CIMSSPyroCb

Multiple PyroCb’s in northwestern Canada

åAfter several days of wildfire activity over parts of northern British Columbia (BC), northern Alberta (AB), and the Northwest Territories (NWT) of Canada (which produced a great deal of smoke, but no pyroCb activity), the conditions of the synoptic-scale environment became more favorable on 14 July 2014, allowing multiple pyroCb events (at least five?) to occur across that particular area. Very warm air was brought far northward — surface air temperatures as warm as 93º F or 33.9º C were seen in the Great Slave Lake region — ahead of a cold frontal boundary that was moving slowly eastward and southeastward across the region (surface analysis maps).

GOES-15 0.63 µm visible channel (left) and 3.9 µm shortwave IR channel (right) images [click to play animation]
GOES-15 0.63 µm visible channel (left) and 3.9 µm shortwave IR channel (right) images [click to play animation]
A comparison of GOES-15 (GOES-West) 1-km resolution 0.63 µm visible channel and 4-km resolution 3.9 µm shortwave IR channel images (above; click image to play animation) showed the widespread fire hot spots (dark black to red shortwave IR pixels) and the pyroCb clouds that developed in association with some of the larger fires.

The corresponding GOES-15 4-km resolution 10.7 µm IR channel images (below; click image to play animation; also available as a MP4 movie file) revealed that there were a few pyroCb clouds associated with the larger fires over northern BC, northern AB, and the NWT which began to exhibit cloud-top IR brightness temperature values of -40º C and colder (bright green color enhancement), indicating complete glaciation of the convective cloud top.

GOES-15 10.7 µm IR channel images [click to play animation]
GOES-15 10.7 µm IR channel images [click to play animation]
A higher spatial resolution view was provided by Suomi NPP VIIRS 375-meter (projected onto  a 1-km AWIPS grid) 0.64 µm visible channel, 3.74 µm shortwave IR, and 11.45 µm IR channel images at 21:10 UTC (below). The 4-letter identifier for regional upper air reporting sites are labeled in cyan.

Suomi NPP VIIRS 0.64 µm visible channel, 3.74 µm shortwave IR channel, and 11.45 µm IR channel images
Suomi NPP VIIRS 0.64 µm visible channel, 3.74 µm shortwave IR channel, and 11.45 µm IR channel images

On the corresponding VIIRS Red/Green/Blue (RGB) true-color image from the SSEC RealEarth web map server (below), the dense wildfire smoke was easy to identify due its gray appearance (in contrast to the brighter white clouds).

Suomi NPP VIIRS true-color Red/Green/Blue image
Suomi NPP VIIRS true-color Red/Green/Blue image

For 3 of the larger of the BC, AB, and NWT fires, NOAA ARL HYSPLIT model 180-hour forward air parcel trajectories (below) suggested a variety of long-range smoke transport pathways. The altitudes selected for the trajectories (8, 9, and 10 km) bracketed the approximate altitude of the -40º C level on the Fort Smith NWT (CYSM) and Fort Nelson, BC (CYYE) 12 UTC rawinsonde data.

HYSPLIT forward trajectories from BC pyroCb
HYSPLIT forward trajectories from BC pyroCb
HYSPLIT forward trajectories from AB pyroCb
HYSPLIT forward trajectories from AB pyroCb

HYSPLIT forward trajectories originating from NWT pyroCb

On the following morning of 15 July, Suomi NPP VIIRS visible and IR images (below) showed a large remnant pyroCb cloud that had drifted to the east of Great Slave Lake. The coldest VIIRS IR brightness temperature was -56º C, which was close to the tropopause temperature on the 12 UTC  Fort Smith (CYSM) sounding.

Suomi NPP VIIRS 0.64 µm visible, 3.74 µm shortwave IR, and 11.45  µm IR channel images
Suomi NPP VIIRS 0.64 µm visible, 3.74 µm shortwave IR, and 11.45 µm IR channel images

PyroCb in northern Alberta, Canada

GOES-13 0.63 µm visible (left) and 3.9 µm shortwave IR (right) images [click to play animation]
GOES-13 0.63 µm visible (left) and 3.9 µm shortwave IR (right) images [click to play animation]
Kudos to Mark Ruminski (NOAA/NESDIS Satellite Analysis Branch) for spotting this pyroCB event in far northern Alberta, Canada late in the day on 14 June 2014. McIDAS images of GOES-13 1-km resolution 0.63 µm visible channel (left panels) and GOES-13 4-km resolution 3.9 µm shortwave IR channel (right panels) data (above; click image to play animation; also available as an MP4 movie file) showed the initial subtle signal of a fire “hot spot” at 19:30 UTC (exhibiting an IR brightness temperature 293.1 K), whose temperature increased rapidly to 320.6 K at 19:37 UTC. By 21:55 UTC, the maximum IR brightness temperature of the fire hot spot was 337.7 K.

