Volcanic ash fall plume over the Kamchatka Peninsula

March 7th, 2013 |
Suomi NPP VIIRS 0.64 µm visible channel images

Suomi NPP VIIRS 0.64 µm visible channel images

AWIPS images of Suomi NPP VIIRS 0.64 µm visible channel images (above) revealed some interesting curved ice floe gyres in the Bering Sea just off the eastern coast of the Russian Kamchatka Peninsula on 07 March 2013. Also evident near the center of the visible images was a long, narrow, and slightly darker feature that was oriented approximately west-to-east, and located to the northwest and north of the village of Ust’-Kamchatsk (station identifier 32408). This darker feature was a volcanic ash fall plume from the Sheveluch Volcano (located 31 miles or 50 km to the northwest), which had experienced eruptions producing volcanic ash (photos) on 02 March and 04 March — the darker color of the narrow strip of volcanic ash made it stand out against the adjacent snow-covered areas (annotated visible image).

A comparison of a Suomi NPP VIIRS 0.64 µm visible channel image with the corresponding false-color Red/Green/Blue (RGB) image (below) also showed the contrast between the narrow strip of ash-covered snow and the surrounding undisturbed snow cover (snow and ice appear as darker shades of red in the RGB image).

Suomi NPP VIIRS 0.64 µm visible channel image + False-color Red/Green/Blue (RGB) image

Suomi NPP VIIRS 0.64 µm visible channel image + False-color Red/Green/Blue (RGB) image

A comparison of Suomi NPP VIIRS 0.64 µm visible channel, 3.74 µm shortwave IR channel, and 11.45 µm IR channel images (below) showed that the strip of ash-covered snow appeared significantly warmer (darker) on the shortwave IR image, due to the fact that the volcanic ash particles were efficient reflectors of incoming solar radiation. The ash-covered snow even appeared slightly warmer (darker) on the 11.45 µm IR image, since the lower albedo of the ash-covered snow allowed it to absorb more incoming solar radiation.Also evident on the shortwave IR image was a distinct hot thermal anomaly (yellow to red color enhancement) associated with the active Kizimen volcano.

Suomi NPP VIIRS 0.64 µm visible channel, 3.74 µm shortwave IR channel. and 11.45 µm IR channel images

Suomi NPP VIIRS 0.64 µm visible channel, 3.74 µm shortwave IR channel. and 11.45 µm IR channel images

An animation of McIDAS images of MTSAT-2 0.73 µm visible channel data (below; click image to play animation) confirmed that the darker volcanic ash fall plume was a stationary feature, and not an airborne volcanic ash plume. The animation also showed the anticyclonic rotation of the gyres of ice floes just off the east coast of Kamchatka.

MTSAT-2 0.73 µm visible channel images (click image to play animation)

MTSAT-2 0.73 µm visible channel images (click image to play animation)

Undular bore over Texas and the Gulf of Mexico

March 5th, 2013 |
MODIS IR brightness temperature difference

MODIS IR brightness temperature difference “fog/stratus product”, 3.7 µm shortwave IR, 11.0 µm IR window, and 6.7 µm water vapor channel images

A comparison of AWIPS images of MODIS 11.0-3.7 µm IR brightness temperature difference “fog/stratus product”, 3.7 µm shortwave IR, 11.0 µm IR window, and 6.7 µm water vapor channel images (above) showed the night-time (08:04 UTC or 3:04 AM local time) development of parallel cloud bands associated with an undular bore that was forming in advance of a strong cold frontal boundary which was  moving southward across Texas on 05 March 2013. Note how the cloud band features showed up with better clarity in the 3.7 µm IR image compared to the 11.0 µm IR image, since the shortwave IR channel is more sensitive to warmer temperatures (the IR brightness temperatures of the cloud bands averaged about +5º C).

After sunrise, the undular bore cloud bands coud be seen moving southeastward off the coast of Texas and across the adjacent offshore waters of the Gulf of Mexico on McIDAS images of GOES-13 0.63 µm visible channel data (below; click image to play animation).

GOES-13 0.63 µm visible channel images (click image to play animation)

GOES-13 0.63 µm visible channel images (click image to play animation)

As the leading edge of the bore passed through Corpus Christi, Texas (CRP on the GOES-13 visible images), surface observations (below) indicated that winds gusted to 38 knots or 44 mph at 12:27 UTC.

Corpus Christi surface observations

Corpus Christi surface observations

The 12 UTC morning rawinsonde data from Corpus Christi (below) revealed a very strong and deep boundary layer temperature inversion (with a top around 962 hPa or 2460 feet), which was acting to duct the undular bore as it propagated southeastward.

Corpus Christi, Texas rawinsonde data

Corpus Christi, Texas rawinsonde data

MODIS 0.65 µm visible channel image and MODIS Sea Surface Temperature product

MODIS 0.65 µm visible channel image and MODIS Sea Surface Temperature product

It is interesting to note that in the wake of the undular bore passage, there appeared to be a signal of Gulf of Mexico water wave activity in both the MODIS Sea Surface Temperature product (above) and the Suomi NPP VIIRS 11.45 µm IR channel image (below). On each corresponding visible channel image, a subtle wave signature could also be seen, but these waves did not appear to be cloud features. Could the strong winds of the bore passage have created wave swells which then acted to mix the water surface enough to allow a small amount of cold water upwelling?

