Transcript THUNDERSTORMS

THUNDERSTORMS
CHAPTER
11
HOMEWORK
• AOPA Weather Wise: Thunderstorms
and ATC due next class
• READ: Chapter 11
THUNDERSTORMS
• Begins with the formation of a
convective cloud type such as
cumulus or altocumulus
castellanus.
• Usually form when an air mass
is unstable through a very
deep layer, and is very moist
in its lower levels.
THUNDERSTORMS
• Cumulonimbus - Heavy, dense
cumuliform clouds with
considerable vertical development
in the form of massive towers.
Cumulonibus develop from
cumulus clouds, and the tops of
the towers , which are often in the
shape of an anvil or massive
plume , extend upward for many
thousand feet.
THUNDERSTORMS
• Cumulonimbus - Lightning,
thunder, and often hail
accompany a cumulonimbus; and
virga, percipitation and low,
ragged clouds, called scud or
shelf, often form under their dark
bases. Can also produce
tornadoes or waterspouts and
severe icing in cloud.
THUNDERSTORMS
• Drafts and gusts are prominent
features of thunderstorms. Drafts
can be either updrafts or
downdrafts and are large enough
that they can move the aircraft
vertically. The aircraft can be
wholly contained within the draft
and although a thousand feet or
more may be gained or lost there
may be little turbulence or severe
turbulence.
THUNDERSTORMS
• Superimposed upon the large-scale
continuous flow of the drafts are
numerous irregular random sudden
and brief turbulent motions called
“Gusts”. They have a significant
effect upon the aircraft causing
pitch, roll and yaw movements. The
gusts vary in size from a few inches
to whirling masses or air several
hundred feet in diameter.
THUNDERSTORMS
• Gusts are produced by the shearing
action between drafts and the air
surrounding the drafts, or between
adjacent updrafts and downdrafts. In
the aircraft they can be felt as vertical
or horizontal jolts. Going any where
near a cell tighten your seatbelt. These
jolts are extremely sharp and will cause
items not tied down to fly around and
maybe hit your head on the ceiling.
THUNDERSTORMS
• The upward motion of the initial
updraft in the cloud is accelerated
by the release of latent heat, first as
water vapour condenses to water
droplets and then, higher in the
cloud as water droplets freeze to
become ice crystals.
THUNDERSTORMS
• In order for a thunderstorm to form the
air needs three things:
• A lifting agent
• Unstable lapse rate
• Sufficient water vapor (should also have
Nuclei)
THUNDERSTORMS LIFE
CYCLE
• All thunderstorms progress through
a life cycle from their initial
development through maturity into
a dissipating stage. This life cycle
typically takes from one to three
hours, but can be much longer.
THUNDERSTORMS LIFE
CYCLE
• The 3 stages of a thunderstorm
are:
–The Cumulus Stage
–The Mature Stage
–The Dissipating Stage
CUMULUS STAGE
• The first stage of a thunderstorm
cell is the Cumulus Stage.
• Several small convective clouds will
merge and begin to grow rapidly
into a very large convective cell.
The base may expand to four miles
across and the cloud top may rise
to over 20,000 feet.
CUMULUS STAGE
• Only updrafts are present in the
cloud and air is drawn into the sides
as well as into the base of the
cloud. The updraft speed is
greatest in the upper levels and can
reach 3,000+ fpm.
• Most airplanes are not capable of
out climbing a rapidly developing TS
CUMULUS STAGE
• Early during this stage, water
droplets are quite small but grow to
raindrop size as the cloud grows.
The upwelling air carries the liquid
water above the freezing level
creating an icing hazard.
• Typical life cycle 20 minutes for the
cumulus Stage.
MATURE STAGE
• Precipitation beginning to fall from
the cloud base is your signal that a
downdraft has developed and a cell
has entered the mature stage. The
cloud continues to grow and
updrafts reach their maximum
speed, possibly reaching 6,000 +
fpm.
• Usually lasts 20-30 minutes
MATURE STAGE
• The cloud can reach the tropopause if
the updraft is particularly strong, it may
even burst into the stable air of the
stratosphere for 5,000 or 10,000 feet.
• The strong winds at the tropopause
carry the cloud ahead of the storm,
forming an anvil shape with the
inversion above the tropopause acting
as a lid to hold the anvil beneath it.
THUNDERSTORM ANVIL
MATURE STAGE
• Cold rain in the downdraft retards
compressional heating, and the
downdraft remains cooler than
surrounding air. Downdrafts typically
are around 2,500 fpm
• The downrushing air spreads outward
at the surface producing strong, gusty
surface winds, a sharp temperature
drop and a rapid rise in pressure.
