Typhoon

1
Typhoon

• What Do You Know?

2
Roadmap

• Common terms
• Naming
• Definitions
• Common expressions

3
Typhoons, Hurricanes and Tropical Cyclones

• Cyclone (generic term)
• Tropical Cyclone
• Typhoon
• Hurricane
• Cyclone (one of tropical cyclones)
• Extratropical Cyclone
• Willy-Willy
• Tornado

4
Cyclone

• Cyclone is the most general term to refer to a
  low-pressure system.
• Typhoons and other types of low pressure systems
  are all cyclones. The direction of rotation is
  opposite in the northern hemisphere and the
  southern hemisphere, but other essential features
  of a cyclone are shared in both hemispheres.

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Tropical Cyclone

• Tropical cyclone is in general a cyclone formed
  in the tropical areas.
• The word "tropical" does not refer to the place
  of formation, and it actually refers to the
  structure of a cyclone.
• Typhoons, hurricanes and others are all "intense"
  tropical cyclones, so they are regarded as same
  meteorological phenomena. It is, however, still
  unclear whether there is subtle regional
  differences between tropical cyclones in the
  world.

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Extratropical Cyclone

• Extratropical cyclone literally means a cyclone
  outside of the tropical areas. Just like a
  tropical cyclone, this term also does not refer
  to the place of formation, but refers to the
  structure of a cyclone.
• Formation
• tropical cyclone warm air only
• extratropical cyclone consists of both cold air
  and warm air.
• Finally, we often see a tropical cyclone
  transformed into an extratropical cyclone, but
  the inverse is rare.

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Typhoon

• Typhoon is a tropical cyclone located in the
  western north Pacific basin (between 100E and
  180E in the northern hemisphere). The category of
  a typhoon is decided by the maximum sustained
  winds.
• Finally, among tropical cyclones in the world,
  the typhoon is the most frequent and the
  strongest tropical cyclone.

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Hurricane

• Hurricane is a tropical cyclone located in the
  north Atlantic, eastern north Pacific (east of
  180W in the northern hemisphere), eastern south
  Pacific (east of 160E in the southern
  hemisphere).
• The category of a hurricane follows the same
  international standard as the typhoon based on
  the maximum sustained wind.
• When a hurricane goes across the 180 degree date
  line and enters into the basin of the typhoon, it
  starts to be called a typhoon.

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Cyclone (Contd.)

• Originally a generic term for a cyclonic system.
• It is also used to refer to something equivalent
  to a typhoon (tropical cyclone) when there is no
  special term available. Indian Ocean, western
  south Pacific, and Australia are the examples of
  this area.

10
Willy-Willy

• Willy-Willy is often introduced as the name of a
  tropical cyclone around Australia.
• But it seems that it actually means something
  like a dust devil, and has little relationship
  with a tropical cyclone.
• A dust devil is a rotating updraft, 1000 meters
  high or more and tens of meters in diameter. They
  are distinct from the common dust storms of this
  area, because they resemble small tornados.

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Tornado

• The tornado and the tropical cyclone share the
  same feature as the vortex of atmosphere, but
  other features, such as formation, structure,
  scale and duration, are totally different.
• For example, the scale of a tornado is usually on
  the order of 100m-1000m, while a tropical cyclone
  is on the order of 100km-1000km.

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Naming Typhoons

• Number-based conventions and a list-based
  convention.
• The latter convention is more popular in most
  countries, such as human names for hurricanes.

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Number-based Conventions

• Number-based conventions are based on the
  sequential number from the beginning of a typhoon
  season.
• For example, Typhoon No. 14 is the 14th typhoon
  of the typhoon season.
• On the other hand, a 4-digit YEARNUMBER
  identification code such as Typhoon 0314, or
  T0314 for short, is a more preferred convention
  in technical and professional areas.
• Number-bases conventions, however, directly use
  sequential numbers, so it is sensitive to
  subsequent changes of orders.
• Secondly, when the order of birth is changed,
  names do not change to reflect the actual order.

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List-based Conventions

• List-based conventions are based on the list of
  typhoon names defined in advance by the committee
  of meteorological organizations worldwide.
• A new name is automatically chosen from the list
  upon the genesis of a typhoon. The list is
  defined for each basin and managed by the
  meteorological organization responsible for the
  respective basin.
• The majority of countries in the world seems to
  prefer list-based conventions to number-based
  conventions.
• Advantages explicit representation of the
  sequential order of the typhoon during the
  typhoon season
• Disadvantage similarity of all names which leads
  to the difficulty of making distinction.

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Named after Women?

• The most famous list with the longest history is
  the list of hurricane names of the Atlantic
  Ocean. This list contains alphabetically-ordered
  names from A (Q, U, X, Y, Z are skipped).
• On the birth of a new hurricane, a new name is
  chosen in the alphabetical order, and the next
  list is in use when the current list is
  exhausted.
• Only female names were used in the beginning,
  because hurricanes were named after girlfriends
  or wives of US Army Air Corp and Navy
  meteorologists. In 1979, however, male names are
  included in the list from an argument on gender
  equality.

