Transcript Introduction (PowerPoint)

Meteorology 110
Fall 2015
Why should you study the weather?
Weather is always “front-page“ news.
Superstorm Sandy flooding Rockaway, Long Island, Oct, 2012
Exceptional drought in Nevada and California.
CLIMATE REPORT
NATIONAL WEATHER SERVICE NEW YORK NY
...THE ISLIP NY CLIMATE SUMMARY FOR AUGUST 13 2014…
PRECIPITATION:
Yesterday: 13.51”
OLD RECORD (YEAR): 0.91” (2013)
All the severe thunderstorms in the U.S. in 2014
We had 1057 tornadoes (red), 5537 large hail events (green), and 11986 cases of
severe straight-line winds (blue).
Here are the 1057 tornadoes, every one of them.
The U.S. gets more tornadoes than anyplace else on the planet. Still, 2014
was just an average year.
On the other hand, 2011 set all kinds of records, including
the single-day greatest tornado outbreak, April 27 with 292
tornadoes.
But does the weather really affect you?
We need to study how the weather works because
it affects everybody.
We start with the basics. Be patient. We will
eventually get to the precision-guided ball
lightning (or its real equivalent).
See how thin the
Atmosphere really is?
The density of
gases
decreases
rapidly with
height. The
atmosphere just
“peters” out as
you get higher.
Even in outer
space, there are
a few gas
molecules.
95% of the atmosphere is
found around 12 miles and
below. That is called the
troposphere.
The Earth is around 8000
miles in diameter (it’s not a
perfect sphere) so how thin
is the troposphere where we
live?
Photographs from spacecraft show the troposphere is a very thin layer.
99% of the air is Nitrogen and Oxygen. All other gases fit into the
last 1% and most of that is Argon, an inert gas.
You don’t need to memorize these numbers but you must know
the most abundant gases (N2 and O2)
How did the
Atmosphere get to it’s
modern composition?
Our original
atmosphere was
mostly Hydrogen and
Helium, the most
abundant elements in
the universe.
Planets with strong
gravity (like Jupiter
and Saturn) keep
their original
atmospheres. Earth
did not.
Replacing the ancient atmosphere with an Oxygen-Nitrogen one
Stromatolites
Cyanobacteria
Cyanobacteria were the first to perform photosynthesis, taking in CO2 and releasing O2. They can
be found in communities called Stromatolites. Around 2 million years ago, they drove up the
Oxygen content of the atmosphere, making it possible for complex plants to develop.
Source: http://journal.frontiersin.org/article/10.3389/fpls.2011.00028/full
High Oxygen levels allow bugs to become much larger than today.
Lets talk about the sun…
The Earth gets almost all its energy from the sun
as we go around once per year (here the orbit is
viewed almost side-on)
This figure and those from the next two slides are from
http://daphne.palomar.edu/jthorngren/tutorial.htm
The sun’s rays spread out in all directions, so the farther away
you are, the less energy is actually received.
In fact, the sun is so far away (average of 93,000,000 miles),
that the rays reach us essentially parallel to each other.
It looks like this:
Incoming solar radiation
is called insolation.
When the sun angle changes, so does the insolation.
Do you see why?
Of course it’s the Earth that revolves around the sun, not
the other way around. In lab this week, we’ll study this.
Next: How do we measure the properties of the
atmosphere?
Measuring the properties of
atmospheric gases:
We measure the weight of the
gases with barometers.
Torricelli’s barometer design is
still used today. We have one in
the Meteorology lab.
Once Torricelli began measuring
air pressure, he noticed that
when it changed, so did the
weather.
What changes air pressure?
a. Fewer gas molecules (lower density)
hitting each other = lower pressure
b. More gas molecules (higher density)
hitting each other = higher pressure
c. More energetic gas molecules (higher
temperature) hitting each other = higher
pressure
This is the gas law:
Pressure changes with density and
temperature
Rather than inches of
mercury, meteorologists
measure pressure in
millibars (mb). In this
course, we will also do
that.
The standard unit is
actually hectopascals.
1 hPa = 1 mb.
Typically sea-level
pressure is around 1000
mb which is rather
convenient.
While we are familiar
with the Fahrenheit
scale, the rest of the
world uses Celsius
(also known as
Centigrade). The
Kelvin scale is used
by scientists.
We need to know how
to convert from
Fahrenheit to Celsius
and Kelvin
temperatures. We’ll
practice it in lab 3.
This is one of Anders Celsius’ original thermometers.
The way temperature
changes with height is called
a lapse rate.
The sign (+/-) of the lapse rate
separates the atmosphere
into layers to which we give
names.
We live in the troposphere
where the temperature
decreases with height. The
top of the troposphere is the
tropopause, a very important
level. Above that is the
stratosphere.
If air rises, the pressure on it goes down. If it sinks,
the pressure goes up.
That’s independent of the ambient lapse rate and not caused
by heat gain or loss. The word for that is ADIABATIC.
Divide the atmospheric into pieces, called air parcels. An air parcel is a
small, representative sample of air. They are usually considered to be
around 1 square meter or about 3 feet by 3 feet.
The molecules are all moving and banging into each other. We feel that
as temperature. More collisions = higher temperature.
When the air parcels rise or sink, the pressure on them changes. With
more molecules near the ground, the pressure is highest there. That
forces the molecules in the air parcel into a smaller volume.
Smaller volume means more collisions. Result? Higher
temperature!
The air parcel is cooler when it reaches Oneonta, about 1400
feet above sea level.
Let’s try another one. Colorado is bisected by the Rocky Mountains
What happens to air parcels as they descend the Rockies?
Where else in the U.S. could you get a “Chinook”-like wind?
Next: Add water vapor
(humidity, clouds, precipitation)