气团和锋的天气特征和对飞行的影响

1、气团和锋的天气特征和对飞行的影响Air Masses and Fronts学习要求:（1）了解气团的概念（2）熟悉冷、暖气团在变性时的天气特征；（3）了解锋的概念和空间结构，（4）掌握锋面附近气象要素的分布；（5）理解锋的分类（6）掌握暖锋的云系分布及天气特征；（7）暖锋对飞行的影响；（8）急行冷锋和缓行冷锋（9）冷锋天气及对飞行的影响；（10）静止锋天气及对飞行的影响。第一节 气 团 Air Mass 定义：水平方向上气温、湿度等物理属性分布比较均匀的大范围空气。尺度：水平几百几千km，垂直几km十几km成因：大范围下垫面性质均匀（冷暖、干湿）气团源地空气稳定少动（几天：蒸发凝结、辐射，风、

2、湍流、垂直运动） 形成过程 Arctic Air 北极气团 Antarctic Air 南极气团Tropical Air 热带气团Equatorial-Air 赤道气团Continental Air 大陆气团 Marine Air 海洋气团热力分类：根据气团温度和气团所经过的下垫面温度对比 Cold Air Mass 冷气团， Warm Air Mass 暖气团湿度分类：干气团，湿气团稳定分类：稳定气团，不稳定气团Air-mass Modification 气团变性气团的变性：气团在移动过程中与下垫面产生热量和水汽的交换，使气团的物理属性发生变化。（移经暖地表的）冷气团的天气特征 冷气团：具有

3、不稳定天气的特征。（移经冷地表的）暖气团的天气特征 暖气团：具有稳定天气的特征。冷气团天气特点1)冷气团所经之处气温下降2)冷气团南下时，因辐射、湍流、对流、蒸发凝结，逐渐变暖3)低层增温，气层不稳定冷气团常不稳定性天气 When air is warmed from below, it rises and causes instability. 4)夏季冷空气可形成强对流。能见度好。5)冬季冷空气一般水汽含量少，多好天气。有时近地面因辐射冷却，可有雾。Characteristics of an unstable air mass include: cumuliform clouds, sho

4、wery precipitation, rough air (turbulence), and good visibility. 问: 暖气团天气特点？思考：暖气团的天气特点 提示：从暖气团的定义出发思考。 回忆关于气层稳定的概念。 回忆有关云形成的稳定度条件。 答： 暖气团天气特点要点所经之处气温升高，气团逐渐变冷低层降温，气层稳定暖气团为稳定性天气：暖气团中水汽含量多时，多有层状云或降毛毛雨。冬季暖空气从海洋移入我国大陆，常伴随平流雾，能见度变坏。暖气团干燥时，为少云、无云好天气。Characteristics of a stable air mass include: stratifor

5、m clouds and fog, continuous precipitation, smooth air, and fair to poor visibility in haze and smoke.影响我国的气团我国位于中纬度偏南地区，不利于气团生成。多为外来变性气团：西伯利亚气团中纬度大陆气团，干冷热带太平洋气团热带海洋气团，暖湿我国境内的气团 活动与气团天气冬季：西伯利亚气团（大陆极地气团）影响； 源地：西伯利亚和蒙古。 特点：*地面流场为冷性反气旋； *中低空为下沉逆温； *控制区为干冷天气；与热带海洋气团 相遇，在华南沿海等地构成阴雨天气； *北极气团 南侵我国，可造成强寒潮 天

6、气。夏季：西伯利亚气团：在长城以北和西北活动频繁，与南方热带海洋气团 交绥，是盛夏南北方区域性降水的主要原因； 热带大陆气团：常影响我国西部地区，干旱酷热与此有关； 赤道气团（来自印度洋，又称季风气团） 造成长江以南大量降水；春季： 西伯利亚气团与热带海洋气团 势力相当，是锋面及气旋活动最盛时期；秋季：变性的西伯利亚气团占主要地位，热带海洋气团退居东南海上，我国东部地区秋高气爽。第二节 锋 Front概念锋/锋面/锋区：温度密度差异很大的两个气团之间的界面。锋线：锋面与地面的交线。The zone between two different air masses is a frontal zo

