1、第二章 气压和高度测量Atmospheric Pressure and Altimetry本章要点：本章要点：气压随高度的变化气压随高度的变化气压随温度的变化气压随温度的变化气压场气压场高度测量高度测量第一、二节第一、二节 气压概念和测量气压概念和测量Concept and MeasuringConcept and Measuring1、气压概念气压：单位面积上空气分子运动的压力。气象中气压单位面积上铅直大气柱的重量。Atmospheric pressure is the force per unit area exerted by the weight of the atmosphere.2
2、、气压单位气压单位：1Pa=1牛顿/米2 1hPa 1mb millibar，inches of mercury,millimeters of mercury,一个大气压1013.25hPa 29.92inches Hg =760mmHg 14.7pounds/square inch3、常用气压值本站气压本站气压：气象台站气压表观测的气压。百叶箱场面气压场面气压(QFE)：着落跑道入口端最高点的气压。通常用机场标高机场标高处气压代替。Station pressurepressure measured at a station or airport,the actual pressure at
3、field elevation.标准海平面气压（标准海平面气压（QNE）：）：标准大气的海平面气压。为一个大气压。standard sea level pressure (航线飞行时按标准海平面气压拨定气压高度表拨定气压高度表。固定值）修正海平面气压修正海平面气压(QNH)：场面气压按照标准大气推算到海平面高度MSL处的气压。Figure 2-2 mean sea level（MSL）修正海平面气压修正海平面气压(QNH)Figure 2-2.Reduction of station pressure to sea level.Pressure increases about 1 inch p
4、er 1,000 feet from the station elevation to sea level.第三节第三节 气压变化气压变化Pressure Variation1、随高度增加，气压降低气压以指数规律递减低空递减快，高空递减慢。Within the lower few thousand feet of the troposphere,pressure decreases roughly one inch for each 1,000 feet increase in altitude.2、随温度 Pressure is equal at the bottom of each Pre
5、ssure is equal at the bottom of each column and equal the top of each column.column and equal the top of each column.热胀冷缩；热胀冷缩；Pressure decreases most rapidly with Pressure decreases most rapidly with height in the cold air and least rapidly height in the cold air and least rapidly in the warm air.i
6、n the warm air.冷气柱单位气压高度差小，暖气柱冷气柱单位气压高度差小，暖气柱单位气压高度差大。如下表。单位气压高度差大。如下表。冷气柱单位高度气压差单位高度气压差大，暖气柱单位高度气压差小。3 气压随时间的变化 日变化，年变化纬度低，日较差大；陆年较差大，海年较差小。4、气压分析 气压空间变化的描述空间气压场等压面（reference ISA）水平气压场等压线isobarsConstant pressure analysis:e.g.700-millibar constant pressure surfaceHeight contours on a constant pressu
7、re chartOn weather maps,the lines drawn to connect points of equal pressure show pressure contours called isobars.气压场的形式 pressure systems低压 LOW/CYCLONE高压 HIGH/ANTICYCLONE低压槽 TROUGH (the lowest pressure along a line marking maximum cyclonic curvature.)A trough is defined as an elongated area of low p
8、ressure.高压脊 RIDGE鞍形区 COL水平气压场形式Figure 2-3.Pressure systems.You can identify highs,lows,ridges,troughs and cols when isobars are plotted on a weather chart.补充：补充：气压梯度从高压指向低压，方向：垂直于等压面（线），大小：单位距离内的气压差。水平（1hPa/100km)、垂直气压梯度(1hPa/8m)等压线疏密程度等压线疏密程度 反映反映 水平气压梯度大小。水平气压梯度大小。第四节第四节 Altimetry 高度测量高度测量复习：The d
9、ecrease of pressure with height varies with temperature.Pressure decreases most rapidly with height in the cold air and least rapidly in the warm air.高（Height）是指自某一个特定基准面量至一个平面、一个点或者可以视为一个点的物体的垂直距离。高度(Altitude)是指自平均海平面量至一个平面、一个点或者可以视为一个点的物体的垂直距离。飞行高度层（Flight Level）是指以1013.2百帕气压面为基准的等压面，各等压面之间具有规定的气压
10、差。飞机上常用的测高方法及特点无线电高度表测高：较精确地测得飞机距地表的距离气压式高度表测高：根据气压随高度变化原理可以表示飞机相对高度的高低。高度表的原理是标准大气的气压高度关系转换。高度表根据测量的高空气压,换算出来相应的标准大气高度（标准大气中，该气压值所对应的高度）。实际大气因为温度分布并非标准大气，而飞机高度表指示的是标准大气高度，该值往往不是飞机所在的实际海拔高度。When cold and mountainous areas,account this.汉语高度描述：场压高度（场高）：是指以着陆区域最高点气压，调整高度表数值为零（以该气压的标准大气高度为零高度），上升至某一点的垂直
11、距离。（过去，飞机起落时可以按场压QFE来拨正气压式高度表，指示飞机相对于跑道的高度。）修正海平面气压高度（修正海压高度或海压高度或海高）：是指以海平面气压调整高度表数值为零，上升至某一点的垂直距离。（在飞机起降时用修正海压QNH拨正高度表。此时将高度表指示高度减去机场标高就等于飞机距机场跑道面的高度。）标准气压高度：是指以标准大气压（其值为1013.2百帕或760毫米汞柱或29.92英寸汞柱）修正高度表压力值，上升至某一点的垂直距离。（飞机在航线上飞行时，按标准海平面气压QNE拨正高度表，指示航线高度。）问题：飞机着陆后，机上高度表指示的高度是问题：飞机着陆后，机上高度表指示的高度是_？高度