GUST FRONT
MATURE STAGE
• Can get severe downdrafts or “Microburst”
(exceptionally violent winds that last for
only a few minutes and that are only
about a mile across).
• A roll cloud may form near the main cloud
base in the shear area at the front of the
cloud where the downdraft comes out of
the cloud base and the updraft enters it.
(can also be a shelf cloud)
MATURE STAGE & HAIL
• Most likely to occur in the mature
stage. Super-cooled raindrops above
the freezing level begin to freeze. As
they fall, other drops coalesce on
them and freeze and the hail stone
grows in size. If the hail falls into a
strong updraft area, they are carried
back aloft, continuously growing until
they are too large for the updrafts to
carry and they fall.
MATURE STAGE & HAIL
• As hail falls below the freezing level,
they begin to melt and may reach the
ground as either rain or hail. For this
reason, hail is most prevalent and
larger above the freeezing level.
DISSIPATING STAGE
• Downdrafts characterize the
dissipating stage of the
thunderstorm cell and the storm cell
dies sometimes slowly other times
rapidly. When the rain has ended
and downdrafts have abated, the
dissipating stage is complete.
DISSIPATING STAGE
• The anvil may remain for a
considerable time. The dissipating
stage may last for one or 2 hours
and is the most prolonged of the
three stages of the thunderstorm
cell and is also the least hazardous
LIFE CYCLE OF TS
LIFE CYCLE OF TS
• An individual thunderstorm usually
consists of two or more cells in
different stages of their life cycles.
It may cover an area from around
10 miles in diamater to as much
as 100 miles. Things alive!
• http://www.youtube.com/watch?v=_cl0a
w87LqA
• http://www.youtube.com/watch?v=LOy5
C6JZG4o
• http://www.youtube.com/watch?v=pRv1
UHYvRuA&feature=related
LIGHTNING
LIGHTNING
LIGHTNING
• The cloud is now composed of strong
up and downdrafts occurring side by
side. Water droplets, hail and snow
are moving up and down and it is in
these complex and changing
conditions that lightning occurs. Areas
of positive and negative charge
accumulate in different parts of the
cloud until the difference in electrical
potential reaches a critical value.
LIGHTNING
• When this occurs a lightning discharge
takes place, sometimes from one part
of the cloud to another, sometimes
from one cloud to another, or from
cloud to ground
• Occassionally a discharge takes place
from the top of the cloud to the
atmosphere above the cloud, and on
rare occasions, from the ground to the
cloud.
LIGHTNING
• As a thunderstorm grows, electrical charges
build up within the cloud. Oppositely charged
particles gather at the ground below. The
attraction between positive and negative
charges quickly grows strong enough to
overcome the air's resistance to electrical flow.
Racing toward each other, they connect and
complete the electrical circuit. Charge from the
ground then surges upward at nearly one-third
the speed of light and we see a bright flash of
lightning.
ANATOMY OF LIGHTNING
STROKE
• Stepped Leader: Electrons which have
negative charge, begin zigzagging
downwards.
ANATOMY OF LIGHTNING
STROKE
• Attraction: As the step leader nears the
ground, it draws a streamer of positive
charge upward.
ANATOMY OF LIGHTNING
STROKE
• Flowing Charge: As the leader and
streamer come together, powerful
electric current begins to flow
ANATOMY OF LIGHTNING
STROKE
• Contact: Intense wave of positive charge,
a return stroke “travel is upward at
60,000 miles per second.
THUNDER
• Thunder is the noise made as a result
of the lightning heating the air so
rapidly that it expands faster than the
speed of sound. The rumbling is due
to the distance between the listener
and the various parts of the lighting
channel. The distance in miles to the
lightning strike can be estimated by
counting seconds between lightning
and thunder and dividing that number
by five.
THUNDER
• Normally, thunder can be heard up to 10 miles from
the lightning that makes it. Lightning heats the air
around it to as much as 60,000 degrees, producing
sound waves by the quick expansion of the heated
air. Since light travels at 186,000 miles per second,
you see the lightning the instant it flashes. But
sound, including thunder, travels about a mile in five
seconds near the ground. If 15 seconds elapse
between seeing a lightning bolt and hearing its
thunder, the lightning was about three miles away.
THUNDER
LIGHTNING
LIGHTNING
LIGHTNING
LIGHTNING
• http://lightning.pwr.eng.osakau.ac.jp/lrg/temp/plane.html
• Excellent video in Osaka Japan of an
airliner getting hit by lightning.
