Air Pressure & Precipitation: Understanding the Atmosphere

1. BEFORE THE BELL RINGS • Please copy your homework into your assignment book

2. Warm-up What instrument is used to measure air pressure? What are condensation nuclei and why are they important? End

3. Tuesday, January 10, 2017 • Warm-up • Review air pressure, precipitation, water cycle, and clouds • Work on Midterm Review • Homework: Midterm Exam Review due 1/17

4. AIR PRESSURE

5. Keeping an Atmosphere • Atmosphere is kept by the world’s gravity • Low mass (small) worlds = low gravity =almost no atm. • High mass (large) worlds = high gravity = thick atm. • Gravity and pressure • Air pressure depends on how much gas there is • i.e. The atmospheric thickness.

6. Gravity and Atmospheric Pressure • The stronger the gravity, the more gas is held by the world and the greater the weight of atm. on a point

7. Earth’s Atmosphere • About 10 km thick • Consists mostly of molecular nitrogen (N2) and oxygen (O2)

8. The air is made up of molecules.

9. Gravity pulls the air molecules toward the earth, giving them weight. The weight of the air molecules all around us is called the air pressure.

10. High altitudes = lower pressure Low altitudes = higher pressure

11. Atmospheric Pressure Gas pressure depends on both density and temperature. Adding air molecules increases the pressure in a balloon. Heating the air also increases the pressure.

12. Air pressure is equal in all directions. Pressure = force per unit area

13. Barometric pressure goes down. As elevation goes up This is an inverse relationship.

14. A Barometer is used to measure air pressure.

16. Changing Pressure A rising barometer = increasing air pressure. This usually means: Rising barometer readings indicate that a high pressure system is approaching. Higher atmospheric pressure is usually associated with fair weather and clearing skies.

17. Changing Pressure A falling barometer = decreasing air pressure. This usually means: Falling barometer readings usually indicate the approach of an area of low pressure. Low pressure readings are usually associated with storm systems. Tornadoes and hurricanes can produce very low barometric readings.

18. PRECIPITATION

19. What is Precipitation? • Precipitation is the falling of any form of water from the air to Earth’s surface. Examples: Rain Snow Sleet Hail Freezing Rain • Condensation Nuclei anything water vapor can condense onto such as dust, smoke, salt, etc.

20. Types of Precipitation • RAIN: (Condensation) Forms when condensed water vapor forms tiny water droplets in clouds. When the droplets get big enough (Coalesce), they fall to the Earth.

21. Types of Precipitation 2.SNOW (Deposition) Forms when the air temperature is below freezing, water vapor turns directly into a solid. These ice crystals fall to Earth as Snow.

22. Types of Precipitation 3. SLEET: (Snow-Rain-Freeze) Forms when rain passes through a layer of air which is below freezing. The rain then freezes into ice and falls to the Earth.

23. Types of Precipitation 4. FREEZING RAIN: (Snow-Rain) Forms when the Earth’s surface is below freezing but the atmosphere is warm. When rain hits the surface, it freezes on contact creating a layer of ice on the ground, trees, cars, power lines, etc.

24. Types of Precipitation 5. HAIL: (Summer-Time) Forms when a rain drop in a cumulonimbus cloud is blown to the top of the cloud and freezes. This frozen drop then falls down through the cloud where it “grows” by collecting more liquid water. This process continues until the hail stone is too heavy to stay in the cloud and falls to Earth.

25. Water Processes • Liquid water turns into a Solid (ice) • FREEZING • Solid water (ice) turns into a liquid • MELTING • Liquid water turns into a gas (water vapor) • EVAPORATION • Water vapor (gas) turns into a liquid • CONDENSATION • Water vapor (gas) turns into a solid (ice) • DEPOSITION • Solid Water (ice) turns into water vapor (gas) • SUBLIMATION

27. The Water Cycle • The Water Cycle (also known as the hydrologic cycle) is the journey water takes as it circulates from the land to the sky and back again. • The Sun evaporates water from the Earth's surface (oceans, lakes, etc.). The water vapor eventually condenses, forming tiny droplets in clouds. When the clouds meet cool air over land, precipitation (rain, sleet, or snow) begins. The water flows downhill as runoff (above ground or underground), eventually returning to the seas where the process begins again.

28. CLOUDS Chapter 11.3 notes

29. Cloud Formation • Clouds form as warm moist air is forced upwards, cools and water vapor condenses to form tiny water droplets. • Millions of tiny water droplets gather together to form a cloud

30. Cloud Formation • Dry Adiabatic Lapse Rate – • how fast unsaturated air will cool as it rises DAR = 100C for every 1000m rise • The height at which the dew point is reached and a cloud begins to form, the Lifted Condensation Level (LCL) has been reached. • Usually, the LCL is marked by the base or bottom of the cloud • Moist Adiabatic Rate - how fast saturated air cools above the LCL • MAR = avg. 60C for every 1000m rise

31. Cloud Formation • OrographicClouds • are clouds that are formed as moist air rises over mountains or other major geographic features. The air floats up the side of the mountain and cools quickly, condensing and turning into a cloud.

32. Cloud Classification • Two common ways to classify clouds: • 1. By Their Shape • Stratus • Cumulus • Cirrus • 2. By Their Height • Cirro • Alto • Strato

33. Stratus Clouds

34. 3 Cloud Types Based on Shape • 1. Stratus • Form in layers or smooth even sheets • Usually low altitude clouds • Associated with fair weather or drizzle • Sometimes forms a gray blanket covering the entire sky and produces light rain or drizzle

35. Cumulus Clouds

36. 3 Cloud Types Based on Shape • 2. Cumulus • Masses of puffy white clouds • Associated with fair weather but may possibly produce thunderstorms

37. Cirrus Clouds

38. 3 Cloud Types Based on Shape • 3. Cirrus • High, thin, white, feathery clouds • Associated with fair weather • Indicate that bad weather may be approaching

39. Height – Prefixes for Cloud Base • Cirro – High Level Clouds • Alto – Middle Level Clouds • Strato – Low Level Clouds

40. Other Types of Clouds • Vertical Development • High, towering clouds usually with a low altitude base • Nimbus • Dark clouds associated with heavy rain and storm

41. Cirrus Cirrostratus Cirrocumulus AltoStratus Stratus Altocumulus Cumulus Stratocumulus Nimbostratus Cumulonimbus 10 Common Cloud Names

42. Altocumulus Clouds

43. Altostratus Clouds

44. Cirrocumulus

45. Cirrostratus Clouds

46. Cirrus Clouds

47. Cumulonimbus Clouds

48. Cumulus Clouds

49. Stratus Clouds

50. Nimbostratus Clouds