Preprints
https://doi.org/10.5194/egusphere-2024-1057
https://doi.org/10.5194/egusphere-2024-1057
31 May 2024
 | 31 May 2024
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

Remote Sensing detectability of airborne Arctic dust

Norman T. O’Neill, Keyvan Ranjbar, Liviu Ivănescu, Yann Blanchard, Seyed Ali Sayedain, and Yasmin AboEl-Fetouh

Abstract. Remote sensing (RS) based estimates of Arctic dust are oftentimes overestimated due to a failure in separating out the dust contribution from that of spatially homogeneous clouds or low-altitude cloud-like plumes. A variety of illustrations are given with a particular emphasis on claims of using brightness temperature differences (BTDs) as a signature indicator of Arctic dust transported from mid-latitude deserts or generated by local Arctic sources. While there is little dispute about the presence of both Asian and local dust across the Arctic, the direct RS detectability of airborne dust, as ascribed to satellite (MODIS and AVHRR) measurements of significantly negative brightness-temperature differences at 11 and 12 µm (BTD11-12) has been misrepresented in certain cases. While it is difficult to account for all examples of strongly negative BTD11-12 values in the Arctic, it is unlikely that airborne dust plays a significant role. One, much more likely contributor would be water plumes in the Arctic inversion layer.

The RS detectability of the impact of Arctic dust (notably due to Arctic dust from local sources) can, however, be of significance. Sustained dust deposition can substantially decrease (visible to shortwave IR) snow and ice reflectance albedo (pan-chromatic reflectance) and the signal measured by satellite sensors. Significantly negative BTD11-12 values would however only represent a limited area near the drainage basin sources according to our event-level case studies. The enhanced INP (Ice Nucleating Particle) role of local Arctic dust can, for example, induce significant changes in the properties of low-level mixed-phase clouds (cloud optical depth changes <~ 1) that can be readily detected by active and passive RS instruments. It is critical that the distinction between the RS detectability of airborne Arctic dust versus the RS detectability of the impacts of that dust be understood if we are to appropriately parameterize, for example, the radiative forcing influence of dust in this climate sensitive region.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this preprint. The responsibility to include appropriate place names lies with the authors.
Norman T. O’Neill, Keyvan Ranjbar, Liviu Ivănescu, Yann Blanchard, Seyed Ali Sayedain, and Yasmin AboEl-Fetouh

Status: open (until 12 Jul 2024)

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Norman T. O’Neill, Keyvan Ranjbar, Liviu Ivănescu, Yann Blanchard, Seyed Ali Sayedain, and Yasmin AboEl-Fetouh
Norman T. O’Neill, Keyvan Ranjbar, Liviu Ivănescu, Yann Blanchard, Seyed Ali Sayedain, and Yasmin AboEl-Fetouh

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Short summary
Dust from mid-latitude deserts or from local drainage basins is a weak component of atmospheric aerosols in the Arctic. Satellite-based dust estimates are often overestimated because dust and cloud measurements can be confused. Illustrations are given with an emphasis on the flawed claim that a classic indicator of dust (negative brightness temperature differences) is proof of the presence of airborne Arctic dust. Low altitude “warm” water plumes are the likely source of such negative values.