JMA Himawari-8 AHI “Red” Visible (0.64 µm), Shortwave Infrared (3.9 µm) and “Clean” Infrared Window (10.4 µm) images (above) showed the development of a pyroCb cloud produced by bush fires northwest of Sydney, Australia (station identifier YSSY) on 22 November 2019 (surface analyses). In the 3.9 µm images, hot thermal signatures of the bush fires (darker black to red pixels) were apparent; in addition, the cloud tops of the pyroCb cloud appeared warmer (darker gray) than surrounding convective cloud tops. The pyroCb exhibited cloud-top 10.4 µm brightness temperatures colder than -40ºC.
Himawari-8 “Red” Visible (0.64 µm, top), Shortwave Infrared (3.9 µm, middle) and “Clean” Infrared Window (10.4 µm, bottom) [click to play animation | MP4]
VIIRS True Color Red-Green-Blue (RGB) and Infrared Window (11.45 µm) images from Suomi NPP and NOAA-20 as viewed using RealEarth are shown below. Cloud-top 11.45 µm brightness temperatures of the northern pyroCb thunderstorm were in the -70 to -75ºC range on the later 0407 UTC Suomi NPP image.
VIIRS True Color RGB and Infrared Window (11.45 µm) images from Suomi NPP and NOAA-20 [click to enlarge]
The coldest Himawari-8 10.4 µm brightness temperature (BT) associated with the southernmost thunderstorm was -67.0ºC at 0520 UTC (with the northern pyroCb thunderstorm, closer to the fire complex, reaching -66.9ºC at 0500 UTC). According to 00 UTC rawinsonde data
from nearby Williamtown (below),
those BTs were 2-3ºC colder than the coded tropopause temp of -64.5ºC at 12.6 km. The VIIRS 11.45 µm BTs were nearly 10ºC colder than the tropopause, suggesting significant penetration of overshooting tops into the lower stratosphere.
Plot of rawinsonde data from Williamtown, New South Wales [click to enlarge]