Post on 28-Mar-2015
transcript
Dust-Climate Interactions
in HadGEM2
Stephanie Woodward
Met Office Hadley Centre
(stephanie.woodward@metoffice.gov.uk)
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