United Airlines flight 1676 enroute from Denver, Colorado KDEN to Billings, Montana KBIL (flight track) encountered severe turbulence at an altitude of 34,000 feet over Wyoming on 17 February 2014. Three crew members and two passengers were injured, and taken to hospitals upon landing in Billings. An AWIPS image of 1-km resolution Aqua MODIS 6.7 µm water vapor channel data (above) showed a number of pilot reports of moderate turbuence over Wyoming between the altitudes of 33,000 and 45,000 feet around that time; the United 1676 pilot report of severe turbulence is highlighted in red.

On the MODIS water vapor image, note the appearance of distinct signatures of non-parallel mountain waves just to the east of that turbulence plot (in the vicinity of KIDV) — these closely-spaced bands of descending dry air (darker blue to yellow color enhancement) and ascending moist air (lighter blue to pale white color enhancement) were just east (downwind) of the Bighorn Mountains. The corresponding MODIS 0.65 µm visible channel and 11.0 µm IR channel images (below) showed that there were no cloud features associated with the entire extent of these mountain waves — they were were essentially occurring in “clear air”. This example demonstrates the value of high spatial resolution water vapor imagery for helping to identify signatures of potential clear air turbulence.

An animation of 4-km resolution GOES-13 6.5 µm water vapor channel images (below; click image to play animation) showed that there were numerous other reports of moderate and even severe turbulence over Wyoming between about 20:00 UTC and 23:40 UTC. On the final 23:40 UTC image, there was a pilot report of severe turbulence as high as 47,000 feet in that same general area. The mountain wave signature to the lee of the Bighorn Mountains was not stationary, but was seen to exhibit some meandering during that time period.

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AWIPS images of GOES-13 0.63 µm visible channel data (above; click image to play animation) displayed a number of interesting Lake Michigan features on 16 February 2014: (1) the motion of lake ice in the northern and far eastern portions of the lake, (2) the formation of parallel cloud streets over the ice-free waters of the central part of lake, and (3) the development of a mesoscale vortex (or “mesovortex”) over the southern end of the lake.

Northerly winds were blowing down the long axis of Lake Michigan in the wake of a departing area of low pressure; Metop ASCAT surface scatterometer wind speeds were as high as 35 knots at 15:26 UTC (below).

False-color Red/Green/Blue (RGB) images created from Suomi NPP VIIRS 0.64 µm visible and 1.61 µm “snow/ice channel” data (below) helped to disctiminate between snow cover and ice fearures (which appeared as varying shades of red) and supercooled water droplet cloud features (which appeared as brighter shades of white). Even in the relatively short 1.5 hour period separating the two VIIRS RGB images, a significant amount of ice motion could be seen.

As an aside, another feature of interest seen in the GOES-13 visible images included arc-shaped aircraft dissipation trails (or “distrails”), created by air traffic that was likely circling upon approach or departure from the Chicago O’Hare or Midway airports (below; click image to play animation). Partcles in the aircraft exhaust acted as ice condensation nuclei, glaciating a trail as they penetrated the supercooled water droplet cloud deck.

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McIDAS-X images of MTSAT-1R 10.8 µm IR channel data (above; click image to play animation; also available as an MP4 animation) showed the rapid expansion of the volcanic umbrella cloud resulting from the eruption of Kelut (aka Kelud) on the Indonesian island of Java on 13 February 2014. The MTSAT-1R satellite was in rapid scan mode, providing images at 10-minute intervals (with some gaps). The initial signal of a volcanic cloud appeared as a small cluster of cold pixels on the 16:09 UTC (11:09 PM local time) IR image.

The dramatic signature of a distinct circular-shaped warm core (shades of red, around -60º C) surrounded by a ring of colder (shades of white, -75º to -80º C) cloud-top IR brightness temperatures possibly indicated that a portion of the cloud plume associated with the explosive eruption rose well into the lower stratosphere, and was therefore radiating at the warmer temperatures that existed far above the tropopause. The leading edge of the top of the cloud plume eventually exhibited IR brightness temperatures colder than -80º C (shades of violet) as it drifted toward the west-southwest, with a minimum of -84.5º C on the 19:29 UTC image. Along the upwind (eastern) portion of the volcanic cloud, a signature of “bow shock waves” was evident: an indication that the massive and dense volcanic cloud was acting as a barrier to the ambient easterly flow across the region. Volcanic lightning was also generated by the rising ash plume (see photos on the Wired Science “Eruptions” blog posts 1 and 2).

A more detailed view was provided by McIDAS-V images of Suomi NPP VIIRS 375-meter resolution 11.45 µm IR channel and 750-meter resolution 0.7 µm Day/Night Band data (above; images courtesy of William Straka, CIMSS). A ring of gravity waves could be seen around the periphery of the volcanic cloud shield; the coldest IR brightness temperature within the small cluster of “overshooting tops” was 175 K or -98º C (closer view). Since the Moon was in the Waxing Gibbous phase at 98% of full, it provided ample illumination for a “visible image at night” using the VIIRS Day/Night Band — note how the ash-laden volcanic cloud exhibited a darker gray appearance compared to the surrounding brighter white meteorological clouds.

