Earth Sciences 2240F/G Lecture 11: Chapter 11 Cyclonic Storms
11 Jun 2018
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Chapter 11 Cyclonic Storms
1.0 Introduction
• smallest cyclonic storm is a thunderstorm
• largest is a hurricane or typhoon
2.0 Thunderstorms
• form when there is:
o moisture
o atmospheric instability
o a lifting mechanism
• ultimate sources of moisture for most storms in north America are
the oceans, gulf of mexico and the great lakes
• proximity to a large body of water will increase the number of
thunderstorms in that area
• unstable air masses will move in any direction they are nudged (up
or down)
o these have a temperature gradient, warm, moist air at
bottom and cooler, drier air above
o rising air cools causing some of the water vapour to
condense, forming tall cumulonimbus clouds
▪ typical clouds of a thunderstorm
• 3 ways air rises
o Differential Heating:
▪ Uneven heating of the ground and uneven heating of
the air in the lower atmosphere will create pockets of
warm air called thermals that tend to rise
o Cold Fronts:
▪ Front: when boundary of different air masses of
different temperatures meet
▪ Cold air masses are more dense and will move under a
warmer air mass causing uplift of the warmer air, uplift
find more resources at oneclass.com
find more resources at oneclass.com
Chapter 11 Cyclonic Storms
of moist, unstable air will result in thunderstorms along
the cold front
o Terrain:
▪ As air moves laterally across a landscape and is forced
up over mountains, upslope thunderstorms can form
2.1 Life Cycle of a Thunderstorm
• result from formation of a thunderstorm cell that will last on
average 30 minutes
• 1st Stage: Towering Cumulus Stage
o cumulus cloud grows vertically up to about 6 km
o dominant air movement is upwards with turbulence at edges
• 2nd Stage: Mature Stage
o storm can grow to heights of 12-18 km
o air movement upwards and downwards
o updrafts can be extremely strong; stronger the updraft, the
more weight of rain and hail that can be supported
o the most dangerous stage
• 3rd Stage: Dissipating Stage
o downward air movement dominated (downdrafts)
o upward supply of cold air has been cut off and the cumulus
begins to dissipate
o see lighter rain and weak winds and cloud will have a
remnant anvil-shaped top
2.2 Thunderstorm Types
• above is lifecycle of one thunderstorm cell
• a storm can consist of many cells in various stages merging
together
• called multi-cell storms and can last for several hours, producing
large hail, damaging winds, flash flooding and isolated tornados
• can form a squall line hundreds of miles long
• storms with squall lines last for hours and produce damaging winds
and hail
• as line moves forward, air is cooled by rain and this cool ‘gust front’
lifts more warm moist air to continue the storm
• Derecho- if cells in squall line produce winds exceeding 93 km/h
and the length of the squall line exceeds 450 km
• Supercell- occur when winds are turning clockwise with height and
where there is a change in wind speed or direction with height
(known as wind shear)
o Giagantic, long lasting single-cell thunderstorms that produce
high winds, hailstorms, flash flooding and most of the
significant tornados in the USA
o Lower part of the cloud termed wall cloud, can be a precursor
of a tornado
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
1. 0 introduction: smallest cyclonic storm is a thunderstorm largest is a hurricane or typhoon. Chapter 11 cyclonic storms of moist, unstable air will result in thunderstorms along the cold front: terrain, as air moves laterally across a landscape and is forced up over mountains, upslope thunderstorms can form. 2. 3 thunderstorm hazards lightening, hail and erratic strong winds lightening kills more people in usa than tornados and hurricanes combined. 20 degrees from the equator: rotates counterclockwise around an eye" with minimum wind speeds of 119 km/h, other terms for hurricane: typhoon, severe tropical cyclone, Severe cyclonic storm or tropical cyclone: all only originate in tropical trade winds where the temperatures are warm. Chapter 11 cyclonic storms: a disorganized masses of thunderstorms, next stage is called tropical storm (when a name is given to them, difference between tropical storm and hurricane is wind velocity.
