Atmosphere and weather Flashcards
Absorption of energy
The process whereby incoming and outgoing radiation is absorbed by gases in the atmosphere such as ozone water vapour and carbon dioxide, as well as by the land and oceans
Advection fog
Condensation of atmospheric vapour at low levels due to cooling of relatively warm, moist air by contact with a cold surface. Local examples include Seafret of north east England and Haar of south east Scotland. Both are caused by warm continental air being chilled to its dew point temperature by contact with the cold North Sea
Aerosols
Solid particles of dust, pollution etc which act as condensation nuclei
Air mass
A large body of air with relatively uniform the temperature and humidity characteristics, generally characterised as polar or tropical, maritime or continental
Albedo
The fraction of incoming radiation reflected by a given surface
Anticyclone
A slow moving area of relatively high atmospheric pressure covering thousands of kilometres squared, often referred to as simply as high. Usually these pressure systems give clear skies and cold weather
Cloud
A visible mass of microscopic water droplets and or ice crystals held in suspension by air currents, they are formed by condensation of water vapour around condensation nuclei such as smoke pollen dust salt
Cold front
A long thin band of clouds and precipitation making the boundary between an advancing cold air mass and a retreating warm air mass
Condensation
Process by which water vapour turns into water droplets when the temperature falls to dew point and the air become saturated with moisture
Condensation level
The altitude at which rising air has been cooled to its dew point and water vapour has begun to condense into tiny cloud droplets
Condensation nuclei
The process by which heat energy is transferred directly from a warmer to cooler substance, by molecular movement, e.g. from a warm ground surface to cooler air above
Conduction
The process by which heat energy is transferred directly from a warmer to cooler substance by molecular movement
Convection
The vertical transfer of heat energy by rising air currents warm land or sea surface heat the air above it, the air becomes less dense and rises up through the atmosphere, carrying heat energy with it
Convectional precipitation
Caused by air rising above its condensation level to produce large cumulus clouds, usually occurs when relatively cool moist air is heated as it passes over relatively warm land or sea
Coriolis effect
The deflection caused to moving air as it moves across the face of the rotating Earth, in the northern hemisphere is deflected to the right causing air to rotate anticlockwise around Lows and clockwise around highs
Cumulus
Bubbly cauliflower clouds generated by relatively warm, moist air, they may be small, Fairweather cumulus or very large tall cumulonimbus clouds which generate heavy showers
Depression
A low-pressure system developed on the polar front in the mid-latitude marked by a warm and cold front and warm sector. Often simply called a low
Dew
Condensation at ground level, which usually occurs at night on that clear skies and light or, Calm winds, allowing plenty of heat loss
Dew point
The temperature at which air become saturated with moisture and condensation begin to take place
Drizzle
Drops of liquid precipitation less than 0.02 mm in diameter often associated with warm sectors of mid latitude Lows
Environmental lapse rate
The rate at which the temperature of the atmosphere changes with height, measured in degrees Celsius per 100 m altitude. The temperature normally decreases at about 0. 6°C per 100 m, except when there is a temperature inversion, do not confuse this with the rate of temperature change experienced by a parcel of air
Evaporation
The process by which liquid water transformed to gaseous water vapour
Fog
Condensation of water vapour into cloud droplets at ground level, subdivided into radiation fog caused by overnight heat loss and advection fog, caused by warm moist air passing over a cold surface
Freezing fog
Fog in the form of tiny crystals suspended in the air which sometimes occurs when the air temperature falls below 0°C
Front
a band of clouds and precipitation occurs along the line of convergence of two air masses, one warm and one cold
frontal ppt
rain, snow etc. which occurs along a front as warm air is forced to rise over cold air, or cold air undercuts warm air.
frost
occurs when temperatures fall below 0oC; air frost occurs when the air (Stevenson screen) temperature falls below 0oC; ground frost when surface temperature is <0oC.
general circulation
the global pattern of atmospheric movement.
greenhouse effect
the warming of the atmosphere by the trapping of long-wave terrestrial re-radiation by certain gases such as CO2, water vapour and various pollutants.
Hadley cell
the circulation of the atmosphere between the tropics of Cancer and Capricorn. Hot, moist air rises in the equatorial low, diverges towards higher latitudes, and then descends in the lower mid-latitudes to form the sub-tropical highs, returning to the equator as the Trade Winds.
heat island
a zone of slightly higher temperatures associated with an urban area compared with surrounding rural areas. It can be caused by the absorption and storage of solar radiation by building materials as well as by the heat generated by traffic, industry and domestic heating systems.
horizontal heat transfers
the transfer of heat across the globe by ocean currents, and by weather systems as both sensible and latent heat.
hygroscopic nuclei
small particles in the air which attract water vapour which condenses to form cloud droplets; includes volcanic and desert dust, pollen, salt particles and many pollutants. Also called condensation nuclei.
insolation
the incoming energy of the sun (heat, light, ultra-violet rays etc.)
itcz
the zone of rising air and associated low pressure broadly coincident with the equator.
latent heat
heat in a “hidden form” which changes the nature of a surface. Latent heat is absorbed (used) by water as it turns into vapour (evaporation), or when ice melts; it is released when condensation and freezing occur.
long wave earth radiation
the long-wave heat energy given off by the earth back to space. Atmospheric gases such as water vapour and Carbon Dioxide absorb much of this radiation, causing the greenhouse effect.
net radiation
the difference between incoming insolation and outgoing terrestrial re-radiation; an important determinant of temperature.
