Atmospheric Structure and Circulation Quiz

Atmospheric Structure and Composition

• Atmosphere: Mixture of gases surrounding Earth, fairly uniform in proportion up to 260,000 feet.
• Layered structure: Defined by criteria like temperature.
• Troposphere: Surface to ~36,000 feet, higher in summer and at the equator. Most weather occurs in this layer.
• Tropopause: Top of troposphere, marks location of jet streams and thunderstorms.
• Stratosphere: Extends to ~160,000 feet.
• Mesosphere and Thermosphere: Higher layers with differing compositions.
• Composition: Nitrogen (78%), Oxygen (21%), Other (1%), Water Vapor (0-4%).

Atmospheric Circulation

• Driven by Unequal Heating: Earth's rotation and differential solar radiation.
• Convection: Warmer, less dense air rises (equator), cooler, denser air sinks (poles), creating a circulation pattern.
• Three-Cell Pattern: Hadley, Ferrel, and Polar cells.
• Atmospheric pressure: Unequal heating leads to variations in air density and atmospheric pressure.

Atmospheric Pressure and Winds

• Isobars: Lines connecting points of equal pressure, used on weather maps.
• Pressure Gradient: Change in pressure over distance. Close isobars = strong gradient, resulting in stronger winds.
• Pressure Systems: High pressure (clockwise flow), Low pressure (counterclockwise flow), ridges, and troughs.
• Air Flow: From high-pressure, cool, dense air to low-pressure, warm, less dense air.
• Coriolis Force: Deflection of air due to Earth's rotation (to the right in the Northern Hemisphere, to the left in the Southern Hemisphere. Affects air flow path; deflection increases with speed.
• Friction: Slows air near Earth's surface, minimizing Coriolis effect. Pressure gradient force is still greater, driving air toward low pressure.

Local Wind Patterns

• Sea Breeze: Daytime heating of land causes rising air, cooler air from the sea moves in to replace it (10-20 knots, 1500-3000 ft AGLL).
• Land Breeze: Land cools faster than water at night, reversing the sea breeze (1000-2000 ft AGL).
• Valley Breeze: Mountain slopes heated by the sun causing warm air to ascend (5-20 knots, max several hundred feet).
• Mountain Breeze: Nighttime cooling of mountains causes cooler air to descend into valley (5-15 knots, max 25 knots).
• Katabatic Winds: Strong downslope winds, often over ice or snow-covered terrains (speeds can exceed 100 knots).
• Warm Downslope Winds: Warm air descending mountains, compression and warming of air (20-50 knots). Examples: Chinook, Föhn, Santa Ana.

Atmospheric Stability and Temperature

• Stability: Resistance to vertical motion (stable = smooth air, unstable = turbulence, clouds).
• Adiabatic Heating/Cooling: Temperature changes during air movement due to expansion/compression.
• Lapse Rate: Rate of temperature decrease with altitude, averages 2ºC per 1,000 ft. Moist air cools slower.
• Temperature Inversions: Temperature increasing with altitude, creating a lid, poor visibility, stable air.
  • Frontal Inversions: Temperature inversions related to fronts.
  • Radiation Inversion: Temperatures near the ground fall below those above due to cooling of surface.

Moisture and Precipitation

• Humidity: Moisture content in the air, including relative humidity (actual vs. possible).
• Dewpoint: Temperature at which air becomes saturated.
• Dew and Frost: Condensation and deposition, respectively, form on surfaces below the dewpoint.
• Clouds: Formed when air cools to saturation, diverse types categorized by altitude.
• Precipitation: Water or ice falling from the atmosphere; causes many aviation challenges.
• Types of Precipitation: Drizzle (liquid) etc...

Aviation Implications

• Many aspects of weather directly impact aircraft operations.
• Temperature, moisture, and air stability all influence turbulence and visibility, which affect safety and flight planning.