Denali (“Mt. McKinley”) erupts!

June 11th, 2009 |
GOES-11 visible images

GOES-11 visible images

Well, not really — but a very interesting cloud plume formed yesterday and streamed off the 20,318-ft (6194-m) summit of Denali (“Mt. McKinley”) in southern Alaska on 10 June 2009, which almost had the  appearance of a volcanic eruption plume. GOES-11 visible images (above) showed this thin cloud plume spreading out as it curved to the southeast and then to the south, eventually moving over Anchorage and then the Kenai Peninsula.

A 1-km resolution NOAA-18 AVHRR 10.8 µm IR image (below) indicated that IR brightness temperatures were quite warm for such a high-altitude cirrus plume, barely reaching the -15 to -20º C range. Due to the thin nature of this cloud plume, a significant amount of radiation from the warmer ground surfaces below was bleeding upward through the thin cloud layer and reaching the satellite detectors.

NOAA-18 AVHRR 10.8 µm IR image

NOAA-18 AVHRR 10.8 µm IR image

A false-color NOAA-18 Red/Green/Blue (RGB) image (below) showed the “transparent” nature of the cloud plume, with snow cover features on the ground clearly recognizable beneath the cloud.

NOAA-18 AVHRR false color RGB image

NOAA-18 AVHRR false color RGB image

Tracking the location of the leading edge of the thin cloud plume feature was difficult using single-channel satellite imagery, which underscores the importance of using multi-spectral satellite products such as the 10.8 – 12.0 µm IR difference  (below) to correctly analyze the cloud location. Areas where the IR difference product reached +7 to +10 K (cyan colors) corresponded to the thicker portions of the cloud plume.

NOAA-18 IR difference product (10.8 - 12.0 µm, channel 04 - 05)

NOAA-18 IR difference product (10.8 - 12.0 µm, channel 04 - 05)

The cloud plume was curving to the southeast and then to the south due to the presence of a ridge of high pressure aloft over southern Alaska, as seen on an AWIPS image of the GOES-11 IR channel with an overlay of the GFS model 500 hPa winds (below).

GOES-11 10.7 µm IR image + GSF 500 hPa winds

GOES-11 10.7 µm IR image + GSF 500 hPa winds

A tip of the hat to Emily Niebuhr, UW-Madison / AOS graduate student, who is currently up in Alaska and brought this to our attention!