1. Page 1© Crown copyright 2004 WP5.3 Assessment of Forecast Quality ENSEMBLES RT4/RT5 Kick Off Meeting, Paris, Feb 2005 Richard Graham

2. Page 2© Crown copyright 2004 Met Office seasonal/multi-annual/decadal runs Model DePreSys (HadCM3) Current oper. range decadal assimilation method GloSea (HadCM3) later HadGEM Seasonal (6months) Conventional (OI type) calibrated anomalies 9-ensemble experiments 1991-2001 pert. ODA pert. phys. lagged avge pert. phys. lagged avge Hindcasts period: 1991 - 2001 GloSea: ->7m:1 st /15 th May/Nov 1 st June/Dec ->14m:1 st May/June/Nov/Dec -> 10y:1 st May 1964, 1994 DePreSys: -> 10y:1 st May/Nov (all years)

3. Page 3© Crown copyright 2004 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 (1 st and 15 th 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

4. Page 4© Crown copyright 2004 Example: model comparison GloSea Vs HadAM3 ROC for outer quintile precip 1-month lead, JJA

5. Page 5© Crown copyright 2004 Upper tercile Vs Upper quintile ROC score Skill for upper quintile, MAM Skill for upper tercile, MAM T2m precip T2m precip

6. Page 6© Crown copyright 2004 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 - Plot for multi-annual runs –upper ocean heat content intrinsic envelope?

7. Page 7© Crown copyright 2004 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