ahrens chp 01 ace 2005 ani

Chapter 1 - Title

Chapter 1 –

The Earth’s Atmosphere(pp. 1-23)

Contents

• composition of the atmosphere• vertical structure• weather and climate

View From Space

• Earth’s atmosphere is a thin gaseous envelope

• No upper limit, merges with space

• Ocean is to ________ as air is to _________

• Consequences of no atmosphere?– No lakes or oceans

– No sound

– No clouds

– Cold night, hot day

– No weather

6400 km

30 km

Questions

1. What %-age of the total diameter of the Earth is the Earth’s atmosphere?

2. If the Earth was a basketball, how thick would its atmosphere be?

3. What holds the atmosphere to

the Earth’s surface? 6400 km

30 km

0.2 %

1 mm

Gravity

Experiment

• Design an experiment to determine the percentage of O2 in the air

• What are the results? What is the conclusion?

• The flame burns off the O2, the decrease in pressure causes the height of water in the jar to increase by 1/5 (~21%).

• Combustion products are H2O vapor which condenses to liquid water and CO2 which dissolves in the water.

Candle Experiment (Cont.)

Questions• Why is the ‘Candle Experiment’

outlined above considered to be ‘junk science’?

• Can you think of a better way to prove that there is 21% O2 in air?

What could this O2 absorber be?

Atmospheric Composition

• Permanent gases- Nitrogen (78%)- Oxygen (21%) (*)- Argon (1%)

• Variable gases

- Water vapor (0-4%), carbon dioxide, methane, ozone (all <1%) plus others important for Earth’s temperature

*how do we know this?

QuestionComplete the following table:

Gas Symbol % (by vol) ImportanceN2 78 N-cycle

Oxygen 21

Ar 1 Inert

Water vapor 0-4 GH + Heat transport

CO2 0.04 GH + photosynthesis

Methane 0.00017 GH gas

Nitrous oxide N2O 0.00003

O3 0.000004

Particles/aerosols NA 0.000001 Energy budget

Nitrogen

Respiration

Argon

Carbon Dioxide

CH4

Ozone

GH gas

Protection from UV

The Water Cycle

• USGS image

Water Vapor

• Invisible gas, becomes visible on change to liquid and solid particles

– Condensation: Gas liquid– Evaporation: liquid gas

• Releases large amount of ‘latent heat’ on change from vapor to liquid or gas– LH is an important energy source for thunderstorms and hurricanes

• Potent greenhouse gas – absorbs outgoing radiant energy (along with CO2 etc.)

Therefore it is pretty important!!!

Greenhouse Effect and Global Warming

• What is the significance of the Keeling curve?

A good movie

What could be responsible for this up-down fluctuation?

Consequences of a Warmer World

• Sea level rise, erosion

• Weather extremes, heat waves

• Loss of biodiversity, extinction

• Drought, flooding, water stress

• Loss of forests

• Agricultural yield decrease

The Early Atmosphere

4.6 billion yrs ago:• Earth’s gravity to weak to hold hydrogen

and helium (unlike Sun, Jupiter, Saturn, Uranus)

• Earth’s present atmosphere from volcanoes (outgassing)– Water vapor condensed to form

oceans– CO2 went into oceans and rocks– N2

• Oxygen forms by break-up of water by sunlight, later from plants(photosynthesis)

Review

• The Earth’s atmosphere is a mixture of gases, ____ % nitrogen and ____% oxygen.

• Water vapor can condense into liquid cloud droplets or transform into delicate ice crystals. It is the only substance found naturally as a gas (_____ _____), a liquid (____), and a solid (____)

• Water vapor and carbon dioxide are important ___________ gases.

• The majority of water is believed to have come from the Earth’s hot interior via a process known as ____________.

Vertical Structure of the Atmosphere

• Density• Temperature• Pressure

Density

• Density = mass/volume

• High density means lots of material in a small volume

• Air density decreases with height exponentially

• Air density near surface: 1kg/m3 (2 lb/yd3)

• Liquid water density is 1000 kg/m3 (1700 lb/yd3)

Questions

1. If the density of water is 1000 kilograms per cubic meter, then how may kilograms of water will there be in a glass container having a volume of 5 m3?