SEVERE STORM STRUCTURE
• The more severe thunderstorms have a
slightly different structure. If horizontal wind
speeds increase markedly with height,
considerable tilt develops in the updraft and
cloud. With the tilt precipitation falls through
only a small portion of the rising air. Since
the drag of falling raindrops is not imposed
upon the rising currents in the cloud, the
updrafts can continue. If there is a layer of
dry air at mid levels through which the rain is
falling, evaporation cooling enhances the
downdraft speed.
SEVERE STORM STRUCTURE
• In the presence of this cold
downdraft, the tilted updraft becomes
part of an overturning of the air in a
deep layer of the troposphere and the
ascending air can reach velocities in
excess of 10,000 fpm. It may
penetrate several thousand feet into
the stratosphere then settle back into
the anvil.
SEVERE STORM STRUCTURE
• Storms developing in this way become
persistent and self-propagating and
may develop tornadoes. Also called a
steady state thunderstorm.
SEVERE STORM STRUCTURE
• Steady state thunderstorm - Generally
form in lines, last for several hours,
dump heavy rain and possibly hail,
and strong gusty winds.
TORNADOES
TORNADOES
• Tornadoes are violent rotating
columns of air that descend out of a
thunderstorm in the shape of a funnel.
A tornado vortex is several hundred
yards in diameter with wind rotating
rapidly around it with exremely low
pressure in the centre. If the vortex
touches the ground, it is called a
“Tornado”, if it remains aloft handing
from the cloud base it is called a
funnel cloud
TORNADOES
• Both a tornado and a funnel cloud can
extend upward into the cloud for over
30,000 feet. They are most common
in the south and southwest parts of a
thunderstrom and may enter the cloud
in a line of innocent looking cumulus
in a rain free area extending several
miles away from the parent storm.
They tend to occur as families so if
one is seen others are probably
occuring. Over water “Waterspout”
TORNADOES
• Both a tornado and a funnel cloud can
extend upward into the cloud for over
30,000 feet. They are most common
in the south and southwest parts of a
thunderstrom and may enter the cloud
in a line of innocent looking cumulus
in a rain free area extending several
miles away from the parent storm.
They tend to occur as families so if
one is seen others are probably
occuring. Over water “Waterspout”
TORNADOES
TORNADOES
TORNADOES
TORNADO SCALE
TORNADO SCALE
•
The Fujita Scale of Tornado Damage
•
F-0: (Light Damage) Chimneys are damaged, tree branches are broken, shallow-rooted trees are
toppled.
•
F-1: (Moderate Damage) Roof surfaces are peeled off, windows are broken, some tree trunks are
snapped, unanchored manufactured homes are over-turned, attached garages may be destroyed.
•
F-2: (Considerable Damage) Roof structures are damaged, manufactured homes are destroyed,
debris becomes airborne (missiles are generated), large trees are snapped or uprooted.
•
F-3: (Severe Damage) Roofs and some walls are torn from structures, some small buildings are
destroyed, non-reinforced masonry buildings are destroyed, most trees in forest are uprooted.
•
F-4: (Devastating Damage) Well-constructed houses are destroyed, some structures are lifted from
foundations and blown some distance, cars are blown some distance, large debris becomes airborne.
•
F-5: (Incredible Damage) Strong frame houses are lifted from foundations, reinforced concrete
structures are damaged, automobile-sized debris be-comes airborne, trees are completely debarked.
•
Safety and Preparedness It is important to remain alert to signs of an approaching tornado and seek
shelter if threatening conditions exist. Look for environmental clues including a dark sky, large hail or
a loud roar. If a warning is issued, move to a pre-designated shelter such as a basement; stay away
from windows; get out of automobiles and lie flat in a ditch or depression; do not try to outrun a
tornado in your car.
The Fujita Scale was first proposed by Dr. Fujita in 1971. It is used by meterologists to estimate the
speed of winds after a tornado by studying the damage caused by the tornado to structures.
Recently the scale has been used to confirm the idea that some hurricane damage is caused by
torndoes that form within hurricanes.
TORNADOES
• Tornadoes and destructive
winds are generally associated
with steady state
thunderstorms associated with
cold fronts or squall lines.
CLASSIFICATION OF
THUNDERSTORMS
• TS are classified according to the trigger
action that sets off the instability.
• Frontal Thunderstorms
• Squall Line Thunderstroms
• Air Mass Thunderstorms
• Convective Thunderstorms
• Orographic Thunderstorms
• Nocturnal Thunderstorms
FRONTAL THUNDERSTORMS
SQUALL LINE
THUNDERSTORMS
• May be more violent then cold front TS.
• Bases often lower, tops higher
• Usually associated with heavy hail, strong
winds, and tornadoes.
