GEOL 106 Lecture Notes - Lecture 38: Jet Stream, Extratropical Cyclone, Atmospheric River
26 May 2018
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- mature hurricane will typically have forward speed of 19 – 27 km/hr
o this slow forward speed will mean that hurricane is a two day event for communities
directly in path of storm
o toward end of hurricane, its forward speed may suddenly increase to 73 – 93 km/hr
▪ happens to many hurricanes that move up East Coast past Cape Hatteras,
toward coastal Canada
▪ rapid increase in forward speed can be dangerous if it results in early landfall for
hurricane
o once over land or having moved into cooler waters of North Atlantic → hurricane
rapidly lose strength and usually dissipate within few days
EXTRATROPICAL CYCLONES
- 2 key ingredients contributing to formation and movement of extratropical cyclone:
1. strong temperature gradient in air near surface
2. wind patterns within jet stream
o surface temperature gradients are generally strongest along cold, warm, stationary front
o most extratropical cyclones develop along fronts
- large high pressure ridges and low pressure troughs in upper troposphere cause jet streams to bend
north or south of their normal path → produces long meanders or waves in their flow
o jet stream may also split in two around isolated high pressure centres and reunite down
flow
o extratropical cyclones often develop in area where jet stream winds curve cyclonically or
diverge (e.g. east side of trough)
- bending or splitting → can cause polar jet stream to dip southward and subtropical jet stream to flow
northeastward into conterminous US
o southern branch of split polar jet stream in Pacific Ocean brigs war moist air out of tropics
and can be recognized on infrared satellite images as a band of clouds extending
northeastward from equatorial Pacific Ocean
- during some winters: series of extratropical cyclones with track northeastward along southern branch
→ Pineapple Express (atmospheric river) because of its origin near Hawaii
- on Atlantic Seaboard: extratropical cyclones of nor’easters often form when bends of polar and
subtropical jet streams begin to merge off the southeastern coast of the US
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
During some winters: series of extratropical cyclones with track northeastward along southern branch. Pineapple express (atmospheric river) because of its origin near hawaii. On atlantic seaboard: extratropical cyclones of nor"easters often form when bends of polar and subtropical jet streams begin to merge off the southeastern coast of the us. Case study 10. 2 hurricane katrina: the most anticipated natural disaster in american. 10. 3 geographic regions at risk for cyclones tropical and extratropical cyclone pose threats to different parts of us and canada tropical cyclones: greatest on coastal areas with warm offshore waters like gulf of mexico and gulf. Hurricanes: most threat to eastern contiguous us, puerto rico, virgin islands, us territories in pacific. Us as far east as texas east and gulf coast of us have the highest risk for tropical storms and hurricanes in na and experience five hurricanes each year on average. [type here: although hurricanes and tropical storms sometimes form in gulf of mexico and caribbean.
