Chapter 14 – The Atmosphere

Weather and Climate

• The average weather conditions over the year in a particular location determine its climate.

• “Climate is what you expect, but weather is what you get.”

The modern atmosphere• Two most abundant gases: 78% N2 and 21% O2

– Neither of these gases influence weather phenomena

• Argon (< 1%) inert gas• Water vapor (varies from 1 to 4%)

– Source of all clouds and precipitation– Absorbs and releases latent heat during phase change– Greenhouse gas (traps atmospheric heat)

• CO2 (.039% or 39 ppm) – Greenhouse gas

• Non-gaseous components: water droplets, dust, pollen, soot and other particulates– Act as condensation surfaces for water in atmosphere– Block sunlight and act as a cooling agent.

Fig. 17.6, p.437

Solar radiation and the atmosphere• Much of the highest

frequencies (x-rays, gamma rays) are absorbed by oxygen atoms in the thermosphere and O2 gas in the mesosphere.

• Much ultraviolet (uv) absorbed by the ozone in the stratosphere.

• Visible light waves (still considered shortwave) pass through atmosphere and are absorbed by earth.

Ozone formation in stratosphere

Depletion of the ozone layer• Ozone – O3 forms in the stratosphere and

absorbs UV energy, which can be harmful• Halons and Chlorofluorocarbons (CFCs), – are

organic compounds that destroy ozone in the ozone layer

Depletion of the ozone layer

• Ozone hole – reported in 1985 and linked to CFCs in Antarctic ice clouds

• Many nations of the world agreed to reduce or stop use of these CFCs and halons

• Most industrial countries no longer produce CFCs.

• Since banning CFCs, the hole may be decreasing

Ozone high and low

• The ozone layer in the stratosphere is a good thing because it protects life on Earth from harmful UV rays

• The Ozone in the troposphere is a bad thing because it damages hearts and lungs.

Thermal Structure of Atmosphere: Troposphere• Extends to about 12 km

(40,000 ft) elevation• All clouds & water vapor

and most weather• Temperature decreases as

elevation increases, because chief source of heat is radiated heat from the earth’s surface

• Tropopause: boundary between troposphere and stratosphere.

Environmental Lapse Rate• Lapse rate: the rate at which air temperature decreases with altitude.•The environmental lapse rate is the overall temperature decrease in the troposphere with altitude•The normal environmental lapse rate is 6.5°C/1000m, however various factors can change this.•The illustration shows an environmental lapse rate of 0.5°C/100m, which equates to 5°C/1000m.•Question 7, in the homework, uses this concept.

Example problem using normal lapse rate

It is 25 H C at the surface. Under normal conditions, what is the air temperature at 4 kilometers (4000 meters) above the surface. The normal lapse rate is 6.5 H C/1000m

a.21 H C

b.19.5 H C

c.Still 25 H C

d.-1 H C

Example problem using normal lapse rate

It is 25 H C at the surface. Under normal conditions, what is the air temperature at 4 kilometers (4000 meters) above the surface. The normal lapse rate is 6.5 H C/1000m

a.21 H C

b.19.5 H C

c.Still 25 H C d.-1 H C (this is about 30 degrees F)

Thermal Structure of Atmosphere: Upper Layers

• Stratosphere – heated primarily by solar radiation– Ozone (O3) layer

absorbs UV energy, causing temperatures to rise

– Above 55km (stratopause) temps fall again

• Mesosphere – thin air (can’t absorb energy), very cold up to 80km

• Thermosphere – above 80km, temps rise rapidly (to just below freezing!)

Earth rotates around an axis from the North to South Pole

• Lines of latitude: imaginary horizontal rings around the axis– Equator is at 00 latitude– Geographic poles at 900

latitude– Arctic and Antarctic

circles at 66.50 latitude– Tropic of Cancer (N),

Capricorn (S) at 23.50 latitude, define tropics

Earth rotates around an axis from the North to South Pole

• Lines of longitude (meridians): imaginary vertical lines that run north to south.

• Line through Greenwich, England (Prime Meridian) at 00 longitude.

• Longitude increases both east and west of Prime Meridian and meets at 1800 longitude, the International Date Line.

The Earth’s axis is tilted 23.50 from the perpendicular to the orbital plane.

AXISPerpendicular to

orbital plane

In this picture, the northern hemisphere is tilted away from the Sun. In 6 months, when the earth has orbited to the other side of the Sun, the northern hemisphere will be tilted towards the Sun.

On Earth, heat energy comes from light energy

• One energy “unit” can be concentrated in a relatively small surface, or spread out over a large surface, depending on the angle of incidence.

• The more the energy is spread out, the less heat it generates.

