Significant eruption from the Soufriere Hills volcano on Montserrat

February 11th, 2010
GOES-12 visible images + METAR surface reports

GOES-12 visible images + METAR surface reports

A major eruption followed a partial dome collapse in the crater of the Soufriere Hills volcano on the West Indies island of Montserrat during the daytime hours on 11 February 2010. McIDAS images of the GOES-12 visible channel data (above) showed the rapid east-southeastward expansion of the volcanic cloud following the eruption around 17:00 UTC. Pilot reports placed the maximum height of the volcanic cloud around 50,000 feet above ground level (see the NOAA/NESDIS/SSD/OSDPD archive of Volcanic Ash Advisories and satellite images).

GOES-12 3.9 µm shortwave IR images (below) showed a thermal anomaly or “hot spot” during the hours leading up to the major eruption, with a maximum IR pixel value of 322 K or 49º C (yellow color enhancement) at 16:45 UTC. Also note the darker appearance of the western and southern portions of the volcanic cloud: these were areas of the cloud that were composed primarily of supercooled water droplet clouds, which strongly reflect solar radiation (which then leads to much warmer shortwave IR brightness temperature values).

GOES-12 3.9 µm shortwave IR images

GOES-12 3.9 µm shortwave IR images

GOES-12 10.7 µm longwave IR images (below) revealed an initial pulse of very cloud cloud top IR brightness temperatures within a couple of hours following the eruption — as cold as -75º C at 19:15 UTC — before the volcanic cloud appeared to thin out and exhibit warmer IR brightness temperatures as it spread eastward.

GOES-12 10.7 µm longwave IR images

GOES-12 10.7 µm longwave IR images

AWIPS images of high-altitude GOES-12 derived atmospheric motion vectors in the vicinity of the volcanic plume (below) were generally in the 40-55 knot range — the 12 UTC rawinsonde data from station TFFR (Le Raiset, Guadaloupe) had maximum west-northwesterly winds of 68 knots at 280 hPa (around the 41,000 foot level).

GOES-12 IR images + GOES-12 atmospheric motion vectors

GOES-12 IR images + GOES-12 atmospheric motion vectors

A comparison of 4-km resolution GOES-12 3.9 µm and 1-km resolution NOAA-15 AVHRR 3.7 µm shortwave IR images (below) showed the advantage of higher spatial resolution for detecting the magnitude of the volcano’s hot spot — the hottest pixel seen on the NOAA-15 image was 330 K or +57º C (red color enhancement), compared to only 293.5 K or +20º C (black color enhancement) on the GOES-12 image.

GOES-12 (top) and NOAA-15 (bottom) shortwave IR images

GOES-12 (top) and NOAA-15 (bottom) shortwave IR images

Similarly, the coldest longwave IR brightness temperature value seen on the 1-km resolution NOAA-15 AVHRR image was -72º C, compared to only -55º C on the 4-km resolution GOES-12 image (below).

GOES-12 (top) and NOAA-15 (bottom) longwave IR images

GOES-12 (top) and NOAA-15 (bottom) longwave IR images

A natural color Red/Green/Blue (RGB) composite image using Aqua MODIS channels 01/04/03 (below) showed the volcanic cloud at 17:20 UTC, about 20 minutes after the explosive eruption. The tall volcanic cloud was casting a long shadow toward the north-northeast at that time. In addition, the hazy signal of previous volcanic emissions from earlier in the day could be seen covering a much larger portion of the region.

Aqua MODIS natural color Red/Green/Blue (RGB) image

Aqua MODIS natural color Red/Green/Blue (RGB) image

A few hours later, a false-color Red/Green/Blue (RGB) composite image using NOAA-15 AVHRR channels 01/02/04 (below) shows a view of the volcanic cloud at 21:02 UTC. Again, the tall cloud feature was still seen to be casting a long shadow toward the north-northeast at that time. The thermal anomaly from the volcano hot spot appeared as the small yellow area on the RGB image.

