A comparison of McIDAS images of 1-km resolution GOES-13 (GOES-East) Visible (0.63 µm) and 4-km resolution Shortwave Infrared (3.9 µm) data (above) revealed a number of ship tracks in the marine boundary layer stratocumulus cloud deck over the western Atlantic Ocean on 13 April 2013. Aerosols from the exhaust of ships causes a “cloud seeding effect”, which results in a higher concentration of smaller cloud droplets compared to the surrounding undisturbed cloud deck. These smaller cloud droplets are more effective reflectors of sunlight, resulting in a warmer (darker gray) signature on the 3.9 µm imagery.

A more detailed view of the ship tracks was provided using AWIPS images of 1-km resolution MODIS Visible (0.65 µm), Shortwave Infrared (3.7 µm) and Infrared Window (11.0 µm) images (below). Note that the ship track features could not be identified on the 11.0 µm image, since the cloud-top infrared brightness temperatures were essentially the same over that region.

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A late-season winter storm brought heavy snowfall to much of the central US — Rapid City, South Dakota (station identifier RAP) set records that included 20.0 inches on 09 April 2013 (most snowfall on a calendar day) and 28.2 inches on 08 April – 10 April (greatest muti-day snowfall). McIDAS images of 4-km resolution GOES-13 6.5 µm water vapor channel data covering the 08 April – 10 April period (above; click image to play animation; also available as a QuickTime movie) showed the development of several convective elements that helped to enhance snowfall rates as they moved northward across the region on 09 April, as well deformation bands that formed as the circulation of the upper-level low slowly migrated over western South Dakota and western Nebraska on 10 April.

An AWIPS image of 1-km resolution MODIS 0.65 µm visible channel data (below) showed some of the convective elements responsible for producing a period of heavy snow at Rapid City on 09 April. Large thunderstorms were also seen at the time over notheastern Nebraska and southeastern South Dakota.

A surface meteorogram (below) shows the conditions at Rapid City Regional Airport during the 08-10 April period.

===== 12 April Update =====

Widespread cloudiness masked a good view of the areal extent of the resulting snow cover across South Dakota, but farther to the south over Nebraska and far northern Kansas an AWIPS comparison of 1-km resolution Suomi NPP VIIRS 0.64 µm visible channel and false-color Red/Green/Blue (RGB) images (below) showed interesting detail in a number of mesoscale bands of snow cover. Snow appears as white on the visible image, and as darker shades of red on the RGB image; supercooled water droplet clouds are lighter shades of white, while ice crystal clouds appear as shades of pink on the false-color image.

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A comparison of AWIPS images of Suomi NPP VIIRS 0.64 µm visible channel and false-color Red/Green/Blue (RGB) images (above) showed the extent of ice in the Bering Sea (snow and ice appear as shades of red in the RGB image), along with curved bands of cloud streets due to cold air advection as arctic high pressure moved toward the area from Siberia on 08 April 2013.

Consecutive VIIRS 0.64 µm visible channel images from 22:39 on 07 April and 00:21 UTC on 08 April (below) showed the amount of sea ice motion in the short time span (less than 2 hours) between the 2 images.

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Continuing on the theme of the previous blog post, AWIPS images of Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) data (above) showed another large mesoscale convective system over the eastern Gulf of Mexico at 06:45 UTC or 4:45 AM local time (06 UTC surface analysis) on 05 April 2013. The Day/Night Band revealed numerous bright streaks denoting cloud tops illuminated by lightning activity — and the coldest cloud-top infrared brightness temperature was -89C (darker violet color enhancement).

Overlays of conventional lightning data (below) showed that there were 1493 negative and 180 positive cloud-to-ground strikes detected within a 15-minute period across that region.

One subtle feature seen on the VIIRS Day/Night Band image was the presence of concentric waves propagating northward through eastward away from the core of the convective complex (below). These features were “mesospheric airglow waves” — essentially “night glow” emitted from a variety of high-altitude (80-105 km) gases (primarily the sodium layer) near the mesopause — that were forced by the intense convective complex in the troposphere. Note that these mesospheric airglow waves do not show up on the corresponding VIIRS Infrared Window image.

The signature of mesospheric airglow waves was also seen on the previous night (below), again forced by intense convection in the Gulf of Mexico.

Thanks to Steve Miller (CIRA) for offering an explanation of these wave features, and providing the reference “Suomi satellite brings to light a unique frontier of nighttime environmental sensing capabilities”

===== 08 April Update =====

A few days later, yet another example of mesospheric airglow waves was seen in Day/Night Band imagery — but in this case, the waves were forced not by deep tropospheric convection, but by the interaction of strong winds with the rugged topography of the Southwest US. The flow throughout the depth of the troposphere was quite strong as a 120-knot jet upper-tropospheric jet streak was moving southward along the west side of a trough that was deepening over the western US on 08 April 2013. A series of mesospheric airglow waves could be seen traveling southeastward across the Gulf of California and adjacent portions of Baja California and Mexico at 09:10 UTC or 2:10 AM local time (below). Again, note that there was no wave signature apparent on the corresponding VIIRS Infrared Window image.

During the subsequent daytime hours, GOES-15 (GOES-West) and GOES-13 (GOES-East) Water Vapor (6.5 µm) images (below) revealed a complex pattern of mountain waves across the region — surface wind gusts were as high as 88 mph in California, 70 mph in Nevada, and 63 mph in Arizona.

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