The NWS National Hurricane Center has requested GOES-16 1-min mesoscale imagery to support monitoring of Hurricane Florence since September 5. Previous blog posts have discussed the value of 1-min satellite imagery for analyzing tropical cyclones, particularly for identifying a center of circulation and for monitoring thunderstorm evolution. The Florence center of circulation appeared to have briefly revealed itself in 1-min VIS during the morning of 9 September (Fig 1). Thunderstorms in the vicinity of the storm center quickly obscured the view.
By 5 AM Monday, Florence had strengthened to a category 2 storm, with an eye apparent in satellite imagery. The storm was also quite large, as depicted in Figure 2, which shows the storm with respect to the full 1000 x 1000 km (at nadir) 1-min mesoscale sector. The westward shift of the sector is captured in the middle of the animation. Bermuda was well to the north of the forecast path.
A little later in the morning on September 10, the NHC requested 30-second imagery over Florence (Fig 3). As a reminder, two sectors of 1-min imagery can be collected, OR one sector of 30-second imagery, from an ABI.
Have you noticed stray light contamination in visible, near-IR and SWIR imagery at night (~0400 – 0600 UTC) recently? Missing pieces of images as well? Odd GLM behavior? This is due to light from the sun directly entering the imaging sensors during a period known as the eclipse season. The eclipse season occurs in the Northern Hemisphere during the Spring (late Feb to mid April) and Fall (late Aug to mid-Oct) every year. During this period, the satellite enters the shadow of the Earth during the late night hours. Sunlight enters the sensors and impacts the VIS/NIR/SWIR imagery and GLM as the satellite enters and leaves the Earth’s shadow. More details on this phenomenon can be found on the NESDIS/OSPO webpage here. According to NESDIS for the current eclipse season:
“Stray light contamination and truncated swaths during the GOES-East Fall 2018 eclipse season will be apparent on ABI imagery: Starting August 8, 2018 from approximately 0415 UTC – 0545 UTC each day in the Northern Hemisphere until September 22, 2018.”
Examples below are from GOES-16 (East) ABI and GLM. Figures 1, 2, and 3 are early in the eclipse season (20 August), and reveal the vertical beam of stray light contamination in ABI imagery. Notice the beam is apparent in the visible and shortwave IR channel, but is not apparent in the IR window channel.
Figure 1: 20 August 2018 GOES-16 5-min 0.64 um VIS. Notice vertical beam of light passing across CONUS. Full res
Figure 2: 20 August 2018 GOES-16 5-min 3.9 um SWIR. Notice warming of features, especially cold cloud tops, as beam of light moves through region. Full res
Figure 3: 20 August 2018 GOES-16 5-min 10.3 um IRW. Full res
Figures 4, 5, and 6 are later in the eclipse season. Stray light is still apparent, as well a canceled frames in all of the channels.
Figure 4: 4 September 2018 GOES-16 5-min 0.64 um VIS. Notice canceled frames and vertical light beam extending south. Full res
Figure 5: 4 September 2018 GOES-16 5-min 3.9 um SWIR. Notice canceled frames and warming of cold cloud tops. Full res
Figure 6: 4 September 2018 GOES-16 5-min 10.3 um IRW. Notice canceled frames. Full res
GLM data are also impacted during the same period, with the solar intrusion causing false events (Fig 7).
Figure 4: 5 September 2018 GOES-16 5-min IRW and 1-min GLM FED. False detections from GLM are apparent over the western half of the US between 0430 UTC and 0445 UTC. Full res
The default scan mode (as of the writing of this blog post) for GOES-16 (GOES-East), mode 3, provides a full disk image every 15-min, a CONUS image every 5-min, and two movable 1-min sectors. The GOES-East mesoscale sectors have default locations over the eastern half of the United states, and can be positioned anywhere within the full disk upon request. NWS entities have the highest priority for making requests, and any NWS WFO can make a request through their regional request focal point office.
Figure 1: GOES-East Mesoscale Domain Sector coverage for the afternoon of 3 September 2018. The sector over the northern plains covers a SPC slight risk, while the sector over Florida covers TS Gordon. Full res
When making a meso request, individuals should provide: their office, desired begin and end date/time of sector coverage, the center lat/lon of the sector in decimal degrees, and the rationale for the request. Try to make the request early in the day before the event begins, if possible.
In the event of more than two requests, a priority list is consulted. The priority list can be found in the document or slides at this NOAA VLAB page. When offices make a request, they should refer to this list and make sure they use the highest possible reasoning that applies to their CWA.
When deciding on the center lat/lon of the sector, offices should consider the threat not only within their CWA, but also around them. Instead of simply using a lat/lon in the center of the CWA, requestors should choose a lat/lon that covers their area plus as much of the rest of the threat area as possible. For example, choose a lat/lon that will cover most of the SPC convective outlook area, or SPC fire weather outlook area, or WPC excessive rainfall outlook area, etc. Also, try to keep most of the sector in CONUS in order to benefit as many NWS offices as possible. One can visualize the coverage of a sector given a center lat/lon by consulting this CIRA webpage (Fig 2).
Figure 2: Screenshot from CIRA MDS preview webpage. Full res
Finally, if you think the 1-min imagery will be even remotely helpful in your area, make the request! If there are no requests, the sectors simply scan from their default locations, possibly going unused. National Centers also make requests, but offices should not assume this will happen. For severe threats, SPC will likely make requests for ENH or higher, and often will for SLGT as well. But it is recommended the WFO make the request to ensure coverage, especially for MRGL and SLGT. And remember, once GOES-17 goes operational as GOES-West, there will be four total 1-min mesoscale sectors to work with!