404 Flashcards
Jetstream
- current of fast moving air found in the upper levels of the atmosphere
- thousands of kilometers long
- few hundred kilometers wide
- few kilometers thick
- found between 10-15km above the earths surface
Structure of the jetstream
- flows from the west
- are of thermal origin
- thermal winds are added to actual wind up to the tropopause, then the thermal wind will be opposite in the stratosphere
Jetstream wind speeds
- each point on it’s axis must have a minimum of 60 kts
- weak jet stream - less than 120 kts
- MDT jetstream -120-150 kts
- Strong Jetstream - greater than 150 kts, rarely exceeding 250 kts
Jetstream wind shear
-horizontal wind shear on south side of jet - 20-30 kts per 100nm
-horizontal windshear on north side is 2-3 times higher, 40-90 kts per 100nm
-vertical windshear is 3-7 kts per 1000ft
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Jetstream Height
- Varies with the height of the warm air tropopause
- Arctic jet - Arctic front
- Maritime Jet - Maritime front
- Polar jet - Polar front
250 hPa chart
- produced twice daily from 00 and 12z obs, transmitted 3.5 hours after obs
- 10400m (34000)
- covers CA, USN, ATL ocean, ARC ocean, W Europe, E and N asia
- -Solid lines - pressure level 250 hPa analyzed at 120m intervals, labelled in decameters, ref line is 1044 dm
- -Dashed lines - Isotachs analyzed at 30kt intervals
Determining the jetcore
- Temps equal on both sides = jetcore at that height
- left side cold = above 250 hPa level
- left side warm = below 250 hPa level
High level SIG WX (FL250 - FL360)
-produced twice daily for specific valid times
-includes:
TS and CBs
tropical cyclones
severe squall lines
MDT or SVR TURB
MDT or SVR ICG
Widespread SS or DS
well defined convergence zones
volcanic eruptions
North Atlantic TURB forecast charts
-MDT to SVR TURB between FL280 and FL430
-Issued 3 times a day at 1030z,1715z and2230z
-Includes:
Areas of turbulence
motion of areas of TURB
Characteristics of the areas ofturbulence
horizontal position of the Jetcore
altitude of jet core
motion of the jetcore
tops of convective cloud
Turbulence forecast for canada
- Includes entire CDA, from north pole southward to 100nm S of CA USA border
- 12 hr forecast period
- issued at 1030z and 2230z, valid 1.5 hours later