NOAA-15 AVHRR false-color Red/Green/Blue (RGB) image at 21:02 UTC

NOAA-15 AVHRR false-color Red/Green/Blue (RGB) image at 21:02 UTC

A sequence of three sets of of images from the GOES-12 sounder (below) shows the sounder longwave IR window image (top panels) along with a sounder IR difference product (7.4 µm – 13.3 µm, bottom panels) before, during, and after the eruption. The darker gray to black image features intermingled with the brighter white water vapor and volcanic ash clouds are signals of a high concentration of SO2. The GOES Sounder is able to detect SO2 from a volcanic eruption, as long as it is not masked by both the water vapor and volcanic ash during and immediately following the eruption. This particular case was a situation where the extensive water vapor and volcanic ash clouds did in fact mask the SO2 signal resulting from the eruption of Soufriere Hills volcano. (GOES-12 sounder images provided by Tony Schreiner, CIMSS)

GOES-12 sounder IR images (top) and IR difference images (bottom)

GOES-12 sounder IR images (top) and IR difference images (bottom)

===== 12 FEBRUARY UPDATE =====

The series of 4-panel displays below (provided by Mike Pavolonis, NOAA/NESDIS/ASPB) show AVHRR RGB images along with volcanic ash derived products (ash loading, ash height, and ash effective radius). Of particular interest was the fact that the maximum ash height decreased rather quickly, from 15.73 km (at 21:02 UTC on 11 February) to 5.58 km (at 06:24 UTC on 12 February) to 4.93 km (at 09:19 UTC on 12 February).

AVHRR RGB image and ash retrieval products

AVHRR RGB image and ash retrieval products

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AVHRR RGB image and volcanic ash retrieval products

AVHRR RGB image and volcanic ash retrieval products

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AVHRR RGB image and volcanic ash retrieval products

AVHRR RGB image and volcanic ash retrieval products

GOES-12 6.5 µm water vapor imagery with an overlay of Canadian Meteorological Center 400 hPa winds (below) revealed that an anticyclone was building aloft over the region following the eruption of the Soufriere Hills volcano — this would provide an environment of increasing mid-tropospheric subsidence that could explain the rapid decrease in retrieved volcanic ash heights. Subsequently, the water vapor image brightness temperature values were also increasing in the area of the building ridge, as seen by the warming trend of brightness temperatures averaging around -20º C (yellow color enhancement) to values averaging around -15º C (orange color enhancement).

GOES-12 water vapor images + CMC 400 hPa winds

GOES-12 water vapor images + CMC 400 hPa winds

Strong potential vorticity anomaly off the California coast

February 9th, 2010
GOES waver vapor imagery + PV1.5 pressure + 500 hPa geopotential height

GOES waver vapor imagery + PV1.5 pressure + 500 hPa geopotential height

A strong potential vorticity (PV) anomaly was propagating southeastward just off the California coast on 09 February 2010 — and this feature had a striking presentation on AWIPS images of GOES-11 water vapor channel data (above), with a pronounced arc of very dry air (yellow color enhancement) seen around the periphery of the circulation. According to the CRAS model fields, the tropopause (taken to be the pressure of the PV1.5 surface) was being brought downward as low as the 600 hPa pressure level within the core of the PV anomaly.

Images of the GOES-11 sounder Total Column Ozone derived product (below) depicted ozone values as high as 430 Dobson Units (red color enhancement) in the vicinity of the PV anomaly, supporting the idea that the tropopause height was very depressed within the circulation feature.

GOES sounder Total Column Ozone + PV1.5 pressure + 500 hPa geoptential height

GOES sounder Total Column Ozone + PV1.5 pressure + 500 hPa geoptential height

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GOES-11 Sounder and Imager water vapor channel images

GOES-11 Sounder and Imager water vapor channel images

A 4-panel comparison of the three water vapor channels on the GOES-11 Sounder (6.5 µm, 7.0 µm, and 7.4 µm) and the GOES-11 Imager 6.7 µm water vapor channel (above) showed that the dry air signature was even quite evident on the Sounder 6.5 µm channel (darker blue color enhancement, upper left panels) — this particular water vapor channel weighting function normally peaks quite high in the atmosphere (around 325 hPa), where these types of water vapor gradients and signatures are usually not as well-defined.

However, due to the dry air within the middle to upper troposphere associated with the PV anomaly, the weighting functions of all 4 of the GOES-11 water vapor channels (calculated using rawinsonde data from Vandenberg Air Force Base) peaked at altitudes that were quite a bit lower compared to the more “normal” conditions that would be seen in a US Standard Atmosphere or USSA environment (below). Convection moving onshore across southern California that day was responsible for at least one sighting of a waterspout in the San Diego area, and inland precipitation amounts of 1.0 to 1.5 inch were widespread.

