Meteorology – Core Vocabulary

A comprehensive set of vocabulary flashcards covering the key meteorological terms, phenomena and instruments discussed in the lecture notes. Use these cards to reinforce definitions and core concepts ahead of the exam.

Rotation of the Earth

Daily west-to-east spin on its N-S axis that creates day-night cycles.

Orbit of the Moon

Anti-clockwise revolution around Earth every ≈27½ days; main cause of tides.

Orbit of the Earth

Anti-clockwise, elliptical revolution around the Sun taking ≈365 days.

Tilt of the Earth

23.5° inclination of Earth’s axis that produces the seasons.

Seasons

Periodic changes (equinoxes & solstices) caused by Earth’s axial tilt.

Sun’s Energy

Uneven solar heating of Earth’s surface that drives weather patterns.

Troposphere

Lowest atmospheric layer (≈16 km at equator, 6 km at poles) where all weather occurs.

Conduction

Heat transfer by molecular contact; most effective in solids at Earth’s surface.

Convection

Heat transfer by movement of fluids; warm, less-dense air rises, cool air sinks.

Radiation

Heat transfer by electromagnetic waves; allows energy flow through a vacuum.

Atmospheric Physics

Interplay of pressure, temperature, density, water vapour and air motion controlling weather.

Density (air)

Molecules per unit volume; decreases with altitude.

Atmospheric Pressure

Weight of a column of air above a unit area; measured in millibars.

Average Sea-Level Pressure

Standard value of 1013.25 mb.

Isobar

Line on a synoptic chart joining points of equal pressure.

Pressure Gradient

Rate of pressure change over distance.

Pressure Gradient Force

Net force pushing air from high toward low pressure.

Barometer

Instrument that measures atmospheric pressure (mercury, water or aneroid).

Aneroid Barometer

Portable barometer using a sealed metallic cell instead of liquid.

Barograph

Recording aneroid barometer producing a barogram of pressure over time.

Altitude Correction

Add 1 mb per 10 m the barometer sits above sea level.

Index Error (barometer)

Manufacturer or calibration error corrected by comparison with a reference instrument.

Dry Adiabatic Lapse Rate

Temperature drops 1 °C per 100 m ascent for unsaturated air.

Wind

Horizontal movement of air produced by the Pressure Gradient Force.

Coriolis Force

Apparent deflection of moving air due to Earth’s rotation (right in NH, left in SH).

High-Pressure System (Anticyclone)

Area of highest pressure; clockwise flow in NH, fair weather and light winds.

Low-Pressure System (Cyclone)

Area of lowest pressure; counter-clockwise flow in NH, cloudy, windy, wet weather.

Geostrophic Wind

Upper-air wind that flows parallel to straight isobars where PGF equals Coriolis force.

Boundary Layer Wind

Surface wind modified from geostrophic flow by friction within the lowest 1–2 km.

Land Breeze

Night-time offshore flow caused by faster cooling of land than water.

Sea Breeze

Day-time onshore flow caused by faster heating of land than water.

Buys Ballot’s Law

With wind at your back, low pressure lies 90–130° to the left (SH) or right (NH).

Anemometer

Device for measuring wind speed; fixed or hand-held.

Single-Cell Model

Ideal, non-rotating Earth circulation with one convection cell per hemisphere.

Hadley Cell

Tropical convection cell between equator and ≈30°, rising at ITCZ, sinking at subtropical highs.

Ferrel Cell

Mid-latitude cell between 30° and 60°, powered by adjacent cells.

Polar Cell

High-latitude cell with sinking air at poles and rising air near 60°.

Intertropical Convergence Zone (ITCZ)

Equatorial zone of low pressure and converging trade winds; shifts seasonally.

Trade Winds

Persistent NE (NH) and SE (SH) surface winds blowing toward the ITCZ.

Prevailing Westerlies

Surface winds from the west in mid-latitudes (30–60°).

Polar Easterlies

Cold surface winds blowing from the east near the poles.

Air Mass

Large body of air with uniform temperature and moisture characteristics.

Maritime Air Mass (m)

Moist air mass formed over oceans.

Continental Air Mass (c)

Dry air mass formed over land.

Equatorial Air Mass (E)

Hot, humid air mass originating near the equator.

Tropical Air Mass (T)

Warm air mass formed in the tropics.

