Lesson 2-3 Aviation Weather

1. Lesson 2-3Aviation Weather

2. Lesson Overview • Causes of atmospheric instability • Types and causes of turbulence • How types of severe weather affect aviation Chapter 2, Lesson 3

3. Quick Write What is the story behind Colonel Duckworth and his AT-6 trainer aircraft--why did he decide to fly into a hurricane…twice? What happened? Chapter 2, Lesson 3 Courtesy of the National Museum of the USAF

4. Causes of Atmospheric Instability • Small vertical movements grow until they produce turbulent airflow and air circulation • Why does air cool as it rises and warm as it falls • Adiabatic means no heat is gained or lost in a system • Adiabatic cooling and heating take place in upward and downward moving air • When air rises, volume increases while pressure and temperature decreases • When air descends the opposite is true Chapter 2, Lesson 3 Reproduced from NOAA/National Weather Service

5. Causes of Atmospheric Instability, cont. • Water vapor is less dense than air • Moisture decreases air density, causes air to rise • As air becomes drier, air becomes denser and sinks • Lapse Rate: The rate at which temperature decreases with increasing altitude • It is different between moist and dry air • Moist air cools at a slower rate than dry air • Combination of moisture and temperature determines air stability and weather • Cool, dry air is very stable and resists vertical movement • Warm, moist air produces the greatest instability

6. Turbulence • What is it? • Produced by an unstable atmosphere • A sign of rapidly rising and falling currents of air • Can occur anywhere from ground to tropopause

7. Thermal Turbulence • Rise of warm air, taking place on a local scale • Plowed ground, rocks, sand, and barren land emit a large amount of heat • Water, trees, and other growing things absorb heat • These reactions to sun’s energy results in uneven heating of the air, creates small areas called convective currents

8. Convective Currents • Create bumpy, turbulent air • On low-altitude flight, pilots may run into updrafts over pavement or barren places, and downdrafts over water or forests • To avoid these turbulent conditions, they can fly at higher altitude, even above cumulus clouds

9. Mechanical Turbulence • Generated by resistance of an object moving over another • As air moves over Earth’s surface, friction that develops between air and surface modifies the air’s movement • Large objects—mountains to man-made structures such as buildings—generate mechanical turbulence

10. Wind Shear • Abrupt, dramatic change in wind speed and/or direction • Low-level are linked with thunderstorms, and temperature inversions, with strong upper-level winds • Extremely dangerous due to proximity of ground • High-Level begins around 18,000 feet and can produce clear air turbulence (CAT) • Most CAT takes place around, but not in, jet streams

11. Thunderstorms • Convection triggers thunderstorms • Water vapors rising with warm air condense into clouds • Convection process then continues within the clouds • At the tropopause the unstable atmosphere stabilizes Chapter 2, Lesson 3 Reproduced from NOAA/Earth System Research Laboratory

12. Thunderstorms • To form, three things are needed: • Enough water vapor • An unstable lapse rate • Lifting action to power up the storm • As warm moist air rises, it condenses into clouds • Condensation give off heat, further warming the air • Process can continue until clouds reaches tropopause • As raindrops form and begin to fall, the air compresses and cools, slowing convection until the storm and clouds break up Chapter 2, Lesson 3 Reproduced from US Department of Transportation/Federal Aviation Administration

13. Thunderstorm Stages • Cumulus Stage • Lifting action, vertically growing clouds • Strong updrafts stop moisture from falling • Mature Stage • Most violent time for the cloud • Rain begins to fall, causing cooler downdrafts that cause violent wind sheers with warmer updrafts • As cooler downdrafts hit surface, they move horizontally in front of storm producing gust fronts • Dissipating Stage • Downdrafts spread out and replace warm updrafts that were feeding the storm • To form, three things are needed: • Enough water vapor • An unstable lapse rate • Lifting action to power up the storm • As warm moist air rises, it condenses into clouds • Condensation give off heat, further warming the air • Process can continue until clouds reaches tropopause • As raindrops form and begin to fall, the air compresses and cools, slowing convection until the storm and clouds break up

14. ThunderstormsAir Mass vs Steady-State • Air mass Thunderstorm • Occur in unstable air and only last an hour or two • Usually caused by warm surface temperatures • Steady-state Thunderstorm • More threatening than air mass thunderstorm • Caused by: • Fronts • Big winds that run into one another • A long stretch of low pressure called a trough • Often form into narrow band of active thunderstorms called squall lines • Updrafts grow stronger • Can last much longer than 2 hours

15. Hazards to Aircraft • Look for squall lines, tornadoes, turbulence, icing, hail, lightning, and poor visibility • Light aircraft won’t be able to fly over thunderstorms • Air Force instructs pilots to fly 20 miles from the storm’s edge

16. Squall Lines • Develop in moist, unstable air, on or in advance of a cold front • Often contain steady-state thunderstorms • Form quickly, are strongest in the late afternoon and early evening

17. Tornadoes • Materialize out of the most violent thunderstorms • Can sharpen into a powerful vortex that reaches from the ground into the clouds • Funnel-shaped cloud that stretches earthward from a cumulonimbus base • 200+ mph winds

18. Turbulence • Pilots encounter strongest turbulence inside a cloud • Turbulence can occur outside of thunderstorm clouds • Several thousand feet above • 20 miles sideways • Gust fronts can be up to 15 miles ahead of any storm

19. Icing—Hail • Icing, is a product of updrafts • In a thunderstorm, the updraft lifts water vapor above freezing level, the water supercools • Hail, another form of supercooledwater • Can be just as dangerous to aircraft as turbulence

20. Lightning—Poor Visibility • Lightning—hazard that’s most closely associated with thunderstorms • Can puncture an aircraft’s skin, damage its communications and navigational equipment • Visibility is near zero within a thunderstorm cloud

21. Activity: AtmosModeler LabTemperature and Altitude • Use the AtmosModeler interactive simulation software to investigate how changes in altitude affect temperature • Gather and record data on temperature and altitude then use that information to make calculations Chapter 2, Lesson 3

22. Next…. • Done – aviation weather • Next – weather forecasting Chapter 2, Lesson 3 Courtesy of NASA/George Shelton