Transcript Tropical storm

Geography 1000
For Quiz #3 (covers most of Chapters 7-9)
Part 1 of 4 Parts
 “Super-Storm Sandy” in October, 2012 caused more than $55
Billion in financial losses and cost more than 300 lives.
 Most of these losses were preventable. People living along the
sea coast are “gamblers” - - hoping that a big storm won’t really
affect them.
 As of October, 2013, some people in New Jersey still do not have
electricity and/or drinking water.
 People in New Jersey can say the same thing about us: we think
that a big earthquake won’t really be that bad.
Photo taken by a friend of Nick Urban, who was a Geography 1700
student Fall 2013
Consider that counter-clockwise (cyclonic) rising air is condensing vapor back into liquid
water as it rises, decompresses and cools.
In the center, rain is falling as the “bucket” over-fills. Downdrafts may occur there also.
At the edges, a ‘wall cloud’ and a funnel cloud may form due to rapidly rising air.
Great turbulence and severe wind can result from air rising and falling.
U.S. Storms
•
Tornadoes in 2011 killed more than 550 Americans.
• At least one tornado in 2013 was among the largest ever
recorded – more than two miles wide on the ground and
exhibiting wind speeds above 300 miles per hour.
• The 1925 “Tri-State Tornado” may have been much larger than
any tornado ever ‘recorded.’ This one cyclone lasted for hours –
killing more than 700 people. <What would happen now if that
same ‘twister’ occurred again?>
• Cyclones can occur anywhere cold/dry and warm/wet air meet,
usually in mid-latitudes where large continents create extremes
and where coriolis force is active.
Severe Weather and World-Class Storms
• The United States is regarded as having the greatest variety of bad
weather. Why? <Large continents have interiors far from mild ocean
influence, cold-dry air collides with warm-wet air and coriolis force causes spin
acceleration -- faster wind.>
• Typhoons in the Pacific Ocean and ‘cyclones’ in the Indian Ocean
have killed as many as 500,000 people in one storm alone. Even so,
the USA can be worse due to having more cold-dry air than
Bangladesh, which collides with wet-warm.
• Why does it matter that Americans tend to be some of the world’s
best gamblers? <Americans can run fast or hide quicker than people in most
poor countries.>
• More than 90% of the world’s tornadoes occur in the USA.
Anatomy of ‘bad’ weather
The “Big Six” Attributes of the Atmosphere
-
Differential heating of the earth causes air pressure
-
air moves from higher pressure to lower pressure as wind.
-
Moving air and heat evaporate water – energy becomes latent <hidden> in
water vapor, called humidity.
-
Wind carries water vapor and heat to other places.
-
When that air cools, latent heat and liquid water return as warm clouds.
-
Precipitation occurs when liquid or frozen water falls from clouds.
How a rainy day can turn violent.
“Sometimes Mikey likes it”
Any time air becomes laden with moisture it will tend to be more buoyant than drier air
elsewhere. When that air also becomes warm it can become even more buoyant. It
could start rising on its own (convective rising).
In dry Utah, when wind moves air upward over a mountain, the cooling effect can cause
condensation, releasing heat and producing clouds.
If air is wet enough, a simple rainy episode on the mountainside could turn into a
genuine ‘convective’ uplift, leading to more substantial precipitation, stronger wind and
so on.
So, humidity that moves through Utah might not have turned into a genuine stormy day
were it not for mountains that started the air moving upward. Afterward, the humid took
over and caused its own rising and more storminess.
A few times each year, there is enough water in Utah air to cause a strong convective
uplift that could produce a tornado.
This photo of Tooele County illustrates how Utah can have severe weather anytime
there is enough moisture in the air.
Humidity is water vapor that contains latent (hidden) heat.
Severe storms are caused by heat stored as water vapor
in the atmosphere.
• Modern science is now able to provide 10-11 minutes of warning ahead of
cyclones. <what does ‘warning’ mean?>
• Severe storms are part of the normal water cycle. Without hurricanes, Florida
would have persistent drought. Dangerous cyclones in India, Myanmar and
Bangladesh are part of the vital monsoon season that helps prevent famine and
starvation.
• Understand adjustments that can minimize damage and personal injury from
coastal cyclones
• Know the prudent actions to take for hurricane or extra-tropical cyclone watches
and warnings
Cyclones
• An area or center of low pressure with rotating winds
– Counter-clockwise in Northern Hemisphere
– Clockwise in Southern Hemisphere
• Tropical or extra-tropical
– Based on origin and core temperature
– Tropical storms may become more intense as they move out of the
tropics and into the sub-tropics and mid-latitudes
Some major regional storm categories
• Nor’easter - Extra-tropical cyclone that moves along northward along East Coast
U.S.
