1. Dynamic meteorology without tears Part I b: Jet Streams
10/05/2018
Monday 11 April lecture B Anders Persson, Uppsala University

2. Monday 11 April lecture B Anders Persson, Uppsala University
1. More about the “geostrophic” wind
10/05/2018
Monday 11 April lecture B Anders Persson, Uppsala University

3. Monday 11 April lecture B Anders Persson, Uppsala University
The erroneous text book image of geostrophic adjustment in a constant pressure field
Low pressure Vg 2
High pressure
10/05/2018
Monday 11 April lecture B Anders Persson, Uppsala University

4. The real image of motion of an air parcel in a constant pressure field
Super geostrophic
Low pressure
2Vg
2Vg
V=0
V=0
High pressure
10/05/2018
Monday 11 April lecture B Anders Persson, Uppsala University

5. . . . when it in reality is more like road rage
Like a motorist smoothly entering the motorway . .
. . . when it in reality is more like road rage
10/05/2018
Monday 11 April lecture B Anders Persson, Uppsala University

6. The motion can be seen as a combination of straight acceleration and inertia circle motion
Pressure gradient force
Low pressure
2Vg
Coriolis
force
High pressure
10/05/2018
Monday 11 April lecture B Anders Persson, Uppsala University

7. The motion evolves into cycloids
max
max
zero
Prolate cycloid
max
max
backwards
10/05/2018
Monday 11 April lecture B Anders Persson, Uppsala University

8. This is not playing with mathematics but opens up to an understanding of three important meteorological features:
2.1 Nocturnal jet stream
2.2 Synoptic scale jet streams
(2.3 Aspects of the general circulation)
10/05/2018
Monday 11 April lecture B Anders Persson, Uppsala University

9. Monday 11 April lecture B Anders Persson, Uppsala University
2.1 Nocturnal jet streams
10/05/2018
Monday 11 April lecture B Anders Persson, Uppsala University

10. Monday 11 April lecture B Anders Persson, Uppsala University
The forces acting on a moving air parcel (wind) with pressure gradient force (PGF), Coriolis force (2ΩV) and friction balancing each other
PGF V
acc F
2φV
10/05/2018
Monday 11 April lecture B Anders Persson, Uppsala University

11. PGF V F 2φV . . . and the net acceleration returns, now unbalanced
When night falls the winds above the friction layer loses contact with the ground and the frictional resistance
PGF V
acc
. . . and the net acceleration returns, now unbalanced F
2φV
10/05/2018
Monday 11 April lecture B Anders Persson, Uppsala University

12. We now introduce the geostrophic wind Vg
PGF V
acc Vg
2φV
2φVg
10/05/2018
Monday 11 April lecture B Anders Persson, Uppsala University

13. We translate the acceleration vector
PGF V
acc Vg
2φV
10/05/2018
Monday 11 April lecture B Anders Persson, Uppsala University

14. Monday 11 April lecture B Anders Persson, Uppsala University
We now introduce the difference between the geostrophic and ageostrophic winds V-Vg
PGF
acc
90° !! V
V-Vg Vg
2φV
10/05/2018
Monday 11 April lecture B Anders Persson, Uppsala University

15. The acceleration is orthogonal to the ageostrophic wind
PGF
acc V Vg
2φV
10/05/2018
Monday 11 April lecture B Anders Persson, Uppsala University

16. The acceleration carries the air parcel aroundV
Super geostrophic winds Vg
10/05/2018
Monday 11 April lecture B Anders Persson, Uppsala University

17. The acceleration carries the air parcel aroundVg V
Sub geostrophic winds
acc
10/05/2018
Monday 11 April lecture B Anders Persson, Uppsala University

18. Monday 11 April lecture B Anders Persson, Uppsala University
Authentic inertial oscillation, “nocturnal jet” over hours (Netherlands)
theoretical
Gale force winds
obs
In this nocturnal jet the wind varies between 5 and 16 m/s
10/05/2018
Monday 11 April lecture B Anders Persson, Uppsala University

19. Monday 11 April lecture B Anders Persson, Uppsala University
2.2 Synoptic jet streams
10/05/2018
Monday 11 April lecture B Anders Persson, Uppsala University

20. The real image of motion of an air parcel in a constant pressure field
Low pressure
2Vg
2Vg
V=0
V=0
High pressure
10/05/2018
Monday 11 April lecture B Anders Persson, Uppsala University

21. Monday 11 April lecture B Anders Persson, Uppsala University
The pressure field and the winds will mutually adjust to each other and stretch the cycloid from a normal to a curtate
Low pressure
<2Vg
V>0
V=0
High pressure
10/05/2018
Monday 11 April lecture B Anders Persson, Uppsala University

22. In this case the motion evolves into this type of curtate cycloid
max
max
min
10/05/2018
Monday 11 April lecture B Anders Persson, Uppsala University

23. Monday 11 April lecture B Anders Persson, Uppsala University
The unperturbed mid-latitude jetstream (similar to the Subtropical in appaearance) J
10/05/2018
Monday 11 April lecture B Anders Persson, Uppsala University

24. Monday 11 April lecture B Anders Persson, Uppsala University
END
10/05/2018
Monday 11 April lecture B Anders Persson, Uppsala University