PyroCb

On 20 June according to the Alaska Interagency Coordination Center the Blair Fire started in the interior of Alaska (south of Fairbanks) at 64.3º N 147.3º W. On 24 June at 20:15 UTC a pyroCb formed from this fire. GOES-15 detected the smoke plume and pyroCb cloud, as well as the fire hot spot. Starting at 19:00 UTC on 24 June, the animation below shows visible (.63 μm) on the left and shortwave IR (3.9 μm) on the right (click image to play animation). In the shortwave IR images the darker black to red pixels indicate very hot IR brightness temperatures exhibited by the fire source region.

GOES-15 0.63 μm visible (left) and 3.9 μm shortwave IR (right) images (click to play animation)

Also, using GOES-15 10.7 μm IR channel imagery the cloud-top IR brightness temperature could be determined. The animation below, starting at 19:00 UTC on 24 June, shows the brightness temperature of this pyroCb reaching -53.6ºC (lime green/yellow color enhancement) around 21:45 UTC.

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

A timely overpass of the Suomi NPP satellite provided a good view of the pyroCb cloud very soon after its formation — a comparison of 20:18 UTC VIIRS 0.64 µm visible channel, 3.74 µm shortwave IR channel, and 11.45 µm IR channel images is shown below. On the visible image, the tall pyroCb cloud casts a shadow onto the dense layer of smoke below; the fire hot spot (black to yellow to red pixels) can be seen along the southeastern edge of the cloud; the minimum cloud-top IR brightness temperature was -56º C, which corresponded to an altitude of approximately 10.8 km (using data from the 00 UTC Fairbanks sounding). At the time of the VIIRS images, smoke was reducing the surface visibility at Fairbanks (PAFA) to 3/4 of a mile, and to the west-northwest at Tanana (PATA) the occasional fall of wildfire ash was being reported at the surface.

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

A sequence of daily Suomi NPP VIIRS true-color image composites from 18 June to 24 June (below) showed a dramatic increase in the areal coverage of dense wildfire smoke over Alaska during that period. A post on the Wildfire Today site mentioned the high number of lightning strikes that had occurred over the region in recent days, with a record  of over 14,000 lightning strikes in a single day on 21 June. A closer view of the 24 June VIIRS true-color image with an overlay of AVHRR-detected fire hot spots can be seen here. Due to the dense smoke , the Air Quality Index at Fairbanks on 24 June was 242 (on a scale of 0-500), placing it in the “Very Unhealthy” category.

Daily composites of Suomi NPP VIIRS true-color images during the 18 June – 24 June 2015 period

Regarding the “smoke vortex” seen over northern Alaska on the 24 June VIIRS images above, GOES-15 0.63 µm visible channel images (below; click to play animation) showed the development and motion of this feature during the day. A pair of fires seemed to intensify in the southern foothills of the Brooks Range, north-northeast of Fort Yukon (PFYU), as the vortex passed — perhaps this was a boundary layer feature that helped to increase surface winds in its wake.

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

On 24 June OMPS Aerosol Index (AI) images were useful to see the transport of the smoke. From the AI image (below; courtesy of Colin Seftor and Rene), it can be seen that the smoke was being transported eastward. Region 1 has a max value of 3.6 which is consistent with the time and location of the max value of 7.5 on 23 June. These values both trace back to the region where five pyroCbs developed in Alaska between 21:45 UTC on 22 June and 07:30 UTC 23 June. Region 2 has a max value of 2.9 and is from the northern British Columbia pyrocb. Region 3 has a max value of 7.2 and is from the pyroCb produced by the Blair fire that is discussed above. Region 4 has the highest value on the map at 7.8 but can’t be traced directly back to a source, most likely from the numerous fires burning close by.

OMPS Aerosol Index image on 24 June (click to enlarge)

On 22 June and 23 June 2015 there were multiple fires in Alaska that produced pyroCb. GOES-15 detected the smoke plumes and pyroCb clouds, as well as the fire hot spots. Starting at 21:00 UTC on 22 June, the animation below shows visible (.63 μm) on the left and shortwave IR (3.9 μm) on the right (click image to play animation).  In the shortwave IR images the red pixels indicate very hot IR brightness temperatures exhibited by the fire source region.

GOES-15 0.63 μm visible (left) and 3.9 μm shortwave IR (right) images (click to play animation)

Also the GOES-15 10.7 μm IR channel images helped to analyze the cloud-top IR brightness temperatures (below; click to play animation).

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

The first pyroCb was seen at 64.2º N 149.4º W around 21:45 UTC on 22 June. GOES-15 is magnified to this specific pyroCb and detects the smoke plume and the hotspot from this particular fire. Starting at 21:00 UTC the animation below shows visible (.63 μm) on the left and shortwave IR (3.9 μm) on the right (click image to play animation). In the shortwave IR images the darker black to red pixels indicate very hot IR brightness temperatures exhibited by the fire source regions.

GOES-15 0.63 μm visible (left) and 3.9 μm shortwave IR (right) images (click to play animation)

Also, using GOES-15 10.7 μm IR channel the cloud-top IR brightness temperature could be determined. The animation below starting at 21:00 UTC shows the brightness temperature of this pyroCb reaching -47.2 ºC (lime green color enhancement) around 21:45 UTC.

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

The second pyroCb was located at 65.9º N 149.1º W, starting around 01:00 UTC on 23 June. GOES-15 is magnified to this specific pyroCb and detects the smoke plume and the hotspot from this particular fire. Starting at 00:00 UTC on 23 June the animation below shows visible (.63 μm) on the left and shortwave IR (3.9 μm) on the right (click image to play animation). In the shortwave IR images the darker black to red pixels indicate very hot IR brightness temperatures exhibited by the fire source regions.

