Download The modern atmosphere

Meteorology 10 - Weather and Climate
Fall 2008
CHAPTER 1
FOCUS: atmospheric composition
Structure of Earth’s Atmosphere
The atmosphere didn’t always look like this...
Earth’s First
Atmosphere 4.5 billion
years ago
•
The primitive atmosphere was probably comprised of
hydrogen and helium
• These gases were lost to space early in Earth's
history, because:
Weak gravity allowed lighter gases to escape
Second atmosphere - 4 billion years ago
‘Outgassing’ from
volcanoes (H2O, CO2, N2,
SO2)
Comet impacts (H2O)
Second Atmosphere’s Composition
• Mostly water vapor (80%)
• CO2 200-1000 times more than present (10%)
• Small amounts of nitrogen, sulfur, methane
• Trace amounts of O2
Result: Very Tall and Dense Atmosphere!
Almost no Oxygen!
And then two major events came into play…
1) As Earth cooled, precipitation started…
Rain resulted in fundamental changes to atmosphere:
A) Most water vapor (H2O) moved from atmosphere to global
oceans
B) Most carbon dioxide (CO2) was removed
-Dissolved into rainwater and
-ocean surface
-Carbonic acid leached into rocks and
deposited carbon
Result: Atmosphere became MUCH thinner...
~ most of the atmosphere was locked up on the earth’s surface
2) Then… LIFE emerged - toward the modern atmosphere
Cyanobacteria
Origin of O3
2.8 BY ago: cyanobacteria first appeared
Photosynthesis
CO2 + H2O + Light » CH2O + O2
Result : Oxygen became abundant in the Earth’s atmosphere
Oxygen in the atmosphere is a telltale sign of life!!!
Chapter 1: The Earth’s
Atmosphere
• Overview of the Earth’s atmosphere
• Vertical structure of the atmosphere
• Weather and climate
Overview of the Earth’s Atmosphere
• The atmosphere, when the earth is scaled to the size of an
apple, is no thicker than the skin on that apple.
Composition of the Atmosphere
• permanent gases
• roles of nitrogen and oxygen
• variable gases
• role of water vapor
Table 1-1, p. 3
Composition of the Atmosphere
•
•
•
•
Carbon dioxide and the greenhouse gases
ozone
aerosols
pollutants
• Ozone at high altitudes (stratosphere) is “good”;
ozone at low altitudes (troposphere) is “bad.”
The modern atmosphere - composition
Nitrogen - (N2) - 78% - inert
Oxygen (O2) - 21%
Argon - 0.9%
Carbon Dioxide - (CO2) - 0.037%
Water Vapor - (H2O) - 0% to 4%
Trace Gases (neon, helium,
methane, hydrogen, ozone)
The atmosphere’s
composition is in
balance!
The composition of Earth’s Atmosphere is
maintained in balance by interactions with life and
the Earth’s surface
Global Vegetation - Seasonal Change
January
May
September
NDVI Vegetation Index (NASA)
March
July
November
In what month
is there the least
amount of
carbon dioxide
in the
atmosphere??
Upward trend
Related to fossil fuel burning and
global warming
Annual Cycle
Related to the growing season
of vegetation in the Northern
Hemisphere
Ahrens
FIGURE 1.3 The main
components of the
atmospheric carbon
dioxide cycle. The gray
lines show processes that
put carbon dioxide into
the atmosphere, whereas
the red lines show
processes that remove
carbon dioxide from the
atmosphere.
Stepped Art
Fig. 1-3, p. 4
A Brief Recap of Air Pressure
and Air Density
• air density
• air pressure
• sea-level pressure
• Baseballs travel farther in higher-altitude air (Denver)
than they do in lower-altitude air.
Layers of the Atmosphere
•
•
•
•
•
vertical temperature profile
troposphere
stratosphere
mesosphere
thermosphere
• Temperatures, winds,
humidity and pressures high
above the ground are
measured twice-daily by
radiosonde.
Segway: The Ionosphere
• electrified regions of the atmosphere
• D, E and F regions
• radio waves
• When the radio was invented by G. Marconi in the
early 20th century, it was not known how radio
waves traveled long distances through the
atmosphere.
Fig. 1-11, p. 13
Vertical temperature structure: “layers of the atmosphere”
Heterosphere:
The region of the
atmosphere above 85 km
where the composition of
the air varies with height.
Homosphere:
The region of the
atmosphere below about
85 km where the
composition of the air
remains fairly constant
Two Criteria
• Two criteria are used to organize the layers of
Earth’s atmosphere
– Temperature or how temperature changes in the layer –
lapse rate
– And the depth or extent of that layer
• Use these two criteria to characterize each layer
Troposphere (0 - 12km)
All weather is in this layer
Lapse rate: Air cools with height,
6.5oC per kilometer (lapse rate)
Atmosphere heated from below,
causing air to rise
“Tropopause”
All weather that
affects us occurs in
the troposphere…..
Rondônia, Brazil
Stratosphere (12 - 50km)
Temperature increases with
height (means something is
adding heat there)
No weather
Ozone production heats the
stratosphere
Stratopause
Mesosphere (50 - 85km)
Temperature decreases with
height
Thin ‘noctilucent’ clouds
Meteors burn up here
Mesopause
Even though weather occurs only in the
troposphere, in these upper atmospheric
layers, there are some “clouds”…
Noctilucent Clouds in the Mesosphere (~70km altitude)
Ionized Meteor Trail in the Mesosphere (~60 km)
Thermosphere
(80 - 500 km)
High temperatures from
few, high energy, gas
molecules
Low-orbit satellites fly here
Realm of the aurora
“Ionosphere”
Ionosphere: aurora (ionized gas) seen from surface
Aurora in the ionosphere as seen from the space shuttle
Exosphere (above 500 km)
Just a few stray molecules….
Weather and Climate
What is the difference?
Elements of Weather
•
•
•
•
•
•
•
air temperature
air pressure
humidity
clouds
precipitation
visibility
wind
• Certain weather elements, like
clouds, visibility and wind, are
of particular interest to pilots.
Climate
• average weather, over time, for a given region
• extremes – comparatively short duration, but the
frequency of these events also help to distinguish and
determine the climate of one region compared to
another similar region
A Satellite’s View of the Weather
• geostationary satellites
• Atmospheric observation
from satellites was an
important technological
development in
meteorology. Other
important developments
include computer modeling,
internet, and Doppler radar.
Storms of all Sizes
•
•
•
•
midlatitude cyclonic storms
hurricanes and tropical storms
thunderstorms
tornadoes
• Storms are very exciting, but they also play an
important role in moving heat and moisture around
throughout the atmosphere. Lets take another look.
A Look at a Weather Map
• wind speed and direction
• cyclones and anticyclones
• fronts
• Wind direction is defined in the opposite way as
ocean currents: a southerly current means water is
moving towards the south.
Fig. 1-13, p. 17
Weather and Climate in our Lives
•
•
•
•
wind chill, frostbite and hypothermia
heat exhaustion and heat stroke
cold spells, dry spells and heat waves
severe thunderstorms and flash floods
• The mathematical formula for determining the wind
chill temperature has recently been revised due to new
experiments.
Figure 1.16: Ice storm near Oswego, New York, caused utility poles and power lines to be
weighed down, forcing road closure.
Fig. 1-16, p. 19
Figure 1.18: Flooding during April, 1997, inundates Grand Forks, North Dakota, as
flood waters of the Red River extend over much of the city.
Fig. 1-18, p. 20