Weather

1. Weather What is the connection between the water cycle and tornadoes, floods, droughts, and hurricanes?

2. States of Water Water is known to exist in three different states; as a solid, liquid or gas. Clouds, snow, and rain are all made of up of some form of water. A cloud is comprised of tiny water droplets and/or ice crystals, a snowflake is an aggregate of many ice crystals, and rain is just liquid water. Image/Text/Data from the University of Illinois WW2010 Project."

3. Water on the Earth • Water covers 70% of the earth's surface, but it is difficult to comprehend the total amount of water when we only see a small portion of it. • Look at the volumes of water contained on land, in oceans, and in the atmosphere. Arrows indicate the annual exchange of water between these storages. Image/Text/Data from the University of Illinois WW2010 Project."

4. Water on the Earth • The oceans contain 97.5% of the earth's water, land 2.4%, and the atmosphere holds less than .001%, which may seem surprising because water plays such an important role in weather. • The annual precipitation for the earth is more than 30 times the atmosphere's total capacity to hold water. • This fact indicates the rapid recycling of water that must occur between the earth's surface and the atmosphere.

5. Water Cycle • Water in the different states move through the water cycle. • Liquid • Solid • Gas in the form of water vapor

7. Evaporation • Water is transferred from the surface to the atmosphere through evaporation, the process by which water changes from a liquid to a gas. • Approximately 80% of all evaporation is from the oceans, with the remaining 20% coming from inland water and vegetation. • Winds transport the evaporated water around the globe, influencing the humidity of the air throughout the world. Image/Text/Data from the University of Illinois WW2010 Project."

8. Evaporation

9. Water existing as a gas is called water vapor. • When referring to the amount of moisture in the air, we are actually referring to the amount of water vapor. • Common sources of moisture for the United States are the warm moist air masses that flow northward from the Gulf of Mexico and western Atlantic Ocean as well as the moist Pacific air masses brought onshore by the westerlies. Image/Text/Data from the University of Illinois WW2010 Project."

10. Key process in the production of clouds and precipitation Imagine a block of air, or air parcel, rising upward through the atmosphere. The air parcel expands as it rises and this expansion causes the temperature of the air parcel to decrease. Rising Air Image/Text/Data from the University of Illinois WW2010 Project."

11. Condensation • Condensation is the change of water from its gaseous form (water vapor) into liquid water. • Condensation generally occurs in the atmosphere when warm air rises, cools and looses its capacity to hold water vapor. • As a result, excess water vapor condenses to form cloud droplets. • The upward motions that generate clouds can be produced by convection in unstable air, convergence associated with cyclones, lifting of air by fronts and lifting over elevated topography such as mountains. Image/Text/Data from the University of Illinois WW2010 Project."

12. Condensation

13. The upward motions that generate clouds and lead to precipitation can be produced by convection in unstable air, convergence of air near cloud base, lifting of air by fronts and lifting over elevated topography such as mountains. Condensation Image/Text/Data from the University of Illinois WW2010 Project."

14. As the earth is heated by the sun, bubbles of hot air (called thermals) rise upward from the warm surface. A thermal cools as it rises and becomes diluted as it mixes with the surrounding air, losing some of its buoyancy (its ability to rise). Lifting By Convection Image/Text/Data from the University of Illinois WW2010 Project."

15. When a deep stable layer exists just above the cloud base, continued vertical growth is restricted and only fair weather cumulus are able to form. However, if a deep unstable layer (cold air aloft) is present, continued vertical growth is likely, leading to the development of a cumulonimbus cloud, which contains raindrops. Image/Text/Data from the University of Illinois WW2010 Project."

16. Relative Humidity • Indicates how moist the air is • Relative humidity may be defined as the ratio of the water vapor density (mass per unit volume) to the saturation water vapor density, usually expressed in percent: Relative Humidity =

17. Precipitation • If the cloud is sufficiently deep or long lived, precipitation will develop. • As the parcel rises, its humidity increases until it reaches 100%. When this occurs, cloud droplets begin forming. Image/Text/Data from the University of Illinois WW2010 Project."

18. Rain or Snow • Dependent upon temperature • Typically forms high in the atmosphere where the temperature is below freezing. • As ice crystals form aloft and fall toward the surface, they collect each other to form large snowflakes. • If ground temperature is above 32 F, the freezing level must be located somewhere above the ground. • As the falling snow passes through the freezing level into the warmer air, the flakes melt and collapse into raindrops. Image/Text/Data from the University of Illinois WW2010 Project."

