Eddy in Lake Michigan

April 8th, 2017 |

GOES-16 Visible (0.64 µm) images, with hourly surface and ship reports plotted in yellow [click to play animation]

GOES-16 Visible (0.64 µm) images, with hourly surface and ship reports plotted in yellow [click to play animation]

** The GOES-16 data posted on this page are preliminary, non-operational data and are undergoing testing. **

GOES-16 Visible (0.64 µm) images (above) revealed the presence of an eddy in the high-turbidity nearshore waters of southern Lake Michigan on 08 April 2017. The animation was created using 5-minute “CONUS” Sector images; an animation using 1-minute Mesoscale Sector images is available here.

A sequence of Terra and Aqua MODIS true-color Red/Green/Blue (RGB) images viewed using RealEarth (below) showed that the eddy began to develop on 07 April.

Terra and Aqua MODIS true-color RGB images from 07 and 08 April [click to enlarge]

Terra and Aqua MODIS true-color RGB images from 07 and 08 April [click to enlarge]

The Split Window Difference as a measurement of Atmospheric Moisture

April 7th, 2017 |

GOES-16 Split Window Difference (10.33 µm – 12.30 µm) with 850-mb Dewpoint Temperatures from the Rapid Refresh overlain (Click to enlarge)

GOES-16 data posted on this page are preliminary, non-operational data and are undergoing testing.

GOES-16 includes both a clean infrared window (10.33 µm) and a so-called ‘dirty’ infrared window channel (12.30 µm). The clean infrared window is in a part of the electromagnetic spectrum where there is very little absorption of energy by water vapor; in the dirty infrared window, modest amounts of water vapor absorption occur. The brightness temperature difference, nicknamed the Split Window Difference (SWD for short), can highlight differences in moisture in clear skies.

The toggle above shows the SWD (10.33 µm – 12.30 µm) at 1430 UTC on 7 April 2017. A pronounced gradient stretches southeast to northwest from Louisiana to northeast Kansas and extreme southeastern Nebraska.  Values over Missouri, for example, are around 0.9-1.0 K vs. 1.7-2.2 K over Oklahoma.  The gradient in the brightness temperature difference aligns very neatly with the 850-mb dewpoint temperature from the Rapid Refresh. You can use this product to monitor moisture return from the Gulf of Mexico.

AWIPS Note: The Default enhancement in AWIPS for the Split Window Difference, shown above, does not include large enough negative values. The Split Window Difference value can exceed -5 K in regions of dust. See this link for a different enhancement for this case with a wider range of temperature differences. A similar image uses the mean 1000-700 mb dewpoint temperature rather than values from the single 850-mb level.

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An animation of this imagery (not shown) shows general increases in the SWD values with time.  A consistent signal of moisture will be present only if the temperature decreases with height in the moist layer (that is — if there is no inversion).  An increase in the SWD does not necessarily show an increase in moisture — it can, rather, signify an increase in near-surface temperature (for more information, consult this article by Lindsey et al.). The gradient in the field can remain, however, as in this example.

The Split Window Difference field does an exemplary job of detecting contrails over the southern Plains. The toggle below shows that the SWD signal of cirrus is more distinct than in the 1.378 µm Cirrus Channel! (Thanks to Matt Bunkers of WFO Rapid City for noting this!)

Cirrus Channel (1.378 µm ) and Split Window Difference (10.33 µm – 12.30 µm) at 1607 UTC on 7 April 2017 (Click to enlarge)

(Note that the SWD was something that was available from GOES-8 through GOES-11. Link)

Thermal signature of missile strikes at Shayrat Air Base in Syria

April 7th, 2017 |

EUMETSAT Meteosat-10 Shortwave Infrared (3.9 µm) images, with hourly surface reports; Shayrat Air Base is located at the center of the cyan circle [click to play animation]

EUMETSAT Meteosat-10 Shortwave Infrared (3.9 µm) images, with hourly surface reports; Shayrat Air Base is located at the center of the cyan circle [click to play animation]

EUMETSAT Meteosat-10 Shortwave Infrared (3.9 µm) images (above) showed the thermal signature or “hot spot” (darker black pixels) of fires resulting from US missile strikes at Syria’s Shayrat Air Base on 07 April 2017. The warmest infrared brightness temperature was 300.22 K on the 0030 UTC image (the SEVIRI instrument was scanning the Shayrat region at 00:40 UTC), which was about 25 K warmer than the surrounding background temperatures; though the fires were much smaller than the nominal 3 km spatial resolution of the 3.9 µm detector, the sub-pixel effect enables a signal of the fire radiative power to be registered.

A toggle between the 0015 and 0030 UTC images displayed using McIDAS-V (below; courtesy of William Straka, SSEC) highlights the appearance of the thermal signature at Shayrat Air Base. Two persistent hot spots located northeast of Palmyra could have been due to refinery or mining activities.

EUMETSAT Meteosat-10 Shortwave Infrared (3.9 µm) images at 0015 and 0030 UTC [click to enlarge]

EUMETSAT Meteosat-10 Shortwave Infrared (3.9 µm) images at 0015 and 0030 UTC [click to enlarge]

Using GOES-16 visible and near-infrared imagery to diagnose areas of flooding

April 6th, 2017 |

Flood Warnings (green) in effect at 7:43 pm CDT on 06 April 2017 [click to enlarge]

Flood Warnings (green) in effect at 7:43 pm CDT on 06 April 2017 [click to enlarge]

** The GOES-16 data posted on this page are preliminary, non-operational data and are undergoing testing. **

Following several days of heavy rainfall across northwestern Missouri, Flood Warnings remained in effect for many areas on 06 April 2017 (above).

A comparison of GOES-16 Visible (0.47 µm and 0.64 µm) and Near-Infrared (0.86 µm and 1.61 µm) images at 1507 UTC (below) shows that the Vegetation and Snow/Ice spectral bands are useful for identifying areas of swollen rivers and adjacent flooded lands (since water appears darker on those 2 images).

GOES-16 Visible (0.47 µm and 0.64 µm) and Near-Infrared (0.86 µµ and 1.61 µm) images [click to enlarge]

GOES-16 Visible (0.47 µm and 0.64 µm) and Near-Infrared (0.86 µµ and 1.61 µm) images [click to enlarge]