• Absolute Humidity:: The amount of water vapour in the air at any given time e.g 6 grams in a cubic metre of air. See Humidity
  • Accretion:: Process by which water droplets stick with ice in a cloud causing the ice to become bigger. Responsible for hail formation.
  • Adiabatic Lapse Rate:: This shows the rate at which an air parcel’s temperature decrease if lifted or increase if it descends. See Lapse Rates
  • Adiabatic Temperature Change:: Temperature changes occurring within an air parcel without the addition or subtraction of heat. Pressure changes are inversely proportional to temperature, high pressure => low temperatures, low pressure => high temperature.
  • Advection:: When warm air parcels move along a cold surface causing them to be cooled to dew point temperature. Occurs mainly along coasts where differential heating of ocean and land exists.
  • Advection Fog:: A type of fog found along coasts formed when warm air parcels condense along a cold surface.
  • Aggregation:: Partially melted ice crystals with their liquid coating stick with solid ice crystals forming hexagonal snowflakes. Responsible for snow formation.
  • Albedo:: The reflectivity of a surface.
  • Air Mass:: A large body of air whose characteristics temperature, pressure and humidity are acquired from source region and placed in the path of movement. See air masses.
  • Altitude:: Height above sea level.
  • Altocumulus:: A middle level cloud with a white grey appearance and a layered puffy structure.
  • Altostratus:: A uniform grey or bluish, middle level cloud that often covers the whole sky. A glimpse of the sun is seen. Drizzles are common with this type of cloud.
  • Anabatic Wind:: A warm air rising up a mountain.
  • Anticyclone:: An area of high pressure where winds converge at high elevations, descend and then diverge on the surface. Characterized by stable weather conditions.
  • Collision Coalescence:: The process whereby small and large water droplets collide and join (coalesce) together in a cloud. See Collision Coalescence
  • Chlorofluorocarbon:: Abbreviated as CFC. An ozone depleting compound of chlorine, fluorine and carbon. Often used in refrigerants and aerosol propellants.
  • Cirrocumulus:: An uncommon high level cloud with thin broken ripples. Usually these clouds are remnants of cirrus or cirrostratus.
  • Cirrostratus:: A high level cloud appearing as a milky white veil. Very thin and almost transparent and often producing a halo effect.
  • Cirrus:: The highest level cloud with a wispy and feathery filament appearance. Mostly composed of ice crystals.
  • Climate:: The prevailing weather conditions of a broad area over a given period of time (30-50 years).
  • Climate Change:: A long term shift of global temperature
  • Cold Front:: When cold air moves in an area formerly occupied by warm air. See fronts
  • Condensation:: A process whereby water vapour (gas) changes into liquid. See condensation
  • Condensation Nuclei:: Minute particulates such as dust and ash found in the atmosphere which where water vapour accumulate to form tiny water droplets.
  • Conditional Instability:: This occurs when the environmental lapse rate is lower (cooling at a slower rate) than the DALR (cooling at a first rate) but higher than the saturated adiabatic lapse rate (cooling at a lower rate). See Stability and Instability
  • Conduction:: The transfer of heat through matter from high to low pressure.
  • Convection:: The process by which air parcels are heated by the earth’s surface causing them to become lighter, rises and cools.
  • Convectional Rainfall:: A type of rainfall where air parcels are heated by the earth’s surface causing them to become lighter, rises, cools and condenses producing towering cumulonimbus clouds with heavy rainfall.
  • Convergence:: A type of rainfall whereby two bodies of air usually originating from the sea rises together on a low pressure area usually over land.
  • Coriolis Effect:: A type of force caused by the rotation of earth which deflect winds in their direction of motion. Winds are deflected left in the Southern Hemisphere and to the right in the Northern Hemisphere. See Coriolis Effect
  • Cumulonimbus:: A towering cloud of great vertical extent producing heavy rainfalls and thunderstorms
  • Cumulus:: A middle to low-level cloud with a cauliflower appearance that grows vertically. They have a bright sharp outline and dark flat base. Often these clouds are small replicas of cumulonimbus
  • Cyclone:: System of winds that converge and rises on a low pressure area producing heavy rainfalls and unstable weather conditions.
  • Deposition:: Direct change from gas to solid.
  • De-sublimation:: See deposition
  • Dew:: A type of precipitation where water vapour condenses into droplets on a cold surface. See Dew
  • Dew Point Temperature:: The temperature needed for an air parcel to be saturated.
