AOS 100Lecture 3

Atmospheric Variables Chapter 1

Homework #1 Due September 19, 2014

TYU Ch1: 3,4,5,8,11,13,16,19; TYPSS Ch 1: 1

TYU Ch 2: 1,2,6,9,13,16,20,22,23,25; TYPSS Ch 2: 2

TYU Ch 3: 1,2,3,7,8,11,12; TYPSS Ch 3: 2

TYU Ch 4: 1,5,8,10,12,18,24 TYPSS Ch 4: 1

Web site of the Day

• CIMSS Tropical Cyclone Site

http://tropic.ssec.wisc.edu/

This site displays imagery of all of the tropical cyclone activity globally

http://cup.aos.wisc.edu (Professor tripooili’s model web site)

Composition of the Atmosphere

Composition of the Atmosphere

Other 0.06%

CO2 .035%

Ne .018%

He .0052%

CH4 .0014%

KR .0010%

N2O .0005%

H2 .0005%

O3 .00007%

Basic Variables Defining the State of the Atmosphere

• Temperature (Kelvin, Celsius, Fahrenheit)

• Pressure (Force/Area=Newtons/m2=Pa)

• Density (mass of air/volume=kg/m3)

• Humidity (mass of water/mass of air)

• Wind (direction and speed)

Note: Only 2 of the 3 quantities P,T, density can be independently measured

Temperature

What is Temperature?• Temperature is proportional to the molecular scale kinetic energy, or the energy

associated the molecule’s velocity• Kinetic energy of a molecule in one of a class of energies that are stored in molecules

referred to as “thermal” energy• All thermal energies have to do with a molecule’s movement• Types of molecular movement that contribute to thermal energy:

1. Speed of translation

2. Spin

1. Single atom in a gas=> moment of inertia small

2. Multiple molecules: How many axes?

3. Solid crystal? Can not spin!

3. Vibrate

1. attachment bonds between atoms

2. Single atom..can not vibrate!

3. Solid: bonds between molecules• How thermal energy is partitioned between spin, vibration and translation is a

characteristic of the molecule type . The ratio between heat stored to the temperature change and to the mass of a substance is its “heat capacity”

Temperature Scales

Density

• Density is the mass per unit volume of the air (kg/m3). Density is affected by:– The mass of each molecule– The number of molecules– The distance between molecules

Pressure

• Pressure is the force per unit area exerted on a surface (of random orientation) by air molecules hitting that surface and reflecting off that surface. Pressure is affected by:– the number of molecules hitting the surface

and the average mass of the molecules is (air density)

– The speed of the molecules hitting the surface (temperature)

Pressure

Pressure

Is the net force exerted against the wall /unit area

F

A=length x width

Surface Pressure

Variation of Pressure with Altitude

Variation of Pressure Across Topography

Humidity

• A measure of the amount of water vapor in the air– Absolute humidity the amount of water in the

air measured as:• Vapor density (mass of vapor/volume of air) • Vapor pressure (amount of total pressure due to

the contribution of water vapor pressure)• Mixing ratio (mass of water per mass of dry air)• Specific humidity (mass of water vapor per total

mass of moist air)

Humidity

– Relative Humidity (vapor pressure of air per saturation vapor pressure of air)

• This is the humidity relative to how much humidity a parcel can hold before it becomes saturated with humidity, and water begins to condense

• Expressed as a percentage, ie multiply the fraction by 100%

Vertical Structure ofAtmospheric Temperature

• Affected by :– Where thermal energy enters and leaves the

atmosphere• Solar radiation (primarily heats the ground)• Terrestrial radiation emitted by the atmosphere and

the ground – Some gasses emit more than others– Water vapor biggest emitter– CO2 good emitter

Vertical Structure ofAtmospheric Temperature

• Affected by :– Advective Transport– Convection transport

• Shallow dry convection, i.e. dry thermals• Deep convection• Adverction by other weather systems

Vertical Temperature structure of atmosphere

Heat vs. Temperature• Temperature is proportional to the heat

per unit mass of a substance– Proportionality constant is called the “heat

capacity” of a substance– The higher the heat capacity, the more

thermal energy that is stored per change of temperature

• Heat is the amount of thermal energy transferred from one place to another during a thermodynamic process.

Heat• Heat is energy and is measured in energy

units or Joules (J) or Calories (1 Calorie=4.18 J)

• Heating is measured as a rate of energy change (Joules/second or J s-1)

• 1 J s-1 = 1 Watt (W)

• Heat Flux is measured as the rate that heat is transferred across a unit area and is measured as energy/area the units of which are W m-2

Examples of energy Units

• I consumed 2000 calories of energy yesterday

• I consumed 8400 J or energy• My body burns energy at an average rate of

8400 J / 86400s~0.1W • Energy from Sun is hitting Earth (at the top

of the atmosphere) at 1361 W m-2

• Energy is drawn from the ocean surface by a hurricane at a rate of 3000 W m-2

Energy and Temperature

• I have 1kg of water at a temperature of 20C.• The total energy stored in this water is

E=Cenergy/mass/T x masskilograms x Tkelvin

= C 1kg (273.16+20)K

The heat capacity for water is C=4.17Jg-1K-1

And so

E= 293.16 K * 4.17Jg-1K-1 *1000g kg-1

=1.22 x 106 J

Energy Transfer

• Energy transfer (or heat transfer) occurs by:– Conduction, or direct contact of a substance with

another substance• Moving molecules of one substance strike against

molecules of another substance causing those of the two substances to equalize their speeds, the temperature of the two substances will equilibrate. (principle behind a thermometer)

• This is the primary way heat is transferred from the air to your body

Energy Transfer

• Energy transfer (or heat transfer) occurs by:– Radiation, emission or absorption of electromagnetic

radiation• A substance will emit and absorb a spectrum or

electromagnetic radiation according to its atomic and molecular and chemical construction and its temperature

• This is how heat is transferred in a home heated by radiators

• This is a secondary way that heat is transferred to your body (sun shining on your body, feel radiative loss to a cold surface, like a window in the winter, or gain from a warm surface, like a hot stove)

Energy Transfer

• Energy transfer (or heat transfer) occurs by:– Convection, or the mixing of substances having

different temperatures• This is how heat is transferred in a forced air home heating

system• a cold breeze is convective heat transfer to your body• Meteorological Definitions

– The transfer of heat and other air properties by simple movement of air is referred to as the “ADVECTION” of that property

– The transfer heat and other air properties by the buoyant rise (i.e. warm air rises) of a plume is what meteorologists refer to as “CONVECTION”

Energy transfer in the atmosphere

• Except for ozone, atmosphere is mostly transparent to the suns radiation (light) and so that goes to the ground where it is absorbed and conducted into the atmosphere

• For the most part, the energy enters the atmosphere from the surface and leaves the atmosphere by radiation to space– (Sensible) Heat flux into air from ground (conduction)– Latent heat flux into atmosphere from ground (evaporation)

• Transfer of heat energy by conduction through the air is very, very, very slow..air is a great insulator!

• Convection moves the heat and latent heat through up and down air currents