Severe thunderstorms in Argentina

January 25th, 2019 |

GOES-16

GOES-16 “Red” Visible (0.64 µm) images [click to play MP4 animation]

On 25 January 2019 a GOES-16 (GOES-East) Mesoscale Domain Sector was positioned over Argentina in support of the RELAMPAGO-CACTI field experiment, providing imagery at 1-minute intervals. “Red” Visible (0.64 µm) images (above) showed thunderstorms that developed and moved northward over the Córdoba (SACO) area — surface observations there (plot | list) showed a sharp drop in temperatures along with wind gusts to 37 knots during the thunderstorm, which also produced hail and heavy rainfall. Two important features were revealed in the imagery: (1) an outflow boundary (from the decay of a large and long-lived Mesoscale Convective System to the southeast) which was moving slowly northward between between Rio Cuarto (SAOC) and Córdoba, likely helping to enhance boundary layer convergence and lift, and (2) a southward/southwestward flow of moist, unstable air — indicated by a plume of agitated cumulus clouds — approaching Córdoba. Toward the end of the day, the presence of an Above-Anvil Cirrus Plume also became evident in the Visible imagery.

The corresponding GOES-16 “Clean” Infrared Window (10.3 µm) images (below) showed that infrared brightness temperatures of the pulsing thunderstorm overshooting tops were frequently -90ºC or colder (yellow pixels embedded within darker purple). This indicates a significant overshoot of the tropopause, which had an air temperature of -72.1ºC at an altitude of 15.2 km on 12 UTC rawinsonde data. Also note the development of a pronounced cold/warm thermal couplet over the core region of the storm, as an enhanced-V storm top signature formed.

GOES-16 "Clean" Infrared Window (10.3 µm) images [click to play MP4 animation]

GOES-16 “Clean” Infrared Window (10.3 µm) images [click to play MP4 animation]

A side-by-side comparison of GOES-16 Visible and Infrared images is displayed below.

GOES-16 "Red" Visible (0.64 µm, left) and "Clean" Infrared Window (10.3 µm, right) images [click to play MP4 animation]

GOES-16 “Red” Visible (0.64 µm, left) and “Clean” Infrared Window (10.3 µm, right) images [click to play MP4 animation]

A toggle between NOAA-20 VIIRS True Color Red-Green-Blue (RGB) and Infrared Window (11.45 µm) images at 1734 UTC as viewed using RealEarth (below) showed the early stage of convective development south of Córdoba, as well as the large decaying MCS to the southeast. Cloud-top infrared brightness temperatures with the developing storms were already -80–C and colder (violet enhancement), about 10ºC colder than what was observed using lower-resolution GOES-16 imagery at that same time.

NOAA-20 VIIRS True Color Red-Green-Blue (RGB) and Infrared Window (11.45 µm) images [click to enlarge]

NOAA-20 VIIRS True Color RGB and Infrared Window (11.45 µm) images at 1734 UTC [click to enlarge]



PyroCumulonimbus cloud in Australia

January 25th, 2019 |

Himawari-8

Himawari-8 “Red” Visible (0.64 µm, top), Shortwave Infrared (3.7 µm, middle) and Infrared Window (10.3 µm, bottom) images [click to play to animation | MP4]

JMA Himawari-8 “Red” Visible (0.64 µm), Shortwave Infrared (3.7 µm) and Infrared Window (10.3 µm) images (above) showed the development of a pyroCumulonimbus (pyroCb) cloud from a bushfire that was burning in the eucalypt forests of eastern Victoria, Australia on 25 January 2019. A rapid-scan “Target” sector was positioned over the region beginning at 0522 UTC, providing images every 2.5 minutes (instead of the routine 10-minute interval). Cloud-top infrared brightness temperatures became colder than -40ºC (the threshold for pyroCb classification) after 0230 UTC, and eventually cooled to around -55ºC (orange enhancement). This temperature roughly corresponded to an altitude around 12 km, according to nearby Melbourne rawinsonde data (plot | text).

A closer view of Himawari-8 “Red” Visible (0.64 µm) and Shortwave Infrared (3.7 µm) images (below) revealed the rapid southeastward run of the fire, as shown by the growth of the “hot spot” (black to red pixels) on Shortwave Infrared images. The darker gray appearance of the pyroCb cloud is due to the presence of smaller ice crystals at the cloud top — these smaller ice crystals are more efficient reflectors of incoming solar radiation, making the cloud tops appear warmer than those of conventional cumulonimbus. Vigorous updrafts driven by the intense heat of the fire limit the in-cloud residence time for ice crystal growth, which leads to smaller particles being ejected at the pyroCb cloud top.

Himawari-8 "Red" Visible (0.64 µm, left) and Shortwave Infrared (3.7 µm, right) images [click to play to animation | MP4]

Himawari-8 “Red” Visible (0.64 µm, left) and Shortwave Infrared (3.7 µm, right) images [click to play to animation | MP4]

In a comparison of VIIRS True Color Red-Green-Blue (RGB) and Infrared Window (11.45 µm) images from Suomi NPP (at 0311 UTC) and NOAA-20 (at 0501 UTC) images viewed using RealEarth (below), cloud-top infrared brightness temperatures were in the -55 to -58ºC range (darker shades of orange).

VIIRS True Color RGB and Infrared Window (11.45 µm) images from Suomi NPP (0311 UTC) and NOAA-20 (0501 UTC) images [click to enlarge]

VIIRS True Color RGB and Infrared Window (11.45 µm) images from Suomi NPP (0311 UTC) and NOAA-20 (0501 UTC) images [click to enlarge]