Gwendal Rivière12 Collaboration: Philippe Arbogast, Alain Joly

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Presentation transcript:

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

The case of 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) EKE=u’2/2 (650-850 mb) Approach: separation into a background flow and a perturbation by time filtering L Perturbation wind Mean westerlies 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)

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

The eddy kinetic energy (EKE) equation Φ geopotential u geostrophic wind ua ageostrophic wind Horizontal ageostrophic geopotential fluxes Vertical ageostrophic geopotential fluxes Baroclinic conversion Pressure work Omega equation Q-vector Diagnostic equation for ageostrophic scalar

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

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)

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

f-plane Cyclonic shear β-plane Anticyclonic shear Combined effects of anticyclonic shear / PV gradient in EKE redistribution f-plane t=12h Cyclonic EKE redistribution Cyclonic shear y (1000km) X (1000km) EKE accumulation to the east β-plane EKE accumulation to the west Anticyclonic shear y (1000km) X (1000km)

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

Evolution of the idealized jet-crossing cyclone Jet axis t=48H Jet axis t=36H Jet axis t=12H Jet axis t=24H 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 !

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

A 3D view as a summary Downward EKE transfer –ω’Φ’k Mid-tropospheric baroclinic conversion Lower-tropospheric cyclonic EKE redistribution u’aΦ’ EKE Spain Atlantic Ocean The background flow controls the EKE redistribution !

Relation with jet-crossing cyclones. 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) (Browning, 2004; Gray et al. 2011; Martinez-Alvarado, 2014) ? Relation with jet-crossing cyclones.