  • Drizzle:: Fine and light rainfall.
  • Dry Adiabatic Lapse Rate:: The decrease in temperature of air parcels with height. The rate of decrease is 9.8oC/1000m. See DALR
  • Environmental Lapse Rate:: The decrease in temperature of the atmosphere (in the troposphere) as we ascend high.
  • Exosphere:: The outer space.
  • Ferell Cell:: The cell lying between the Hardley and Polar cell. See Tricellular Model
  • Fog:: A ground level cloud with a visibility of less than 1 km.
  • Fohn Wind:: A hot and dry wind found on the leeward side of a mountain formed from descending and compressing air. See Fohn Wind
  • Front:: Boundary separating two air masses of different densities and characteristics. See Weather Fronts
  • Frontal Rainfall:: A type of rainfall where one air mass (cold or warm) is forced on top of another resulting in condensation. Rainfall intensity vary depending on the type of front. See Fronts
  • Freezing:: Change of state from liquid to solid.
  • Frost:: Ice crystals formed on a surface below freezing point from the deposition of water vapour.
  • Geostrophic Wind:: When wind flows parallel to the isobars caused by a balance between the Coriolis force and the PGF. See Geostrophic Winds
  • Glaze:: An even glassy appearance caused by the freezing of rainwater on a freezing surface. See Precipitation on Ground Level
  • Global Warming:: The intense increase in global temperatures caused by an enhanced greenhouse.
  • Greenhouse Effect:: A layer of gases in the atmosphere surrounding the earth which allows incoming shortwave radiation to pass but refracts and retains outgoing longwave radiation. See Greenhouse Effect and Global Warming
  • Hail:: Rainfall with stone-like ice usually ranging from 4mm-5mm. Typically formed in cumulonimbus cloud with high convectional currents. See Precipitation
  • High Pressure:: See Anticyclone
  • Hoar:: A type of frost formed when water vapour directly changes into ice crystals (deposition) on a surface below freezing point. Can be referred to as frost only.
  • Humidity:: The water vapour (moisture) content in the atmosphere. See Humidity
  • Hurricane:: A tropical storm originating from the Atlantic Ocean. This is the term used in the Caribbean and North America.
  • Ice:: The solid form of liquid.
  • ITCZ:: A belt of low pressure that move relative to the sun where North and South easterly trade winds meet. See ITCZ
  • Kanabatic Wind:: A cold wind that descends down a mountain.
  • Land Breeze:: A phenomenon where a cool wind blows from the high pressure sea to low pressure land.
  • Latent Heat:: The heat used to change the state of a substance without altering its temperature.
  • Leeward:: The side of a mountain where moisture deprived air descends causing high temperatures and dryness.
  • Longwave Radiation:: The outgoing terrestrial radiation from the earth in the longwave form.
  • Low Pressure:: Characterised by unstable weather conditions and high temperatures.
  • Mesosphere:: The third layer (going up) of the atmosphere is characterised by very low temperatures. The upper boundary is referred to as mesopause. See Atmosphere Structure
  • Mist:: A thin fog with visibility of more than a kilometre. See Mist
  • Nimbostratus:: A low level, expansive, dark grey cloud characterised by heavy prolonged rainfalls.
  • Ocean Currents:: The huge movement of water in the ocean which transports warm water from the equator to the poles and vice versa. Responsible for distributing heat to areas of heat deficit.
  • Orographic Rainfall:: A type of rainfall where moist air usually originating from the ocean rises cools and condenses producing heavy rainfalls on the windward side.
  • Ozone:: An oxygen molecule containing three oxygen atoms that is found in the stratosphere; responsible for trapping the dangerous ultraviolet radiation from reaching the earth. See Ozone and Its Significance
  • Photochemical Smog:: A toxic smog formed when particulates in the atmosphere react with sunlight.
  • Precipitation:: Any form of water deposition originating on or above the earth’s surface. See Precipitation Types and Precipitation on Ground
  • Pressure Gradient:: The initial driving force of wind. Closely spaced isobars result in a steep (high) PGF thus high wind speeds while a weak PGF is caused by widely spaced isobars.
  • Radiation:: Earth’s surface absorb solar radiation which in turn returns and heat the air above it.
  • Rainfall:: The process whereby water droplets fall to the surface.
  • Rime:: A type of frost where supercooled water droplets freeze on top of one another on a freezing object. This creates a feathery appearance of ice on the windward side of the object. See Rime

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