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WP5.3 Assessment of Forecast Quality

ENSEMBLES RT4/RT5 Kick Off Meeting, Paris, Feb 2005

Richard Graham

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Met Office seasonal/multi-annual/decadal runs

ModelDePreSys(HadCM3)

Currentoper. range

decadal

assimilationmethod

GloSea(HadCM3)

later HadGEM

Seasonal(6months)

Conventional (OI type)

calibrated anomalies

9-ensembleexperiments1991-2001

pert. ODA

pert. phys.

lagged avge

pert. phys.

lagged avge

Hindcasts

period: 1991 - 2001

GloSea:->7m: 1st/15th May/Nov 1st June/Dec ->14m: 1st May/June/Nov/Dec-> 10y: 1st May 1964, 1994

DePreSys:

-> 10y: 1st May/Nov (all years)

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RT5.3 Analysis

Main aim (18m): compare benefits of systems/methods Diagnostics/tools, seasonal-range

Key variables: temperature, precipitation Investigate bias and predictability (as DEMETER, WMO SVS) Adapt score comparison suite from CGCM/AGCM study Focus:

To what range is seasonal (3-month-mean) predictability feasible? Comparative skill for ‘extremes’ (outer quintile, decile) (overlap RT4 Stability with varying starts (1st and 15th of month) Compare skill against persistence (as well as climatology) Statistical significance

Link to European Flood and Drought IP Multi-annual

Adapt and apply assessment methods used for seasonal range How quickly does model converge with climatology? Look at skill for ‘slow’ variables: upper ocean heat content, THC, ENSO

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Example: model comparison

GloSea Vs HadAM3 ROC for outer quintile precip

1-month lead, JJA

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Upper tercile Vs Upper quintile ROC score

Skill for upper quintile, MAM

Skill for upper tercile, MAM

T2mprecip

T2m precip

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CGCM forecast drift (SST)

Met Office GloSea CGCM

15-member hindcasts to 6 month range start each month 1987 - 2001

SST in Niño regions(tropical Pacific)

monthly climatology<forecast> - <obs>

Plot for multi-annual runs –upper ocean heat content

intrinsicenvelope?

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Parameter Perturbations

Convection• Entrainment rate• Intensity of mass flux • Shape of cloud (anvils) • Cloud water seen by radiation

Radiation• Ice particle size/shape• Sulphur cycle• Water vapour continuum absorption

Boundary layer• Turbulent mixing coefficients: stability-dependence, neutral mixing length

• Roughness length over sea: Charnock constant, free convective value

Dynamics• Diffusion: order and e-folding time

• Gravity wave drag: surface and trapped lee wave constants

• Gravity wave drag start level

Land surface processes• Root depths

• Forest roughness lengths

• Surface-canopy coupling

• CO2 dependence of stomatal conductance

Sea ice• Albedo dependence on temperature• Ocean-ice heat transfer

Large Scale Cloud• Ice fall speed• Critical relative humidity for formation• Cloud droplet to rain: conversion rate and threshold• Cloud fraction calculation