7、ne or front. Across this zone, temperature, humidity and wind often change rapidly over short distances. 结构：宽 地面几十km，高空几百km长 几百km几千km厚 1km高 可达对流层顶坡度 1/3001/50 。分类按锋的移动情况：冷锋：冷气团推动暖气团向暖气团一侧移动 。暖锋：暖空气团起主导作用，推动冷气团向冷气团一侧移动 。静止锋：冷、暖气团的势力相当时，锋面的移动十分缓慢或相对静止 。锢囚锋：（冷性锢囚锋、暖性锢囚锋、中性锢囚锋）冷锋追上暖锋或由两条冷锋迎面相遇而构成的复合锋。 按

8、锋的伸展高度：地面锋、对流层锋、空中锋（高空锋）按锋的地理位置：冰洋锋（北极锋）、极锋、副热带（热带）锋The three principal types of fronts are the cold front, the warm front, and the stationary front. 冷锋 cold front 锋面移动过程中，冷气团起主导作用，冷气团推动暖气团向暖气团一侧移动。 暖锋 warm front锋面移动过程中，暖空气团起主导作用，推动冷气团向冷气团一侧移动 静止锋 stationary front当冷、暖气团的势力相当时，锋面的移动十分缓慢或相对静止 。Surface

9、 winds tend to flow parallel to the frontal zone at a stationary front. 锋的分类示意图 (a) 冷锋 (b) 暖锋 (c) 准静止锋锢囚锋 occluded front 锢囚锋的分类示意图 (a) 冷式 (b) 暖式 (c) 中性锢囚锋的形成A cold front occlusion occurs when the air ahead of the warm front is warmer than the air behind the overtaking cold front. Frontal waves and c

10、yclones (areas of low pressure) usually form on slow-moving clod fronts or stationary fronts.冷式锢囚锋 形成过程的物理图像锢囚锋 典型的中纬度波动性气旋中冷式锢囚锋 形成过程的物理图像。 温：水平等温线气团内稀疏(1-2C/100km)、锋区密集(1-2C/10km）。垂直锋面逆温。 锋两侧温差大、小，是锋面强、弱的重要指标。压：锋线处于低压槽中，最大曲率在锋线处。 暖区侧气压变化比冷区侧慢得多。风：锋后到锋前，风呈气旋式；冷区风速大于暖区。暖锋附近有暖平流，自下而上穿越锋区，水平风向随高度增加而呈顺

11、时针旋转；冷锋相反。锋附近气象要素的分布特征锋面附近风、压分布3小时变压在天气分析中，一般分析三小时变压。一般来说冷锋在锋后有三小时的正变压，而冷锋前的气压变化不大（如图a）。 相反在暖锋的锋前有三小时的负变压，而暖锋的锋后的气压变化不大（图b）。 对于锢囚锋来说，一般是由冷锋追上暖锋而形成，所以锢囚锋前多为三小时的负变压，而锢囚锋后多为三小时的正变压（图c，d） ？问题？After an aircraft passes through a front into colder air, atmospheric pressure usually increases. 从冷区一侧到暖区，水平穿越锋

12、面时的气压变化特点是什么？The important thing to remember is that you should promptly update your altimeter setting after crossing a front.3000米以下，自下向上穿越冷锋时，风向怎样变化？There is always a change in wind when you fly across a front. The most easily recognizable change when crossing a front is the change in temperature.

