Prentice Hall Earth Science ch17 atmosphere

transcript

Prentice Hall EARTH SCIENCEEARTH SCIENCE

Tarbuck Lutgens

Chapter

1717The Atmosphere: Structure and Temperature

Composition of the Atmosphere

17.1 Atmosphere Characteristics

Weather is constantly changing, and it refers to the state of the atmosphere at any given time and place. Climate, however, is based on observations of weather that have been collected over many years. Climate helps describe a place or region.

Major Components• Air is a mixture of different gases and particles,

each with its own physical properties.

Volume of Clean, Dry Air

Evolution of Earth’s Atmosphere

• https://youtu.be/ocsV1cA4K4A

Human Influence• Emissions from transportation vehicles account

for nearly half the primary pollutants by weight.

Height and Structure of the Atmosphere

The atmosphere rapidly thins as you get higher in altitude.

• Atmospheric pressure is simply the weight of the air above.

Pressure Changes

Atmospheric Pressure vs. Altitude

Layers of the Atmosphere

Temperature Changes• The atmosphere can be divided into four layers

based on temperature.

1. The tropospheretroposphere bottom layer up to 10 Km. Decreasing

temperatures with height.

2. Where all WEATHER occurs. The stratospherestratosphere is from 10-50

Km. Increasing temperatures.

3. The mesospheremesosphere is from 50 to 80 Km. Decreasing temperatures

with height.

4. The thermospherethermosphere is from 80 to 150 Km. Increasing

temperatures due to solar energy.

Snowy Mountaintops Contrast with Warmer Snow-Free Lowlands

Thermal Structure of the Atmosphere

Earth-Sun Relationships

Earth’s Motions• Earth has two principal motions—rotation and

revolution.

Earth’s Orientation• Seasonal changes occur because Earth’s

position relative to the sun continually changes as it travels along its orbit. 23231/21/2 degree degree tilt on its axis produces 4 seasons.

Tilt of Earth’s Axis

Solstices and Equinoxes

• The autumnal equinox is the equinox that occurs on September 22 or 23 in the Northern Hemisphere.

• The spring equinox is the equinox that occurs on March 21 or 22 in the Northern Hemisphere.

• Equinox means EQUAL day & night.

Solstices and Equinoxes• The summer solstice is the solstice that occurs

on June 21 or 22 in the Northern Hemisphere and is the “official” first day of summer.

• The winter solstice is the solstice that occurs on December 21 or 22 in the Northern Hemisphere and is the “official” first day of winter.

Solstices and Equinoxes

Energy Transfer as Heat

17.2 Heating the Atmosphere

Radiation

• Radiation is the transfer of energy (heat) through space by electromagnetic waves that travel out in all directions.

What Happens to Solar Radiation?

When radiation strikes an object, there usually are three different results.1. Some energy is absorbed by the object.

2. Some radiation travels through substances such as water and air.

3. Some radiation may bounce off the object without being absorbed or transmitted.

Solar Radiation

What Happens to Solar Radiation?

• The greenhouse effect is the heating of Earth’s surface and atmosphere from solar radiation being absorbed and emitted by the atmosphere, mainly by water vapor and carbon dioxide.

• An INCONVENIENT TRUTH.

Why Temperatures Vary

17.3 Temperature Controls

Altitude• The altitude can greatly influence temperatures

experienced at a specific location. As altitude goes UP temperature goes DOWN.

Mean Monthly Temperatures for Guayaquil and Quito

So how can I find the relative humidity and the dewpoint?

Easy. Just get youself a psychrometer. A psychrometer is just two thermometers.

There’s a ‘dry bulb’thermometer which justmeasures the temperatureof the air in the room.....

and there’s a ‘wet bulb’thermometer whose bulbis surrounded by a cottonwick which is soaked withwater.

Great. So how doesit work?

Water evaporates from the wet bulb.It takes 2260 Joules of heat energy to evaporate1 gram of water (ESRT pg 1)

That energy comes from the wet bulb itself.

In other words, the evaporating water pulls heatenergy away from the wet bulb leaving it coolerjust the same way you are cooled when

sweat evaporates from your skin.

The more water that evaporates, the cooler thewet bulb.

So what determines how much water evaporates?

The relative humidity! The drier the air, the more water evaporates and the more the wet bulb is cooled.

In other words, the drier the air, the greater the difference between the dry bulb and the wet bulb!

If the relative humidity was 100% there would be NO evaporation and thetwo thermometers would show the same temperature. No difference.

OK, now what?

Now whip out your reference tables and turn to page 12......

According to our psychrometer (previous slide) the dry bulb is 20oC and thewet bulb is 12oC. Subtract to find the difference. 20 - 12 = 8

Find the dry bulbtemperature (20oC)Find the difference(8oC)Now see wherethey meet.......

The relative humidityis 36%. That’s allthere is to it!

OK, but how do youfind the dewpoint?