Download - Physic Side of a Hurricane
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Physic side:
Hurricanes
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Table of Contest:
Introduction:Physic side of a hurricane:
ACE
Intertropical Convergence Zone Storm Surge
Il Nio and La NiaAppendixSources
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Introduction:
In this paragraph I am going to explain about the physic side of hurricanes. A hurricane needs
some more ingredients to form and in this paragraph we are going to look at that. But these
subjects arent the only physic things of a hurricane, also in the main paragraph we are going
to look to some subjects how reflects to hurricanes, but also to tornadoes.
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Physic side of a Hurricane:
ACE
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Definition:Accumulated Cyclone Energy (ACE) is a number where you can look to the strength of a
season or hurricane/tropical storm system. With these numbers you can also look to the
activity of a hurricane season. The ACE number is only in use with the hurricane season of
the Atlantic Ocean and the Pacific Ocean.
As we concluded and give a short explanation about the ACE in one line, we can say: Howhigher the ACE number is in one season, how stronger the season was. Moreover, how higher
the ACE number is with a storm system (hurricane or tropical storm) how stronger the system
was!
Formula:ACE= (knots) ^2 / 10.000
Every 6 hours the NHC (National Hurricane Center) gives data about the wind speed in knots
of a hurricane or tropical storm how is active on the same time. If you calculate every ACE
number of every 6 hours and count these numbers together, from the moment that a storm
system reaches more than 34 knots till the moment he gets under that number, you have the
total ACE number of one system. If you count all the ACE numbers from a season, you get
the total ACE number which is very useful to look to the activity of a hurricane season.
Categories:You can put the ACE number is different categories. These categories only counts when you
look to the total activity of one season! In the next table we are going to look to these
categories and after that I will explain something more about these categories.
Category: ACE number:
Above normal (Hyperactive) > 103
Above normal > 103Normal All the other seasons
Below normal < 66
Also if a category is giving to a season, the scientist also looks to the number of storm system
that was produced in one season. So a season with an ACE number of 93 can be categorized
as a below normal season, because the season didnt produced many hurricanes or tropical
storm. It can be that there was one hurricane with a very high ACE number, as hurricane Ivan
(2004). Ivan had an ACE number of 70! That can be the total number of one normal season.
The season of 2004 was a hyperactive season with 14 tropical storms, 9 hurricanes and 6
major hurricanes.
Exceptions:Normally every storm system how reach a wind speed of 34 knots gets an ACE number. But
there are some exceptions. A subtropical storm system doesnt get an ACE number. But as we
look for example to subtropical storm Laura (season 2008). Laura got an ACE number, but
what happened. Laura first was a tropical storm. So the only used the numbers of the time
while she was active as a tropical storm.
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Example:On this page I will gave an example how the scientist calculate the ACE of one hurricane. I
used hurricane Ike. Ike was the strongest hurricane of the season 2008 and moreover, Ike had
the highest ACE number.
Date/time: Wind speed:(knots)
Category: ACE number:
01 / 1200 35 Tropical Storm 0.1225
01 / 1800 45 Tropical Storm 0.2025
02 / 0000 45 Tropical Storm 0.2025
02 / 0600 45 Tropical Storm 0.2025
02 / 1200 50 Tropical Storm 0.25
02 / 1800 55 Tropical Storm 0.3025
03 / 0000 55 Tropical Storm 0.3025
03 / 0600 55 Tropical Storm 0.3025
03 / 1200 60 Tropical Storm 0.3603 / 1800 75 Hurricane category 1 0.5625
04 / 0000 105 Hurricane category 3 1.1025
04 / 0600 125 Hurricane category 4 1.5625
04 / 1200 120 Hurricane category 4 1.44
04 / 1800 115 Hurricane category 4 1.3225
05 / 0000 115 Hurricane category 4 1.3225
05 / 0600 115 Hurricane category 4 1.3225
05 / 1200 105 Hurricane category 3 1.1025
05 / 1800 100 Hurricane category 3 1
06 / 0000 100 Hurricane category 3 1
06 / 0600 100 Hurricane category 3 106 / 1200 95 Hurricane category 2 0.9025
06 / 1800 115 Hurricane category 4 1.3225
07 / 0000 115 Hurricane category 4 1.3225
07 / 0600 115 Hurricane category 4 1.3225
07 / 1200 110 Hurricane category 3 1.21
07 / 1800 105 Hurricane category 3 1.1025
08 / 0000 115 Hurricane category 4 1.3225
08 / 0600 100 Hurricane category 3 1
08 / 1200 85 Hurricane category 2 0.7225
08 / 1800 75 Hurricane category 1 0.562509 / 0000 70 Hurricane category 1 0.49
09 / 0600 70 Hurricane category 1 0.49
09 / 1200 70 Hurricane category 1 0.49
09 / 1800 65 Hurricane category 1 0.4225
10 / 0000 65 Hurricane category 1 0.4225
10 / 0600 70 Hurricane category 1 0.49
10 / 1200 80 Hurricane category 1 0.64
10 / 1800 85 Hurricane category 2 0.7225
11 / 0000 85 Hurricane category 2 0.7225
11 / 0600 85 Hurricane category 2 0.7225
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Date/time: Wind speed:
(knots)
Category: ACE number:
11 / 1200 85 Hurricane category 2 0.7225
11 / 1800 85 Hurricane category 2 0.7225
12 / 0000 85 Hurricane category 2 0.722512 / 0600 90 Hurricane category 2 0.81
12 / 1200 90 Hurricane category 2 0.81
12 / 1800 90 Hurricane category 2 0.81
13 / 0000 95 Hurricane category 2 0.9025
13 / 0600 95 Hurricane category 2 0.9025
13 / 1200 85 Hurricane category 2 0.7225
13 / 1800 50 Tropical Storm 0.25
14 / 0000 35 Tropical Storm 0.1225
14 / 0600 35 Tropical Storm 0.1225
14 / 1200 40 Extra tropical 0.1614 / 1800 50 Extra tropical 0.25
15 / 0000 50 Extra tropical 0.25
15 / 0600 40 Extra tropical 0.16
15 / 1200 35 Extra tropical 0.1225
Total: 39.87
If you look to the Wikipedia page with the ACE data of the hurricanes and tropical storms,
you can see that the wound up the number to 39. But you can explain that with the numbers of
the wind speed. The number of the ACE that the NHC gave is a number with more specific
wind speed data. Our numbers are wound up to speed with a difference of 5 knots. That is
why our ACE number is higher than that the National Hurricane Center gave.
