Radiative forcing by mineral dust aerosols: Sensitivity to key variables

Abstract

Abstract. We examine diurnally averaged radiative forcing by mineral dust aerosols in shortwave and longwave spectral regions using a one-dimensional column radiation model. At the top of the atmosphere (TOA), net (shortwave plus longwave) dust radiative forcing can be positive (heating) or negative (cooling) depending on values of key variables. We derive an analytical expression for the critical single-scattering albedo at which forcing changes sign for an atmosphere containing both cloud and aerosol layers. At the surface, net dust forcing can be positive or negative under clear-sky conditions, whereas it is always cooling in the presence of a low-level stratus cloud. Longwave radiative forcing is essentially zero when clouds are present. We also study the sensitivity of dust diurnally averaged forcing to the imaginary part of refractive index (k), height of the dust layer, dust particle size, and dust optical depth. These variables play different roles as follows: (1) under both clear-and cloudy sky conditions, net TOA forcing is more sensitive to k than net surface forcing; (2) clear-sky longwave forcing and cloudy-sky TOA shortwave forcing are very sensitive to the altitude of the dust layer; although clear-sky shortwave forcing is not sensitive to it; (3) clear-sky shortwave forcing is much more sensitive to particle size than cloudysky shortwave forcing; longwave forcing is not sensitive to particle size; and (4) all forcings are sensitive to optical depth except cloudy-sky longwave forcing.

A review of natural aerosol interactions and feedbacks within the Earth system

“…In contrast, dust reduces the planetary albedo over bright surfaces (e.g., snow and ice, some deserts) and has different effects above and below bright clouds. The magnitude of all these effects depends strongly on particle size, refractive index and the altitude of dust layers (Liao and Seinfeld, 1998;Arimoto et al, 2001). The composition of dust is especially important in determining the longwave effect (Sokolik et al, 1998;Highwood et al, 2003) since refractive indices in the infrared vary considerably between dusts from different source regions.…”

A Study of Dust Aerosols Impact on Hurricanes with Multi-Sensors Measurement from Space

“…The extent and the indication of the direct effect of dust depend on its optical properties, vertical distribution, cloud cover, and the albedo of the underlying surface [9]. Also, the *Address correspondence to this author at the School of Physics, Astronomy, and Computational Sciences, George Mason University, 4400 University Drive, Fairfax, Virginia 22030, USA: Tel: (703) 582-8825; Fax: (703) 971-0314; E-mail: mkamal@gmu.edu optical properties of dust depend on its particle size and the refractive index [10].…”

“…Dust affects the weather system by interacting with incoming solar and outgoing long wave radiation and thereby changing humidity and temperature [7]. Any changes in atmospheric dust contents would create a change in the radiation balance and, inevitably, surface temperatures [8,9].…”

Direct radiative effects during intense Mediterranean desert dust outbreaks

“…Osipov et al, 2015), which can be at-tributed to several parameters related either to dust aerosols' physical and optical properties or to external factors (e.g. surface type), which determine both the sign and the magnitude of the DREs (Liao and Seinfeld, 1998). One of the most important factors is the composition of mineral particles determining the spectral variation of the refractive index (Müller et al, 2009;Petzold et al, 2009;Perlwitz et al, 2015a, b;Pérez García-Pando et al, 2016) and subsequently their absorption efficiency (Mallet et al, 2009), which are both critical in radiation transfer studies and are also dependent on the mixing state (either external or internal) of dust aerosols (Scarnato et al, 2015).…”