19. Image/Text/Data from the University of Illinois WW2010 Project."

20. Snow • When the air temperature at the ground is less than 32 F, the snowflakes do not melt on the way down and therefore reach the ground as snow. Image/Text/Data from the University of Illinois WW2010 Project."

21. Thunderstorm Formation • First Condition: Must have moisture in the lower to mid levels of the atmosphere. • As air rises in a thunderstorm updraft, moisture condenses into small water drops which form clouds and eventually precipitation. • When the moisture condenses, heat is released into the air, making it warmer and less dense than its surroundings. • The added heat allows the air in the updraft to continue rising.

22. Thunderstorm Formation •  Second condition: Air mass instability • Air which is pushed upward by some force will continue upward. • An unstable air mass usually contains relatively warm (usually moist) air near the earth's surface and relatively cold (usually dry) air in the mid and upper levels of the atmosphere. • As the low-level air rises in an updraft, it becomes less dense than the surrounding air and continues to rise. • The air will continue to move upward until it becomes colder and more dense than its surroundings.

23. Thunderstorm Formation • Third condition: A Source of lift. • Lift is a mechanism for starting an updraft in a moist, unstable air mass. • As the sun heats the earth's surface, portions of the surface (and the air just above the surface) will warm more readily than nearby areas. • These "warm pockets" are less dense than the surrounding air and will rise. • If the air has sufficient moisture and is unstable, a thunderstorm may form.

24. What is the connection between the water cycle and thunderstorms?

25. SuperCells • Supercells are large thunderstorms with deep rotating updrafts and can have a lifetime of several hours. • Supercells can produce frequent lightning, large hail, damaging winds, and tornadoes. • These storms tend to develop during the afternoon and early evening when the effects of heating by the sun are strongest.

27. Tornados • Thunderstorms develop in warm, moist air in advance of eastward-moving cold fronts. • These thunderstorms often produce large hail, strong winds, and tornadoes. • Tornadoes in the winter and early spring are often associated with strong, frontal systems that form in the Central States and move east.

28. Before thunderstorms develop, a change in wind direction and an increase in wind speed with increasing height creates an invisible, horizontal spinning effect in the lower atmosphere. Tornado Formation

29. Tornado Formation • Rising air within the thunderstorm updraft tilts the rotating air from horizontal to vertical. • The air is cooled as it rises and water vapor condenses to form the familiar funnel shaped cloud.

30. Tornado Formation • An area of rotation, 2-6 miles wide, now extends through much of the storm. Most strong and violent tornadoes form within this area of strong rotation. • As the rotating winds begin to pick up dirt and debris from the ground, the funnel will darken.

31. Tornadoes • The strongest tornadoes occur in supercell thunderstorms which can also produce large hail and strong downbursts.

32. What is the connection between the water cycle and tornadoes?

34. Hurricanes • Hurricanes are formed from simple complexes of thunderstorms. • These thunderstorms can only grow to hurricane strength with cooperation from both the ocean and the atmosphere. • The ocean water itself must be warmer than 26.5 degrees Celsius (81°F). • The heat and moisture from this warm water is ultimately the source of energy for hurricanes. • Hurricanes will weaken rapidly when they travel over land or colder ocean waters -- locations with insufficient heat and/or moisture.

35. Hurricanes • Related to having warm ocean water, high relative humidities in the lower and middle troposphere are also required for hurricane development. • The high humidity reduces the amount of evaporation in clouds and maximizes the latent heat released because there is more precipitation. • The concentration of latent heat is critical to driving the system.

36. Hurricanes • How Wind Shear Develops into Hurricanes: http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hurr/grow/home.rxml • CISK: http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hurr/grow/cisk.rxml

37. What is the connection between the water cycle and hurricanes?

38. Droughts • Drought is when you have less rainfall than you expected over an extended period of time, usually several months or longer. • If rain does occur it usually isn't enough for the ground to absorb before it is evaporated again. • Most droughts tend to occur during summer, as the weather is hot and water is quickly evaporated.

40. What is the connection between the water cycle and droughts?

41. Blizzard Flood

42. What is the connection between the water cycle and blizzards? Floods?