Aqua MODIS Red/Green/Blue (RGB) image

The eruption of the Eyjafjallajokull volcano on southern Iceland continued on 19 April 2010 (in addition, see the previous CIMSS Satellite Blog entries published on 15 April and 21 March). A McIDAS Red/Green/Blue (RGB) image composite using Aqua MODIS channels 01/04/03 (above) revealed yet another large ash plume streaming southward over the North Atlantic Ocean. According to the London Volcanic Ash Advisory Center (VAAC), the ash from this latest eruption was generally confined to 10,000-15,000 feet and lower. With the volcanic ash plume drifting to the south, air traffic in the immediate vicinity of Reykjavik-Keflavik International Airport (station identifier BIKF) was not affected — and after a 5-day shut-down of air traffic across much of Europe, some airports there were finally beginning to allow limited flights to resume.

The corresponding volcanic ash retrieval products (below, courtesy of Mike Pavolonis, NOAA/NESDIS/STAR/CoRP/ASPB) indicated that the total ash loading was 75.82 kilotons, the maximum ash height was 7.37 km, and the mean ash particle effective radius was 3.51 micrometers. Note that these volcanic ash retrieval products are available in near-realtime at this NOAA/NESDIS/STAR/CIMSS site.

MODIS volcanic ash retrieval products

In addition to MODIS instruments on Terra and Aqua, the AVHRR instrument on the NOAA polar orbiters can give information on the state of the eruption. NOAA-19 passed over Iceland at 04:08 UTC 19 April, and NOAA-16 passed over at 09:16 UTC 19 April. What do the two views suggest?

Only the NOAA-16 pass occurred during daylight, and that image, below, centered on the Volcano, shows a plume extending southward from Iceland in the wake of a low pressure system (the cyclonic swirl of clouds in the eastern half of the image) departing to the east.

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Infrared imagery from 0408 UTC and 0916 UTC today suggest how the ash cloud may be changing with time. The 3.74 micron imagery and the 10.8-micron imagery, below, both show an increase in the area covered by the plume. This suggests an ongoing eruption. The 10.8-micron imagery in particular shows a lengthening of the volcanic plume southward from Iceland. The 3.74 micron imagery is affected by radiation reflected from the Sun. The 0408 UTC image occurred before sunrise. Only radiation emitted by the Earth, or clouds, or ash, is detected by the satellite. Note the warm (dark) spot that colocates with the volcano: brightness temperatures there are 20 K warmer than surrounding pixels. The 0916 UTC occurred during daylight, and as such, solar radiation at 3.74 microns can be reflected off the Earth and detected by the satellite. The sum total of radiation (emitted plus reflected) will always be greater than only the emitted radiation, thus the scene will appear warmer (and in the greyscale enhancement, darker): the “extra” radiation detected by the satellite is interpreted to mean a warmer emitting surface. Note the striking appearance of the plume. It is very dark (warm) because the particles in the plume are highly reflective. At 0916 UTC, the volcano still retains its dark spot presence in the 3.74 micron imagery. The brightness temperature remains about 20 K warmer than at surrounding pixels.

MODIS Red/Green/Blue (RGB) and 3.7 µm shortwave IR images

Eyjafjallajökull continued to erupt on 20 April 2010. An Aqua MODIS Red/Green/Blue (RGB) image (above) showed a thin but well-defined cloud plume (likely a plume of volcanic steam) arcing southeastward, with a hint of a broader volcanic ash plume spreading out southward from the volcano. The corresponding MODIS 3.7 µm shortwave IR image displayed a pronounced “hot spot” (yellow to red color enhancement) associated with the source of the eruption.

An animation of Meteosat-9 volcanic ash retrieval products (below) indicated that the cloud heights decreased rapidly with time (likely a result of relatively large particles), and the ash cloud quickly became undetectable with increasing distance from the source volcano, due to its low optical depth and obstruction by meteorological clouds.

Meteosat-9 volcanic ash retrieval products

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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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