Airborne glacial silt from the Copper River Valley in Alaska

October 28th, 2014
GOES-15 0.63 µm visible channel images (click to play animation)

GOES-15 0.63 µm visible channel images (click to play animation)

McIDAS images of GOES-15 0.63 µm visible channel data (above; click image to play animation) showed the hazy signature of airborne glacial silt drifting southward out of the Copper River valley and over the adjacent waters of the Gulf of Alaska on 28 October 2014. The strong winds lofting the silt were very localized to the Copper River valley itself, with cold dense arctic air from further inland (air temperatures were 8 to 10º F at Gulkana, PAGV) accelerating through narrow mountain passes — note how winds at nearby Cordova (PACV) were generally calm during much of the period. As the western edge of the airborne silt reached Middleton Island (PAMD), the surface visibility dropped as low as 5 miles.

AWIPS II images of Suomi NPP VIIRS data provided a better view of the aerial coverage of the glacial silt: a comparison of VIIRS 0.64 µm visible channel and 1.61 µm near-IR “snow/ice channel” images (below) showed that the 1.61 µm image offered better contrast to help locate the edges of the feature. This 1.61 µm channel imagery will be available from the Advanced Baseline Imager (ABI) on GOES-R.

Suomi NPP VIIRS 0.64 µm visible channel and 1.61 µm near-IR

Suomi NPP VIIRS 0.64 µm visible channel and 1.61 µm near-IR “snow/ice channel” images

Two consecutive VIIRS 1.61 µm images (below) revealed the changes in aerosol coverage between 21:43 UTC and 23:22 UTC.

Suomi NPP VIIRS 1.61 µm near-IR

Suomi NPP VIIRS 1.61 µm near-IR “snow/ice channel” images

The more dense portion of the airborne glacial silt particle feature exhibited a slightly warmer (darker gray) appearance on VIIRS 3.74 µm shortwave IR images, due to efficient reflection of incoming solar radiation.

Suomi NPP VIIRS 3.74 µm shortwave IR images

Suomi NPP VIIRS 3.74 µm shortwave IR images

A VIIRS true-color Red/Green/Blue (RGB) image from the SSEC RealEarth site (below) offered a good view of the coverage of the glacial silt at 21:45 UTC.

Suomi NPP VIIRS true-color image

Suomi NPP VIIRS true-color image

An extratropical storm containing the remnants of Ana makes landfall in North America

October 27th, 2014
GOES-15 6.5 µm water vapor channel images (click to play animation)

GOES-15 6.5 µm water vapor channel images (click to play animation)

A strong storm that contains the remnants of former central Pacific Hurricane Ana began to make landfall along the West Coast of North America on 27 October 2014 (12 UTC surface analysis). The 17-day animation of GOES-15 6.5 µm Water Vapor channel imagery, above, shows Ana emerging out of the Intertropical Convergence Zone, skirting south of Hawai’i, weakening and meandering in the central Pacific (showing the effects of strong vertical wind shear), briefly reaching Hurricane intensity again on 25 October, and eventually moving eastward after having been picked up and absorbed by a strong system in the Westerlies. Recurving tropical systems can sometimes be prolific rain producers in the mid-latitudes; however, the animation of MIMIC Total Precipitable Water, below, suggests that most of the tropical moisture that was associated with Ana was no longer present.

MIMIC Total Precipitable Water for 72 hours ending 1200 UTC 27 October 2014 (click to enlarge)

MIMIC Total Precipitable Water for 72 hours ending 1200 UTC 27 October 2014 (click to enlarge)

The annotated animation below shows 1200 UTC imagery from 11-27 October. The red arrow points to Ana, either as a developing tropical cyclone, Hurricane, or post-tropical system. An animation without the red arrow is here.

GOES-15 6.5 µm water vapor channel images (click to play animation)

GOES-15 6.5 µm water vapor channel images (click to play animation)

Shadow of partial solar eclipse

October 23rd, 2014
GOES-15 0.63 µm visible channel images

GOES-15 0.63 µm visible channel images

McIDAS images of GOES-15 (GOES-West) 0.63 µm visible channel data (above) showed the west-to-east progression of the lunar umbra (the Moon’s shadow) from a partial solar eclipse that occurred on 23 October 2014. The shadow was most obvious across the northern portion of the images, moving over Alaska, the Gulf of Alaska, western/northern Canada, and the far northwestern portion of the Lower 48 States of the US. The partial eclipse shadow could also be seen on GOES-13 (GOES-East) 0.63 µm visible channel images (below).

