Atmospheric Physics IPHYS 621, Fall 2011

Dr. Zhibo ZhangContact info:Phone: 410-455-6315 (office)Email: Zhibo.Zhang@umbc.eduOffice hour: Friday, 3:30~4:30 or by appointmentCourse Website: UMBC Blackboard system & http://userpages.umbc.edu/~zzbatmos/research/PHYS621_fall2011.html

TextbooksSalby, Murry L. Fundamentals of Atmospheric Physics1996

Wallace J.M., and Hobbs, P.V. Atmospheric Science 2nd. Ed2006 (don't get the green one)

Grade and Homework• Grade: Homework (30%), Midterm (30%), Final (30%),

Participation/Discussion(10%)• Homework: Submit homework by 4:30pm on the due day (during class,

to my office, or through Email (only pdf format accepted))

• Put your name, student ID number, and e-mail address at the top of the

first page.

• Please STAPLE your homework pages together so that pages do not

become lost.

• Homework solutions can be prepared either with pen/pencil or a word

processor, as long as it looks neat and not sloppy.

• Please solve the homework problems in the order assigned

• Please write on the front of each solution page only and not on the back.

• The homework you turn in must be your own work, in accordance with

the student conduct code mentioned in the syllabus.

Quiz #0

• What ........ is your name?

• What do you expect to learn from this class?

• Have you taken a Thermo course before? Dynamics (e.g.,

fluids, mechanics, etc.)?

• What level of mathematics have you ...

– learned, and

– remember?

• In order to succeed in this class, which (if any) of the

following are true (more than one answer is possible)

– Bribe the professor(s) with frosty beverages.

– Be able to derive and memorize every single equation.

– Show your work on your homework and tests.

– Come to class having read the relevant chapters and notes, ready

to answer questions.

How to succeed in this course(and in graduate school)

• Come to class prepared, take notes, work together on

homework (not tests), and ask lots of questions!

• Be prepared to answer questions in class.

• Teach yourself how to learn independently, manage your time,

and how to study effectively.

• Always show your work – this means using analytic expressions

(equations), figures, dimensional analysis. (see handout)

• Note: Plugging in numbers generally appears at the very last

step in solving a problem!

• Think about your qualifying exam with respect to the lessons

learned in this course.

Lecture 1

Overview of

Earth’s Atmosphere

Sun and Earth

The Sun: Our ultimate source of energy Surface temperature: ~5800K; Distance from Earth:149.6 million km

Mother Earth:Radius: 6371km; Surface temperature: ~287k (14°c);

Earth: Orbit and rotation

Spring Summer

Fall Winter

Latitude and Longitude

Longitude: “Zonal” : East / WestLatitude: “Meridional” : North / South

Spherical coordinate

r: radius of the earthθ: LongitudeΦ: Latitude

Spherical Distance: radius X angle

Distance on a longitude circle

Distance on a latitude circle

Geographic Zones

Tropics

Mid-latitude

Polar

23.5 N

23.5 S

66.5N

66.5S

Tropics

Mid-Latitude

Polar

23.5S ~ 23.5N

23.5N ~ 66.5N23.5S ~ 66.5S

66.5N ~ 90N66.3S ~ 90S

66.5N

66.5S

Composition of atmosphere Gas Volume

Nitrogen (N2) 78.1%

Oxygen (O2) 20.9%

Argon (Ar) 0.93%

Carbon dioxide (CO2) 0.038%

Neon (Ne) 0.002%

Helium (He) 0.0005%

Methane (CH4) 0.0002%

Krypton (Kr) 0.0001%

Hydrogen (H2) 0.00006%

Water vapor (H2O) Variable: 1-4% nearsurface, 0.4% overall

Other constituents: Aerosols (particulates other than water),liquid and solid water, birds, insects, airplanes, kids on trampolines, etc.

Trace

gas

Parts-per expressions• parts-per million (ppm), 1 × 10−6. This is equivalent to one

drop of water diluted into 50 liters (roughly the fuel tank

capacity of a compact car)

• parts-per billion (ppb): 1 × 10−9. This is equivalent to one

drop of water diluted into 250 chemical drums (50 m3), or

about three seconds out of a century.

• Parts-per trillion (ppt): 1 × 10-12, This is equivalent to one

drop of water diluted into 20 Olympic-size swimming pools

(50,000 m3), or about three seconds out of every hundred

thousand years.