• Most intense during the late afternoon and
evening.
• Often develop 100-200 miles ahead of and
roughly parallel to fast-moving cold fronts
SQUALL LINE
THUNDERSTORMS
AIR MASS THUNDERSTORMS
• Form within a warm, moist air mass,
and are in no way associated with
fronts.
• Generally isolated or widely scattered
over a large area. Generally easier to
deal with and fly around.
• May be classified as well as
convective, orographic or nocturnal
CONVECTIVE
THUNDERSTORMS
• May get lift from heating from below
or convergence of the wind flow.
• Seldom found with appreciable wind
flow
OROGRAPHIC
THUNDERSTORMS
• Wind forces moist, unstable air up mountain
slopes. More frequent in the afternoon and
early evening. Windward side of the rocks
NOCTURNAL
THUNDERSTORMS
• Is an air mass thunderstorm found in the
Mid-West. It frequently occurs at night or
early in the morning in the Central Plains
area. These thunderstorms are associated
with unusually moist air aloft. The trigger
action initiating these storms is though to
be night-time radiation from this moist air
layer.
• In Argentina Katabatic winds play the
trigger
HAZARDS
• Turbulence - usually constant throughout. The
Middle of the cell typically is more severe.
Tighten your safety belt
• Cumulonimbos clouds, very frequent lightning,
and roll clouds great sign of bad turbulence
• Look for cap clouds.
• Normally the more lightning the more turbulence.
• Lightning often is the sign of most of the cell
entering the dissipating stage.
HAZARDS
• Embedded thunderstorms:
Thunderstomrs are obscured by
massive cloud layers and cannot be
seen.
• Need a weather radar to fly safely
around.
LIGHTNING HAZARDS
• Lightning - real hard to avoid. Usually
aircraft triggered. Occurs when a
static electric charge builds up on an
aircraft and it then flies through a
strong electric field in the
atmosphere. The aircraft can build up
a static charge by flying through dry
particles such as ice crystals or snow,
or a mixture of rain and snow.
LIGHTNING HAZARDS
• As the static charge builds up on the
aircraft prior to a strike, there will be
a build up of static noise in high
frequency communication equipment.
At night, a corona may be seen across
a windscreen or at extremities of the
aircraft or around the prop (St. Elmos
fire). This build up will continue for
several seconds then a discharge
occurs between the cloud producing
LIGHTNING HAZARDS
• Natural Lightning is quite rare with aircraft
lightning strikes.
• Physical damage due to arcing of the very
large electric current associated with
lightning. Since the lightning enters and
leaves the aircraft at its extremities, these
are the parts normally damaged.
Composite type skins can be severly
damaged because of their inability to carry
the large current of a lightning strike
LIGHTNING HAZARDS
• Indirect effects of a lightning strike. There
is a magnetic field associated with the
lightning and this can induce currents in
various components and avionics. Can
also occur with nearby lightning. Damage
to aircraft electrical systems, instruments,
avionics, and radar is possible. Generators
can drop off line. Lighting, Mag Compass,
and all your electrical equipment could be
lost. Lose your radios etc.
• Navaids like the ADF can point to the core
of intense storms
LIGHTNING HAZARDS
• Have been occasional catastrophic
fuel explosions. In general, JP-4
fuel is significantly more
vulnerable to explosions at
temperatures near 0 degrees C
where most strikes occur.
LIGHTNING HAZARDS
• For Crew - The major hazard of
lightning is blindness or shock.
• Keep your cockpit lights turned up.
• For engines - besides exploding,
Flameouts or compressor stalls of
fuselage-mounted engines have
occurred, due to the result of hot
lightning channel being swept in front
of the engines distrupting the air flow
into them.
HAIL HAZARDS
• Hail - don’t fly through it!!!!!
Sounds like thousands of little
Gremlins with hammers taking a
wack at the aircraft. Buddy of
mine described the sound and
honestly thought.
• Use your weather radar, suggest
you point the radar tilt up.
HAIL HAZARDS
• On June 22, the small town of Aurora, Neb.,
experienced the full fury of Mother Nature as
severe thunderstorms and tornadoes raked
the area. But it was the monster-size hail that
made this a very special event.
• An irregularly shaped hailstone with a
diameter of 7 inches and a circumference of
18.75 inches was recovered, making it the
largest hailstone in U.S. history. The previous
record was set in Coffeyville, Kan., in 1970,
where a hailstone ``only'' 5.7 inches in
diameter was found. It had a circumference
of 17.5 inches and a weight of 1.67 pounds.
