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Grampians bushfire in southeast Australia produces a pyrocumulonimbus cloud

By Scott Bachmeier •

JMA Himawari-9 “Red” Visible (0.64 µm, top), Shortwave Infrared (3.9 µm, center) and “Clean” Infrared Window (10.4 µm, bottom) images from 0330-0640 UTC on 20th December, with hourly plots of surface reports [click to play animated GIF | MP4]

10-minute JMA Himawari-9 AHI “Red” Visible (0.64 µm), Shortwave Infrared (3.9 µm) and “Clean” Infrared Window (10.4 µm) images (above) showed the formation of a pyrocumulonimbus (pyroCb) cloud that was spawned by a wildfire in Grampians National Park in far southeast Australia on 20th December 2024. The pyroCb cloud exhibited cloud-top 10.4 µm infrared brightness temperatures (IRBTs) of -40ºC and colder (denoted by the shades of blue) — attaining a minimum IRBT of -44º C at 0530 UTC (the air temperature at an altitude around 10 km, according to rawinsonde data from Melbourne: plot | text). The pyroCb cloud eventualy drifted southeast over Melbourne Airport (YMML).

Himawari-9 True Color RGB images created using Geo2Grid (below) displayed the broad smoke plume that was being transported east-southeastward from the Grampians bush fire — along with the high-altitude pyroCb cloud that cast a shadow upon the smoke layer below.

JMA Himawari-9 True Color RGB images, from 0350-0640 UTC on 20th December [click to play animated GIF | MP4]

A NOAA-20 (mislabeled as NPP) VIIRS Day/Night Band (0.7 µm) image valid at 0450 UTC (below) provided a view of the pyroCb cloud shortly after its formation.

NOAA-20 VIIRS Day/Night Band (0.7 µm) image valid at 0450 UTC on 20th December; the 0500 UTC surface report for Melbourne Airport YMML is plotted in cyan [click to enlarge]

As a surface trough of low pressure was moving east-northeastward across the state of Victoria (surface analyses), strong S-SW winds behind the trough axis (surface observations at Melbourne and Avalon) helped to intensify the Grampians fire complex — and the pyroCb cloud developed just after the trough passed through the area. Himawari-9 Fire Temperature RGB images (below) revealed (1) the rapid northward run of the Grampians bush fire following the trough passage (which was around 0400 UTC), (2) the pyroCb formation shortly after the time of the trough passage, and (3) the northeastward surge of cooler air (darker shades of purple) in the wake of the trough passage.

Himawari-9 Fire Temperature RGB images, from 2100 UTC on 19th December to 1100 UTC on 20th December [click to play animated GIF | MP4]

Categories: Fire detection, Geo2Grid, Himawari-9, NOAA-20, Red-Green-Blue (RGB) images, VIIRS

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