EVS Test 2 Atmosphere

Atmosphere (current composition)

78% nitrogen (N₂), 21% oxygen (O₂), ~1% argon (Ar), CO₂ (~0.04%), and trace gases.

Early atmosphere

Formed from volcanic outgassing; mostly CO₂, water vapor, ammonia, and methane, with little to no oxygen.

Atmospheric layers

Troposphere, Stratosphere, Mesosphere, Thermosphere, Exosphere

Troposphere

• Altitude: 0–12 km (varies with latitude and season)

• Features: The lowest layer, where we live and where weather happens (clouds, rain, storms).

• Temperature: Decreases with altitude.

• Contains: About 75–80% of the atmosphere’s mass and almost all water vapor.

stratosphere

• Altitude: ~12–50 km

• Features: Contains the ozone layer, which absorbs harmful UV radiation.

• Temperature: Increases with altitude (due to ozone absorbing sunlight).

• Aircraft: Some jet planes and weather balloons fly here.

mesosphere

• Altitude: ~50–85 km

• Features: The layer where meteors burn up upon entering Earth’s atmosphere.

• Temperature: Decreases with altitude — coldest layer of the atmosphere.

thermosphere

• Altitude: ~85–600 km

• Features: Very thin air; auroras (Northern and Southern Lights) occur here.

• Temperature: Increases sharply with altitude (can reach up to 2,500°C or more, but it wouldn’t feel hot due to low particle density).

• Contains: The ionosphere, important for radio communication.

exosphere

• Altitude: ~600–10,000 km (gradually fades into outer space)

• Features: The outermost layer where atoms and molecules escape into space.

• Satellites: Many orbit within this region.

tropopause

Boundary between the troposphere and stratosphere; defined where temperature stops decreasing with height.

vapor pressure

The pressure exerted by water vapor molecules in the air.

saturation vapor pressure

The maximum water vapor pressure possible at a given temperature; increases with temperature.

relative humidity (RH)

(Actual vapor pressure ÷ Saturation vapor pressure) × 100%.

Dew point

The temperature to which air must cool to become saturated (RH = 100%).

Pressure Gradient Force

Force that causes air to move from high to low pressure.

Coriolis Force

Apparent deflection of moving air due to Earth's rotation: right in the Northern Hemisphere, left in the Southern.

geostrophic wind

Wind resulting from balance between PGF and Coriolis force; flows parallel to isobars.

Jet Streams

Fast upper-atmosphere winds flowing west to east (westerlies), formed by strong horizontal temperature gradients.

High Pressure

Descending air → clear, fair weather.

low pressure

Rising air → condensation and cloudy/rainy weather.

global circulation cells

Hadley (0–30°), Ferrel (30–60°), Polar (60–90°).

monsoons

Seasonal reversal of winds due to differential heating of land and ocean.

sea breeze

Daytime coastal wind from ocean to land as land heats faster.

santa ana winds

Warm, dry downslope winds in California caused by high-pressure air descending from inland.

What happens to relative humidity when temperature rises but moisture content stays constant?

RH decreases, because saturation vapor pressure increases with temperature.

You see tightly packed isobars on a map — what does this indicate?

A strong pressure gradient force → stronger surface winds.

How does the Coriolis effect influence cyclones?

In the Northern Hemisphere, they rotate counterclockwise; in the Southern, clockwise.

Why are deserts common near 30°N and 30°S?

Descending dry air in Hadley cell creates high-pressure zones with little precipitation.

Why are the tropics persistently cloudy?

Rising warm, moist air near the equator cools and condenses — upward branch of the Hadley cell.

How do jet streams affect weather?

They steer weather systems and mark boundaries between warm and cold air masses.

How do sea breezes form daily?

Land heats faster → warm air rises over land → cooler air from ocean moves in to replace it.

Why do monsoons bring heavy rain in summer?

Warm land pulls in moist ocean air, which rises and condenses over land.