Estimating the radiative impacts of aerosol using GERB and SEVIRI

H. Brindley

Imperial College

Talk Outline

• Background and motivation• Detection methodology• Success?• Future work

From IPCC, 2001

Model estimates of the geographical distribution of present day annual-average radiative forcing (1750-2000) in W m-2 (Taken from IPCC, 2001)

Biomass Burning aerosols

Mineral dust

SEVIRI GERB

0.6 m

0.8 m

1.6 m

Shortwave Channels

MODIS image from 12:05 pm, 13/12/03 SEVIRI 0.8 m image from 12:00 pm, 13/12/03

GERB SW image from 12:00 pm, 13/12/03

12 m 10.8 m 8.7 m 7.3 m

Thermal Infrared Channels

8.7 - 10.8 m TB 10.8 - 12.0 m TB

10.8 m

8.7 -10.8 m 10.8 -12 m

~ 20° View Zenith~ 40° View Zenith

Test 3: Additional TB10.8-TB7.3 vs TB7.3-TB12.0 threshold applied

Test 1: All clear points rejected (TB8.7-TB10.8 vs TB10.8-TB12.0 simulations)

Test 2: Clear-sky adjustment

1200z1400z1600z1800z2000z2200z0000z0200z0400z0600z0800z

MODIS image from 1155z, 04/03/04

MODIS 27/01/03, 1215GERB reflected shortwave fluxes Temporal evolution of reflected SW flux

Summary

• GERB and SEVIRI are both capable of ‘seeing’ aerosol events

• SEVIRI visible channels should provide a means to classify

aerosol during the day over ocean

• Potential for IR channels to be used at night (and over land)? Needs further assessment of effects of uncertainties in IR dust characteristics and requires accurate surface emissivity values. Will also benefit from including textural analysis

• At present GERB processing flags aerosol as low cloud – needs correction in order for correct radiance to flux conversion

Applications (I): Direct impact

• Model Validation: Can current climate models

(a) Capture the observed aerosol distribution and its evolution with time?

(b) Given this distribution, simulate the observed impact on the TOA radiation budget?

• Comparison with observations from LEO satellites to assess likely impact of imperfect temporal sampling on the global aerosol distribution and radiative forcing estimates

• Investigation into aerosol impacts on the diurnal variation of the

surface radiation budget

Applications (II): Indirect impact

• Record will be on a time resolution ideally suited to investigate aerosol impact on cloud formation, reflectivity and longevity

• A combination of the observed record, in-situ data and climate modelling should permit investigations into dynamical feedbacks via aerosol induced radiative heating/cooling

• Lots of scope for GERB-CERES collaborative efforts!

And hopefully

• The synergy of GERB and SEVIRI will provide the first coupled description of the aerosol loading and direct radiative effect at the TOA over the African and Mediterranean regions on all timescales ranging from minutes to days and ultimately years

• Will be an invaluable resource both for testing the ability of

current climate models to accurately represent aerosol/radiation interactions, and investigating the validity of current ideas concerning aerosol/cloud effects

Image courtesy NASA Ndola, (12°S, 28°E), 18/09/00 Courtesy B. Holben

Image courtesy NASA

Capo Verde, 17/06/99 (courtesy D. Tanré)

Haywood et al., (in press)

Image courtesy NASA