Clouds, Precipitation & Weather

1. Clouds, Precipitation & Weather

2. Biblical Reference Look up at the heavens and see; gaze at the clouds so high above you. Job 35:4

3. Condensation Nuclei • Buoyancy is the tendency for air to rise or sink as a result of differences in density. • Clouds form when warm, moist air rises, expands, and cools in a convection current. • Condensation nuclei are small particles in the atmosphere around which cloud droplets can form.

4. Orographic Lifting • Orographic lifting occurs when wind encounters a mountain and the air has no place to go but up. • The air expands and cools resulting in cloud formation.

5. Cloud Formation • Cloud formation occurs with the collision of air masses of different temperatures. • As warmer air collides with cooler air, the bulk of it will be forced to rise over the more-dense, cold air. • As the warm air cools, the water vapor in it condenses and forms a cloud.

6. Stability • Stability is the ability of an air mass to resist rising. • How rapidly any given mass of air cools determines its stability. • The rate at which an air mass cools depends in part on the temperature of the surface beneath the air. • Air can become unstable if it is cooler than the surface beneath it. • If temperature conditions are right and the air mass rises rapidly, it can produce the type of clouds associated with thunderstorms.

7. Latent Heat • As water vapor in the air condenses, heat is released. • The energy to change liquid water into a gaseous state is stored in the water vapor. • Latent heatis stored energy in water vapor that is not released to warm the atmosphere until condensation takes place. • The amount of water vapor present in the atmosphere is a significant source of energy because of the latent heat it contains

8. Cloud Formation • When a mass of rising air reaches its Lifted Condensation Level (LCL), water vapor condenses. • If the density of these droplets is great enough, they become visible in the form of a cloud. • This process can take place at many different altitudes and form different cloud shapes.

9. Types of Clouds • Clouds are generally classified according to a system originally developed by English naturalist Luke Howard in 1803. • The modern system groups clouds by the altitude at which they form and by their shape: • Low clouds typically form below 2000 m. • Middle clouds form between 2000 m to 6000 m. • High clouds composed of ice crystals form above 6000 m. • Vertical development clouds spread throughout all altitudes at the same time.

11. Low Clouds • If rising air stays warmer than the surrounding air, the cloud will continue to grow. • If the air does not stay warmer than the surrounding air, the cloud will flatten out and winds will spread layered cumulus clouds. • Stratus, a layered cloud that covers much or all of the sky, often forms when fog lifts away from Earth’s surface.

12. Middle Clouds • Altocumulus and altostratus clouds, which form at heights between 2000 m and 6000 m, can be either all liquid or a mixture of liquid and ice crystals. • Middle clouds are usually layered

13. High Clouds • Because they form above heights of 6000 m, where temperatures are below freezing, high clouds are made up of ice crystals. • Cirrus clouds, often have a wispy, indistinct appearance. • Cirrostratus clouds form as a continuous layer that sometimes covers the sky Types of Clouds

14. Clouds of Vertical Development • If the air that makes up a cumulus cloud is unstable enough, the cloud will continue to grow. • As it rises, water vapor condenses, and the air receives additional warmth from the release of latent heat. • If conditions are right, it can reach nearly 18 000 m. • A cumulus cloud can thus develop into a full-fledged cumulonimbus that is capable of producing the torrential rains and strong winds that are characteristic of thunderstorms

15. Precipitation • Coalescence occurs when cloud droplets collide and join together to form a larger droplet. • When the droplet becomes too heavy to be held aloft, gravity takes over and it falls to Earth as precipitation. • Precipitation includes all forms of water, both liquid and solid, that fall from clouds including rain, snow, sleet, and hail.

16. Precipitation • Rain & Drizzle- most common type of precipitation. • Freezing Rain- drizzle from stratus clouds. • Freezing Rain - raindrops freeze when they hit the ground. • Sleet - raindrops that freeze before they hit the ground.

17. Precipitation • Snow - as ice grows and merges into clouds they form snowflakes. • Hail - is the largest type of precipitation. It is comprised of lumps or balls of ice that fall from cumulonimbus clouds in warm weather.