GOES-13 0.63 µm visible channel images

GOES-13 0.63 µm visible channel images

According to EarthSky.org the point of greatest eclipse (75% coverage of the solar disk by the Moon) was near Prince of Wales Island, Nunavut, Canada at 21:44 UTC. In a sequence of before, during, and after-eclipse AWIPS images of Suomi NPP VIIRS 0.64 µm visible channel data (below), a darkening of Canada’s Yukon Territory — which covered most of the center portion of the images — could be seen.

Suomi NPP VIIRS 0.64 µm visible channel images

Suomi NPP VIIRS 0.64 µm visible channel images

Hurricane Ana south of Hawai’i

October 21st, 2014
Advanced Dvorak Technique (ADT) intensity estimate plot for Ana

Advanced Dvorak Technique (ADT) intensity estimate plot for Ana

A plot of the Advanced Dvorak Technique (ADT) intensity estimate for Ana (above) shows that the strength of the tropical cyclone fluctuated during its multi-day lifetime (storm track), initially becoming a strong Tropical Storm on 15 October, weakening on 16 October, and then slowly intensifying into a Category 1 Hurricane. A sequence of Suomi NPP VIIRS 11.45 µm IR channel images (below; click image to play animation) shows Ana at various stages during the 15-21 October period; the coldest cloud-top IR brightness temperature seen was -95º C at 00:40 UTC on 19 October.

Suomi NPP VIIRS 11.45 µm IR channel images (click to play animation)

Suomi NPP VIIRS 11.45 µm IR channel images (click to play animation)

After prior testing of additional Rapid Scan Operations (RSO) capabilities, the GOES-15 satellite was placed into RSO mode over the Hawai’i region to monitor Ana. During the 17-19 October period that Ana was classified as a Hurricane, GOES-15 10.7 µm IR channel images (below; click image to play a 75 MB animated GIF; also available as an MP4 movie file) revealed a number of robust convective bursts, with some exhibiting cloud-top IR brightness temperatures in the -80 to -85º C range (violet color enhancement). This was the first operational implementation of GOES-West RSO imagery over the Hawai’i region since the early 1990s, and the higher frequency of images — 8 images per hour, instead of the routine 4 images per hour — proved to be helpful for monitoring Ana (CPHC forecast discussion).

Longer-term animations of GOES-15 RSO imagery covering the lifetime of Ana are available in YouTube format (IR | visible). Much of the Hawaiian Islands received heavy rain, with amounts in excess of 11 inches reported on Hawai’i and Oahu.

GOES-15 10.7 µm IR channel images (click to play animated GIF)

GOES-15 10.7 µm IR channel images (click to play animated GIF)

Even after Ana was downgraded to a Tropical Storm early on 20 October, a Suomi NPP VIIRS 11.45 µm IR image showed that cloud-top IR brightness temperatures were still as cold as -90º C (yellow pixels within the violet-enhanced cloud tops). Also note the presence of cloud-top gravity waves propagating outward away from the storm center.

Suomi NPP VIIRS 11.45 µm IR channel image, with overlays of surface analysis and surface observations

Suomi NPP VIIRS 11.45 µm IR channel image, with overlays of surface analysis and surface observations

Late in the day on 20 October, GOES-15 0.63 µm visible channel images (below; click to play animation; also available as an MP4 movie file) revealed that the Low-Level Circulation Center (LLCC) of Ana became exposed as it moved to the southwest from beneath the canopy of deep convective cloud tops. This was a result of moderate southwesterly deep-layer wind shear across the region.

GOES-15 0.63 µm visible channel images (click to play animation)

GOES-15 0.63 µm visible channel images (click to play animation)

During the following night, the exposed LLCC was still very apparent on a Suomi NPP VIIRS 0.7 µm Day/Night Band image at 12:30 UTC or 2:30 am local time (below).

Suomi NPP VIIRS 0.7 µm Day/Night Band image