Transcript Met10_lecture_01 - Department of Meteorology and Climate

Meteorology 10: Weather and Climate
Lecture 1
Dr. Craig Clements
San José State University
Jan 24, 2013
What is Meteorology?
The term “meteorology” dates back to Aristotle’s classic text
Meteorologica, written in 340 B.C.
At that time, “meteor” referred to any object in the sky,
including raindrops and snowflakes. Centuries later, when
researchers began to specialize in
the study of
extraterrestrial objects entering Earth’s atmosphere, the
term “meteorology” had already found a home in the context
of weather.
Thus, the science of what we now call meteors became
known as meteoritics, and its practitioners meteoriticists.
(Henson, 2008)
What is weather vs. climate?
• Weather:
– the state of the atmosphere at a particular point
in time.
• Climate:
– the accumulation of daily or seasonal weather
events over a longer time period.
Meteorology and Climatology represent the
study of weather and climate respectively, but
are each components of Atmospheric
Science and are dealt with in this course
Climate vs. Weather
Weather
Shorter-term fluctuations
Climate
Longer-Term Changes
in atmospheric environment
(e.g., temp, press, ws, wdir,
rainfall amount, etc)
broad composite of average (or mean)
condition of a region (e.g., temp, rainfall,
snowfall, ice cover, winds)
Hours, Days, Weeks
Years (and longer)
Specific location for specific time
Mean state of a specific region
(e.g., continent, ocean, or entire planet)
Elements of Weather
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air temperature
air pressure
humidity
clouds
precipitation
visibility
wind
• Certain weather elements, like
clouds, visibility and wind, are
of particular interest to pilots.
Composition of the Atmosphere
What is the Earth’s atmosphere composed of?
The earth’s atmosphere is comprised mostly of:
nitrogen (N2) and oxygen (O2),
with small amounts of other gases, called ‘trace gases’
such as water vapor (H2O) and Carbon Dioxide (CO2)
Composition of the Atmosphere
nitrogen (N2) = 78%
oxygen (O2) = 21%
These gases are fairly constant up to 80 km (50 miles)
Table 1-1, p. 3
Composition of the Atmosphere
Other gases and stuff in the atmosphere are:
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Carbon dioxide and the greenhouse gases
ozone
aerosols
pollutants
• Ozone at high altitudes (stratosphere) is “good”;
ozone at low altitudes (troposphere) is “bad.”
Composition of the Atmosphere
Carbon dioxide (CO2)
Composition of the Atmosphere
Sources of Carbon dioxide (CO2)
What kind of pollutants are emitted from coal plants?
CO, CO2, SO2, NOx
The vertical structure of the earth’s
atmosphere is complex
The atmosphere is composed of different layers
A View from Space. How deep is the atmosphere?
A Brief Look at Air Pressure and Air Density
• air density
• air pressure
• sea-level pressure
• Baseballs travel farther in higher-altitude air (Denver)
than they do in lower-altitude air.
Air density
Air molecules are held near the earth by gravity.
This strong, invisible force pulling down on the air
above squeezes (compresses) air molecules closer
together, which causes their number in a given
volume to increase.
Air density (ρ) is the number of air molecules in a
given volume (space). Air density is greatest at the
surface and decreases with height (as we move up
into the atmosphere).
Atmospheric pressure
Air molecules have weight. Air is surprisingly heavy.
- The weight of all the air on earth is 5600 trillion tons.
The weight of the air molecules acts as a force on earth and
us. The amount of force exerted over an area of surface is
called atmospheric pressure or air pressure.
The pressure at any level in the atmosphere may be
measured as total mass of air above any point.
If we weigh a column of air one square inch in cross
section, extending from average height of ocean surface
(sea level) to the top of the atmosphere, it would weigh 14.7
pounds.
Atmospheric pressure
If more molecules are packed into the column, the density
then ___________
increases and the surface pressure __________.
increases
On the other hand, when there are fewer molecules in the
less
column, the air weighs _______and
the surface pressure
decreases
__________.
Most common units for atmospheric pressure are
millibar (mb) and Hectopascal (hPa). Another unit used is
inches of mercury (Hg).
At sea level, the standard value for atmospheric pressure is:
1013.25 mb = 1013.25 hPa = 29.92 in. Hg.
Atmospheric pressure
A barometer is used to measure atmospheric pressure
and therefore, it is also referred to as barometric
pressure.
