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Title: Hurricanes and Tropical Storms


1
Hurricanes and Tropical Storms
2
Naming Convention
  • Hurricanes extreme tropical storms over Atlantic
    and Eastern
  • Pacific Oceans
  • Typhoons extreme tropical storms over western
    Pacific Ocean
  • Cyclones extreme tropical storms over Indian
    Ocean and
  • Australia

3
Ocean Temperatures and Hurricanes
Hurricanes depend on large pools of warm water
4
Annual Hurricane Frequency
  • There are no hurricanes in the southern Atlantic
    Ocean!
  • The strongest hurricanes occur in the western
    Pacific Ocean
  • (often referred to as super-typhoons.)

5
Hurricane Characteristics
  • Definition Hurricanes have sustained winds of
    120 km/hr (74 mph) or greater.
  • Size Average diameters are approx. 600 km (350
    mi). This is 1/3 the size of a mid-latitude
    cyclone (synoptic storm system).
  • Duration Days to a week or more.
  • Strength Central pressure averages 950 mb but
    may be as low as 870 mb (lower the pressure
    stronger the storm).
  • Power The power released by a single hurricane
    can exceed the annual electricity consumption by
    the US and Canada combined.

6
Hurricane Seasons
  • Hurricanes obtain their energy from latent heat
    release in cloud formation processes.
  • Hurricanes occur where a deep layer of warm water
    exists during the time of the highest SSTs (sea
    surface temps).
  • Northern Hemisphere August through September are
    most active months.
  • Southern Hemisphere January through March are
    the most active months

7
Latent Heat Release Me!
  • Hurricanes draw their power from warm, extremely
    humid air found only over warm oceans.
  • The key energy source is the latent heat that's
    released when water vapor condenses into cloud
    droplets and rain. Tropical storms and hurricanes
    grow best in a deep layer of humid air that
    supplies plenty of moisture.
  • When a substance changes phase, energy must be
    supplied in order to overcome the molecular
    attractions between the constituent particles.
    This energy must be supplied externally, normally
    as heat, and does not bring about a change in
    temperature.

When water is in the vapor state, as a gas, the
water molecules are not bonded to each other.
They float around as single molecules.
When water is in the liquid state, some of
the molecules bond to each other with hydrogen
bonds.  The bonds break and re-form continually.
8
Latent Heat
  • We call the energy needed to change phases latent
    heat (the word "latent" means "invisible"). The
    latent heat is the energy released or absorbed
    during a change of state.
  • To get the molecule of water vapor to become
    liquid again, we have to take the energy away,
    that is, we have to cool it down so that it
    condenses (condensation is the change from the
    vapor state to the liquid state).  When water
    condenses, it releases latent heat.

9
Latent Heat Values
  • The amount of latent heat involved depends to
    some extent on the temperature at which the
    process is occurring. The figures below are those
    normally found in meteorology texts and are for
    temperatures found in the atmosphere, such as 0
    Celsius (32 F).
  • Latent heat of condensation (Lc) Refers to the
    heat gained by the air when water vapor changes
    into a liquid. Lc2500 Joules per gram (J/g) of
    water or 600 calories per gram (cal/g) of water.
  • Latent heat of fusion (Lf) Refers to the heat
    lost or gained by the air when liquid water
    changes to ice or vice versa. Lf333 Joules per
    gram (J/g) of water or 80 calories per gram
    (cal/g) of water.
  • Latent heat of sublimation (Ls) Refers to the
    heat lost or gained by the air when ice changes
    to vapor or vice versa. Ls2833 Joules per gram
    (J/g) of water or 680 calories per gram (cal/g)
    of water.
  • Latent heat of vaporization (Lv) Refers to the
    heat lost by the air when liquid water changes
    into vapor. This is also commonly known as the
    latent heat of evaporation. Lv -2500 Joules per
    gram (J/g) of water or -600 calories per gram
    (cal/g) of water.

