Search the RAMMB website
A Massive African Dust Event (MADE) began about a week ago. GeoColor imagery from GOES-16 ABI, valid 20 August 2021 at 12:20 UTC, shows the region of dust, which extends from Africa westward across much of the Atlantic Ocean to near tropical storm Henri (Figure 1, left). One interpretation of the split window difference (SWD), defined as Tb(10.35 um) – Tb(12.3 um), is that a signature of the dust is also evident by the greenish color (Figure 1, right). Previous research has pointed to the challenge of dust detection over water, particularly at night. Further, recent research at CIRA has suggested that water vapor may mask dust detection (Grasso et al. 2021, Miller et al 2019). Imagery today suggests that dust may be evident in SWD imagery through a reduction of a water vapor signal (orange/red) to a somewhat greenish color. That is, a water vapor signal has a relatively large positive value (orange/red); the addition of dust in a region of less water vapor reduces values of the SWD to smaller positive values (green). In Summary, African dust may, at times, be identified and tracked over the Atlantic Ocean during the day and at night.
Grasso, L. D., D. Bikos, J. Torres, J. F. Dostalek, T.-C. Wu, J Forsythe, H. Q. Cronk, C. J. Seaman, S. D. Miller, E. Berndt, H. G. Weinman, and K. B. Kasper, 2021: Satellite Imagery and Products of the 16-17 February 2020 Saharan Air Layer Dust Event over the Eastern Atlantic: Impacts of Water Vapor on Dust Detection and Morphology Atmos. Meas. Tech., 14, 1615–1634. https://doi.org/10.5194/amt-14-1615-2021
Miller, S. D., Grasso, L., Bian, Q., Kreidenweis, S., Dostalek, J., Solbrig, J., Bukowski, J., van den Heever, S. C., Wang, Y., Xu, X., Wang, J., Walker, A., Wu, T.-C., Zupanski, M., Chiu, C., and Reid, J.: A Tale of Two Dust Storms: Analysis of a Complex Dust Event in the Middle East, Atmos. Meas. Tech., 12, 5101–5118, https://doi.org/10.5194/amt-12-5101-2019, 2019.
Figure 1: Left: GeoColor imagery with a red oval that bounds much of the region of dust from Africa. Also, a region of sun glint, which appears like dust, is indicated by ‘sg’ in the image. Tropical storm Henri is just east of Florida and west of the dust. Right: Corresponding to the region of dust in GeoColor imagery, is an extensive region of small positive values of the SWD (green), which indicates dust. A word of caution: Dust over the Atlantic appears green in the SWD; however, green in the SWD is not necessarily dust in GeoColor. Both images are valid 20 August 2021 at 12:20 UTC and are from GOES-16 ABI.
(POC: Lewis Grasso, Steve Miller, CIRA: Lewis.Grasso@colostate.edu, Steven.Miller@colostate.edu) Funding: GOESR