Abstract
Abstract. The complex nature of mineral dust aerosol emission makes it a difficult process to represent accurately in weather and climate models. Indeed, results in the companion paper indicate that many large-scale models underestimate the dust flux's sensitivity to the soil's threshold friction velocity for erosion. We hypothesize that this finding explains why many dust cycle simulations are improved by using an empirical dust source function that shifts emissions towards the world's most erodible regions. Here, we both test this hypothesis and evaluate the performance of the new dust emission parameterization presented in the companion paper. We do so by implementing the new emission scheme into the Community Earth System Model (CESM) and comparing the resulting dust cycle simulations against an array of measurements. We find that the new scheme shifts emissions towards the world's most erodible regions in a manner that is strikingly similar to the effect of implementing a widely used source function based on satellite observations of dust source regions. Furthermore, model comparisons against aerosol optical depth measurements show that the new physically based scheme produces a statistically significant improvement in CESM's representation of dust emission, which exceeds the improvement produced by implementing a source function. These results indicate that the need to use an empirical source function is eliminated, at least in CESM, by the additional physics in the new scheme, and in particular by its increased sensitivity to the soil's threshold friction velocity. Since the threshold friction velocity is affected by climate changes, our results further suggest that many large-scale models underestimate the global dust cycle's climate sensitivity.
Highlights
Mineral dust aerosols affect the Earth system through a wide variety of interactions, including scattering and absorbing radiation, altering cloud lifetime and reflectance, and serving as a nutrient source (Martin et al, 1991; Miller and Tegen, 1998; Forster et al, 2007)
Through a detailed comparison against measurements, we find that the K14 scheme produces a statistically significant improvement in the representation of dust emission in Community Earth System Model (CESM), and that this improvement exceeds that produced by a source function
These results indicate that the additional physics accounted for by K14, which result in an increased sensitivity of the dust flux to the soil’s threshold friction velocity, reduces the need for a source function in dust cycle simulations, at least in CESM
Summary
Mineral dust aerosols affect the Earth system through a wide variety of interactions, including scattering and absorbing radiation, altering cloud lifetime and reflectance, and serving as a nutrient source (Martin et al, 1991; Miller and Tegen, 1998; Forster et al, 2007). An accurate quantification of dust interactions with the Earth system in past and future climates is hindered by the empirical nature of dust emission parameterizations in climate models. Since these parameterizations are generally tuned to reproduce the current dust cycle (Ginoux et al, 2001; Zender et al, 2003a; Cakmur et al, 2006), applying them to a past or future climate, with substantial differences in global circulation and land surface, could produce large systematic errors. Many dust modules in climate models use a dust source function S (Ginoux et al, 2001; Tegen et al, 2002; Zender et al, 2003b; Grini et al, 2005; Koven and Fung, 2008) to help account for global vari-
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