Eyjafjallajokull, a now-active volcano in southern Iceland that erupted in late March, has recently erupted again, ejecting significant volcanic ash into the atmosphere. Iceland is at high enough latitudes (between 63 and 66.5 degrees north Latitude) that views from geostationary satellites are not as helpful in diagnosing evolving events such as ash clouds as they would be for lower-latitude events. Meteorologists instead rely on polar orbiters to observe the atmosphere surrounding the eruption.

For example, A Terra overpass yesterday allowed MODIS to image the eruption, shown as a true color composite below.

Ash from volcanoes is a significant aviation hazard if it is drawn into jet turbines. For that reason, all flights at London’s Heathrow (and at other airports throughout northern Europe) have been grounded as of mid-afternoon London time on 15 April. The volcanic ash cloud is visible from satellite. The imagery above shows 10.8- and 12.0-micron imagery from a NOAA-18 pass at 0342 UTC on 15 April. The volcanic plume is visible as colder cloud tops arcing eastward from Iceland towards northern Scotland. The color enhancement in the loop shows that the 12.0-micron image has colder brightness temperatures than the 10.8-micron image. For example, the coldest point (red pixels) just off the coast of Iceland have 12.0-micron brightness temperatures of 212.6 K; 10.8-micron temperatures in that region are closer to 214.5 K. This difference in temperature arises because volcanic ash has a lower emissivity at 12.0 microns than at 10.8 microns. Thus, proportionally less radiation compared to a blackbody is being emitted at 12.0 microns than at 10.8 microns. When that emitted radiation is detected by the satellite, the proportionally smaller values at 12.0 microns yield cooler blackbody temperatures.

Indeed, a difference between the two channels can yield a rough approximation of the ash cloud outline, and that is shown above. Colored pixels here have 10.8-micron brightness temperatures at least 2 K warmer than the 12.0-micron brightness temperature. Maximum temperature differences exceed 10 K.

Meteosat-9 volcanic ash products (15 April)

15-16 April Update: The SEVIRI instrument on Meteosat-9, with more spectral resolution than AVHRR, can yield more information about the ash cloud, including total mass, maximum height, and effective radius. These derived products (courtesy of Mike Pavolonis, NOAA/NESDIS/STAR/CoRP/ASPB) are shown for 15 April (above; also available as a QuickTime movie), and for 16 April (below; also available as a QuickTime movie).

Meteosat-9 volcanic ash products (16 April)

18 April Update: below are individual quantitative volcanic ash product images that show characteristics of the volcanic ash features at various times and locations during the 16-18 April period.

Meteosat-9 volcanic ash products at 06:00 UTC on 16 April

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Meteosat-9 volcanic ash products at 18:30 UTC on 16 April

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MODIS volcanic ash products at 03:40 UTC on 17 April

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MODIS volcanic ash products at 04:20 UTC on 18 April

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MODIS volcanic ash products at 12:05 UTC on 18 April

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MODIS volcanic ash products at 14:00 UTC on 18 April

A McIDAS image of a 500-meter resolution Aqua MODIS Red/Green/Blue (RGB) composite using channels 01/04/03 (below) shows a beautiful view of the volcanic ash plume streaming southward on 17 April 2010. Annotated on the image are the tiny village of Skógar, as well as the Mýrdalsjökull Glacier. As an aside, it is interesting to note that a great deal of lightning has been observed associated with the volcanic ash cloud.

Aqua MODIS Red/Green/Blue (RGB) image showing the ash plume on 17 April 2010

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GOES visible, 10.7 µm IR, 3.9 µm IR, and 6.5 µm water vapor images, displayed using AWIPS II

CIMSS has recently begun the process of evaluating and testing satellite imagery and products in the next generation of AWIPS (AWIPS II or AWIPS Migration). GOES 0.65 µm visible channel, 10.7 µm IR channel, 3.9 µm IR channel, and 6.5 µm water vapor channel data from 15 April 2010 are displayed using the Common AWIPS Visualization Environment (CAVE) component of AWIPS II (above). Some features of interest include areas of showers and thunderstorms in parts of Texas and far eastern New Mexico, the large gradient of water temperatures over the far western Atlantic Ocean, and a large area of snow cover in southern Alberta, Canada.

A closer view of the snow cover using GOES 0.65 µm visible channel data (below) shows the areal coverage of the heavy snow that fell on 14 April. Some areas in southeastern Alberta received as much as 60 cm (24 inches) of heavy, wet snowfall which led to widespread power outages and some road closures. The edges of the snow cover can be seen to be melting inward, a testament to the heating power of the higher sun angle of mid-April.

