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The Impact of Moist Singular Vectors and Horizontal Resolution on Short-Range Limited-Area Ensemble Forecasts for Extreme Weather Events. A. Walser 1) M. Arpagaus 1) M. Leutbecher 2) C. Appenzeller 1) 1) MeteoSwiss, Zurich 2) ECMWF, Reading, GB. Perturbations of initial conditions.

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The Impact of Moist Singular Vectors and Horizontal Resolution on Short-Range Limited-Area Ensemble Forecasts for Extreme Weather Events

A. Walser1)

M. Arpagaus1)

M. Leutbecher2)

C. Appenzeller1)

1)MeteoSwiss, Zurich

2)ECMWF, Reading, GB

perturbations of initial conditions
Perturbations of initial conditions
  • Perturbations should match the uncertainties in the initial conditions.
  • Ideally, an ensemble span the entire range of possible solutions.
  • Initial perturbations using “moist” singular vectors (SVs) might account for a more reliable spread in the short-range.
perturbations of initial conditions1
Perturbations of initial conditions
  • Perturbations should match the uncertainties in the initial conditions.
  • Ideally, an ensemble span the entire range of possible solutions.
  • Initial perturbations using “moist” singular vectors (SVs) might account for a more reliable spread in the short-range.
moist vs operational singular vectors coutinho et al 2004
Moist vs. operational singular vectorsCoutinho et al. (2004)
  • ‚opr‘ SVs (T42L31, OTI 48 h): linearized physics package with
    • surface drag
    • simple vertical diffusion
  • ‚moist‘ SVs (T63L31, OTI 24 h): linearized physics package includes additionally:
    • gravity wave drag
    • long-wave radiation
    • deep cumulus convection
    • large-scale condensation

 moist SVs: use of moist processes in SV calculation, but same norm (‚total energy norm‘)  no humidity perturbations.

sleps

dynamical

downscaling

SLEPS
  • SLEPS: Short-range Limited-area Ensemble Prediction System
  • Variant of the operational COSMO-LEPS
  • Motivation: Early warnings for extreme weather events

Limited-area ensemble

Global ensemble

  • 51 ensemble members
  • LM with 10 km grid-spacing and 32 levels
  • 72-h forecasts
  • IFS members use „moist“ singular vectors

LM, x~10 km

IFS (ECMWF), ∆x~80 km, moist SVs

sleps simulations
SLEPS simulations
  • LM 3.92 ensembles using Brasseur (2001) wind gust formulation:
    • ∆x ~80 km (as ECMWF EPS)
    • ∆x ~10 km but ECMWF EPS topography
    • ∆x ~10 km (as COSMO-LEPS)
  • Storm Lothar: 26 December 1999
    • moist SVs ECMWF EPS  SLEPS 19991224 00 UTC, + 72 h
    • opr SVs ECMWF EPS  SLEPS 19991224 00 UTC, + 72 h
  • Storm Martin: 27/28 December 1999
    • moist SVs ECMWF EPS  SLEPS 19991226 00 UTC, + 72 h
    • opr SVs ECMWF EPS  SLEPS 19991226 00 UTC, + 72 h
wind gusts storm lothar 26 12 1999
Wind gusts storm Lothar (26.12.1999)

LM analysis with nudging: Proxy for observations

2 day forecast max wind gusts storm lothar 2
2-day forecast max. wind gusts storm Lothar (2)

SLEPS with opr SVs, ECMWF EPS topography

2 day forecast max wind gusts storm lothar 3
2-day forecast max. wind gusts storm Lothar (3)

SLEPS with moist SVs, ECMWF EPS topography

2 day forecast max wind gusts storm lothar 5
2-day forecast max. wind gusts storm Lothar (5)

SLEPS with moist SV, only 10 members (as COSMO-LEPS)

wind gusts storm martin 27 28 12 1999
Wind gusts storm Martin (27.-28.12.1999)

LM analysis with nudging: Proxy for observations

2 day forecast max wind gusts storm martin 2
2-day forecast max. wind gusts storm Martin (2)

SLEPS with opr SVs, ECMWF EPS topography

2 day forecast max wind gusts storm martin 3
2-day forecast max. wind gusts storm Martin (3)

SLEPS with moist SVs, ECMWF EPS topography

2 day forecast max wind gusts storm martin 5
2-day forecast max. wind gusts storm Martin (5)

SLEPS with moist SVs, only 10 members (as COSMO-LEPS)

conclusions
Conclusions
  • High-Resolution ensemble predictions have potential to detect storms earlier and more reliably in the future.
  • Contribution from moist singular vectors is crucial.

Questions?

parameterization for 10m wind gusts
Parameterization for 10m wind gusts
  • LM („operational“):
  • 3 x double turbulent kinetic energy in Prandtl-Layer:
  • U* : Friction velocity
  • Brasseur wind gust formulation
  • (Mon. Wea. Rev. 129, 5-25, 2001)
sleps clustering
SLEPS clustering

Global ECMWF EPS ensembles with moist singular vectors

50+1 members

Hierarchical Cluster Analysis

area: Europe

fields: 4 variables (U,V,Q,Z) at 3 levels (500, 700, 850) for 3 time steps (24h, 48h, 72 h), number of clusters: fixed to 10

10 clusters

Representative Member Selection

one per cluster:

member nearest (3D) to the mean of its own cluster AND most distant to the other clusters’ means

10 representative members (RMs)

10 Lokal Modell (limited-area) integrations nested into 5 RMs

SLEPS: Short-range limited-area Ensemble Prediction System