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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 bushfire 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 eventually 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 bushfire — 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 another 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 bushfire following the ~0400 UTC trough passage, (2) the pyroCb formation shortly after the time of the trough passage, and (3) the northeastward surge of cooler air (darker shades of purple over cloud-free land surfaces) in the wake of the trough passage. Note that in the Himawari-9 True Color RGB images shown above, the trough passage also initiated a northward transport of boundary layer smoke from the bushfire source region.

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