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WP5.3 Assessment of Forecast Quality ENSEMBLES RT4/RT5 Kick Off Meeting, Paris, Feb 2005

This study compares the benefits of the GloSea and DePreSys models in terms of their forecast quality. It analyzes key variables such as temperature and precipitation, investigates bias and predictability, and compares skill against persistence and climatology. The study also explores the skill for 'extremes' and stability with varying starts, and evaluates statistical significance. Additionally, it examines multi-annual runs and assesses the convergence of the models with climatology.

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WP5.3 Assessment of Forecast Quality ENSEMBLES RT4/RT5 Kick Off Meeting, Paris, Feb 2005

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

  2. Met Office seasonal/multi-annual/decadal runs Model GloSea (HadCM3) later HadGEM DePreSys (HadCM3) Current oper. range Seasonal (6months) decadal 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) assimilation method Conventional (OI type) calibrated anomalies 9-ensemble experiments 1991-2001 pert. ODA pert. phys. pert. phys. lagged avge lagged avge

  3. 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

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

  5. Upper tercile Vs Upper quintile ROC score Skill for upper quintile, MAM T2m precip Skill for upper tercile, MAM T2m precip

  6. 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 intrinsic envelope? CGCM forecast drift (SST)

  7. Parameter Perturbations • Large Scale Cloud • Ice fall speed • Critical relative humidity for formation • Cloud droplet to rain: conversion rate and threshold • Cloud fraction calculation • Boundary layer • Turbulent mixing coefficients: stability-dependence, neutral mixing length • Roughness length over sea: Charnock constant, free convective value • Convection • Entrainment rate • Intensity of mass flux • Shape of cloud (anvils) • Cloud water seen by radiation • Dynamics • Diffusion: order and e-folding time • Gravity wave drag: surface and trapped lee wave constants • Gravity wave drag start level • Radiation • Ice particle size/shape • Sulphur cycle • Water vapour continuum absorption • 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

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