The Day Night Band and Smoke

July 29th, 2021 |
Suomi NPP VIIRS Day Night Band Visible (0.70 µm) image, 0740 UTC on 29 July 2021 (Click to enlarge)

Smoke from fires (unless it is extraordinarily thick) is very challenging to detect at night in infrared imagery. When there is sufficent lunar illumination, however, as occurred on 29 July 2021 over Canada (the image above shows northwestern Ontario and southern Manitoba — Lakes Winnepeg, Winnepegosis and Manitoba are apparent, and the city of Winnipeg’s lights are apparent along the southern border of the image), the pall of smoke can be detected just as during the daytime using Day Night band visible imagery. In the image above, bright signals are showing light emitted by active fires, and streams of smoked from the fires are apparent. The toggle below of the Day Night band image and the VIIRS I04 3.74 µm imagery underscores that the bright spots are also very warm spots; that is: fires. Note that a smoke signal is not present at all in the infrared.

VIIRS Visible (0.7 µm) Day Night Band imagery and I04 Infrared (3.74 µm) imagery, 0740 UTC on 29 July 2021 (Click to enlarge)

Suomi NPP VIIRS Day Night Band Visible (0.70 µm) image, 0740 UTC on 29 July 2021 (Click to enlarge)

A zoomed-out Day Night band image shows the horizontal extent of the smoke pall that extends southward into Minnesota. This kind of night-time imagery can be useful to compare observations to model estimates of smoke coverage as created by the HRRR Smoke model. Compare the image above, for example, to the two-hour forecast of vertically integrated smoke valid at 1300 UTC on 29 July, shown below. There is good agreement in the coverage over northern Minnesota. What does that kind of smoke look like from the ground? Here’s a image from a webcam at Lake Bemidji (from this source). GOES Imagery, at bottom, from just before Noon Central time (and from the CSPP Geosphere site) also shows the very thick smoke over Minnesota.

HRRR Smoke forecast valid at 1300 UTC, a 2-hour forecast from an 1100 UTC/29 July 2021 initialization (Click to enlarge)
CSPP Geosphere True Color imagery, 1650 UTC on 29 July 2021 (Click to enlarge)

Use the Day Night band image (as available here, for example) to identify smoke plumes when lunar illumination is present.

Aerosol Optical Depth and surface visibility

July 22nd, 2021 |
GOES-16 Aerosol Optical Depth and GOES-16 Band 2 Visible (0.64 µm) imagery, 1401 UTC on 22 July 2021

The image above shows the Level 2 GOES-R product, Aerosol Optical Depth (AOD), a product created in clear skies, overlain with the GOES-16 Visible imagery from the same time. AOD measures the extinction of light via scattering and absorption by small particles in the atmosphere, and it can be used as a proxy for particles smaller than 2.5 µm in diameter (PM25). The red regions show the highest values. The plot below shows surface observations of ceilings (plotted to the left of the circles) and visibility (plotted below the circles) at the same time as the AOD image above. Is there a relationship?

Look at the string of lower visibilities stretching along the North Carolina/South Carolina border, extending westward to Tennessee and then northward into Illinois. This is the region where AOD exceeds about 0.4 — cyan in the enhancement used above. In this instance, AOD can be used to highlight regions where surface visibilities are most restricted by aerosols. (Some of these aerosols are likely from smoke. However, this product does not tell you what kind of aerosol is there, only that it is causing extinction).

Surface observations of ceilings and visibilities, 1401 UTC on 22 July 2021

The toggle below steps through the observations, AOD, and Visible imagery at 1401 UTC. Kudos to Frank Alsheimer, the Science and Operations Office (SOO) in Columbia SC, for alerting us to this case.

Surface observations of ceilings and visibilities, GOES-16 Aerosol Optical Depth and GOES-16 Band 2 Visible (0.64 µm) imagery, 1401 UTC on 22 July 2021

True-color imagery, below, (saved in this case from the CSPP Geosphere site, using this link) also shows the extent of the aerosol-rich air.