GOES-11 sounder and imager water vapor weighting functions (Vandenberg vs USSA)

GOES-11 sounder and imager water vapor weighting functions (Vandenberg vs USSA)

Yet another East Coast winter storm

February 6th, 2010
GOES-11/GOES-12 water vapor composite images

GOES-11/GOES-12 water vapor composite images

The Winter of 2009/2010 has brought a number of significant snowfall events to parts of the US East Coast — and another powerful storm affected that region on 05 February06 February 2010. The highest storm total snowfall reported was 40.0 inches at Colesville in Maryland. Washington Dulles International Airport received 32.4 inches of snow (their largest 2-day snowfall on record), and Baltimore-Washington International Airport received 24.8 inches of snow (their second-largest 2-day snowfall on record). So far, this is Philadelphia’s 2nd-snowiest winter on record (56.3 inches) and Washington DC’s 3rd-snowiest winter on record (44.9 inches).

AWIPS images of 3-hourly composites of the GOES-11 and GOES-12 water vapor channel data (above) showed a strong disturbance originating over the Pacific Ocean that was progressing eastward across the southwestern US and northern Mexico during the days leading up to the storm. There was also evidence of a plume of subtropical moisture seen on the water vapor imagery.

The presence of this moisture plume was confirmed on MIMIC Total Precipitable Water (TPW) images (below), which revealed a clear linkage to the rich moisture source within the Inter-Tropical Convergence Zone (ITCZ) over the eastern equatorial Pacific Ocean. MIMIC TPW values were in the 50-60 mm (2.0 – 2.4 inch) range within this moisture plume as it was being drawn northeastward across the Gulf of Mexico — and the Blended Total Precipitable Water product showed a large area of TPW values exceeding 200% of normal from the Gulf of Mexico to the mid-Atlantic states.

MIMIC Total Precipitable Water

MIMIC Total Precipitable Water

4-km resolution GOES-12 water vapor images with an overlay of cloud-to-ground lightning strikes (below) showed 3 important phases of the storm: (1) a expansive area of cold cloud tops associated with the initial round of heavy snowfall later in the day on 05 February; (2) the penetration of a broad dry slot, which helped to release convective instability along it’s leading edge that led to periods of thunder and lightning (especially during the 08-10 UTC time period), and (3) a well-defined deformation zone where additional snowfall banding developed during the final hours of the storm.

GOES-12 6.5 µm water vapor images + cloud-to-ground ligtning strikes

GOES-12 6.5 µm water vapor images + cloud-to-ground ligtning strikes

A series of 1-km resolution AVHRR Cloud Top Temperature product images and MODIS 11.0 µm IR images (below) showed greater detail of some of the banding structures during different phases of the storm.

AVHRR Cloud Top Temperature and MODIS 11.0 µm IR images

AVHRR Cloud Top Temperature and MODIS 11.0 µm IR images

1-km resolution AVHRR visible images (below) displayed the cloud features as the surface low was rapidly deepening just offshore during the day on 06 February.

AVHRR 0.86 µm visible images + surface analyses

AVHRR 0.86 µm visible images + surface analyses

MetOp ASCAT scatterometer winds at 14:05 UTC on 06 February (below) indicated that surface winds were generally in the 30-40 knot range, which were in agreement with offshore buoys which were reporting wind gusts 31-43 knots at 15 UTC. The highest reported gust was 61 mph at Lewes, Delaware during the pre-dawn hours on 06 February.

AVHRR 0.86 µm visible image + ASCAT scatterometer winds

AVHRR 0.86 µm visible image + ASCAT scatterometer winds

===== 07 FEBRUARY UPDATE =====

A comparison of a 1-km resolution MODIS visible channel image and a false-color Red/Green/Blue (RGB) image (below) shows the extent of the snow cover on the morning of 07 February. On the RGB image, snow appears as varying shades of red, in contrast to supercooled water droplet clouds (which appear as brighter features). Even after compaction of the heavy snowfall, there were still a number of sites reporting snow depths in excess of 30 inches that morning. Additional MODIS true color and false color imagery — at resolutions up to 250 meters — can be seen at the SSEC MODIS Today and the SSEC MODIS Direct Broadcast web sites.

MODIS visible + MODIS fasle-color Red/Green/Blue (RGB) image

MODIS visible + MODIS fasle-color Red/Green/Blue (RGB) image

MODIS true color images from the SSEC MODIS Today site can also be displayed using Google Earth (below). The location of 40.0 inch snowfall report (at Colesville, Maryland) is also noted on the image.

MODIS true color image (displayed using Google Earth)

MODIS true color image (displayed using Google Earth)