Both the GOES-16 (GOES-East) and GOES-17 (future GOES-West) ABI’s operated in Mode 4 today (Dec 4, 2018) for close to four hours in order to “test storage updates” (according to NESDIS). Recall Mode 4, also known as Continuous Full Disk Mode, scans a full disk (entire hemisphere) image every five minutes, and that is all. The default Mode 3 “Flex Mode” only scans a full disk image every 15-minutes, but also scans a CONUS image every 5-minutes, and two mesoscale sectors every 1-minute. See Table 1 for a comparison between scan modes. Mode 6 is under evaluation.
|Mode 3||Mode 4||Mode 6|
Figure 1 shows a world perspective of the two ABI’s operating in Mode 4 (1825 UTC to 2200 UTC) and then switching back to Mode 3 (2215 UTC to 0200 UTC). Notice the imagery appears to “speed up” when switching from 5-min to 15-min resolution. Note the 2015 UTC GOES-17 and 2020 UTC GOES-16 images are incomplete.
On a related note, there is not yet a nicely stitched East/West image composite available in AWIPS. Users can easily load both the East and West imagery together (as is done in this post), but there will be a large region of poor quality imagery overlapping better quality imagery along the edge of the top image. This is due to degraded spatial resolution far from the satellite sub-point. Further, the limb cooling effect will lead to differences in brightness temperature for IR channels (especially water vapor) along the transition.
Bill Line, NWS
GOES-17 data are preliminary and non-operational at the time of this post.