Dust-Climate Interactions in HadGEM2 Stephanie Woodward Met Office Hadley Centre ([email protected])

Dust-Climate Interactions

in HadGEM2

Stephanie Woodward

Met Office Hadley Centre

([email protected])

A dust scheme for climate modelling needs to

- work globally (including areas not currently sources)

- respond to changing climate

and so must

- work from model-generated fields

- be physically realistic

.

Outline of HadGEM dust scheme

6 size bins of aerosol.03 – 30 um radius, treated independantly

Interactive emission scheme

Transport as 6 model tracers

Dry deposition through gravitational settling and turbulent mixing in BL

Wet deposition, scavenging coefficients from obs

Resistance analogue method of combining deposition processes

Radiative properties from medians of range of measurements

* Volken & Schumann 1993, Water, Air & Soil Pollution 68

Emission scheme

Soil: 9 size bins .06-2000um diameter

Horizontal flux : Marticorena & Bergametti (bare soil fraction only) U* corrected for scaling effects

U*t = U*t (dry,impact) x f (CorrectedSoilMoisture) f - Fecan scheme, modified at high soil moistures

Vertical flux: only .06-60 um range total flux from log (F/G)=.134(%clay)-6 (M&B, based on Iversen data) size distribution from that of horiz. flux below 60um

Emissions

Deposition

Load

(22Tg)

Comparison with concentrations at U Miami stations

CGr KGI Maw

Pal Fun Nau

Nor ASm Mid

Ohu Chu Fan

Ewt Bar Ber

MaH Mia Iza

Comparison with Aeronet AODs

Cap Verde Solar village

Sede BokerBanizoubou

OugadougouIlorin

Dust & Climate

Objective:To investigate feedbacks between climate and dust

Model: proto-HadGEM2-AO GCM (N96 38 levs), including proto-dust scheme

2 Experiments:

“A” – Active Dust – dust radiative effects included

“P” – Passive Dust – dust radiative effects excluded

Each experiment:

20 years spin upallows climate (including ocean) to come to equilibrium

+10 years run

A

‘A’ concentrations & AODs vs. Observations

Cape Grim (concs) Funafuti (concs)

Midway (concs) Bermuda (concs)

Cape Verde (AOD) Solar Village (AOD)

P

A PA P

A - P

Difference in Load

Difference in emissions

Surface and Tropopause Flux Differences

Surface Temperature Difference ( A – P )

Soil Moisture Difference ( A – P )

Difference in emissions & soil moisture

Emissions increase of 50% over N Africa, due to positive feedback

Surface and Tropopause Flux Differences

Temperature differences ( A – P )

~18km

~8km

~2km

Differences (A – P)

Humidity

A

P

diff

v

u

Summary

Dust scheme developed for HadGEM2Good agreement with obs

Feedbacks on Dust production: Positive in Sahara Negative in moister regime

Shifts in circulation patterns