Loop Heat Pipe Anomaly Impacts on GOES-17 ABI Band 15

August 14, 2020

2 minute read

What is happening to Band 15?

Users of GOES-17 imagery from ABI Band 15 ("Dirty" Longwave Window IR) should begin to notice the degradation of the imagery as a result of the seasonal loop heat pipe anomaly. A visual representation of the anticipated daily impacts for Band 15 can be found here and in Figure 1, below. A "1" in a cell indicates some degree of degradation in the imagery for a given hour on a given day. 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.

Figure 1:  Anticipated impacts for Band 15 from July 24 - September 7

In Figure 1, above, the horizontal axis ranging from 0 to 23 (top) is the hour of the day in UTC
and the vertical axis is the calendar date from July 24 to September 7, 2020 in ascending order.​

 

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.

 

Impacted Data Products

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.

Data Product Link to Quick Guide
Aerosol Detection CIMSS Quick Guide for Aerosol Detection
Clear Sky Mask CIMSS Quick Guide for Clear Sky Mask
Cloud Optical Depth CIMSS Quick Guide for Cloud Optical Depth
Cloud Particle Size Distribution CIMSS Quick Guide for Cloud Particle Size Distribution
Cloud Top Height CIMSS Quick Guide for Cloud Top Height
Cloud Top Phase CIMSS Quick Guide for Cloud Top Phase
Cloud Top Pressure CIMSS Quick Guide for Cloud Top Pressure
Cloud Top Temperature CIMSS Quick Guide for Cloud Top Temperature
Derived Stability Indices CIMSS Quick Guide for Derived Stability Indices
Fire/Hot Spot Characterization CIRA Quick Guide for Fire/Hot Spot Characterization
Land Surface Temperature TOWR-S Quick Guide for Land Surface Temperature
Legacy Vertical Moisture and Temperature Profiles CIRA Quick Guide for Legacy Vertical Profiles
Rainfall Rate/QPE NASA SPoRT Quick Guide for QPE
Sea Surface Temperature CIRA Quick Guide for Sea Surface Temperature
Total Precipitable Water CIRA Quick Guide for Total Precipitable Water
Ash RGB CIRA Quick Guide for Ash RGB
Dust RGB CIRA Quick Guide for Dust RGB
Nighttime Microphysics RGB CIRA Quick Guide for Nighttime Microphysics RGB
Split Window Difference CIMSS Quick Guide for Split Window Difference

 

More Information on the Loop Heat Pipe Anomaly

For additional information regarding the GOES-17 Mode 3 cooling timeline operations, refer to the article linked here. Mark your calendars for Thursday August 20th at 12:00 p.m. EDT when Dave Pogorzala from the GOES-R Program will be presenting in the Satellite Book Club on various types of image artifacts and anomalies that can be seen in GOES-R ABI imagery, explain how and why they occur, and discuss what steps have been taken to address them. Stay tuned for more details on that session!