A 4-panel comparison of GOES-15 (GOES-West) and GOES-13 (GOES-East) visible and shortwave IR images (below; click image to play animation; also available as an MP4 movie file) indicated that with the more favorable western view angle from GOES-15, the fire hot spot was able to be detected at an earlier time (18:30 UTC), and also at a number of later times when the hot spot was obscured from the view of GOES-13 by dense pyroCb clouds.

GOES-15 (left panels) and GOES-13 (right panels) visible and shortwave IR channel images [click to play animation]
GOES-15 (left panels) and GOES-13 (right panels) visible and shortwave IR channel images [click to play animation]
An AWIPS image comparison of 1-km resolution Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel data at 20:51 UTC (below) showed the initial plume of pyroCb clouds drifting northeastward from the fire source (which actually showed up as a hot, dark black cluster of pixels, even on the longwave IR image). The coldest IR brightness temperature of the pyroCb cloud at that time was -53º C.

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images
Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images

A 1-km resolution NOAA-18 AVHRR 10.8 µm IR channel image at 23:11 UTC (below) also showed a minimum IR brightness temperature of -53º C for the pyroCb cloud.

NOAA-18 AVHRR 10.8 µm IR channel image
NOAA-18 AVHRR 10.8 µm IR channel image

The initial northwestward drift of the pyroCb cloud followed by a southwestward drift of the pyroCb cloud is explained by the change in wind direction with height, as seen on a nearby rawinsonde profile from Fort Smith, Northwest Territories (below). According to this sounding, the tropopause was at a height of 10.6 km, where the air temperature was -60º C.

Fort Smith, Northwest Territories rawinsonde profile
Fort Smith, Northwest Territories rawinsonde profile

The fire complex continued to burn into the night; a VIIRS 3.74 µm shortwave IR image at 10:36 UTC on 15 June (below) showed the cluster of fire hot spots (black pixels).

Suomi NPP VIIRS 3.74 µm shortwave IR image
Suomi NPP VIIRS 3.74 µm shortwave IR image

The Suomi NPP OMPS Aerosol Index (below; courtesy of Colin Seftor) showed the signature of fire smoke on 15 June, with a maximum AI value of 5.2.

Suomi NPP OMPS Aerosol Index product
Suomi NPP OMPS Aerosol Index product

Two Bulls Fire near Bend, Oregon

GOES-15 0.63 µm visible channel (left) and 3.9 µm shortwave IR channel (right)  images [click to play animation]
GOES-15 0.63 µm visible channel (left) and 3.9 µm shortwave IR channel (right) images [click to play animation]
On 07 June 2014, McIDAS images of 1-km resolution GOES-15 0.63 µm visible channel and 3.9 µm shortwave IR channel images (above; click image to play animation) showed that the Two Bulls Fire just west of Bend, Oregon (station identifier KBDN) began to burn an area large enough to be detected by satellite around 20:00 UTC (1:00 PM local time), when a shortwave IR brightness temperature of 314.9 K was seen. Within 15 short minutes, the fire “hot spot” exhibited a shortwave IR brightness temperature of 339.6 K — the saturation temperature for the GOES-15 3.9 µm detectors — which continued for another 5.5 hours until 01:41 UTC on 08 June.

The corresponding 4-km resolution GOES-15 10.7 µm longwave IR channel images (below; click image to play animation) offered a hint that there may have been a brief pyrocumulonimbus (pyroCb) cloud at 00:30 UTC on 08 June, when a single pixel exhibited an IR brightness temperature value of -30º C (dark blue color enhancement). However, the GOES-15 satellite was in Full Disk scan mode during the time of formation of this potential pyroCb cloud, so images were only available every 30 minutes during this critical period.

GOES-15 10.7 µm IR channel images (click to play animation)
GOES-15 10.7 µm IR channel images (click to play animation)

Luckily, an overpass of the NOAA-16 polar-orbiting (or POES) satellite offered an excellent 1-km resolution view with the AVHRR 12.0 µm IR channel — a minimum IR brightness temperature of -49.0º C (yellow color enhancement) was detected at 00:32 UTC (below). Other POES AVHRR images can be seen here (courtesy of Rene Servranckx).

POES AVHRR 12.0 µm IR image
POES AVHRR 12.0 µm IR image

The Two Bulls Fire continued to burn into the following night, and a comparison of 375-meter resolution Suomi NPP VIIRS 3.74 µm shortwave IR and 750-meter resolution VIIRS 0.7 µm Day/Night Band images at 09:28 UTC (2:28 AM local time) showed a distinct fire “hot spot” on the shortwave IR, with the DNB image revealing the bright glow of the large fire just west of the glow of the city lights of Bend, Oregon (below). The Bend Municipal Airport is located well to the northeast of the city of Bend, explaining the offset of the city lights and the airport observation.