Warmest (Direct) Less Warm Least Warm

The Seasons (N. Hemisphere)

• Summer is warm– Sun is higher in the sky

so solar energy is more concentrated.

– North Pole receives sun all day long.

– Days are longer than nights.

• Winter is cold– Sun is lower in the sky.– North Pole receives no

sunlight.– Nights are longer than

days.

The Seasons (N. Hemisphere)

• Fall and Spring – Vernal and Autumnal Equinox– Poles not tilted away

or towards the Sun.– Both hemispheres

receive equal amounts of solar energy.

– Days and nights are the same length (12 hours).

Heat, Temperature, and Thermal Energy

•Thermal energy is an energy of the system due to the motion of its atoms and molecules. Any system has  thermal energy even if it is isolated and not interacting  with its environment.

•Heat is energy transferred between the system and the   environment as they interact due to a difference in temperature.

• Temperature quantifies the   “hotness” or “coldness” of a system. Although proportional to the thermal energy of a system, it is not the same thing! A temperature  difference is required in order for heat to be transferred   between the system and the environment.

Methods of Heat Transfer• Radiation is the heat-

transfer mechanism by which solar energy reaches our planet.

• Energy transferred by radiation is called electromagnetic radiation and can travel through a vacuum. This radiation is NOT radioactive!

• All radiation travels at the speed of light in a vacuum.

Electromagnetic Spectrum

Note the distinction between short-wave and long-wave radiation.

Laws Governing Radiation

1. All objects emit radiant energy. This includes the Earth, and its polar ice caps.

2. For a given size, hot object emit more energy than cold objects

3. The hotter the radiating body, the shorter the maximum wavelength. Solar radiation is called short-wave radiation and Earth’s radiation is called long-wave radiation .

Laws Governing Radiation

4. Objects that are good absorbers of radiation are good emitters as well. The Earth and the Sun absorb and radiate with nearly 100% efficiency for their respective temperatures

5. The gases of the atmosphere are not so good. They absorb some wavelengths and then re-emit it. They let other wavelengths pass through with no absorption.

When radiation strikes an Object• Transmission (no change in direction or temperature)• Scattering and Reflection (transmission in another

direction)• Absorption, which is accompanied by change of

temperature for object absorbing the radiation.

Solar Radiation in the Atmosphere

Reflection and Albedo• Reflection–electromagnetic radiation bouncing of

from a surface without absorption or emission, no change in material or energy wavelength

• Albedo – proportional reflectance of a surface– a perfect mirror has an albedo of 100%– Glaciers & snowfields approach 80-90%– Clouds – 50-55%– Pavement and some buildings – only 10-15%– Ocean only 5%! Water absorbs energy.

Typical Albedos of Materials on the Earth

Absorption and Emission

• Absorption of radiation – electrons of absorbing material are “excited” by increase in energy – Increase in temperature; physical/chemical change– Examples: sunburn, cancer

• Emission of radiation – excited electrons return to original state; radiation emitted as light or heat– Example: earth absorbs short wave radiation from

sun (i.e. visible light) and emits longwave (infrared or heat) into the atmosphere

Fig. 18-6, p.432

the Radiation Balance• Sun emits EM radiation of all wavelengths, but

primarily shortwave (i.e. light).– Earth’s surface absorbs this energy– Most is re-emitted upward, as heat (longwave)

• Greenhouse Effect– “greenhouse gases” (water vapor, carbon dioxide,

methane, etc.) let shortwave energy pass, but absorb and longwave energy radiated upward by the Earth.

– this longwave energy is re-radiated in all directions, some of it returning to the Earth’s surface. This is what keeps our atmosphere at a livable temperature of about 15 degrees C (59 degrees F).

Controlling Factors of Temperature

• Latitude: tropics are warmer and higher latitudes are colder temperature due to differences in the Sun’s angle and the length of the day in these locations.

• Land and Water• Altitude (troposphere temperature

decreases with altitude)• Geographic position (windward coast vs.

leeward coast• Cloud cover and albedo

Continental Climate vs Marine Climate: Moderating influence of a

large body of water

Effect of the Gulfstream on Climate

Effect of westerlies carrying marine air mass vs a continental air mass

Siberia (cold arctic wind)

Pacific (moderate ocean wind)

Effect of Clouds on Temperature; cooling effect during the day,

warming effect at night

Global temperature distribution in January• Red-warmer, blue-cooler• Northern hemisphere colder than southern• Coldest/warmest places are on continents• Isotherms bend southward on land in northern hemisphere – means inland is colder

than ocean

Global temperature distribution in July • red-warmer, blue-cooler• Southern hemisphere colder than northern• Coldest place Antarctic continent /warmest places are continental deserts in the northern

hemisphere• Isotherms bend northward on land in northern hemisphere, means inland is warmer than ocean