The Private Pilot

1. The Private Pilot

2. Class 7 - Weather

3. Objective: Weather Theory for pilots, A to Z.

4. The Atmosphere

5. Atmospheric Circulation • Atmospheric circulation is the movement of air around the surface of the Earth. • It is caused by uneven heating of the Earth’s surface and upsets the equilibrium of the atmosphere, creating changes in air movement and atmospheric pressure. • EVERY physical process of weather is accompanied by or is the product of a HEAT EXCHANGE

6. AC • The force created by the rotation of the Earth is known as Coriolis force. • This force is not perceptible to us as we walk around because we move so slowly and travel relatively short distances compared to the size and rotation rate of the Earth. • Atmospheric Circulation is air movement relative to the Earth’s Surface

8. Temperature & Atmospheric Pressure • Unequal heating of the Earth’s surface causes variations in altimeter settings between stations. • High to Low or Hot to Cold “Look Out Below!”

9. High and Low

10. High and Low

11. Under which condition will pressure altitude be equal to true altitude? • When the atmospheric pressure is 29.92 inches Hg. • When standard atmospheric conditions exist. • When indicated altitude is equal to the pressure altitude.

12. If a flight is made from an area of low pressure into an area of high pressure without the altimeter setting being adjusted, the altimeter will indicate • the actual altitude above sea level. • higher than the actual altitude above sea level. • lower than the actual altitude above sea level.

13. If a flight is made from an area of low pressure into an area of high pressure without the altimeter setting being adjusted, the altimeter will indicate • lower than the actual altitude above sea level. The aircraft will be at a higher true altitude above sea level than is indicated.

14. An Effect of Pressure

15. And… • At lower altitudes, friction with the Earth’s surface deflects the wind. • Convective circulation patterns associated with the sea breezes are caused by cool, dense air moving inland from over water.

17. What causes variations in altimeter settings between weather reporting points? • Unequal heating of the Earth's surface. • Variation of terrain elevation. • Coriolis force.

18. The wind at 5,000 feet AGL is southwesterly while the surface wind is southerly. This difference in direction is primarily due to • stronger pressure gradient at higher altitudes. • friction between the wind and the surface. • stronger Coriolis force at the surface.

19. The Most Important part of a weather briefing is Winds Aloft

20. Convective circulation patterns associated with sea breezes are caused by • warm, dense air moving inland from over the water. • water absorbing and radiating heat faster than the land. • cool, dense air moving inland from over the water.

21. Atmospheric Stability • The amount of moisture present in the atmosphere is dependent upon the temperature of the air. • Water vapor is added into the atmosphere only by the processes of evaporation and sublimation. Evaporation is the changing of liquid water to water vapor.

22. Atmospheric Stability • Rising air expands and cools due to the decrease in air pressure as altitude increases. • The opposite is true of descending air; as atmospheric pressure increases, the temperature of descending air increases as it is compressed. Adiabatic heating, or adiabatic cooling, are the terms used to describe this temperature change.

23. Atmospheric Stability • The rate at which temperature decreases with an increase in altitude is referred to as its lapse rate. As air ascends through the atmosphere, the average rate of temperature change is 2°C (3.5°F) per 1,000 feet. • Stability of air can be measured by its ACTUAL lapse rate.

24. What measurement can be used to determine the stability of the atmosphere? • Atmospheric pressure. • Actual lapse rate. • Surface temperature.

25. Atmospheric Stability • STABLE Air - Stratiform Clouds. • When moist stable air flows upslope, stratus type clouds form. • UNSTABLE AIR = turbulence, GOOD surface visibility.

26. What are characteristics of unstable air? • Turbulence and good surface visibility. • Turbulence and poor surface visibility. • Nimbostratus clouds and good surface visibility.

27. What are characteristics of a moist, unstable air mass? • Cumuliform clouds and showery precipitation. • Poor visibility and smooth air. • Stratiform clouds and showery precipitation.

28. A stable air mass is most likely to have which characteristic? • Showery precipitation. • Turbulent air. • Poor surface visibility.

29. Moist, stable air flowing upslope can be expected to • produce stratus type clouds. • cause showers and thunderstorms. • develop convective turbulence.

