GOES-13 10.7 µm IR images

McIDAS images of GOES-13 10.7 µm IR data (above) revealed a classic convective burst signature as Tropical Storm Danielle began to intensity over the middle Atlantic Ocean on 23 August 2010. The coldest cloud top IR brightness temperature during this time period was -90º C at 07:15 UTC.

UPDATE: Danielle continued to intensify during the day, becoming the second hurricane of the 2010 Atlantic Basin Season. Images from the CIMSS Tropical Cyclones site (below) showed that Danielle continued to exhibit a large, cold Central Dense Overcast (CDO) on IR imagery, with a number of overshooting tops being indicated on the IR/Water Vapor difference product. However, a well-defined closed eyewall structure could be seen on SSMI/S-16 microwave imagery.

GOES-13 IR image + GOES-13 IR/Water Vapor difference product + SSMI/S-16 microwave image

The CIMSS Deep Layer (200-850 hPa) Wind Shear product (below) showed that Danielle was within (and moving into) a very low shear environment, which was a favorable factor for further intensification. The nearly circular CDO was characteristic of tropical cyclones that are located within such a low shear environment.

GOES-13 IR image + Deep Layer Wind Shear product

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GOES-15 full disk 6.5 µm water vapor images (at 30-minute intervals)

The normal operational GOES scan schedule provides one full disk image every 3 hours — but as part of the GOES-15 NOAA Science Test, the GOES-15 satellite was placed into a mode which allowed one full disk image to be scanned every 30 minutes. McIDAS images of GOES-15 6.5 µm “water vapor channel” data (above) showed a series of these 30-minute interval full disk images during a 24-hour period during 21 August – 22 August 2010. It should be pointed out that the ABI instrument on the GOES-R satellite will provide a full disk image every 5 minutes!

The image artifacts seen moving from west to east across the northern portion of the images (from 05:15 UTC to 06:45 UTC) were due to stray light contamination. This stray light problem affects the image quality to varying degrees during the Autumn and Spring season “eclipse periods”, since the newer GOES satellites (GOES-13 through GOES-15) have larger batteries that allow them to continue to operate through the eclipse periods when the satellite is in the Earth’s shadow.

Note that some of warmest water vapor brightness temperatures (yellow to orange color enhancement) — which normally indicate areas of very dry air in the middle to upper troposphere — were found over the central US during this particular period. This region of warm/dry air showed up well on GOES-11, GOES-12, GOES-13, and GOES-15 water vapor images (below), although the signal was less obvious on the 6.7 µm GOES-11 imagery (which is a spectrally narrow water vapor channel at an 8 km spatial resolution, compared to the spectrally broad 4-km resolution channels on GOES-12 and later). Each of the water vapor images is displayed in the native projection of the particular satellite.

GOES-11, GOES-12, GOES-13, and GOES-15 water vapor images

A closer view using AWIPS images of GOES-13 6.5 µm water vapor channel data (below) showed the evolution of this feature, which was becoming warmer/drier as a middle-tropospheric ridge of high pressure was building across the region. Water vapor brightness temperatures were as warm as -9.5º C (orange color enhancement), which is very unusual to see covering such a large area over the central US.

GOES-13 6.5 µm water vapor images (with rawinsonde locations)

4-panel images displaying the 3 GOES Sounder water vapor channels (6.5 µm, 7.0 µm, and 7.4 µm) along with the standard GOES-13 imager 6.5 µm water vapor channel are shown below. The water vapor channel weighting function of each of these channels peaks at different altitudes, which is obvious by the difference in water vapor brightness temperatures on each of the images (warmer/drier areas are enhanced with yellow to red colors).

GOES Sounder and GOES Imager water vapor channel images

The GOES-13 sounder and GOES-13 imager water vapor weighting functions for Topeka, Kansas (below) indicated that the altitudes of the weighting function peaks did indeed descend from 12 UTC on 21 August to 00 UTC on 22 August as the middle troposphere became warmer/drier — but the altitudes of the various weighting function peaks were not significantly lower than those computed using the US Standard Atmosphere.

Topeka, Kansas water vapor weighting function plots (compared to US Standard Atmosphere)

The rawinsonde date from Topeka, Kansas at 12 UTC on 21 August and at 00 UTC on 22 August are shown below. While the air aloft was certainly dry, it was also quite warm at those altitudes — and the warm temperature of this mid-tropospheric air was likely contributing to the unusually warm/dry appearance on the water vapor imagery. This case helps to highlight the fact that the water vapor channels are also IR channels, so they are sensitive to temperature as well — and some of the signal of the features seen on the imagery may be due to temperature as well as moisture aloft.

Topeka, Kansas rawinsonde plots (12 UTC 21 August, 00 UTC 22 August)

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GOES-11 0.65 µm visible images

McIDAS images of GOES-11 0.65 µm visible channel data (above) revealed the southern edge of the ice in the Beaufort Sea (north of Alaska and Canada’s Yukon and Northwest Territories) on 18 August 2010.

A closer view using a 1-km resolution NOAA-18 AVHRR false color Red/Green/Blue (RGB) image (below) showed that the ice coverage was very spotty over the Beaufort Sea, even well to the north of the well-defined southern ice edge.

NOAA-18 AVHRR false color Red/Green/Blue (RGB) image

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GOES-15 0.63 µm visible images

An isolated thunderstorm over southwestern Arizona during the afternoon hours on 17 August 2010 was responsible for a report of surface winds of 79 knots (91 mph) along with 0.80 inch of rain in 45 minutes near Ajo (SPC storm reports). McIDAS images of 1-km resolution GOES-15 0.63 µm visible channel data (above) showed the rapid development of this thunderstorm (along with several other storms across Arizona) — the time and location of the surface wind gust is annotated as “G79” on the 20:30 UTC image.

GOES-15 is currently providing imagery during its Post Launch Science Test; real-time GOES-15 imagery is available for viewing on the SSEC Geostationary Image Browser.

The corresponding 4-km resolution GOES-15 10.7 µm IR images (below) revealed that cloud top temperatures quickly cooled to -60º C and colder (red color enhancement).

GOES-15 10.7 µm IR images

An AWIPS image of the 1-km resolution MODIS 11.0 µm IR channel data (below) shortly before the report of strong surface winds indicated that this storm exhibited a subtle “enhanced-v” storm top signature, with a minimum IR brightness temperature of -80º C. There was also a cluster of numerous cloud-to-ground lightning strikes (primarily negative in charge) just east of the vertex of the enhanced-v signature.

MODIS 11.0 µm IR image + Cloud to ground lightning + Wind report

About a half hour before the report of the strong surface winds, the 1-km resolution AVHRR Cloud Top Temperature product indicated a minimum value of -80º C, with a maximum Cloud Top Height of 16 km (below).

POES AVHRR Cloud Top Temperature and Cloud Top Height products

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