Reflection of sunlight from the Topaz Solar Farm in southern California

June 12th, 2019 |

GOES-17

GOES-17 “Red” Visible (0.64 µm) images [click to play animation | MP4]

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.

GOES-17 "Red" Visible (0.64 µm) images [click to play animation | MP4]

GOES-17 “Red” Visible (0.64 µm) images [click to play animation | MP4]

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 is 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.

Multi-panel images of all 16 ABI bands of GOES-17 [click to play animation | MP4]

Multi-panel images of all 16 ABI bands of GOES-17 on 12 June [click to play animation | MP4]

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.

Infrared and Water Vapor weighting functions calculated using rawinsonde data from Vandenberg CA at 00 T on 13 June [click to enlarge]

Infrared and Water Vapor weighting functions calculated using rawinsonde data from Vandenberg Air Force Base CA at 00 UTC on 13 June [click to enlarge]

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.

Multi-panel images of all 16 ABI bands of GOES-17 [click to play animation | MP4]

Multi-panel images of all 16 ABI bands of GOES-17 on 07 June [click to play animation | MP4]

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]

Anomalous cutoff low over the Beaufort Sea

June 12th, 2019 |

GOES-17 Mid-leve Water Vapor (6.9 µm, top) and GOES-15 Water Vapor (6.5 µm. bottom) imagess [click to play animation | MP4]

GOES-17 Mid-level Water Vapor (6.9 µm, top) and GOES-15 Water Vapor (6.5 µm. bottom) images [click to play animation | MP4]

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.

6-hourly GFS 500 hPa geopotential height, wind, and standardized height anomaly [click to enlarge]

6-hourly GFS 500 hPa geopotential height, wind, and standardized height anomaly [click to enlarge]

Inland intrusion of marine stratus in south-central Alaska

June 8th, 2019 |

GOES-17

GOES-17 “Red” Visible (0.64 µm) images [click to play animation | MP4]

1-minute Mesoscale Domain Sector GOES-17 (GOES-West) “Red” Visible (0.64 µm) images (above) showed a fast-moving jet of marine layer stratus moving westward from the Seward-Chenega area into the far southern Cook Inlet in south-central Alaska on 08 June 2019. A narrow finger of the marine stratus penetrated farther inland across the lower elevations of Iliamna Lake (which is located between Pedro Bay and Kokhanok). Note that at 2245 UTC the GOES-17 Mesoscale Sector was shifted southward, to better monitor a Gulf of Alaska storm.

This inland intrusion of marine stratus was driven by the presence of a warm thermal trough across Interior and Southwest Alaska (surface analyses) — animations of 10-minute GOES-17 Full Disk visible imagery (below) included hourly plots of surface wind barbs and air temperature. Note that some sites farther inland across southwestern Alaska had temperatures in the upper 60s to low 70s F.

GOES-17 "Red" Visible (0.64 µm) images [click to play animation | MP4]

GOES-17 “Red” Visible (0.64 µm) images, with hourly surface wind barbs plotted in cyan and temperatures plotted in yellow [click to play animation | MP4]

At Iliamna Airport — located along the northern edge of Lake Iliamna — southeasterly winds gusted to 22 knots at 01 and 03 UTC (below).

Time series plot of surface reports from Iliamna Airport [click to enlarge]

Time series plot of surface reports from Iliamna Airport [click to enlarge]

A similar type of thermally-driven phenomenon is sometimes observed in the San Francisco Bay area, as shown here and here.

Thunderstorms in the Alaska Interior

June 2nd, 2019 |

GOES-17

GOES-17 “Red” Visible (0.64 µm, left) and “Clean” Infrared Window (10.3 µm, right) images, with hourly precipitation type plotted in red [click to play animation | MP4]

GOES-17 (GOES-West) “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.3 µm) images (above) showed thunderstorms that developed across Interior Alaska on 02 June 2019. Some of these storms produced small hail, prompting the issuance of a Severe Thunderstorm Warning:



Usually the GOES-17 Mesoscale Domain Sector #2 is positioned over Alaska to provide 1-minute imagery — but on this day it was relocated to cover severe thunderstorms across New Mexico and Texas — so imagery over Alaska was only available at the 10-minute Full Disk scan interval.

In addition to the hail, these storms also produced heavy rainfall — especially at Fairbanks, with 0.65 inch falling in only 21 minutes.

Time series of surface report data from Fairbanks International Airport [click to enlarge]

Time series of surface report data from Fairbanks International Airport [click to enlarge]