CHAPTER 1

Structure & Composition of Earth’s Atmosphere

THE TURBULENT ATMOSPHERE

CHAPTER 1

Structure & Composition of Earth’s Atmosphere

THE TURBULENT ATMOSPHERE

“Extreme and unusual weather” are the focus of public fears, and are often the impetus behind our quest for knowledge about the atmosphere

In the United States, the risk of death due to a weather event is relatively small when compared to other risks ◦ About two in one million

THREATS FROM THE SKY

Table 1.1, p. 5

Weather-related events cause an estimated $10 billion in property damage annually

Virtually no part of the globe is free of the threat of extreme weather

THREATS FROM THE SKY

Fig. 1.2, p. 5

The total number of billion dollar weather and climate disasters from 1980 through 2004.

Fig. 1.3, p. 5

Note! Represents Percentages in One Year Only: 2000

Weather-related Deaths

There are a number of concerns about the atmosphere that are not related to isolated extreme weather events◦ Global warming◦ Toxic chemicals

A basic understanding of the atmosphere is required for understanding the acute impacts caused by extreme and unusual weather

REASONS FOR CONCERN

Fig. 1.4, p. 7

Table 1.2, p. 6

Our atmosphere is a thin, delicate life-giving blanket of air that surrounds the earth

Warmth for our planet is provided primarily by the sun’s energy

THE EARTH’S ATMOSPHERE

Diagram NOT to scale

Our atmosphere is a thin, delicate life-giving blanket of air that surrounds the earth

Warmth for our planet is provided primarily by the sun’s energy

Radiant energy drives the atmosphere into the patterns of everyday wind and weather, and allows life to flourish

Mean sfc temp is 59F (15C), but can be much more extreme

THE EARTH’S ATMOSPHERE

Mr. Hartwell -- F-M Meteorology

Earth’s Atmosphere

* Formation *

Before the Solar System

• Supernova explosion provides raw materials

• Materials collect around a center of gravity to ignite the Sun

Formation of Earth

•4.6 billion years old•Coalescence of rocky particles

•Atmosphere forms later

Formation of Earth’s Atmosphere

• Original Protoearth was molten • Dense material (molten nickel and iron) flowed

to the center • Lighter material (molten silicon) flows to the top • Earth cools and solidifies into basic core,

mantle and crust structure • The earth has a lot of trapped gasses in its

interior • Movie clip!

Atmosphere #1

• Composition - Probably H2, He • Gases are relatively rare on Earth • Probably lost to space early in Earth's history

because…? – Earth's gravity is not strong enough to hold lighter gases – Earth still did not have a differentiated core (solid

inner/liquid outer core) creates Earth's magnetic field (magnetosphere = Van Allen Belt) deflects solar winds.

• Once the core differentiated the heavier gases could be retained

Atmosphere #2

• Produced by volcanic out-gassing (degassing).

Current Atmosphere

Atmosphere #2

• Produced by volcanic out-gassing (degassing). • Gases produced were probably similar to those

created by modern volcanoes (H2O, CO2, SO2, CO, S2, Cl2, N2, H2) and NH3 (ammonia) and CH4 (methane)

• No free O2 at this time (not found in volcanic gases).

• Ocean Formation - As the Earth cooled, H2O produced by out gassing could exist as liquid in the Early Archean, allowing oceans to form. – Evidence - pillow basalts, deep marine seds in greenstone

belts.

Production of Oxygen

• Photochemical dissociation - breakup of water molecules by ultraviolet light– Produced O2 levels approx. 1-2% current levels

• At these levels O3 (Ozone) can form to shield Earth surface from UV

• Photosynthesis - CO2 + H2O + sunlight = organic compounds + O2 – produced by cyanobacteria, and eventually

higher plants – supplied the rest of O2 to atmosphere. Thus

plant populations

Cyanobacteria that fixes CO2 to release O2

99% of the atmosphere is within 20 miles of the Earth’s surface

N2 78% and O2 21%

The percentages represent a constant amount of gas but cycles of destruction and production are constantly maintaining this amount

Composition of Earth’s current atmosphere

Water is a variable, but very important gas◦ The hydrologic cycle: evaporation, precipitation,

runoff, etc.

