A kinetic-energy budget of the windstorm « Klaus » (January 24, 2009)

G. Rivière, A. Joly

CNRM/GAME, Météo-France/CNRS

Presentation of « Klaus » and its damages

Image from Meteosat 9 (01/24/2009, 06 UTC)

Wind speed maximum

0 50 80 100 120 140 160 180 200 km/h

Trajectory

• Strongest windstorm in France since Christmas 1999 storms « Lothar » and « Martin ». • « Klaus » hit Southwestern France as well as Northern Spain. Trajectory close to the second storm of 1999 « Martin ».

Comparis° between « Klaus » & « Martin » (Dec 26, 1999)

• Even though they have similar trajectories, the timing of the interaction with upper-level structures is quite different. • High-frequency disturbances have a barotropic structure over the whole troposphere at 25°W for « Klaus » and at 0°W for « Martin »

Shading: low-freq (>6d) wind speed (300 hPa) blue: high-freq (<6d) relative vorticity (300 hPa) black: high-freq (<6d) relative vorticity (900 hPa)

« Klaus » « Martin »

Data: operational analysis of the 4DVAR Météo-France ARPEGE system

« Klaus » « Martin »

EKE (500-900 hPa)

Baroclinic conversion

Rel vor maximum (900 hPa)

For « Klaus », the baroclinic interaction occurs 18H before reaching the coasts whereas for « Martin », this happens at the same time.

High-freq kinetic-energy redistribution within “Klaus”

At the end of the life cycle of « Klaus », a large part of the high-freq kinetic energy is redistributed south of the vortex maximum !

Blue: HF wind speed

Shading: total wind speedshading: LF wind speed

: LF wind speed : HF wind speed total wind speed

High-frequency kinetic-energy budget

2/'' 2ueK

Each variable decomposed into a high- (primes) and low- (subscript m) frequency part

High-frequency kinetic energy per unit mass (EKE)

sKDtD

pem Re)..('' m33 uu'u'u'.

Decomposition similar to Orlanski and Katzfey (1991) and Rivière and Joly (2006)

Reynolds stress Residu

,'')''()'.(' pp u'u'. p

Pressure Work

Internal baroclinic conversionHorizontal and vertical ageostrophic geopotential fluxes

Kinetic-energy budget (18 UTC Jan 23, 500-900hPa)

2/'' 2ueK

Pressure Work

Internal convers° + vert ageos fluxes Horizontal ageostrophic geop fluxes

Pressure Work+Reynolds stress

Rel Vor (900hPa)

)'',''( aa vu

• The pressure work dominates over the Reynolds stress term• Horiz ageos geopotential fluxes redistribute EKE southwestward

Kinetic-energy budget (06 UTC Jan 24, 500-900hPa)

Pressure Work

Internal convers° + vert ageos fluxes Horizontal ageostrophic geop fluxes

2/'' 2ueK

Pressure Work+Reynolds stress

Rel Vor (900hPa)

)'',''( aa vu

• The pressure work dominates over the Reynolds stress term• Horiz ageos geop fluxes redistribute EKE south of the vortex and are the only term that may explain EKE increase south of it !

Vertical cross section of the ageostrophic vertical geopotential fluxes

0)''( p

• Ageostrophic vertical geopotential fluxes tend to redistribute EKE downward from 500 hPa to 900 hPa !

zonal average in a band of

longitude 10° centred on the

vortex0)''( p

Conclusions / outlook • Strong winds at the end of « Klaus » life cycle are due to a favorable combination of low-freq westerlies and high-freq kinetic-energy redistribution south of the system.• Horizontal and vertical ageost geop fluxes tend to redistribute within the system eddy kinetic energy southward and downward !!!

• Is this EKE redistribution by ageost geop fluxes a synoptic-scale feature of a sting jet ?• Confirmation of the results by looking at other data (e.g., ecmwf)

Meteosat infrared image

Existence of multiple bands of cold air within the cloud head (similar to sting

jets properties)