GEOL 106 Lecture 36: GEOL 106. NOTEdocx
26 May 2018
School
Course
Professor
[Type here]
9.8 Natural service Functions of Severe Weather
- lightning is primary ignition source for natural wildfires → wildfires are vital in prairie, tundra, forest
ecosystems
windstorms10.1 Introduction to Cyclones
- Hurricane Sandy = cyclone
- cyclone: area of centre of low atmospheric pressure characterized by rotating winds
- due to Coriolis effect → winds in Northern Hemisphere are deflected to the right and blow in
counterclockwise rotation around low pressure centre
o in Southern Hemisphere: Coriolis effect causes winds to rotate clockwise
- cyclones rarely develop within 5 degrees of the equator where Coriolis effect is weakest
- cyclones are classified as tropical or extratropical based on their place of origin and temperature of
their centre or core region
o extratropical: outside of tropics
o tropical cyclones: form over warm tropical or subtropical ocean water between 5 – 20
latitude
▪ they are not associated with fronts (boundaries between warm and cold air
masses) and have warm central cores
o extratropical cyclones: develop over land or water in temperate regions, between 30 –
70 latitude
▪ generally associated with fronts and have cool central cores
- both types of cyclones are characterized by their cyclone intensity: indicated by their sustained wind
speeds and lowest atmospheric pressure
- cyclones are associated with most severe weather in NA
o tropical cyclones include: tropical depressions, tropical storms, hurricanes that can
produce high winds, heavy rains, surges of rising seawater, tornadoes
o extratropical cyclones: can cause strong windstorms, heavy rains, surges of rising
seawater on both West and East Coasts during warmer months and snowstorms and
blizzards during cooler months
▪ most do not produce severe weather, but can produce outbreaks of tornadoes
and severe thunderstorms, especially east of Rocky Mountains in US and Canada
- two types of storms differ in their source of energy and their structure
o tropical cyclones: derive energy from warm ocean water and latent heat that is released
during condensation of rising air to form clouds (latent heat of condensation)
o extratropical cyclones: energy from horizontal temperature contrast between air masses
on either side of front
- in hurricanes: most intense of tropical cyclones; warm air rises to form spiraling pattern of clouds
o rising and warming air surrounding centre of hurricane heats entire core of storm
- most extratropical cyclones in contrast are fed by cold air at surface and another flow of cool, dry air
aloft
o resulting storm has cool core from bottom to top
- tropical cyclones that move over land or cooler water lose their original source of heat-warm ocean
water
o either dissipate or become extratropical cyclones moving along a front
- naming of individual cyclones is limited to more intense tropical cyclones and is a practice that began
in 1940s
find more resources at oneclass.com
find more resources at oneclass.com
[Type here]
-
CLASSIFYING CYCLONES
- cyclone: term applied to large low pressure system with winds circulating inward toward its centre
o but various terms are used to describe these systems in different parts of world
- or’easter: extratropical cyclone that tracks northward along eastern coast of US and Canada
o onshore winds from these storms blow from northeast and can sometimes reach
hurricane strength
- hurricanes: in Atlantic and eastern Pacific Oceans (named after Caribbean word for evil god of winds
and destruction)
- typhoons: in Pacific Ocean west of International Dateline (180 longitude) and north of equator
(meaning scary wind in Chinese)
- cyclone: hurricanes in Pacific Ocean south of equator and Indian Ocean (Greek word meaning coil of
snake)
- call it hurricane from now on
- hurricanes: classified by their wind speed on damage potential scale developed by Saffir and Simpson
- Saffir Simpson Hurricane Scale: 5 categories based on highest 1 minute average wind speed in storm
o typically changes as it intensifies or weakens and all but weakest hurricanes will have
more than one category assigned to them during their lifetime
o ratings used to give an estimate of potential property damage and flooding expected
along coast from a hurricane landfall
o highest current 1 minute average wind speed is determining factor → storm surge values
are highly dependent on slope of continental shelf where hurricane makes landfall
- major hurricanes = category 3 – 5
- as wind speed and category increase → atospheric pressure i stor’s cetre drops
- category 5: central atmospheric pressure of less than 920 millibars
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
9. 8 natural service functions of severe weather lightning is primary ignition source for natural wildfires wildfires are vital in prairie, tundra, forest ecosystems windstorms10. 1 introduction to cyclones. 70 latitude: generally associated with fronts and have cool central cores. Naming of individual cyclones is limited to more intense tropical cyclones and is a practice that began in 1940s. Classifying cyclones cyclone: term applied to large low pressure system with winds circulating inward toward its centre: but various terms are used to describe these systems in different parts of world. (cid:374)or"easter: extratropical cyclone that tracks northward along eastern coast of us and canada: onshore winds from these storms blow from northeast and can sometimes reach hurricane strength. Hurricanes: classified by their wind speed on damage potential scale developed by saffir and simpson. Major hurricanes = category 3 5 as wind speed and category increase at(cid:373)ospheric pressure i(cid:374) stor(cid:373)"s ce(cid:374)tre drops category 5: central atmospheric pressure of less than 920 millibars.