Carbon dioxide concentrations have risen in recent years◦ CO2 is an important greenhouse gas, though not

the only one

Ozone: “Good up high, bad nearby”

Composition of the atmosphere

Lower in summer when plants are active and absorb CO2

Has risen more than 20% since 1958

CO2 concentrations from Mauna Loa, Hawaii

Stepped Art

Fig. 1-4, p. 7

Near the ground, ozone is the main ingredient in smog, irritant to eyes; plants

In the stratosphere, ozone provides a protective shield from ultraviolet radiation

This protective shield erodes over Antarctica in their winter, causing a stratospheric “ozone hole”

Ozone

Low concentrations of ozone over Antarctica, September 2004

Weather and climate Weather: short term air temperature, air

pressure, humidity, clouds, precipitation, visibility, and wind

Climate: long term patterns and average weather; not just magnitude but also frequency.

But climate is not just the average, it also describes the range of possibilities

Atmospheric Pressure Temperature Moisture

◦ Water vapor in the air◦ Precipitation

Wind◦ Direction◦ Speed

The Primary Variables

Atmospheric Pressure is the force per unit area of a column of air above you (extending all the way to the “top” of the atmosphere)

In other words, pressure is the weight of the column of air above you - a measure of how hard this column of air is pushing down

More fundamentally - atmospheric pressure arises from gravity acting on a column of air

Air pressure

Molecules bumping into an object create a force on that object

Pressure is the force applied per unit area◦ P = F/A◦ Which box below is exerting the greatest

pressure upon the ground?

Pressure

Force = mass x gravity

1 kg

1 kg

Pressure is one of the most fundamental forces which produces weather and makes our atmosphere move – the wind!

Pressure defines many of our most important weather patterns: midlatitude cyclones, hurricanes, anticyclones

Pressure is usually in units of millibars (mb), though sometimes in inches of Mercury (in Hg)◦ Barometers with mercury in them can be used to

measure pressure◦ Typical pressure at sea level is 1013.25 mb, or

29.92 in Hg

Why pressure?

Density = mass / volume Denser air displaces less dense air - just like water

displaces air Lower-density air rises when it is surrounded by

denser air - one of the primary forces which produces vertical motions in the atmosphere◦ Think of a ping-pong ball submerged under

water. What happens when you release it?

Density

1 kg

1 kg

Which box is more dense?

Change in pressure and density with height

Most of the air is near the ground

At an altitude of 5.5 km (about 18000 ft), you are above 50% of the air in the atmosphere. At 50000 ft, you are above 90% of the air!

Fig. 1.16, p. 19

Temperature is a measure of the kinetic (motion) energy of air molecules◦ K.E. = ½ mv2 m = mass, v =

velocity◦ So…temperature is a measure of air

molecule speed The sensation of warmth is created by

air molecules striking and bouncing off your skin surface◦ The warmer it is, the faster molecules move

in a random fashion and the more collisions with your skin per unit time

Temperature

Temperature scales

Mr. Hartwell -- F-M Meteorology

Earth’s Atmosphere* Structure *

http://apollo.lsc.vsc.edu/classes/met130/notes/

Recall from Earth Science…

Diagram NOT to scale

Vertical Structure of Atmos.

• Meteorological variables that define layers of the atmosphere:– Density– Pressure– Temperature

• How do each change with increasing altitude?

Density

• Density (mass/volume) decreases with height

Pressure

• Pressure (force/area) decreases with height in the atmosphere

Pressure

• Q: Which exerts more pressure?

–4000lb elephant standing on one leg with foot size of 8”x8”

–120 lb woman standing on one leg in high-healed shoes with a heal size of 1”x1”

Temperature

• Temperature in the atmosphere decreases + increases with height

• Temperature changes denote atmospheric layers:– Troposphere– Stratosphere– Mesosphere– Thermosphere

Troposphere• 0 km (surface) – 12 km altitude• 75% of atmosphere• All weather takes place here

• ‘-pause’—boundary between layers

• Troposphere—contains the jet stream —lid on the weather

Stratosphere• 12 km – 50 km altitude• Contains the Ozone Layer

• Ozone Layer—atmospheric shield for Earth’s surface– Absorbs UV light; temps. increase in strat.

