08. High Level Winds Flashcards
High Level Winds
What is one of the main contributing factors to pressure differences at height that result in wind blowing
TEMPERATURE OF COLUMNS OF AIR
- warm columns of air are much taller than colder columns of air
- High air mass temperature - high pressure aloft
- low air mass temperature - low pressure aloft
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High Level Winds
- If the air mass temperature is HIGH, pressure aloft will be HIGH or LOW
- If the air mass temperature is LOW, pressure aloft will be HIGH or LOW
- HIGH
- LOW
- warm columns of air are much taller than colder columns of air
- High air mass temperature - high pressure aloft
- low air mass temperature - low pressure aloft
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High Level Winds
High level wind is made up of what two components
- WIND AT LOW LEVEL
- THERMAL COMPONENT
- The wind at low level is caused by differences in surface pressure
- The thermal component is caused by differences in temperature at height
- In the diagram example, it is a side profile view of height
- The blue contour lines from right to left are decreasing in value, this reflecting lowering pressure at the surface
- The thermal componet sits between the layer of warm and layer of cold air
- The black line represents the isohypses, which is the contour line of the air mass. In this example, the red arrow follows the 300mb level line
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High Level Winds
What is the name given to the lines that represent contours of the air mass
High Level Winds
- The upper wind blows parallel to ISOBARS or ISOTHERMS or CONTOURS with low pressure on the left in the northern hemsiphere
- Low level wind blows parallel to ISOBARS or ISOTHERMS or CONTOURS with low pressure on the left in the northern hemsiphere
- The Thermal wind blows parallel to ISOBARS or ISOTHERMS or CONTOURS with low temperature on the left in the northern hemsiphere
- CONTOURS
- ISOBARS
- ISOTHERMS
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High Level Winds
Upper winds are indicated by contour charts which are constant pressure charts. It shows pressure level in ____, and points of the same altitude are linked by lines called _____
- GEOPOTENTIAL METERS
- ISOHYPSES
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High Level Winds
Words starting with iso- indicate lines of joining points of equal something. What do the following mean;
- Isobar : equal ____
- Isotherm : equal ____
- Isotach : equal ____
- isohypse : equal ____
- Isobar : equal PRESSURE
- Isotherm : equal TEMPERATURE
- Isotach : equal SPEED
- isohypse : equal HEIGHT
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High Level Winds
An isohypse (height contour) represents the distance from zero geopotential meteres. What does geopotential assume of the earth
PERFECTLY FLAT
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High Level Winds
Countour charts may give the height of the relevent pressure value in what metric of meters
DECAMETERS
(tens of meters)
- 552 is 5520m aka 18,105 ft
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High Level Winds
When cosidering a contour chart, which is a top down view, if the chart were turned on its side to provide a cross section view where you could determine the revelent height of pressure lines;
- The HIGH or LOW pressure would represent a CONVEXED CURVE to the surface
- The HIGH or LOW pressure would represent a CONCAVED CURVE to the surface
Convex TO means bows towards surface
Concave TO means bows away from sur
- LOW
- HIGH
- Low pressure would bow towards the surface
- High pressure would bow away from the surface
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High Level Winds
What does ITCZ stand for, and what is it a line of
- INTER-TROPICAL CONVERGANCE ZONE
- LINE OF HIGH TEMPERATURE
- The ITCZ is a line of high temperature running around the earth following the sun
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High Level Winds
The ITCZ causes the upper winds above to blow in what direction
EASTERLY
- ** REMEMBER** Easterly wind means it blows FROM the east, so arrow points to the west in diagram
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High Level Winds
As air masses move away from the equator at height, the air masses cool down. This means which component will dominate as the wind increases speed
THERMAL COMPONENT
- ** REMEMBER** Easterly wind means it blows FROM the east, so arrow points to the west in diagram
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High Level Winds
As air masses move away from the equator at height, the air masses cool down. This means the thermal component will dominate as the wind increases speed, and will wind will blow from which direction, and are known by what name
- WESTERLY
- TRADE WINDS (upper westerlies)
- ** REMEMBER** Easterly wind means it blows FROM the east, so arrow points to the west in diagram
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High Level Winds
The wind will blow from which direction at the poles
EASTERLY
- The air in the poles is not much colder than the air adjacent to it
- The thermal component dies away
- ** REMEMBER** Easterly wind means it blows FROM the east, so arrow points to the west in diagram
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High Level Winds
The global circulation of air carrying the excess heat energy from the equator to the poles divides the torosphere into four main blocks. These are;
- HOT TROPICAL AIR AT EQUATOR
- WARM SUBTROPICAL AIR (Lat 30° to 50°)
- COLD POLAR AIR (winter only)
- VERY COLD ARCTIC AIR
- There are marked temperature gradients at the boundaries of where each of the blocks meet
- These temperature gradients at height create pressure differences.
