Global dust model intercomparison in AeroCom phase I

Abstract

Desert dust plays an important role in the climate system through its impact on Earth's radiative budget and its role in the biogeochemical cycle as a source of iron in high-nutrient-low-chlorophyll regions. A large degree of diversity exists between the many global models that simulate the dust cycle to estimate its impact on climate. We present the results of a broad intercomparison of a total of 15 global aerosol models within the AeroCom project. Each model is compared to observations focusing on variables responsible for the uncertainties in estimating the direct radiative effect and the dust impact on the biogeochemical cycle, i.e., aerosol optical depth (AOD) and dust deposition. Additional comparisons to Angström Exponent (AE), coarse mode AOD and dust surface concentration are included to extend the assessment of model performance. These datasets form a benchmark data set which is proposed for model inspection and future dust model developments. In general, models perform better in simulating climatology of vertically averaged integrated parameters (AOD and AE) in dusty sites than they do with total deposition and surface concentration. Almost all models overestimate deposition fluxes over Europe, the Indian Ocean, the Atlantic Ocean and ice core data. Differences among the models arise when simulating deposition at remote sites with low fluxes over the Pacific and the Southern Atlantic Ocean. This study also highlights important differences in models ability to reproduce the deposition flux over Antarctica. The cause of this discrepancy could not be identified but different dust regimes at each site and issues with data quality should be considered. Models generally simulate better surface concentration at stations downwind of the main sources than at remote ones. Likewise, they simulate better surface concentration at stations affected by Saharan dust than at stations affected by Asian dust. Most models simulate the gradient in AOD and AE between the different dusty regions, however the seasonality and magnitude of both variables is better simulated at African stations than Middle East ones. The models also reproduce the dust transport across the Atlantic in terms of both AOD and AE; they simulate the offshore transport of West Africa throughout the year and limit the transport across the Atlantic to the summer months, yet overestimating the AOD and transporting too fine particles. However, most of the models do not reproduce the southward displacement of the dust cloud during the winter responsible of the transport of dust into South America. Based on the dependency of AOD on aerosol burden and size distribution we use model data bias with respect to AOD and AE and infer on the over/under estimation of the dust emissions. According to this we suggest the emissions in the Sahara be between 792 and 2271 Tg/yr and the one in the Middle East between 212 and 329 Tg/yr

Recently Deglaciated High-Altitude Soils of the Himalaya: Diverse Environments, Heterogenous Bacterial Communities and Long-Range Dust Inputs from the Upper Troposphere

“…Consequently, previously observed microbial activities in the Himalayan glacier surface (5000 m) or barren (5800 or 6000 m) soils [18] are more likely driven by dust associated organic fraction (>40% of dust mass fraction; [8]) than primary production [46]. The orders of magnitude higher dust deposition rates [47]; [48] distinguish the Himalayan sites from the Andean and point to the imminent role of tropospheric dust on microbial community structure and succession.…”

Association of Kawasaki disease with tropospheric winds in Central Chile: Is wind-borne desert dust a risk factor?

“…Central Chile is subject to subsidence regimes and mountain waves so desert dust can be brought down to ground, as in the west coast of North America (McKendry et al, 2008). In Santiago, the dust comes from regional scale transport whereas in western North America it comes from intercontinental (Goudie, 2014;Huneeus et al, 2010). We have also found that part of the variability in KD cases is related to climate forcing on longer time scales; this is a novel result.…”

The Caspian Sea–Hindu Kush Index (CasHKI): A regulatory factor for dust activity over southwest Asia

“…In this analysis, dust surface concentration and dust AOD at 550 nm were simulated over SW Asia as composite-mean maps for the different CasHKI modes. The model performance for dust simulations over Asia has been evaluated by several studies (e.g., Takemura et al, 2002;Goto et al, 2011;Huneeus et al, 2011;Kaskaoutis et al, 2014a), also including the Sistan basin in eastern Iran (Kaskaoutis et al, 2015a). (Kaskaoutis et al, 2015a) revealed that the combination between the Indian-Pakistan thermal low and the high-pressure system over the CS induces the north Levar wind over eastern Iran, while modifications in the pressure patterns reinforce changes in Levar onset, intensity and duration.…”