VIIRS views of the surface and atmosphere, late September 2020 version

September 24th, 2020 |

VIIRS True-Color imagery on 02 and 22 September 2020 (Click to enlarge). Data from the VIIRS Today website

VIIRS True-Color imagery taken from the VIIRS Today website, above, shows the reddening/yellowing of trees over the upper midwest between 2 September and 22 September 2020. The inexorable slip into autumn and winter is ongoing.

Early in the morning on 24 September, Direct Broadcast NOAA-20 data downloaded at CIMSS and processed with CSPP showed an extensive aurora over much of Canada. (These data are available from the Direct Broadcast ftp site: link; direct link to the NOAA-20 data used below: link — note that this direct link is ephemeral and will disappear after about a week). The Day Night Band imagery is toggled with 11.45 µm infrared imagery.

NOAA-20 remapped VIIRS Day Night Band visible (0.7 µm) imagery and infrared 11.45 µm imagery, 0804 UTC on 24 September 2020

ACSPO Lake Surface Temperatures over the Great Lakes

September 23rd, 2020 |

Great Lakes lake surface temperatures, 0735 UTC on 23 September 2020, as well as zoomed-in views of the individual lakes (Click to animate)

Suomi-NPP’s descending pass at ~0730 UTC (shown here, from this site), had an ideal path — moving south from far eastern Upper Michigan to western Lower Michigan — to view all five Great Lakes.  Sprawling High Pressure and the attendant clear skies meant that a good basin wide view of the lake temperatures was observed, as shown above. (DB imagery from this pass is also available for a short time at the CIMSS DB ftp site) These ACSPO (Advanced Clear-Sky Processor for Ocean) SST fields are available to NWS offices via LDM fields. The default color bar in AWIPS has been changed so that only temperatures between 45º F and 70º F are shown

Lake Temperatures in the imagery above range, for Lake Superior from 47.5º (east of Minnesota) to 66º (just off southwest Upper Michigan); for Lake Michigan from 57º (east of Sheboygan WI) to 67º (mid-lake, east of Chicago); for Lake Huron from 55º (in northwestern Georgian Bay and also northwestern Lake Huron) to 65º (far southern Lake Huron); for Lake Erie from 63º (western Lake Erie) to 69º (central Lake Erie); for Lake Ontario from 62º (western Lake Ontario) to 67º (eastern Lake Ontario).

This view of the Great Lakes from early in September (also from the CIMSS DB site, processed with CSPP), shows — with a color bar that ranges from 41ºF to 86ºF — much warmer water, especially in Lake Superior where the coolest mid-lake temperatures were in the mid-50s. Storms and vertical mixing since early September have cooled the surface waters. GLERL has a website that shows modeled lake surface temperatures, accessible here.

Medicane Ionas after Greece

September 21st, 2020 |

VIIRS Daily True-Color images, 18-21 September 2020 (Click to animate)

What did the Medicane that hit Greece do afterwards?  VIIRS True-color imagery, above, taken from the NASA WorldView site, show an intact feature moving along the northern coast of Africa on 20-21 September towards the Nile Delta.  The amount of cloudiness is in general declining as it moves into a drier environment.  Total Precipitable Water (TPW) from the MIMIC website shows the general drying surrounding the storm.

MIMIC hourly estimates of Total Precipitable Water from 00 UTC on 17 September to 14 UTC on 21 September 2020 (Click to animate)

Rick Kohrs, SSEC/CIMSS, supplied the True-Color multi-day animation from Meteosat-11 imagery below. (Updated on 23 September to include date annotations)

Meteorsat-11 True-Color Imagery over the Mediterranean sea, 15-21 September 2020 (Click to animate)

VIIRS Day Night Band imagery of Beta off the coast of Texas

September 21st, 2020 |

VIIRS Day Night Band Visible (0.7 µm) imagery and I05 11.45 µm imagery over the western Gulf of Mexico, 0813 UTC on 21 September 2020 (Click to enlarge)

Suomi NPP overflew Tropical Storm Beta off the coast of Texas shortly after 0820 UTC on 21 September (NPP orbits over North America on 21 September are shown below, taken from this site). Day Night band visible imagery shows the swirl of clouds at the center of the storm, off the coast of Texas south of Houston/Galveston and east of Corpus Christi. The 11.45 µm infrared imagery (created using CSPP software and the DB data at CIMSS, and available to NWS offices via an LDM feed) shows the convection that surrounds this center, and also the stronger convection over the Gulf of Mexico to the east.

Both visible and infrared imagery in this case show the storm center. That is not always the case. Sometimes the Day Night band alone identifies the storm center without ambiguity. The Day Night Band at 0813 observed no lightning. The light sources over the open Gulf of Mexico south of Louisiana are drilling platforms.

Suomi NPP Orbit Paths over North America, 21 September 2020 (Click to enlarge)

VIIRS Day Night Band Visible (0.7 µm) imagery over the eastern Gulf of Mexico at 0633 UTC on 21 September 2020 (Click to enlarge)

The Suomi NPP pass over the eastern Gulf of Mexico, above, from 06 UTC, shows one horizontal streak of brightness in the central Gulf that is a lighting bolt. The Geostationary Lightning Mapper on GOES-16 also observed lightning flashes — how do the two observations compare?

To make that comparison, it’s necessary to determine exactly when Suomi-NPP overflew the eastern Gulf, and that’s suggested in the orbital path figure above. The time stamp for satellite imagery is not the precise time that scanning occurred; historically, the nominal time of an image is the time of the first scan line in the image. For this descending Suomi NPP pass (the satellite is moving from north to south), that time stamp — 0633 UTC — occurred when Suomi NPP was far north of CONUS, north of Quebec.  (Similarly, the time of the 0813 UTC pass shown above has a time stamp when the Satellite was viewing north of Hudson Bay!  During the afternoon, the time stamp for those ascending passes (the satellite is moving from south to north) occurs when the satellite is far south of CONUS). The actual orbit path mapping suggests a scan time over the Gulf Coast at 0643 or 0644 UTC.  Toggles between the Day Night Band image with the lightning streak and the GLM 1-minute observations at 0643 UTC  and at 0644 UTC are shown below.   It appears that the 0644 UTC data better matches the Day Night band imagery, but the comparison is by no means obvious.  This bears further investigation!

VIIRS Day Night Band visible imagery and GLM Observations at 0643 UTC on 21 September 2020 (Click to enlarge)

VIIRS Day Night Band visible imagery and GLM Observations at 0644 UTC on 21 September 2020 (Click to enlarge)