Re-suspended volcanic ash from the Novarupta volcano in Alaska

September 29th, 2014
GOES-15 0.63 µm visible channel images (click to play animation)

GOES-15 0.63 µm visible channel images (click to play animation)

McIDAS images of GOES-15 0.63 µm visible channel data (above; click image to play animation) showed the hazy signature of a plume of re-suspended volcanic ash originating from the region of the Novarupta volcano in Alaska, moving southeastward over the Shelikof Strait toward Kodiak Island on 29 September 2014. The 1912 eruption of Novarupta left a very deep deposit of volcanic ash, which often gets lofted by strong winds in the early Autumn months before snowfall covers the ash (another example occurred on 22 September 2013). Surface winds gusted as high as 30 knots at regional reporting stations, with numerical models estimating terrain-enhanced winds as high as 40-50 knots over the Novarupta ash field.

An AWIPS II image of POES AVHRR 0.86 µm visible channel data (below) showed the ash plume at 22:46 UTC; a pilot report at 22:45 UTC indicated that the top of the ash plume was between 4000 and 6000 feet above ground level.

POES AVHRR 0.86 µm visible channel image, with METAR surface reports and Pilot reports (PIREPs)

POES AVHRR 0.86 µm visible channel image, with METAR surface reports and Pilot reports (PIREPs)

A sequence of 3 Suomi NPP VIIRS true-color Red/Green/Blue (RGB) images from the SSEC RealEarth web map server (below) indicated that the re-suspended ash plume had been increasing in areal extent during that period.

Suomi NPP VIIRS true-color images from 27, 28, and 29 September

Suomi NPP VIIRS true-color images from 27, 28, and 29 September

A sequence of 4-panel products from the NOAA/CIMSS Volcanic Cloud Monitoring site (below) shows False-color images, Ash/dust cloud height, Ash/dust particle effective radius, and Ash/dust loading (derived from either Terra/Aqua MODIS or Suomi NPP VIIRS data).

4-panel MODIS/VIIRS products: False color image; Ash/dust cloud height; Ash/dust particle effective radius; Ash/dust loading

4-panel MODIS/VIIRS products: False color image; Ash/dust cloud height; Ash/dust particle effective radius; Ash/dust loading

Hat tip to Mark Ruminski (NOAA/NESDIS) for alerting us to this event.

Tropical Invest 97L in the western Atlantic Ocean

September 29th, 2014
GOES-13 0.63 µm visible channel images with METAR surface reports (click to play animation)

GOES-13 0.63 µm visible channel images with METAR surface reports (click to play animation)

Tropical Invest 97L formed near Bermuda during the pre-dawn hours on 29 September 2014. After sunrise, AWIPS II images of GOES-13 0.63 µm visible channel data (above; click image to play animation) revealed a well-defined low-level circulation spinning just to the west of Bermuda. It is interesting to note that at 12:55 UTC a waterspout was reported 4 km to the east of the Bermuda International Airport (station identifier TXKF), associated with a band of deep convection that was moving northward (below).

GOES-13 0.63 µm visible channel image with Bermuda METAR observation

GOES-13 0.63 µm visible channel image with Bermuda METAR observation

An overpass of a Metop satellite at 14:38 UTC provided a good view of the surface wind field with data from the ASCAT scatterometer instrument (below). There was one wind vector with a speed around 30 knots (green) just to the east of the center of circulation.

GOES-13 0.63 µm visible channel image with Metop ASCAT scatterometer surface winds

GOES-13 0.63 µm visible channel image with Metop ASCAT scatterometer surface winds

A comparison of Terra MODIS 0.65 µm visible channel and 11.0 µm IR channel images at 15:25 UTC (below) showed that the coldest cloud-top IR brightness temperatures of -55º C (orange color enhancement) were located to the north of the circulation center.

Terra MODIS 0.65 µm visible channel and 11.0 µm IR channel images

Terra MODIS 0.65 µm visible channel and 11.0 µm IR channel images

Co-registration Issues on GOES-13

September 29th, 2014

Previous posts on this blog (and elsewhere) have detailed the co-registration misalignment that exists between the 3.9 µm and 10.7 µm channels on the GOES-13 Imager. Because of this diurnally-varying co-registration error, a 3.9 µm pixel may be offset to the right or left of a 10.7 µm pixel; if this occurs near a pronounced temperature gradient (such as along a lakeshore), a false brightness temperature difference signal can ensue.

Brightness Temperature Difference (10.7 µm - 3.9 µm), 1825 and 1830 UTC, 26 September 2014 (click to enlarge)

Brightness Temperature Difference (10.7 µm – 3.9 µm), 1825 and 1830 UTC, 26 September 2014 (click to enlarge)

Consider, for example, the toggle above from 26 September 2014. A strong brightness temperature difference exists at 1825 UTC along the shorelines of Lakes Michigan, Huron and Erie; it is gone five minutes later, at 1830 UTC. There is no discernible change in the visible image over the same 5-minute interval (Link).

GOES-13 Imagery (0.63µm , top, 10.7µm , middle and 3.9µm micron, bottom) at 1825 and 1830 UTC, 26 September 2014 (click to enlarge)

GOES-13 Imagery (0.63µm , top, 10.7µm , middle and 3.9µm micron, bottom) at 1825 and 1830 UTC, 26 September 2014 (click to enlarge)

NESDIS operations alters the GVAR signal just before 1830 UTC (when the 3.9 µm imagery is shifted one pixel to the West) and at 0630 UTC (when the 3.9 µm imagery is shifted one pixel to the East) to mitigate the effects of the diurnally-varying co-registrations differences between the 3.9 µm and 10.7 µm channels. The imagery above shows the visible and two infrared (10.7 µm and 3.9 µm) channels at 1825 and 1830 UTC (GOES-13 was in Rapid Scan Operations mode at this time). The 3.9 µm imagery shows a one-pixel westward shift that is especially evident if you look at the unchanging navigation along the eastern shore of Lake Michigan. (1825 UTC imagery: Visible, 3.9µm and 10.7µm; 1830 UTC imagery: Visible, 3.9µm and 10.7µm) A similar link between 1815 and 1830 UTC on 25 September shows the same shift in the shortwave IR. A toggle between 0615 and 0630 UTC on 29 September shows the eastward shift in the 3.9 µm imagery that occurs then.

NOAA/NESDIS continues to monitor this co-registration issue.

Eruption of the Mount Ontake volcano in Japan

September 27th, 2014
Suomi NPP VIIRS true-color images on 27, 28, and 29 September

Suomi NPP VIIRS true-color images on 27, 28, and 29 September

The Mount Ontake volcano erupted on the main Japanese island of Honshu around 02:52 UTC (11:52 AM local time) on 27 September 2014. A sequence of three daily (27, 28, and 29 September) Suomi NPP VIIRS true-color Red/Green/Blue (RGB) images from the SSEC RealEarth web map server (above) showed the volcanic plume drifting eastward then southeastward during that period. The ash plume disrupted air travel in some parts of Japan.

A comparison of pre-eruption (22 September) and post-eruption (28 September) VIIRS true-color images (below) revealed the light gray signature of thick volcanic ash covering the region around the summit of Mount Ontake. There was also a narrow volcanic plume streaming southeastward on the 28 September image.

22 September vs 28 September VIIRS true-color images

22 September vs 28 September VIIRS true-color images