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Structure of Earth’s Atmosphere
Meteorology 10 - Weather and ClimateFall 2008CHAPTER 1
FOCUS: atmospheric composition
The atmosphere didn’t always look like this...
• The primitive atmosphere was probably comprised of hydrogen and helium
Earth’s First Atmosphere - 4.5 billion years ago
• 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
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 O2Result: Very Tall and Dense Atmosphere!
Almost no Oxygen!
‘Outgassing’ from volcanoes (H2O, CO2, N2, SO2)
And then two major events came into play…
1) As Earth cooled, precipitation started…
Rain resulted in fundamental changes to atmosphere:
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
A) Most water vapor (H2O) moved from atmosphere to global oceans
2) Then… LIFELIFE emerged - toward the modern atmosphere
Result : Oxygen became abundant in the Earth’s atmosphereOxygen in the atmosphere is a telltale sign of life!!!
2.8 BY ago: cyanobacteria first appeared
PhotosynthesisCO2 + H2O + Light » CH2O + O2
Cyanobacteria
Origin of O3
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
• variable gases
• roles of nitrogen and oxygenroles of nitrogen and oxygen
• role of water vaporrole 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 high altitudes (stratosphere) is “good”;ozone at low altitudes (troposphere) is “bad.”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 The composition of Earth’s Atmosphere is maintained in balance Atmosphere is maintained in balance by interactions with life and the by interactions with life and the
Earth’s surfaceEarth’s surface
January March
May July
September November
Global Vegetation - Seasonal ChangeGlobal Vegetation - Seasonal Change
NDVI Vegetation Index (NASA)
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)Baseballs travel farther in higher-altitude air (Denver)than they do in lower-altitude air.than they do in lower-altitude air.
Layers of the Atmosphere
• vertical temperature profile• troposphere• stratosphere• mesosphere• thermosphere
• Temperatures, winds, Temperatures, winds, humidity and humidity and pressures high above pressures high above the ground are the ground are measured twice-daily measured twice-daily by by radiosonde.radiosonde.
Segway: The Ionosphere
• electrified regions of the atmosphere
• D, E and F regions• radio waves
• When the radio was invented by G. When the radio was invented by G. Marconi in the early 20th century, Marconi in the early 20th century, it was not known how radio waves it was not known how radio waves traveled long distances through the traveled long distances through the atmosphere.atmosphere.
Fig. 1-11, p. 13
Vertical temperature structure: “layers of the atmosphere”
Homosphere:The region of the atmosphere below about 85 km where the composition of the air remains fairly constant
Heterosphere:The region of the atmosphere above 85 km where the composition of the air varies with height.
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)
Lapse rate: Air cools with height, 6.5oC per kilometer (lapse rate)
Atmosphere heated from below, causing air to rise
“Tropopause”
All weather is in this layer
All weather that affects us occurs in the troposphere…..
Rondônia, Brazil
Stratosphere (12 - 50km)
Ozone production heats the stratosphere
Stratopause
Temperature increases with height (means something is adding heat there)
No weather
Mesosphere (50 - 85km)
Meteors burn up here
Temperature decreases with height
Thin ‘noctilucent’ clouds
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)
Realm of the aurora
“Ionosphere”
High temperatures from few, high energy, gas molecules
Low-orbit satellites fly here
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, likeCertain weather elements, likeclouds, visibility and wind, areclouds, visibility and wind, areof particular interest to pilots.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 Atmospheric observation from observation from satellites was an satellites was an important important technological technological development in development in meteorology. meteorology. OtherOtherimportant important developments developments include computer include computer modeling, modeling, internet, and internet, and Doppler radar.Doppler radar.
Storms of all Sizes
• midlatitude cyclonic storms• hurricanes and tropical storms
• thunderstorms• tornadoes
• Storms are very exciting, but they Storms are very exciting, but they also play an important role in also play an important role in moving heat and moisture around moving heat and moisture around throughout the atmosphere. Lets throughout the atmosphere. Lets take another look.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 asWind direction is defined in the opposite way asocean currents: a southerly current means water is ocean currents: a southerly current means water is moving moving towardstowards the south. 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 windThe mathematical formula for determining the windchill temperature has recently been revised due to newchill temperature has recently been revised due to newexperiments.experiments.
Fig. 1-16, p. 19
Figure 1.16: Ice storm near Oswego, New York, caused utility poles and power lines to be weighed down, forcing road closure.
Fig. 1-18, p. 20
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.