weather systems Flashcards
(29 cards)
air mass
n air massis a large body of air where fairly uniform temperature and moisture characteristics is observed. It can stretch several thousand kilometres across and extend to the top of the troposphere. Each air mass shows a distinctive combination of conditions at the surface, particularly temperature, environmental temperature lapse rate, and humidity. These properties are acquired in source regions over which the air moves slowly or stagnates
2/8/18 2 Five types of air masses are distinguished with respect to latitude
arctic (A), antarctic (AA), polar (P), tropical (T), and equatorial (E)
For the type of underlying surface, two subdivisions are use
: maritime (m) and continental (c
Six important air mass types can be identified from these descriptive labels
s: cA, cP, cT, mP, mE, mT.
north american air masses
mainly cP and cA
Air masses are usually separated by a well-defined boundary between them; these transitional zones are termed
fronts
In North America, the boundary between polar and tropical air masses produces the well-defined _________ that is located below the axis of the polar front jet stream
polar front
2/8/18 4 North American Air MassesAir masses are usually separated by a well-defined boundary between them; these transitional zones are termed fronts. In North America, the boundary between polar and tropical air masses produces the well-defined polar front that is located below the axis of the polar front jet stream. Source: Strahler, Alan and Archibold, O. 2011 Because unequal heating of the Earth’s surface, the atmosphere and oceans exhibit a complex circulation pattern of air and water flows, which in turns, redistribute absorbed solar radiation more evenly by way of various convection loops (poleward heat transport)
ower Latitudes: through thermally direct Hadley Cells. Mid, High Latitudes: through Rossby Wave mechanis
Due to pressure gradients air masses are set in motion between region ______________
f high and low pressure
Then driven along by the general global wind system and by regional pressure gradients associated with centres of high and low pressure
2/8/18 5 Due to pressure gradients air masses are set in motion between regions of high and low pressure. Then driven along by the general global wind system and by regional pressure gradients associated with centres of high and low pressure. Air masses can move far from their source regions since pressure varies regionally over great distances. This type of movement is observed in the midlatitudeatmosphere, where
travelling cyclones and travelling anticyclones contribute to changing weather conditions as they pass across a region
2/8/18 5 Due to pressure gradients air masses are set in motion between regions of high and low pressure. Then driven along by the general global wind system and by regional pressure gradients associated with centres of high and low pressure. Air masses can move far from their source regions since pressure varies regionally over great distances. This type of movement is observed in the midlatitudeatmosphere, where travelling cyclones and travelling anticyclones contribute to changing weather conditions as they pass across a region.Because of convergence and upward motion, in a travelling cyclonic system air will rise and be cooled adiabatically. When the air is moist, condensation or sublimation may lead to
cyclonic precepitation
hen pressure gradients are steep and the air is laden with water vapour, strong winds and heavy rain or snow can accompany them (producing a _______
cyclonic storm
2/8/18 6 Travelling cyclones fall into three types distinguished primarily by their intensity and geographic location:
Midlatitudes, arctic and Antarctic - wave cyclones or depressions 2)Tropical and subtropical – tropical cyclones (which can intensify to hurricanes and typhoons) 3)tornado
a large mass of inward-spiralling air that repeatedly forms, intensifies, and dissolves along the polar front
wave cyclone
wave cyclone usually occurs when
n two large anticyclones lie on either side of the polar front
The boundary between the two high-pressure cells is necessarily a region of lower pressure and so forms a
low pressure trough
swhere warm air is moving over a region of colder air.
warm front
hen a cold air mass advances into the zone occupied by the warm air mass
a cold front is developed
The colder air of the faster-moving cold front remains next to the ground, forcing the warm air ahead of it to rise along the
occluded front
the simplest form of tropical weather system, which is a slowly moving, convectively active trough of low pressure that is driven westward by the trade winds.
easterly wave
, a disturbance that forms near the centre of the equatorial trough.
weak equatorial low
Polar OutbreaksOccasionally, the penetration of powerful tongues of cold polar air from the midlatitudes into very low latitudes cause another distinctive feature of low-latitude weather. The leading edge of these polar outbreaks is marked b
squalls along the cold front, and is followed by unusually cool, clear weather with strong, steady Winds (best developed in the Americas).
Tropical weather disturbances range from weak tropical lows to powerful and destructive
tropical cyclones(“a storm of tropical origin of small diameter with a minimum surface pressure below 95 kPa, with violent winds greater than 125 kph, and accompanied by torrential rain.”)
tropical cyclone is known variously as a
as a hurricane in the western hemisphere, a typhoon in the western Pacific, and a cyclone in the Indian Ocean
