Download The Atmosphere

EES 717: The Atmosphere
Things to review:
•
Atmospheric Composition and
Structure
•
Heat Budget – Energy
Transfer
•
Electromagnetic Radiation
•
The Greenhouse Effect
•
Feedbacks - Clouds
•
Global Circulation
II. Atmospheric Composition and Structure
The Atmosphere
Vertical (thermal) structure of the
atmosphere
O3
absorbs
UV Solar
Radiation,
heats
Atm.
• Troposphere: lowest layer 0-12 km,
temperature decreases with altitude
• Tropopause: minimum temperature
zone between the troposphere and
stratosphere
• Stratosphere: layer above
tropopause 12-50 km, temperature
increases with altitude
• Mesosphere: layer above
stratosphere 50-90 km, temperature
decreases with height
• Thermosphere: layer above
mesosphere >90 km, extends out to
space
Density of air depends on temperature, water vapor and altitude
•Temperature decrease =
density increase
•Water vapor increase =
density decrease
•Altitude increase
=
density decrease
Globally Average Energy Budget
Heat budget
• Solar input must balance solar output
• Temperature increases/decreases if input is
greater/less than output
• Average Earth Temperature is 16oC
• Solar Energy is reradiated from the surface as a long
wave.
• Surface of Earth (including oceans) is heated from
above
• Atmosphere is heated from below
Modes of Energy Transfer in the Atmosphere
ELECTROMAGNETIC SPECTRUM
http://www.lbl.gov/MicroWorlds/ALSTool/EMSpec/EMSpec2.html
BLACKBODY RADIATION
Planck function
Wien’s Law
T = temperature (K)
s = Stefan – Boltzman constant
Stefan-Boltzman law
The Earth is in Thermal Balance
Visible
Range
H2O
CO2
CH4
O2, O3
Spectrum of the
Sun’s Incoming
Radiation
N2O
Total
~400 nm ~700 nm
Spectrum of
the Earth’s
Outgoing
Radiation
The greenhouse effect
During the past 20 years, about three-quarters of human-made
carbon dioxide emissions were from burning fossil fuels
Greenhouse gases are accumulating in Earth’s atmosphere as a
result of human activities, causing surface air temperatures and subsurface ocean temperatures to rise
There is uncertainty in how the climate system varies naturally
and reacts to emissions of greenhouse gases
Effects of Global Warming
• Climate Change
• Sea Level Rise
• Changes to Ecology
• Desease Vectors spreading to new places
The greenhouse effect  increase of global
temperature
The molecules responsible
for this phenomenon are
called greenhouse gases,
i.e. water (H2O), nitrous
oxide (N2O), methane
(CH4), and carbon dioxide
(CO2) because they act
like the glass in a
greenhouse, “trapping” reradiated energy.
The Greenhouse Effect
What controls concentrations of CO2 in the atmosphere?
OK, let’s have it that rising temperatures may, in turn, produce
changes in weather, sea levels, and land use patterns, commonly
referred to as “climate change.”
Earth’s radiation balance,
Energy and hydrological cycles,
Exchanges between the biosphere and the atmosphere
Exchanges between the ocean and the atmosphere
Feedbacks?
Remember the Earth
Climate is a
system, with many
components,
interacting all of the
time!
The Carbon Cycle
There is uncertainty in how the climate system varies
naturally and reacts to emissions of greenhouse gases.
Uncertain feedback effects underlie these uncertainties
of climate forecasting
•
•
•
•
•
•
Water vapor feedback
Cloud feedback
Aerosol feedback
Ice-albedo feedback
Ocean circulation feedback
Biosphere feedback
Effects of Clouds on the
Atmospheric Radiation Budget: SW radiation
SW
A*SW
SW
A*SW
Effects of Clouds on the
Atmospheric Radiation Budget: LW radiation
Effect of Aerosols
cooling effect overall
Let’s get ‘grounded’ again! The importance of the land surface: it
controls the
* partitioning of incoming energy at the surface between sensible
and latent heat flux
* partitioning of available water between evaporation and runoff
* it is the location of the terrestrial carbon sink/source (?)
Consequently, it affects
convection, precipitation and the general circulation
Heterogeneities in the LS on many scales provide many challenges
to modeling LS, and its coupling with the atmosphere, accurately.
The Earth Climate System and atmosphere:
it is all about CIRCULATION – circulation – CIRCULATION –
circulation – and then again circulation!
