what direction do cyclones rotate in the Northern vs Southern Hemisphere
Counterclockwise in NH
Clockwise in SH
what causes low-pressure systems to form in the midlatitudes
baroclinic instability
what is baroclinic instability
a process where large temperature gradients cause the jet stream to become unstable forming cyclones and anticyclones
what do baroclinic waves (cyclones) accomplish dynamically
the mix warm and cold air, reducing temperature gradient in the lower troposphere
what are the 3 main airstreams in an extratropical cyclone
warm converyor belt
cold conveyor belt
dry air stream
what is the warm conveyor belt
a stream of warm air that ascends over the warm front and produces clouds and preciptation
what us the cold conveyor belt
a near-surface flow of cold air that wraps around the low abd contributes to cloud and precipitation patterns
what is the dry airstream
descending dry air from the upper troposphere that produces a dry slot in the cyclone (cloud free)
what does a mature extratropical cyclone look like on satellite images
a comma-shaped cloud pattern with the ‘head’ near the low centre
when was the shapiro keyser cyclone model developed
1990
How does a Shapiro–Keyser cyclone differ from the Norwegian model?
it has a frontal fracture where the cold front weakens and forms a back-bent front and a warm core seclusion
what is a warm-core seclusion
a region of relatively warm air trapped at the centre of a mature cyclone
what is the sting jet
a narrow region of very strong winds that descends from the tip of the back-bent front
what famous event is associated with a sting jet
the great storm of October 1987 UK
What determines whether a cyclone evolves as Norwegian or Shapiro–Keyser type?
The cyclone’s position within the jet stream (entrance vs exit region).
What happens in the jet stream’s exit region?
The jet weakens (diffluence), stretching the cyclone north–south—more Norwegian-like.
What happens in the jet stream’s entrance region?
The jet strengthens (confluence), stretching the cyclone east–west—more Shapiro–Keyser-like.
Why do anticyclones generally bring fair weather?
Air descends, suppressing cloud formation.
What are two situations when anticyclones can cause concern?
- Air-pollution episodes
- Cold-air outbreaks
What caused the Great Smog of London in December 1952?
A stagnant anticyclone trapping pollutants near the surface.
What causes cold-air outbreaks?
Polar air being advected equatorward on the east side of a high-pressure system.
What is the “Beast from the East”?
A weather pattern bringing cold, snowy air from the European continent across the North Sea to the UK.