Suomi NPP VIIRS 3.74 µm shortwave IR and 0.7 µm Day/Night Band images
Suomi NPP VIIRS 3.74 µm shortwave IR and 0.7 µm Day/Night Band images

A comparison of the 375-meter resolution Suomi NPP VIIRS 3.74 µm with a 4-km resolution GOES-15 3.9 µm shortwave IR images around 09:30 UTC (below) demonstrated the clear advantage of improved spatial resolution for the detection of fire hot spot: VIIRS gave a maximum shortwave IR brightness temperature of 52.5º C, compared to only 14.5º C on the GOES-15 image.

Suomi NPP VIIRS 3.74 µm and GOES-15 3.9 µm shortwave IR images
Suomi NPP VIIRS 3.74 µm and GOES-15 3.9 µm shortwave IR images

On the following morning of 08 June, GOES-15 0.63 µm visible channel images (below; click image to play animation) showed that large amounts of smoke had been transported southward over northern California, and especially southeastward over Nevada. Later in the day on 08 June, pilot reports over northern California indicated that the top of the smoke layer was at an altitude of 11,000 feet.

GOES-15 0.63 µm visible channel images (click to play animation)
GOES-15 0.63 µm visible channel images (click to play animation)

PyroCb in the Irkutsk region of Siberia

COMS-1 0.675 µm visible channel images (click to play animation)
COMS-1 0.675 µm visible channel images (click to play animation)

The first unambiguous pyroCb event of the 2014 Northern Hemisphere wildfire season occurred in the Irkutsk region of Siberia, Russia on 18 May 2014. Korean COMS-1 satellite 0.675 µm visible channel images (above; click image to play animation; also available as an MP4 movie file) showed an increasing amount of smoke output from numerous fires burning northwest of Lake Baikal; toward the end of the day, a strong cold front moving eastward across the region appeared to be the catalyst for producing a pair of pyroCb events in the vicinity of Bratsk (station identifier UIBB).

A time series of surface weather for Bratsk (below) showed that smoke had been reducing surface visibility to 3-4 miles during the overnight and early morning hours, but the visibility then dropped to 1.9 miles as south-southeasterly winds began to increase ahead of the arrival of the cold front. Once the cold front passed, the surface air temperature dropped from 73ºF (22.8ºC) at 08 UTC to 43ºF (6.1ºC) at 13 UTC, as westerly winds gusted as high as 33 knots.

Bratsk (UIBB) time series of surface data
Bratsk (UIBB) time series of surface data

The  corresponding COMS-1 10.8 µm IR channel images (below; click image to play animation; also available as an MP4 movie file) indicated that for the second, more explosive pyroCb northeast of Bratsk the cloud-top IR brightness temperature crossed the -40ºC threshold at 10:45 UTC, and then became colder than -50ºC at 11:00 UTC (IR/visible image comparison). The coldest cloud-top IR brightness temperature was -57.8 at 13:15 UTC.

COMS-1 10.8 µm IR channel images (click to play animation)
COMS-1 10.8 µm IR channel images (click to play animation)

Looking at the 12 UTC rawinsonde data from Bratsk (below), the -57.8ºC cloud-top IR brightness temperature roughly corresponded to an altitude of 10.2-10.7 km.

Bratsk rawinsonde data ( 12 UTC on 18 May 2014)
Bratsk rawinsonde data ( 12 UTC on 18 May 2014)

Multi-angle Imaging SpectroRadiometer (MISR) smoke plume heights (below) confirmed that the maximum height of the smoke plume was in the 11-12 km range.

Multi-angle Imaging SpectroRadiometer (MISR) smoke plume heights
Multi-angle Imaging SpectroRadiometer (MISR) smoke plume heights

Using the NOAA ARL HYSPLIT model, forward airmass trajectories originating at the 2 pyroCb initiation sites near Bratsk (below) suggested an anticyclonic transport aloft over far northeastern Russia, eventually crossing over the Sea of Okhotsk.

NOAA ARL HYSPLIT forward airmass trajectories
NOAA ARL HYSPLIT forward airmass trajectories

The anticyclonic transport of smoke was confirmed by images of Suomi NPP OMPS Aerosol Index on 19 and 20 May (below; courtesy of Colin Seftor).

Suomi NPP OMPS Aerosol Index
Suomi NPP OMPS Aerosol Index

A similar anticyclonically-curved signal of smoke aloft was seen on the AIRS Carbon Monoxide mixing ratio product from 18 May (below).

AIRS Carbon Monoxide mixing ratio
AIRS Carbon Monoxide mixing ratio