GOES-16 ‘True-Color’ imagery at 1401 UTC on 22 July 2021

The relationship between AOD values and surface visibility persisted on 23 July 2021, below.

GOES-16 Aerosol Optical Depth and GOES-16 Band 2 Visible (0.64 µm) imagery, 1201 UTC on 23 July 2021

Blowing dust in the Upper Midwest

May 25th, 2021 |

GOES-16 Split Window Difference images, with plots of wind barbs and gusts [click to play animation | MP4]

GOES-16 Split Window Difference images, with plots of wind barbs and gusts [click to play animation | MP4]

GOES-16 (GOES-East) Split Window Difference images (above) showed widespread strong winds across the Dakotas and northern Minnesota which were responsible for producing plumes of blowing dust (darker shades of gray) — most notably from eastern North Dakota into northwestern Minnesota — on 24 May 2021.

The corresponding GOES-16 Split Window Difference images with plots of surface visibility are shown below — at 23 UTC the visibility dropped to 4 miles at Grand Forks, North Dakota as a dense dust plume moved through that location (where southwesterly winds were gusting to 31 knots at that time).

GOES-16 Split Window Difference images, with plots of surface visibility [click to play animation | MP4]

GOES-16 Split Window Difference images, with plots of surface visibility [click to play animation | MP4]

GOES-16 True Color RGB images [click to play animation | MP4]

GOES-16 True Color RGB images [click to play animation | MP4]

GOES-16 True Color RGB images (above) and Dust RGB images (below) created using Geo2Grid highlighted the more dense plumes of blowing dust — the source region for the more prominent dust plumes appeared to be dry agricultural fields in southeastern North Dakota that had received very little rainfall during the preceding week.

GOES-16 Dust RGB images [click to play animation | MP4]

Ground-based lidar data from Grand Forks indicated that the dust was lofted to altitudes of around 10,000 feet.


===== 25 May Update =====

GOES-16 Dust RGB images, with and without plots of surface reports [click to play animation | MP4]

GOES-16 Dust RGB images, with and without plots of surface reports [click to play animation | MP4]

Strong winds persisted across that same region on 25 May — and GOES-16 Dust RGB images (above) again displayed the subtle signature of blowing dust (light shades of pink/magenta) along the leading edge of cloudiness that was moving eastward into northwestern Minnesota.

GOES-16 True Color RGB images (below) once again showed the hazy signature of blowing dust.

GOES-16 True Color RGB images [click to play animation | MP4]

GOES-16 True Color RGB images [click to play animation | MP4]

Blowing dust across Mongolia and China

May 6th, 2021 |

Himawari-8 Dust RGB images [click to play animation | MP4]

Himawari-8 Dust RGB images [click to play animation | MP4]

JMA Himawari-8 Dust RGB images (created using Geo2Grid) covering the 48-hour period from 21 UTC on 04 May to 21 UTC on 06 May 2021 (above) revealed multiple plumes of blowing dust (brighter shades magenta/pink) which originated over parts of Mongolia — and were then transported southeastward and eastward across northeastern China.

Surface analyses from the Korean Meteorological Agency (below) showed an impressive pressure gradient between a midlatidude cyclone (moving southeastward from Mongolia into China) and high pressure moving southward behind it. Some of the airborne dust was entrained into the circulation of this low pressure system.

Surface analyses during the period from 21 UTC on 0 May to 21 UTC on 06 May [click to enlarge | MP4]

Surface analyses during the period from 21 UTC on 04 May to 21 UTC on 06 May [click to enlarge | MP4]

VIIRS True Color RGB mages from Suomi NPP and NOAA-20 viewed using RealEarth (below) showed the hazy arc of blowing dust along the trailing cold front (south of the cyclone in northeastern China) on 6 May.

VIIRS True Color RGB mages from Suomi NPP and NOAA-20 [click to enlarge]

VIIRS True Color RGB mages from Suomi NPP and NOAA-20 [click to enlarge]