AOS 100: Weather and
Climate
Instructor: Nick Bassill
Class TA: Courtney Obergfell
Miscellaneous
• New Homework
• “Forecasting” Assignment
• Exam Results
Review of December 8th:
Winter Weather
• The three types of winter precipitation are snow,
freezing rain, and sleet
• The type is determined by the profile of temperature in
the atmosphere
• Snow happens when the entire atmosphere is below
freezing
• Sleet happens when the falling snow melts, but
refreezes in a deep freezing layer closer to the surface
• Freezing rain happens when falling snow melts, then
passes through shallow freezing layer lose to the
surface, causing the rain to freeze on contact with the
frozen ground
Review Continued
• Snow ratios describe the ratio of amount of snow to the
liquid equivalent of that snow
• High snow ratios happen in cold environments and low
ratios occur in warm environments
• Major WI snowstorms require a source of warm, moist
air
• This air will rise above cold air (as in a warm front) and
produce precipitation
• Generally, stronger areas of low pressure are better at
transporting the warm, moist air needed for big
snowstorms
• This is one of the reasons we often associate strong
winds with snowstorms
• Two common winter snowstorm tracks are the
“Panhandle Hook” and the “Alberta Clipper”
Classic
Wisconsin
Snowstorm
Location of heaviest snow
L
Storm Track
*
Review Continued
• Once a forecaster sees precipitation in a model,
he/she would look at the following, amongst others:
– Is your location characterized by a 500-1000 mb
thickness less than 540 dm? (This would indicate that
the atmosphere is fairly cold, and it’s a rough
approximation of the rain-snow line.)
– Are the temperatures in the lower atmosphere below
freezing? (So that snow doesn’t melt on the way
down.)
– Are ground temperatures going to be below freezing?
(So that the falling snow can stick to the ground.)
– How much is the liquid equivalent of that
precipitation? What would the snow ratios be? (Once
you know these answers, you can predict a snowfall
amount.)
By: Jeremy John Parker
By: Dan Metzger
By: Bridget Martin
Back to Climate Change …
Feedbacks
• A “feedback” is what happens due to the
result of some action (sort of like cause
and effect)
• Feedbacks are extremely important when
discussing the Earth’s climate
• “Positive feedbacks” (those that cause a
continuation of the initial action) are
especially important
• Let’s look at some examples …
The Ice-Albedo Feedback
• Recall that snow and ice have a high albedo
(meaning it reflects a lot of sunlight)
• If we warm the Earth a little (the “cause” in this
example), then some of that snow and ice will
melt, leaving bare ground or water
• But ground and water do not reflect as much
sunlight as snow or ice, meaning that it absorbs
more radiation
• This means that it will get even warmer!
• This is an example of a positive feedback
Oceans and CO2
• Water can absorb some CO2 from the
atmosphere
• However, cold water can hold more CO2
than warm water
• These means that as the oceans warm,
they can’t take in as much CO2, meaning
that there’s more in the atmosphere
• And more CO2 leads to a warmer Earth,
meaning that this is another example of a
positive feedback
Volcanic Eruptions & Aerosols
• When a volcano erupts, it puts a lot of
“aerosols” (ash, smoke, and other
particulates) into the atmosphere
• These aerosols can help block sunlight
from reaching the Earth’s surface when
they are in the atmosphere
• However, over time they gradually fall out
of the atmosphere by themselves, or
carried down by rain and snow
An Example
Weather vs. Climate
• Weather describes what is happening right now
• Climate represents the average weather conditions
over an extended period of time (think decades or
longer)
• Therefore, just because it may have been cold one
month or rainy another, it’s not really possible to say
the climate is getting colder or rainier, unless those
conditions persist for a long time
• This is why having a record snowfall doesn’t
disprove global warming
• The time-scales are so dramatically different that
they’re practically unrelated (one snowstorm and
climate)
From: http://www.noaanews.noaa.gov/stories2009/images/statewidetrank_200910.jpg
Climate
• As just shown, even the weather over an
entire country as large as the United
States for an entire month can be very
different from the whole world
• This is a perfect example of why it isn’t
possible to extend local weather
conclusions to the whole globe, or to
global warming
Ozone and The
Ozone Hole
• Ozone (O3) is a
naturally occurring gas
in the atmosphere
which protects us from
harmful ultraviolet
(UV) radiation
• Without ozone in the
atmosphere, more UV
radiation would make
it to the surface,
leading to more
cancer and genetic
mutations
• Ozone (O3)
absorbs UV
radiation and
splits into O2
and O
Chlorofluorocarbons (CFCs)
• CFCs are a manmade gas (used in things like
spray paint) that destroys Ozone in the
atmosphere due to an interaction between the
Chlorine in CFCs and Ozone
• CFCs have an extremely long lifetime in the
atmosphere (up to 100 years or more), so even
a small amount is very damaging
• Thankfully, most nations began phasing out
CFCs in products beginning about 15 years ago,
so they have been in slow decline since
The Ozone Hole
• Due to several factors,
such as the long
nighttime and global
circulation patterns, the
south pole is extremely
susceptible to Ozone
loss
• This is where the
“Ozone Hole” is located
• However, since CFCs
have begun to slowly
diminish in the
atmosphere, the Ozone
Hole has generally
stopped worsening
From: http://upload.wikimedia.org/wikipedia/commons/0/00/Min_ozone.jpg
Average Yearly Sea-level
Temperature