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Gwendal Rivière12 Collaboration: Philippe Arbogast, Alain Joly

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Presentation on theme: "Gwendal Rivière12 Collaboration: Philippe Arbogast, Alain Joly"— Presentation transcript:

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 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 ( mb) Data: ERAinterim (0.75° grid spacing) EKE=u’2/2 ( 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)

3 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

4 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

5 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)

6 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)

7 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)

8 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)

9 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

10 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 !

11 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)

12 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 !

13 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.

14 Other slides

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

16 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)

17 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)

18 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

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

20 Conclusions / schematic
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)

21 3D view of Klaus –ω’Φ’k u’aΦ’ EKE

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