GOES 0.65 µm visible images, displayed using AWIPS II

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Animation of rooftop camera images from the University of Wisconsin - Madison / AOS / SSEC building (looking west)

The break-up of a meteor entering the Earth’s atmosphere caused a large “fireball” of light that was seen  across parts of the Upper Midwest region around 10:00 pm local time on 14 April 2010 (or 03:00 UTC on 15 April 2010). The images above — also available as a QuickTime animation — were taken at 10 second intervals from a rooftop camera (facing to the west) on the Atmospheric and Oceanic Sciences (AOS) / Space Science and Engineering Center (SSEC) building — a very bright flash is briefly seen (which also happens to illuminate 2 aircraft contrails aloft).

It’s admittedly very subtle, but a comparison of a highly-enhanced nighttime visible image from the GOES-11 (GOES-West) satellite and a radar reflectivity image from the Davenport, Iowa WSR-88D (below) seems to corroborate the reports from the public of the meteor flash appearing to move “from west to east” (or in this case, from northwest to southeast). The exact time that GOES-11 was scanning the area of the slightly brighter streak was 03:03 UTC (10:03 pm local time), and our best guess of the exact time of the enhanced reflectivity feature on the WSR-88D radar image is 03:04 UTC (10:04 pm local time). GOES-11 and radar images courtesy of Mat Gunshor, CIMSS.

GOES-11 enhanced nighttime visible image + Davenport IA WSR-88D radar reflectivty

Related links:

• SSEC Spotlight
• UW AOS
  
• NWS La Crosse WI
• NWS Davenport IA
• AccuWeather
• National Public Radio
  

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GOES-12 0.65 µm vs GOES-13 0.63 µm visible images

As of 18:34 UTC on 14 April 2010, GOES-13 (launched May 2006, with a Post Launch Test in December 2006) replaced GOES-12 (launched July 2001) as the operational GOES-East satellite  — for more information, see the NOAA NESDIS Satellite Services Division. A sequence of AWIPS images (above) shows the last three GOES-12 visible images followed by the first three GOES-13 visible images centered over the Upper Midwest region of the US during the satellite transition period. Both the GOES-12 and the GOES-13 visible images are enhanced using the “Linear” AWIPS enhancement (see below for more details).

Note that areas of dense vegetation (for example, over river valleys, and also across much of southern Indiana) appear slightly darker on the GOES-13 visible channel images. This is due to the fact that the visible channel on the newer GOES series — GOES-13 and beyond — is a narrower channel (centered at 0.63 µm, vs 0.65 µm for the older GOES satellites) that misses the “brighter” portion of the grass/vegetation spectrum (green plot) that begins to increase rapidly at wavelengths higher than about 0.7 µm (below). You will also notice that the cloud features appear slightly brighter in the last three GOES-13 images — this is due to the fact that the GOES visible detector performance tends to degrade over time, so the visible images from the much  older GOES-12 satellite appear slightly “washed out” in comparison.

GOES-12 vs GOES-13 visible channel spectral response function plots

Note to AWIPS users: because of the different characteristics of the GOES-13 visible channel, it is suggested that you change the default GOES visible image enhancement from “ZA” to “Linear” — as seen in a GOES-13 visible image comparison with those 2 enhancements (below), the GOES-13 imagery can appear too dark with the default “ZA” enhancement.

GOES-13 visible image: “ZA” enhancement vs “Linear” enhancement

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GOES-12 vs GOES-13 Sounder 4.5 µm shortwave IR images

There are also significant improvements in the quality of the GOES-13 Sounder data, due to the fact that GOES-12 had been experiencing filter wheel problems for quite some time. AWIPS comparisons of the last GOES-12 and the first GOES-13 Sounder 4.5 µm shortwave IR images (above) and 6.5 µm water vapor channel images (below) clearly demonstrate the dramatic reduction in noise — in these Sounder composite images, the western portion of the image is GOES-11 (GOES-West) data, while the eastern portion of the image is either GOES-12 or GOES-13 (GOES-East) data. In particular, the 6.5 µm water vapor image is “cleaner” on GOES-13 as a result of “colder” detectors on the newer spacecraft design, which more effectively radiate to space.

GOES-12 vs GOES-13 Sounder 6.5 µm water vapor channel images

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