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Psychic side of a hurricane:
Intertropical Convergence Zone
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Definition:
Intertropical convergence zone is the zone on earth near the equator. This zone is the zone
where the weather is the most unpredictable. The warmest air on earth is rising up there,
which can cause large low pressure areas, which can develop into a hurricane. The rising air
movement is caused by the fast amount of the condensation of the seawater.
As you can see in this picture the wind (the surface winds) is pulled to an Intertropical
Convergence Zone. (Low-pressure area in the neighbourhood of the equator) For the North
there are 2 different surface winds that come together. This causes heavy rainfall and tropical
storms. With these winds and the warm air there are enough elements to produce a heavy
hurricane. What you also see with hurricanes is that tropical waves from Africa help to
develop the hurricane even more.
Zenith point:
The Intertropical Convergencezone can be over land. When this
happens, the surface winds move
slowly back to the suns zenith
point. A zenith point is the place
where the distance to the sun is
the lowest. In our case this is the
equator. As you can see in this
picture, the man in the middle is
the equator and if you look you
can see that the spot right above
him is the zenith spot. The area
right above the equator is the
suns zenith.
The Intertropical convergence zone is never the same line. The line is not the equator but the
line is always different. But the line is always close to the equator.
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Convergence or Divergence:As you can see here on the right, is a
picture that shows how the
convergence zone between the
Caribbean Sea works. This is a typical
example of the working of the surfacewinds to hurricanes. What you can see
is that a hurricane (if it forms before it
comes in the waters of the Caribbean
Sea) can choose between 2 directions.
To the north (further on the Atlantic
Ocean) or to the south (in the
Caribbean Sea, or even later to the
Golf of Mexico). This choice is made
by the surface winds, that push the
hurricane into a direction. If a
hurricane is above the Lesser Islands, the chances are very high that the hurricane will movefurther on the Atlantic Ocean, but there is a small chance (25 to 50%) that it goes to the
Caribbean Sea, by moving over Cuba or Dominican Republic.
But if it is right above Puerto Rico, or just below Puerto Rico, the surface winds push the
hurricane into the Caribbean Sea.
This theory is very useful to predict
the path of a hurricane. If you know
where the hurricane is when he
passes the Lesser Islands, you know
where the hurricane is heading for.
The surface winds are the winds
that push the hurricanes into a
direction. Of course the hurricane
moves by itself, but the surface
winds are just like a wheel of a car.
In the picture on the left, you can
see how the surface winds move in
the Oceans. This means, this is the
direction where the low pressure
systems are pushed.
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Physic side of a hurricane:
Storm Surge
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Definition:A storm surge is a flood of water that threatens the coast area. This surge is most of the time
caused by a storm or in our case a hurricane. The wind pushes the seawater up, and this
causes a sort of flood. When the flood is near the shore, it will rise, by the withdrawing of the
seawater on the beach. This makes the storm surge even higher.
The picture on the right explains a little bit more about how a storm surge works.
Height:The height of a storm surge from a hurricane is different for each category of a hurricane. In a
table, I will show you the heights of a storm surge with a landfall of a hurricane with different
categories.
Category: Pressure: Storm Surge:
Tropical Depression >1010 None
Tropical Storm 990 till 1010 Above the normal high tide
Hurricane Category 1 980 till 989 1.2 till 1.6 meters
Hurricane Category 2 965 till 979 1.7 till 2.5 meters
Hurricane Category 3 945 till 964 2.6 till 3.7 meters
Hurricane Category 4 920 till 944 3.8 till 5.4 meters
Hurricane Category 5 < 920 Above the 5.4 meters!
