Atmospheric Physics I
PHYS 621, Fall 2011
Dr. Zhibo Zhang
Contact info:
Phone: 410-455-6315 (office)
Email: Zhibo.Zhang@umbc.edu
Office hour: Friday, 3:30~4:30 or by appointment
Course Website: UMBC Blackboard system &
http://userpages.umbc.edu/~zzbatmos/research/
PHYS621_fall2011.html
Textbooks
Salby, Murry L.
Fundamentals of Atmospheric
Physics1996
Wallace J.M., and Hobbs, P.V.
Atmospheric Science 2nd. Ed
2006 (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
Fall
Summer
Winter
Latitude and Longitude
Latitude: “Meridional” : North / South
Longitude: “Zonal” : East / West
Spherical coordinate
r: radius of the earth
θ: Longitude
Φ: Latitude
Spherical Distance: radius X angle
Distance on a longitude circle
Distance on a latitude circle
Geographic Zones
66.5N
23.5 N
Tropics
23.5 S
Mid-latitude
66.5S
66.5N
Tropics
Mid-Latitude
Polar
66.5S
Polar
23.5S ~ 23.5N
23.5N ~ 66.5N 23.5S ~ 66.5S
66.5N ~ 90N
66.3S ~ 90S
Composition of atmosphere
Nitrogen (N2)
Oxygen (O2)
Argon (Ar)
Carbon dioxide (CO 2)
Neon (Ne)
Helium (He)
Methane (CH4)
Krypton (Kr)
Hydrogen (H2)
Water vapor (H2O)
Volume
78.1%
20.9%
0.93%
0.038%
0.002%
0.0005%
0.0002%
0.0001%
0.00006%
Variable: 1-4% near
surface, 0.4% overall
Trace gas
Gas
Other constituents: Aerosols (particulates other
than water),liquid and solid water, birds, insects,
airplanes, kids on trampolines, etc.
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.
volume mixing ratio
Carbon-dioxide : 0.038% = 380x10-6=380ppm
Methane: 0.0001745% = 1745x10-9=1745ppb
Pressure and Density
Volume: V
Density: ρ
Gravity:g
Area: A
Density: mass/volume~kg/m-3
Pressure: mass x gravity / area=kg x m/s-2 / m-2= kg·m−1·s−2
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
Hydrostatic equilibrium
Ftop = (P + dP)A
Hydrostatic equilibrium:
z+dz
Density: ρ
Fbot− Ftop= G
-dP A = ρ g A dz
z
G=ρ g A dz
Fbot = P A
Hydrostatic Equation
dP/dz = -ρg
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 m3)
• 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 efolding depth, p0 is the reference pressure,
usually at sea-level (z=0).
Temperature
Temperature: 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
Stratosphere:
A thick ozone layer (or not
~ ozone whole)
in stratosphere protects us
from “bad” UV
Troposphere:
Where we live in
Contain: 75% of mass and
99% water of the whole atms.
Lapse Rate: local rate of decrease of temperature (T) with altitude (z):
Typical lapse rate close to surface: 6.5K/km
Wind
A vector: speed and direction
Wind Direction
North wind
West wind (westly)
Prevailing Wind
Tropical: Eastly trade wind
Mid-latitude : Westly
“Trade” wind
Spanish
Portuguese
Precipitation
Rain, 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 times
Reservoir
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
Water Residence Time =
9 days
capacity of the system
flow for the system
Carbon Cycle
Atmospheric CO2
Global Energy Budget
Incoming Solar Radiation
Outgoing Longwave Radiation
To keep Earth’s Energy Budget Balance
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
Base Units
Name
Unit symbol
Quantity
meter
m
length
kilogram
kg
mass
second
s
time
kelvin
K
temperature
mole
mol
Amount of substance
Prefix of SI units