Fig. 1-7, p. 8
Fig. 1-8, p. 9
Layers of the Atmosphere
Vertical temperature profile
Indicates different layers:
• troposphere
• stratosphere
• mesosphere
• thermosphere
How do we measure
the vertical structure
of the atmosphere?
A weather balloon!
A radiosonde balloon ready to
be launched by SJSU graduate
student, Scott Strenfel, July
2008.
What layer in the atmosphere does ‘most’ of our weather occur?
Troposphere!
Depth: surface to ~11 km (~36,000 feet) above the surface.
This is where lots of mixing occurs due to rising and sinking air
motions
Air cools with height (on average) in the troposphere. This is
due to the fact that sunlight warms the surface of the earth
and, in turn, warms the air above it.
The rate at which the air temperature decreases with height is
called the temperature lapse rate.
The average lapse rate in the troposphere is 6.5 degrees
Celsius (ºC) for every 1000 meters (m). This is approximately
3.6 degrees Fahrenheit (ºF) for every 1000 ft rise in elevation.
Stratosphere
Depth of the stratosphere is located above the troposphere
from approximately 12 km to about 50 km.
Temperature increases with height in the stratosphere. This
temperature structure (temperature inversion) helps keep
mixing limited to the troposphere.
Temperatures in the stratosphere are cold, averaging less
than -46°C.
The reason for the inversion in the stratosphere is that the
ozone, which is fairly abundant in the stratosphere, absorbs
(UV) solar radiation. Some of this absorbed energy warms
the stratosphere.
Mesosphere
The air in the mesosphere (middle sphere) is extremely thin
and pressure is low. While the percentage of nitrogen and
oxygen in this layer is about the same as at the surface, there
are fewer oxygen molecules here.
The mesosphere is located above the stratosphere from
approximately 50 km to about 85 km.
Temperature decreases with height in the mesosphere.
Temperatures at the top of the mesosphere represent the
coldest in our atmosphere, averaging -90°C!
Thermosphere
The layer above the mesosphere is the thermosphere “hot
layer”.
The thermosphere is located above the mesosphere from
approximately 85 km to 500 km.
Oxygen molecules in this layer absorb energetic solar rays
which warm the air. Since there are few atoms and molecules
the absorption of a small amount of solar energy can cause a
large increase in temperature that may exceed 500°C!
It is in this layer that charged particles from the sun interact
with air molecules to produce aurora displays.
Ionosphere
This layer is not really a separate ‘sphere’, but rather an
electrified region within the upper atmosphere where fairly large
concentrations of ions and free electrons exist.
A bulk of the ionosphere is in the thermosphere, 60 km and up.
An ion is an atom that has lost (or gained) one of more
electrons. Atoms lose electrons and become positively charged
when they cannot absorb all of the energy transferred to them by
a colliding energetic particle.
The ionosphere plays a major role in AM radio communications.
When the radio was invented by G. Marconi in the early 20th
century, it was not known how radio waves traveled long
distances through the atmosphere.
Scales of Atmospheric Motion
Motion in our atmosphere occurs at multiple
spatial scales. These range from large planetary
waves to turbulence inside the class room due to
air conditioning.
Typical scales of motion that we will be discussing in this
course are:
1. Global scale: planetary waves, 5000 km
2. Synoptic scale: cold fronts, air masses, hurricanes 2000
km
3. Mesoscale: thunderstorms, sea breeze, 20 km
4. Microscale: turbulence, winds around buildings, 2 m
Lets look at a weather Map
We need to understand a few things on a weather
map.
First, when we talk about wind, we need to
understand how we describe wind direction.
In meteorology, when winds are blowing from
North to South we call that a north wind. If it
blows from the west, we can that a west wind.
Winds are referenced from where they are
blowing from not to.
Lets look at a weather Map
Fronts are boundaries that separate different air
masses.
A cold front is a boundary of cold air and a warm
front is a boundary of warm air.
On a weather map, “L” represents low pressure
while an “H” represents high pressure.
A view from
a satellite in
space.
Hurricane Gustav: August 31, 2008
Units
• Our class will use both English and Metric
unit systems.
• Most important:
– Distance (kilometres and miles)
– Temperature (ºC and ºF)
• Conversions:
1.6 km = 1 mile; 1 km = 0.61 miles
(9/5 x ºC) + 32 = ºF
(ºF – 32) x 5/9 = ºC
HW 1: Unit Review
Due: Wednesday Sept. 8
(show all your calculations)
Convert the following:
1.75.4°F to °C
2.100°C to °F
3.-40°C to °F
4.-1°C to °F
5. 10 km to miles
6. 1 km to feet