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

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

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

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

. . . 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

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

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

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

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

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

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

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

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

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

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

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

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

Monday 11 April lecture B Anders Persson, Uppsala University Authentic inertial oscillation, “nocturnal jet” over 14-15 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

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

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

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

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

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

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