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.

Microwave rain estimates with an MCS

July 29th, 2021 |
VIIRS NPP Day Night Band visible (0.70 µm) imagery from Suomi-NPP (0740 UTC) and NOAA-20 (0831 UTC) on 29 July 2021 (Click to enlarge)

Severe thunderstorms developed (in a moderate risk region from the Storm Prediction Center; here are the Storm Reports) over northern Wisconsin late in the day on 28 July 2021 and moved to the southeast (here is an mp4 animation of GOES-16 imagery courtesy of Tim Schmit, NOAA). The Day Night Band imagery, above, from Suomi NPP (0740 UTC) and NOAA-20 (0831 UTC), shows snapshots of the storms as they moved southward into Illinois. The 0740 UTC image include more evidence of lightning — especially in southwestern Wisconsin (the horizontal streaks of light) and just southwest of Dubuque. At 0831 UTC, lightning is not detected in the Day Night Band image.

In addition to carrying the VIIRS (Visible-Infrared Imaging Radiometer Suite) instrument, Suomi-NPP and NOAA-20 also carry the Advanced Technology Microwave Sounder (ATMS), and microwave data from that instrument can be used to infer rain rates (using MIRS — Microwave Integrated Retrieval System — algorithms, that are part of Community Satellite Processing Package — CSPP — software available to use at Direct Broadcast sites). The toggles show the Day Night Band image, the ATMS-derived Rain Rate (the green region at 0742 UTC is >3″/hour!), and the base reflectivity at 0740 UTC (below) and at 0831 UTC (bottom). The MIRS Rain Rate (0742 UTC; 0833 UTC) product does outline regions where rain is likely falling, and gives credible values where the heaviest rains are falling. Note the diminishing rain rate over southwestern WI, for example, between 0740 and 0830 UTC — indicative of weaker convection — an observation echoed in the changes in lightning detection with the Day Night band. Changes in radar to reflect that difference in microwave-estimated rain rate are a little more subtle.

Because microwave estimates of rain rate are affected by background emissivity, and because water has a much lower microwave emissivity than land, you can sometimes view land/water boundaries (as in the 0742 UTC Rain Rate, below).

MIRS Rain Rate gives useful information about rains when radar observations cannot be accessed.

Suomi NPP Day Night Band visible (0.70 µm) image, ATMS estimates of Rain Rate, and 0.5-degree Reflectivity from a radar composite, all at 0740 UTC on 29 July 2021 (Click to enlarge)
NOAA-20 Day Night Band visible (0.70 µm) image, ATMS estimates of Rain Rate, and 0.5-degree Reflectivity from a radar composite, all at 0830 UTC on 29 July 2021 (Click to enlarge)

MIRS Rain Rate products are available via an LDM feed from CIMSS; they are produced using the Direct Broadcast antenna at CIMSS and are thus very timely.

SAR winds near Tropical Storm Nepartak

July 27th, 2021 |
RCM1 SAR Winds over Tropical Storm Nepartak just east of Honshu, 0828 UTC on 27 July 2021 (Click to enlarge)

RADARSAT Constellation Mission One (RCM1) passed over Nepartak at 0828 UTC on 27 July 2021, and the image above shows the Synthetic Aperture Radar (SAR) winds derived at that time. There is a widespread region of ~40-knot winds (cyan to green in the color enhancement), a bit stronger than the 30-knot winds viewed by MetopA at 1040 UTC (shown here, in this blog post). How certain can a forecaster be of the even-stronger winds that exist in an area near the coast near 37.4ºN, 141.4ºE, and in an arc from 37.5ºN, 142.5ºE to 37.2ºN, 144ºE? There are isolated SAR estimates in that band that are near 60 knots! Are there other data sources to confirm that kind of wind? (See information at the bottom for clarification!)

The image below shows Himawari-8 Clean window imagery at 0829 UTC, just after the image above. Three points with cold cloud tops, suggestive of more vigorous convection, are indicated: (37.6ºN, 141.18ºE); (37.57ºN, 143.01ºE); (37.35ºN, 144.01ºE). The structures in the infrared imagery do match the structures in the SAR winds, but offset a bit to the north in the Himawari-8 imagery, as expected because of the parallax shift: features will be displaced away from the sub-satellite point, with the displacement increasing for higher clouds, and for greater distance from the sub-satellite point (on the Equator at 140.2ºE for Himawari-8). Convective downdrafts could be responsible for the highest winds shown in the SAR analysis.

Himawari-8 Clean Window Infrared (10.41 µm) imagery, 0829 UTC on 27 July 2021 (Click to enlarge)

The strong winds in the image are not observations of strong winds by SAR. Rather, these are most likely the result of reflection off of ice in the atmosphere — ice that is likely to be present around convective towers that have glaciated. (Thanks to Christopher Jackson, GST/NOAA, for this information!)

Severe thunderstorms in northern Minnesota

July 26th, 2021 |
GOES-16 “Red” Visible (0.64 µm) images (top) and “Clean” Infrared Window (10.35 µm) images (bottom), with plots of SPC Storm Reports [click to play animation | MP4]

GOES-16 “Red” Visible (0.64 µm) images (top) and “Clean” Infrared Window (10.35 µm) images (bottom), with plots of SPC Storm Reports [click to play animation | MP4]

1–minute Mesoscale Domain Sector GOES-16 (GOES-East) “Red” Visible (0.64 µm) images and “Clean” Infrared Window (10.35 µm) images (above) include time-matched plots of SPC Storm Reports produced by supercell thunderstorms that moved east-southeastward across northern Minnesota during the afternoon and early evening hours on 26 July 2021. Severe reports included a tornado at 2213 UTC and hail as large as to 3.0 inches in diameter at 2334 UTC. These storms developed near and north of a warm/stationary frontal boundary (surface analyses).