• Hurricanes - Tropical cyclones in Atlantic and eastern Pacific Oceans
• Typhoon - Tropical and Extra-tropical cyclones in Pacific Ocean west of
International Dateline and north of the equator
• Cyclones – same kind of storm, but in the Indian Ocean.
• Monsoon – a seasonal shift in wind, but often brings too much rain (or not
enough)
Tropical Depressions and Tropical
Storms
• Tropical depressions
– Tropical disturbance wind speeds increase and begin to spin.
– A low pressure center is formed.
• Tropical storm
– Winds increase to 63 km (39 mi) ph.
– Storm is given a name.
Hurricanes, cont.
• Rain bands
– Clouds that spiral inward around center
– Increase in intensity towards the center of the hurricane
• Eyewall
– Innermost band of clouds
– Contain the greatest winds and rainfall
• Eye
– Area of calm at center of the hurricane
– Often sunny and even downdrafts
– After storm ‘eye’ passes, 2nd half of hurricane will arrive
Hurricane Structure
• Warm, moist air spirals upward around eyewall.
• Air rises and cools, then condenses out clouds and hidden heat
• Release of heat and moisture promotes more rising air, sometimes with
increasing speed
• Upward rotation draws air from eye, causing dry air to sink back into
center.
• Upward rotation also causes air to flow out the top of the storm
concentrated in exhaust jets.
• Allows additional warm, wet air to feed in at the base of the storm
• Storm will continue until warm, wet air supply ends at the base
Cross-Section of a meso-scale cyclone
What sustains “extra-tropical” storms?
– A cyclone will run out of energy when the difference in moisture and
temperature inside the storm is not much greater than the drier/cooler
air outside.
– Passing over dry land or over cool water will tend to drain a cyclone of
energy.
– However, an extra-tropical storm that collides with a relatively cold
blizzard or “Nor’easter” can rebuild temporarily by having something
cooler and drier to use for ‘pushing-off’ and rising again for a while.
Extra-tropical Cyclone Development
• Low pressure develops along fronts.
–
–
–
–
Cold front on southwest, warm front on east.
Cold air circulates counter-clockwise.
Warm air rises on the southeast side.
Dry air aloft feeds the cyclone from behind the cold front.
• Occluded front develops, trapping warm air aloft.
• Pressure gradient weakens and storm dissipates.
Air will flow when there is a ‘gradient’ or “slope” between high
and low pressure. Air pressure results from differences in
temperature. High pressure flows to low pressure. WIND.
Here we see how the jet
stream (with storm track)
helps pull low and high
pressure cells toward each
other.
The difference between
warm/wet and cool/dry
helps produce rising air,
high wind, precipitation,
hail, lightning.
Warm, wet air rises
above cool/dry air
classic “frontal”
storm.
Hurricanes in East and Gulf Coasts
• Usually, take one of three
paths
• Season starts June 1 and
ends Nov 30
Figure 9.21
Figure 9.23
Geographic Regions at Risk for Cyclones, cont.
What makes the USA so
unusual in severe storms?
Because, we should have desert in Alabama - - but we
don’t. Instead, we have “fight club” -- ”tornado alley”.
Track of Extra-Tropical Storms
Trade winds from east to west collect ocean transfer ocean heat to air vapor where it can collide with drier air
further north.
This red arrow is
probably wrong.
Hurricanes do not
reach Los Angeles.
Hurricanes west of Mexico tend
to blow away from land because
of the same trade winds that
blow hurricanes toward land in
the Gulf and Atlantic.
Geographic Regions at Risk for
Cyclones
Our definition of
‘cyclones’ should
include “tornado alley”.
All together, the
United States
collects more than
90% of the world’s
tornadoes.
The coast is
“hurricane”
country, but
cyclones
include
tornadoes that
occur across
much of the
USA.
Hurricane
regions are
also tornado
regions.
North American Regions at Cyclone Risk
– Atlantic coast of eastern USA and Gulf Coast and
islands
– Baja California and West Coast Mexico
– Hawaii
– Winter windstorms in Pacific Coast
– Winter snow Sierra Nevada, Rocky Mountains, and
east
– Spring and summer thunderstorms and tornadoes
in U.S. and Canada