POLAR FRONT THEORY PHASE 1: STATIONARY FRONT
- prior to the development of a midlatitude cyclone, a stationary front will exist at the surface (no low pressure yet)
- winds of either side of the front will blow in opposite directions
POLAR FRONT THEORY PHASE 2: FRONTAL WAVE
- winds blowing in opposite directions trigger a ‘kink’ in the isobars
- surface pressure begins to fall
- surface low forms at the ‘kink’
- rotation around the low spurs the development of a cold and warm front
POLAR FRONT THEORY PHASE 3: OPEN WAVE
- cold air advection and warm air advection strengthen
- cold front becomes oriented from NE to SW
- surface pressure falls
- defined warm sector exists
POLAR FRONT THEORY PHASE 4: MATURE
- distinct cold and warm fronts still exist
- cold front becomes oriented from N to S and nearly intersects warm front
- surface pressure continues to fall
- warm sector shrinks
POLAR FRONT THEORY PHASE 5: OCCULUSION OR ADVANCED OCCLUSION
- cold front now intersects the warm front
- occlusion front forms
- low has reached maximum intensity
- warm sector is now removed from surface low
POLAR FRONT THEORY PHASE 6: CUT-OFF CYCLONE OR DECAY STAGE
- surface low is totally removed from any temperature gradient
- low spins and fills (pressure increases) in the cold air
- residual stationary front is left to the SE
what is cyclogenesis and cyclolysis?
what are common regions of cyclogenesis in the U.S.?
what is meant by explosive cyclogenesis (i.e., ‘bombs’)
- cyclogenesis: development of cyclones
- cyclists: weakening or terminating of a cyclonic circulation in the atmosphere
- Alberta Clipper, Colorado Low, Nor’easters, Hatteras Low
- “bomb” = cyclones whose pressure drops 24mb in 24 hours
how do dynamic low and high pressure systems differ?
- dynamic low = intensity with height
- higher pressure at its center than the areas around it
what is divergence, and what two types of divergence (convergence) are there?
- stronger wind moves away from a weaker wind or when air streams move in opposite directions
- ?
what is meant by a baroclinic and barotropic atmosphere?
does a barotropic or baroclinic atmosphere favor the strengthening of a midlatitude cyclone and its fronts?
- barotropic: no temperature advection
- baroclinic: strong temperature advection
- needs baroclinic instability for midlatitude cyclone
what role does the jet stream play in cyclone development?
jet stream linked to the frontogenesis process in midlatitudes, as the acceleration/deceleration of the air flow induces areas of low/high pressure
what is vorticity, and how to absolute and relative vorticity differ?
- vorticity: measure of the spin of air parcels
- absolute relativity: sum total of planetary, curvature, and shear vorticities
- relative vorticity: rotation of an object based upon its location in an air current
how does vorticity strengthen a developing low pressure center?
divergence aloft causes an increase in the cyclonic vorticity of surface cyclones
what are the three main types of thunderstorms?
- air mass (ordinary cell) storms
- multi-cell storm
- supercell storm
ordinary cell storm?
- little to no vertical wind speed shear
- last an hour or less, rarely severe weather
- precipitation enhances entrainment, leads to the formation of the downdraft
- gust front: where the cold downdraft reaches the surface and spreads out
multi-cell storm?
- t-storms that contain a number of convection cells
- moderate to strong vertical wind shear
- can last for several hours and become severe
supercell storm?
- large, long-lasting thunderstorm with a single rotating draft
- strong vertical wind shear (directional and speed)
- outflow never undercuts updraft
- mesocyclone: column of rotating air
- wall cloud: cloud that forms at the base, often will rotate along with mesocyclone
what are downbursts and straight line winds? How do they differ?
downbursts: intense downdrafts which hit the surface and spread radially
straight line winds: thunderstorm winds that have no rotation
what are squall lines and mesoscale convective complexes, and what type of thunderstorm do they occur with?
squall lines: line of multi-cell thunderstorms
mesoscale convective complexes: cluster of individual multi-cell thunderstorms grow in size and organize into a large circular convective weather system
- OCCUR W MULTI-CELL STORMS
how are tornadoes defined, and how do they differ from funnel clouds?
- tornado: rapidly rotating column of air, blows around a small area of intense low pressure, circulation reaches the ground
- funnel cloud: rotation not in contact with the ground
how does the (enhanced) Fujita scale classify tornado intensity?
based upon damage by storm
what are the basic requirements for tornadic formation?
instability - warm moist air near the ground, with cooler dry air aloft and wind shear - a change in wind speed and/or direction with height
what is a hurricane?
tropical cyclone is a rapidly rotating storm system characterized by a low-pressure center, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and squalls
what conditions are necessary for hurricane development and maintenance?
- deep layer of high humidity (up to tropopause ideal)
- light winds with little to no shear
- a trigger mechanism to start up drift
