{"id":622,"date":"2008-03-12T23:59:59","date_gmt":"2008-03-12T23:59:59","guid":{"rendered":"http:\/\/cimss.ssec.wisc.edu\/satellite-blog\/archives\/622"},"modified":"2013-10-22T18:21:31","modified_gmt":"2013-10-22T18:21:31","slug":"bennett-island-plume","status":"publish","type":"post","link":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/archives\/622","title":{"rendered":"Bennett Island plume"},"content":{"rendered":"

\"NOAA-18<\/a><\/p>\n

[Hat-tip to Gregg Gallina (NOAA\/NESDIS Satellite Analysis Branch) for bringing this interesting case to our attention…]<\/em> A false-color RGB image derived from 1-km resolution NOAA-18 AVHRR data (above)<\/strong><\/em> showed a long, narrow cloud plume streaming northwestward from Bennett Island<\/strong><\/a> (or “Ostrov Bennetta”, a tiny island north of Russia in the East Siberian Sea; latitude <\/em>76.5\u00c2\u00b0N, longitude 149\u00c2\u00b0E ; maximum elevation 426 m or 1398 ft)<\/em> on 12 March 2008<\/strong><\/a>.<\/p>\n

A large number of similar “plume features” have been detected on polar-orbiting satellite imagery in that same region since the 1970s and 1980s, but the explanation for their cause and composition (volcanic ash? methane plume? secret Soviet nuclear weapons testing?)<\/em> remained elusive until aircraft studies in the 1990s determined that they were orographically-induced cloud plumes, <\/strong>enhanced by a vertically propagating mountain wave<\/strong> (Reference #1<\/strong><\/a> | Reference #2<\/strong><\/a>).<\/p>\n

\"MODIS
\n<\/a><\/p>\n

A 250-meter resolution Terra MODIS visible image (above)<\/strong><\/em> shows a closer view of Bennett Island and the source of the cloud plume (note that this satellite image is not<\/strong> re-mapped, so the top of the image is oriented toward the northeast).<\/em> You can also see that there is a polynya<\/strong><\/a> — an area of open water — just to the lee (northwest, or left)<\/em> of the island; could this warm water have served as a source of low-level instability to help initiate vertical motions that contributed to the cloud plume formation?<\/p>\n

\"NOAA-18<\/a><\/p>\n

A comparison of the five 1-km resolution NOAA-18 AVHRR channels (above)<\/strong><\/em> revealed several important points: (1)<\/strong> the visible channels (channels 01 and 02)<\/em> showed that there was a large shadow being cast by the cloud plume feature, suggesting that the plume was at a high altitude;<\/em> (2)<\/strong> the “darker appearance” on the 3.7 \u00c2\u00b5m shortwave IR (channel 03)<\/em> image was suggestive of reflection of solar radiation off the tops of a cloud that was composed of either supercooled water droplets <\/em>or very small<\/em> ice crystals; (3)<\/strong> the 10.8 \u00c2\u00b5m and 12.0 \u00c2\u00b5m longwave IR (channels 04 and 05)<\/em> brightness temperature values were generally in the -28\u00c2\u00ba C to -45\u00c2\u00ba C<\/strong> range (darker blue to violet colors),<\/em> again suggesting a high-altitude plume;<\/em> and (4) <\/strong>at lower altitudes, small-scale wave clouds immediately downwind of Bennett Island confirmed that the topography of the island was having some effect on lee cloud formation.<\/p>\n

The issue of cloud composition (supercooled water droplets, or ice crystals?)<\/em> vs. cloud top brightness temperature is perplexing, however: supercooled water cloud droplets are known to exist at temperatures as cold as -25\u00c2\u00ba to -35\u00c2\u00ba C<\/strong>, but the spontaneous freezing of supercooled droplets (via homogeneous nucleation)<\/em> is thought to occur around -36\u00c2\u00ba to -40\u00c2\u00ba C<\/strong> (smaller<\/em> droplets freeze at colder<\/em> temperatures). It is possible that the lower- to middle-altitude portions of the cloud plume did consist of supercooled water droplets (giving a relatively high 3.7 \u00c2\u00b5m reflectance),<\/em> but the higher-altitude portions of the cloud plume were likely made up of ice crystals. Note that the coldest NOAA-18 IR cloud-top temperatures (-47\u00c2\u00ba C<\/strong>, red colors)<\/em> were near the plume source, immediately downstream of the highest terrain of Bennett Island — this was due to a greater amplitude near the source of the vertically-propagating mountain wave, which was producing the highest cloud-top altitude<\/em> at that particular location.<\/p>\n

