Atmospheric Gases, Layers, and Climate: Key Concepts for Students

What is the difference between permanent and variable gases?

Permanent gases occur in nearly the same proportions across space and time and have long residence times. Variable gases have concentrations that change across space and time and generally have shorter residence times.

What are the main permanent gases emphasized in class?

N₂, O₂, and Ar.

Why are variable gases important even though their concentrations are low?

They have some of the largest impacts on weather and climate. Important examples are H₂O and CO₂.

Why is water vapor (H₂O) important?

It exists as gas, liquid, and solid and is important to Earth's water and energy cycles.

Why is CO₂ important?

CO₂ is a greenhouse gas, making it important to Earth's energy cycle. It is added through respiration, volcanic activity, decay, and combustion and removed through photosynthesis and dissolving in ocean water.

What are aerosols?

Solid or liquid particles suspended in the atmosphere. They can absorb and reflect sunlight and act as condensation nuclei for precipitation.

What are the four atmospheric layers from lowest → highest?

Troposphere → Stratosphere → Mesosphere → Thermosphere.

What happens to temperature with height in each layer?

Troposphere → ↓

Stratosphere → ↑

Mesosphere → ↓

Thermosphere → ↑

Where does virtually all weather occur?

Troposphere.

Why does the stratosphere get warmer with height?

Ozone absorbs ultraviolet radiation, warming the upper stratosphere.

What happens to atmospheric pressure and density as altitude increases?

Both decrease exponentially with height

What is atmospheric pressure?

The weight of the air in the column above a location.

Why is most of the atmosphere close to Earth's surface?

Gravity pulls gases toward Earth, and gases are compressible, so air is denser near the surface.

What is hydrostatic balance?

The upward pressure-gradient force balances the downward gravitational force.

What relationships does the Ideal Gas Law show?

Pressure and density → direct relationship.

Pressure and temperature → direct relationship.

Density and temperature → inverse relationship.

What are the three methods of energy transfer?

Conduction, convection, radiation.

What is conduction?

Molecules transfer energy by colliding with each other when objects are touching.

What is convection?

A fluid moves from one location to another and carries heat energy with it.

What is radiation?

Energy transfer that does not require matter and can travel through space as electromagnetic waves.

Convection vs. advection in atmospheric science?

Convection = vertical movement of air. Advection = horizontal movement.

What does the First Law of Thermodynamics say?

Energy can be stored, moved, and transformed, but the total amount of energy never changes.

What does the Second Law of Thermodynamics say in these notes?

Energy flows "downhill" from highly concentrated/hot forms toward dilute/cold forms.

Stefan-Boltzmann Law?

F = σT⁴

The amount of radiation emitted increases dramatically with temperature.

If an object's absolute temperature doubles, how does its emitted radiation change?

16× greater, because 2^4=16.

Wien's Law?

λmax = b/T

As temperature ↑, peak wavelength ↓.

Hotter objects emit at _____ wavelengths and emit _____ energy.

Shorter wavelengths; more energy.

What type of radiation does the Sun primarily emit?

Shortwave/visible radiation. Peak ≈ 0.5 μm.

What type of radiation does Earth primarily emit?

Longwave/infrared radiation. Peak ≈ 10 μm

What can happen when radiation strikes an object?

t can be absorbed, reflected, or transmitted.

Conservation of radiation equation?

Incoming = absorbed + reflected + transmitted.

What does equilibrium mean for an object's energy?

Absorbed = emitted, meaning there is no temperature change.

What is albedo?

The fraction of incoming radiation that is reflected.

α = reflected / incoming.

Earth's approximate albedo used in class?

0.30 → 30% of incoming solar radiation is reflected.

Why isn't Earth's surface temperature the same as the "bare rock" calculation?

Earth's atmosphere and greenhouse effect warm the surface.

Bare-rock Earth's calculated average temperature?

255 K.

Earth's actual average surface temperature?

288 K = 15°C.

How does visible solar radiation interact with the atmosphere?

It passes almost freely through the atmosphere.

What happens to UV radiation?

It is absorbed by ozone (O₃).

What happens to Earth's emitted infrared radiation?

Some escapes through an atmospheric window, while some is absorbed by greenhouse gases, including H₂O and CO₂.

In simple terms, how does the greenhouse effect warm Earth's surface?

Sunlight passes through the atmosphere → surface absorbs energy and emits infrared → atmosphere absorbs infrared → atmosphere emits infrared upward and downward → downward radiation adds energy to the surface.

What three major things determine solar energy received at a particular location/time?

1. Earth's spherical shape

2. Earth's orbit + 23.5° axial tilt

3. Earth's rotation + day length

What is solar angle?

How directly the Sun's rays strike Earth's surface.

Why does a high solar angle produce greater heating?

Solar energy is concentrated over a smaller surface area.

Why does a low solar angle produce less heating?

The beam spreads over a larger area and experiences greater beam depletion.

Why do lower latitudes generally absorb more solar energy?

