South Sandwich Islands lee waves

January 16th, 2021 |

GOES-16 "Red" Visible (0.64 µm) images [click to play animation | MP4]

GOES-16 “Red” Visible (0.64 µm) images [click to play animation | MP4]

GOES-16 (GOES-East) “Red” Visible (0.64 µm) images created using Geo2Grid (above) revealed long trails of lee waves extending northeastward from many of the South Sandwich Islands on 16 January 2021. These lee waves were generated by strong southwesterly winds within the marine boundary layer interacting with the topography of the islands — wind speeds had increased across that portion of the South Atlantic Ocean, in response to the tight pressure gradient between high pressure north of the islands and a deepening area of low pressure southeast of the islands (MSLP analyses).

A toggle between two NOAA-20 VIIRS True Color RGB images as viewed using RealEarth (below) provided a higher-resolution view of the lee waves extending from the island chain.

NOAA-20 VIIRS True Color RGB images [click to enlarge]

NOAA-20 VIIRS True Color RGB images [click to enlarge]

Many of these islands contain active volcanoes, which frequently produce plumes (which are primarily comprised of steam). A closer look at the lee waves emanating from one of the northernmost islands (below) appeared to suggest that a brighter white volcanic plume existed within the train of waves.

NOAA-20 VIIRS True Color RGB images [click to enlarge]

NOAA-20 VIIRS True Color RGB images [click to enlarge]

GOES-R Fog/Low Stratus products are in RealEarth

January 5th, 2021 |

RealEarth instance of 1401 UTC GOES-16 IFR Probability fields, 5 January 2021, over the Mississippi River Valley (click to enlarge)

GOES-16 versions of the GOES-R Fog/Low Stratus products, such as IFR/Low IFR/Marginal VFR Probability fields, and GOES-R Cloud Thickness, are now available in RealEarth. These products are still available at the CIMSS GEOCAT site as well (link, for an image like this), but RealEarth offers pan, zoom and overlay capabilities. The RealEarth image from 1401 UTC on 5 January is shown above; the same time image from AWIPS is shown below. This link shows a more recent image in RealEarth.

AWIPS Screen Capture of IFR Probability and surface observations of ceilings and observations, 1401 UTC on 5 January 2020 (Click to enlarge)

GOES-17 IFR Probability will become available once that product is deemed Operational. Additional information on IFR Probability products is available at the Fog Blog.

The breakup of Iceberg A68a

December 26th, 2020 |

GOES-16 “Red” Visible (0.64 µm) images [click to play animation | MP4]

GOES-16 “Red” Visible (0.64 µm) images [click to play animation | MP4]

A sequence of GOES-16 (GOES-East) “Red” Visible (0.64 µm) images covering the 14 December – 26 December 2020 period (above) showed that after Iceberg A68a encountered the more shallow continental shelf waters southwest of South Georgia island earlier in the month (NOAA-20 True Color RGB images, 02-13 December), the large iceberg then began to move south-southeastward, shear apart and release 3 smaller orphan icebergs (in addition to widespread small ice floes).

A toggle between NOAA-20 VIIRS True Color RGB images on 23 December and 25 December viewed using RealEarth (below) provided a higher-resolution view of the numerous small ice floes that resulted from the iceberg fracturing process.

NOAA-20 VIIRS True Color RGB images [click to enlarge]

NOAA-20 VIIRS True Color RGB images [click to enlarge]

Solar eclipse shadow moving across South America

December 14th, 2020 |

GOES-16 “Red” Visible (0.64 µm), Shortwave Infrared (3.9 µm) and

GOES-16 “Red” Visible (0.64 µm), Shortwave Infrared (3.9 µm) and “Clean” Infrared Window (10.35 µm) images [click to play animation | MP4]

1-minute Mesoscale Domain Sector GOES-16 (GOES-East) “Red” Visible (0.64 µm), Shortwave Infrared (3.9 µm) and “Clean” Infrared Window (10.35 µm) images (above) showed the passage of a total solar eclipse shadow across parts of Chile and Argentina, along with the land surface thermal response due to the interruption of incoming solar radiation. In areas of Argentina beneath the path of totality, the infrared brightness temperature of the land surface decreased by as much as 20-30ºC within the umbral shadow.

A larger-scale view of the path of the eclipse shadow was provided by GOES-16 CIMSS Natural Color RGB images (below).

GOES-16 CIMSS Natural Color RGB images [click to play animation | MP4]

GOES-16 CIMSS Natural Color RGB images [click to play animation | MP4]

GOES-16 Near-Infrared “Vegetaton” (0.86 µm) images (below) highlighted an advantage of that spectral band — namely, brighter surface values over land (due to the higher reflectivity of vegetation at that wavelength), providing more contrast between the land surface and the darker eclipse shadow. The 0.86 µm band is also used to simulate a “green” component for RGB images such as the CIMSS “Natural Color” product.

GOES-16 Near-Infrared

GOES-16 Near-Infrared “Vegetaton” (0.86 µm) images (credit: Tim Schmit, NOAA@CIMSS) [click to play animation | MP4]

A closer look at the eclipse shadow passage using 1-minute 0.86 µm imagery is shown below (with the corresponding CIMSS Natural Color RGB images here).

GOES-16 Near-Infrared "Vegetaton" (0.86 µm) images (credit: Tim Schmit, NOAA@CIMSS) [click to play animation | MP4]

GOES-16 Near-Infrared “Vegetaton” (0.86 µm) images (credit: Tim Schmit, NOAA@CIMSS) [click to play animation | MP4]

In a comparison of GOES-16 “Blue” Visible (0.47 µm), “Red” Visible (0.64 µm), Near-infrared “Vegetation” (0.86 µm), CIMSS “Natural Color” RGB and Rayleigh-corrected “True Color” RGB images (below), it can be seen that the Rayleigh-corrected “True Color” is not optimal for displaying features such as solar eclipse shadows (due to over-saturation).

GOES-16

GOES-16 “Blue” Visible (0.47 µm), “Red” Visible (0.64 µm), Near-infrared “Vegetation” (0.86 µm), CIMSS “Natural Color” RGB and Rayleigh-corrected “True Color” RGB mages (credit: Tim Schmit, NOAAf@CIMSS) [click to enlarge]

Incidentally, although the path of totality passed to the north, some reduction of incoming sunlight was apparent over the A68a iceberg (located just southwest of South Georgia island) on GOES-16 Visible images created using Geo2Grid (below).

GOES-16 "Red" Visible (0.64 µm) images [click to play animation | MP4]

GOES-16 “Red” Visible (0.64 µm) images [click to play animation | MP4]

NOAA-20 VIIRS True Color RGB images viewed using RealEarth (below) showed views before and during the time of closest passage of the eclipse shadow.

NOAA-20 VIIRS True Color RGB images [click to enlarge]

NOAA-20 VIIRS True Color RGB images [click to enlarge]

Other blog posts that show solar eclipse shadows can be seen here.