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Eddy kinetic-energy redistribution within real and idealized extratropical storms

Eddy kinetic-energy redistribution within real and idealized extratropical storms

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Eddy kinetic-energy redistribution within real and idealized extratropical storms

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  1. Eddy kinetic-energy redistribution within real and idealized extratropical storms Gwendal Rivière12 Collaboration: Philippe Arbogast, Alain Joly 1 LMD-ENS, IPSL/CNRS, Paris 2 CNRM-GAME, Météo-France & CNRS, Toulouse

  2. A 3D easterly view of the storm Christian (Oct 2013) Forecast from Arpege, 00 UTC 28 October, step 9h L North Cold front South Warm front Max u (900 mb): poisonous tail of the bent-back warm front

  3. Approach: separation into a background flow and a perturbation by time filtering EKE=u’2/2 (650-850 mb) Mean westerlies L L Perturbation wind Another example: the storm Klaus (24/01/09) 12 UTC 23 Jan 00 UTC 24 Jan θe (900hPa) L Warm front L Warm front Cold front Cold front Max wind speed (650-850 mb) Data: ERAinterim (0.75° grid spacing) Early stage: strongest wind speeds are reached along the WCB Later stage: strongest wind speeds are reached in the frontal fracture zone (e.g. Gronas, 1995)

  4. Idealized study: use of the two-layer quasi-geostrophic model Klaus case ζ’ (300mb) >0 300mb Rossby radius of deformation ζ’ (900mb) >0 Basic state Isolated cyclonic anomalies Upper layer Lower layer

  5. Pressure work Baroclinic conversion Horizontal ageostrophic geopotential fluxes Vertical ageostrophic geopotential fluxes Diagnostic equation for ageostrophic scalar Omega equation Q-vector The eddy kinetic energy (EKE) equation Φgeopotential ugeostrophic wind uaageostrophic wind

  6. β-plane, linear t=0H t=12H EKE accumulation east of the low X (1000km) EKE redistribution at the lower layer in presence of the vertical shear f-plane, linear North t=0H West East y (1000km) South t=12H y (1000km) EKE accumulation west of the low X (1000km)

  7. Role of β and the vertical shear in EKE redistribution No β With β β increases the upward transfer and decreases the downward transfer, so a sink of energy for the lower layer !!! Wavelike disturbance assumption (wavenumbers m, K)

  8. Nonlinear t=0H t=12H EKE accumulation southwest of the low X (1000km) Role of nonlinearities in EKE redistribution Linear f-plane t=0H y (1000km) t=12H y (1000km) X (1000km)

  9. Nonlinear Cyclonic EKE redistribution EKE accumulation X (1000km) Role of background lateral shear in EKE redistribution Linear f-plane t=12H Cyclonic shear y (1000km) Anticyclonic shear y (1000km) X (1000km)

  10. Combined effects of anticyclonic shear / PV gradient in EKE redistribution t=12h f-plane, nonlinear β-plane, nonlinear EKE accumulation to the west EKE accumulation to the east Anticyclonic shear y (1000km) X (1000km) X (1000km) The stronger the vertical average of the PV gradient, the more important the EKE accumulation to the east

  11. Isolated cyclonic anomalies initiated south of a westerly jet Isolated cyclonic anomalies initialized south of a meridionally confined zonal jet ζ’ (300mb) >0 300mb ζ’ (900mb) >0 Basic state Isolated cyclonic anomalies Upper layer Lower layer

  12. Evolution of the idealized jet-crossing cyclone t=36H t=48H t=12H Jet axis Jet axis Jet axis t=24H Jet axis The key finding: once the cyclone has crossed the large-scale jet, EKE is cyclonically redistributed by ageostrophic geopotential fluxes in regions where the eddy and mean winds align with each other !

  13. Interpreting EKE distribution during for the storm Klaus 00 UTC 23 Jan 2009 06 UTC 23 Jan 2009 12 UTC 23 Jan 2009 18 UTC 23 Jan 2009 00 UTC 24 Jan 2009 L environment Data: ERAinterim (0.75° grid spacing)

  14. A 3D view of Klaus at the later stage Downward EKE transfer –ω’Φ’k Mid-tropospheric baroclinic conversion Lower-tropospheric cyclonic EKE redistributionu’aΦ’ EKE Spain Atlantic Ocean Confirmation of dry simulations of NWP model (Papritz and Schemm, 2013)

  15. Conclusions EKE Max |u| Schematic of EKE redistribution processes for jet-crossing cyclones following the Shapiro-Keyser conceptual model • Before jet crossing: both the background anticyclonic shear and PV gradient explain EKE accumulation to the southeast • After jet crossing: rapid cyclonic EKE redistribution to the southwest by ageostrophic geopotential fluxes (also nonlinear advection) due to the action of the cyclonic shear Rivière et al (2014a,b; QJRMS)

  16. Outlook Friedhelm at 12 UTC 8 Dec 2011 L From Baker et al (2013) • What is the role played by the synoptic-scale EKE redistribution in the formation of mesoscale jets (sting jets, cold-conveyor-belt jets) (Browning, 2004; Gray et al. 2011; Martinez-Alvarado, 2014) ? • Relation with jet-crossing cyclones.

  17. Other slides

  18. EKE budget for the idealized cyclone at the lower layer EKE budget in the cyclone frame of refrence (c phase speed of the cyclone)

  19. EKE budget for the storm Klaus (650-850 hPa) EKE budget in primitive equations in the cyclone frame of refrence (c phase speed of the cyclone) Data: ERAinterim (0.75° grid spacing, 3 hour time steps)

  20. EKE budget for the storm Friedhelm (650-850 hPa) EKE budget in primitive equations in the cyclone frame of refrence (c phase speed of the cyclone) Data: ERAinterim (0.75° grid spacing, 3 hour time steps)

  21. 3D viewof Klaus (u’a,ω’ k)Φ’ u’aΦ’ EKE