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Aviation Weather. Quote. “Just remember, if you crash because of weather, your funeral will be held on a sunny day” – Layton A. Bennett. The Atmosphere & Global Circulation. Atmospheric Composition.
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Quote • “Just remember, if you crash because of weather, your funeral will be held on a sunny day” – Layton A. Bennett
Atmospheric Composition • Earth's atmosphere has a unique composition of gases when compared to that of the other planets in the solar system.
At greater altitudes, the same volume of air contains fewer molecules of the gases that make it up. This means that the density of air decreases with increasing altitude.
The earth's atmosphere thins rapidly with increasing altitude.
Global Wind Patterns • Hot air rises over the equator due to the fact that it is less dense. • The air then travels north and south at high altitude. • The cooled air descends to reach the surface at about 24 ON and 24 OS of the equator. • This forms a high pressure area • The great deserts of the world are located in this high pressure area
An object in motion in the northern hemisphere appears to turn to the right. • An object in motion in the southern hemisphere appears to turn to the left.
Global Circulation • With Globe, Coriolis • Seasons – Have kid stand on table as sun • Chris Columbus - trades • With Fan, demonstrate orthographic lifting
Cyclones L • Cyclone • A low pressure area with winds moving into the low pressure area and being forced upward • Winds are counter-clockwise around the low pressure system • Anticyclone • A high pressure center • Winds are clockwise H
Weather Fronts • Front • A boundary between two different air masses • Cold Front • When a cold air mass moves into a warmer area, displacing the warm air mass • Provides lift to adiabatically cool the warm air, resulting in towering cumulus and thunderclouds.
Boundaries between air masses = fronts • Cold • Warm • Stationary • Occluded Types of Fronts
Warm Front When a warm air mass moves into an area, displacing the cold air mass A gently sloping front as the Warm air moves over top of the cooler air. StationaryFront When the edge of a front ceases to advance
Air Masses • Polar air mass • An air mass that moves from a cold region • Tropical Air Mass • An air mass that moves from a warm region • Continental Air Mass • Moves in from a land mass • Maritime Air Mass • Moves in from over an ocean
Occluded Front • Cold front overtakes a warm front • Warm front is “sandwiched” • Lifted off the ground • Has a low pressure center and possible cyclonic activity
Stability • Air may be: • Unstable • Cumulus clouds • Stable • Stratus clouds
How a Cloud Forms • Temperature and Dewpoint Converge • Water Condenses on Particles (Dirt, Dust, Smoke)
Calculate the altitude of this cloud. Surface Temperature = 68° Dewpoint = 59° Moist Air 68-59 = 9, 9/4.5 = 2 2 = 2,000 foot bases
This figure compares the size of the condensation nuclei to the size of typical condensation droplets. Note that 1 micron is 1/1,000 mm. Condensation Nucleus (0.2 microns) Average Cloud Droplet (20 microns) Large Cloud Droplet (100 microns) Drizzle Droplet (300 microns) Average Rain Drop (2000 microns)
Types of Fog • Radiation (ground) fog • Advection fog • Requires wind • Warm air over colder land or water • Upslope fog • Requires wind • Higher ground
Radiation Fog From the Air
Thunderstorms • Thunderstorms require • Unstable air • Moisture • Lifting mechanism • T-storms always have lightning • Thunder is the sound of lightning • T-storms are reported when thunder is heard • Automatic Wx Obs Systems (AWOS) detects lightning discharge
Types of Thunderstorms • Air mass • Associated with local heating • Downdrafts cut off updrafts quickly • Short lived
Types of Thunderstorms • Steady – State • Associated with weather systems • Precipitation falls outside the updrafts • Continues unabated for several hours
Types of Thunderstorms • Squall Line • Group of storms arranged in a line • High wind and heavy rain • Most violent of the thunderstorms • Cumulonimbus Mammatus, funnel clouds, tornados
Embedded Thunderstorms • Unstable cumulus clouds hidden among straitform clouds • Bad clouds obscured by good clouds