PyroCb over Bolivia

GOES-16

GOES-16 “Red” Visible (0.64 µm, top), Shortwave Infrared (3.9 µm, middle) and “Clean” Infrared Window (10.35 µm, bottom) images [click to play animation | MP4]

GOES-16 (GOES-East) “Red” Visible (0.64 µm), Shortwave Infrared (3.9 µm) and “Clean” Infrared Window (10.35 µm) images (above) showed the formation of a pyroCb cloud over far southeastern Bolivia on 18 August 2019. The small anvil cloud briefly surpassed the -40ºC pyroCb threshold from 1800-1820 UTC, attaining a minimum cloud-top infrared brightness temperature of -45.2ºC along the Bolivia/Paraguay border at 1800 UTC. This pyroCb formed over the hottest southern portion of an elongated fire line, as shown in the Shortwave Infrared imagery.

A 1.5-day animation of GOES-16 Shortwave Infrared images (from 12 UTC on 17 August to 2350 UTC on 18 August) revealed the rapid southeastward run of the fire to the Bolivia/Paraguay border on 17 August, followed by the eastward expansion of the fire line on 18 August (below).

GOES-16 Shortwave Infrared (3.9 µm) images [click to play animation | MP4]

GOES-16 Shortwave Infrared (3.9 µm) images [click to play animation | MP4]

A toggle between Suomi NPP VIIRS True Color Red-Green-Blue (RGB) and Infrared Window (11.45 µm) images as viewed using RealEarth (below) showed the large and dense smoke plume streaming southeastward, with the small pyroCb along the Bolivia/Paraguay border at 1745 UTC — the brighter white tops of the pyrocumulus and pyrocumulonimbus clouds reached higher altitudes than the tan-colored smoke plume. The coldest cloud-top infrared brightness temperature was about -55ºC (orange enhancement), which corresponded to an altitude around 9 km according to rawinsonde data from Corumbá, Bolivia.

Suomi NPP VIIRS True Color Red-Green-Blue (RGB) and Infrared Window (11.45 µm) images [click to enlarge]

Suomi NPP VIIRS True Color Red-Green-Blue (RGB) and Infrared Window (11.45 µm) images [click to enlarge]



Strong northerly to northwesterly surface winds were blowing across the region, in advance of an approaching cold front (surface analyses) — at Robore, Bolivia (located just north-northwest of the fires), winds were gusting to 25-28 knots during much of the day (below).

Time series of surface report data from Robore, Bolivia [click to enlarge]

Time series of surface report data from Robore, Bolivia [click to enlarge]

This is possibly the second documented case of a South American pyroCb (the first being on 29 January 2018) — in addition, it’s the second pyroCb documented in the tropics and the first pyroCb documented during a winter season. Thanks to Mike Fromm (NRL) for bringing this case to our attention!

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