The document discusses jet streams, which are narrow currents of strong winds that can exist at several levels of the atmosphere but are most often found near the tropopause. It provides details on jet stream characteristics like speeds over 250 mph, stronger winds in winter, and association with temperature gradients. The document also discusses the discovery of jet streams, their relationship to the tropopause and temperature through thermal wind balance, and different jet stream configurations.

1. Jet Stream
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/~ha
kim/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, ~250-300 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.edu/wxwise/AckermanKnox/chap7/subtropical_jet.html

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
Warm Cold
Psurface

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

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.

49. 850 hPa

50. 700 hPa

51. 500 hPa

52. 250 hPa

53. 100 hPa

62. Why is the jet stream typically
located at the tropopause?