Eruption of the Tungurahua volcano in Ecuador

July 14th, 2013 |
GOES-13 false-color Red/Green/Blue (RGB) image

GOES-13 false-color Red/Green/Blue (RGB) image

Tungurahua is an active stratovolcano in Ecuador (Wikipedia); a Landsat-8 false-color image showed the partially snow-covered dome of the volcano on 13 July 2013. On the following day, the Washington Volcanic Ash Advisory Center issued a volcanic ash advisory due to an explosive eruption that occurred at 11:51 UTC on 14 July 2013. A GOES-13 false-color Red/Green/Blue (RGB) image created using the NOAA/CIMSS GOES-R Volcanic Ash Detection Algorithm (above) highlighted a warm thermal anomaly and a volcanic cumulonimbus (based upon very rapid cloud top cooling rates and cold IR brightnesss temperature values) minutes after the eruption began — during the “11:45 UTC” GOES-13 image, the satellite was actually scanning the region of the volcanic eruption at 11:58 UTC.

GOES-15 (left), GOES-12 (center), and GOES-13 (right) visible images

GOES-15 (left), GOES-12 (center), and GOES-13 (right) visible images

A comparison of the early stages of the volcanic cloud as viewed from GOES-15 (GOES-West), GOES-12 (GOES-South America), and GOES-13 (GOES-East) is shown with visible channel images (above) and IR channel images (below). The actual times that each of the satellites were scaning the region of the volcanic eruption are noted in the labels, and the images are shown in the native projection for each individual satellite.

The GOES-13 satellite was the first to detect to volcanic cloud, since it was scanning the area at 11:58 UTC (about 7 minutes after the beginning of the eruption). The oblique viewing angle from the GOES-15 satellite helped to highlight the darker gray appearance of the ash-laden volcanic cloud, and reveal the long shadow being cast to the west of the tall feature (estimated to be as high as 45,000 feet above ground level). The volcanic cloud appeared largest on the GOES-12 images due to the more direct viewing angle, as well as the later scan time.

GOES-15 (left), GOES-12 (center), and GOES-13 (right) IR images

GOES-15 (left), GOES-12 (center), and GOES-13 (right) IR images

Animations depicting the volcanic cloud evolution are shown using GOES-12 0.65 µm visible channel, 6.5 µm water vapor channel, and 10.7 µm “IR window” channel images (below). Since a large amount of water vapor is usually exhaled during such explosive eruptions, the extent of the volcanic cloud can be more easily followed on the water vapor channel images.

GOES-12 0.65 µm visible channel images (click image to play animation)

GOES-12 0.65 µm visible channel images (click image to play animation)

GOES-12 6.5 µm water vapor channel images (click image to play animation)

GOES-12 6.5 µm water vapor channel images (click image to play animation)

GOES-12 10.7 µm IR channel images (click image to play animation)

GOES-12 10.7 µm IR channel images (click image to play animation)

Chantal

July 9th, 2013 |
Stereoscopic View of Tropical Storm Chantal

Stereoscopic View of Tropical Storm Chantal

Tropical Storm Chantal, the third named storm of the northern Atlantic Tropical Season, has rapidly moved through the Lesser Antilles and into the eastern Caribbean Sea. The stereoscopic view of Chantal, above, uses visible (0.65 µm) imagery from GOES-12 (over the Equator at 60 W) and visible (0.63 µm) imagery from GOES-13 (over the Equator at 75 W) and shows Chantal as it moved between Martinique and St. Lucia. A similar image, but at 10.7 µm, is here. Coldest brightness temperatures northeast of the storm center were -78 C.

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

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

The GOES-13 satellite had been placed into Rapid Scan Operations (RSO) mode, providing images as frequently as every 5-10 minutes. Visible imagery (above; click image to play animation) revealed the presence of low-level convective outflow boundary cloud arcs along the western periphery of Tropical Storm Chantal. The appearance of these cloud arcs can be an indication that a tropical cyclone has encountered an area of dry air aloft (generally either from the Saharan Air Layer, or a mid-latitude dry air intrusion), which can sometimes have a negative effect on the rate of intensification of the storm. However, in this case, Chantal slowly intensified during the day as it moved over the warm waters and high ocean heat content that were in place over the western Caribbean Sea.

Morphed Microwave Estimates of Total Precipitable Water

Morphed Microwave Estimates of Total Precipitable Water

The morphed animation of Total Precipitable Water (TPW) from the CIMSS MIMIC site, above, shows the maximum in TPW associated with Chantal moving west-northwestward across the tropical Atlantic on a path towards the Greater Antilles — likely Hispaniola. (Note to NWS WFOs: MIMIC TPW is available via LDM subscription and can be displayed in AWIPS). Several products available at the CIMSS Tropical Cyclones website (in addition to the MIMIC TPW above) can be used to diagnose the environment around the system and the strength of the system.