- The points of the maximum pressure gradient is where the strongest winds are found - Jetstreams
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High Level Winds
“A strong narrow current of air on a nearly horizontal axis in the upper troposphere or low stratosphere, characerised by strong lateral and vertical windsheers. The wind speed must be more than 60 kts”
This is the definition of what sort of wind
JETSTREAM
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High Level Winds
To be characterised as a jetstream, the wind must blow more than how many knots
60 kts
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High Level Winds
The jetstreams form where the pressure gradient between two air masses is greatest. The warm air is usually around or ABOVE or BELOW the tropopause level
AT OR BELOW
High Level Winds
The core of a jetstream is found in the WARM or COLD front of air
WARM
- Hetstream core at height will always be in the warmer air
- Because the fgront slopes, when you look at the situation in profile view, the jstream will actually appear to be on the cold air side.
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High Level Winds
In the Northern Hemisphere, the fronts which move with the seasons, in winter, will usually be FASTER or SLOWER
FASTER
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High Level Winds
The polar front jetstream is typically found at around ____ft
30,000 ft
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High Level Winds
The Sub-tropical jet stream is higher than the polar jetstream as it is in the warmer, tropical air. It is usually around ____ft
40,000 ft
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High Level Winds
- The polar front jestreams reach speeds of ____kts
- The sub-tropical jetstreams reach speeds of ____kts
- 200 kts
- 100 kts
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High Level Winds
Long polar nights in the winter of the hemisphere cools polar air. This forms a distinct ____
ARCTIC AIR MASS
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High Level Winds
The winter of the hemisphere cools the polar air forming distinct arcitc air masses between ____° latitude and the pole
70°
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High Level Winds
Jetstreams are FASTER or SLOWER in winter and CLOSER or FURTHER from the equator
- FASTER
- CLOSER
- In winter the air masses in the poles cool significantly
- This is enough to form an arctic air mass
- The land is cooler in higher latitudes, so this causes the jetstream to move closer towards the equator
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High Level Winds
The core of an arctic jetstream can be found at ____ft with max speeds up to ____kts
- 20,000 ft
- 80 kts
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High Level Winds
When the cooling of the polar air is very severe, this cools not only the air in the troposphere, but also the stratosphere above it. This causes what jetstream to form.
POLAR NIGHT JETSTREAM
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High Level Winds
The polar night Jetstream occurs around ____° latitude, and approximately ____ft
- 70°
- 80,000 ft
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High Level Winds
Jetstreams are all Westerly, apart from which jetstream, which is easterly
EQUATORIAL JETSTREAM
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High Level Winds
What is the cause of the Easterly jetstream
SUMMER HEATING
- Summer heating of the Indian sub-continental, and the West African coastal regions
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High Level Winds
The Easterly jetstream is caused by summer heating of the Indian sub-continental, and the West African coastal regions. The surface heating is so intense it is transferred to the upper air where a marked temperature difference develops between the UPPER or LOWER air over land, and that over the sea
UPPER
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High Level Winds
The Easterly Jestream can reach speeds of over ____kts and the jet core lines approximately between ____ft and ____ft
- 100 kts
- 45,000 ft to 50,000 ft
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High Level Winds
Low jetstreams can form when there is a marked difference between the air masses at a lower height. This can occur from approximately ____ft and is usually about ____kts in speed
- > 5,000 ft
- 70 kts
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High Level Winds
Low level jetstreams move PARALLEL or VERTICAL to the WARM or COLD front
- PARALLEL
- COLD FRONT
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High Level Winds
A jetstream will typically be;
- ____nm long
- ____nm wide
- ____ft deep
- 1000 NM LONG
- 150-200 NM WIDE
- 12,000 ft DEEP (2 NM)
