Atmosphere, Climate, and Ocean Circulation

Why is the atmosphere important to oceanography?

It controls heat budgets, drives the hydrologic cycle, exchanges gases, and generates winds.

Why can oceans store so much heat?

Water has a high heat capacity and high latent heat of evaporation.

What are the three major layers of the atmosphere?

The troposphere (weather), stratosphere (ozone), and mesosphere.

What causes ozone depletion?

Chlorofluorocarbons (CFCs).

What is saturation vapor pressure?

The maximum amount of water vapor air can hold; increases with temperature.

Why is moist air less dense than dry air?

Water molecules are lighter than nitrogen and oxygen molecules, making moist air rise.

What is adiabatic cooling?

Cooling that occurs as rising air expands under decreasing pressure without heat exchange.

Why does precipitation form when air rises?

Rising air cools, lowering saturation vapor pressure until condensation and clouds form.

What is latent heat?

Energy released when water vapor condenses into liquid water (~540 cal/g).

Why is latent heat important?

It warms surrounding air, causing further rising and powering storms and hurricanes.

What is Earth's heat budget?

The equilibrium where incoming solar energy equals outgoing infrared energy.

Why is there a latitudinal heat imbalance?

The high angle of incidence at the equator causes heat gain; the poles lose heat.

How is heat transferred from the equator to the poles?

Through atmospheric winds, latent heat transport, and ocean currents.

What force initiates wind?

Pressure Gradient Force (PGF).

What is the Pressure Gradient Force?

The force driving wind from high pressure to low pressure areas.

What are the four forces governing winds?

Pressure Gradient Force, Coriolis Force, Centrifugal Force, and Friction.

What causes the Coriolis Effect?

Earth's rotation.

How does the Coriolis Effect deflect motion?

To the right in the Northern Hemisphere; to the left in the Southern Hemisphere.

Where is Coriolis strongest?

At the poles.

Where is Coriolis weakest?

At the equator, where it is zero.

What two variables determine Coriolis acceleration?

Velocity and latitude.

What are the three atmospheric circulation cells?

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

What happens in the Hadley Cell?

Air rises at the equator, sinks at 30°, and produces the Trade Winds.

What happens in the Ferrel Cell?

It produces the Prevailing Westerlies.

What happens in the Polar Cell?

It produces the Polar Easterlies.

What are the major planetary winds?

Trade Winds (0-30°), Westerlies (30-60°), and Polar Easterlies (60-90°).

Why are Trade Winds called easterlies?

Because they blow from the east.

What is the ITCZ?

Intertropical Convergence Zone: low salinity, rising air, and heavy rain near the equator.

What are the doldrums?

The calm wind region associated with the ITCZ.

What are the horse latitudes?

Dry, high-pressure zones around 30° latitude with sinking air.

What pressure belts occur with latitude?

Low at 0° and 60°; High at 30° and 90°.

What is geostrophic balance?

The balance between the Pressure Gradient Force and the Coriolis Force.

How do geostrophic winds flow?

Parallel to isobars.

What is a cyclone?

A low-pressure system (counterclockwise in Northern Hemisphere, clockwise in Southern Hemisphere).

What is an anticyclone?

A high-pressure system (clockwise in Northern Hemisphere, counterclockwise in Southern Hemisphere).

What does ENSO stand for?

El Niño Southern Oscillation.

How often does ENSO occur?

Every 3-5 years.

What are normal Pacific conditions?

Strong trade winds, warm water near Indonesia, and high productivity upwelling off Peru.

What happens during El Niño?

Trade winds weaken, warm water moves east, upwelling stops, and Peru receives rain.

What happens during La Niña?

Trade winds strengthen, upwelling increases, and the eastern Pacific becomes cooler.

What drives surface circulation?

Wind.

What part of the ocean is affected by wind-driven circulation?

The upper ~200 meters.

What is a gyre?

A large rotating ocean current system.

How do subtropical gyres rotate?

Clockwise in the Northern Hemisphere; counterclockwise in the Southern Hemisphere.

How do subpolar gyres rotate?

Counterclockwise in the Northern Hemisphere.

What is the Ekman Spiral?

A current spiral caused by friction and Coriolis deflection that decreases in speed with depth.

What direction does the surface current move relative to wind?

About 45° from the wind direction.

What direction is net Ekman transport?

90° right in the Northern Hemisphere; 90° left in the Southern Hemisphere.

What causes convergence?

Water masses moving together.

What happens at convergence zones?

Water piles up and downwelling occurs.

What causes divergence?

Water masses moving apart.

What happens at divergence zones?

Water rises and upwelling occurs.

Why is upwelling important?

It brings cold, nutrient-rich water to the surface, boosting biological productivity.

Where does major upwelling occur?

At the equator, Peru coast, and other eastern boundary regions.

What causes sea surface height differences?

Wind-driven Ekman transport.

Why is sea level elevated in subtropical gyres?

Water converges and piles up in the center.

What force pushes water outward from a sea surface mound?

Pressure Gradient Force.

Why doesn't the subtropical gyre mound collapse?

The Coriolis force balances the pressure gradient, producing geostrophic flow.

How do geostrophic currents flow?

Parallel to pressure contours.

What is westward intensification?

Western boundary currents become faster, narrower, and stronger.

Why does westward intensification occur?

Because the Coriolis force increases with latitude.

What is the best example of westward intensification?

The Gulf Stream.

Which currents are warm western boundary currents?

The Gulf Stream and the Kuroshio Current.

Which currents are cold eastern boundary currents?

The California, Canary, and Peru Currents.

What does thermohaline mean?

Thermo = temperature; Haline = salinity.

What is thermohaline circulation?

Global circulation driven by density differences, also called Meridional Overturning Circulation.

What drives deep circulation?

Density differences.

What increases seawater density?

Lower temperature and higher salinity.

Why can deep water only form in polar regions?

Cooling increases density to cause sinking; heating cannot cause sinking.

What processes increase density?

Cooling, evaporation, and sea-ice formation.

What is brine rejection?

Salt exclusion during ice formation, which increases water salinity and density.

What is AABW?

Antarctic Bottom Water: the densest, coldest water mass, formed in Weddell/Ross seas.

What is NADW?

North Atlantic Deep Water: forms in Greenland/Norwegian/Labrador seas and drives AMOC.

What is AIW?

Antarctic Intermediate Water: cold, fresh, salinity-minimum water formed near 50°S.

What is Mediterranean Intermediate Water?

Warm, highly saline water exiting the Mediterranean at ~1000 m depth.

What is AMOC?

Atlantic Meridional Overturning Circulation: northward surface heat transport and southward deep return.

Why is AMOC important?

It transports heat toward northern latitudes and regulates climate.

How can climate change weaken AMOC?

Freshwater input lowers salinity and density, preventing deep-water sinking.