Satellite Operations Updates - Total Operational Weather Readiness - Satellites (TOWR-S)

Loop Heat Pipe Anomaly Impacts on GOES-17 ABI Bands 11 & 15

October 15, 2020

3 minute read

Background

Users of satellite imagery from GOES-17 ABI Band 11 (Cloud-Top Phase IR) and Band 15 ("Dirty" Longwave Window IR) will begin to notice degradation of the imagery as a result of the seasonal loop heat pipe anomaly. In each of the figures below, a yellow cell with a "1" indicates estimated minimal to moderate degradation in the imagery for a given hour on a given day. Similarly, a red cell with a "2" indicates estimated severe degradation to the point that the imagery becomes unusable. The hour of day is at the top along the horizontal axis in UTC. The date is to the left along the vertical axis in ascending order. The TOWR-S team will provide additional updates with information on anticipated impacts as the imagery from the other infrared (IR) bands begin to degrade next week.

Band 11 Impacts

The table below includes the GOES-17 data products that will be impacted by the degradation of Band 11. A quick guide for each data product is linked in the right column.

Figure 1:  Anticipated impacts for Band 11 from October 9 - November 25

Operational Impacts from Band 11 Degradation

Band 11 (8.5 µm) is the "Cloud-Top Phase R" band on the ABI.  As a "window" channel, there is little atmospheric absorption of energy in clear skies at this wavelength (unless SO2 from a volcanic eruption is present). This channel is sensitive to SO2, and therefore has a significant role in detecting volcanic ash. Additionally, when compared with the 11.2 um (window IR channel 14), their different emissivity properties result in the ability to determine cloud phase. The impact of the loop heat pipe anomaly degradation to this band includes decreased ability to monitor volcanic activity, to monitor convective growth potential via cloud phase changes, and to delineate cirrus thickness. More information on Band 11 can be found in this quick guide from CIMSS and this article published in the Journal of Operational Meteorology.

Band 15 Impacts

The table below includes the GOES-17 data products that will be impacted by the degradation of Band 15. A quick guide for each data product is linked in the right column.

Figure 2:  Anticipated impacts for Band 15 from October 9 - November 25

Operational Impacts from Band 15 Degradation

Band 15 (12.3 µm) is the "Dirty Window IR" band on the ABI. As a "window" channel, there is little atmospheric absorption of energy in clear skies at this wavelength. In this band, the absorption and re-emission of water vapor, particularly in the lower troposphere, slightly cools most (non-cloud) brightness temperatures (BTs) compared to other IR window channels. If there is more water vapor, then the BT differences with respect to Band 15 are also greater. As a result, Band 15 and Band 13 (10.3 µm) are used to compute the well-known 'split window difference (SWD),' which can highlight both moisture and airborne dust. This channel therefore plays a significant role in a number of GOES baseline products, as shown in the list below. One impact of the loop heat pipe anomaly degradation to Band 15 includes a decreased ability to detect airborne dust (via the SWD), which may play a role in suppressing cyclogenesis. More information on Band 15 can be found in this quick guide from CIMSS and this article published in the Journal of Operational Meteorology.

More Information on the Fall Season Loop Heat Pipe Anomaly

For additional information regarding this seasonal loop heat pipe anomaly event, including the ongoing GOES-17 Mode 3 cooling timeline operations, refer to the article linked here.