12、。高度。其数值为其数值为 。图示为Cessna 182SCessna 182S气压式高度表，有三支指针：长针（蓝点）表示100英尺，中针（黄点）1000英尺，短 针（绿 针）表 示10000英尺，现在高度是3650英尺。实际拨正高度表时候，不是把高度表真放到海平面、地表等位置而设置到指针为零，而是拨仪表盘上拨正窗口的气压。窗口气压拨为标准海压时，指针的数值就是标准气压高度；拨到修正海压时，指针的数据就是修正海压高度。QNH修正海平面气压QNE标准海平面气压高度表拨正规定中国民用机场高度表拨正程序和过度高度层配备.htmQNH水平范围：半径55km（30knots），垂直范围：altitude1
13、200米内机场3000米。Altitude Description in English:True Altitudethe actual or exact aircrafts altitude/height above mean sea level(MSL)Absolute Altitudethe height of an aircraft above the terrain over which it is flying Indicated Altitudethe altitude above mean sea level indicated on the altimeter when se
14、t at the local altimeter setting，this is the uncorrected altitude read directly from that altimeter Figure 2-4.Indicated altitude depends on air temperature below the aircraft.Since pressure is equal at the bases and equal at the tops of each column,indicated altitude is the same at the top of each
15、column.When air is warmer than standard(the upper diagram),the altimeter reads lower than true altitude.When air is colder than average(the lower diagram),the altimeter reads higher than true altitude.即：当气温高于标准大气，altimeter表读数低于真实高度true altitude。Figure25 The effect of temperature on altitude.WARMERCO
16、LDERSince altimeter readings are adjusted for changes in barometric pressure but not for temperature changes,an airplane will be at lower-than-indicated altitude when flying in colder-than-standard air.On warm days,an airplane will be at a higher altitude than the altimeter indicates.Altimeter setti
17、ng is the value to which the scale of the pressure altimeter is set so the altimeter indicates true altitude.Takeoff and landing are the most critical phases of flight;therefore,airport elevation is the most desirable altitude for a true reading of the altimeter.Corrected Altitude(approximately true
18、)indicated altitude corrected for the temperature of the air column below the aircraft,the correction being based on the estimated departure of the existing temperature from standard atmospheric temperature.Pressure Altitude after adjusting the altimeters setting to 29.92 inches,altitude in the stan
19、dard atmosphere where pressure is the same as where you are;a change of one inch in the pressure setting will change the altimeter reading by 1,000 feet Figure 2-5.When flying from high pressure to lower pressure without adjusting your altimeter,you are losing true altitude.按仪表高度按仪表高度pressure altitu
20、de飞行从低压上空飞向高飞行从低压上空飞向高压上空，实际高度变高，高度表小于压上空，实际高度变高，高度表小于实际高度实际高度。Atmospheric pressure decreases about 1 in.Hg for every 1,000 ft.of altitude gained.Changing the altimeter setting changes the indicated altitude in the same direction and by 1,000 ft.for every inch of change.Why?For example,changing from
21、 29.92 in.to 30.92 in.increases indicated altitude by 1,000 ft.,or from 30.15 in.to 30.25 in.increases indicated altitude by 100 ft.Density Altitudealtitude in the standard atmosphere where air density is the same as where you are.密度高度飞行高度上的实际空气密度在标准大气中所对应的高度。是个高度概念。热天，飞机所在的高度密度小，相当于标准大气较高高度的密度值。这时的密度高度叫高密度高度。降低飞机操纵的效率，易危险易危险。reduces power，Reduces thrust,reduces lift冷天，低密度高度。能增加飞机操纵效率。热天冷天On warm days,(an airplane will be at a higher altitude than the altimeter indicates.)And density altitude will be higher than pressure altitude.3习题-上课 Aeronautical Meteorology.doc