2. Why are there more air molecules near the ground than higher in the atmosphere?

Density = mass / volume

Mass = Density x Volume = 1000 kg / m3 x 5 m3

= 5000 kg

Gravity

Pressure

• Pressure = force/area

• Mean sea level pressure of air

= 15 lb/sq in

= 30 in. Hg (inches of mercury)

= 1013 mb (millibars)(units used on TV) = 1013 hPa (hectopascals) (metric system)

* Where force = mass x gravity

Question

• Which exerts more pressure, a 4000 lb elephant standing on one leg with a foot size of 8" x 8" or a 120 lb woman standing on one leg in high-healed shoes with a heal size of 1"x1"?

P = F/A4000/64 = 62.5 p.s.i120/1 = 120 p.s.iso the woman exerts more pressure

Temperature

• How do you think temperature varies with height????

Why are these L.R’s not equal?Temperature

Ht.

Layers of the Atmosphere

• Hot top: oxygen absorbs sunlight

• Warm middle: ozone absorbs ultraviolet (UV)

• Warm surface: surface absorbs sunlight

• (pp. 9-11)

Troposphere - ‘Weather Breeder’

• extends from surface to about 10-12 km

• top of troposphere is called the tropopause-separates troposphere from stratosphere

• where all the weather occurs - ‘weather breeder’

• Inherently unstable - what does "unstable" mean?

• rate of temperature decrease is about 6.5 degrees Celsius per 1 km (called the lapse rate)

• higher in summer, lower in winter– tropopause height is proportional to mean tropospheric temperature

• find the tropopause with real data (see CW1)

Stratosphere - ‘Sun Screen’

• Extends from the tropopause to about 50 km

• Contains the ozone (O3) layer

– peak concentrations are at about 20-30 km

• Temperature increases with height (Inversion Layer)

Questions

1. Why does the temperature increase with height in the stratosphere?

2. Are inversion layers (and therefore the stratosphere) stable or unstable?

Ozone absorbs ultraviolet radiation (UV), reaction gives off heat energy.

The ozone then reemits this energy in the form of heat into the stratosphere, warming it up in the mid-upper parts of the layer.

Radiosonde: Weather Balloon

• $75 - $100 for balloon and instruments

• Instruments hang 75 feet below balloon, measures temperature, pressure and relative humidity

• Winds: track balloons radio• Has a radio transmitter• Balloon pops over 15 mi up

(30 km), parachutes down, some recovered

• Very expensive!

Vertical Profile Based on Composition

• Homosphere - N2 and O2 are uniformly mixed

• Heterosphere - N2 and O2 are not uniformly mixed

Classification: temperature, composition, electrical properties

Questions

1. If there were no ozone layer, sketch the vertical distribution of temperature from 0-120 km

2. The mean lapse rate of the troposphere is 6.5°C per km. If the surface temperature is 30°C, what is the temperature at the top of Mt. Everest which is 9 km above the surface?

3. If the surface temperature is 30°C and the temperature at the top of Mt. Everest is -30°C, what is the lapse rate?

Why are these L.R’s not equal?

Mesopause

Thermosphere

Temperature

Ht.

-28.5 °C

6.7 ºC/km

Review

• Atmospheric pressure represents the total mass of air above that level, and atmospheric pressure always ____________ with increasing height.

• The atmosphere may be divided into layers (or regions) according to its vertical profile of temperature, its gaseous composition, or its electrical properties.

• Ozone at the earth’s surface is the main ingredient of _____________ smog, whereas ozone in the stratosphere protects life on earth from the sun’s harmful ______________ rays.

Weather and Climate

• Weather: condition of atmosphere at any particular time or place

- Temperature, pressure, humidity, clouds, precipitation, visibility, wind

• Climate = weather statistics

• Climatological normals: average over last 30 years (1961 – 1990)

Brief History of Meteorology*

Date Event

ca. 340 BC Aristotle writes Meteorologica

1597 Galileo invents the thermometer

1643 Toricelli invents the barometer

1843 Morse invents the telegraph

post-WWII RADAR used to detect cloud

1950 1st computer forecast

1960 ‘TIROS 1’ first weather satellite launched

(*Meteoros = high in the air)

The study of the atmosphere and its phenomena

Storms of All Sizes

Mid-latitude storms, Hurricanes, Thunderstorms, Tornado (too small for satellite photo)

Hurricane

Thunderstorm

Mid-latitude storm

Question

Spatial Scale Phenomena

1 cm ~ ½ in Wind Gust

1 m ~ 3 ft

1 km ~ ½ mile

10 km ~ 6 miles Sea Breeze

100 km ~ 60 miles

1000 km ~600 miles

Complete the following table

Tornado

Hurricane

Mid-Latitude Storm

Thunderstorm

Thunderstom development along a cold frontThunderstom development along a cold front