In the overnight to early morning hours on Thursday, 1 February 2018, Volcan de Fuego in Guatemala awoke and produced a rather impressive ash plume that was easily observable in GOES-16 (east) imagery. The eruption started around 0200 UTC and ended around 2200 UTC, with the majority of ash occurring from ~0900 UTC to 1800 UTC. The Washington Volcanic Ash Advisory Center (VAAC) located at the NESDIS Satellite Analysis Branch (SAB) has access to various satellite channels and products, including the Ash, Dust, and SO2 RGB products. Questions have arisen over the years on the most appropriate times to use these products (no two eruptions are alike) and this particular eruption provided the analysts the opportunity to evaluate each RGB against the visible and infrared channels.
Jamie Kibler (Ops and VAAC Manager) provided some valuable insight on how each channel or products behaved, so the remainder of this blog post will be his critique.
“Channel 2 VIS (substituted the GeoColor product for this animation) – did well picking up the ash, but the real thin ash moving northerly from the summit – due to clouds could not really see it after a couple of hours. But everything else looked good.” Note: Also notice the cooling signature (light blue coloring moving slowly over the water) south of Mexico due to the gap winds (Tehuano wind) over the Gulf of Tehuantepec.
“Channel 11 – SO2 – it picked up the SO2/ash content, but only during peak and was very light in detection – not as clear cut. Really would not use it in most cases.”
“RGB Ash – Did a very nice job picking up ash in all directions and could track it well, but as it got more thin over time (19z-23z) could not really see it very well……too pixelated and not very bright (possibly due to limited colors in N-AWIPS)”
“Dust and SO2 RGBs – did a really good job detecting the ash and even as it thinned it still did a good job in detecting the Ash/SO2 – the winner of all the channels/rgbs. Both just showed up much brighter than Ash RGB”
“In much smaller events – Ash and Dust RGBs are equal.”
Due to the extent of the ash plume, SAB called for a Mesoscale Domain Sector (MDS) to be place over Central America from ~2045 UTC on 01 February 2018 to ~1200 UTC on 02 February 2018. The 0.64 𝞵m visible animation above shows the ash drifting west over the nearshore waters of Guatemala. This was the first official MDS request by the Washington VAAC!
I’d like to thank Jamie for contributing on this very interesting event!
Thanks for reading!
For additional satellite blog entries on this event:
CIMSS Satellite Blog: http://cimss.ssec.wisc.edu/goes/blog/archives/26889
CIRA blog: http://rammb.cira.colostate.edu/training/visit/blog/index.php/2018/02/02/fuego-de-volcan-guatemala/
The Ash and Dust RGBs look very different, but I thought they were almost exactly the same formula to calculate?
Eric, this is a great point and upon some quick research, it looks like the temperature ranges are the main difference. For example:
Red = IR12.0-IR10.8 (-4°C to+2°C)
Green = IR10.8-IR8.7 (0°C to 15°C)
Blue = IR10.8 (12°C to 16°C)
Red = IR12.0-IR10.8 (-4°C to +°2C)
Green = IR10.8-IR8.7 (-4°C to +°5C)
Blue = IR10.8 (-30°C to 30°C)