10
Latent Heat
  • As water vapor evaporates from the warm ocean
    surface, it is forced upward in the convective
    clouds that surround the eyewall and rainband
    regions of a storm. As the water vapor cools and
    condenses from a gas back to a liquid state, it
    releases latent heat. The release of latent heat
    warms the surrounding air, making it lighter and
    thus promoting more vigorous cloud development.
  • The release of latent heat warms the surrounding
    air, making it lighter and thus promoting more
    vigorous cloud development.
  • Animation http//svs.gsfc.nasa.gov/vis/a000000/a0
    01600/a001605/cloud.mov

11
Energy of Latent Heat
Air parcel dew point temperature (oC) Approximate amount of water vapor (g) in an air parcel (kg) at saturation (by the way, in text books referred to as the saturation mixing ratio) Approximate amount of potential heating due to latent heat release (calories) if all the water vapor condenses
0 4 2360
10 8 4720
20 16 9440
30 32 18880
40 64 37760
  • Condensation releases latent heat. This causes
    the temperature of a cloud to be warmer than it
    otherwise would have been if it did not release
    latent heat. Anytime a cloud is warmer than the
    surrounding environmental air, it will continue
    to rise and develop.
  • The more moisture a cloud contains, the more
    potential it has to release latent heat.
  • Temperatures in the middle of the rising air in
    cumulonimbi there may be as much as 15-20C
    (28-38F) warmer than air outside the storm. For
    Hurricane Rita, observations showed that, at 700
    mb (approximately 10000 feet), the interior
    temperature of Rita was 31C and about 20C warmer
    than the outside of the storm at the same
    elevation.

12
Hurricane Structure
  • A central eye is surrounded by large cumulonimbus
    thunderstorms occupying
  • the adjacent eyewall.
  • Weak uplift and low precipitation areas are
    separated by individual cloud
  • bands.

13
Temperature Structure
  • Hurricanes characterized by a strong thermally
    direct circulation with rising of warm air near
    center of storm and sinking of cooler air
    outside.
  • The warm core of the hurricane serves as a
    reservoir of potential energy which is
    continually being converted to kinetic energy by
    thermally direct circulation

14
Pressure Structureof Hurricanes
  • The horizontal pressure gradient with altitude
    decreases slowly
  • From surface to 400 mb cyclonic circulation.
  • At about 400 mb, the pressure inside the storm is
    approx. that of outside of the storm.
  • From 400 mb to tropopause anticylonic
    circulation.
  • The upper portions of the storm are blanketed by
    a cirrus cloud cap due to overall low
    temperatures.

15
(No Transcript)
16
Hurricanes and Tropical Storms
17
Naming Convention
  • Hurricanes extreme tropical storms over Atlantic
    and Eastern
  • Pacific Oceans
  • Typhoons extreme tropical storms over western
    Pacific Ocean
  • Cyclones extreme tropical storms over Indian
    Ocean and
  • Australia

18
Ocean Temperatures and Hurricanes
Hurricanes depend on large pools of warm water
19
Annual Hurricane Frequency
  • There are no hurricanes in the southern Atlantic
    Ocean!
  • The strongest hurricanes occur in the western
    Pacific Ocean
  • (often referred to as super-typhoons.

20
Hurricane Characteristics
  • Definition Hurricanes have sustained winds of
    120 km/hr (74 mph) or greater.
  • Size Average diameters are approx. 600 km (350
    mi). This is 1/3 the size of a mid-latitude
    cyclone (synoptic storm system).
  • Duration Days to a week or more.
  • Strength Central pressure averages 950 mb but
    may be as low as 870 mb (lower the pressure
    stronger the storm).
  • Power The power released by a single hurricane
    can exceed the annual electricity consumption by
    the US and Canada combined.

21
Hurricane Seasons
  • Hurricanes obtain their energy from latent heat
    release in cloud formation processes.
  • Hurricanes occur where a deep layer of warm water
    exists during the time of the highest SSTs (sea
    surface temps).
  • Northern Hemisphere August through September are
    most active months.
  • Southern Hemisphere January through March are
    the most active months

22
Latent Heat Release Me!
  • Hurricanes draw their power from warm, extremely
    humid air found only over warm oceans.
  • The key energy source is the latent heat that's
    released when water vapor condenses into cloud
    droplets and rain. Tropical storms and hurricanes
    grow best in a deep layer of humid air that
    supplies plenty of moisture.
  • When a solid substance changes phase, energy must
    be supplied in order to overcome the molecular
    attractions between the constituent particles.
    This energy must be supplied externally, normally
    as heat, and does not bring about a change in
    temperature.

When water is in the vapor state, as a gas, the
water molecules are not bonded to each other.
They float around as single molecules.
When water is in the liquid state, some of
the molecules bond to each other with hydrogen
bonds.  The bonds break and re-form continually.
23
Latent Heat
  • We call the energy needed to change phases latent
    heat (the word "latent" means "invisible"). The
    latent heat is the energy released or absorbed
    during a change of state.
  • To get the molecule of water vapor to become
    liquid again, we have to take the energy away,
    that is, we have to cool it down so that it
    condenses (condensation is the change from the
    vapor state to the liquid state).  When water
    condenses, it releases latent heat.

