1. A jet stream (or jet) is a narrow current of strong winds.
Can exist at several levels, but most often applied to the high velocity winds in the vicinity of the midlatitude tropopause

2. Midlatitude Jet Stream Facts
Can reach 250 mph (or more)
Centered on the upper troposphere…around 250 hPa
Stronger in winter. Generally, weakens and moves northward during summer.
Closely associated with a tropospheric temperature gradient (thermal wind!)
Not uniform zonally

3. Wasaburo Oishi, Japanese Discoverer (1920s)

5. Fu-Go Balloon Weapon During WWII

7. Strahlstromung (German) for “jet stream” first used in 1939
Big effects on bomber flights during WWII

8. Jet Stream winds are not uniform

9. 250 mb isotach

10. Shaded 70—110 knot

11. Jet Stream versus Jet Streak A matter of size Term ”jet stream” used for features of 1000’s of km. ”Jet streak” use for features of 100’s to 1000 km
Note that air blow through the jet streak isotachs…the feature propagates more slowly than the strongest winds.

12. Main Upper Tropospheric Jets Closely Associated with the Tropopause

13. Tropopause

14. General Definition
Tropopause: a boundary region or surface between the troposphere and stratosphere
Marked by a change in lapse rate from a typical tropospheric lapse rate (~6.5C per km) to isothermal or inversion conditions.
Sometimes hard to find, particularly near jet cores.
Can multiple tropopauses above a location
Lower in polar region than in the tropics.

15. Official WMO Definition
“the point on the soundings where the lapse rate becomes less than 2C per km and remains less than that for a least 2 km”

16. Finding the Tropopause

18. Real World Examples: http://weather.uwyo.edu/upperair/sounding.html

19. Tropopause is modulated synoptically
High in ridges, Low in troughs
Higher in tropics, lower towards poles

20. Tropopause Height https://atmos.washington.edu/~hakim/tropo/trop_pres.html

22. There are TWO types of upper tropospheric jet streams
Polar front jet: associated with main midlatitude frontal/baroclinic zone. Typically 30-45N, ~ hPa
Subtropical jet: associated with the northern portion of the tropical Hadley circulation. Typically around 30N, ~200 hPa

23. Subtropical Jet Stream

26. Subtropical Jet Stream Often Associated with a cloud band

27. http://itg1. meteor. wisc

28. Jet Stream’s Relationship to Temperature Is Expressed Through Thermal Wind Arguments

29. Thermal Wind Equation

30. 250 mb isotach

31. 1000-500 mb thickness-large thickness gradient and thus thermal wind near jet core

32. Or alternatively…

33. The Jet Stream Recall the horizontal temperature effects
on the pressure:
500 mb
700 mb
850 mb
Psurface
Warm
Cold

34. The Jet Stream Consider the balance of forces at each level: Co PGF
500 mb
700 mb
850 mb Ps
Warm
Cold

35. The Midlatitude Jet Stream is not uniform, which has to do with non-uniform temperature

38. Where are largest temperature gradients?

39. The thermal wind equation is a diagnostic equation, something needs to supply the momentum for the jets
The polar or midlatitude jet is often called the “eddy driven jet” because the convergence of momentum by eddies (storms) is important.
The subtropical jet is associated with Coriolis force acceleration of northerly branch of the subtropical jet.

40. There are a variety of jet stream configurations that are well-known

48. Horizontal cuts through the troposphere, jet, and stratosphere
Reversal of horizontal temperature gradient between troposphere and stratosphere
Tropopause break at jet.