Using GOES-16 to view clouds over snow

May 1st, 2017 |

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

A late-season snow storm dropped a band of heavy snow over Colorado, western Kansas and western Nebraska on 29-30 April 2017. In the visible image above from sunrise on 1 May 2017, it is difficult to guess where the cloud features sit on top of the snow (Click here for a visible image with a map), even with the knowledge that they are casting shadows in this early morning imagery. GOES-16 includes a 1.61 µm channel, however; radiation at that wavelength is absorbed strongly by ice — either in the form of cirrus clouds, or snow, so that reflectance is small over ice features. The toggle below between the 1.61 µm “Snow/Ice” Channel and the 0.64 µm “Red Visible” channel shows ice and snow as dark. Clouds that are made up of water droplets are highly reflective in the 1.61 µm and in the 0.64 µm channels; such water clouds (there are only a few of them!) show up as very bright against the dark background of snow in the 1.61 µm channel.

Note in the toggle above that shadows are much darker in the 1.61 µm channel. Why?

Atmospheric scattering is stronger at shorter wavelengths in the atmosphere; there is more scattering of 0.64 µm radiation than of 1.61 µm radiation. In the shadow regions, more 0.64 µm radiation than 1.61 µm is being scattered back towards the satellite for detection. Shadows in the 0.47 µm “Blue Visible” band should be even less distinct. Non-annotated versions of imagery are available here for 0.64 µm and here for 1.61 µm.

During the subsequent late morning and early afternoon hours, the edges of the long swath of snow cover were seen to melt quickly — due to heating from the high May sun angle — on GOES-16 Visible (0.64 µm) and Snow/Ice (1.61 µm) images, below. The Snow/Ice images helped to highlight bright cumulus clouds (composed of supercooled water droplets) drifting southeastward across the snow cover.

GOES-16 Visible (0.64 µm, left) and Snow/Ice (1.61 µm, right) images [click to animate]

GOES-16 Visible (0.64 µm, left) and Snow/Ice (1.61 µm, right) images [click to animate]

Animations of GOES-16 Visible vs Snow/Ice images from the previous day (when the southwestern portion of the swath of fresh snow cover first became evidentt as clouds from the parent storm departed) are available here: Animated GIF | MP4.

Aeroflot 270 encounters severe turbulence approaching Thailand

May 1st, 2017 |

Himawari-8 Water Vapor (6.9 µm) images, with plots of turbulence intensity along the flight path [click to enlarge]

Himawari-8 Water Vapor (6.9 µm) images, with plots of turbulence intensity along the flight path [click to enlarge]

Aeroflot Flight 270 encountered severe turbulence just off the coast of Myanmar (CNN | Aviation Herald) as it was flying toward its destination of Bangkok, Thailand on 01 May 2017. According to information from FlightRadar24 (flight map) and FlightAware (flight map | flight log) the time and location of the turbulence was around 23:54-23:56 UTC, near 16.4 N latitude, 97.4 East longitude, at the cruising altitude of 35,000 feet. Himawari-8 Water Vapor (6.9m) images (above; courtesy of Sarah Griffin, CIMSS) indicated that the aircraft made a slight course correction to fly over or through a small cluster of rapidly-developing thunderstorms — this convection was the likely cause of the turbulence.

Closer views of Himawari-8 Visible (0.64 µm), Water Vapor (6.9 µm) and Infrared Window (10.4 µm) images, centered at the location of the turbulence encounter (below), showed the rapid development of individual convective elements within this cluster of thunderstorms. Cloud-top infrared brightness temperatures were around -70º C on the 01 May / 00:10 UTC image.

Himawari-8 Visible (0.64 µm, top), Water Vapor (6.9 µm, middle) and Infrared Window (10.4 µm, bottom) images [click to enlarge]

Himawari-8 Visible (0.64 µm, top), Water Vapor (6.9 µm, middle) and Infrared Window (10.4 µm, bottom) images [click to enlarge]