30. What would decrease the stability of an air mass? • Warming from below. • Cooling from below. • Decrease in water vapor.

31. What would decrease the stability of an air mass? • Warming from below. Stability is altered by a change in the lapse rate of an air mass. Warming from below or cooling from above will increase the lapse rate and make the air LESS stable.

32. What is a characteristic of stable air? • Stratiform clouds. • Unlimited visibility. • Cumulus clouds.

33. Atmospheric Stability • When the temperature of the air rises with altitude, a temperature inversion exists. • Inversion layers are commonly shallow layers of smooth, stable air close to the ground. The temperature of the air increases with altitude to a certain point, which is the top of the inversion.

34. Atmospheric Stability • The air at the top of the layer acts as a lid, keeping weather and pollutants trapped below. • If the relative humidity of the air is high, it can contribute to the formation of clouds, fog, haze, or smoke, resulting in diminished visibility in the inversion layer.

35. Atmospheric Stability • The most frequent type of ground or surface-based inversion is that which is produced by terrestrial radiation on a clear, relatively still night. • Beneath a low-level temperature inversion, when the relative humidity is high, can be expected smooth air, poor visibility, fog, haze, or low clouds.

36. The most frequent type of ground or surface-based temperature inversion is that which is produced by • terrestrial radiation on a clear, relatively still night. • warm air being lifted rapidly aloft in the vicinity of mountainous terrain. • the movement of colder air under warm air, or the movement of warm air over cold air.

37. Which weather conditions should be expected beneath a low-level temperature inversion layer when the relative humidity is high? • Smooth air, poor visibility, fog, haze, or low clouds. • Light wind shear, poor visibility, haze, and light rain. • Turbulent air, poor visibility, fog, low stratus type clouds, and showery precipitation.

38. Temperature Inversion -- Stable Layer

39. What feature is associated with a temperature inversion? • A stable layer of air. • An unstable layer of air. • Chinook winds on mountain slopes.

40. A temperature inversion would most likely result in which weather condition? • Clouds with extensive vertical development above an inversion aloft. • Good visibility in the lower levels of the atmosphere and poor visibility above an inversion aloft. • An increase in temperature as altitude is increased.

41. MoistureDewpoint and temperature • The dewpoint, given in degrees, is the temperature at which the air can hold no more moisture. When the temperature of the air is reduced to the dewpoint, the air is completely saturated and moisture begins to condense out of the air in the form of fog, dew, frost, clouds, rain, hail, or snow. • The Amount of water vapor which air can hold depends on the AIR TEMPERATURE

42. The other Most Important part of a weather briefing is Temperature Dewpoint Spread

43. Atmospheric Stability & Moisture • When lifted, unsaturated air cools at a rate of 5.4°F per 1,000 feet and the dewpoint temperature decreases at a rate of 1°F per 1,000 feet. • Convergence of temperature and dewpoint is at a rate of 4.4°F (2° C). • The convergence rate determines the height of the cloud base.

44. Atmospheric Stability & Moisture • Temperature (T) = 85°F • Dewpoint (DP) = 71°F • Convergence Rate (CR) = 4.4° T – DP = (TDS) Temp-dewpoint spread TDS ÷ CR = X X × 1,000 feet = height of cloud base AGL

45. What is meant by the term 'dewpoint'? • The temperature at which condensation and evaporation are equal. • The temperature at which dew will always form. • The temperature to which air must be cooled to become saturated.

46. The amount of water vapor which air can hold depends on the • dewpoint. • air temperature. • stability of the air.

47. What is the approximate base of the cumulus clouds if the surface air temperature at 1,000 feet MSL is 70 °F and the dewpoint is 48 °F? • 4,000 feet MSL. • 5,000 feet MSL. • 6,000 feet MSL.

48. Ceiling • the lowest layer of clouds reported as being broken or overcast, or the vertical visibility into an obscuration like fog or haze. • Clouds are reported as broken when five-eighths to seven-eighths of the sky is covered with clouds. Overcast means the entire sky is covered with clouds.

49. CLOUDS, FOG or DEW will ALWAYS form when water vapor CONDENSES

50. Clouds, fog, or dew will always form when • water vapor condenses. • water vapor is present. • relative humidity reaches 100 percent.