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PyroCumulonimbus cloud in Australia

By Scott Bachmeier •

Himawari-8

Himawari-8 “Red” Visible (0.64 µm, top), Shortwave Infrared (3.7 µm, middle) and Infrared Window (10.3 µm, bottom) images [click to play to animation | MP4]

JMA Himawari-8 “Red” Visible (0.64 µm), Shortwave Infrared (3.7 µm) and Infrared Window (10.3 µm) images (above) showed the development of a pyroCumulonimbus (pyroCb) cloud from a bushfire that was burning in the eucalypt forests of eastern Victoria, Australia on 25 January 2019. A rapid-scan “Target” sector was positioned over the region beginning at 0522 UTC, providing images every 2.5 minutes (instead of the routine 10-minute interval). Cloud-top infrared brightness temperatures became colder than -40ºC (the threshold for pyroCb classification) after 0230 UTC, and eventually cooled to around -55ºC (orange enhancement). This temperature roughly corresponded to an altitude around 12 km, according to nearby Melbourne rawinsonde data (plot | text).

A closer view of Himawari-8 “Red” Visible (0.64 µm) and Shortwave Infrared (3.7 µm) images (below) revealed the rapid southeastward run of the fire, as shown by the growth of the “hot spot” (black to red pixels) on Shortwave Infrared images. The darker gray appearance of the pyroCb cloud is due to the presence of smaller ice crystals at the cloud top — these smaller ice crystals are more efficient reflectors of incoming solar radiation, making the cloud tops appear warmer than those of conventional cumulonimbus. Vigorous updrafts driven by the intense heat of the fire limit the in-cloud residence time for ice crystal growth, which leads to smaller particles being ejected at the pyroCb cloud top.

Himawari-8 "Red" Visible (0.64 µm, left) and Shortwave Infrared (3.7 µm, right) images [click to play to animation | MP4]

Himawari-8 “Red” Visible (0.64 µm, left) and Shortwave Infrared (3.7 µm, right) images [click to play to animation | MP4]

In a comparison of VIIRS True Color Red-Green-Blue (RGB) and Infrared Window (11.45 µm) images from Suomi NPP (at 0311 UTC) and NOAA-20 (at 0501 UTC) images viewed using RealEarth (below), cloud-top infrared brightness temperatures were in the -55 to -58ºC range (darker shades of orange).

VIIRS True Color RGB and Infrared Window (11.45 µm) images from Suomi NPP (0311 UTC) and NOAA-20 (0501 UTC) images [click to enlarge]

VIIRS True Color RGB and Infrared Window (11.45 µm) images from Suomi NPP (0311 UTC) and NOAA-20 (0501 UTC) images [click to enlarge]

Categories: Fire detection, Himawari-8, NOAA-20, RealEarth, Red-Green-Blue (RGB) images, Suomi NPP, VIIRS