An earth-shaking refinery explosion (News story 1, 2) occurred in Philadelphia, PA under variably cloudy skies on Friday morning 21 June 2019. The toggle above shows GOES-16 3.9 µm Shortwave Infrared imagery from the mesoscale sector (with 1-minute imagery) and from the CONUS sector (with 5-minute imagery) at similar nominal times, 0821 UTC. There is a noticeable difference between the character of the signal in the mesoscale sector and the CONUS sector. This chart shows that a CONUS sector scan (shown in Blue at that link for Mode 6A that applies to GOES-16) occurs over a span of time from either 76 seconds to 233 seconds, or from 376 seconds to 533 seconds every 10 minutes (600 seconds). The nominal time of the image will be when the scan starts. Thus, the CONUS time at 08:21 UTC — that shows a very hot spot — is scanning over Philadelphia at some time in the following 2+ minutes after the scan start time (08:21:54). The Meso scale time of 08:21 UTC is scanning Philadelphia at very close to 08:21:05 UTC.

The mesoscale sector from 0820 to 0826 UTC shows no scene quite so hot as the CONUS sector. The warmest brightness temperature from the mesoscale sector, 51.5 C, occurs in the 0823 UTC image. This contrasts with the warmest brightness temperature of 118.2 C in the CONUS sector! This suggests an ephemeral explosion or rapidly-changing cloud cover that frequently masked the view (or both!).  The GOES-16 CONUS sector scanned just at the right time; the Mesoscale sector, even with higher temporal resolution, did not see the worst of the explosion.

Toggles between the CONUS image at 0821 and the mesoscale sectors at 0822 UTC and at 0823 UTC suggest that GOES-16 CONUS sector scanned Philadelphia shortly after 0822 UTC. The shift between the CONUS and mesoscale sectors is in opposite directions at the two times. (Note that Philadelphia County is outlined in both of those linked-to toggles.)

As has been observed with other similar events (for example, here, here and here), a closer look at the area showed that a nighttime thermal signature of the fire was also evident in GOES-16 Near-Infrared 1.61 µm and 2.24 µm imagery (below).

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1-minute Mesoscale Domain Sector GOES-17 (GOES-West) “Red” Visible (0.64 µm) and Shortwave Infrared (3.9 µm) images (above) showed a smoke plume and pyrocumulus clouds in addition to the thermal anomaly (or “hot spot”) associated with the lightning-initiated North River wildfire burning in the far eastern Seward Peninsula of Alaska on 16 June 2019. It is interesting to note that shortly after the wildfire exhibited a peak Shortwave Infrared brightness temperature of 94.5ºC at 2124 UTC, a distinct pyrocumulus cloud “jump” was seen in the Visible imagery (which appeared to peak in vertical extent around 2131 UTC, as seen in this short animation).

A sequence of 3 Suomi NPP VIIRS Shortwave Infrared (3.74 µm) and Visible (0.64 µm) images (below) also showed the fire thermal anomaly (black to red pixels) and the smoke plume.

In fact, the south-southwestward transport of smoke restricted the surface visibility to 5 miles at Unalakeet and 4 miles at St. Michael (below), located about 100 to 150 miles from the fire respectively.

A NOAA-20 VIIRS True Color Red-Green-Blue (RGB) image viewed using RealEarth (below) showed significant residual smoke aloft (from the previous day of that wildfire’s growth) arcing westward then southward over the Bering Sea; however, since smoke is effectively transparent at the 11.45 µm Infrared Window wavelength, there was no smoke signature seen in that particular image.

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1-minute Mesoscale Domain Sector GOES-17 (GOES-West) “Red” Visible (0.64 µm) images (above) revealed a bright reflection of sunlight off the large arrays of solar panels at Topaz Solar Farm in southern California (Google maps) — located between Black Mountain and California Valley — on 12 June 2019. Of particular interest are the vertical “stripes” emanating from the bright reflection signature in the 0.64 µm images, extending both northward and southward from the solar farm. These image artifacts are likely related to saturated ABI detector column amplifiers, due to an excess charge induced by intense sunlight reflection off the large solar panels.

Visible images displayed using McIDAS (below) are in the native GOES-17 satellite projection — removing the re-mapping inherent in the AWIPS images shown above — so the vertical striping artifacts are correctly oriented with respect to how the ABI swaths are scanned.

In multi-panel GOES-17 images that showed all 16 ABI bands (below) this reflection signature was apparent in the other visible and in most of the other infrared channels. The reflected energy was so intense that the Shortwave Infrared (3.9 µm) images displayed infrared brightness temperatures of 138.7ºC (411.85 K), the saturation temperature of the 3.9 µm detectors. Another interesting artifact: the so-called “Dark Pixels Around Bright Objects” that appear in the Visible (0.47 µm and 0.64 µm) and Near-Infrared (0.86 µm, 1.61 µm and 2.24 µm) spectral bands.

However, note the absence of a solar farm signature in the Cirrus (1.37 µm), Water Vapor (7.3 µm, 6.9 µm and 6.2 µm) and CO2 (13.3 µm) images — the presence of a layer of moisture within the mid-troposphere (centered near the 500 hPa pressure level) absorbed upwelling radiation from the surface, then re-emitted radiation at the colder temperature of that moisture aloft (thereby masking the bright/hot solar farm signature). Plots of Infrared and Water Vapor weighting functions (below) showed significant peaks at higher altitudes (due to the aforementioned layer of mid-tropospheric moisture) for Bands 8, 9, 10 and 16 — while the other Infrared spectral bands had their strongest weighting function peaks at the surface, with minimal contributions from higher altitudes.

It is interesting to examine GOES-17 imagery from 5 days earlier (below) — due to a drier air mass over the area on 07 June (with a Total Precpitable Water value of 0.57 inch, vs 0.70 inch on 12 June), a faint signature of the solar farm reflection could even be seen in the Band 4 Cirrus (1.37 µm) imagery.

Plots of the Infrared and Water Vapor weighting functions for that earlier day (below) showed higher-altitude peaks for bands 8, 9, 10 and 16 (similar to what was seen in the 12 June case).

Infrared and Water Vapor weighting functions calculated using rawinsonde data from Vandenberg Air Force Base CA at 00 UTC on 08 June [click to enlarge]

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A comparison of Water Vapor images from GOES-17 (GOES-West) and GOES-15 Water Vapor images (above) showed the signature of an anomalously-deep closed low that was moving southeastward over the Beaufort Sea north of Alaska during the 11 June – 12 June 2019 period. The images are shown in the native projection of each satellite — GOES-17 is positioned over the Equator at 137.2º W longitude, while GOES-15 is located at 128º W. The improved GOES-17 spatial resolution (2 km at nadir, vs 4 km for GOES-15) and more frequent imaging (every 10 minutes, vs every 30 minutes for GOES-15) allowed for a better depiction of this cutoff low — including smaller-scale features near the center of the broad circulation.

GFS model 500 hPa geopotential height, wind, and standardized height anomaly (source) analyses at 6- hour intervals (below) indicated 500 hPa geopotential height anomaly values reached -3 to -4 sigma (lighter shade of violet) for this cutoff low.

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