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Asian Names of the Typhoon

• The Asian names are list of words submitted to
  the typhoon committee, consisting of
  meteorological organizations of 14 countries and
  regions in the Asia / Pacific, that belongs to
  Tropical Cyclone Programme, World Meteorological
  Organization (WMO).
• This list contains words of so diverse meanings
  -- such as animals, plants, and natural phenomena
  -- that preference to human names do not remain
  any more.
• Asian names are sorted according to the
  alphabetical name of countries, so typhoon names
  themselves are not necessarily arranged in an
  alphabetical order.
• When a hurricane moves across the 180 degree line
  and enters into the basin of the typhoon, it
  starts to be called a typhoon. A new Asian name,
  however, is not assigned in this case, and the
  hurricane name is kept as the name of the
  tropical cyclone.

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Common Problems

• One problem with typhoon names is the ambiguity
  of typhoon names. That is, we sometimes have
  multiple typhoons with the same name in history,
  and that causes the problem of resolving
  ambiguities. This is in particular a big problem
  with the natural language processing of
  typhoon-related text, or named entity
  recognition, because the computer should
  disambiguate the typhoon name automatically by
  the contents of the text.

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Retiring Typhoon Names

• To cope with the ambiguity problem, the typhoon
  name is sometimes "retired," and removed from the
  list.
• This case happens when the typhoon has a severe
  impact on lives or the economy to the level that
  is remembered for generations after the
  devastation. Whenever a typhoon has had this
  level of impact, any country affected by the
  storm can make a request to the World
  Meteorological Organization (WMO) that the name
  of the typhoon be retired to facilitate historic
  references, legal actions, insurance claim
  activities, etc.

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The Nameless Cyclone and No-Name Typhoons

• An article from NASA on April 2, 2004 says that
  we finally had "the nameless cyclone
  (hurricane)." The story goes that they observed a
  cyclone in the South Atlantic basin where
  tropical cyclones have never been observed
  before. The list of cyclone names for this basin
  was therefore not prepared so this cyclone could
  not be named.
• (Note) It seems that this hurricane is now called
  Catarina after the name of the place it made
  landfall.

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The Definition of Typhoon Season

• Generally speaking, the term "typhoon season" is
  a period of time during which we have frequent
  typhoon effects.
• Within the recording of typhoons this term means
  the borders of one year in terms of the formation
  of typhoons. The starting point of counting for
  the number-based conventions of typhoon names is
  based on the typhoon season.
• Northern hemisphere Western North Pacific Basin
  From January to December
• Southern hemisphere Western South Pacific Basin
  From July to June (next year)

21
Unit of Pressure and Wind

• Hecto Pascal (hPa) is a unit for pressure, and,
  used mainly for representing the central pressure
  of a typhoon.
• Knot (kt) is a unit for speed, used mainly for
  representing the maximum wind speed at the center
  of a typhoon. Conversion of units is 1kt 1.852
  km/h 0.514 m/s, so roughly speaking, 2 kt 1
  m/s and 1 kt 2 km/h.

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The Life Period of Typhoons

• "Typhoon" is a name given to a tropical cyclone
  with the maximum wind of more than 34 knots.
• The difference between a tropical depression and
  a typhoon is merely the difference of the
  strength of the wind.
• The ground truth measurement of the maximum wind
  speed around the center is not always possible.
  So whether a tropical cyclone should be called a
  typhoon cannot be decided automatically and this
  decision making requires the skills of human
  experts.
• Human experts declare their birth and death, so
  we can explicitly define the life period of
  typhoons. This is one of the unique
  characteristics of the typhoon.
• Some typhoons come to life again after weaken
  into tropical depressions. We even have a typhoon
  with two rebirths. Hence there are two
  possibilities as to the definitions of the life
  period of the typhoon in those cases.
• The period between the first birth and the last
  death of the typhoon.
• The period as above except for the period of its
  being a tropical depression, or not being a
  typhoon.

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Understanding some common expressions

• The typhoon is changed to the extratropical
  cyclone
• change of structure, not the change of intensity.
• More specifically, this expression is used when
  the structure of the typhoon is changed from a
  tropical cyclone to an extratropical cyclone.
• In most cases this change does not go backward.
• The typhoon is changed to the tropical
  depression
• the change of intensity, not the change of
  structure.
• More specifically, this expression is used when
  the maximum wind around the center happens to be
  smaller than the threshold to be a typhoon.
• It only means that the maximum wind is below the
  threshold, so we sometimes see a tropical
  depression revives as a typhoon.
• In short, change from a typhoon to an
  extratropical cyclone means structural change,
  while change from a typhoon to a tropical
  depression means intensity change.
• We should be aware that these expressions do not
  imply the typhoon to be weakened in terms of
  rainfall.