- 121 Views
- Uploaded on
- Presentation posted in: General

Friction in Mid-latitude Cyclones

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Friction in Mid-latitude

Cyclones

Ian Boutle

Bob Plant, Stephen Belcher, Bob Beare, Andy Brown

- Many studies have shown the significance of friction in formation and dissipation of cyclones
- Up to 50% reduced growth rate
- Met Office Unified Model still has trouble with cyclone depth
- Underlying physical mechanism not well understood

0 h

Near-surface Temperature

24 h

Tropopause

Upper Level

Trough

48 h

Idealised, dry setup – only dynamics and boundary layer scheme operating

- Boundary layer forces convergence
- Continuity forces ascent:
- Ascent squashes
- vortex, reducing
- vorticity
- What about
- temperature?

L

- Frictional Term:
- Ekman pumping
- Baroclinic mechanism

- Diabatic Term:
- Surface heat fluxes
- Latent heat fluxes

Warm Conveyor Belt

Depth averaged PV generation in boundary layer:

Depends on alignment of surface and thermal winds

Mainly Static

Stability Anomaly

PV accumulates above

Low centre

~PV

~Ekman

PV mainly

in SBL

Unstable

(Convective) BL

Stable BL

Surface

stress

mainly

In CBL

- Boundary layer friction has a large affect on cyclone development
- Ekman pumping is significant, but not the only process acting
- PV perspective provides another mechanism, which appears similarly important

- Surface stress parameterised in terms of “eddy diffusivities”
- Define SBL by
- Set here