\"Terra<\/a><\/p>\n

An IR difference product using Terra MODIS 8.5 \u00c2\u00b5m – <\/em>11.0 \u00c2\u00b5m (channel 29 – channel 31)<\/em> data suggests that the upper portion of the long cloud plume was composed primarily of ice crystals — a positive<\/em> IR difference value of several degrees K (brighter white enhancement)<\/em> indicates the presence of ice crystals<\/strong>. However, another item of curiosity is the initial “rotor cloud” feature immediately downwind of the island: note the darker “donut hole” appearance on the MODIS IR difference product, which suggests that the center part of the cloud top was composed primarily of supercooled water droplets<\/strong>; perhaps that rotor cloud was in the process of rapidly glaciating during that time?<\/p>\n

\"AWIPS<\/a><\/p>\n

700 hPa wind fields (from a 00:00 UTC global model analysis) plotted on an AWIPS image of the 03:00 UTC global IR satellite composite (above)<\/strong><\/em> indicated that there was a southeasterly flow of 30-35 knots at that level over the Bennett Island region (located near the center of the image),<\/em> which explains the southeast-to-northwest orientation of the cloud plume on the NOAA-18 AVHRR imagery.<\/p>\n

\"NOAA
\n<\/a><\/p>\n

Polar cloud-tracked atmospheric motion vectors (winds)<\/strong><\/a> derived from NOAA-15 and NOAA-17 AVHRR InfraRed data (above)<\/strong><\/em> also showed that a southeasterly flow aloft dominated across that region early in the day on 12 March. The Bennett Island cloud plume can be seen as a thin white streak on the final 05:42 UTC NOAA-17 image (since no wind vectors were plotted over the top of the cloud feature at that time).<\/em><\/p>\n

\"Chokurdah<\/a><\/p>\n

The 00:00 UTC rawinsonde report from Chokurdah along the north coast of Siberia (above)<\/strong><\/em> indicated that there was a strong temperature inversion below the 850 hPa pressure level; air temperatures in the -28\u00c2\u00ba C to -45\u00c2\u00ba C range (similar to those seen in the NOAA-18 IR imagery above)<\/em> were found between 700 – 450 hPa (where there was still a southeasterly flow, albeit somewhat slower in velocity).<\/em><\/p>\n

It is still unclear why the cloud plume feature formed at a relatively high altitude, when the island itself has a maximum altitude of only 1398 ft. As stated at the conclusion of Reference #2<\/strong> above: “But the Bennett Island plumes have not yielded all their mystery. Meteorologists must now explain why the plumes form at an unusually high altitude, more than 3 kilometers above the mountaintops, says Schnell.”<\/em> I only wish that I<\/strong> were the meteorologist to do that…<\/p>\n","protected":false},"excerpt":{"rendered":"

[Hat-tip to Gregg Gallina (NOAA\/NESDIS Satellite Analysis Branch) for bringing this interesting case to our attention…] A false-color RGB image derived from 1-km resolution NOAA-18 AVHRR data (above) showed a long, narrow cloud plume streaming northwestward from Bennett Island (or “Ostrov Bennetta”, a tiny island north of Russia in the East Siberian Sea; latitude 76.5\u00c2\u00b0N, […]<\/p>\n","protected":false},"author":18,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[37,22,10,12,26,45,25],"tags":[],"class_list":["post-622","post","type-post","status-publish","format-standard","hentry","category-arctic","category-avhrr","category-general-interpretation","category-modis","category-poes","category-redgreenblue-rgb-images","category-satellite-winds"],"acf":[],"_links":{"self":[{"href":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-json\/wp\/v2\/posts\/622","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-json\/wp\/v2\/users\/18"}],"replies":[{"embeddable":true,"href":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-json\/wp\/v2\/comments?post=622"}],"version-history":[{"count":4,"href":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-json\/wp\/v2\/posts\/622\/revisions"}],"predecessor-version":[{"id":14190,"href":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-json\/wp\/v2\/posts\/622\/revisions\/14190"}],"wp:attachment":[{"href":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-json\/wp\/v2\/media?parent=622"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-json\/wp\/v2\/categories?post=622"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-json\/wp\/v2\/tags?post=622"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}