Dust emission size distribution impact on aerosol budget and radiative forcing over the Mediterranean region: a regional climate model approach

Abstract

Abstract. The present study investigates the dust emission and load over the Mediterranean basin using the coupled chemistry-aerosol-regional climate model RegCM-4. The first step of this work focuses on dust particle emission size distribution modeling. We compare a parameterization in which the emission is based on the individual kinetic energy of the aggregates striking the surface to a recent parameterization based on an analogy with the fragmentation of brittle materials. The main difference between the two dust schemes concerns the mass proportion of fine aerosol that is reduced in the case of the new dust parameterization, with consequences for optical properties. At the episodic scale, comparisons between RegCM-4 simulations, satellite and groundbased data show a clear improvement using the new dust distribution in terms of aerosol optical depth (AOD) values and geographic gradients. These results are confirmed at the seasonal scale for the investigated year 2008. This change of dust distribution has sensitive impacts on the simulated regional dust budget, notably dry dust deposition and the regional direct aerosol radiative forcing over the Mediterranean basin. In particular, we find that the new size distribution produces a higher dust deposition flux, and smaller top of atmosphere (TOA) dust radiative cooling. A multi-annual simulation is finally carried out using the new dust distribution over the period [2000][2001][2002][2003][2004][2005][2006][2007][2008][2009]. The average SW radiative forcing over the Mediterranean Sea reaches −13.6 W m −2 at the surface, and −5.5 W m −2 at TOA. The LW radiative forcing is positive over the basin: 1.7 W m −2 on average over the Mediterranean Sea at the surface, and 0.6 W m −2 at TOA.

Direct radiative effects during intense Mediterranean desert dust outbreaks

“…On average, dust outbreaks reduce the downwelling NET radiation at the ground level (DRE SURF ) by up to −14.7 ± 14.6 W m −2 (NSD), −18.0 ± 19.3 W m −2 (SDD) and −14.2 ± 14 W m −2 (MSD) while the corresponding DRE NETSURF levels are equal to −9.6 ± 10.2 W m −2 , −9.1 ± 11.2 W m −2 and −10.8 ± 11.2 W m −2 , respectively. Our results for the SW and LW radiation in the SDD are in a good agreement with the annual averages for the year 2008 presented by Nabat et al (2012) over northern Africa. …”

“…Our model computed dustinduced planetary warming above western Africa is comparable to similar results reported in previous studies focusing on the same or similar desert areas (e.g. Pérez et al, 2006;Mallet et al, 2009;Wang et al, 2010;Nabat et al, 2012;Kalenderski and Stenchikov, 2016).…”

“…Such a reverse of DRE TOA sign has been also reported in previous studies (e.g. Santese et al, 2010;Nabat et al, 2012;Papadimas et al, 2012). Over highly reflective surfaces (i.e.…”

“…However, the obtained results were representative at a local scale and, considering the high spatial variability of desert dust outbreaks, the optimum solution of assessing in a comprehensive way their impacts on weather and climate is provided by atmospheric-dust models. To this end, the induced DREs by the Mediterranean desert dust outbreaks have been analysed through short-term numerical simulations (Pérez et al, 2006;Santese et al, 2010;Remy et al, 2015) while similar studies have been conducted either at a seasonal (Nabat et al, 2015a) and annual scale (Nabat et al, 2012) or for extended time periods (Spyrou et al, 2013;Nabat et al, 2015b), pointing out the key role of desert dust aerosols in the Mediterranean climate.…”

In situ measurements of desert dust particles above the western Mediterranean Sea with the balloon-borne Light Optical Aerosol Counter/sizer (LOAC) during the ChArMEx campaign of summer 2013

“…Alpert et al, 1998;Chaboureau et al, 2011); radiative budget and climate (e.g. Nabat et al, 2012Nabat et al, , 2015a; precipitation chemistry (Chester et al, 1996;Loÿe-Pilot et al, 1986;Avila and Rodà, 2002); soil formation (Nihlén et al, 1995); and biogeochemistry of forest ecosystems (Avila and Peñuelas, 1999), oligotrophic lakes (Morales-Baquero et al, 2006;Reche et al, 2009), and marine surface waters (Guerzoni et al, 1999;Herut et al, 1999;Guieu et al, 2014).…”