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High Level Winds
The maximum CAT occurs in the WARMER or COLDER air, on the WARM or COLD side of the core, slightly ABOVE or BELOW the core
- WARM AIR
- COLD AIR SIDE
- BELOW THE CORE
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High Level Winds
The strongest wind speeds occur in the jet core. The nromal speeds in teh core of the polar jet, which are the fastest jetstream, are between ____kts and ____kts, but can reach speeds as fast as ____kts
- 130 kts to 200 kts
- 350 kts
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High Level Winds
The strongest wind speeds occur in the jet core. The nromal speeds in teh core of the polar jet, which are the fastest jetstream, are between 130 kts and 200 kts, but can reach speeds as fast as 350 kts. Speeds are the highest when the jetstream runs between a ____ and a ____, accentuating the pressure gradient
- TROUGH
- RIDGE
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High Level Winds
“The wind vector changes rapidly over relatively short distances”
This is a definition of what type of wind effect
WINDSHEAR
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High Level Winds
The worst turbulence i.e. windsheer, will occur in what part of the CAT
IN WARM AIR ON COLD SIDE OF CORE
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High Level Winds
In a typical jetstream when windshear is encountered, the windspeed may go from ____ kts to ____ kts in ____km or ____ft vertically
- 60 kts to 150 kts
- 150 km
- 5000 ft
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High Level Winds
What is the best way to avoid windsheer aka turbulence, in a jetstream
CLIMB or DESCEND
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High Level Winds
In the abscence of a modern navigation system, which includes a read out of wind and making a jet core easy to identify, a core can be found in flight by carefully monitoring what
OUTSIDE AIR TEMPERATURE
(OAT)
High Level Winds
The air over a cold sector of air is COLDER or WARMER than the air over a warm sector of air where the fronts meet
WARMER
- The air in the cold sector would steadily decrease with altitude
- Warmer air sits on top of the coler air
- As you breakthrough the ceiling of the cold air sector, the temperature will increase
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High Level Winds
3 aircraft are flying towards the jetstream. They are in the northerm hemsiphere flying southernly, so from a cold sector to a warm sector.
Aircraft 1 - is flying above the jet core (> 45,000 ft)
Aircraft 2 - is flying level to the jet core (35,000 ft)
Aircraft 3 - is flying below the jet core (< 25,000 ft)
What would the temperature profile show for each of the aircrafts as the flew on track over, through, and below the jetstream i.e. will temperatures INCREASE or DECREASE
AIRCRAFT 1 - STEADILY DECREASE
AIRCRAFT 2 - NO CHANGE
AIRCRAFT 3 - STEADILY INCREASE
AIRCRAFT 1
* Remember that air above the cold sector is warmer than the cold sector itself as the air beneath it is compressed and the warmer air sits on top of colder air
* As the aircraft flies over the jet core, the warmer column of air is taller and expanded further, meaning the air temperature over the warm column of air is actually colder than the air over the cold sector
AIRCRAFT 2
* As the aircraft flies on track, the air temperature is approximately the same so little change will be noticed
* If wind speed were beign detected however, there would be a significant increase in wind speed as the core was penetrated, followed by a sudden decrease in wind speed on the other side
AIRCRAFT 3
* Remember that the colder sector of air is more compressed than the warmer sector of air.
* This means that the aircraft is flying from more compressed air to less compressed air, where the air is expaneded and taller
* As a result, the aircraft will fly from colder into warmer air, and the temperature will slowly increase
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High Level Winds
What type of clouds can be associated with jetstreams when there is high level moisture present
CIRROFORM
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High Level Winds
Dnese jet stream cirriform clouds are most prevalent along which 2 points
- MID-LATITUDE
- POLAR JETS
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High Level Winds
What are the approximate jet stream levels;
- Arctic ____ ft
- Polar Front ____ ft
- Sub-Tropical ____ft
- Equatorial ____ft
- Arctic 20,000 ft
- Polar Front 30,000 ft
- Sub-Tropical 40,000 ft
- Equatorial 50,000 ft
High Level Winds
Which jetstream blows all year around over the northerm hemisphere
ARCTIC or SUBTROPICAL or EQUATORIAL
SUBTROPICAL
- The polar front and subtropical jetstreams blow all year round