18. The Water Cycle • At any one time, only a small percentage of water is present in the atmosphere. • This water continually moves between the atmosphere and Earth’s surface. • The water Cycleis the constant movement of water between the atmosphere and Earth’s surface. • The Water Cycle includes precipitation, evaporation, transpiration, condensation, surface-water flow, and groundwater flow

20. Pop Quiz Match the following terms with their definitions. ___ condensation nuclei ___ stability ___ coalescence • ___ latent heat B D A C A. process by which cloud droplets collide and join to form a larger droplet B.small particles in the atmosphere around which cloud droplets can form C.stored energy in water vapor that is not released to warm the atmosphere until condensation takes place D. the ability of an air mass to resist rising

21. Pop Quiz What is the source of energy that fuels the water cycle? The water cycle receives its energy from the Sun.

22. Meteorology • Meteorology is the study of atmospheric phenomena. • Cloud droplets and forms of precipitation that contain water in any phase are known as hydrometeors. • Smoke, haze, dust, and other condensation nuclei are called lithometeors. • Thunder and lightning are examples of electrometeors, which are visible or audible manifestations of atmospheric electricity

23. Weather vs. Climate • Weather is the current state of the atmosphere, including short-term variations that affect our lives. • Climate describes the average weather over a long period of time and is usually averaged over the course of 30 years or more.

24. A Question of Balance • In meteorology, a crucial question is how solar radiation is distributed around the planet. • The Sun feels hotter in the tropics because its rays strike Earth more directly, than it does in the polar regions where its rays strike Earth at a low angle. • Because the Sun’s rays are more spread out when they strike Earth at a low angle, the same amount of energy is spread over a larger area

25. Balancing the Budget • Most locations maintain fairly constant average temperatures because heat energy is redistributed around the world. • The continual motion of air and water reallocates heat energy among Earth’s surface, oceans, and atmosphere and brings it into balance. • Virtually everything that we consider to be weather is part of a constant redistribution of Earth’s heat energy

26. Air Masses • An air mass is a large body of air that takes on the temperature and moisture characteristics of the area over which it forms. • Meteorologists call the region over which an air mass forms the source region. • Air masses that form over land are generally drier than those that form over water.

27. Air Mass Classification • Air Masses are classified by: • Temperature • Moisture Content • Where they are Formed • Land = Continental • Water = Maritime • Cold Areas = Polar • Warm Areas = Tropical • Over the Poles = Arctic (North) & Antarctic (South)

28. 5 Main North American Air Masses

29. Arctic Air Masses (A) • Source Region: Siberia and the Arctic Basin • Contain bitterly cold, dry air • Can bring temperatures down to -40C

30. Continental Polar Air Masses (cP) • Source Region: Interior of Canada & Alaska • Land cannot transfer moisture as well as oceans • Continental Air Masses are Dry • Bring Cold Temperature in Winter and Cool Weather in the Summer. • Fast-Moving

31. Maritime Polar Air Masses (mP) • Source Region: northern Atlantic or Pacific Oceans • Cold and Humid • Bring Cloudy, Rainy Weather

32. Continental Tropical Air Masses (cT) • Source Region:the desert southwest & Mexico • Continental Tropical Air Masses are Hot and Dry • Bring Clear Skies and High Temperatures • Usually form only during the Summer

33. Maritime Tropical Air Masses (mT) • Source Region: the Gulf of Mexico, the Caribbean Sea and the eastern Pacific Ocean. • Summer: Bring hot, humid air to southeastern U.S. • Winter: Bring heavy snowfall • Moist Air Masses

34. Air Mass Video

35. Air Mass Modification • Eventually, air masses move, transferring heat from one area to another and thus establishing the heat balance. • As an air mass moves, it acquiures some of the characteristics of the new surface beneath it. • Air mass modification is the exchange of heat or moisture with the surface over which an air mass travels. • Eventually, an air mass becomes modified so much that its characteristics are almost the same as the new surface over which it is traveling.

36. Pop Quiz Match the following terms with their definitions. ___ meteorology ___ weather ___ climate • ___ air mass • ___ air mass • modification B A C E D A. the current state of the atmosphere B.the study of atmospheric phenomena C.the average weather over a long period of time D. the exchange of heat or moisture with the surface over which an air mass travels E. a large body of air that takes on the characteristics of an area over which it forms

37. Identify the winter characteristics of each air mass. ___ A ___ cP ___ cT ___ mP (Pacific) ___ mP (Atlantic) ___ mT (Pacific) ___ mT (Atlantic) A. warm, humid B.bitter cold, dry C.cold, humid D. mild, humid E. warm, dry F. very cold, dry B F E D C A A

38. Pop Quiz Why does the angle that the sun’s rays strike Earth’s surface affect regional temperatures? When the sun’s rays strike Earth at a lower angle, the same energy is spread out over a much larger area than when the rays strike Earth more directly.