A shortwave trough digging into northern Mexico on 5 Feb 2020 brought gusty winds to the surface, leading to areas of lofted blowing dust, primarily from sources marked at points A and B (Fig 1). The lofted dust had traveled as far as Houston, TX, per media reports of dust being deposited at the surface.
There were two regions in particular from which a significant amount of surface material was lofted and subsequently carried a long distance. These locations, marked in Fig 2 and 3, include red earth from central Zacatecas (point A), and sand from southwest Coahuila (point B), where many sand dunes are present.
GOES-East 5-min CONUS imagery captured the onset of lofted dust from the aforementioned regions, along with it’s evolution as it wrapped around the southeast portion of the trough and was carried northeast into south Texas. The high spatial resolution afforded by the 500 m 0.64 um visible band provides the most detailed look of the lofted dust as it elaves it’s source, particularly toward sunset (Fig 4). Figure 5 provides a zoomed in look at lofted dust from the red earth (point A) region.
The Geocolor product developed at CIRA combines Channels 1, 2, and 3 and additional computations (making up for the lack of a green channel) to create pseudo-true color imagery during the day. In this case, the daytime geocolor imagery captured the dust plumes quite well, and differentiated the lofted red earth (shades of red) from the red earth region in the south and lofted sand (tan/gray) from the sand dune region to the north (Fig 6). The two source regions also appear red and tan, respectively. Animation here.
Infrared imagery can also be used to capture lofted dust. The 10.3 – 12.3 um split window difference, previously discussed here for detecting dust, provides a very clear dust signature (negative difference values, dark gray to black; Fig 7).
Including the split window difference in the Dust RGB, along with the SO2 difference and 10.3 um IR window band, allows for dust detection (bright magenta to pink) along with cloud classification (Fig 8).
A daytime SNPP VIIRS pass at 1926 UTC over the area provided high resolution still images of the lofted dust from the red earth region shortly after onset. Similar products are available as above, but with better spatial resolution and slightly difference spectral specifications (Figs 9-13). Recall, the I bands provide the highest spatial resolution (375 m), while M band imagery is 750 m. Animation comparing various VIIRS products here.
Continuing the GOES-East IR-based detection animations into the overnight hours (SWD in Fig 14, Dust RGB in Fig 15), detection becomes difficult as the lofted dust becomes increasingly dispersed, and cloud cover increases. However, careful analysis of the imagery allows one to diagnose the plumes extending northeast across southern Texas through the evening, with the faint remnants of the southern plume making it well up the Texas Gulf Coast.
Bill Line, NESDIS and CIRA