HAIL HAZARDS
• On June 23 and 25, 2003, the Hastings National
Weather Service Office conducted damage surveys
documenting the size of the hail and damage in the
city of Aurora. The largest stone found on June 23 is
shown here (Fig.5a) which measured 6.5 inches in
diameter, 17 3/8 inches in circumference and a
certified weight of 1.33 pounds. Larger hailstones
were reported and verified on June 25 with this
hailstone measuring 7.0 inches in diameter and a 18
3/4 inch circumference shown here (Fig.5b). Many
very large impact craters were noted in some yards,
with the largest measuring 12 inches wide and 3
inches deep (Fig. 6 & 7)
HAZARDS
• Icing - is usually severe. Can literally
watch the ice grow. Turn on your
icing equipment
• Altimetry -TS approaches abrupt fall
in pressure; TS over get an abrupt
rise in pressure associated with rain
showers; TS leaves returns to normal
pressure
• Can have an error of 100- 150 feet
HAZARDS
• Heavy Rain - Avoid flying through a
rain shaft that you can not see. Use
your weather radar. Going to run the
risk of IFR conditions for a short
period of time, hail, strong
downdrafts.
HAZARDS
• Heavy Rain - Avoid flying through a
rain shaft that you can not see. Use
your weather radar. Going to run the
risk of IFR conditions for a short
period of time, hail, strong
downdrafts.
HAZARDS
FLIGHT PROCEDURES
• Read the hand out
• AVOID THUNDERSTORMS
STEAR CLEAR, KNOW YOUR
AIRCRAFT!!!!!!!!!!!
•
Question
How is a plane protected from Lightning strikes?
Asked by: Sridhar Narayanan
Answer
Since the outer skin of most airplanes is primarily aluminum, which is a very
good conductor of electricity; the secret to safe lightning hits is to allow the
current to flow through the skin from the point of impact to some other point
without interruption or diversion to the interior of the aircraft.
•
Estimates show that each commercial airliner averages one lighting hit per
year but the last crash that was attributed to lightning was in 1967 when the
fuel tank exploded, causing the plane to crash. Generally, the first contact
with lightning is at an extremity...the nose or a wingtip. As the plane
continues to fly through the areas of opposite charges, the lightning transits
through the aircraft skin and exits through another extremity point,
frequently the tail (as shown by Gauss's Law).
•
Another related problem with lightning is the effect it can have on computers
and flight instruments. Shielding and surge suppressors insure that electrical
transients do not threaten the on board avionics and the miles of electrical
wiring found in modern aircraft. All components that are vital to the safe
operation of commercial aircraft must be certified to meet the stringent
regulations of the FAA for planes flying into the United States.
Answered by: Rich Uranis, B.S., University of Michigan, Ann Arbor
•
Aircraft, and by that I mean the body of the aircraft and not the occupants inside, are protected from
lightning strikes by two things. The first and most important of these is the brains of the pilot and the
weathermen who predict where violent storms are likely to be. The second is through a small unsung
device called the "static wick".
•
Most aircraft do not fly into lightning storms, or fly through storms or areas where lightning is likely
to be present. What we see as lightning is really a massive flood of electrons seeking equilibrium,
either from cloud-cloud or from cloud-ground. In both cases, huge amounts of electric charge build
up at the edges of the cloud. The electricity finds it's way from one place to the other via what's
called a "step leader".
•
The sheer power of the cloud will start to attract electrons from the ground. These electrons will
gather on anything that gathers charge (like a fence) or sticks up in the air (like a person), or that
does both (like a telephone pole). That electric charge will start to work it's way through the air,
ionizing it, until the leader working it's way down, and the leader trying to get up finally meet. When
they do - there's lightning. An aircraft flying between the highly charged portions of a cloud will act
as a conduit for step leaders, being able to produce one in each direction. If either of them meets a
leader coming the other way... ZAP.
•
The way an aircraft tries to dissipate these step leaders is through the use of something called a
"static wick". A static wick is a piece of metal connected electrically to the frame of the aircraft, with
one or two spikes or needles on the end. It is housed in a fiberglass rod to insulate it from the
airplane. Because the spikes concentrate the electric charge around them, and they are connected to
the airframe, they allow the airplane to dissipate any static electricity it may build up out into the air.
Also - if lightning DOES strike the plane, the chances are that the electricity will go through the
dissipator and not through the airplane. You can see pictures of these dissipators on the 737
webpage below.
•
So, when discussing how an airplane is protected from a lightning strike, the best safety feature is
the pilot who checks the weather before he flies and makes smart decisions about where to fly. If the
plane is forced to fly through a storm, the static wicks on the wing's trailing edges should help keep
the plane safe.