13、 锋面天气The type and intensity of frontal weather depend on several factors, including :the availability of moisture, the stability of the air being lifted, and the speed of the frontal movement. Other factors include the slope of the front and the moisture and temperature variations between the two fr

14、onts.冷锋云系（暖气团稳定）从暖区到冷区（低到高）：Sc Ns As Cs Ci锋面陡、云降水区150200km锋线附近Sc St Fs稳定性天气特征冷锋云系（暖气团不稳定)对流云Cb在锋线附近。Cb As/Ac Cs Ci对流云区积冰、乱流。冷锋过境期间气象要素的变化Table adapted from: Ahrens, (1994) Before PassingWhile PassingAfter PassingWindssouth-southwestgusty; shiftingwest-northwestTemperaturewarmsudden dropsteadily drop

15、pingPressurefalling steadilyminimum, then sharp riserising steadilyCloudsincreasing: Ci, Cs and CbCbCuPrecipitationshort period of showersheavy rains, sometimes with hail, thunder and lightningshowers then clearingVisibilityfair to poor in hazepoor, followed by improvinggood, except in showersDew Po

16、inthigh; remains steadysharp droplowering急行冷锋暖空气不稳定：移动速度快的冷锋，锋面陡，空气上升强烈。云系、降水在锋线前及其附近狭窄区内。锋面温湿差大。积状云带沿锋线，旺盛Cb，云顶10km以上。狂风、乌云、暴雨、雷电、冰雹短暂暖空气稳定：层状云系、云区窄、锋后大风。Upper winds blowing across the front usually cause rapid movement of surface fronts. Squall lines usually develop ahead of a cold front. (a)在陸上衰弱

17、中的冷鋒，(b)移至海上時，已漸不明顯 暖锋云系（暖气团稳定）暖锋移来，Ci Cs As Ns云系水平几百km，近锋线云层越低、越厚（厚可十km）连续性降水范围广，宽度300400km。冷气团中Sc St Fs， 锋前雾150200km（雨滴下降蒸发）锋线附近、降水区能见度很差。碎云高度很低。Steady precipitation preceding a front is usually an indication of a warm front, which results from warm air being cooled from the bottom by colder air.

18、This results in stable air with stratiform clouds and little or no turbulence. 暖锋云系（暖气团不稳定）增加Cb，隐藏雷暴。阵性降水严重积冰，锋面两侧温差大（510C）地面有冰丸时，高空存在冻雨。The weather associated with an advancing warm front that has moist, unstable air is cumuliform clouds, turbulent air, and showery-type precipitation. A stratus lay

19、er may form in a mildly stable layer while convective clouds penetrate the layer and form thunderstorms, which may be entirely embedded in a massive stratus layer and pose an unseen threat to instrument flight. Embedded thunderstorms means that the thunderstorms are embedded in clouds or thick haze

20、layers and cannot be seen. Embedded thunderstorms are obscured because they occur in very cloudy conditions or thick haze layers. Before PassingWhile PassingAfter PassingWindssouth-southeastvariablesouth-southwestTemperaturecool-cold, slow warmingsteady risewarmer, then steadyPressureusually falling

21、leveling offslight rise, followed by fallCloudsin this order: Ci, Cs, As, Ns, St, and fog; occasionally Cb in summerstratus-typeclearing with scattered Sc; occasionally Cb in summerPrecipitationlight-to-moderate rain, snow, sleet, or drizzledrizzle or noneusually none, sometimes light rain or shower

22、sVisibilitypoorpoor, but improvingfair in hazeDew Pointsteady risesteadyrise, then steady暖锋经过期间的气象要素变化暖锋天气复习天气特征：锋面坡度小，移动速度慢；云序依次是从高云到低云；连续性降水常出现在锋前（雨层云）；锋下冷气团中水汽充沛，常有层积云、层云和碎层云；若暖气团不稳定，地面锋线附近会出现雷阵雨天气。影 响：暖气团稳定时，云中气流比较平稳，多数不会影响飞行，但能见度很差，碎云高度很低具有复杂气象条件；暖空气潮湿不稳定时，形成的积雨云（雷暴）常隐藏在云层之中；暖锋中容易产生严重积冰，锋两侧温差可达

23、510度锋面两侧积冰区高度不一。当地面报告有冰丸时，在较高的高度上会碰到冻雨。最好是在云上飞行Comparison of Cold and Warm Fronts P40 Speed： Coldfronts ， move at 20 to 35 m.p.h., very quickly warm fronts， 10 to 25 m.p.h. Composition： Coldfronts ， a steeper frontal slope. warm fronts， 10 to 25 m.p.h. weather phenomenon： cold fronts ，squall lines d

