Meteorological Satellite Monitoring of Volcanic Ash Plumes from Kilauea Summit – May 15, 2018

The USGS Hawaiian Volcano Observatory raised the aviation alert level for Kilauea from Orange to Red on Tuesday, 15 May 2018.  The alert level was raised in response to an increase in the intensity of ash emissions from the summit crater.

False color imagery from the Himawari-8 satellite can be used to identify and track ash emissions.  One of the more relevant false color images is sometimes called the ash/dust RGB.  While interpretation of the ash/dust RGB is anything but straightforward, it is very useful for identifying ash and SO2 emissions under the right conditions.  SO2 emissions were discussed in a previous post.  In this post, 15 May 2018 ash emissions from Kilauea are highlighted.  A loop of Himawari-8 Ash/Dust RGB imagery from 1800 UTC 15 May to 0600 UTC 16 May 2018 is shown below.  There are two notable emissions of ash from Kilauea during this period.  The first ash emission, identifiable in loop below, occurs shortly after 1800 UTC.  A small, faint pink area emerges from the summit and is advected to the southwest, moving parallel to the Big Island coast from 1830 to 2130 UTC 15 May 2018, until the volcanic ash is obscured by higher meteorological clouds.  A second emission occurs in the 2100 – 2200 UTC timeframe, evidenced by the pink/gray color near the summit at 2110 UTC.  Meteorological clouds make the plume difficult to distinguish around 2200 UTC, but by 2300 UTC, the plume is again distinguishable as the pink/gray region south of the Kilauea summit extending over offshore regions.  The subtle ash feature slowly moves southwest, reaching the southern tip of the Big Island and offshore regions to the south by 0200 UTC 16 May 2018 and eventually becomes diffuse by 0400 UTC.

Volcanic ash tends to appear red/pink in this type of false color imagery largely because ash often absorbs radiation more strongly around 10-11 um than 12 um, while the opposite is true for meteorological clouds.  For Himawari-8, the 12-10 um brightness temperature difference (BTD) is placed on the red color gun.  Due to the aforementioned absorption effects, the 12 – 10 um BTD tends to be larger (compared to meteorological clouds) when ash is present.  The larger 12 – 10 um BTD results in a larger contribution from the red color gun in the RGB image.  It is important to keep in mind that there are numerous caveats associated with interpreting any satellite image, especially false color images that utilize several spectral channels, as the relationship between spectral channels is highly complicated.  False color images, like the one shown below, are available in near real-time on the VOLcanic Cloud Analysis Toolkit website.