Transcript Slide 1 - Atmospheric Sciences

Climate Responses to Biomass Burning Aerosols over South Africa
Naoko Sakaeda
Department of Atmospheric Sciences (Mentors: Robert Wood and Phil Rasch)
Results
Introduction
The effects of aerosols emitted by biomass
burning on Earth’s radiation budget are significant
but their magnitude and extend are not yet fully
understood. Southern Africa is one large region
where intense biomass burning emissions are
observed especially during the months of June to
October. The reflection and absorption of solar
radiation by the aerosols change the radiative
balance of the lower atmosphere and may affect
other fields of climate. This study focuses on
examining the dependence of the aerosols’ direct
radiative forcing and its indirect effects on
radiation budget on the surface properties.
F: Net Solar Flux at TOA
FCLR: Clearsky Net Solar Flux at TOA
FCLDY: Cloudy-sky Net Solar Flux at TOA
CF: Total cloud fraction
Δ: Change from zero to with carbon output
Term1: Direct radiative forcing weighted by
clearsky fraction
Term2: Indirect radiative effect weighted by
mean cloud fraction
Term3: Change in cloud fraction weighted
by the difference in mean cloudy and
clearsky fluxes
Term1
Term2
Term3
F  (FCLR (1  CF ))  (CF  F )  (CF ( F CLDY  F CLR ))
Over ocean
Over land
Variable
Mean
value
Standard
deviation
Mean
value
Standard
deviation
CF
CF
0.540
0.122
0.489
0.267
0.036
0.037
0.0034
0.022
F CLDY (W/m2)
FCLDY (W/m2)
F CLR (W/m2)
FCLR (W/m2)
251.49
25.92
245.58
39.26
5.46
6.74
8.83
6.61
341.91
29.43
329.30
28.63
-4.43
2.64
-2.32
2.16
Term1 (W/m2)
-1.92
1.10
-0.99
1.30
Term2 (W/m2)
3.32
4.74
3.87
3.37
Term3 (W/m2)
-3.22
3.61
-0.49
1.90
F (W/m2)
-1.82
3.86
2.40
3.94
Figure 1: MODIS Aqua image on July 11,
2003 over Central and Southern Africa.
Red dots show locations of detected fires.
Figure #:
Figure #: Aerosols layer seen over clouds by
CLIPSO over SE Aatlantic Ocean
Aerosols over clear sky
(top-left): Change in net solar flux, (bottom, left to right): Term1
direct radiative effect, Term2 indirect radiative effect, Term3
change in cloud fraction
Methodology
+
We use a global atmospheric model, the
Community Atmosphere Model (CAM) to interpret
the impact of the biomass burning aerosol layer in
the regional scale. By comparing a 20 year
simulation in which the aerosol layers are present
with a simulation in which the aerosols are
removed in the region [10N-30S, 20W-50E], we
can examine the effect of the aerosols on the
climate system.
Overall flux change
Conclusion
Figure #:
Total aerosol
optical depth
output by the
model in a
simulation in
which
carbons are
present
Figure #: Initial profiles of mixing ratio of
carbons and cloud fractions at a certain
location over ocean and land. Over ocean,
aerosol layer is above the low clouds while
over land carbon mixing ratio maximizes at
the surface. Cloud fraction over land is much
smaller and it is mostly at higher altitudes.
=