Metr 100 Section 1Metr 100 Section 1

Wednesday (9/2/09)Wednesday (9/2/09) Announcements:Announcements: Reading assignment: Chapters 1 & 2, Ahrens: Reading assignment: Chapters 1 & 2, Ahrens:

Essentials of Meteorology.Essentials of Meteorology. A look at the GOES East satellite today A look at the GOES East satellite today

(hurricane discussion)(hurricane discussion) Temperature profiles of the atmosphereTemperature profiles of the atmosphere Why does the temperature decrease in Why does the temperature decrease in

troposphere and increase in stratosphere?troposphere and increase in stratosphere? Pressure and density profile of the atmospherePressure and density profile of the atmosphere Atmospheric composition (partial pressures)Atmospheric composition (partial pressures) A look at a recent soundings (uwyo)A look at a recent soundings (uwyo)

Hurricane JimenaHurricane Jimena

National Hurricane National Hurricane CenterCenter

Website: Website: http://www.nhc.noaa.govhttp://www.nhc.noaa.gov

http://hoot.metr.ou.edu/satellite/GOES-W/full/1B

Oklahoma Weather Lab

GOES-W Full View Infrared

Definition of temperatureDefinition of temperature

Temperature of gases is a measure of Temperature of gases is a measure of the average the average kinetic energy kinetic energy (energy (energy of motion) of the molecules of the of motion) of the molecules of the gas.gas.

Kinetic energy is proportional to the Kinetic energy is proportional to the mass of the molecules times the mass of the molecules times the squaresquare of their velocity of their velocity

Expressed in units of Expressed in units of degrees Celsius degrees Celsius (°C) , degrees Kelvin (°K = °C+273)(°C) , degrees Kelvin (°K = °C+273) or (in the US only) or (in the US only) degrees degrees Fahrenheit (°F)Fahrenheit (°F)

Definition of air pressureDefinition of air pressure

The force per unit area exerted by air The force per unit area exerted by air molecules (nitrogen, oxygen, argon, molecules (nitrogen, oxygen, argon, water vapor, etc.) on any surface water vapor, etc.) on any surface (the ground, your face, your inner (the ground, your face, your inner ear, etc.)ear, etc.)

Expressed in units of Expressed in units of millibars (mb), millibars (mb), or hectoPascals (hPa) or hectoPascals (hPa) oldold: inches-: inches-HgHg

What is the unit of pressure we use in What is the unit of pressure we use in the US to check our tire inflation? the US to check our tire inflation?

Pounds/square inch {over Pounds/square inch {over atmosphere}atmosphere}

Definition of DensityDefinition of Density

The The ratioratio of the of the massmass of a substance to of a substance to the the volumevolume occupied by it occupied by it

Expressed in units of Expressed in units of kilograms per kilograms per cubic metercubic meter

The vertical temperature distribution of the atmosphere

Graph of pressure vs. Graph of pressure vs. heightheight

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 Composition of the AtmosphereAtmosphere

•Nitrogen 78% of moleculesNitrogen 78% of molecules•Oxygen, 21% of moleculesOxygen, 21% of molecules•Argon, ~ 1% of moleculesArgon, ~ 1% of molecules

• Water vapor concentrations are variable, up to 4% of Water vapor concentrations are variable, up to 4% of totaltotal

Dry Air

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 of dry airConstituent Molecular Weight Fraction Product

Nitrogen (N2) 28 .78

21.84

Oxygen (O2) 32 .21

6.72

Argon (A) 40 .01 0.40

Sum 1.00 28.96

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 TemperatureGreen lines are adiabats (neutral buoyancy)Pt. Barrow, AK 71.3°NVandenberg AFB, CA 34.75°NCanal Zone 10.0°N

Pressure, Height,&Temperatureof Tropopause

Station Latitude P(mb) Ht(km) T(°C) T250

Pt.Barrow 71.3 230 11 -56 -52Vandenberg 34.75 150 14 -65 -48Canal Zone 10.0 130 15 -77 -42

Local (OAK) 8/31 12Z sounding

Balloon broke at 150 mbDisplay to 700 mbNote temperature inversion andrapid drop in moisture (top of fog layer)Conditions conducive to refraction of VHF/UHF radio wavesNote lapse rate < adiabatic--> stable

University of Wyoming Web Site

http://weather.uwyo.edu