Building on the blog post by Bill Line on 03/30/17, Paul Iniguez (SOO-Phoenix WFO) put together the following case study on the synoptic scale dust event that affected much of the Southwestern U.S., most notably, the Mojave Desert.
A strong upper level low quickly moved into the Southwest U.S. on Thursday 30 March 2017. The rapid airmass change brought about very strong winds across the region, as depicted above. Most of the significant impacts were in the Mojave Desert, including wind gusts up to 80 mph, power outages, and a few tipped semis. [LINK] Dust was very widespread with this event, with very low visibility reported. [LINK]
With the new GOES-16 data, we were able to see several phenomena that were not previously detectable with GOES-15. To begin with, here is an eight hour loop of GOES-16 Ch 2 (red visible). Some interesting things to note in the data. Watch the numerous dry lake beds/playas become “activated” as the winds pick up ahead of the incoming front. Watch the initial wall of dust form as it moves south through the Mojave, and a second wall form in the far southern edge of the Mojave that moves into the Sonoran Desert toward sunset.
*Preliminary, Non-Operational Data*
Looking closer, this second loop over Imperial County, CA shows several benefits of the GOES-16 data over the GOES-15. Note that this loop does not account for the typical latency of GOES-16.
First, we see the obvious improvement in resolution, 0.5 km vs 1 km. Because of this, and the increased sensitivity of the instrument (higher bit rate, meaning it can resolve finer features), GOES-16 is capturing a lot of blowing dust moving out across the Salton Sea that GOES-15 simply doesn’t see. It is only much later, around 2330Z, that GOES-15 finally picks up a more substantial plume. With the GOES-16, we can also see blowing dust coming off the agricultural fields north of the sea moving to the southeast. Finally, perhaps because of the increased sensitivity and difference in position of the satellites, the GOES-16 data is usable for much longer. GOES-16 is returning useful data to 02Z and thus captures the incoming second wall of dust.
Of course the dust lasted beyond sunset. The GOES-16 Legacy IR (Ch 14) was able to better discern the boundary, again likely due to improved resolution and increased sensitivity, compared to GOES-15. In fact, with GOES-16, you can arguably get better a sense of optical depth, perhaps useful in figuring out where the worst dust is. With further research, perhaps we’ll be able to get a sense of dust density (thus visibility). Of course this is only useful if the surface features are not obscured by higher clouds, which here could be separated out by their brighter appearance.
Thanks for reading!
Paul Iniguez (SOO – Phoenix WFO) and Michael Folmer (CICS)
“The GOES-16 data posted on this page are preliminary, non-operational data and are undergoing testing. Users bear all responsibility for inspecting the data prior to use and for the manner in which the data are utilized.”
With regards to: “First, we see the obvious improvement in resolution, 1 km vs 2 km. Because of this, and the increased sensitivity of the instrument (higher bit rate, meaning it can resolve finer features)”. For the 0.64 µm (ch 2 GOES16 vs. ch 1 GOES-15), it should be 0.5 km (that was fixed in AWIPSII – correct? vs. 1 km). That alone makes a HUGE difference in resolving finer features. Can you clarify the second sentence? To me, rate in the context you are talking about implies over time – which we can see the benefit of 5 minute vs 15 minute data. Do you mean bit depth – the number of bits of information in each pixel which is higher for GOES 16 than GOES-15? For this case, can you say that the narrower bandwidth on GOES-16 compared to GOES-15 also helps with distinguishing features?
From Paul Iniguez: Yes, I was incorrect with the resolution. It is 0.5 km against 1 km.
As for rate, the “bit rate”, or bit depth, is the level of detail provided, specifically two raised to the provided bit depth power. For example, 8-bit is 2^8 which means 256 levels. Think of them as shades of gray. The bit depth on the GOES-13/15 is 10 (1,024 levels) while on GOES-16 it is 12 (4,096 levels). That means we have 4x the level of shading, allowing for finer features to be resolved. Such as the blowing dust.