Tropical Storm Alberto

May 19th, 2012
AVHRR 10.8 µm, MODIS 11.0 µm, and VIIRS 11.45 µm IR images

AVHRR 10.8 µm, MODIS 11.0 µm, and VIIRS 11.45 µm IR images

The 2012 Atlantic Basin tropical cyclone season began with the formation of Tropical Storm Alberto off the coast of South Carolina on 19 May 2012. A sequence of AWIPS images of 1-km resolution POES AVHRR 10.8 µm, Terra/Aqua MODIS 11.0 µm, and Suomi NPP VIIRS 11.45 µm IR images (above) showed the growth of deep convecion associated with Alberto as the system moved southwestward — cloud top IR brightness temperatures were as cold as -72º C on the MODIS image at 16:03 UTC.

A comparison of the 18:27 UTC 1-km resolution Suomi NPP VIIRS 11.45 µm IR image with the 18:15 UTC 4-km resolution GOES-13 10.7 µm IR image (below) demonstrated the improvement in cloud top feature identification with higher spatial resolution, as well as showed the effect of parallax due to the large satellite viewing angle from GOES-13.

GOES-13 10.7 µm IR + Suomi NPP VIIRS 11.45 µm IR image

GOES-13 10.7 µm IR + Suomi NPP VIIRS 11.45 µm IR image

An animation of GOES-13 0.63 µm visible channel images from the CIMSS Tropical Cyclones site (below) showed the development of a more organized cloud structure during the day. In addition, a 21 UTC ship report near the center of Alberto noted wind gusts to 65 knots, which promted NHC to issue an update to note an increase in intensity.

GOES-13 0.63 µm visible channel images + Ship reports

GOES-13 0.63 µm visible channel images + Ship reports

========== 20 May Update ==========

An AWIPS night-time image of the Suomi NPP VIIRS 0.7 µm “Day/Night Band” (below) revealed some of the cloud structure associated with Tropical Storm Alberto at 06:45 UTC (2:45 am local time). Given that there was a “New Moon” phase at this time, not a great deal of reflected light was avaiable to allow the Day/Night Band imagery to show more cloud detail.

Lights from cities and towns across the far southeastern US could also be seen in the Day/Night Band image (although some of the urban area light signatures were attenuated somewhat by overhead cloud cover).

Suomi NPP VIIRS 0.7 µm Day/Night Band image

Suomi NPP VIIRS 0.7 µm Day/Night Band image

Posted in AVHRR, GOES-13, MODIS, POES, Suomi NPP, Tropical cyclones, VIIRS | No Comments »

Pyrocumulus clouds from Sunflower Fire in Arizona

May 15th, 2012
GOES-15 (left) and GOES-13 (right) 0.63 µm visible channel images (click image to play animation)

GOES-15 (left) and GOES-13 (right) 0.63 µm visible channel images (click image to play animation)

 

McIDAS images of GOES-15 (GOES-West) and GOES-13 (GOES-East) 0.63 µm visible channel data (above; click image to play animation) revealed the large smoke plume associated with the “Sunflower Fire” that was burning near Payson, Arizona on 15 May 2012. Note toward the end of the animation the appearance of pyrocumulous clouds with overshooting tops over the fire source region. Due to the different satellite viewing angles, the overshooting tops were brightly illuminated on the GOES-15 images, while casting a distinct shadow onto the top of the cloud/smoke plume on the GOES-13 images. Photos of the Sunflower fire from the ground can be seen on the Weather Underground site. Other fires were also burning at that time in Arizona, including the “Gladiator Fire“  located to the northwest of the Sunflower fire.

The GOES-13 satellite was placed into Rapid Scan Operations (RSO) mode later in the day, providing images as frequently as every 5-10 minutes (compared to the routine 15-minute image interval with GOES-15).

Posted in Fire detection, GOES-13, GOES-15 | No Comments »

GOES-13 Band Co-Registration

May 15th, 2012
GOES-13 enhanced Fog Product (10.7 µm - 3.9 µm)

GOES-13 enhanced Fog Product (10.7 µm - 3.9 µm)

On the morning of May 14th, a clear morning, the GOES-13 Legacy “Fog Product” that exploits the brightness temperature differences observed by the GOES Imager at 3.9 µm and 10.7 µm, which differences arise because of wavelength-dependent emissivity differences in water clouds, showed fog first on the eastern shores of Lakes Huron and Michigan (at 1015 UTC), and then on the western shores of Lakes Huron and Michigan (at 1401 UTC, and afterwards). These returns occurred despite clear skies.

A similar effect occurred on the morning of May 15th. The image at 1015 UTC showed fog along the eastern side of the Lakes, and the image at 1255 UTC showed fog along the western side of the Lakes. (Note that more widespread mid-level clouds reduced the signal on this day). A POES Fog Product image from 1020 UTC on May 15th (link) did not show the fog signal along the shoreline.

GOES-13 10.7 µm and 3.9 µm channel images (click image to toggle between images)

GOES-13 10.7 µm and 3.9 µm channel images (click image to toggle between images)

The image toggle above shows highly magnified imagery over Lake Michigan at 1255 UTC on May 15 2012. There is an apparent 1-pixel shift between the 3.9 µm and the 10.7µm imagery. If the start element of the image is shifted by 1 infrared pixel, then the toggle between the two images contains no shift. The legacy ‘Fog Product’ is therefore diagnosing fog because the 3.9 µm pixel is over water (cold) and the 10.7 µm pixel is over land (warm). When the 1-pixel shift is rectified, both pixels are either over water, or both over land.

Scientists at SSEC are working to find the source of this difference.

Posted in General interpretation, GOES-13 | No Comments »

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