Direct radiative effects during intense Mediterranean desert dust outbreaks

Abstract

Abstract. The direct radiative effect (DRE) during 20 intense and widespread dust outbreaks, which affected the broader Mediterranean basin over the period March 2000-February 2013, has been calculated with the NMMB-MONARCH model at regional (Sahara and European continent) and shortterm temporal (84 h) scales. According to model simulations, the maximum dust aerosol optical depths (AODs) range from ∼ 2.5 to ∼ 5.5 among the identified cases. At midday, dust outbreaks locally induce a NET (shortwave plus longwave) strong atmospheric warming (DRE ATM values up to 285 W m −2 ; Niger-Chad; dust AODs up to ∼ 5.5) and a strong surface cooling (DRE NETSURF values down to −337 W m −2 ), whereas they strongly reduce the downward radiation at the ground level (DRE SURF values down to −589 W m −2 over the Eastern Mediterranean, for extremely high dust AODs, 4.5-5). During night-time, reverse effects of smaller magnitude are found. At the top of the atmosphere (TOA), positive (planetary warming) DREs up to 85 W m −2 are found over highly reflective surfaces (Niger-Chad; dust AODs up to ∼ 5.5) while negative (planetary cooling) DREs down to −184 W m −2 (Eastern Mediterranean; dust AODs 4.5-5) are computed over dark surfaces at noon. Dust outbreaks significantly affect the mean regional radiation budget, with NET DREs ranging from −8.5 to 0.5 W m −2 , from −31.6 to 2.1 W m −2 , from −22.2 to 2.2 W m −2 and from −1.7 to 20.4 W m −2 for TOA, SURF, NETSURF and ATM, respectively. Although the shortwave DREs are larger than the longwave ones, the latter are comparable or even larger at TOA, particularly over the Sahara at midday. As a response to the strong surface day-time cooling, dust outbreaks cause a reduction in the regional sensible and latent heat fluxes by up to 45 and 4 W m −2 , respectively, averaged over land areas of the simulation domain. Dust outbreaks reduce the temperature at 2 m by up to 4 K during day-time, whereas a reverse tendency of similar magnitude is found during nighttime. Depending on the vertical distribution of dust loads and time, mineral particles heat (cool) the atmosphere by up to 0.9 K (0.8 K) during day-time (night-time) within atmospheric dust layers. Beneath and above the dust clouds, mineral particles cool (warm) the atmosphere by up to 1.3 K (1.2 K) at noon (night-time). On a regional mean basis, negative feedbacks on the total emitted dust (reduced by 19.5 %) and dust AOD (reduced by 6.9 %) are found when dust interacts with the radiation. Through the consideration of dust radiative effects in numerical simulations, the model positive and negative biases for the downward surface SW or LW radiation, respectively, with respect to Baseline Surface Radiation Network (BSRN) measurements, are reduced. In addition, they also reduce the model near-surface (at 2 m) nocturnal cold biases by up to 0.5 K (regional averages), as well as the model warm biases at 950 and 700 hPa, where the dust concentration is maximized, by up to 0.4 K. However, improvements are relatively small and do not happen in all ...

Particulate Matter Concentrations in a Middle Eastern City – An Insight to Sand and Dust Storm Episodes

“…Sahara SDS crossing over the Mediterranean Sea was reported in the literature (Gkikas et al, 2018;Solomos et al, 2018). Solomos et al, (2018) Alam et al, (2014) and Nabavi et al, (2016) focused on the aerosol optical depth and climatology of some dust outbreaks originated in the Middle East and the Arabian Peninsula that affected west-south Asia.…”

“…Sahara SDS crossing over the Mediterranean Sea was reported in the literature (Gkikas et al, 2018;Solomos et al, 2018). Solomos et al, (2018) Alam et al, (2014) and Nabavi et al, (2016) focused on the aerosol optical depth and climatology of some dust outbreaks originated in the Middle East and the Arabian Peninsula that affected west-south Asia. According to these studies, the dust transport in the Middle East and North Africa (MENA) region is transported from west to east (Alam et al, 2014;Nabavi et al, 2016;Naimabadi et al, 2016;Khaniabadi et al, 2017;Rashki et al, 2017;Gkikas et al, 2018).…”

“…Solomos et al, (2018) Alam et al, (2014) and Nabavi et al, (2016) focused on the aerosol optical depth and climatology of some dust outbreaks originated in the Middle East and the Arabian Peninsula that affected west-south Asia. According to these studies, the dust transport in the Middle East and North Africa (MENA) region is transported from west to east (Alam et al, 2014;Nabavi et al, 2016;Naimabadi et al, 2016;Khaniabadi et al, 2017;Rashki et al, 2017;Gkikas et al, 2018). This consistent with previous observation in Jordan that most of the SDS was mainly started from North Africa and transported to the Middle East after crossing/circulating over the Arabian Peninsula and the Levant.…”

From Tropospheric Folding to Khamsin and Foehn Winds: How Atmospheric Dynamics Advanced a Record-Breaking Dust Episode in Crete

“…Mineral dust particles that are emitted from the desert areas in the Sahara and the Middle East travel long distances in the atmosphere and affect air quality, weather, climate and local ecosystems at the Mediterranean basin [1][2][3][4]. Dust affects the radiative transfer in the area [5][6][7], and cloud processes due to the activation of dust particles as cloud condensation nuclei (CCN) and ice nuclei (IN) [8,9]. Moreover, the ocean depositions of dust affect biogeochemical processes and phytoplankton blooming [10,11].…”

Saharan Dust Modeling Over the Mediterranean Basin and Central Europe: Does the Resolution Matter?

“…Several works have studied the sensitivity of dust models to several parameterizations such as emission schemes (Flaounas et al, 2017), dust properties (Colarco et al, 2014) or the inclusion of ARI+ACI processes (Solmon et al, 2008;Baró et al, 2017;Palacios-Peña et al, 2017Gkikas et al, 2018;Klingmüller et al, 2019). Nevertheless, the literature focused on the impact of the spatial resolution on the modeled dust intrusion is limited.…”