{"id":50364,"date":"2023-02-09T17:22:00","date_gmt":"2023-02-09T17:22:00","guid":{"rendered":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/?p=50364"},"modified":"2023-02-10T18:33:19","modified_gmt":"2023-02-10T18:33:19","slug":"sar-observations-over-american-samoa-part-iv","status":"publish","type":"post","link":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/archives\/50364","title":{"rendered":"SAR Observations over American Samoa (part IV)"},"content":{"rendered":"\n
\"\"<\/a>
GOES-18 Clean Window Infrared (10.3 \u00b5m) imagery, Visible (0.64 \u00b5m) imagery, RADARSAT-2 SAR Winds, 0550 UTC on 9 February 2023 (Click to enlarge)<\/figcaption><\/figure>\n\n\n\n

RADARSAT-2 passed over Samoan waters again on 9 February 2023, just after sunset (above) and near sunrise (at bottom). The imagery above compares the SAR winds to GOES-18 visible (with a changed enhancement to account for low light conditions, with reflectance values ranging from 0 to 6.3 only vs. the maximum default of 130) and infrared imagery at the same time. Several features of note deserve comment: both the strong convection just west\/southwest of Savai’i, Samoa, and the cold cloud tops at the southern edge of the domain, have very little signal in the surface wind field.<\/p>\n\n\n\n

A feature of interest to me is the slight change in windspeeds highlighted in the toggle below, extending north from the Samoan Islands. Is this slight change in SAR-derived winds, from 6 knots (bright purple, to the west) to 8 knots (darker purple, to the east) related to any obvious linear feature in the visible and infrared imagery? At first blush, a disappointing no is the answer!<\/p>\n\n\n\n

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SAR Winds and GOES-18 visible (Band 2, 0.64 \u00b5m) and infrared (Band 13, 10.3 \u00b5m) imagery zoomed in over the region north of the Samoan Islands, 0550 UTC on 9 February 2023 (Click to enlarge)<\/figcaption><\/figure>\n\n\n\n

An image below shows RADARSAT-2 SAR winds at 0552 and 1655 UTC (Note: the color enhancement of the winds has been changed to have a maximum of 25 kts, vs. 40 knots in the imagery above). When SAR observations occurred over Guam in November 2022, the effect of the Marianas island chain on winds extended a significant distance downwind of the island, as shown in this image<\/a> from 0840 UTC on 10 November from this blog post<\/a>. Why might the effects of the Samoan Islands not extend as far downstream; that is, why is the effect of the island not trapped? The toggle below shows the Guam SkewT from 1200 UTC on 10 November 2022<\/a> and the SkewT from Pago Pago at 1200 UTC on 9 February 2023<\/a>; (both SkewTs are from the University Of Wyoming sounding site<\/a>). One thing the Guam sounding features that is missing from the Pago Pago sounding is a stable layer from 850 to 750 hPa; that stable layer might affect how the Island Effect persists downwind.<\/p>\n\n\n\n

\"\"<\/a><\/figure>\n\n\n\n
\"\"<\/a>
RADARSAT-2 SAR Winds over the Samoan Islands, 0552 and 1655 UTC on 9 February 2023 (Click to enlarge)<\/figcaption><\/figure>\n\n\n\n

The toggle below compares SAR winds with GOES-18 clean window imagery. At 1655 UTC, the coldest cloud tops are related to perturbations in the wind field, especially in the southern part of the domain.<\/p>\n\n\n\n

\"\"<\/a>
GOES-18 Clean Window infrared (10.3 \u00b5m) imagery and RADARSAT derived SAR winds, 1650-1655 UTC on 9 February 2023 (Click to enlarge)<\/figcaption><\/figure>\n","protected":false},"excerpt":{"rendered":"

RADARSAT-2 passed over Samoan waters again on 9 February 2023, just after sunset (above) and near sunrise (at bottom). The imagery above compares the SAR winds to GOES-18 visible (with a changed enhancement to account for low light conditions, with reflectance values ranging from 0 to 6.3 only vs. the maximum default of 130) and […]<\/p>\n","protected":false},"author":19,"featured_media":50368,"comment_status":"closed","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[114,104,25],"tags":[],"class_list":["post-50364","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-goes-18","category-sar","category-satellite-winds"],"acf":[],"_links":{"self":[{"href":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-json\/wp\/v2\/posts\/50364","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\/19"}],"replies":[{"embeddable":true,"href":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-json\/wp\/v2\/comments?post=50364"}],"version-history":[{"count":3,"href":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-json\/wp\/v2\/posts\/50364\/revisions"}],"predecessor-version":[{"id":50394,"href":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-json\/wp\/v2\/posts\/50364\/revisions\/50394"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-json\/wp\/v2\/media\/50368"}],"wp:attachment":[{"href":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-json\/wp\/v2\/media?parent=50364"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-json\/wp\/v2\/categories?post=50364"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-json\/wp\/v2\/tags?post=50364"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}