24
Latent Heat Values
  • The amount of latent heat involved depends to
    some extent on the temperature at which the
    process is occurring. The figures below are those
    normally found in meteorology texts and are for
    temperatures found in the atmosphere, such as 0
    Celsius (32 F).
  • Latent heat of condensation (Lc) Refers to the
    heat gained by the air when water vapor changes
    into a liquid. Lc2500 Joules per gram (J/g) of
    water or 600 calories per gram (cal/g) of water.
  • Latent heat of fusion (Lf) Refers to the heat
    lost or gained by the air when liquid water
    changes to ice or vice versa. Lf333 Joules per
    gram (J/g) of water or 80 calories per gram
    (cal/g) of water.
  • Latent heat of sublimation (Ls) Refers to the
    heat lost or gained by the air when ice changes
    to vapor or vice versa. Ls2833 Joules per gram
    (J/g) of water or 680 calories per gram (cal/g)
    of water.
  • Latent heat of vaporization (Lv) Refers to the
    heat lost by the air when liquid water changes
    into vapor. This is also commonly known as the
    latent heat of evaporation. Lv -2500 Joules per
    gram (J/g) of water or -600 calories per gram
    (cal/g) of water.

25
Latent Heat
  • As water vapor evaporates from the warm ocean
    surface, it is forced upward in the convective
    clouds that surround the eyewall and rainband
    regions of a storm. As the water vapor cools and
    condenses from a gas back to a liquid state, it
    releases latent heat. The release of latent heat
    warms the surrounding air, making it lighter and
    thus promoting more vigorous cloud development.
  • The release of latent heat warms the surrounding
    air, making it lighter and thus promoting more
    vigorous cloud development.
  • Animation http//svs.gsfc.nasa.gov/vis/a000000/a0
    01600/a001605/cloud.mov

26
Energy of Latent Heat
Air parcel dew point temperature (oC) Approximate amount of water vapor (g) in an air parcel (kg) at saturation (by the way, in text books referred to as the saturation mixing ratio) Approximate amount of potential heating due to latent heat release (calories) if all the water vapor condenses
0 4 2360
10 8 4720
20 16 9440
30 32 18880
40 64 37760
  • Condensation releases latent heat. This causes
    the temperature of a cloud to be warmer than it
    otherwise would have been if it did not release
    latent heat. Anytime a cloud is warmer than the
    surrounding environmental air, it will continue
    to rise and develop.
  • The more moisture a cloud contains, the more
    potential it has to release latent heat.
  • Temperatures in the middle of the rising air in
    cumulonimbi there may be as much as 15-20C
    (28-38F) warmer than air outside the storm. For
    Hurricane Rita, observations showed that, at 700
    mb (approximately 10000 feet), the interior
    temperature of Rita was 31C and about 20C warmer
    than the outside of the storm at the same
    elevation.

27
Hurricane Structure
  • A central eye is surrounded by large cumulonimbus
    thunderstorms occupying
  • the adjacent eyewall.
  • Weak uplift and low precipitation areas are
    separated by individual cloud
  • bands.

28
Temperature Structure
  • Hurricanes characterized by a strong thermally
    direct circulation with rising of warm air near
    center of storm and sinking of cooler air
    outside.
  • The warm core of the hurricane serves as a
    reservoir of potential energy which is
    continually being converted to kinetic energy by
    thermally direct circulation

29
Pressure Structureof Hurricanes
  • The horizontal pressure gradient with altitude
    decreases slowly
  • From surface to 400 mb cyclonic circulation.
  • At about 400 mb, the pressure inside the storm is
    approx. that of outside of the storm.
  • From 400 mb to tropopause anticylonic
    circulation.
  • The upper portions of the storm are blanketed by
    a cirrus cloud cap due to overall low
    temperatures.

30
Hurricane Eye and Eyewall
  • A shrinking eye indicates storm intensification
  • The eyewall is moves at a speed of 20 km/hour and
    the calm weather associated with the eye will
    last less than 1 hour
  • The hurricane eye is an area of descending air,
    relatively clear sky and light winds 25 km (15
    mi) diameter on average.
  • The eyewall is comprised of the strongest winds,
    the largest clouds and the heaviest precipitation
    with rainfall rates as high as 2500 mm/day (100
    inches/day).

