GOES-13 Sounder Anomalies continue

November 4th, 2013 |
Composite of GOES-15/GOES-13 3.9 µm shortwave IR images (click image to play animation)

Composite of GOES-15/GOES-13 3.9 µm shortwave IR images (click image to play animation)

The GOES-13 Sounder has been experiencing anomalies that manifest themselves as missing pixels since mid-Summer. The missing pixels apparently arise because of slight fluctuations in the speed of the sounder instrument filter wheel. The number of missing pixels per Sounder image peaked in late September, just after the Equinox, with up to 700 missing pixels (out of 63000) per Sounder image over CONUS. At present, missing pixels vary between 100 and 250, with a maximum typically around 2200 UTC and a minimum between 0600 and 1000 UTC. In the animation above, the missing pixels show as black; the GOES-15 Sounder data have no missing pixels.

Realtime GOES Sounder imagery is available at this link. The Sounder anomalies are present in all 19 of the GOES-13 spectral bands, as evident in the toggle below between an image in late September (when error counts were highest) and early November (when error counts were lower). GOES Engineers continue to monitor this situation and investigate possible solutions.

GOES-13 Sounder 19-band display, 1800 UTC 27 September and 1600 UTC 4 Nov 2013 (click image to enlarge)

GOES-13 Sounder 19-band display, 1800 UTC 27 September and 1600 UTC 4 Nov 2013 (click image to enlarge)

Aircraft dissipation trails over the Lake Ontario region

November 4th, 2013 |
GOES-13 0.63 µm visible channel images (click to play animation)

GOES-13 0.63 µm visible channel images (click to play animation)

Hat tip to NWS Buffalo NY forecasters Jon Hitchcock and David Zaff for letting us know about a number of aircraft dissipation trails (also known as “distrails” or “hole punch clouds”) over the Lake Ontario region on 04 November 2013. A series of McIDAS images of 1-km resolution GOES-13 0.63 µm visible channel data (above; click image to play animation) showed these features as they drifted eastward during the day.

A comparison of AWIPS II images of 375-meter resolution Suomi NPP VIIRS 0.64 µm visible channel data and the corresponding false-color”Snow Cloud Discrimination” Red/Green/Blue (RGB) product at 18:17 UTC (below) indicated that the cloud layer penetrated by the aircraft was composed of supercooled water droplets (which appear brighter on the RGB image) — but the particles in the aircraft exhaust acted as ice nuclei and caused the cloud to glaciate (ice crystal clouds appear as varying shades of red on the RGB image).

Suomi NPP VIIRS 0.64 µm visible channel and

Suomi NPP VIIRS 0.64 µm visible channel and “Snow Cloud Discrimination RGB” images

AWIPS images of the POES AVHRR CLAVR-x Cloud Type product confirmed that the cloud layer over the Lake Ontario region was a supercooled water droplet cloud (green color), with the Cloud Top Height product indicating tops in the 7-9 km range (below). However, higher-altitude cirrus clouds were beginning to overspread the region from the west (cirrus=orange; thick ice=yellow; overlap=violet).

POES AVHRR 0.86 µm visible channel image, Cloud Type product, and Cloud Height produc

POES AVHRR 0.86 µm visible channel image, Cloud Type product, and Cloud Height product