24、uring the summer as far as 200 miles in advance of a severe cold front. cold fronts， Violent weather activity along the frontal boundary, bring sudden storms, gusty winds, turbulence, and sometimes hail or tornadoes. warm fronts， low ceilings, poor visibility, and rain, cold fronts bring sudden stor

25、ms, gusty winds, turbulence, and sometimes hail or tornadoes. Prediction：Cold fronts，with little or no warning, make a complete weather change in just a few hours. The weather clears rapidly after passage and drier air with unlimited visibilities prevail. Warm fronts, provide advance warning of thei

26、r approach ，take days to pass through a region. The threat of low-level wind shear occurs just before the warm front passes the airport. With a cold front, the most critical period for wind shear occurs just as or just after the cold front passes the airport. （准）静止锋天气 天气特征：坡度最小，云层和雨区比暖锋更为宽广；降水强度小的持续

27、时间长的连阴雨天气；若暖空气不稳定，会出现积雨云和雷阵雨天气。（广、小、长）影 响：可进行复杂气象条件的训练飞行鋒面系統的演變 Frontal waves normally form on slow-moving cold fronts or stationary fronts. If a frontal wave were to form on a stationary front running east and west across the U.S., that portion east of the wave would normally become a warm front an

28、d that portion west of the wave would become a cold front. 鋒面系統的演變锢囚锋天气 天气特征：在锢囚点附近天气比原来两条锋面天气更差。影 响：在锢囚点以上，会遇到宽广的云层和降水，还可能有雷暴、积冰和颠簸，以下低层广大范围内存在相当恶劣的能见度和低的云幕。（后期会好转）In a cold front occlusion, the air ahead of the warm front is warmer than the air behind the overtaking cold front. An occlusion is com

29、posed of two fronts as a cold front overtakes a warm front.The jet stream is usually to the north of surface lows and fronts. The development of a surface low usually is south of the jet stream and moves nearer as the low deepens. The occluding low moves north of the jet stream, and the jet stream c

30、rosses the frontal system near the point of occlusion. 复习 有关云图的常识1.在卫星云图上，可见光云图的色调取决于( ).A目标反射太阳辐射的大小；B目标的温度；C目标的高低2在卫星云图上，红外云图的色调取决于( ).A反射太阳辐射的大小；B目标的温度；C目标的高低江淮切变线切变线：气旋式切变的风场不连续线。春末秋初，700、850hPa中低空常见。江淮切变线：江淮一带700、850hPa等压面上近于东西向的风场不连续线。江淮切变线6、7月出现时，90%以上有暴雨。冬季则多连续性降水。切变线的云雨带多呈纬向分布选择：1、在锋面经过机场时，

31、要特别注意的是（ ）。 A可能出现高度极低的风切变 B可能出现风沙天气 C. 雨层云中的连续性小雨2、高空锋区偏在地面锋线的（ ）。 A后面 B暖气团一侧 C. 冷气团一侧3、在锋面两侧，下面何种气象要素的差异最大 A气温； B气压； C空气湿度4、在稳定的暖锋上由东北向西南飞行时，经过云系所排列的次序是 A、Ci-Cs-As-Ns B、Cs-As-Ci-Ns C、Ci-Cc-Ac-Ns D、Ns-As-Cs-Ci5、稳定的缓行冷锋来临时，所看到的层状云出现的次序是 A、Ci-Cs-As-Ns B、As-Ns-Cs-Ci C、Ci-As-Cs-Ns D、Ns-As-Cs-Ci6、飑线通常与下列何种锋面有关 A静止锋； B快速移动的冷锋； C快速移动的暖锋7、夏季，当报告江南一地区有锋面形成时，那个地区机场的天气是 A、风速不断加大、降水加强、云中气流很不稳定，很可能有埋置雷暴 B、云体包厚度越来越小，天气将好转 C、在锋生区内肯定全部是稳定的层状云降水区分槽线、切变线:1、在空中等压面图上分析的槽线和切变线，它们的相同之处在于A两侧都有较大的风切变； B两侧都有较大的气压差C.