GOES-13 6.5 µm water vapor channel images (click to play animation)

A large mid-latitude cyclone exhibited explosive development over the North Atlantic Ocean (south of Greenland) on 13 October 2014. This storm produced hurricane-force winds, according to surface analyses from the Ocean Prediction Center. GOES-13 6.5 µm water vapor channel images (above; click image to play animation; also available as an MP4 movie file) showed the intrusion of very dry air (yellow to orange color enhancement) associated with the approach of a potential vorticity anomaly early in the day, followed by the the cyclone wrapping up after it reached the occluded phase during the afternoon hours.

GOES-13 0.63 µm visible channel images (below; click image to play animation) revealed the very pronounced signature of cold air advection from the western to the southern quadrants of the storm, in the form of open-cell and closed-cell convective clouds.

GOES-13 0.63 µm visible channel images (click to play animation)

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GOES-13 0.63 µm Visible Imagery, 13 October (click to play animation)

Tropical Storm Gonzalo is moving through the Leeward Islands today, October 13. The animation above shows the visible imagery from GOES-13. Slow strengthening of the storm is indicated. Eye formation may be occurring in the later part of the animation. (Note that imagery over the Leeward Islands is available only every half-hour because of an RSO called for GOES-13 associated with severe weather; in normal operations, the Caribbean is scanned every 15 minutes as discussed here).

Suomi NPP Day Night Band visible (0.70 µm) and 11.35 µm infrared imagery at 0456 UTC, 13 October (click to enlarge)

Suomi NPP overflew the developing system at 0456 UTC on 13 October, and a toggle between the Day Night Visible Band and the 11.35 infrared imagery (courtesy of W. Straka, CIMSS) is above. Cold cloud tops associated with numerous overshooting tops are obvious. (Click here for a graph of the number of overshoots as detected from GOES-13 as a function of time)

Saharan Air Analysis from Meteosat, 1200 UTC 12 October through 1200 UTC 13 October (click to play animation)

The Atlantic Tropical Storm season has been comparatively quiet this year in part because of strong Saharan Air Layer events (discussed in Blog Posts here and here). When this dry air that originates over the Sahara moves over the tropical Atlantic, the convection necessary for tropical storm formation is suppressed. Lately, however, Saharan Air Layer events have decreased, and tropical systems are developing in the tropical Atlantic. The 24-hour animation above (from CIMSS Tropic Web site) shows very little Saharan Air over the Atlantic, and two named storms — Fay (at 50 º W on the northern border of the domain) and Gonzalo (approaching the Leeward Islands) — are present. In addition, a strong tropical wave is moving across the tropical Atlantic at 15 º N, 40 º W. MIMIC Total Precipitable Water animations (below) also show a moist environment over much of the tropical Atlantic.

MIMIC Total Precipitable Water for the 72 hours ending 1200 UTC 13 October 2014 (click to enlarge)

GOES-13 10.8 µm Infrared Imagery every six hours from 2045 UTC 12 October through 1445 UTC 13 October (click to play animation)

A storm-centered animation of the 10.8 µm imagery from GOES-13, above, shows the gradual organization of Gonzalo as it moved towards the Leeward Islands. In particular, between 0845 and 1445 UTC on 13 October (the last two images in the 4-frame loop), a central dense overcast (CDO) has formed, and outflow to the east has become established. Gonzalo’s projected path (see below, from here) is over very warm water, and through an atmosphere with little shear; slow strenghtening is expected. See the National Hurricane Center website for more details, including warnings for the Leeward Islands.

Analyses of Sea Surface Temperatures and Shear, 1200 UTC 13 October 2014 (click to enlarge)

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Suomi NPP 0.7 µm Day Night Band imagery at 0907 and 1048 UTC over central California with surface observations of ceilings and visibilities (click to enlarge)

The Suomi NPP VIIRS Day Night Band during a Full (or near-Full) Moon yields striking visible imagery at night because of abundant reflected lunar illumination. Sequential orbits along the west coast of the Pacific on the morning of 10 October showed the penetration of coastal stratus and fog inland at two times (click here for the images above without the surface observations). A similar case study from 9 October is shown here. The slow inland penetration of stratus/fog is captured by the scenes: tendrils of fog extend up small valleys along the edge of the Salinas Valley, for example, and the fog extends farther down the valley at 1048 UTC. Similar expansion of fog occurs over Sonoma Valley north of San Francisco Bay.

