Atmospheric Forces, Circulation, and Moisture

Vocabulary flashcards covering wind mechanics, pressure systems, atmospheric circulation cells, humidity, and adiabatic lapse rates.

Wind

Horizontal movement of air caused by differences in atmospheric pressure.

Pressure Gradient Force (PGF)

Force that drives air from high toward low pressure; greater pressure differences over shorter distances produce stronger winds.

Coriolis Force

Apparent deflection of moving air caused by Earth's rotation; deflects to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.

Friction

Force that slows wind near Earth's surface, reducing the Coriolis effect.

Gravity

Force that pulls air toward Earth and contributes to atmospheric pressure.

Isobars

Lines connecting areas of equal atmospheric pressure; closely spaced isobars indicate stronger winds.

Geostrophic Wind

Wind that flows parallel to isobars when the pressure gradient force and Coriolis force balance.

Primary Circulation

Large-scale global wind patterns.

Secondary Circulation

Moving high- and low-pressure systems.

Tertiary Circulation

Local winds and short-term weather patterns.

Cyclone

Low-pressure system where surface air converges and rises, often producing cloudy, wet weather.

Anticyclone

High-pressure system where surface air diverges and sinks, often producing clear, dry weather.

Convergence

Air moving together toward a central area, forcing air upward.

Divergence

Air spreading outward from an area.

Subsidence

Sinking air that compresses and warms, reducing cloud formation.

Northern Hemisphere Rotation

Cyclones rotate counterclockwise; anticyclones rotate clockwise.

Southern Hemisphere Rotation

Cyclones rotate clockwise; anticyclones rotate counterclockwise.

Hadley Cell ($0\text{--}30^\circ$)

Atmospheric circulation pattern where warm air rises near the equator, moves poleward, and sinks near $30^\circ$ latitude.

Ferrel Cell ($30\text{--}60^\circ$)

Midlatitude atmospheric circulation associated with prevailing westerlies.

Polar Cell ($60\text{--}90^\circ$)

Atmospheric circulation pattern where cold air sinks at the poles and moves toward $60^\circ$ at the surface.

ITCZ (Intertropical Convergence Zone)

Low-pressure zone near the equator where trade winds converge, causing rising air and heavy precipitation.

Equatorial Low

Low-pressure belt near $0^\circ$ where warm air rises.

Subtropical High

High-pressure belt near $30^\circ$ where air sinks, creating dry conditions.

Subpolar Low

Low-pressure belt near $60^\circ$ where air rises and produces unsettled weather.

Polar High

High-pressure region near the poles where cold, dense air sinks.

Trade Winds

Surface winds blowing toward the equator from the northeast in the Northern Hemisphere and southeast in the Southern Hemisphere.

Prevailing Westerlies

Winds blowing generally west to east between $30^\circ$ and $60^\circ$ latitude.

Polar Easterlies

Winds blowing generally east to west near the poles.

Jet Streams

Fast-moving upper-atmosphere winds that influence weather systems.

Seasonal Shift of the ITCZ

The migration of the Intertropical Convergence Zone north during Northern Hemisphere summer and south during Southern Hemisphere summer.

Humidity

Amount of water vapour in the air.

Relative Humidity (RH)

Percentage showing how close air is to saturation at its current temperature.

Saturation

State reached when air achieves $100\%$ relative humidity.

Dew Point ($T_d$)

Temperature at which air becomes saturated and condensation can begin.

Condensation

Phase change where water vapour turns into liquid water, releasing latent heat.

Evaporation

Phase change where liquid water changes into water vapour, absorbing latent heat.

Latent Heat

Energy absorbed or released during a change of state.

Condensation Nuclei

Tiny particles, such as dust, that water vapour condenses onto.

Collision and Coalescence

Process where cloud droplets collide and combine into larger droplets that may eventually fall as rain.

Precipitation (P or PPT)

Liquid or solid water that falls from clouds toward Earth's surface.

Adiabatic Process

Temperature change without adding or removing heat from an air parcel.

Adiabatic Cooling

Cooling that occurs when rising air expands as pressure decreases, causing its temperature to drop.

Adiabatic Warming

Warming that occurs when sinking air compresses as pressure increases, causing its temperature to rise.

Environmental Lapse Rate (ELR)

Average atmospheric temperature decrease of approximately $6.5^\circ\text{C/km}$.

Dry Adiabatic Lapse Rate (DALR)

Rate at which unsaturated rising air cools, approximately $10^\circ\text{C/km}$.

Moist Adiabatic Lapse Rate (MALR)

Rate at which saturated rising air cools, approximately $6^\circ\text{C/km}$. Condensation releases latent heat, offsetting some of the cooling.