1. + = 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.
Figure 1: MODIS Aqua image on July 11, 2003 over Central and Southern Africa. Red dots show locations of detected fires.
Term1
Term2
Term3
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
Variable
Over ocean
Over land
Mean value
Standard deviation
0.540
0.122
0.489
0.267
0.036
0.037
0.0034
0.022
(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
-1.82
3.86
2.40
3.94
Figure #:
(top-left): Change in net solar flux, (bottom, left to right): Term1 direct radiative effect, Term2 indirect radiative effect, Term3 change in cloud fraction
Figure #: Aerosols layer seen over clouds by CLIPSO over SE Aatlantic Ocean
Aerosols over clear sky
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.