Weather and Climate

1. Weather and Climate Chapter 23

2. Weather Temperature Rainfall Humidity

3. Hydrologic cycle Evaporation from the ocean Transport through the atmosphere Condensation and precipitation Return to the ocean Many smaller sub cycles

5. Cloud-forming processes Clouds form when air masses are cooled to their dew point Generally cooled by upward movement Cloud formation depends on atmospheric stability

6. Atmosphereic Stability Stable atmosphere lifted parcel of air to cooler (and denser) than surrounding air lifted parcel returns to the original level

7. Unstable atmosphere lifted parcel of air is warmer (and less dense) than surrounding air Moved to a higher level, it will continue to rise “thermals”

8. Upward mobility and moist air Rising moist air cools and eventually reaches the dew point Droplets condense around condensation nuclei in saturated air no condensation nuclei: supersaturated air

9. In a state of atmospheric instability, a parcel of air will always be warmer, and therefore less dense, than the surrounding air at any altitude. The parcel will, therefore, continue on in the direction pushed when the upward force is removed. In a state of atmospheric stability, the parcel of air will always be cooler, and therefore more dense, that he surrounding air at any altitude. It will, therefore, return to the original level when the upward force is removed.

10. Cooling of rising air slowed by release of latent heat of vaporization Huge numbers of droplets appear as clouds

11. Origin of precipitation Precipitation Water returning to Earth’s surface Dew and frost are surface processes, not precipitation

12. Precipitation forms in two ways Coalescence of cloud droplets Growth of ice crystals

13. Coalescence process takes place in warm cumulus clouds, near the tropic oceans clouds contain giant salt condensation nuclei

14. Ice-crystal process Takes place in clouds of middle latitudes Ice crystals capture nearby water molecules and grow Fall as snow in the winter; melt and turn to rain in summer

15. Weather producers Idealized model Region 10oN and 10oS of equator receives more direct solar energy Air heats up, rises and spreads toward poles

16. Air cools and becomes more dense as it rises sinking back to the surface at latitudes 30oN and 30oS

17. End Result Band of low pressure near the equator, bands of higher pressure 30oN and 30oS of the equator Large convective cells form to equalize pressure

18. Air Masses Large, horizontally uniform bodies of air Moisture and temperature conditions nearly the same

19. Four main types Continental polar Maritime polar Continental tropical Maritime tropical

20. Dictate air mass weather weather conditions remain the same over several days weather changes when a new mass moves in or when the air mass acquires local conditions

21. Weather fronts Boundaries between air masses at different temperatures Cold front cold air mass moves into and displaces warmer air upward moist rising air cooled

22. Warm front Warm air mass advances over a cooler air mass Long, gently sloping front Clouds and rain may form in advance of the front

23. Stationary front Forces influencing warm and cold air masses become balanced

27. Waves and Cyclones Mechanisms Bulges or waves often form between air masses Overriding, uplifted cold air produces a low pressure area

28. Further cold front motion leads to an occluded front and a cyclone storm Cyclone Low pressure area with inflowing, upward force winds

29. Circulation pattern caused by the Coriolis effect Anti-cyclone High pressure area Air sinks, is warmed, relative humidity is lowered

33. Major Storms Rapid, violent weather changes Often associated with frontal passage

34. Three major types thunderstorms tornadoes hurricanes

35. Thunderstorms Usually develops in warm, very moist, and unstable air Three stages Cumulus – associated with convection, mountain barriers, or a cold front

36. Mature Updraft can no longer support growing ice crystals and snow flakes Falling frozen water melts and becomes rain Hail formed through ice accumulation cycles

37. Final All updrafts are exhausted

39. Lightning and thunder Updrafts, downdrafts and circulating precipitation separate electrical charges Charges accumulate in different parts of the thunderhead

40. Lightning Discharge between charge centers Can be cloud to ground, ground to cloud, or cloud to cloud Expanding pressure wave from heated air produces crack of thunder

42. Tornadoes Smallest, most violent weather disturbance Rapidly whirling column of air diameter of 100-400 meters wind speeds up to 480 km/h

43. Damage produced high winds drop in pressure at center flying debris Associated with intense thunderstorms

47. Hurricanes Tropical depression Tropical Storm Hurricane

48. Tropical depression area of low pressure winds generally moving at 55 mph or less

49. Tropical storm more intense low pressure areas Winds between 56 and 120 mph

50. Hurricanes Very intense low pressure Winds in excess of 120 km/h Fully developed hurricane has a calm eye surrounded by intense rain and thunderstorms