Water in the Atmosphere

1. Water in the Atmosphere Evaporation, transpiration, (evapotranspiration), dew, frost, fog (advection, radiation, upslope), saturated air, humidity, condensation, dew point, cloud formation, types of clouds (cumulous, stratus, cirrus), types of precipitation, orographic, convection, and frontal (cyclonic), thunder and lightening http://www.nasa.gov/centers/goddard/news/topstory/2005/warm_wetworld.html

2. Moisture moves into the atmosphere from evaporation and transpiration • When that water vapour converts back to liquid water, it is called condensation http://www.tapintoquality.com/facts/glossary/evaporation.jpg http://www.sjrcd.org/et/index.htm

3. Relative humidity and the dew point • Humidity - the amount of water in the air compared to how much the air can hold • as a percent of the total amount of water based on how much it can hold • When the air contains as much water as it can hold (at a certain temperature), it is SATURATED. • Dew point – the temperature to which the air must be cooled to reach the saturation point • The temperature at which water vapour will condense • Hotter air can hold more moisture than colder air

4. Dew • When the surface temperature cools, it cools the air next to it • Water condenses out of the air and forms on surfaces • When the temperature of the surface is below freezing, the deposition is frost • http://www.its.caltech.edu/~atomic/snowcrystals/frost/frost.htm

5. Fog • Condensation of water vapor near the earth’s surface • Requires that the air mass be humid, rather than dry • If the air reaches saturation (air that cannot hold any more water at that temperature), fog will be produced as soon as it gets colder

6. Radiation or Ground Fog • Occurs at night, as the earth cools through radiation • This cools the moist air layer near the surface to the saturation or dew point • The moisture in these nearby layers condenses into water vapour • Usually on clear nights, when heat can escape the lower atmosphere (cloud cover traps heat) • Also, calm nights when no wind mixes the layers of air

7. http://www.williamsclass.com/EighthScienceWork/Atmosphere/AtmosphereFog.htmhttp://www.williamsclass.com/EighthScienceWork/Atmosphere/AtmosphereFog.htm

8. Upslope Fog

9. Valley Fog A type of radiation fog

10. Advection Fog • Occurs when a warm front moves in horizontally over a cold surface, such as a snow pack, or • Warm, moist air comes off the ocean onto the colder land

11. Evapouration Fog • A type of advection fog • Cold air flows out onto warm water, or • The warm, moist air contains water that has evapourated into it • As it rises, it cools and fog forms as the vapor condensates • Swimming pools, hot tubs, bodies of water in the fall

12. Orographic Precipitation • Remember that orogeny is the study of mountains? • Orographic precipitation is caused by mountains • Wind pushes warm moist air up the slope of the mountain • Air cools, water vapor condenses, rain falls http://geography-info.com/physical/atmosphere1.html

13. Convectional Precipitation • Hot summer days • Sun heats the surface • Moisture enters the air through evapouration • Warm air rises, cools, clouds form, precipitation falls http://www.es.flinders.edu.au/~mattom/IntroOc/notes/figures/convection2.html

14. Frontal Precipitation • There are different types of fronts – we’ll look at this later • Remember that a front is the line between a warm and cold air mass • As the warm air in this example rises and cools over the cold air mass, clouds form, rain falls