Abstract
Abstract. Lofted mineral dust over data-sparse regions presents considerable challenges to satellite-based remote sensing methods and numerical weather prediction alike. The southwest Asia domain is replete with such examples, with its diverse array of dust sources, dust mineralogy, and meteorologically driven lofting mechanisms on multiple spatial and temporal scales. A microcosm of these challenges occurred over 3–4 August 2016 when two dust plumes, one lofted within an inland dry air mass and another embedded within a moist air mass, met over the southern Arabian Peninsula. Whereas conventional infrared-based techniques readily detected the dry air mass dust plume, they experienced marked difficulties in detecting the moist air mass dust plume, becoming apparent when visible reflectance revealed the plume crossing over an adjacent dark water background. In combining information from numerical modeling, multi-satellite and multi-sensor observations of lofted dust and moisture profiles, and idealized radiative transfer simulations, we develop a better understanding of the environmental controls of this event, characterizing the sensitivity of infrared-based dust detection to column water vapor, dust vertical extent, and dust optical properties. Differences in assumptions of dust complex refractive index translate to variations in the sign and magnitude of the split-window brightness temperature difference commonly used for detecting mineral dust. A multi-sensor technique for mitigating the radiative masking effects of water vapor via modulation of the split-window dust-detection threshold, predicated on idealized simulations tied to these driving factors, is proposed and demonstrated. The new technique, indexed to an independent description of the surface-to-500 hPa atmospheric column moisture, reveals parts of the missing dust plume embedded in the moist air mass, with the best performance realized over land surfaces.
Highlights
The monitoring of mineral dust life cycle is a high priority for the global aerosol community in terms of basic research, climate, and operational purposes (Benedetti et al, 2018)
A highly useful case allowing us to explore the impacts of water vapor on SWBTD occurred during early August 2016, when two dust storms met in east–west alignment over the southern Arabian Peninsula of southwest Asia
Considering the modeled sensitivity of the SWBTD dust signal to column water vapor and to the location of the dust in the profile, we examined to what extent the detection might be improved by incorporating atmospheric column moisture and expected dust layer altitude as a priori information into SWBTD-based detection algorithms
Summary
Jennifer Bukowski, Susan C. van den Heever, Yi Wang, Xiaoguang Xu3,a, Jun Wang, Annette L. Walker, Ting-Chi Wu1, Milija Zupanski, Christine Chiu, and Jeffrey S. Reid4 1Cooperative Institute for Research in the Atmosphere, Colorado State University, Fort Collins, CO, USA 2Department of Atmospheric Science, Colorado State University, Fort Collins, CO, USA 3Department of Chemical and Biochemical Engineering, University of Iowa, Iowa City, IA, USA 4U.S. Naval Research Laboratory, Monterey, CA, USA anow at: Joint Center for Earth Systems Technology, University of Maryland, Baltimore County, MD, USA. Received: 1 March 2019 – Discussion started: 12 March 2019 Revised: 25 July 2019 – Accepted: 12 August 2019 – Published: 24 September 2019
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