HIGH ALTITUDE WX
CHAPTER 13
HIGH ALTITUDE
WEATHER PHENOMENA
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Tropopause
Jet Stream
Cirrus Clouds
Clear Air Turbulence
Condensation Trails
High Altitude Haze Layers,
Canopy Static
TROPOPAUSE
• Temperature and wind vary greatly
in the vicinity of the tropopause
affecting efficiency, comfort, and
safety of flight
• Maximum winds generally occur at
levels near the tropopause.
TROPOPAUSE
• Tropopause - is a thin layer
forming the boundary between
the _______ and the
__________.
• Troposphere and Stratosphere
TROPOPAUSE
• Tropopause - Height varies from
about 65,000 over the equator to
20,000 feet over the poles
TROPOPAUSE
• Tropopause - Generally descends
step-wise from the Equator to the
poles
TROPOPAUSE
• Tropopause - Abrupt change in
temperature lapse rate
characterizes the tropopause
JET STREAM
Discovery
• After the 1883 eruption of the Krakatoa volcano, weather
watchers tracked and mapped the effects on the sky over several
years. They labelled the phenomenon the "equatorial smoke
stream". [3][4] In the 1920s, a Japanese meteorologist, Wasaburo
Oishi,[5] detected the jet stream from a site near Mount Fuji. He
trackedpilot balloons, also known as pibals (balloons used to
determine upper level winds),[6] as they rose into the
atmosphere. Oishi's work largely went unnoticed outside Japan.
American pilot Wiley Post, the first man to fly around the world
solo in 1933, is often given some credit for discovery of jet
streams. Post invented a pressurized suit that let him fly above
6,200 metres (20,300 ft). In the year before his death, Post made
several attempts at a high-altitude transcontinental flight, and
noticed that at times his ground speed greatly exceeded his air
speed.[7]
LOCATION
• The northern hemisphere polar jet stream is
most commonly found between
latitudes 30°N and 60°N, while the northern
subtropical jet stream located close to
latitude 30°N.
POLAR & SUBTROPICAL JET
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JET STREAM FACTS
• Narrow river of wind
• Usually in a wave like pattern
• Must be 50 knots or greater to be classified
as a jet stream. In Canada 60 Knots
• 100-400 miles wide, 1000’s of miles long
• 1 mile thick or (3000-7000feet)
• Polar front 37,000 feet
• Maritime front 33,000
• Arctic front 28,000
JET STREAM FACTS
• Usually occurs in the break in the
tropopause in an area of intensified
temperature gradients characteristic of the
break.
JET STREAM FACTS
• stronger in winter than summer
• farther south in winter than summer
• Not constant; rather it is broken into
segments, shaped like a boomerang
JET STREAM FACTS
• Maximum wind speeds can be in
excess of 200 knots. Speed drops
off abruptly above, below and to
either side of the jet core
WIND SPEED WITH HEIGHT
JET IN RELATION TO
FRONTS
• Lies to the north of the system where
the temperature gradient is greatest and
roughly parallels it.
• If a wave and a low form on the front,
they will lie well south of the jet.
• Jet is named after the frontal system
causing it ie. Polar, Maritime or Artic.
JET IN RELATION TO
FRONTS
JET IN RELATION TO
FRONTS
• Position of the jet core in relation to a
frontal surface and to the warm air
tropopause and cold air tropopause.
JET DOWNWIND
• Looking downwind, the air in a jet core
slowly rotates in a counterclockwise
fashion. If the air is moist the ascending air
on the warm air side will cause cirrus cloud
to form.
• The strong vertical wind shear may be quite
evident from the very wind-swept
appearance of the trailing ice crystals of
hook shaped cirrus.
JET ON SATELITE
El Niño/La NiñaSouthern Oscillation
• or ENSO, is a quasiperiodic climate pattern that
occurs across the tropical Pacific Ocean roughly
every five years. The Southern Oscillation refers to
variations in the temperature of the surface of the
tropical eastern Pacific Ocean (warming and cooling
known as El Niño and La Niña respectively) and in
air surface pressure in the tropical western Pacific.
The two variations are coupled: the warm oceanic
phase, El Niño, accompanies high air surface
pressure in the western Pacific, while the cold
phase, La Niña, accompanies low air surface
pressure in the western Pacific.
LA NINA
EL NINO
EL NINO/NINA FORECAST
• http://www.elnino.noaa.gov/forecast.html
CAUSE OF THE JET STREAM
• Great contrast of temperatures in adjacent
air frontal zones
• rapid change in temp causes rapid change in
pressure
• steep pressure gradient intensifies wind
speed and causes the Jet
• temp difference is greatest in winter
between polar and tropical air masses
CONSERVATION OF
ANGULAR MOMEMTUM
• air moves closer to axis of rotation
• air must move faster east which looks like a
wind out of the west to an observer on the
ground
• the best example is an ice skater
JET STREAM TURBULENCE
JET STREAM TURBULENCE
• find more serious turbulence on the polar
side of the Jet
• rate of decrease of wind speed is greater on
polar side
• usually associated with an upper level
trough
• the bend caused by the trough is where
pressure gradients change over the smallest
distance increasing the chance for
turbulence (CAT)
JET STREAM TURBULENCE
• Wind Distribution - Very rapid
change of wind speed within short
distance of the jet core. Vertical
shear may vary from around 5
knots per 1000 feet to 20 knots per
1000 feet. Generally close to the
same intensity both above and
blow the core.
