Chaiten Erupts

May 6th, 2008 |

Channel Difference 11-12 microns

Chile is one of the most volcanically active countries on Earth. The latest volcano to erupt is Chaiten, which had previously lain dormant for at least 1000 years. Chaiten is at approximately 42 degrees South latitude, 72 degrees west longitude, close to Golfo de Ancud. A series of eruptions, starting on May 2, has prompted the evacuation of Chaiten, a provincial capital with a population of 4000.

GOES-10 captured the plume of an eruption that started near 12 UTC on 6 May. Volcanic ash does not have an emissivity of 1; that is, it does not emit as a blackbody. The emissivity at 10.7 microns is smaller than the emissivity at 12 microns. The smaller signal received at 10.7 microns (relative to the assumed blackbody) is interpreted as a cooler emitting surface. If the blackbody temperatures at 10.7 and 12.0 microns are compared, then, values at 12.0 microns are warmer. A channel difference can be used to highlight the horizontal extent of the volcanic ash. In the loop shown, the bluest pixels correspond to a blackbody temperature difference of nearly 10 K. That is, the 12 micron blackbody temperature is 10 K warmer than the 11 micron blackbody temperature. The remnants of an older eruption are also noted near the Atlantic Coast of Argentina.

A sequence of GOES-10 imager and sounder IR difference products during the 02-08 May period (below) shows evidence of plumes from multiple eruptions of the Chaiten Volcano. The GOES-10 Imager can provide nearly continuous (15 minute) coverage of the evolving ash cloud, while the GOES-10 Sounder can provide details on the upper-level SO2 plumes once every four hours. The former is derived utilizing the 11.0 micrometer and 12.0 micrometer bands from the Imager. SO2 plumes are revealed by differencing the 7.4 micrometer and 13.3 micrometer bands from the Sounder.

GOES-12 imager and sounder difference products (Animated GIF)

Click here to see an animated gif every from every four hours — that is, each hour for when sounder data are available.

An AVHRR false color image from 05 May (below, viewed using Google Earth) revealed a long plume from the Chaiten volcano, which stretched eastward across Argentina and then southeastward over the South Atlantic Ocean.

AVHRR false color image

Using GOES-10 imagery to detect ash clouds from the Tungurahua volcano in Ecuador

February 10th, 2008 |

GOES-10 imager and sounder products (Animated GIF)

The Tungurahua Volcano in Ecuador began to have a series of eruptions during the first 2 weeks of February 2008 (Washington VAAC advisories). A comparison of 4 different GOES-10 Imager and Sounder products (above) shows the Imager 10.5µm “IR window”, the Imager 10.5-12.0µm “split window difference”, the Sounder 11.0-12.0µm “split window difference”, and the Sounder 7.4-13.3µm “SO2 detection product”. A volcanic ash plume was evident on both the Imager and Sounder split window difference products, moving southwestward away from the volcano at 16:31-16:45 UTC on 06 February 2008. The lack of a signal on the SO2 detection product could have been due to masking by clouds, or the fact that very little SO2 was present in that particular volcanic ash plume.

GOES-10 spilt window + IR images (Animated GIF)

A comparison of GOES-10 split window difference and IR window images from 06:15-13:15 UTC on 06 February (above) show the improved volcanic ash detection capability of the 11-12µm technique — ash shows up as red features in the split window difference product.

GOES-10 visible images (Animated GIF)

An animation of the GOES-10 visible channel imagery from 06 February 2008 (above) shows the plume of volcanic ash drifting southwestward.

GOES-10 IR + IR difference images (Animated GIF)

An animation of GOES-10 IR “split window difference” (10.5µm – 12.0µm, top panel) and IR window (10.5µm, bottom panel) imagery from (above) showed two separate pulses of volcanic ash cloud (gray enhancement) that were drifting southwestward on that day. Two days later, on 08 February (below), a new ash cloud was seen to be drifting almost due west.

GOES-10 IR + IR difference images (Animated GIF)

Then on 10 February (below), two separate ash clouds could be seen — one drifting eastward, and one drifting westward — as changes in wind direction with height (wind shear) moved the volcanic ash plumes in different directions.

GOES-10 IR + IR difference images (Animated GIF)

Tropical Storm Olga

December 11th, 2007 |

GOES-10 IR image + QuikSCAT winds

GOES-10 IR imagery with QuikSCAT winds (above) sourced from the CIMSS Tropical Cyclones site showed that the maximum surface winds associated with Subtropical Storm Olga were located well to the north of the center of the circulation early in the day on 11 December 2007. However, ASCAT wind data later in the day (below) indicated that the radius of the maximum surface winds had decreased somewhat, suggesting a transition from subtropical storm to tropical storm status. Reconnaissance aircraft data confirmed this trend, and Olga was named a Tropical Storm late in the day. Olga produced nearly 10 inches of rain across the island of Puerto Rico.

GOES-10 IR image + ASCAT winds

A NOAA-17 AVHRR 3-channel red/green/blue (RGB) false-color image (below) revealed that the center of Olga was partially exposed as the storm began to interact with the rugged terrain on the island of Hispaniola, with some convection around the core of the storm (primarily within the northern quadrant).


Subtropical Storm Olga

December 10th, 2007 |

GOES-10 IR images (Animated GIF)

Just as the 2007 Atlantic Tropical Cyclone season started off a bit early (with Subtropical Storm Andrea in early May), it also is ending a bit late with the formation of Subtropical Storm Olga on 10 December 2007. An animation of GOES-10 IR images (above) sourced from the CIMSS Tropical Cyclones site shows the cluster of cold cloud top temperatures (red to white enhancement) associated with Olga, moving just north of Puerto Rico.

GOES-10 IR image + deep layer mean winds

An analysis of the Deep Layer Mean wind field (above) indicated that an upper level low existed just to the south of Olga. The majority of the 00 UTC 11 December 2007 model forecast tracks (below) moved Olga westward toward the Dominican Republic and Jamaica.

GOES-10 IR image + model forecast tracks