CHAPTER 1

THE TURBULENT ATMOSPHERE

CHAPTER 1

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

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

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

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

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

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

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”

Lower in summer when plants are active and absorb CO2

Has risen more than 20% since 1958

Stepped Art

Fig. 1-4, p. 7

“Good up high, bad nearby”

Near the ground, ozone is the main ingredient in smog, which irritates the eyes and throat and damages 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”

Low concentrations of ozone over Antarctica, September 2004

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

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

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?

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

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?

1 kg

1 kg

Which box is more dense?

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

measure of the motion (kinetic energy) of air molecules. Degrees Celsius (Centigrade) deg C = 5/9 (deg F -32) Degrees Fahrenheit deg F = 9/5 (deg C) +32 Kelvin K = deg C + 273.16 1 deg Celsius change = 1.8 deg Fahrenheit change 10 deg Celsius change = 18 deg Fahrenheit change

deg C

-40 -17.8 0 10 20 30 100

deg F

-40 0 32 50 68 86 212

K 233.16 290.94 273.16 283.16 293.16 303.16 373.16

What is 25° in F?

Layers of the Atmosphere◦ Troposphere: Where weather happens and

where we live!◦ Stratosphere: temperature increases with

height, contains lots of ozone◦ Mesosphere: temperature decreases with

height again◦ Thermosphere: hot! Very little air

At the top of each layer is a “pause”: the tropopause is at the top of the troposphere, etc.

Stepped Art

Fig. 1-11, p. 13

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)

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 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 ExamplesScales of Motion Examples

Most meteorologists refer to this as the synoptic scale.

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

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

As a parcel of air (think of a large balloon) is lifted up a mountain, the pressure surrounding it decreases – it must expand

The energy that goes into the expansion is lost, and the parcel cools

As it sinks, the pressure outside the parcel increases – it is compressed

As it compresses, the molecules inside move faster, leading to a higher temperature

Rising air expands and cools, sinking air compresses and warms

Rising air causes clouds◦ Air parcel◦ Air that rises expands and cools◦ Dew point◦ Air that sinks compresses and warms

Wind chill Drought Heat waves Tornadoes (cyclones, twisters) Thunderstorms (lightning, 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.

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

◦ Some are recorded by people, others are automated

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

◦ The College Station observation is taken at Easterwood airport, and has the code CLL

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 Corpus Christi, Dallas/Fort Worth, Shreveport, and Lake Charles, LA

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

Tropopause

Inversion (temperature increases with height)