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1、氣象專業(yè)英語5 大氣環(huán)流:一般是指具有世界規(guī)模的、大范圍大氣環(huán)流:一般是指具有世界規(guī)模的、大范圍的大氣運(yùn)行現(xiàn)象,既包括平均狀態(tài),也包括瞬的大氣運(yùn)行現(xiàn)象,既包括平均狀態(tài),也包括瞬時現(xiàn)象,其水平尺度在數(shù)千公里以上,垂直尺時現(xiàn)象,其水平尺度在數(shù)千公里以上,垂直尺度在度在10km以上,時間尺度在數(shù)天以上。以上,時間尺度在數(shù)天以上。 大氣大范圍運(yùn)動的狀態(tài)。大氣大范圍運(yùn)動的狀態(tài)。 某一大范圍的地區(qū)(如歐亞地區(qū)、半球、全某一大范圍的地區(qū)(如歐亞地區(qū)、半球、全球),某一大氣層次(如對流層、平流層、中球),某一大氣層次(如對流層、平流層、中層、整個大氣圈)在一個長時期(如月、季、層、整個大氣圈)在一個長時期(如

2、月、季、年、多年)的大氣運(yùn)動的平均狀態(tài)或某一個時年、多年)的大氣運(yùn)動的平均狀態(tài)或某一個時段(如一周、梅雨期間)的大氣運(yùn)動的變化過段(如一周、梅雨期間)的大氣運(yùn)動的變化過程都可以稱為大氣環(huán)流。程都可以稱為大氣環(huán)流。 大氣環(huán)流通常包含平均緯向環(huán)流、平均水平環(huán)流和平均經(jīng)圈環(huán)流3部分。平均緯向環(huán)流。指大氣盛行的以極地為中心并繞其旋轉(zhuǎn)的緯向氣流,這是大氣環(huán)流的最基本的狀態(tài),就對流層平均緯向環(huán)流而言,低緯度地區(qū)盛行東風(fēng),稱為東風(fēng)帶(由于地球的旋轉(zhuǎn),北半球多為東北信風(fēng),南半球多為東南信風(fēng),故又稱為信風(fēng)帶);中高緯度地區(qū)盛行西風(fēng),稱為西風(fēng)帶(其強(qiáng)度隨高度增大,在對流層頂附近達(dá)到極大值,稱為西風(fēng)急流);極地還有

3、淺薄的弱東風(fēng),稱為極地東風(fēng)帶。 平均水平環(huán)流。指在中高緯度的水平面上盛行的疊加在平均緯向環(huán)流上的波狀氣流(又稱平均槽脊),通常北半球冬季為3個波,夏季為4個波,三波與四波之間的轉(zhuǎn)換表征季節(jié)變化。平均經(jīng)圈環(huán)流。指在南北-垂直方向的剖面上,由大氣經(jīng)向運(yùn)動和垂直運(yùn)動所構(gòu)成的運(yùn)動狀態(tài)。通常,對流層的徑圈環(huán)流存在3個圈:低緯度是正環(huán)流或直接環(huán)流(氣流在赤道上升,高空向北,中低緯下沉,低空向南),又稱為哈得來環(huán)流;中緯度是反環(huán)流或間接環(huán)流(中低緯氣流下沉,低空向北,中高緯上升,高空向南),又稱為費(fèi)雷爾環(huán)流;極地是弱的正環(huán)流(極地下沉,低空向南,高緯上升,高空向北)。 控制大氣環(huán)流狀態(tài)的基本因子 大氣本身的

4、特殊尺度(準(zhǔn)水平) 太陽輻射隨緯度分布的不均勻性(三圈環(huán)流)地球自轉(zhuǎn)(準(zhǔn)地轉(zhuǎn))地球表面的不均勻性(海陸分布、陸地起伏)地面摩擦(東西風(fēng)維持)赤道無風(fēng)帶是指赤道附近南、北緯赤道無風(fēng)帶是指赤道附近南、北緯5之間的地帶。之間的地帶。這里太陽終年近乎直射,是地表年平均氣溫最高地這里太陽終年近乎直射,是地表年平均氣溫最高地帶。由于溫度的水平分布比較均勻,水平氣壓梯度帶。由于溫度的水平分布比較均勻,水平氣壓梯度很小,氣流以輻合上升為主,風(fēng)速微弱,故稱為赤很小,氣流以輻合上升為主,風(fēng)速微弱,故稱為赤道無風(fēng)帶。它控制下的天氣特點(diǎn)是氣壓低、濕度大、道無風(fēng)帶。它控制下的天氣特點(diǎn)是氣壓低、濕度大、多云、多雷暴,是海

5、上航行時要避開的區(qū)域。多云、多雷暴,是海上航行時要避開的區(qū)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 the general circ

6、ulation 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 terrestrial

7、 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 ba

8、sic 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 particula

9、rly 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

10、depth of 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

11、 cells are in 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.

