Evaluation of clouds and radiation in the Met Office global forecast model using GERB/SEVIRI data

GERB/CERES Meeting 2006 Exeter

Evaluation of clouds and radiation in the Met Office global forecast model using GERB/SEVIRI data

Richard Allan, Tony Slingo

Environmental Systems Science Centre University of Reading, UK

Sean Milton, Malcolm Brooks

Met Office, Exeter, UK

With thanks to the GERB International Science Team including colleagues at Imperial College and the Royal Meteorological Institute of Belgium

GERB/CERES Meeting 2006 Exeter

Objectives

• Validation of new datasets (GERB/SEVIRI)

• Timely Model Evaluation• Understanding of physical processes

GERB/CERES Meeting 2006 Exeter

Recent ComparisonGERB Model

OLR:

SW Albedo:

SEVIRI Channels: WV (top) and IR (bottom)

GERB/CERES Meeting 2006 Exeter

Evaluation of clear-sky fluxes

Allan et al. (2005) JGR, 110, D14111, 10.1029/2004JD005698

GERB/CERES Meeting 2006 Exeter

Model evaluation: near-real time

• Change in model minus GERB flux differences

• Relate to change in model physics implemented

13th March | 14th March

Model SW albedo

2005 2006

OLR

ALB

Model-GERB: tropical land

GERB/CERES Meeting 2006 Exeter

Model evaluation: near-real time

• Change in model minus GERB flux differences

• Relate to change in model physics implemented

13th March | 14th March

Model SW albedo

2005 2006

Model-GERB: tropical land

ΔOLR

ΔALB

GERB/CERES Meeting 2006 Exeter

Time-series: 1200 UTC data

OLR

(Wm-2)

SW Albedo

GERB/CERES Meeting 2006 Exeter

July 2006 mean

Model GERB (Edition 1) CERES

OLR

α

GERB/CERES Meeting 2006 Exeter

Systematic biases

All-sky:

Clear-sky:

Desert dust aerosol

ITCZ

Low cloud

Surface albedo

Convective

cloud

Water vapour

LW Model minus GERB 1200 UTC SW

GERB/CERES Meeting 2006 Exeter

Model Evaluation: Namibian Stratocumulus region

31st March 2004

Mod

el

Leve

l

GERB/CERES Meeting 2006 Exeter

More recent example5th June 2006

Mod

el

Leve

l

GERB/CERES Meeting 2006 Exeter

Stratocumulus: composites

(Edition 1 data)

Model overestimates cloud albedo

Reasonable simulation of cloud fraction

GERB/CERES Meeting 2006 Exeter

Composites: April-July 2006

• Sample only where stratocumulus identified

• Model: reasonable simulation of cloud cover and longwave radiative effects

• Underestimation of SW albedo

LWCF (Wm-2)

ALB CF:

Frequency of Sc:

GERB/CERES Meeting 2006 Exeter

Diurnal Cycle

GERB/CERES Meeting 2006 Exeter

Time series

GERB/CERES Meeting 2006 Exeter

Large error in model simulated clear-sky OLR over west Sahara identified in July 2003 also present in 2006 for Edition 1 GERB data

Partially explained by large mineral dust aerosol optical depth

See RADAGAST project: http://radagast.nerc-essc.ac.uk and also: Haywood, Allan, Slingo et al. (2005) J. Geophys. Res. 110

GERB/CERES Meeting 2006 Exeter

Summary

• Ongoing near-real time comparisons of GERB/SEVIRI and Model

• Validation of new datasets– GERB/SEVIRI, surface observations

• Timely model evaluation– e.g. new physical parametrizations

• Process studies– e.g., stratocumulus, surface properties, mineral dust,

radiative flux divergence…

GERB/CERES Meeting 2006 Exeter

Time-series: Model-GERB∆OLR

(Wm-2)

∆SW Albedo

GERB/CERES Meeting 2006 Exeter