Polar Air Mass (P)

Cool to cold air mass from higher latitudes.

Arctic/Antarctic Air Mass (A)

Very cold, dry air from polar regions.

Humidity

Amount of water vapour in a mass of air.

Saturation

State when air holds maximum possible water vapour at a given temperature.

Relative Humidity

Ratio of actual water vapour to saturation amount, expressed as a percentage.

Dew Point

Temperature to which air must be cooled at constant pressure to become saturated.

Hygrometer

Instrument for measuring humidity (wet- and dry-bulb thermometers).

Condensation Nuclei

Tiny particles (dust, salt, smoke) around which water vapour condenses.

Orographic Lift

Rising of air forced over mountains, leading to cooling and cloud formation.

Frontal Lift

Warm air forced upward over a colder air mass at a front.

Convergence Lift

Air uplift created where surface winds meet in a low-pressure area.

Thermal (Convection) Lift

Rising of warm surface-heated air parcels.

Turbulence Lift

Mechanical eddies over rough surfaces that push air upward.

Cloud Classification – Cumulus

Heap-shaped clouds with cauliflower tops.

Cloud Classification – Stratus

Featureless layer clouds forming sheets.

Cloud Classification – Cirrus

High, wispy ‘hair-like’ ice clouds.

Cloud Classification – Nimbus

Rain-bearing, dark grey clouds.

Low Clouds

Base from surface to 2 000 m: St, Sc, Ns.

Medium Clouds

Base 2 000–5 500 m: Ac, As.

High Clouds

Base 5 500–14 000 m: Ci, Cc, Cs.

Cumulonimbus (Cb)

Towering thunderstorm cloud with anvil top, producing heavy rain and hail.

Visibility

Greatest distance an object can be seen with the unaided eye.

Fog

Cloud with base on/near ground that lowers visibility below 1 000 m.

Advection (Sea) Fog

Moist warm air cooled by contact with a cold surface, often along coasts.

Radiation Fog

Night-time fog from radiational cooling of the ground and adjacent air.

Frontal (Precipitation) Fog

Fog formed as rain evaporates into cooler underlying air at a front.

Valley Fog

Cold, dense air draining into valleys and reaching saturation.

Upslope Fog

Air cooled adiabatically as it glides up a slope.

Arctic Sea Smoke

Steam-like fog when very cold air moves over warmer water.

Precipitation

Liquid or solid water particles falling to the ground from clouds.

Collision-Coalescence

Warm-cloud process where larger droplets grow by colliding with smaller ones.

Ice-Crystal (Bergeron) Process

Cold-cloud mechanism where ice crystals grow at expense of super-cooled droplets.

Rain

Liquid water drops >0.5 mm diameter falling from clouds.

Drizzle

Very small, closely spaced water droplets (<0.5 mm).

Snow

Ice crystals that fall as flakes.

Sleet

Frozen raindrops or ice pellets.

Hail

Balls/lumps of ice formed in vigorous updrafts of thunderstorms.

Glazed Frost

Smooth ice coating from freezing rain.

Dew

Liquid water condensed on surfaces cooled to dew point.

Hoar Frost

Ice crystals deposited directly from vapour on cold surfaces.

Rime

White granular ice formed by freezing fog droplets on cold objects.

Thunderstorm

Storm with cumulonimbus clouds, lightning, thunder, heavy rain, squalls.

Towering Cumulus Stage

First thunderstorm phase with updrafts and growth up to ≈6 km.

Mature Stage (Thunderstorm)

Peak phase with strong up- & downdrafts, hail, severe winds, heavy rain.

Dissipating Stage

Final phase where downdrafts dominate and storm weakens.

Lightning

Visible electrical discharge within cloud or to ground.

Thunder

Sound from rapid air expansion along lightning channel.

Monsoon

Seasonally reversing wind system with corresponding rainfall changes.

Winter Monsoon

High pressure over land drives cool, dry offshore winds.

Summer Monsoon

Low pressure over heated land draws moist onshore winds causing heavy rain.

Front

Boundary separating two differing air masses.

Stationary Front

Almost motionless front where air flows parallel to the boundary.

Cold Front

Cold air advancing under warm air; marked by blue spikes on charts.

Warm Front

Warm air overrunning retreating cold air; shown with red semicircles.