Carbon-dioxide : 0.038% = 380x10-6=380ppm

Methane: 0.0001745% = 1745x10-9=1745ppb

volume mixing ratio

Pressure and Density

Density: ρ

Air density: 1.25 kg m-3 (water~1000kg m-3)

Surface Pressure: 1013 hPa = 101,300 N/m-2 or 101,300 kg·m−1·s−2

Area: A

Volume: V

Gravity:g

Density: mass/volume~kg/m-3

Pressure: mass x gravity / area=kg x m/s-2 / m-

2= kg·m−1·s−2

Hydrostatic equilibrium

Density: ρ

Ftop = (P + dP)A

Fbot = P A G=ρ g A dz

Hydrostatic equilibrium: Fbot− Ftop= G

-dP A = ρ g A dz

 Hydrostatic Equation dP/dz = -ρg

z

z+dz

Pressure and Density

• The atmosphere is approximately in hydrostatic balance

• The pressure at any point in the atmosphere is equal to the weight per unit area of the atmosphere above that point.

• Units of pressure: Pascal [Pa] = 1 N m-2

• Air density (sea level): • ~ 1.25 kg m-3

• (The ocean: ~ 1000 kg m-

3)• Air pressure (sea level):

• ~ 1013 hPa • (1 hPa = 100 Pa = 1 mb)

Scale Height

• Pressure (and density) generally

decrease exponentially with height.

• H is the “scale height”, which is the e-

folding depth, p0 is the reference pressure,

usually at sea-level (z=0).

TemperatureTemperature: a measure of the average kinetic energy of the molecules in an object/gas

The temperature of a classical ideal gas is related to its average kinetic energy via the equation

Kinetic energy ~: on average, how fast the small balls move and their mass

Temperature: A macro-physical parameter to measure the microphysical movement

Surface temperature

Vertical structure

Lapse Rate: local rate of decrease of temperature (T) with altitude (z):

Typical lapse rate close to surface: 6.5K/km

Troposphere:Where we live inContain: 75% of mass and99% water of the whole atms.

Stratosphere:A thick ozone layer (or not ~ ozone whole) in stratosphere protects us from “bad” UV

WindA vector: speed and direction

Wind Direction

North wind

West wind (westly)

Prevailing Wind

Tropical: Eastly trade wind

Mid-latitude : Westly

“Trade” wind

SpanishPortuguese

PrecipitationRain, Snow, Hail…

• Important:

– A major component of the water cycle

– Responsible for depositing most of the fresh water on the

planet.

• Numbers:

– Approximately 505,000 km3 of water falls as precipitation

each year

– Global annual mean precipitation rate ~990mm (39 in)

or 2.7mm/day

NOT Distributed Evenly

Residence time The Capacity of a system to hold a substance

The Rate of flow of the substance into the system

The smaller the Residence Time ~ The faster the Cycle

Average reservoir residence timesReservoir Average residence time

Antarctica 20,000 years

Oceans 3,200 years

Glaciers 20 to 100 years

Seasonal snow cover 2 to 6 months

Soil moisture 1 to 2 months

Groundwater: shallow 100 to 200 years

Groundwater: deep 10,000 years

Lakes 50 to 100 years

Rivers 2 to 6 months

Atmosphere 9 days

Water Residence Time = capacity of the system

flow for the system

Carbon Cycle

Atmospheric CO2

Global Energy Budget

To keep Earth’s Energy Budget Balance

Incoming Solar Radiation=Outgoing Longwave Radiation

Incoming Solar Radiation

Outgoing Longwave Radiation

Global Energy Budget

342-107=235

Review

• Important things to remember

– Surface temperature of Sun and Earth

– Atmospheric composition

– Atmospheric vertical structure

– Sea surface pressure

• Important concepts to understand

• Spherical coordinate

• Hydrostatic equilibrium

• Lifetime and cycles

• Energy budget balance concept

Things for you to do next:

• Read: Chapter 1 in both Salby and

WH, also your handout . Read

Chapter 2 of WH.

• Homework: Due on next Thursday

(Sep.8th )

System of units

Name Unit symbol Quantity

meter m length

kilogram kg mass

second s time

kelvin K temperature

mole mol Amount of substance

Base Units

Prefix of SI units