Transcript Chapter 6 and 7

Chapter 6 and 7:
Properties of the Atmosphere AND
Weather Systems
Origin and Structure of the
Atmosphere:
• Erupting volcanoes – outgassing – put a
lot of water vapor, CO2 and Nitrogen in the
air during the early years of the Earth.
• Eventually, photosynthetic organisms put
Oxygen into the air.
• The atmosphere is divided into layers (see
p. 14 in the ESRTs) based on temperature
differences.
Changes in Air Pressure:
• Altitude, temperature and humidity
differences create air pressure differences.
• When altitude increases, the pressure
decreases. (see p. 14 in ESRTs!!)
• When temp increases, pressure also
decreases!
• When humidity increases, pressure ALSO
decreases.
Moisture in the atmosphere:
• When air is “filled” to its capacity with
water vapor, it is saturated.
• If the air is cooled to its dewpoint it is
saturated.
• So, air that is the most humid either has:
– A- a lot of moisture that have evaporated into
the air OR
– B- been cooled to its dewpoint.
Measuring Moisture:
• A psychrometer (wet-and dry-bulb
thermometer) is used to measure relative
humidity and dewpoint.
• Use the charts on p. 12 in the ESRTs!
• Don’t forget: You must remember to subtract
the wet-bulb temp from the dry-bulb temp.
• If there is a difference of “0” between the wetand dry-bulb temps, the R.H. is 100% and the air
temp is AT D.P.!
What Causes the Wind?
• Unequal heating and the resulting air pressure
differences result in wind.
• When the air is heated (like over the land area
during a summer day) it rises.
• Cool areas (like over the water during the DAY)
have higher pressure and the air sinks.
• Winds blow from high pressure to LOW!
• Thanks to wind, our world has more moderate
temps. The “wind” helps to even out the energy
around the world.
• The Coriolis effect occurs due to the
Earth’s rotation. This makes the winds
curve as they blow! (see p. 150 in the rev.
bk)
• The jet stream general info can be found
on p. 150 in the rev. bk and on p. 14 in the
ESRTs.
• Prevailing winds are also on p. 14 in the
ESRTs.
What is weather?
• Meteorologists study changeable
atmospheric conditions to make weather
predictions.
• See p. 152 for info on how weather
variables are related.
• Clouds form when a series of different
events occurs:
– Air rises
– Air cools…. (see next slide for more)
• Air cools to its DEWPOINT!
• Once at the dewpoint, water vapor can go
through condensation and form droplets on tiny
“condensation nuclei” – little bits of stuff in the
air.
• Voila! A cloud!
• Why does air cool as it rises?
– Higher altitude = fewer air molecules.
– Expansion of the air molecules = adiabatic
cooling.
– This is why a CO2 cartridge gets COLD after being
used!
How does energy enter the
atmosphere?
• Energy from the sun comes in the form of
“electromagnetic radiation” – primarily via
visible light.
• When this energy strikes the Earth, a LOT
gets used just to make water evaporate!
• See p. 164-166 in the rev. bk. For great
illustrations!
What is a Synoptic Weather Map?
• Station models are used to display LOTS
of weather info. (See p. 13 in the ESRTs
for an example!)
• The info from many, many station models
can be used to draw in isolines – like
isotherms (temp), isobars (air pressure),
etc.
• We can track the movement of air masses
on weather maps.
• Air Masses are defined by their temp and
moisture content. (c or m? P, T or A?)
• The leading edge of vastly different air
masses creates fronts.
• The front symbol (warm? Cold?) shows
the direction the front is moving!
• To predict the weather, meteorologists look
for High or Low pressure areas moving
toward a region. (Generally from the
WEST to the EAST in the continental US)
• High pressure = nice, clear, maybe a little
cool weather.
• Low pressure = cloudy, unsettled, maybe
stormy weather.
• The weather at fronts also tends to be
unsettled because there is low pressure
occurring at fronts!
• Why? Because when warm and cool air
meet, the warm air will rise. Rising air =
low pressure! (see p. 170 in the rev. bk!)
Natural Hazards
• Know the safety advice for the storms
listed and described on p. 175-178.