Ice in the Sea of Okhotsk

April 18th, 2019 |

Himawari-8

Himawari-8 “Red” Visible (0.64 µm) images [click to play animation | MP4]

JMA Himawari-8 “Red” Visible (0.64 µm) images (above) revealed circulations of ice within the Sea of Okhotsk (east of Sakhalin Island — station identifier UHSS is Yuzhno-Sakhalinsk, Russia) on 17-18 April 2019. Wind stress from an occluded Gale Force Low moving through that region on the previous day (surface analyses) likely helped to enhance some of the ice circulations.

In a comparison of Himawari-8 “Red” Visible (0.64 µm) and Near-Infrared “Snow/Ice” (1.61 µm) images (below), note that the ice appears much darker than cloud features (since ice is a strong absorber of radiation at the 1.61 µm wavelength).

Himawari-8 "Red" Visible (0.64 µm, left) and Near-Infrared "Snow/Ice" (1.61 µm, right) images [click to play animation | MP4]

Himawari-8 “Red” Visible (0.64 µm, left) and Near-Infrared “Snow/Ice” (1.61 µm, right) images [click to play animation | MP4]

Thanks to Thomas Birchard (NWS Honolulu) for bringing this interesting feature to our attention!

Mesoscale disturbance over northern Alaska

April 17th, 2019 |

GOES-17

GOES-17 “Red” Visible (0.64 µm) and Low-level Water Vapor (7.3 µm) images [click to play animation | MP4]

1-minute Mesoscale Domain Sector GOES-17 (GOES-West) “Red” Visible (0.64 µm) and Low-level Water Vapor (7.3 µm) images (above) showed a mesoscale disturbance that was moving northward over the eastern Brooks Range in far northeastern Alaska on 17 April 2019. The curved configuration of the associated cloud structure suggested that a closed circulation center was present (or had just recently developed) — while surface analyses showed an area of low pressure much farther to the south along the Alaska/Yukon border, there were no features moving northward across the region shown in the GOES-17 imagery.

Light to moderate snow was reported at Arctic Village as this mesoscale disturbance moved over the area (below).

Time series of surface weather observation data from Arctic Village [click to enlarge]

Time series of surface weather observations from Arctic Village [click to enlarge]

375-meter resolution Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images at 2131 and 2313 UTC (below) provided a more detailed view of this feature, in which the clouds exhibited an appearance suggestive of embedded convection. Cloud-top infrared brightness temperatures were as cold as -50ºC just southwest of Arctic Village on the 2313 UTC image — this corresponded to an altitude of 8.5 km on the 00 UTC Fairbanks rawinsonde data.

Suomi NPP VIIRS Day/Night Band (0.7 µm) images at 2131 and 2313 UTC [click to enlarge]

Suomi NPP VIIRS Day/Night Band (0.7 µm) images at 2131 and 2313 UTC [click to enlarge]

Suomi NPP VIIRS Infrared Window (11.45 µm) images at 2131 and 2313 UTC [click to enlarge]

Suomi NPP VIIRS Infrared Window (11.45 µm) images at 2131 and 2313 UTC [click to enlarge]

13-km NAM model fields (below) showed no clear signature of either a closed circulation or a discrete vorticity center — so satellite imagery was depicting the presence of an important feature that was not captured by numerical models. While the 18 UTC model run did show an area of light precipitation moving northward toward the region, the 00 UTC model run scaled back the areal coverage of this precipitation.

3-km NAM 500 hPa height, wind and absolute vorticity [click to enlarge]

3-km NAM 500 hPa height, wind and absolute vorticity [click to enlarge]

3-km NAM Mean Sea Level Pressure and 1-hour accumulated precipitation [click to enlarge]

3-km NAM Mean Sea Level Pressure and 1-hour accumulated precipitation [click to enlarge]

Satellite signatures of the Notre Dame Cathedral fire in Paris, France

April 15th, 2019 |

EUMETSAT Meteosat-11 Shortwave Infrared (3.92 µm) images, with airport identifiers plotted in red [click to play animation | MP4]

EUMETSAT Meteosat-11 Shortwave Infrared (3.92 µm) images, with airport identifiers plotted in red [click to play animation | MP4]

The subtle thermal anomaly (or “hot spot”) from the Notre Dame Cathedral Fire was evident in 4.8-km resolution (at satellite nadir) EUMETSAT Meteosat-11 Shortwave Infrared (3.92 µm) imagery (above) as a cluster of brighter yellow pixels just north of Paris Orly International Airport (LFPO) near the center of the images on 15 April 2019.

The fire reportedly began around 1650 UTC; the maximum 3.92 µm brightness temperature sensed by Meteosat-11 was 284.5 K (11.35ºC) on the 1745 UTC image, not long after the fire had spread to the large spire of the cathedral (Meteosat-11 was actually scanning the Paris area at 1756 UTC, since the Meteosat Second Generation satellites scan each Full Disk from south to north). Clouds approaching from the west began to mask the fire signature at 1930 UTC.

Even though high clouds had begun to move overhead, a thermal signature (darker black pixel) could still be seen in 1-km resolution Metop-A and Metop-C Shortwave Infrared (3.75 µm) images at 2009 and 2048 UTC (below, courtesy of William Straka, CIMSS). The maximum 3.75 µm brightness temperature detected by Metop was 291.1 K (18.0ºC).

Metop-A and Metop-C Shortwave Infrared (3.74 µm) images at 2009 and 2048 UTC [click to enlarge]

Metop-A and Metop-C Shortwave Infrared (3.75 µm) images at 2009 and 2048 UTC [click to enlarge]

GOES-17 Loop Heat Pipe Effects on 14 April 2019

April 15th, 2019 |

16-Panel GOES-17 Full-Disk Advanced Baseline Imager (ABI) Imagery, 0010 – 2340 UTC on 14 April 2019 (Click to play mp4 animation)

Solar illumination of the GOES-17 Advanced Baseline Imagery (ABI) was at a maximum on 14 April, so that the effects of the Loop Heat Pipe that is not operating at its designed capacity (and therefore cannot keep the ABI detectors as cold as preferred) were at their worst. (This image of the predicted Focal Plane Temperature from this blog post shows the mid-April peak to be warmest). The animation above shows that only Band 14 (11.2 µm) was able to send a useable signal during the entire night. The Band 14 data are biased, however. The image below compares GOES-16 and GOES-17 temperatures over a region on the Equator (here, from the GOES-17 perspective, and here, from the GOES-16 perspective, from this website) equidistant between the two sub-satellite points (75.2º W for GOES-East, 137.2º W for GOES-West).  GOES-17 slowly cools relative to GOES-16 (assumed to be ‘truth’) before undergoing a series of cold/warm/cold oscillations relative to GOES-16.   So while a useful signal is preserved, algorithms that rely on threshold temperatures, or brightness temperature difference fields (such as the 3.9 µm – 11.2 µm Brightness Temperature Difference), would likely produce unexpected results.

ABI Band 14 (11.2 µm) temperature differences, GOES-17 – GOES-16 on 14 April 2019 (Click to enlarge). Representative Band 14 images during a time largely unaffected by Loop Heat Pipe issues are shown at top.

 

Loop Heat Pipe issues should slowly subside over the coming weeks.  ‘Predictive Calibration’ is likely to be in place by the time the (Northern Hemisphere) Autumnal Equinox arrives.  This will extend the useful signal for the ABI channels.  One might even conclude that this current episode will have the worst impact on useable imagery from the ABI.