The influence of simulated surface dust lofting and atmospheric loading on radiative forcing
Authors: Saleeby Stephen M. , van den Heever Susan C. , Bukowski Jennie , Walker Annette L. , Solbrig Jeremy E. , Atwood Samuel A. , Bian Qijing , Kreidenweis Sonia M. , Wang Yi , Wang Jun , Miller Steven D. 
Published: August 2019

Abstract. This high-resolution numerical modeling study investigates the
potential range of impact of surface-lofted dust aerosols on the mean
radiative fluxes and temperature changes associated with a dust-lofting
episode over the Arabian Peninsula (2–5 August 2016). Assessing the
potential for lofted dust to impact the radiation budget and temperature
response in regions of the world that are prone to intense dust storms is
important due to the impact of such temperature perturbations on thermally
driven mesoscale circulations such as sea breezes and convective outflows.
As such, sensitivity simulations using various specifications of the dust-erodible fraction were performed using two high-resolution mesoscale models
that use similar dust-lofting physics based on threshold friction wind
velocity and soil characteristics. The dust-erodible fraction, which
represents the fraction (0.0 to 1.0) of surface soil that could be
mechanically lifted by the wind and controls the location and magnitude of
surface dust flux, was varied for three experiments with each model. The
“Idealized” experiments, which used an erodible fraction of 1.0 over all
land grid cells, represent the upper limit on dust lofting within each
modeling framework, the “Ginoux” experiments used a 1∘ resolution,
spatially varying erodible fraction dataset based on topographic
depressions, and the “Walker” experiments used satellite-identified, 1 km
resolution data with known lofting locations given an erodible fraction of
1.0. These simulations were compared with a “No-Dust” experiment in which no
dust aerosols were permitted. The use of erodible fraction databases in the
Ginoux and Walker simulations produced similar dust loading which was more
realistic than that produced in the Idealized lofting simulations. Idealized
lofting in this case study generated unrealistically large amounts of dust
compared with observations of aerosol optical depth (AOD) due to the lack of
locational constraints. Generally, the simulations with enhanced dust mass
via surface lofting experienced reductions in daytime insolation due to
aerosol scattering effects as well as reductions in nighttime radiative
cooling due to aerosol absorption effects. These radiative responses were
magnified with increasing amounts of dust loading. In the Idealized
simulation with extreme (AOD > 5) dust amounts, these
radiative responses suppressed the diurnal temperature range. In the Ginoux
and Walker simulations with moderate (AOD ∼1–3) amounts
of lofted dust, the presence of dust still strongly impacted the radiative
fluxes but only marginally modified the low-level temperature. The
dust-induced near-surface temperature change was limited due to competing
thermal responses to changes in the net radiative fluxes and the dust-layer
radiative heating rates. Compared to the Ginoux simulation, the use of
increased resolution in dust-erodible fraction inventories in the Walker
simulations led to enhanced fine-scale horizontal variability in lofted dust
and a modest increase in the mean dust concentration profile and
radiative or thermal responses. This study discusses the utility of using
high-resolution dust source databases for simulating lofted dust, the need
for greater spatial coverage of in situ aerosol observations in dust-prone
regions, the impacts of dust on the local radiation budget and surface
thermal conditions, and the potential dust radiative impacts on thermally
driven mesoscale features.