Other atmospheric layers

Mesosphere• 50 km – 80 km altitude• Shields Earth from meteoroids

Thermosphere• +80 km altitude• High heat; UV energy turned to heat• Contains the Ionosphere & Exosphere

Red line shows temperature

Temperature decreases with height in troposphere and mesosphere; increases with height in thermosphere

The change in temperature with height is called the lapse rate

In the troposphere, on average, the temperature decreases 6.5° Celsius for every kilometer that you go up

Sometimes, though, it’s the opposite: when temperature increases with height, it is called an inversion

If temperature is constant with height: isothermal (iso=same, thermal=temperature)

Lapse rate

Electrified region of the thermosphere (not really a layer)

The ionosphere extends from approximately 60 km above ground to the top of the atmosphere

Three regions within the ionosphere: D, E, and F

The “D” region absorbs AM radio waves, but it disappears at night.

The “E” and “F” regions reflect AM waves back toward the ground

This is why you can often hear AM stations from all over the country at night

The ionosphere

Moving air – determines many aspects of the weather

Wind is the atmosphere’s response to pressure differences

We care about both the wind speed and direction

Units: ◦ Meters per second (m/s)◦ Miles per hour (mph)◦ Nautical miles per hour (knots)

1 meter/second = 2.24 miles/hour = 1.94 knots A hurricane has sustained winds greater than 74

mph, or 64 knots, or 33 m/s

Wind

Wind from the north 0°Wind from the east 90°Wind from the south 180°Wind from the west 270°Wind toward the north 180°Wind toward the west 90°Wind from the northeast 45°

Wind Direction

N 0o or 360o

E 90o

S 180o

W 270o

45o

135o225o

315o

• In meteorology, we describe the wind in terms of where it is coming from• So, a “west wind” blows from west to east

Fig. 1.17, p. 20

Scales of Motion Examples

Most meteorologists refer to this as the synoptic scale.

Or, the size of a large thunderstorm or cluster of storms.

PROPERTIES OF THE ATMOSPHERE Moisture

◦ Clouds and precipitation are associated with surface low pressure; clear skies with surface high pressure.

◦ Relative humidity does not tell us how much water vapor is actually in the air; rather, it tells us how close the air is to being saturated.

◦ The dew point temperature is the temperature to which air would have to be cooled in order for saturation to occur.

Fig. 1.20, p. 21

Fig. 1.21, p. 22

Fig. 1.22, p. 22

Fig. 1.23, p. 24

Appetite Whetting: EXTREMES OF WEATHER & CLIMATE

Wind chill Drought Heat waves

Tornadoes (cyclones, twisters) Thunderstorms (lightening, flash floods,

downburst) Mid-latitude cyclones Hurricanes

Fig. 1.24, p. 26

Fig. 1.25, p. 27

Fig. 1.26, p. 28

Fig. 1.27, p. 29

Fig. 1.28, p. 29

Fig. 1.29, p. 30

Fig. 1.30, p. 30

Surface observing stations◦ Mostly at airports, but now

also at schools, along highways, etc.

◦ Describe conditions near the ground---temperature, humidity, winds, precipitation, etc.

◦ Some are recorded by people, others automated

◦ Used by many people: pilots, farmers, weather forecasters, and the public!

How do we measure the troposphere?

Upper-air observations◦ Weather balloons are launched twice a day from

locations around the world◦ Attached to the balloons is an instrument called a

“radiosonde”◦ This measures the temperature, pressure, humidity,

and winds◦ The vertical structure is also measured by satellites

and ground-based instruments◦ The hurricane hunter airplanes use “dropsondes”:

instead of a balloon going up, the instruments are on a parachute going down

There isn’t a station very close to here…the surrounding stations are in Binghamton, NY

How do we measure the troposphere?

Movie Clip of Downsondes

http://www.weather.gov/data/obhistory/KSYR.html

Surface observation

Upper-air observation

Tropopause

Zoomed in at low levels

Inversion (temperature increases with height)