Quantifying the dust direct radiative effect in the Southwestern United States: findings from multiyear measurements
Abstract. Mineral aerosols (i.e., dust) can affect climate and weather by absorbing and scattering shortwave (SW) and longwave (LW) radiation in the Earth’s atmosphere (the direct radiative effect). It is thought that the dust direct radiative effect is sufficiently strong that the presence of dust can significantly alter surface temperatures, static stability of the atmosphere, and the top of the atmosphere energy balance. Yet despite its importance, understanding of this parameter is so poor that, for example, the sign of the net direct radiative effect at top of the atmosphere is unconstrained, and thus it is unknown if changes in dust over time cool or warm Earth’s climate. Here we develop and apply new methods to estimate the SW direct effect via observations of aerosols and radiation made over a three-year period in a desert region of the southwestern United States. We generate region-specific dust optical properties via a novel data set of soil mineralogy from the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) instrument, which are then used to model the SW and LW dust direct radiative effect. From the observations and model output we find that the net dust direct radiative effect, on average, is −6 ± 1 and −2 ± 1 W m−2 at the surface and top of the atmosphere, respectively. Our results suggest that the magnitude of the SW component is about twice that in the LW, underscoring the importance of quantifying the iron oxide content of dust since these minerals strongly affect dust SW absorbtivity.
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