Calbuco volcanic eruption in Chile

April 23rd, 2015
GOES-13 (GOES-East) 0.63 µm visible and 10.7 µm IR channel images at 2138 UTC (with surface reports)

GOES-13 (GOES-East) 0.63 µm visible and 10.7 µm IR channel images at 2138 UTC (with surface reports)

The Calbuco volcano in southern Chile erupted around 2103 UTC or 6:03 pm local time on 22 April 2015. The first good satellite view of the volcanic cloud was provided by the 2138 UTC or 6:38 pm local time GOES-13 (GOES-East) 0.63 µm visible channel and 10.7 µm IR channel images (above). The coldest cloud-top IR brightness temperature at that time was -65º C, which was very close to the tropopause temperature as indicated on the nearby Puerto Montt rawinsonde reports from 1200 UTC on 22 April and 23 April — the height of the tropopause was between 12.3 and 15.6 km on each day (there were 2 tropopause levels coded in both of the upper air reports).

However, before the volcanic cloud was seen, a well-defined thermal anomaly or “hot spot” was evident on the previous GOES-13 3.9 µm shortwave IR image at 2045 UTC or 5:45 pm local time (below). The hottest 3.9 µm IR brightness temperature at that time was 340.8 K (red pixel), which is very close to the saturation temperature of the GOES-13 3.9 µm detectors.

GOES-13 3.9 µm shortwave IR image at 2045 UTC

GOES-13 3.9 µm shortwave IR image at 2045 UTC

An oblique view of the early stage of the volcanic cloud was captured on a 2100 UTC GOES-15 (GOES-West) 0.63 µm visible image (below; closer view).

GOES-15 (GOES-West) 0.63 µm visible image at 2100 UTC

GOES-15 (GOES-West) 0.63 µm visible image at 2100 UTC

A sequence of GOES-13 (GOES-East) 10.7 µm IR channel images (below; click image to play animation; also available as an MP4 movie file) revealed that there was a second explosive eruption that began sometime before the 0508 UTC or 2:08 am local time image on 23 April. The coldest cloud-top IR brightness temperature with this second eruption was -68º C at 0808 UTC. Also, at 0508 UTC mesospheric airglow waves were seen with Suomi NPP VIIRS Day/Night Band imagery.

GOES-13 (GOES-East) 10.7 µm IR images (click to play animation)

GOES-13 (GOES-East) 10.7 µm IR images (click to play animation)

On the morning of 23 April, a 1200 UTC GOES-15 (GOES-West) 0.63 µm visible image (below) provided a good view of the large areal coverage of volcanic cloud material resulting from the 2 eruptions.

GOES-15 (GOES-West) 0.63 µm visible image

GOES-15 (GOES-West) 0.63 µm visible image

Finally, a before-eruption (21 April) and post-eruption (23 April) comparison of Aqua MODIS true-color Red/Green/Blue (RGB) images as visualized using the SSEC RealEarth web map server (below) showed the effect of ashfall on some of the higher terrain downwind of Calbuco, which was particularly evident on the snow-capped summits of the Osorno and Puyehue volcanoes (yellow arrows).

Before (21 April) and after (23 April) Aqua MODIS true-color RGB images

Before (21 April) and after (23 April) Aqua MODIS true-color RGB images

—– 24 April Update —–

A series of GOES-13 and Terra/Aqua MODIS volcanic ash height retrieval images from the SSEC Volcano Monitoring site (below; click image to play animation) showed that the ash from each of the two explosive eruptions reached heights of around 20 km (black color enhancement), which was well into the stratosphere.

GOES-13 and Terra/Aqua MODIS volcanic ash height retrieval values (click to play animation)

GOES-13 and Terra/Aqua MODIS volcanic ash height retrieval values (click to play animation)

Ice over the Great Lakes

April 17th, 2015
Suomi-NPP Imagery:  Visible (0.64µm), Day Night Band (0.70µm) and near-IR (0.85µm) (click to enlarge)

Suomi-NPP Imagery: Visible (0.64µm), Day Night Band (0.70µm) and near-IR (0.86µm) images (click to enlarge)

Visible Imagery over the Great Lakes on Friday April 17th showed mostly open waters over the five lakes, with regions that could be ice confined to coastlines of Lakes Superior, Huron, Erie and Michigan. The animation above is of Suomi NPP VIIRS visible (0.64µm and 0.70µm) and near-infrared (0.86µm) data. Can you tell with certainty which of the white features over the lakes are clouds vs. ice?

Suomi-NPP Infrared Imagery (3.74 µm),  (click to enlarge)

Suomi-NPP Infrared Imagery (3.74 µm) (click to enlarge)

Infrared data can give clues. The 3.74 µm imagery, above, shows the brightness temperature. Note how the white regions over Lakes Superior, Michigan and Ontario are about the same temperature as the surrounding water. In contrast, white regions over Lakes Erie and Ontario are much darker (warmer) in the 3.74 µm than the surrounding water. This is testimony to the superior scattering abilities around 3.74 µm of water-based clouds compared to lake ice. More solar radiation scattered towards the satellite by the clouds means a warmer temperature is detected.

Suomi-NPP Imagery:  Toggle between Visible (0.64µm) and near-IR (1.61 µm) (click to enlarge)

Suomi-NPP Imagery: Visible (0.64µm) and near-IR (1.61 µm) (click to enlarge)

The 1.61 µm near-infrared channel is useful because ice strongly absorbs solar radiation at that wavelength, appearing dark. The toggle above, of visible (0.64) and near-infrared (1.61) neatly distinguishes between clouds and ice. Ice (dark in the 1.61 µm because it does not reflect; at that wavelength, it absorbs) is apparent over eastern Lake Superior, eastern and northern Lake Huron and some small bays in northern Lake Michigan. There is no ice apparent on Lakes Erie or Ontario: features there exhibit signatures which are white in both visible and at 1.61 µm.

