儀表等級飛行員理論培訓stage3-214A WX FACTORS

1、Weather FactorslComposition of Airl78% Nitrogenl21% Oxygenl1% Other (trace gasses)Permanent Proportions = Carbon Dioxide, Ozone, Neon, Argon, HeliumVariable Gases = Water Vapor(0-4%)Ozone (O3) located 50,000-100,000- blocks UVslP/DT=RThe temperature around the globe is a result of the tilt, rotation

2、, and orbit of the earth around the sun.Heat transfer is affected by terrestrial radiation, conduction, and convection/advectionWhy the temp rise? *Ozone absorbs solar radiation *Troposphere:Lowest level of atmosphereless at polesbulges at equatorAverage = 37,000 thickTemperature decreases with alti

3、tude (positive lapse rate)Most weather occurs in troposphere99.5% of water in troposphereTropopauseBoundary level - acts as lid to keep water in troposphereLower near poles, higher near equatorLower in winter, higher in summerLittle temperature change (neutral lapse rate)Most weather (clouds) do not

4、 penetrate this layerContains turbulence, jet streams, and high thunderstormsStratosphere:Starts about 66,000 and is 15 miles thickTemperature increases with altitude (negative lapse rate)High concentration of ozoneAir is stable, very little weatherStratopause:Boundary level between stratosphere and

5、 mesosphereApproximately 160,000 highMesosphere:Temperature once again begins to drop with altitudelDifference in pressure between two points divided by the distance between the pointslCirculation is due to Convection.lAs temperature rises, molecules spread apart. lLess dense air moves upward (conve

6、ction).lAn area of low pressure is left behind.lHigher pressure air moves in to fill the void (advection).lIsobars lines of equal pressurelPressure Gradient - change in pressure over distanceWide or dashed is weakClose spacing is stronglRule of Thumb but not always:High pressure - descending air / g

7、ood wxLow pressure - ascending air / worse wxNorthern Hemisphere: A mass traveling great N-S or S-N distances , ie. Rockets, Oceans, Air Masses, will deflect to the right.Southern Hemisphere: opposite effect.lEarth Spins on Axis (1 revolution in 24 hours):lPoles rotate in space.lAt same time, a spot

8、 on equator travels 25,000 miles (1040 miles per hour).lIf we stand on top of the north pole and throw a baseball toward China, it will take time for the baseball to get to China.lWhile the ball is on its way, the Earth continues to rotate.lBy the time the ball gets to where we threw it, the earth h

9、as moved.lBecause the earth moved out from under the ball, the ball lands in the ocean. Not in China. lIf we look at the path the ball took across the ground, it will have curved to the rightl1. in the northern hemisphere, the geostrophic wind is parallel to the isobars with the lowest pressure on t

10、he left.l2. the closer together the isobars, the stronger the pressure gradient/geostrophic wind speed. l3. In the Northern Hemisphere, winds tend to blow counterclockwise around low pressure centers and clockwise around high.l4. geostrophic balance does not occur in small scale circulations such as

11、 sea breezes, thunderstorms, tornadoes, and dust devils because pressure gradient force is greater here than coriolis.l1. winds increase with altitude in the atmospheric boundary layer, with the greatest increases just above the surface.l2. the wind changes direction clockwise (veers) with increasin

12、g altitude.l3. when winds near the surface are strong, the boundary layer is turbulent and winds are gusty. As you descend into the boundary layer to land on a windy day, the air becomes rougher as you get closer to the ground.l4. The boundary layer is deeper during the day and in the warmer months

13、of the year. It is shallower at night and during the colder months.l5. when winds are strong, the boundary layer is deeper over rough terrain. l6. Winds near the ground tend to spiral counterclockwise into a cyclone and spiral clockwise out of anticyclones.lStrong accelerations and vertical developm

14、ent can produce quick and large pressure gradients. Examples include wind accelerating over hills, and down drafts from rain. Convection Orographic Convergence/Divergence FrontalBased upon the difference between the adiabatic lapse rate of a parcel of air compared to the ambient lapse rate of the su

15、rrounding air.lFriction from the surface slows air blow it and causes it to tumblelBased upon lapse rateslStandard: 2C per 1000lDry: 3C per 1000lMoist: 1.2C 2.8C per 1000lAdiabatic Cooling/warming:lChange in temperature due to a change in pressurelAs air rises, it expands and cools.Adiabatic cooling

16、lLapse ratesDALR - 3 C/ 1000SALR - VariableIf lower than ambient, then unstableStandard Lapse Rate - 2C/1000lTemp inversion occurs in stable airlEvaporation - heat is added to water, changing it to a gaslSublimation - ice directly to water vaporlCondensation - air becomes saturated, and water vapor

