1 / 10

Friction in Mid-latitude Cyclones

Friction in Mid-latitude Cyclones. Ian Boutle Bob Plant, Stephen Belcher, Bob Beare, Andy Brown. Motivation. Many studies have shown the significance of friction in formation and dissipation of cyclones Up to 50% reduced growth rate

dewitt
Download Presentation

Friction in Mid-latitude Cyclones

An Image/Link below is provided (as is) to download presentation 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. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Friction in Mid-latitude Cyclones Ian Boutle Bob Plant, Stephen Belcher, Bob Beare, Andy Brown

  2. Motivation • 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

  3. 0 h Model Setup Near-surface Temperature 24 h Tropopause Upper Level Trough 48 h Idealised, dry setup – only dynamics and boundary layer scheme operating

  4. Ekman Pumping • Boundary layer forces convergence • Continuity forces ascent: • Ascent squashes • vortex, reducing • vorticity • What about • temperature? L

  5. Potential Vorticity • Frictional Term: • Ekman pumping • Baroclinic mechanism • Diabatic Term: • Surface heat fluxes • Latent heat fluxes

  6. Warm Conveyor Belt Baroclinic Mechanism Depth averaged PV generation in boundary layer: Depends on alignment of surface and thermal winds

  7. Baroclinic Mechanism 2 Mainly Static Stability Anomaly PV accumulates above Low centre

  8. ~PV ~Ekman Boundary Layer Stability PV mainly in SBL Unstable (Convective) BL Stable BL Surface stress mainly In CBL

  9. Summary • 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

  10. Switching off BL • Surface stress parameterised in terms of “eddy diffusivities” • Define SBL by • Set here

More Related