31
Hurricane Formation
  • Tropical Disturbance Clusters of small
    thunderstorms.
  • Tropical Depression When at least 1 closed
    isobar is present (organized center of low
    pressure).
  • Tropical Storm Further intensification to wind
    speeds of 60 km/hr (37 mph).
  • Hurricane Hurricane status is gained when the
    winds reach a sustained 120 km/hr (74 mph).

32
Tropical Disturbances and Easterly Waves
  • Some tropical disturbances form from mid-latitude
    troughs migrating
  • towards lower latitudes, some form from ITCZ
    convection, but most
  • develop from easterly waves.
  • Easterly Waves, or undulations in the trade wind
    patterns, spawn
  • hurricanes in the Atlantic.
  • Only 10 of tropical disturbance become more
    organized, rotating
  • storms.

33
Conditions necessary for Hurricane Formation
  • Hurricanes only form over deep (several 10s of
    meters) water layers with temperatures in excess
    of 27 degrees C.
  • Poleward to about 20 degrees, water temperatures
    are usually below this threshold.
  • Coriolis effect is an important contributor,
    hurricanes do not form from equator to 5 degrees.
  • Need unstable atmosphere available in western
    parts of oceans but not in eastern parts of
    ocean.
  • Strong vertical shear must be absent. (both
    magnitude and direction).
  • Vertical shear changing of wind speed and/or
    direction with height of the atmosphere.

34
Hurricane Movement
  • Tropical depressions and disturbances are largely
    regulated by trade wind flow move westward.
  • Tropical storms hurricanes upper-level winds
    and ocean temperatures gain importance.
  • Fully developed hurricanes will move poleward
    (stronger upper winds will steer the hurricanes
    northward).

35
Hurricane Dissipation
  • After making landfall, a hurricane may die
    completely within a couple of days (no longer has
    moisture to feed into storm).
  • Even as storm weakens, it can still have large
    effects on land (especially flooding).
  • Hurricanes will also dissipate over cooler waters
    or if they encounter strong vertical shear.
  • Animation http//svs.gsfc.nasa.gov/vis/a000000/a0
    01600/a001605/coldwater.mov

36
Hurricane Damage
  • Heavy rainfall
  • Strong winds
  • Tornadoes (generally F0-F2)
  • Storm surge rise in water level induced by the
    hurricane.

37
Tornado formation in hurricanes
  • Most hurricanes contain clusters of tornadoes.
  • Most tornadoes occur in right front quadrant of
    the storm.
  • It appears that slowing of wind by friction at
    landfall contributes to the formation of these
    tornadoes.

38
Storm Surges
  • Process 1 Hurricane winds drag surface waters
    forward and pile water near coasts.
  • Process 2 Lower atmospheric pressure raises sea
    level (for every 1mb pressure decrease, sea level
    raises 1 cm)
  • Storm surges raise sea level by a 1-2 m for most
    hurricanes, as much as 7 m (a real problem when
    coastal locations are at or below sea-level)

39
Hurricane Wind Structure
  • Winds and surge are typically strongest at right
    front quadrant of storm where wind speeds combine
    with speed of storms movement to create the
    highest area of potential impact.

40
Trends for Atlantic
  • Mid 1990s-now A significant increase in the
    numbers of hurricanes and intense hurricanes
    making landfall in US.
  • 1970s-mid 1990s Lower than normal incidence of
    Atlantic Hurricanes.
  • Debate Is the recent increase in hurricanes part
    of a natural cycle, global climate change or a
    combination?

41
Forecasting
  • National Hurricane Center responsible for
    Atlantic and eastern/central Pacific.
  • Data gathered through satellite, surface
    observations and aircraft using dropsondes
    (dropping of instruments through hurricane)
  • Computer models assist in predictions.

42
Hurricane Watch and Warning
  • Hurricane Watch if an approaching hurricane is
    expected to make landfall within 24 hours.
  • Hurricane Warning if the time frame is less,
    then its a warning.

43
Naming of Hurricanes
  • When a tropical disturbance reaches a tropical
    depression, the storm will be given a name.
  • The name comes from an A-W list given by World
    Meteorological Organization (WMO).
  • The names of hurricanes with devastating effects
    are retired.

44
Hurricane Intensity Scale
  • Saffir-Simpson Scale
  • Five Categories the larger numbers indicate
    lower central
  • pressures, greater winds and stronger storm
    surges
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