Objectively-determined Overshooting Tops over the Tropical Atlantic, 1915 UTC 9 July 2013

Objectively-determined Overshooting Tops over the Tropical Atlantic, 1915 UTC 9 July 2013

For example, Tropical Overshooting Tops (TOTs) (at this site), are related to the vigor of the convection that is sustaining the Tropical Storm. The objectively-determined TOTs, above, show a cluster within the convective envelope of the system. This suggests ongoing strong convection and a storm that is at minimum maintaining its strength at present. (Given that the upper-level environment can change rapidly, the presence of TOTs may not be well-correlated with strengthening, however). This line plot shows the maximum sustained winds of the system plotted with the number of TOTs near the system.

Saharan-Air Layer Analysis, Tropical Atlantic, 1800 UTC 9 July 2013

Saharan-Air Layer Analysis, Tropical Atlantic, 1800 UTC 9 July 2013

Dust from the Sahara Desert that is lofted by winds and transported into the atmosphere above the tropical Atlantic has a well-known suppressing effect on convection and therefore tropical cyclone development and strengthening. It is often visible from satellite. The SAL analysis, above, (from this site) shows little to impede Chantal as it moves into the Caribbean. Most of the SAL at present is behind the storm.

Wind Shear and Tendency, derived from Satellite data, 1800 UTC 9 July 2013

Wind Shear and Tendency, derived from Satellite data, 1800 UTC 9 July 2013

Other data at the CIMSS Tropical Cyclones site can be used to judge the environment that the storm is in. Around Chantal, for example, wind shear values (above, from here) are modest (and decreasing), but they increase in the direction that the storm is moving. Oceanic Heat Content in the Caribbean Sea surrounding Chantal is sufficient to support strengthening, and the current National Hurricane Center forecast does modestly strengthen the storm before landfall on or near Hispaniola.

Update on GOES-12 Cycle Slips

June 7th, 2012 |
GOES-12 10.7 µm IR image using Side 1 electronics (left) and Side 2 electronics (right)

GOES-12 10.7 µm IR image using Side 1 electronics (left) and Side 2 electronics (right)

At 1645 UTC on 6 June, an Electronics Side Swap occurred for GOES-12 to mitigate the effects of Cycle Slips that were occurring around 0800-1300 UTC each day (See this link for an explanation). No Cycle Slips occurred in the GOES-12 imager data on 7 June; as a result, the images are much cleaner. The image above shows an enhanced 10.7 µm image from June 4 2012 using the Side 1 electronics, which side was plagued by cycle slips, and from June 7 2012 using the Side 2 electronics, which show no cycle slips.

GOES-12 Imager (all channels) for 0945 UTC on June 4th and on June 7th (click image to play animation)

GOES-12 Imager (all channels) for 0945 UTC on June 4th and on June 7th (click image to play animation)

The Cycle Slips affected all bands. Click the image above to see the improvement across all bands between 0945 UTC on 4 June and 0945 UTC on 7 June. Note that there will be slight differences for a given input radiance in the computed brightness temperature for each band for the Side 2 Planck conversion coefficients versus the Side 1 Planck conversion coefficients. Those differences are, for Band 2, 0.0001K for both detectors; for Band 3, -0.0001 K for detector ‘a’, 0.0631 K for detector ‘b’; for Band 4, -0.0001 K for both detectors and for Band 6, 0.0119 K. These differences are much smaller than the instrument noise.

Real-time imagery of GOES-South America imager and sounder data are available here.

GOES-12 Imager Cycle Slips

May 9th, 2012 |
GOES-12 Imager from 1045 UTC 9 May 2012 (click image to play animation of all bands)

GOES-12 Imager from 1045 UTC 9 May 2012 (click image to play animation of all bands)

GOES-M was launched in 2001 and as GOES-12 served as the operational GOES-East satellite from April 1, 2003 until April 14th, 2010, and has been serving recently as GOES-South America, providing Weather Services on that Continent with routine Imager and Sounder data.

Recently, the GOES-12 Imager has been experiencing ‘cycle slips‘, which manifest themselves in imagery as lines that are shifted, as shown in the loop above of the 5 Imager channels (Individual channels are here: 0.65 µm, 3.9 µm, 6.5 µm, 10.7 µm, 13.3 µm). Cycle slips occur as the satellite on-board software loses track of where the image mirror used to view the Earth is in its scan cycle. After the scan system initializes at the start of a scan cycle, the system expects consistent behavior, and no resources are allocated to track which cycle the mirror is in. Only increments are tracked. If the mirror is moving and a hiccup occurs, that anomaly (which is manifest as a shift in the center of the line) continues until the next system initialization.

The reason for the uptick in the number of Cycle Slips is unknown.

The images in this blog entry were generated using McIDAS-V.

(Update, 4 June 2012: An Imager Electronics Side Swap is scheduled for June 6, 2012, for GOES-12 (GOES-South America) based on the Manufacturer’s Recommendation as a potential remedy to mitigate the ongoing Cycle Slips. The side switch will be performed at 1615 UTC on 6 June 2012. The duplicate sensors that will now be used have not yet been used during GOES-12’s life. Because new sensors are being used, new look-up tables and calibration coefficients have been computed and are available here. Also, see page 29 in this pdf for more information on the two detector sets. Here is the notification of coming changes.)