12、Convection is most intense in low latitudes and thus for equilibrium to occur the Hadley cells must rotate faster than the Ferrel cells.全球大氣環(huán)流示意全球大氣環(huán)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. Observati

13、on shows that the Hadley 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

14、by heating and cooling in the 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 pola

15、r regions, reaching 100 mb in late May. 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 tropica

16、l 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 easterlies begin retreating to their minima, in November

17、 and December, respectively. In general, the picture at 10 mb is of a slow, steady transition from summer easterlies to winter westerlies, but during January and February 1958 this simple pattern broke down in a very complex manner.P8: General models of the upper atmospheric circulation have been pr

18、oduced by Keliogg and Schilling (1951), Murgatroyd (1957), and Batten (1961). According to Bettens model, the major center of westerly winds is in the winter hemisphere, although these winds also cross the equator into the summer hemisphere. Easterlies occur in spring in the lower ionosphere, buildi

19、ng down from the mesosphere as westerlies develop aloft; in turn, the westerlies then build down as easterlies develop aloft. Small easterly centers occur in the lower mesosphere in late winter and spring. The stratosphere winds above the Pacific equatorial region are extremely variable. P9: Importa

20、nt elements of the stratospheric circulation include the Berson westerlies and the Krakatoa easterlies. The former, first discovered at 50 to 60 mb over central Africa, but now known to occur anywhere up to 10 mb, form a continuous ribbon around the equator: the westerlies and easterlies alternate,

21、one half-cycle being 12 to 15 months. The Krakatoa easterlies occur at 25 mb: their existence was first inferred from the movement of volcanic dust after Krakaroa eruption. Radar wind observations now indicate that Krakatoa westerlies also occur. P10: The geographical importance of these stratospher

22、ic winds is that they make any simple, intuitive model of the atmospheric circulation untenable. In such a model, the rotation of the Earth from west to east is assumed to drag the lower part of the atmosphere with it, imparting a westerly motion to these layers. Thus slight variations in the moment

23、um of the west-east rotating atmosphere would be interpreted at the Earths surface as indicating winds apparently coming from different directions. A local excess of momentum in the atmosphere, causing the latter to move more rapidly from west to east than the Earths surface, would be described as a

24、 west wind. A local deficit of momentum, causing the atmosphere to move less rapidly than the Earths surface, would give rise to an east wind.P11:Recent observations indicate that the high atmosphere contains many circulation features that cannot be explained by a simple intuitive model. Thus, chang

25、es in the rotation of Sputnik 3 can be explained by the existence of a strong westerly wind, accompanying the Earths rotation, but well above any region of possible frictional drag with its surface. Slow oscillations, representing a balance between inertia and Coriolis forces and static stability(靜力

26、), have been measured by radarsonde theodolites(經(jīng)緯儀) at Crawley. They have period of 12 hours or so, and are due to disturbances with vertical and horizontal dimensions of 1 km and several 100km, respectively. The complexity of data for the high atmosphere has made it necessary to split the circulat

27、ions observed into mathematical components.P12:The circulation models discussed so far have been on diffusion. In Brewers model, based on the diffusion of ozone and water vapor, air rises through the equatorial tropopause, which acts as a cold trap owing to its low temperature (around 80). The cold,

28、 dry air then moves horizontally, finally sinking in middle and high latitudes. According to Dobsons model, ozone-enriched air arriving via Brewers meridional circulation is stored in the stratospheric polar-night jet, i.e., in the cold pool over the winter pole. From here, it gradually sinks into t

29、he lower stratosphere at temperate latitudes in late winter and spring. P13: In Spars model, which is based on the diffusion of radioactive debris (放射性碎片), the main exit for air from the stratosphere is through the gap in the tropopause, in which turbulent mixing takes place. More mixing takes place

30、 in the polar stratosphere (particularly in winter) than elsewhere, and much less mixing in the equatorial stratosphere than in the Brewer-Dobson model, which describes only one part of the whole circulation. The highest parts of the Brerrer-Dobson circulation reach 80,000 feet; above the atmosphere

31、 was envisaged by Brewer and Dobson as stagnant region is moist, and meridional transfer is affected by small-scale turbulent diffusion. The height of the transition from meridional-circulating to meridional-stagnant air varies both in time and in latitude. P14: In the Goldsmith-Brown model, rising

32、air at the equator does not reach great heights, but turns poleward almost immediately above the tropopause. The meridional circulation is rapid just above the tropopause, the air taking slightly more than two months to reach temperate zones. The upper flow is much slower, so that air remains in the ozone-producing layers for about a year. From there, ozone

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