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20 Cards in this Set
- Front
- Back
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air mass
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A. An immense body of air, usually 1000 miles or more across and several kms thick, characterized by homogenous physical properties at any given weather
weather is a result of interactions between air masses used to predict weather |
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difference and similarity between air mass and air parcel
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i. both have their own temperature and relative humidity!
ii. BUT air parcels are smaller, air masses are immense |
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two criteria for source region of air mass
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ii. regions dominated by stationary or slow-moving anticyclones (H) with their extensive areas of calms of light winds
extensive and physically uniform area |
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lake effect snow
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A. Highly localized storms occurring along the leeward shores of lakes called snowbelts
i. one part of the lake gets a lot more snow than the other side ii. dumps heat and moisture on other side B. Cause: i. differential heating between land and water ii. see other reasons on slide |
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fronts
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A. When two air masses collide, the boundary between them is called a front
B. Definition i. Fronts are boundary surfaces that separate air masses of different densities ii. one air mass is usually warmer and contains more moisture than the other |
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indications a cold front is coming
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wind shift – direction of wind changes
when temperature goes down air pressure increases (because it's cooler) cirrus clouds appear 1-2 days before the cold front squall line clouds in a straight line because warm air is pushed up immediately (not a gradual lift) |
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effects of cold front
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brings northerly winds
leads to a lot of precipitation very fast – warm air is lifted |
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why there are spikes of warmth in atmosphere
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vi. If temperature spikes up top instead of dropping (like inversion that caused London Smog) it's a result of warm air on top
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why shouldn't we use temperature to predict fronts?
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i. Weather stations can't measure difference if warm air goes on top
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jet stream
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A. Definition:
i. Fast flowing, narrow air currents located near the tropopause B. air has to move fast; moves in direction of rotation of the earth |
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why are there two jet streams?
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Because there are two tropopauses
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effect of earth's rotation on jet streams
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a) fastest at the equator and not rotating at all at the poles
ii. air at higher levels of the atmosphere must travel very fast to keep up air at lower levels a) air at higher levels “slips” and falls behind iii. pressure builds up behind the “slipped” air |
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Rossby waves: definition and origin
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A. Definition
i. giant meanders in high-altitude winds that affect weather B. Origin i. due to the shear in rotation fluids so that the coriolis force changes along the sheared coordinate a) sometimes air will converge, sometimes they move and diverge b) creates lows and highs!! ii. due to the variation in coriolis effect with latitude |
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how are midlatitude cylones formed?
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when loops n Rossby waves become pronounced, they detach the masses of cold, or warm
a) makes mid-latitude cyclone cyclone winds around a low pressure area anticyclones form around high pressure areas |
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D. Favourable and unfavourable conditions for mid-latitude cyclone formation
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i. no way to go when converging but down, can't go to stratosphere; moves down to low pressure areas where it pushes back to diverging area. This creates a cycle, making your cyclone!!
a) when rossby waves meander and convergence produced. From upper atmosphere. |
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lifecycle of the midlatitude cyclone
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i. Cyclogenesis
a) stationary front b) two air masses moving parallel to the front c) but opposite direction so a wave develops ii. open stage a) warm air moves poleward b) cold air moves equatorwards c) in some books called mature stage – may be on test!! d) there is a characteristic “V” shape (this is also on test) e) Why are isobars straight between “V” in open stage? Test question No more gradual change; move up immediately iii. occluded stage a) occlusions: cold b) circulates counter clockwise, but cold is a lot faster than warm front so eventually overtakes it. When they together form cumulo nimbus and severe weather, represented as occluded front iv. dissolving stage v. stops until there's a new low... when there's another convergence in the upper atmosphere a new low is formed and the cycle starts again |
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typical paths of mid-latitude cyclones (example names)
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Alberta Clipper
Colorado Low Gulf low Hatteras low |
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Why do air masses only form in high pressure areas?
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ii. regions dominated by stationary or slow-moving anticyclones (H) with their extensive areas of calms of light winds
can't continue to move, or it won't grow and develop needs to move from high to low |
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difference between rossby waves and jet steam
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rossby waves are upper atmospheric circulation that moves around jet steam.
rossby waves produce cells of cold and warm pressure (ridges and troughs) |
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squall
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a line of severe thunderstorms that can form along or ahead of a cold front
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