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.