Abstract:
The sensitivity of climate models to the characterization
of African aerosol particles is poorly understood.
Africa is a major source of dust and biomass burning aerosols
and this represents an important research gap in understanding
the impact of aerosols on radiative forcing of the climate
system. Here we evaluate the current representation of
aerosol particles in the Conformal Cubic Atmospheric Model
(CCAM) with ground-based remote retrievals across Africa,
and additionally provide an analysis of observed aerosol optical
depth at 550 nm (AOD550 nm) and Ångström exponent
data from 34 Aerosol Robotic Network (AERONET) sites.
Analysis of the 34 long-term AERONET sites confirms the
importance of dust and biomass burning emissions to the
seasonal cycle and magnitude of AOD550 nm across the continent
and the transport of these emissions to regions outside
of the continent. In general, CCAM captures the seasonality
of the AERONET data across the continent. The
magnitude of modeled and observed multiyear monthly average
AOD550 nm overlap within 1 standard deviation of each
other for at least 7 months at all sites except the Réunion
St Denis Island site (Réunion St. Denis). The timing of modeled
peak AOD550 nm in southern Africa occurs 1 month prior
to the observed peak, which does not align with the timing
of maximum fire counts in the region. For the western
and northern African sites, it is evident that CCAM currently overestimates dust in some regions while others (e.g., the
Arabian Peninsula) are better characterized. This may be due
to overestimated dust lifetime, or that the characterization of
the soil for these areas needs to be updated with local information.
The CCAM simulated AOD550 nm for the global
domain is within the spread of previously published results
from CMIP5 and AeroCom experiments for black carbon, organic
carbon, and sulfate aerosols. The model’s performance
provides confidence for using the model to estimate largescale
regional impacts of African aerosols on radiative forcing,
but local feedbacks between dust aerosols and climate
over northern Africa and the Mediterranean may be overestimated.