North Atlantic drift
the relatively warm ocean current flowing northeastwards across the Atlantic Ocean, as an extension of the Gulf Stream, from the region around Florida towards Britain and Norway.
ocean currents
large-scale circulations of ocean water carrying large quantities of heat from lower to higher latitudes, e.g. the North Atlantic Drift and the returning cold currents, e.g. the Canaries Current, taking the water back for re-heating.
orographic ppt
rain, snow etc. generated by the forced uplift of moist air over mountains.
ozone layer
a layer approximately between 15km and 55km above the earth’s surface where O3 is concentrated sufficiently to absorb significant amounts of ultra-violet radiation.
polar cell
circulation of the atmosphere in the vertical and horizontal planes around the poles; air flows towards the poles at high altitudes, descends to the surface at the poles and flows away, as cold winds, from the poles at the surface.
polar continental
air mass originating from northern Europe, Scandinavia and Siberia. Very cold and dry at source, but it picks up heat and moisture over the North sea and becomes unstable in its lower layers, generating cumulus clouds and snow showers.
polar front
the junction between cold polar and warm tropical air along which depressions are generated.
ppt
all forms of liquid drops and solid ice particles falling from clouds; includes rain, drizzle, sleet, snow, hail, mizzle, snizzle and fog-drip
pressure gradient force
the difference in pressure (in millibars) per unit distance (in 100 km) between two places; the steeper the pressure gradient the stronger the wind.
radiation
the transfer of energy (including heat and light) by electromagnetic waves of different wavelengths. Radiation is able to pass through gases, liquids, and solids or through a vacuum.
solar radiation
the transfer of energy (including heat and light) by electromagnetic waves of different wavelengths. Radiation is able to pass through gases, liquids, and solids or through a vacuum.
radiation fog
condensation (ground level cloud) generated by overnight heat loss; commonest on clear, calm winter nights when most radiation is lost from the ground.
rain
drops of water of 0.02mm to 5mm diameter falling from clouds.
rain shadow
an area on the sheltered side of a mountain range which receives less precipitation than on the windward side. Most of the precipitation falls as the moist air is forced to rise over the mountains (orographic precipitation), leaving the air drier as it descends again.
reflection
the amount of radiation which bounces off an object. See albedo.
relative humidity
the amount of water vapour in the air expressed as a percentage of the maximum amount could be held at the same temperature.
scattering
process whereby insolation is scattered in all directions by dust and gases in the atmosphere, some reaching the earth’s surface as diffuse radiation.
sensible heat
literally heat which can be felt – i.e. the heat of a substance as measured by its temperature; warm and cold air masses transporting heat energy between higher and lower latitudes.
sleet
either partially melted, wet snow, or a mixture of rain and snow falling together.
snow
large agglomerations of ice crystals falling from clouds.
stratosphere
the next atmospheric layer above the troposphere, c.10 – 50km altitude.
stratus clouds
layered clouds, classified according to their altitude; cirrostratus = highest, altostratus = middle, nimbostratus = lowest etc.
sthp
region of high pressure found between latitudes 200 and 300 North & South, where the air in the Hadley Cell reaches the surface.
temperature inversion
an increase in temperature with altitude, rather than the normal decrease. It can be caused by overnight cooling of the ground surface, warm air passing over a cold surface, or cold denser air sinking to ground level leaving warmer air above.
terrestrial radiation
long-wave heat radiation given off by the earth/ oceans/ atmosphere back to space.
trade winds
tropical winds blowing from the subtropical high to the equatorial low (ITCZ); NE Trades in northern hemisphere; SE Trades in southern hemisphere.
tropopause
the imaginary boundary between the top of the troposphere and the bottom of the stratosphere; marked by a temperature inversion and acting as a vertical limit to cloud development.
troposphere
the lower atmosphere in which all normal weather phenomena occur; from the surface up to the tropopause which varies between 18km altitude at the equator to 8km at the poles, depending on temperature, season etc.
vertical heat transfers
transfer of heat up through the atmosphere by radiation, conduction and convection.
warm fronts
band along which warm air rises up and over colder air, producing cloud and precipitation; usually stratus clouds and relatively light rain and drizzle.