Wind bands – Three convection
cells in each hemisphere
Trade winds = NE (30°N to
0°) and SE (30°S to 0°)
Westerlies = 60°N to
30°N and 60°S to 30°S
Polar easterlies = 90°N
to 60°N and 90°S to
60°S
Low pressure at 0°, 60°N,
and 60°S
Low pressure, ascending air,
clouds, increased
precipitation
High pressure at 30°N, 30°S,
90°N, and 90°S
High pressure, descending
air, clear skies, low
precipitation
Convection? oh no, here we go again!
Scales of motion in the atmosphere range from the very localized sea/land-breeze
circulation to the larger mesoscale convective cells to the planetary scale winds and
meridional thermal cells, all of which participate in the transport and mixing of ‘stuff’
(energy and material properties) locally, regionally and globally.
The same can be said about the oceans
light color  surface
dark color  deep
1. The Gulf Stream which transports heat from the tropics to northern Europe. 2. North
Atlantic Deep Water formation which results from strong cooling. 3. Antarctic Bottom
Water formation due to sea ice production around Antarctica.
Atmospheric Circulation:
1. Keep in mind the atmosphere is flowing in response to horizontal
differences in air pressure generated by unequal heating of the
Earth’s surface
2. Air flow is influenced by pressure gradient force, coriolis force,
and friction
3. Vertical pressure gradients are typically balanced by gravity, large
scale vertical movements of air tend to be slow
4. Frictional forces are greatest within the first 2km of the surface
and will force air to converge beneath a low pressure region and
diverge under a high pressure region
Latitudinal Effects
Isotherms trend W-E
Sun Angle Migration
Hotspot movement
Differential Heating
hottest/coldest temps
over land
Ocean Currents
bending of isotherms
World Distribution of Temperature Range
Equator –vs- Poles
Land –vs- Water
N.H. Land –vs- S.H. Land
Key Points: Summary of Chapter 2
1. The global wind system acts to redistribute heat between
lows and high latitudes.
2. Coriolis force influences the direction of winds as they
move from regions of high pressure to regions of low
pressure.
3. Differential heating between land and water greatly
influences global wind patterns.
4. Mid-latitude weather is systems are cyclones and
anticyclones. Low latitude circulation is characterized by
spiraling Hadley cells.
5. Heat is transported to higher latitudes through convective
motions and latent heat transfer.
6. Ocean-Atmosphere interactions are most intense (strong
coupling) in the tropics.
The Tropics
Pressure and
Winds
Circulation around
Highs and Lows &
Re-distribution of
Heat
Extratropical Circulation –
Planetary Waves
Extropical
Dynamics –
Frontogenesis
Fluid Stability
Ocean-Atmosphere Interactions
Intense coupling in the tropics
Moisture content and stability
SST – Hadley Cell Intensity – Location ITCZ
Warmer SST = More buoyancy = Inc. Convection
Cyclones – Hurricanes – Typhoons
low pressure centers, depressions from higher
latitude, vortices associated with ITCZ, easterly
waves (O 2500km)
Western basin – trade wind T inversion weakest
Cylone (anticylone) generation requires geostrophic conditions
Intense convection of warm humid air = cumulonimbus clouds & Thunder storms
Release of latent heat increases buoyancy of upper air = enhanced convection
Critical SST 27o – 29o C
Surface winds influence deeper ocean structure
Thickness of Mixed Layer
Decay: land, cooler water, upper level wind shear
http://svs.gsfc.nasa.gov/vis/a000000/a003200/a003261/
TRMM Microwave Imager (TMI) sea-surface temperatures
from August 22 - Sept. 23, 1998. Blues represent cooler water,
greens and yellows are warmer water.
Deadliest Hurricanes in the United States (U.S. Mainland)1
Rank Hurricane
Year
Category2
Deaths
3
1.
Galveston, Tex.
1900
4
8,000
2.
Lake Okeechobee, Fla.
1928
4
2,500
3.
Katrina (La./Miss.)
2005
3
1,800
4.
Florida Keys/S. Tex.
1919
4
600
5.
New England
1938
3
600
6.
Florida Keys
1935
5
408
7.
Audrey (SW La./N. Tex.)
1957
4
390
8.
NE U.S.
1944
3
390
9.
Grand Isle, La.
1909
4
350
10.
New Orleans, La.
1915
4
275
10.
Galveston, Tex.
1915
4
275
1. 1900–2007.
2. At landfall. Saffir-Simpson Hurricane scale: Cat. 1 = weak; Cat. 5 = devastating.
3. May actually have been as high as 10,000 to 12,000.
4. Approximated.
5. Over 500 of these lost on ships at sea; 600–900 estimated deaths.
6. Some 344 of these lost on ships at sea.
Source: National Oceanic and Atmospheric Administration (NOAA).
5
6
4