加拿习加国学习met3

1、METEOROLOGYSECTION 3Section 3.1The Earths AtmosphereThe Earths AtmosphereComposition of the atmosphere:78% Nitrogen.21% Oxygen.1% Argon, water vapour, and other gases.Water Vapour is an important component of the air.Composition (cont)WHY?Because it can change into water droplets or ice crystals.It

2、is responsible for the formation of cloudsThe amount of water vapour in the air is difficult to predict, because it varies with temperature. TroposphereLowest layer of the atmosphereVaries from 28,000 feet at the poles to 54,000 feet at the equator.The Pressure, Temperature and Density decrease with

3、 height.Most of the weather occurs in this region because of the presence of water vapour and vertical current.TroposphereIn the upper regions the wind is very strong and is known as the JETSTREAM.The top layer is known as the TropopauseStratosphereExtends from the tropopause for a distance of about

4、 50,000 feet.The pressure continues to decrease.Temperature remains relatively constant at -56CIt is thick over the poles, and thin over the equator.StratosphereWater vapour is non existent, air currents are minimal.The top layer is known as the the STRATOPAUSE.MesosphereCharacterized by an increase

5、 in temperature to +10C at an altitude of approximately 150,000 feet.Due to the ozone, which absorbs more of the suns radiation.The top layer is known as the MESOPAUSE, where the temperature drops again.-100C at approximately 250,000 feet AGL.ThermosphereTemperature rises for an indefinite distance

6、into space.Temperatures can rise as high as C at 400 miles above the earth. Based on the kinetic theory of gases.The spectacular auroras form in the upper regions of the thermosphere. Better known as the Northern Lights.ThermosphereThe layer within the thermosphere, from 50 miles to 250 miles AGL is

7、 known as the IONOSPHERE.This layer affects Radio Communication due to the amount of free electron density.ExosphereBeyond the ionosphere lies a layer that is so thin that pressure drops to little more than a vacuum.Temperature in this layer has little meaning.SpaceNo one actually knows where space

8、begins.At an altitude of 90 to 100 miles, one is entering the realm of satellites and aerodynamic lift is no longer a requirement to maintain altitude.90 miles AGL is recognized as the limit of national sovereignty. The Standard AtmosphereThe International Civil Aviation Organization (ICAO) standard

9、 atmosphere is defined as:The air is a perfectly dry gas.A mean sea level pressure of 29.92 inches of mercury.A mean sea level temperature of 15C.The rate of decrease of temperature with height is 1.98C per 1000 feetThis is for North America, based on summer and winter averages at latitude 40.Proper

10、ties of the AtmosphereThe 3 principal properties of the atmosphere are:MobilityExpansionCompressionSection3.2ATMOSPHERIC PRESSUREAtmospheric PressureWhy are we using atmospheric pressure?Aircraft are using the altimeter which is based on the operation of the atmospheric pressure. Pressure distributi

11、on in the atmosphere control the winds.Pressure MeasurementsThe pressure at any point is due to the weight of the overlying air.Pressure is measured by a mercury barometer and expressed in inches of mercury (Hg).Pressure is however, a force and it is common to apply a unit.Pressure MeasurementsThis

12、unit is known as a Hectopascal (hPa).1 hPa = the pressure exerted on an area of 1 square inch by a force of 1000 dynes.hPa is used in meteorological work, and on TV (kPa).29.92 Hg = 1013.2 hPa = 101.32 kPa.DefinitionsStation Pressure:actual atmospheric pressure at the elevation of the observing stat

13、ion. (Actual weight of the column of air extending up from the station level to the outer limit of the atmosphere).Directly read from the mercury barometer.DefinitionsMean Sea Level (MSL) Pressure:it is necessary to reduce the station pressure to a common level to have a consistent record of the dis

14、tribution of atmospheric pressure.The reduction to MSL involves adding the weight of a column of air extending from the station level down to mean sea level.Temperature is taken into account and is based on the average of the surface temperature at the time of observation and for 12 hours before the

15、 time of observation.DefinitionsAltimeter setting:true height above the MSL assuming that the atmosphere is in ICAO standard atmospheric pressure (1.98C per 1000 feet)Pressure Altitude:indicated altitude corrected for non standard pressure or when 29.92 is setDensity Altitude:pressure altitude corre

16、cted for non standard temperaturePressure SystemsLOW:An area of low pressure is also called a CYCLONE or DEPRESSION.A low is a region of relatively low pressure with the lowest pressure at the center.Rate of movement: 500 miles/day in summer 700 miles/day in winterdrift: NE to SEspin: counter-clockw

17、ise, the air is converging to the center of the low and ascendingAssociated with bad weather.Pressure SystemsHigh:area of relatively high pressure, also called ANTICYCLONE, with the highest pressure in the center.Rate of movement is slow and can remain stationary for days at a time.Spin: clockwise,

18、and the air blows outwards into the lows.Weather: usually good weather, light wind, occasionally, however a persistent cloud sheet develops, causing dull, gloomy weather.Pressure SystemsSecondary Low:smaller disturbance of a cyclonic nature which forms within the area dominated by the main depressio

19、n.Associated with thunderstorms in the summer, and gales or heavy precipitation in the winter.Trough:this is an elongated U-shape area of Low pressure with higher pressure on either side.Also applies to the V-shape formed by sharp bending of the isobars along a frontal surface.Pressure SystemsRidge:

20、Is a ridge of high pressure with lower pressure lying on either side.The weather is usually fine to fair.Col.:Is a neutral region between 2 Highs and 2 LowsKnown to be regions of undependable weatherWeather: in winter: fogin summer: thunderstormsIsobarsIsobars are the lines on the weather map that join areas of equal barometric pressure.The lines are spaced at 4 hPa intervals above and below the value of 1000 hPa.Isobars will never cross one another.Pressure C