JET STREAM TURBULENCE
• Horizontal shear on the cold air side of
the core (left hand side polar side
looking downwind) is stronger than on
the warm air side and can vary from
around 24 knots per 100 miles to
extremes of 100 knots per 100 miles.
On the warm air side it is about one
third of this. Note particularly that the
vertical shear is many times stronger
than the horizontal shear.
JET STREAM TURBULENCE
CLEAR AIR TURBULENCE
• cold air colliding with warm air causes
shear and presto CAT
• is greatest in winter when temp differential
is greatest
• located most of the time in an upper trough
on the polar side of the jet
• cat is found in sharply curved contours of
strong lows, troughs and ridges
JET STREAM TURBULENCE
CLEAR AIR TURBULENCE
• Turbulence is greatest where
greatest wind velocity is found
• on the polar side where there is
combo of strong shear curvature in
the flow and cold air advection
CLEAR AIR TURBULENCE
• Strong Temperature Gradient stronger wind with a steeper temp.
gradient. More pronounced in the
winter months.
• Isotachs - Lines of equal wind
speed.
HIGH LEVEL CLEAR AIR
TURBULENCE
JET STREAM TURBULENCE
• Jet stronger than 110knots vertical shear 5
knots per 1000 feet or horizontal shear 30
knots per 100 miles tend to produce
turbulence. Below areas wind shear
greatest.
JET STREAM TURBULENCE
• Frequently turbulent area is 2000 feet deep,
20 miles wide and 50 miles long, although
they can vary markedly from the average.
JET STREAM TURBULENCE
• Avoiding jet turbulence - if encountered
with direct tailwinds or headwings, a
change I nflight level or course should be
initiated sice these turbulent areas are
elongated with the wind, and are shallow
and narrow. A turn towards the warm air
side of the jet will place the aircraft in more
favourable winds. If a turn is not feasible
due to airway restrictions, a climb or
descent to the next flight level will usually
find smoother air.
JET STREAM TURBULENCE
• If turbulence is encountered in a crosswind,
it is not so important to change course or
flight level since the rough areas are narrow
across the wind. However, if it is desired to
traverse the CAT area more quickly, either
climb or descend after watching the
temperature guauge for a minute or two. If
temp. is falling descend, rising climb.
• Application of these rules will prevent
following the sloping tropopause or frontal
surface. Temp. Constant climb or descend.
JET STREAM TURBULENCE
ODDS OF HITTING FORCAST
TURBULENCE
• Light 10-15% of the time
• Moderate 2-3% of the time
• Severe to Extreme 2/10ths of 1%
of the time or 1 in 50 chance
AVOIDING CAT
• Usually climbing or descending will get you
out of it
• use FSS and/or Flight Watch on 122.00 find
out pireps
• remember stress is cumulative (Turb +
Manev = total stress)
• maintain constant attitude, slow to Va,
accept variations
CAT IS STRONG AT TIMES
• Apr 4, 1981 DC 10 at 37,000 over central
Illinois
• dropped 2,000 feet
• 21 out of 154 injured including
• fractured hip
• jabbed nose with a fork then landed in the
seat in front of him on it
CON TRAILS
• found in cold humid air
• 2 types
EXHAUST
• caused by the addition of water vapor from
the exhaust gases to the point of saturation
CONDENSATION
TRAILS
• An aircraft leaves a condensation trail
(contrail) behind it when the moisture
formed during combustion and emitted
with the exhaust gases is sufficient to
saturate the air, and subsequently
causing condensation.
CONDENSATION
TRAILS
• For each pound of aircraft fuel burned,
approx. 1.4 pounds of water vapour are
formed and ejected with the engine exhaust
gases. This increases the RH in the wake of
the aircraft.
• Generally the contrail forms one to two
thousand feet behind the aircraft as the
exhaust cools at altitude.
AERODYNAMIC
• pressure reduction around wings, props,
engine nacelles cools the air to the dew
point
• wing tip vortices
• vortices from outboard edges of flaps
DISSIPATION TRAILS
• aircraft warms air (exhaust) enough to
evaporate part of the cloud
CANOPY STATIC
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St. Elmo’s fire
dust, ice crystals, volcanic ash
may eliminate it by changing altitude
noisy disturbance that interferes with radio
reception
THUNDERSTORMS
• AVOID BY AT LEAST 20 MILES THE
SEVERE ONES.
QUESTIONS
• In the winter the jet steams migrate or shift
in the Northern Hemisphere (north or south)
• South
• In the winter the jet steams speed in the
Northern Hemisphere (increases or
decrease)
• Increase
QUESTIONS
• What type of jet stream may cause the
greater turbulence? (Straight/Wide isotherm
spacing/curving/in the summer at a low
altitude)
• The curving jet can expect greater
turbulence.
QUESTIONS
• In the jet stream core you can
expect wind shear to form where?
• Polar side and above. Usually a
descending right turn out of the
core leaves less turbulence.
QUESTIONS
• CAT can be expected more
frequently when?
• Temperature contrast is the
greatest (usually the winter
months)
QUESTIONS
• Where do you normally find jet
streams?
• In the breaks in the tropopause