Another method to aid in the discrimination of snow/ice vs supercooled water droplet clouds is the creation of Red/Green/Blue (RGB) products. The example below toggles between the 0.64 µm visible image and an RGB image (which uses the VIIRS 0.64 µm/1.61 µm/1.61 µm data as the R/G/B components) — snow cover and ice appear as darker shades of red on the RGB image (in contrast to supercooled water droplet clouds, which are brighter shades of white). The snow depth on the morning of 17 April was still 13 inches at Munising in the Upper Peninsula of Michigan.

Suomi NPP VIIRS 0.64 µm visible and false-color RGB images (click to enlarge)

Suomi NPP VIIRS 0.64 µm visible and false-color RGB images (click to enlarge)

On this day there was only 1 pass of the Landsat-8 satellite over any of the ice-covered portions of the Great Lakes; the 15-meter resolution panchromatic visible (0.59 µm) image below shows a very detailed view of the far western portion of the ice that was north of the Keweenaw Peninsula in Lake Superior (zoomed image).

Landsat-8 panchromatic visible (0.59 µm) image (click to enlarge)

Landsat-8 panchromatic visible (0.59 µm) image (click to enlarge)

Terra and Aqua both carry the MODIS sensor, and MODIS can detect radiation at 1.38 µm, a wavelength at which cirrus is highly reflective. A 1.38 µm image from the 17th, below, shows the horizontal extent of cirrus.

MODIS Imagery:  near-IR (1.38 µm) (click to enlarge)

MODIS Imagery: near-IR (1.38 µm) (click to enlarge)

Dust storm in southern Nevada and California

April 14th, 2015
GOES-13 0.63 µm visible channel images (click o play animation)

GOES-13 0.63 µm visible channel images (click o play animation)

GOES-13 (GOES-East) 0.63 µm visible channel images (click image to play animation; also available as an MP4 movie file) showed the hazy signature of a cloud of thick blowing dust moving southward across southern Nevada and parts of southern California, along and behind a strong cold frontal boundary on 14 April 2015.

Areas where the dust cloud was more dense could be identified using the Terra and Aqua MODIS 11-12 µm IR brightness temperature difference (BTD) product (below). The 12 µm IR channel is no longer available on the imager instrument of the current series of GOES satellites — however, the ABI instrument on the upcoming GOES-R satellite will have a 12 µm IR channel, allowing the creation of such BTD products to aid in the identification and tracking of similar dust features.

Terra and Aqua MODIS 11-12 µm IR brightness temperature difference

Terra and Aqua MODIS 11-12 µm IR brightness temperature difference

At 1833 UTC, a pilot reported that the top of the dust cloud was at 11,500 feet near its leading edge (below). Farther to the south, strong winds interacting with the terrain were causing pockets of moderate to severe turbulence.

Terra MODIS 11-12 µm IR brightness temperature difference, with pilot reports

Terra MODIS 11-12 µm IR brightness temperature difference, with pilot reports

The blowing dust cloud was also evident on true-color Red/Green/Blue (RGB) images from MODIS and VIIRS, as visualized using the SSEC RealEarth web map server (below).

MODIS and VIIRS true-color RGB images

MODIS and VIIRS true-color RGB images

Major sandstorm in the Arabian Peninsula

April 2nd, 2015
Visible satellite images and surface observations (click to play animation)

Visible satellite images and surface observations (click to play animation)

Visible satellite images from the SSEC RealEarth web map server (above; click image to play animation) revealed the hazy light gray signature of a major sandstorm that was advancing south-southeastward across the Arabian Peninsula on 02 April 2015. An Aqua MODIS true-color Red/Green/Blue (RGB) image (actual satellite overpass time was 10:20 UTC or 2:20 PM local time) is shown below — the dense cloud of airborne sand appeared as a lighter shade of tan.

Aqua MODIS true-color image

Aqua MODIS true-color image

A Suomi NPP VIIRS true-color image from the previous day (below) depicted the beginning phase of the sandstorm in the northern portion of Saudi Arabia, which consisted of a number of smaller plumes of blowing sand prior to consolidating into the large feature seen on 02 April.

Suomi NPP VIIRS true-color image (01 April)

Suomi NPP VIIRS true-color image (01 April)

The blowing sand reduced surface visibility to near zero at some locations, disrupting ground transportation, air traffic, and also closing schools. Visibility was reduced to 0.1 mile for several hours at Dubai International Airport (below), which is one of the world’s busiest in terms of volume of flights.

Time series of weather conditions at Dubai International Airport

Time series of weather conditions at Dubai International Airport

During the previous nighttime hours, McIDAS-V images of Suomi NPP VIIRS 0.7 µm Day/Night Band data (below; images courtesy of William Straka, SSEC) showed the arc-shaped leading edge of the sandstorm as it stretched from the United Arab Emirates across Saudi Arabia at 22:01 UTC or 1:01 AM local time. Since the Moon was in the Waxing Gibbous phase (at 98% of Full), it provided ample illumination for these “visible images at night”.

Suomi NPP VIIRS 0.7 µm Day/Night Band image

Suomi NPP VIIRS 0.7 µm Day/Night Band image

Suomi NPP VIIRS 0.7 µm Day/Night Band image

Suomi NPP VIIRS 0.7 µm Day/Night Band image