Impact of mineral dust on cloud formation in a Saharan outflow region

Abstract

Abstract. We present a numerical modelling study investigating the impact of mineral dust on cloud formation over the Eastern Mediterranean for two case studies: (i) 25 September 2008 and (ii) 28/29 January 2003. In both cases dust plumes crossed the Mediterranean and interacted with clouds forming along frontal systems. For our investigation we used the fully online coupled model WRF-chem.The results show that increased aerosol concentrations due to the presence of mineral dust can enhance the formation of ice crystals. This leads to slight shifts of the spatial and temporal precipitation patterns compared to scenarios where dust was not considered to act as ice nuclei. However, the total amount of precipitation did not change significantly. The only exception occurred when dust entered into an area of orographic ascent, causing glaciation of the clouds, leading to a local enhancement of rainfall. The impact of dust particles acting as giant cloud condensation nuclei on precipitation formation was found to be small. Based on our simulations the contribution of dust to the CCN population is potentially significant only for warm phase clouds. Nevertheless, the dust-induced differences in the microphysical structure of the clouds can contribute to a significant radiative forcing, which is important from a climate perspective.

An outstanding Saharan dust event at Mt. Cimone (2165 m a.s.l., Italy) in March 2004

“…Even if the effects of dust on visibility and human health (e.g., are fairly well known (e.g., Middleton et al, 2008;Zauli Sajani et al, 2011), the impact on ecosystems and on cloud processing has been focused only recently (see for example Okin et al, 2004;Bangert et al, 2012;Smoydzin et al, 2012). Mineral dust particles deeply affect climate, acting both directly (by scattering and absorbing radiation) and indirectly (through the modification of the optical properties of clouds and cryosphere such as albedo) on the Earth's radiation balance (IPCC, 2013).…”

Assessing atmospheric dust modelling performance of WRF-Chem over the semi-arid and arid regions around the Mediterranean

“…The WRF-Chem model has been previously used in several studies to investigate dust storms and dust interactions with atmospheric thermodynamics and radiation using different dust emission parametrisations (e.g. Zhao et al, 2010;Smoydzin et al, 2012;Kalenderski et al, 2013). Su and Fung (2015) used WRF-Chem to assess its performance to simulate dust concentrations over East Asia using two different dust emission parametrisations.…”

Long‐range transport across the Atlantic in summertime does not enhance the hygroscopicity of African mineral dust

“…Therefore, dust hygroscopic properties may change as the dust undergoes atmospheric processing during long-range transport. An accurate description of the temporal evolution of dust hygroscopic properties is crucial to quantify dust impact on the climate system that is a challenge for models [Smoydzin et al, 2012].…”