17、in air becomes liquidlDeposition - water vapor freezes directly to icelAmount of water vapor air can hold decreases with air temperature.lDewpoint temperature is full saturationlFrostDewpoint is below freezing, and the surface is below dewpointWater vapor depositionlLatent heat of evaporationHeat to

18、 vaporize 1 gram of water (540 cal)lLatent heat of condensationWater vapor gives back heatViolent energy is released when thousands of tons of moisture condense into a thunderstorm cloudLatent Heat and Stability When air becomes saturated and cloud formations occurs, heat is released when water turn

19、s from a vapor to a liquid (condensation). This is important when air is rising and cooling adiabatically the stability can be changed due to this latent heat. Adibitaic cooling can be somewhat offest from latent heat.Revision 1.0Formation of Fog / Clouds: A cloud is the visible collection of suspen

20、ded water or ice particles in the air. Fog is a cloud near the earths surface. Formed by: (requires there to be water vapor, condensation nuclei) Air is cooled to its dew point. (through adiabatic expansion or cold surface contact) Moisture is added to air until saturation occurs.Condensation nuclei

21、 Microscopic particles such as dust and salt that provide a surface for water to form on. Examples are fog forming on populates near cities.Sierra Academy of AeronauticsInternational Training CenterPrivate Pilot Ground CourseRevision 1.0Fog: Steam Fog Upslope Fog Precipitation Fog Advection Fog Radi

22、ation FogSierra Academy of AeronauticsInternational Training CenterPrivate Pilot Ground CourseRevision 1.0Steam Fog: Very cold, dry air moves over warmer water. Air near water surface picks up moisture due to evaporation and heat. This warmer, moist air rises, cools, and reaches its dewpoint.Sierra

23、Academy of AeronauticsInternational Training CenterPrivate Pilot Ground CourseRevision 1.0Upslope Fog: Warm, moist air is pushed up sloping terrain by wind. Air cools adiabatically to dewpoint.Sierra Academy of AeronauticsInternational Training CenterPrivate Pilot Ground CourseRevision 1.0Precipitat

24、ion Fog: Warm rain falls through cold air. Air picks up moisture from evaporation and quickly reaches its saturation point.Sierra Academy of AeronauticsInternational Training CenterPrivate Pilot Ground CourseRevision 1.0Advection Fog: Wind blows warm, moist air over a cooler surface. Air near surfac

25、e is cooled to its dewpoint. Sea Fog: Warm, moist air from a warm sea flows over a colder sea.Sierra Academy of AeronauticsInternational Training CenterPrivate Pilot Ground CourseRevision 1.0Radiation Fog: Moist air is heated during day. Nighttime terrestrial radiation cools earth and nearby calm ai

26、r to dewpoint. Valley Fog Ground Fog Ice FogSierra Academy of AeronauticsInternational Training CenterPrivate Pilot Ground CourseRevision 1.0 Valley Fog: Air is moist due to rivers or lakes, calm air pools in valleys. Ground Fog: Occurs after rain or moist earth is cooled. Ice Fog: Radiation fog in

27、artic regions where dewpoint is -25 F or colder.Radiation Fog:Cloud heights, amounts, and type Cloud height or ceilings is defined as the eight above the earths surface of the lowest layer reported as broken or overcast, or as the vertical visibility into an indefinite ceiling. Cloud amounts- measur

28、ed in eights of the celestial dome. type of cloud is on the basis of what the cloud looks like in its height, shape, and behaviorlFour Groups or FamiliesLow (surface to 6500AGL)Middle (6500 to 20,000AGL - alto)High (above 20,000AGL)Extensive Vertical DevelopmentlNamesCumulus Stratus Nimbus CirrusNoI

29、magelDrizzlelRain/rain showerslSnow/snow showers/snow grainslIce pelletslHaillJust because there is %100 saturation doesnt mean there will be precipitation, most clouds dont precipitate.l1. Precipitation particles must be much larger than cloud particles so they can fall out of the cloud and exist l

30、ong enough to reach the ground.l2. Most of the time, processes that produce small cloud particles are not very effective in producing large precipitation particles.l3. Efficient precipitation producing processes mainly occur in certain cloud types (usually Nimbostratus and cumulonimbus .lTwo process

31、es by which precipitation forms- condensation/deposition and collision/coalescence.lWater droplets that have coalesced!lVirgaLow relative humidityEvaporates before contact with groundlSupercooled waterRemains liquid though cooled freezingTurns to ice or freezing rainNoImagelBoundary between air masseslFrontal passage changes:TemperatureWind directionWind speedlFactors affecting intensity:1) moisture 2) stability of