Careful inspection of the imagery shows parallel lines along the western edge at 0907 UTC and along the eastern edge at 1048 UTC. In addition, city lights and topographic features are displaced somewhat along the eastern edge of the 1048 UTC image. These are all artifacts of the VIIRS instrument viewing geometry (that is, parallax) and post-processing that is necessary near the edges to maintain high-resolution imagery there.

A toggle between the corresponding VIIRS 11.45 µm – 3.74 µm infrared brightness temperature difference images (commonly referred to as the “fog/stratus product”), below, similarly shows gradual expansion of water-based clouds between 0907 and 1048 UTC. There are also image features, color enhanced as black, that suggest very thin cirrus is moving over the coast. These clouds are thin enough that they cannot be discerned in the Day Night Band imagery, but their presence nevertheless inhibits the detection of low clouds in places, such as over the southernmost part of the Salinas Valley at 1048 UTC.

Suomi NPP Brightness Temperature Difference (11.45 µm – 3.74 µm) Imagery at 0907 and 1048 UTC over central California (click to enlarge)

Suomi NPP 0.7 µm visible Day Night Band imagery at 0907 and 1048 UTC over Washington State with surface observations of ceilings and visibilities (click to enlarge)

The image toggle above shows similar features over Washington State. Fog/stratus tendrils move up river valleys in the ~90 minutes between the two polar-orbiting satellite passes, and areas of fog increase in size. (click here for the same images without observations). Because the first image is very near the edge of the VIIRS instrument scan swath, there is also a shift in city lights and some geographic features, again an artifact of scanning geometry (parallax) and the post-processing to maintain high-resolution imagery at the scan edges.

Suomi NPP Brightness Temperature Difference (11.45 µm – 3.74 µm) Imagery at 0907 and 1048 UTC over Washington State (click to enlarge)

The IR brightness temperature difference product over Washington, above, also shows evidence of a slow increase in the areal coverage of fog/stratus near the coast. The effects of limb brightening are also present in the first image. When a satellite scans near the edge of its domain, the path from the point on the Earth to the satellite traverses more of the upper atmosphere, and a colder sensed temperature results. This effect is wavelength-dependent. For example, at one point (47º N, 125º W) in the stratus (with fairly uniform temperature) off the west coast of the Washington, in the stratus (which should have a fairly constant temperature), brightness temperatures were about 1º C cooler in 11.35 µm imagery, but closer to 2.5º C cooler in the 3.74 µm imagery. Hence, the brightness temperature difference signal is larger at 0906 UTC.

Both brightness temperature difference fields show signals over dry land that are related to emissivity differences in the soils. These occur over central Washington, above and over Nevada in the images centered over California.

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A “Blood Moon” total lunar eclipse occurred between 09:15 UTC and 12:34 UTC on 08 October 2014. One effect of this eclipse can be seen in a comparison of nighttime “during eclipse” and “after eclipse” Suomi NPP VIIRS 0.7 µm Day/Night Band images (above). The 11:33 UTC “during eclipse” Day/Night Band image appears somewhat dim and washed out, due to limited illumination by only red sunlight being refracted by the Earth’s atmosphere into the eclipse shadow. Less than 2 hours later, the 13:14 UTC Day/Night Band image appears much more bright with crisp cloud feature details, due to an abundance of illumination from the Full Moon.

A few hours after sunrise in North America, a portion of the Moon was captured on the GOES-13 (GOES-East) 0.63 µm visible channel image at 16:30 UTC (below). Note how the edges of the Moon appear slightly jagged, caused by the fact that it was moving (setting) behind the Earth as the GOES-13 imager instrument was scanning horizontally step-wise from north to south. In addition, at the point where the edge of the Moon meets the edge of the Earth, there is a “lensing effect” where the Earth’s atmosphere is refracting light from the Moon and creating the illusion of a curved wedge of dark space that is visible within the atmosphere.

Speaking of sunrise, an interesting aspect of this lunar eclipse was that it was a rare “selenelion”, when the rising sun in the east could be seen at the same time as the non-eclipsed portion of the setting moon in the west (Space.com article). This selenelion was captured at 12:03 UTC or 7:03 am local time by the east-looking and west-looking rooftop cameras on the Space Science and Engineering Center building (below; image captures courtesy of John Lalande, SSEC).

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