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Pressure compared to a storm surge:Pressure is an important thing to form a storm surge even if the wind is forming the storm
surge. The pressure is formed by the rapidly decreasing air from the storm system. If this
happens, there is a sort of pressure that arises. The faster the air is decreasing, the lower the
pressure in the centre of the storm is. This decreasing air is pressed to the seawater. This
seawater is pushed back, and a sort of flood arises by the decreasing air. The picture herebelow will show you this a little bit better. The air is dropping in the eye and pushes the
seawater back. Because of this a higher level and a lower level of the seawater arise. This
causes the storm surge.
Landfall:
On the right we see a picture of astorm surge from a hurricane making
landfall to United States. In this
picture we clearly see that before the
eye hits land, there is an amazing
storm surge between 8 and 9 feet. This
is an amount of 3 meters high. This is
definitely a hurricane with the strength
of category 3 on the scale from Saffir/
Simpson. The red spot in the centre
represents the highest waves. If you
look very well, you can see a blackline with a red spot at the end. This
represents the track of the eye of a
hurricane. The closer the hurricane is
getting to land, the higher the storm
surge will be.
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Physic side of a hurricane:
El NioLa Nia
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Definition:El Nio and La Nia are two different things how can affect the atmosphere and the seawater.
The La Nia causes warmer seawater and can cause more hurricanes. On the next two
pictures I will show you the different between an El Nio and a La Nia.
El Nio:
This picture shows how the El Nio affects the seawater and the weather in the colored area.
La Nia:
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I will first explain the colours in the picture, after that I will explain something more about the
El Nio and La Nia.
Colour: Meaning:
Cool air
Wet airDry and cool air
Warm and dry air
Cool and Wet air
Wet and Cool air
Warm air
Dry
Wet and Warm
As you can see if there is El Nio conditions, which affects the water in the Atlantic Ocean,
the seawater changes dramatic. The ocean atmosphere and also the seawater become colder
and even weather condition become wetter. So more rainfall in the Caribbean area.
The normal conditions for the Pacific Ocean are the warm water in the west and cold water in
the area of the South American coast line. That is the reason, why hurricanes cant approach
San Francisco in normal conditions of the seawater.
The El Nio conditions causes that the warmer water comes in the area of the South American
coast line. The normal conditions of the colder air do not take place and this cause for
increasing warmer air and seawater.
The La Nia causes only that the warmer water is further west than usually. These
phenomenon most have a magnitude 0.5 Celsius and most last long for more than 5 months to
name it a El Nio or La Nia episode (year). If this is not, but the magnitude is over the 0.5Celsius, than these ocean conditions called El Nio or La Nia conditions. One episode of an
El Nio or La Nia can last for 2 years with a break of 2-7 years.
Signs:El Nio:
Higher air pressure in the area of the Indian Ocean, Indonesia and Australia
Lower air pressure in the area of Tahiti and central and eastern Pacific Ocean
Trade winds weaken in the south Pacific Warmer air in Peru, with causes rainfall in the dessert of Peru
Decreased fishing activity in Peru Extensive drought in the West Pacific Ocean
Rainfall in dry areas of the East Pacific Ocean
La Nia:
Cold ocean temperatures in the East Pacific Ocean
Atlantic hurricane activity can be increased by the La Nia episode. This means, that
the hurricanes or tropical storms in the Atlantic Ocean, can be better developed and
also more dangerous than in a non La Nia year.
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Stages:El Nio:
Stage 1:The seawater is getting warmer
by the effects of the El Nio.
Stage 2:The seawater is still getting
warmer. The blue (colder) areas are
slowly disappearing.
Stage 3:The evolution of the El Nio is
almost done. The blue areas arealmost gone, only in the north
and the south. In these areas is
still colder seawater. As you look
to the equator, the seawater
around this area is very hot in
compare to the first stage.
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Stage 4:The evolution from the El Nio is
complete. The seawater on the
south coast of the Middle Americancontinent is very hot and all the
cooler seawater in this area is
almost gone. This is now a perfect
spot for hurricanes to develop.
These stages where made in the El Nio episode in 1997. Two years later after the El Nio a
La Nia episode reaches the Pacific Ocean.
La Nia:
Stage 1:The seawater in the south area of
the Pacific Ocean is showing
some cooling. But the Atlantic
Ocean and the Gulf of Mexico is
getting hotter.
Stage 2:The cooling is still in progress andthe warmer areas are slowly
disappearing to the west.
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Stage 3:The cooling process is almost
done. The warmer seawatermoved to the south and the west.
But on the Atlantic Ocean there
are still signs of the warmer
seawater, what can caused a
perfect spot for hurricanes to
develop!
Stage 4:The La Nia evolution is complete.
The colder water has taking place
for the warmer seawater. Moreover
the seawater in the Atlantic Ocean
is still warmer than normal.
These stages represent the La Nia event in 1999. Short after the El Nio episode two years
earlier.
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Appendix:
This paragraph contains a lot of information about hurricanes, but this isnt everything to
understand how a hurricane works. The time was too short to do research to that. But these
subjects are the most important to understand how this beautiful weather phenomena works. I
hope you can use this information to understand hurricanes and maybe some other weatherphenomenas.
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