Comparison of GERB L2 fluxes (V002 and V999) with CERES

and the Met Office global forecast model

Richard Allan

Environmental Systems Science Centre, University of Reading

Recent comparison:

12th December 2005 1200 UTC

November 2005 animation.

GERB (BARG) Model

Spot the difference…

Comparison of V002 and V999 L2 GERB fluxes

- Diurnal cycle- Monthly mean comparison with CERES- Comparison with Met Office global model- Time-series including latest data

V999 V002

Diurnal animations of V999 and V002 OLR, July 2004

V999 Improvements

• Dawn/Dusk “wobble” and artifacts• Line of anomalously high OLR ~ equator• Hot spots removed (N. Sahara)

• ?problem with sun-glint

• Also note: Gulf of Guinea, Brazil convection, mid-latitude “noise” (see Ruth’s talk)

Comparison with CERES monthly-mean ERBE-like data

Use combined Aqua-Terra FM1+FM4 ES4 product

July 2004 monthly-diurnal mean

GERB (BARG, V999) CERES FM1+FM4

OLR

Albedo

July 2004 monthly-diurnal mean differences GERB (BARG, V999) minus CERES FM1+FM4

∆OLR~ -6 Wm-2

∆RSW~ -8 Wm-2

∆Albedo~ 0.02

∆ISW ~ .2 Wm-2

July 2004 monthly-diurnal mean differences GERB (BARG, V002) minus CERES FM1+FM4

∆OLR~ -5 Wm-2

∆RSW~ -2 Wm-2

∆ISW~ 0 Wm-2

∆Albedo~ -0.01

December 2004 monthly-diurnal mean diffs GERB (BARG, V999) minus CERES FM1+FM4

∆Albedo~0.03

∆OLR~ -6 Wm-2

∆RSW~ 10 Wm-2

∆ISW~ 0 Wm-2

CERES comparison: summary

• LW: GERB is 2.5% < CERES (~ 6 Wm-2)– V999 has removed view-angle dependence

• SW: GERB(V999) ~10% > CERES– ~10 Wm-2 RSW or 0.02-0.03 albedo – V002: smaller differences

• Differences apply for July and December 2004

Comparison with Met Office global model simulations:

SINERGEE

∆OLR ∆AlbedoJuly 2004 1200 UTC

Model minus GERB

V002

V999

OLR

OLRc

AOD

0.55um

Daytime clear-sky OLR: model minus GERB (Jun/Jul/Dec) V002 V999

Daytime clear-sky άSW: model minus GERB (Jun/Jul/Dec)

V002 V999

0000 0600 1200 1800

Model minus GERB, December 2004. V002(top); V999 (bottom)

December 2004

1200 UTC

Model minus GERB

∆OLR ∆Albedo

V002

V999

November 2005

1200 UTC

Model minus GERB

Clear-sky

V002

∆OLR ∆Albedo

Summary: V002-V999

• Improved diurnal cycle of OLR (sunglint?)• Monthly-diurnal mean vs CERES

– GERB LW ~2.5% < CERES (V002 similar)– GERB SW ~10% > CERES (V002 less)

• Sahara: increase in model-GERB diffs in LW and SW– but regions of known error (mineral dust, surface albedo)

• Oceans: reduction in model-GERB SW difference– Model low-clouds are too reflective

• Clear-sky fluxes over ocean: agreement with model remains– some improvement although GERB is now more reflective over

Mediterranean and Canaries

“Global” Ocean, 1200 UTC data

Differences (model minus GERB)

“Global” Ocean, 1200 UTC data

CLEAR-SKY differences (model minus GERB)

“Global” Ocean, 1200 UTC data

Clear-sky Mediterranean 1200 UTC

Stray Light: evident in 0000 UTC comparisons

Continuing model evaluationComposites

Model-GERB OLR (0, 6, 12, 18 UTC)

Model-GERB RSW (6, 12, 18 UTC)

Clear-sky composites 2003-2005

MODEL

GERB

Clear-sky LW clear-sky SW

Analysis of model marine strato-

cumulus

Cloud radiative effect and fraction

composites:

Model (left) GERB(right)

Diurnal & daily variation in stratocumulus (July 2004):

Model

MPEF

RMIB

PLANS

• SINERGEE– Continued near-real time comparisons– July 2004 model experiments– SEVIRI simulations?

• DABEX

• RADAGAST

Model simulations…

Proving problematic!

DABEX/RADAGAST