A plot of the 13 February/12:00 UTC rawinsonde data from the nearby (map/IR image comparison) Surabaya/Juanda International Airport (above) showed that a very moist and marginally unstable (Lifted Index of only  -1.7) atmosphere existed over the region about 4 hours prior to the eruption — the tropopause was located at 105 millibars (mb), at an altitude of 16.29 km where the air temperature was -84.5º C. According to the volcanic ash advisory issued by the Darwin VAAC at 00:43 UTC on 14 February, the top of the volcanic ash extended to 55,000 feet or 16.76 km — somewhere between 100 mb and 87.1 mb on the Surabaya sounding. The warmest temperature recorded in the stratosphere by the sonde instrument was -71.3º C at 64.9 mb or 19.02 km.

A GOES-R Volcanic Ash Height product (VISITview lesson | PowerPoint) — derived using MTSAT-2 data — indicated that downwind portions of the ash cloud reached the 18-20 km ASL range (black color enhancement), with a maximum ash height value of 22 km (below; click image to play animation). CALIOP data from a CALIPSO overpass of the Kelut volcanic cloud just around 18:13 UTC on 13 February showed that the top of the volcanic cloud was generally at an altitude of 18-19 km, with some cloud/ash material reaching a maximum height of 26 km; taking that data source into consideration, a subsequent volcanic ash advisory issued by the Darwin VAAC at 17:09 UTC on 14 February revised the maximum ash height to 65,000 feet or 19.8 km.

With the arrival of early morning daylight, MTSAT-1R 0.68 µm visible channel images (below) showed the dense volcanic ash plume drifting west-southwestward; there was also a subtle signature of the “bow shock waves” seen along the eastern edge of the ash plume, similar to what was observed on the IR imagery.

Back to the topic of the 26 km height seen on the CALIPSO data: on the 10-minute interval MTSAT-1R 10.8 µm IR imagery, the warmest cloud-top IR brightness temperature within the “circular warm spot” of the volcanic cloud was -56ºC at 17:19 UTC. The 13 February/12 UTC Surabaya/Juanda rawinsonde only made it up to 64.9 mb or 19.02 km (where it was -71.3ºC) — however, the 14 February/00 UTC rawinsonde ascended all the way to 10 mb (below). So using this later sounding, the air temperature of -56ºC corresponded to an height somewhere between 24.9 mb (24.8 km) and 20 mb (26.2 km) — which roughly agrees with the 26 km height seen on the CALIOP data.

Additional satellite products showing details of the Kelut volcanic eruption can be found on Nicarnica Aviation blog posts (1 | 2).

 

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Examples of “industrial-enhanced snow” were seen in the Texas Panhandle region on 10 February 2014. In the overnight hours, areas downwind of agricultural plants near Borger (KBGD) received anywhere from 3.0 to 4.3 inches of snowfall. During the following morning and early afternoon hours, the particles contained within the hot, moist plume emanating from a factory located just northeast of Amarillo (KAMA) acted to glaciate the supercooled water droplets within the surrounding stratus deck — as the ice particles fell out of the cloud as snow, the cloud deck began to partially dissipate as seen in McIDAS images of 1-km resolution GOES-15 (GOES-West) and GOES-13 (GOES-East) 0.63 µm visible channel data (above).

A similar comparison of 4-km resolution GOES-15 and GOES-13 3.9 µm shortwave IR images (below) confirmed that the plume streaming southward from the Amarillo area was indeed glaciated — the plume appeared significantly colder (brighter white) compared to the surrounding supercooled water droplet stratus cloud deck, which appeared warmer (darker gray) due to the shortwave IR channel’s sensitivity to the reflection of solar radiation off the liquid droplet cloud tops.

A comparison of AWIPS images of 1-km resolution Terra MODIS 0.65 µm visible channel, 3.7 µm shortwave IR channel, and 11.0 µm IR window channel images (below) provided a slightly sharper view than the GOES images. Again, the glaciated plume south of Amarillo appeared colder (brighter white) than the surrounding supercooled water droplet clouds; on the IR window channel image, the slightly warmer (darker gray) signature was due to the satellite sensing radiation from the warmer ground surface through the thinner glaciated areas of the cloud plume.

A 250-meter resolution Terrra MODIS true-color Red/Green/Blue (RGB) image from the SSEC MODIS Today site (below; visualized using Google Earth) showed that the plume was drifting southward over parts of Interstate 27; one inch of snowfall was reported as far south as Happy, in the far northern part of Swisher county.

===== 11 February Update =====

On the folllowing day, a Terra MODIS true-color image at 17:44 UTC (below; visualized using Google Earth) provided a fantastic view of the mesoscale patch of snow cover southwest of Borger, Texas.

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