GOES-15 0.63 μm visible (left) and 3.9 μm shortwave IR (right) images (click to play animation)

Also, using GOES-15 10.7 μm IR channel the cloud-top IR brightness temperature could be found. The animation below starting at 00:00 UTC shows the brightness temperature of this pyroCb reaching -58.4 ºC (yellow color enhancement) around 06:00 UTC.

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

The third pyroCb was located at 65.4º N 151.7º W, and started around 2:00 UTC on 23 June. GOES-15 is magnified and centered to this specific pyroCb and detects the smoke plume and the hotspot from this particular fire. Starting at 02:00 UTC on 23 June the animation below shows visible (.63 μm) on the left and shortwave IR (3.9 μm) on the right (click image to play animation). In the shortwave IR images the darker black to red pixels indicate very hot IR brightness temperatures exhibited by the fire source regions.

GOES-15 0.63 μm visible (left) and 3.9 μm shortwave IR (right) images (click to play animation)

Also, using GOES-15 10.7 μm IR channel the cloud-top IR brightness temperature could be found. The animation below starting at 05:00 UTC shows the brightness temperature of this pyroCb reaching -51.4ºC (lime green color enhancement) around 06:00 UTC.

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

There are two additional pyroCb that have occurred: the fourth at 65.º N 148.3º W, and the fifth at 65º N and 153.6º W. Since there are so many pyroCbs in the area it hard to distinguish between the different pyroCbs. With this being said the images for these pyroCbs can be seen in the above animations. The fourth pyroCb was found to have a minimum brightness temperature of -47.6º C, and the fifth pyroCb  a minimum brightness temperature of -47.2º C. These are indicated by a lime green color enhancement in the GOES-15 10.7 μm IR channel animations.

The overpass of the Suomi NPP satellite at 12:00 UTC on 23 June allowed a better view of the pyroCb clouds and the smoke that was produced from these fires. The VIIRS true-color image below shows the many different fires that were occurring and the pyroCbs that resulted from some of the larger fires. Widespread smoke from this fire activity can also be seen, which exhibits a hazy white to light tan appearance.

Suomi NPP VIIRS True-Color image on 23 June (click to enlarge)

On 22 June OMPS Aerosol Index (AI) images were useful to see the transport of the smoke. From the AI image (below; courtesy of Colin Seftor), it can be seen that the smoke was being transported southwestward. 

OMPS Aerosol Index image on 22 June (click to enlarge)

In addition, the image below shows a MODIS true-color image with an overlay of the OMPS Aerosol Index (courtesy of Colin Seftor).

MODIS true-color image with an overlay of OMPS Aerosol Index on 22 June (click to enlarge)

Again on 23 June OMPS AI Index images were used to see the transport of the smoke. From the AI images below (courtesy of Colin Seftor), the smoke is now moving eastward. At 20:40 UTC the max AI was 7.5 at 65.3 N and 142.18 W. Also, at 22:20 UTC the max AI was 6.7 at 65.32 N 141.28 W.  From these AI values it is apparent the smoke is now moving eastward into Canada, which is different from the previous day.

OMPS Aerosol Index images on 23 June (click to enlarge)

On 20 June 2015 there was a possibility that the Michigan Creek fire at 64.1º N 144.4º W  in southern Alaska produced a pyroCb; after further analysis it was determined that this fire did indeed produce a pyroCb. GOES-15 (GOES-West) detected the smoke plume and pyroCb cloud, but unfortunately it was too cloudy for the shortwave IR imagery to consistently detect the fire hotspots. Starting at 22:00 UTC on 20 June the animation below shows visible (.63 μm) on the left and shortwave IR (3.9 μm) on the right (click image to play animation).

GOES-15 0.63 μm visible (left) and 3.9 μm shortwave IR (right) images (click to play animation)

In addition, using GOES-15 10.7 μm IR channel images the cloud-top IR brightness temperature can be found. The coldest brightness temperature of the pyroCb cloud was -60.1ºC around 01:00 UTC on 21 June. This is indicated in the animation by an orange color enhancement, and is seen moving southwest. Based on the Fairbanks and Whitehorse soundings the top of the cloud is therefore estimated to be around 11 km.

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

An overpass of the Suomi NPP satellite at 23:12 UTC on 20 June allowed a better view of the fire hot spot, along with the growing pyroCumulus cloud that was drifting northwestward away from the hot spot. A comparison of the VIIRS 3.74 µm shortwave IR, 11.45 µm IR, and 0.64 µm visible channel images (below) showed the Michigan Creek fire hotspot which was located about 30 miles northeast of Delta Junction / Ft. Greely (station identifier PABI); the young pyroCumulus cloud just to the northwest of the fire hot spot exhibited a minimum IR brightness temperature of -34º C (darker blue color enhancement).

Suomi NPP VIIRS 3.74 µm shortwave IR, 11.45 µm IR, and 0.64 µm visible channel images (click to enlarge)

At 12:00 UTC on 21 June the pyroCb can be seen on an Aqua MODIS true-color image (below).

Aqua MODIS true-color image (click to enlarge)

On 21 June OMPS AI Index image were used again to see the transport of the smoke. From the AI image (below; image courtesy of Colin Seftor), the smoke is moving southeast. This is not consistent with the visible and IR images above. From that animation we saw that the smoke was moving southwest then west, indicating the max AI on this image isn’t from the smoke from this fire. However, there is a signature right above the coordinates for the fire around 63 N 144 W.

OMPS Aerosol Index images on 21 June (click to enlarge)