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images

Polar low over the western Bering Sea

March 3rd, 2013 |
Suomi NPP VIIRS 0.7 µm Day/Night Band images

Suomi NPP VIIRS 0.7 µm Day/Night Band images

AWIPS images of 1-km resolution Suomi NPP VIIRS 0.7 µm Day/Night Band data (above) showed the development of a small polar low in the far western Bering Sea during the 02 March – 03 March 2013 period. A string of breaking Kelvin-Helmholtz waves could be seen feeding into the circulation of the developing low. Station identifiers 25941, 25954, and 21956 denote the villages of Cemurnaut, Korf, and Apuka (respectively) located on the northern end of the Kamchatka Peninsula of Russia.

The corresponding Suomi NPP VIIRS 11.45 µm IR channel images (below) indicated that cloud top IR brightness temperatures were colder than -30º C (darker blue color enhancement) near the center of the polar low circulation.

Suomi NPP VIIRS 11.45 µm IR channel images

Suomi NPP VIIRS 11.45 µm IR channel images

Suomi NPP VIIRS false-color Red/Green/Blue (RGB) images (below) showed that the polar low was developing just south of the sea ice edge (snow and ice appear as darker shades of red). The appearance of red shading also indicated that the cloud tops along the string of Kelvin-Helmholtz waves were beginning to glaciate. Note from the distance scale plotted on the lower left that the diameter of the polar low circulation was less than 100 miles.

Suomi NPP VIIRS false-color Red/Green/Blue (RGB) images

Suomi NPP VIIRS false-color Red/Green/Blue (RGB) images

A larger-scale view using a Suomi NPP VIIRS 0.64 µm visible channel image (below) helped to emphasize the small size of the Bering Sea polar low, especially when compared to the much larger storm system that was located just south of the Aleutian Islands at that time. The tightly-packed isobars of another strong storm approaching from the North Pacific Ocean could also be seen.

Suomi NPP VIIRS 0.64 µm visible channel image + Surface reports and surface analysis

Suomi NPP VIIRS 0.64 µm visible channel image + Surface reports and surface analysis

McIDAS images of MTSAT-2 0.73 µm visible channel data (below; click image to play animation) indicated that the polar low was initially moving southeastward away from the Kamchatka Peninsula, but then began to reverse direction and move back northwestward due to strong southeasterly flow in advance of the large and intense storm over the North Pacific Ocean.

MTSAT-2 0.73 µm visible channel images (click image to play animation)

MTSAT-2 0.73 µm visible channel images (click image to play animation)

Mountain wave “banner cloud” over Montana

March 1st, 2013 |
GOES-15 (left) and GOES-13 (right) 6.5 µm water vapor channel images (click image to play animation)

GOES-15 (left) and GOES-13 (right) 6.5 µm water vapor channel images (click image to play animation)

McIDAS images of 4-km resolution GOES-15 (GOES-West) and GOES-13 (GOES-East) 6.5 µm water vapor channel images (above; click image to play animation) showed a well-defined high altitude mountain wave cloud (or “banner cloud”) immediately downwind of the high elevations of the Rocky Mountains in western Montana on 01 March 2013.

A comparison of AWIPS images of 1-km resolution Suomi NPP VIIRS 0.64 µm visible channel, 11.45 µm IR channel, and 3.74 µm shortwave IR channel image at 20:47 UTC (below) revealed that this banner cloud exhibited 11.45 µm IR cloud top brightness temperatures as cold as -70º C (darker black color enhancement), yet on the 3.74 µm shortwave IR image the cloud top brightness temperatures were as warm as +24º C. These very warm shortwave IR brightness temperature values indicated that the banner cloud was composed of ice crystals that were quite small, and were thus very efficient reflectors of incoming solar radiation (reference: Ackerman, S. A., C. C. Moeller, K. I. Strabala, H. E. Gerber, L. E. Gumley, W. P. Menzel, and S-C Tsay, 1998: Retrieval of Effective Microphyscial Properties of Clouds: a Wave Cloud Case Study, Geophys. Res. Lett., 25, 1121-1124.)

Suomi NPP VIIRS 0.64 µm visible channel, 11.45 µm IR channel, and 3.74 µm shortwave IR channel images

Suomi NPP VIIRS 0.64 µm visible channel, 11.45 µm IR channel, and 3.74 µm shortwave IR channel images

The 1-km resolution POES AVHRR Cloud Top Height product (below) indicated that portions of this banner cloud were as high as 12 km (or around 39,000 feet). While an AIRMET had been issued advising of the possibility of moderate turbulence below 20,000 feet across the region, there was one pilot report of moderate turbulence at 38,000 feet earlier in the day at 16:37 UTC in the vicinity of the banner cloud.

POES AVHRR Cloud Height product

POES AVHRR Cloud Height product

Strong westerly to southwesterly winds flowing across the higher elevations of the Rocky Mountains were causing a chinook wind event to occur, as adiabatic compression of the downsloping winds warmed the air. Some of the warmest surface air temeratures were seen in areas of southern Alberta, Canada that were free of snow cover — in that region MODIS Land Surface Temperature values exceeded 60º F (below).

MODIS Land Surface Temperature product + MODIS 0.65 µm visible channel image

MODIS Land Surface Temperature product + MODIS 0.65 µm visible channel image

===== 02 March Update =====

In a night-time comparison of Suomi NPP VIIRS 0.7 µm Day/Night Band, 11.45 µm IR channel, and 3.74 µm shortwave IR channel images at 09:02 UTC or 3:02 AM local time (below), note that in the absence of reflcted sunlight the coldest shortwave IR brightness temperatures seen within the banner cloud (-63º C) were much closer to those seen on the 11.45 µm IR image (-69º C).

Suomi NPP VIIRS 0.7 µm Day/Night Band, 11.45 µm IR channel, and 3,74 µm shortwave IR channel images

Suomi NPP VIIRS 0.7 µm Day/Night Band, 11.45 µm IR channel, and 3,74 µm shortwave IR channel images