Atmospheric Physics IPHYS 621, Fall 2011
Dr. Zhibo ZhangContact info:Phone: 410-455-6315 (office)Email: [email protected] 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.
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);
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
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
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
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
Global Energy Budget
To keep Earth’s Energy Budget Balance
Incoming Solar Radiation=Outgoing Longwave Radiation
Incoming Solar Radiation
Outgoing Longwave Radiation
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 )