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Pyrocumulonimbus clouds in Western Australia

By Scott Bachmeier •

Himawari-8

Himawari-8 “Red” Visible (0.64 µm) images [click to play animation | MP4]

Large bushfires burning in the southern portion of the state of Western Australia produced three pyroCumulonimbus (pyroCb) clouds on 01 March 2019. JMA Himawari-8 “Red” Visible (0.64 µm) images (above) showed that the pyroCb clouds drifted southeastward after formation.

Himawari-8 “Clean” Infrared Window (10.4 µm) images (below) further revealed the 3 distinct pyroCb pulses — 2 originating from the southernmost fire located near 29.5ºS / 124.4ºE, and a smaller one originating from a fire located farther to the northwest. Cloud-top infrared brightness temperatures cooled to the -59 to -63ºC range for the pair of larger pyroCbs (which was close to the tropopause temperature of -64ºC on Perth soundings: plot | data) with temperatures reaching -51ºC with the smaller northernmost pyroCb. Also apparent was a surge of cooler air moving northeastward behind a surface trough, whose arrival appeared to coincide with the pyroCb formation. A time series of surface data from Forrest (YFRT) clearly showed the arrival of the cool, moist air behind the trough.

Himawari-8 "Clean" Infrared Window (10.4 µm) images [click to play animation | MP4]

Himawari-8 “Clean” Infrared Window (10.4 µm) images [click to play animation | MP4]

Suomi NPP VIIRS True Color RGB and Infrared Window (11.45 µm) images at 0537 UTC [click to enlarge]

Suomi NPP VIIRS True Color RGB and Infrared Window (11.45 µm) images at 0537 UTC [click to enlarge]

As shown using RealEarth, an overpass of the Suomi NPP satellite provided a more detailed view of the first (and largest) pyroCb at 0537 UTC (above), with NOAA-20 capturing the second pyroCb cloud about an hour later at 0628 UTC (below). The coldest cloud-top infrared brightness temperature on the 0537 UTC Suomi NPP VIIRS image was -70ºC (darker black enhancement); in addition, there appeared to be an Above-Anvil Cirrus Plume associated with that pyroCb, extending southeastward from a subtle Enhanced-V signature at the upshear (northwestern) edge of the cloud (where the warmest temperature was -48ºC, green enhancement).

NOAA-20 VIIRS True Color RGB and Infrared Window (11.45 µm) images at 0628 UTC [click to enlarge]

NOAA-20 VIIRS True Color RGB and Infrared Window (11.45 µm) images at 0628 UTC [click to enlarge]

On Himawari-8 Shortwave Infrared (3.9 µm) images (below), the pyroCb clouds exhibited a warmer (darker gray) appearance compared to adjacent conventional cumulonimbus clouds — this is due to the fact that ice crystals ejected into the pyroCb anvils are smaller (due to their shorter residence time within the intense updrafts above the fires), and these smaller ice crystals are more effective reflectors of incoming solar radiation. The large flare-up of red-enhanced land during the day is due to highly reflective soils of the Great Victoria Desert that quickly become very hot.

Himawari-8 Shortwave Infrared (3.9 µm) images [click to play animation | MP4]

Himawari-8 Shortwave Infrared (3.9 µm) images [click to play animation | MP4]

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