Lothar (T+42 hours)

5-Day ECMWF Ensemble Prediction of Typhoon Rusa

Extreme rainfall as a function of spatial scale (observational study: Olsson et al, 1999)

EPS cannot resolve circulation features in this range (cf lack of k-5/3 spectrum in model)

Global NWP models cannot predict extremes of precipitation: need for coupling to LAMs

ECMWF EPS – current operational configuration

1. 51 members. TL255L40. Once per day (12z). 25 Initial + Evolved dry singular vectors T42L40. 48 hour optimisation. Energy metric.

2. Stochastic physics

D+2

D+4

D+7

spread

control error

Spread

Skill

ECMWF EPS

BSresol

BSrel

10-members

10-members

Multi-analysis EPS

• MA EPS: 6-member ensemble

• Compare with EPS for 500 hPa height, spring 2002 (90 cases)

• Spread less than EPS

• Worse probability scores than EPS

Solid red: EPS; dash blue: MA EPS

Solid red: EPS; dash blue: MA EPS

Possible Revisions to EPS 2003-2004

1. Twice a day running (12z and 0z) +improved scheduling

2. Dry T42 singular vectors 48hr optimisation Moist T63 singular vectors 24hr optimisation

3. TL255L40TL319-TL399L65

4. Hessian (possibly RRKF) metric

Dry vs moist SVs 27/12/99. M.Coutinho, Reading U

24-hr optimisation

T63 resolution

Dry vs moist SVs

15/10/87

Dry vs moist SVs

2/8/97

0

10

00

00

10

0 ,

,max

,

,max

00 txAtx

txMMtx

txAtx

txtxtxtx

01

0 txAtxMM

To find the initial perturbation, consistent with the statistics of initial error, which evolves into the perturbation with largest total energy

Singular vectors of M

In principle, A is the analysis error covariance matrix. In practice, A is approximated by a simplified metric (eg total energy)

Isopleth of initial pdf

Isopleth of forecast pdf

0, ttM

Singular vectors for T1/Lothar computed with different initial time metrics

• total energy, Hessian metric with/without observations

•optimization period: 24 Dec 1999, 12 UT +48h

Initial time metric and SV structure

Initial time metric and SV structure

Hessian

Total energy

{

temperature at 45N of leading SV optimized for Europe

Initial time metric and SV structureVertical correlations 700hPa, 5leading SVs optimized for Europe

Total energy

Local bulk formula representing the mean effect of neglected scales - driven by resolved scales (eg diffusion)

Residual, =0 in most GCMs. Represent as stochastic noise

=P in ECMWF model where is a stochastic variable?

RXPXFX ];[][

Let X the state vector in an NWP model

Terms retained in the Galerkin basis projection of the underlying pde

PPDX

ECMWF stochastic physics scheme(s)

is a stochastic variable, drawn from a uniform distribution in [-0.5, 0.5], constant over time intervals of 6hrs and over 10x10 lat/long boxes

DPDX

)( DPPDX

i

ii

iii

2-day forecasts differing only in realisations of the stochastic physics parametrisation

Area under ROC curve. E: precip>40mm/day. Winter- top curves. Summer – bottom curves

Stoch phys

No stoch phys

Buizza et al, 1999

Stochastic Physics has a positive impact on ensemble skill