Metr 100 Section 1
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Wednesday (9/2/09)
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Announcements:
Reading assignment: Chapters 1 & 2, Ahrens: Essentials
of Meteorology.
A look at the GOES East satellite today (hurricane
discussion)
Temperature profiles of the atmosphere
Why does the temperature decrease in troposphere and
increase in stratosphere?
Pressure and density profile of the atmosphere
Atmospheric composition (partial pressures)
A look at a recent soundings (uwyo)
Hurricane Jimena
National Hurricane Center
Website: http://www.nhc.noaa.gov
Oklahoma Weather Lab
GOES-W Full View Infrared
http://hoot.metr.ou.edu/satellite/GOES-W/full/1B
Definition of temperature
Temperature of gases is a measure of the
average kinetic energy (energy of motion)
of the molecules of the gas.
Kinetic energy is proportional to the mass of
the molecules times the square of their
velocity
Expressed in units of degrees Celsius (°C)
, degrees Kelvin (°K = °C+273) or (in
the US only) degrees Fahrenheit (°F)
Definition of air pressure
The force per unit area exerted by air
molecules (nitrogen, oxygen, argon, water
vapor, etc.) on any surface (the ground,
your face, your inner ear, etc.)
Expressed in units of millibars (mb), or
hectoPascals (hPa) old: inches-Hg
What is the unit of pressure we use in the
US to check our tire inflation?
Pounds/square inch {over atmosphere}
Definition of Density
The ratio of the mass of a substance to the
volume occupied by it
Expressed in units of kilograms per cubic
meter
The vertical temperature distribution of the
atmosphere
Graph of pressure vs. height
How air density changes with height
Dalton’s Law of Partial Pressures
The total pressure exerted by a mixture of
gases which do not interact chemically is
equal to the sum of the partial pressures of
the gases. The partial pressure of a gas is
the pressure it would exert at the same
temperature as the mixture if it alone
occupied the volume that the mixture
occupies.
Composition of the
Atmosphere
•Nitrogen 78% of molecules
•Oxygen, 21% of molecules
•Argon, ~ 1% of molecules
Dry Air
• Water vapor concentrations are variable, up to 4% of total
Total cannot be more than 100%; e.g.
If water vapor is present, reduce proportion of dry air, as
shown in calculations of molecular weight following
Composition
dry air
Constituent
Molecular Weightof
Fraction
Product
Nitrogen (N2)
Oxygen (O2)
6.72
Argon (A)
0.40
Sum
28.96
28
32
.78
.21
40
.01
21.84
1.00
The average molecular weight of dry air ≈ 29
Composition of very moist air (4%)
Constituent Molecular Weight Fraction Product
Nitrogen (N2)
28
.78 x .96
20.97
Oxygen (O2)
32
.21 x .96
6.45
Water Vapor (H2O) 18
.04
0.72
Argon (A)
40
.01 x .96
0.38
Sum
1.00
28.52
The molecular weight of moist air is less than that
for dry air 28.52 for 4% water vapor vs 28.96.
Radiosonde soundings from a variety
of latitudes.
P(mb) vs T(°C)
Left trace is Dew Point Temperature (ignore)
Right trace is Temperature
Green lines are adiabats (neutral buoyancy)
Pt. Barrow, AK 71.3°N
Vandenberg AFB, CA 34.75°N
Canal Zone 10.0°N
Pressure, Height,&Temperature
of Tropopause
Station Latitude P(mb) Ht(km) T(°C) T250
Pt.Barrow
71.3 230
11
-56 -52
Vandenberg 34.75 150
14
-65 -48
Canal Zone 10.0 130
15
-77 -42
Local (OAK) 8/31 12Z sounding
Balloon broke at 150 mb
Display to 700 mb
Note temperature inversion and
rapid drop in moisture (top of fog layer)
Conditions conducive to refraction of
VHF/UHF radio waves
Note lapse rate < adiabatic--> stable
University of Wyoming Web Site
http://weather.uwyo.edu