Earth's spherical shape causes sunlight to strike lower latitudes at a more direct angle.

Why does day length matter for temperature?

Longer daylight = more time to absorb solar energy.

What causes Earth's seasons?

The combination of Earth's 23.5° axial tilt and orbit, which changes solar angle and daylight hours through the year.

Four major geographic influences on annual average surface temperature?

Latitude/elevation, cloud cover/ice, land vs. water, and ocean currents.

What is temperature range?

Maximum temperature − minimum temperature.

What is temperature lag?

Temperature changes after incoming solar radiation changes because the surface continues warming while incoming energy exceeds outgoing energy.

When is solar radiation strongest during a normal day vs. when is temperature usually highest?

Solar peak ≈ noon; temperature peak ≈ 3-4 PM.

Why isn't noon usually the hottest time of day?

After noon, the surface is still receiving more energy than it loses, so it continues warming. Temperature peaks only after outgoing energy begins exceeding incoming energy.

What is weather?

Short-term atmospheric conditions at a particular place and time.

What is climate?

Long-term average patterns and variability of weather for a region.

Weather or climate: "Tomorrow's forecast calls for rain."

Weather

What does latitude measure?

Position north or south of the Equator.

What does longitude measure?

Position east or west of the Prime Meridian.

Tropic of Cancer

23.5° N

Tropic of Capricorn

23.5° S

Arctic Circle

66.5° N

Antarctic Circle

66.5° S latitude, polar region boundary.

Equator

0° latitude

Prime Meridian

0° longitude

International Date Line

Approximately 180° longitude.

Residence time equation

Residence time = amount in system ÷ rate entering or leaving system.

Approximately what percentage of the atmosphere is oxygen?

21%.

Approximately what percentage of the atmosphere is nitrogen?

78%.

What causes the yearly up-and-down pattern in atmospheric CO₂?

The seasonal cycle of photosynthesis and respiration.

Major atmospheric sink for CO₂?

Dissolving into ocean water and photosynthesis. The review's practice question specifically lists dissolving into ocean water as a removal process.

Where would you generally expect the most atmospheric water vapor: low or high latitudes?

Low latitudes, especially near the Equator, because warmer air can contain more water vapor. The review specifically tests 0° versus higher latitudes.

Common units used for atmospheric pressure?

mb (millibars), hPa, atm, psi.

What does "mb" measure?

Pressure.

Ideal Gas Law

p = ρRT

p = pressure

ρ = density

R = gas constant

T = temperature in Kelvin.

Hydrostatic equation

ΔP/Δz = −ρg

Where is the vertical pressure-gradient force strongest?

Near Earth's surface, where pressure changes most rapidly with altitude. This appears directly in the practice questions.

Rotation vs. revolution?

Rotation: Earth spinning on its axis, about once every 24 hours. Revolution: Earth orbiting the Sun, about once per year.

What is the circle of illumination?

The boundary separating Earth's daylight side from its nighttime side.

What happens during an equinox?

The Sun is directly over the Equator, and day/night are approximately equal in length.

Around when are the equinoxes?

March and September.

Northern Hemisphere summer solstice?

Around June 21; maximum NH daylight and high solar angle.

Northern Hemisphere winter solstice?

Around December 21; minimum NH daylight and low solar angle.

When does the Southern Hemisphere have its longest day?

December solstice

In what season is beam spreading greatest at a location?

Winter, because the Sun is lower in the sky and its energy spreads across a greater surface area.

Does Earth's distance from the Sun cause the seasons?

No. Seasons primarily result from Earth's 23.5° axial tilt, changing solar angle and day length.

What is sensible heat?

Energy transfer that causes a temperature change that can be measured.

What is latent heat?

Energy absorbed or released during a phase change without changing temperature.

What happens to energy during evaporation?

Water absorbs energy from the surface, cooling the surface.

What happens to latent heat during condensation?

Energy is released to the atmosphere, warming it.

Evaporation at the surface + condensation in the atmosphere causes what overall effect?

Cools the surface and warms the atmosphere.

What is heat capacity?

The amount of energy required to raise the temperature of an object by a certain amount.

What is specific heat?

The amount of energy required to raise the temperature of a given mass of a substance.

Water vs. land: which has higher specific heat?

Water. It heats and cools more slowly than land.

Electromagnetic spectrum from shortest → longest wavelength

Gamma → X-ray → UV → visible → infrared → microwave → radio

Approximate visible-light wavelength range

0.4-0.7 μm.

UV wavelength compared with visible light?

Shorter.

Infrared wavelength compared with visible light?

Longer.

What radiation does ozone in the stratosphere absorb?

Ultraviolet (UV).

What radiation do greenhouse gases primarily absorb and emit?

Infrared radiation.

A very cold object such as 3 K emits primarily what type of radiation?

Microwave.

According to the energy-budget figure, about what percentage of incoming sunlight is reflected by Earth's surface specifically?

7%. This is different from Earth's total ~30% planetary albedo; the practice question asks specifically about reflection by the surface.