Global distribution of Asian, Middle Eastern, and North African dust simulated by CESM1/CARMA

Abstract

Abstract. Dust aerosols affect the radiative and energy balance at local and global scales by scattering and absorbing sunlight and infrared light. A previous study suggests that dust size distribution is one of the major sources of uncertainty in modeling the dust global distribution. Climate models overestimate the fine dust (≤5 µm) by an order of magnitude, while underestimates of the coarse dust (≥5 µm) range between 0.5 to 1.5 orders of magnitude compared with the global observations. Here we improved the simulated size distribution of dust aerosol using a sectional aerosol model (Community Aerosol and Radiation Model for Atmospheres) coupled with the Community Earth System Model (CESM1/CARMA). Simulated dust mass size distributions peak at around 2–3 µm in diameter and increase by 4 orders of magnitude from 0.1 to 2 µm. Our model demonstrates that North African, Middle Eastern, and Asian dust accounts for ∼ 59.7 %, 12.5 %, and 13.3 % of the global annual mean dust emissions, with the remaining 14.5 % originating from scattered smaller dust sources. The model dust vertical distributions are validated against the NASA Atmospheric Tomography (ATom) field campaign datasets. Both simulations and ATom in situ measurements during the ATom field campaign suggest that dust mass concentrations over the remote ocean drop by 2 to 3 orders of magnitude from the surface to the upper troposphere (200 hPa). Our model suggests that Asian dust contributes to more than 40 % of annual mean dust mass abundances in the global upper troposphere and lower stratosphere (UTLS). The model suggests that Asian dust dominates the dust mass budget in the UTLS of the Asian summer monsoon (ASM) region, with a relative contribution 1–2 orders of magnitude higher than the dust originating from the North African and Middle Eastern deserts.

Opinion: Tropical cirrus – from micro-scale processes to climate-scale impacts

“…Competing ice nucleation appears to occur frequently during the formation of cirrus clouds (DeMott et al, 2003;Froyd et al, 2022). While significant progress has been achieved in studying aerosol-cirrus interactions by coupling cloud and aerosol schemes within global models, parameterized cirrus and aerosol microphysics must be supplemented by parameterizations of the underlying small-scale dynamical forcing of ice supersaturation.…”

“…In this way, INPs, if present, weaken or prevent homogeneous freezing, thus lowering ice crystal number concentrations in cirrus. Mineral dust is widely recognized to be the most important INP in the upper troposphere, well-characterized in terms of both ice activity (Atkinson et al, 2013;Ullrich et al, 2017) and number concentrations (Froyd et al, 2022). However, properties of other INP types remain poorly constrained by observations, especially in the TTL (Sect.…”

“…Simulating mineral dust and BC particles in global models also presents a significant challenge due to uncertainties associated with source specification, transport, and scavenging by clouds. Comparisons between global model simulations and observations of dust and BC particles have shown significant discrepancies (Zhang et al, 2020;Lian et al, 2022). Aerosols in the TTL consist of aqueous, sulfate-containing particles with other (largely unspecified) organic compounds.…”

Reconsidering the Existence of a Trend in the Asian Tropopause Aerosol Layer (ATAL) From 1979 to 2017

“…In our model simulations, dust is largely the dominant aerosol type, by mass concentration, in our ATAL simulations (up to a factor 10 larger than sulfate aerosols). However, it has to be noted that other model set‐ups on dust in the upper troposphere identify significantly lower values of dust (e.g., Froyd et al., 2022; Lian et al., 2022). The high amount of dust found in our model could be explained by excessive convective transport, a lack of secondary activation of aerosols entrained into convective updrafts, a too strong dust transport in the upper troposphere from Africa and the Middle East (Wu et al., 2018), as well as the sensitivity of dust emissions to the resolution of the model (Brühl et al., 2018; Wu et al., 2018).…”

“…(2022) and Lian et al. (2022)). Simulation shortcomings concerning the aerosol transport above convective systems have been revealed in Yu et al.…”