Download Water in the Atmosphere

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
http://www.tapintoquality.com/facts/glossary/evaporation.jpg
http://www.sjrcd.org/et/index.htm
• Moisture moves into
the atmosphere from
evaporation and
transpiration
• When that water
vapour converts back
to liquid water, it is
called condensation
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
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/fro
st/frost.htm
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
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
http://www.williamsclass.com/EighthScienceWork/Atmosphere/AtmosphereFog.htm
Upslope Fog
Valley Fog
A type of
radiation fog
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
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
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
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/convecti
on2.html
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