The difference between births and deaths in a population. Natural change can be an increase or decrease. See Population Terminologies
Climatology Glossary Terms
A
Absolute Humidity
The amount of water vapour in the air at any given time e.g 6 grams in a cubic metre of air.
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.
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 condenses along a cold surface.
Aerosol
A substance enclosed under pressure and released by a propellant gas such as aCFC as spray
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.
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, descends and then diverge on the surface. Characterized by stable weather conditions.
A mixture of gases surrounding earth.
C
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).
When cold air moves in an area formerly occupied by warm air. See fronts
Collision Coalescence
A process of rain formation where small water droplets collide and merge together forming bigger droplets which then split again to form rain droplets. See Rainfall Formation Theories
Condensation
A process whereby water vapour (gas) changes into liquid.
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.
Cumulonimbus
A towering cloud of great vertical extent. These clouds begin at lower levels stretching all the way to higher elevations. Heavy rainfalls with hail are most common.
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.
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.
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 deposition of water vapour.
G
Geostrophic Wind
When wind flows parallel to the isobars caused by a balance between the Coriolis force and the PGF.
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
H
Hail
Rainfall with stone like ice usually ranging from 4mm-5mm formed in a cumulonimbus cloud with high convectional currents. See Precipitation
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.
Hurricane
A tropical storm originating from the Atlantic Ocean. This is the term used in the Caribbean and North America.
I
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
K
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 longwwave form.
Low Pressure
Characterised by unstable weather conditions and high temperatures.
M
Mesosphere
The third layer (going up) of the atmosphere characterised by very low temperatures. The upper boundary is referred to as mesopause.
Monsoon
Mist
A thin fog with visibility of more than a kilometre.
N
Nimbostratus
A low level, expansive, dark grey cloud characterised by heavy prolonged rainfalls.
O
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.See Factors Affecting Temperature Distribution
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 and is responsible for trapping the dangerous ultraviolet radiation from reaching the earth.See Ozone and Its Significance
P
Photochemical Smog
A toxic smog formed when particulates in the atmosphere react with sunlight.
Precipitation
Any form of water deposition originate on or off the earth's surface.
Pressure Gradient
The initial driving force of wind. Closely spaced isobars results in a steep (high) PGF thus high wind speeds while a weak PGF is caused by widely spaced isobars.
R
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 were supercooled water droplets freeze on top of another on a freezing surface creating a feathery appearance of ice on the windward side.
S
Saturated Adiabatic Lapse Rate
The rate at which a wet (saturated) air parcel rises above the condensation level. The rate of cooling is 5oC/ 1000m which is lowered by the addition of latent heat released during condensation. See Lapse Rates
Sensible Heat Transfer
The transfers of heat by air parcels in and out of an area being observed.
Sleet
A type of precipitation containing a mixture of snow and partially melted ice.
Smog
A mixture of fog and smoke.
Snow
A type of precipitation formed by aggregation containing hexagonal ice crystals (snowflakes).See Precipitation.
Stratosphere
The second layer (going up) of the atmosphere characterised by high temperatures and ozone. The upper boundary is referred to as stratopause.
Stability
An atmospheric condition characterised by clear and stable weather conditions formed when the environmental lapse rate is lower (cooling at a slower rate) than the dry adiabatic lapse rate (cooling at a faster rate) causing the dense cold air parcel to sink.
Sublimation
The direct change of state from solid to gas.
Subsurface Surface
The supply of heat that was trapped by the surface during the day to the surface at night.
Supercooled Droplets
Very cold water droplets below freezing point. These droplets tend to freeze instantly upon encountering a freezing object.
Stratus
A low level grey cloud that expansively flattens in the atmosphere and produce light drizzles.
Stratocumulus
A low level, puffy and broken grey clouds that produce light to moderate rainfalls. May grow into nimbostratus.
The last layer of the atmosphere before the outer space stretching from about 80 km and is characterised by high temperatures.
Troposphere
The first layer in which we live in whereby temperature decreases with height. All weather phenomenons occur in this layer. See Atmosphere Structure
Tropical storm
A heavy rotating storm characterised by intense low pressure and strong winds fueled on warm waters where air parcels converge, rises and condenses. See Tropical Storms
Typhoon
A tropical storm of the western Pacific Ocean.
U
Urban Heat Island
A term used to describe intense temperatures over cities than surrounding areas. See Urban Climate
V
Vapour Pressure
The pressure exerted by air on a liquid or ice surface.
W
Warm Front
When warm air moves in a region formerly occupied by cold air air.
Water Vapour
Water in its liquid state
Weather
The prevailing conditions in the atmosphere at any given period of time.
Wind
The horizontal movement of air.
Windward
The side from which wind blows, but in terms of orographic rainfall it is the side of a mountain receiving warm moist air (wind) from the ocean that rises, cools and condenses.
Definition of the Day
New!
Geomorphology Cheatsheet
