air risingu To take the place of the rising air, a current moves up valleys from the plainsThe types of windnAt nightuthe hill slopes are chilled by radiation.u The cooler, denser hill slope air

54、then moves valleyward, down the hill slopes, to the plain below, downslope windsDaytime development of valley breeze. Mountain- Valley Breezen Day: lmountain hill slopes heated intensely by sun. lRise up valley.n At nightl hill slopes chilled.l Dense air sinks down valleyNightime development of mountain breezeThe types of windlThese winds are