Pavlof Volcano (located at about 55.5 N, 162 W) in the Aleutian Islands had been experiencing a series of small eruptions that were captured by the constellation of polar-orbiting satellites that pass over the region. For example, a MODIS 11.0 Âµm IR Window channel image from 08:07 UTC on 16 May (above) showed a dark (warm) pixel over the volcano. That 0Âº C pixel was surrounded by values closer to -15Âº C.
A comparison of Suomi NPP VIIRS 0.7 Âµm Day/Night Band (DNB) and 3.74 Âµm shortwave IR images at 12:12 UTC on 16 May 2013 (above) showed the bright glow of the volcano on the DNB, centered over a warm thermal anomaly of 47.5Âº C (orange color enhancement) on the shortwave IR. These were both signatures of hot lava flows from the summit and down along the northwest flank of Pavlof.
The high spectral resolution of MODIS — 36 different channels in the visible and infrared — on board the Terra and Aqua satellites allows for creation of products that quantitatively describe the volcanic ash cloud, beyond just locating the hot spot of the volcano itself. False color imagery, shown above (top left panel, derived from the brightness temperature differences indicated in the figure) from Aqua MODIS at 13:50 UTC, nicely outlines the volcanic ash plume in shades of red. The other three figure panels show the Ash Cloud Height (very important information for aviation concerns), the Ash Cloud Particle Size (which is related to how long it will take to settle out — small particles stay in the atmosphere for a longer time) and Ash Cloud Loading (what is the mass of volcanic ash in the column?).
A later 4-panel suite of products derived from MODIS data on Terra, at 21:31 UTC, is shown below. In addition to the high spectral resolution on MODIS, the polar orbiter satellites have good horizontal resolution over Alaska as well.
A comparison of Suomi NPP VIIRS 0.64 Âµm visible channel and 3.74 Âµm shortwave IR channel images at 22:08 UTC (below) showed the hazy signature of the volcanic plume on the visible image, as well as a warm thermal anomaly exhibiting a brightness temperature of 40Âº C (yellow color enhancement) on the shortwave IR image. A Volcanic Ash Advisory had been issued for altitudes between the surface and 15,000 feet, as the volcanic plume drifted southeastward at 15 knots.
GOES imaging of this eruption suffers because of limited channels (5) on the GOES Imager, and because of degraded spatial resolution at the high latitudes (as result of the very large satellite viewing angle). However, the hazy signature of the volcanic plume could still be seen drifting southeastward from Pavlof on GOES-15 0.63 Âµm visible channel images (below; click image to play animation). The location of the Pavlof volcano is denoted by the “P” on the images. Also of interest in the animation is the motion of sea ice in the Bering Sea north of the Aleutians, which could be seen once a break in the clouds moved over that area.