HIGH ALTITUDE WX CHAPTER 13

HIGH ALTITUDEWEATHER PHENOMENA

• 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

http://upload.wikimedia.org/wikipedia/commons/6/62/Aerial_Superhighway.ogv

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 Niña-Southern 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

• 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