Category 5 Cyclone Pam in the South Pacific

March 12th, 2015 |
MTSAT-2 10.8 µm IR images (click to play animation)

MTSAT-2 10.8 µm IR images (click to play animation)

Cyclone Pam in the South Pacific Ocean was rated at Category 5 intensity by the Joint Typhoon Warning Center at 18 UTC on 12 March 2015. MTSAT-2 10.8 µm IR channel images (above; click image to play animation; also available as an MP4 movie file) showed the well-defined eye as the storm moved southwestward across the Vanuatu archipelago during the 12-13 March time period.

The corresponding MTSAT-2 0.7 µm visible channel images (below; click image to play animation) revealed a complex structure of gravity waves and transverse banding surrounding the eye.

MTSAT-2 0.7 µm visible channel images (click to play animation)

MTSAT-2 0.7 µm visible channel images (click to play animation)

A comparison of the 12 March 21:32 UTC MTSAT-2 visible image and the 21:44 UTC Metop ASCAT surface scatterometer winds from the CIMSS Tropical Cyclones site is shown below.

MTSAT-2 visible image and Metop ASCAT surface scatterometer winds

MTSAT-2 visible image and Metop ASCAT surface scatterometer winds

Just prior to the time when Pam was beginning to enter a period of rapid intensification (ADT intensity estimate plot), a nighttime comparison of Suomi NPP VIIRS 0.7 µm Day/Night Band and 11.45 µm Infrared images at 13:37 UTC on 11 March is shown below.

Suomi NPP VIIRS 0.7 µm Day/Night Band and 11.45 µm Infrared images

Suomi NPP VIIRS 0.7 µm Day/Night Band and 11.45 µm Infrared images

Satellite detection of ice-glazed snow cover

March 5th, 2015 |
Suomi NPP VIIRS 0.64 µm visible and 1.61 µm near-IR

Suomi NPP VIIRS 0.64 µm visible and 1.61 µm near-IR “snow/ice channel” images (04 March)

Comparisons of Suomi NPP VIIRS 0.64 µm visible channel and 1.61 µm near-IR “snow/ice channel” images on 04 March 2015 (above) and 05 March 2015 (below) revealed a large area of ice-glazed snow cover in the Upper Midwest. On 03 March, a northeastward surge of moisture ahead of an approaching strong arctic cold front produced areas of light snow, freezing rain, freezing drizzle, and fog across parts of southeastern Minnesota, eastern Iowa, southern and central Wisconsin, and northern Illinois — and farther to the south from northeastern Missouri into central Illinois it was warm enough for rain as the precipitation type. This precipitation fell onto a pre-existing snow cover (NOHRSC 03 March snow depth), making the skin of the snow cover icy and/or wet (depending on the air temperature); with the passage of the strong arctic cold front,  this icy and/or wet snow surface quickly froze, creating a large area of ice-glazed snow cover.

At the 1.61 µm wavelength, since ice is a stronger absorber of radiation than snow, the ice-glazed snow areas appeared darker black compared to the surrounding snow cover; areas with a dense concentration of trees (cities; river valleys) tended to diminish this darker black signal.

Suomi NPP VIIRS 0.64 µm visible and 1.61 µm

Suomi NPP VIIRS 0.64 µm visible and 1.61 µm “snow/ice channel” images (05 March)

A toggle between the 04 March and 05 March 1.61 µm snow/ice channel images (below) showed more of the darker ice-glazed snow cover area as the clouds began to clear the region on 05 March (NOHRSC snow depth: 04 March | 05 March).

Suomi NPP VIIRS 1.61 µm near-IR

Suomi NPP VIIRS 1.61 µm near-IR “snow/ice channel” images (04/05 March)

A photo of the ice-glazed snow cover in Middleton, Wisconsin (a western suburb of Madison) on 05 March is shown below.

Photo of ice-glazed snow cover in Middleton, Wisconsin (05 March)

Photo of ice-glazed snow cover in Middleton, Wisconsin (05 March)

Rapidly-melting snow in the south-central US

March 5th, 2015 |
GOES-13 0.63 µm visible channel images (click to play animation)

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

GOES-13 (GOES-East) 0.63 µm visible channel images (above; click image to play animation; also available as an MP4 movie file) showed how rapidly the streaks and patches of snow cover melted across parts of the south-central US (primarily Kansas, Oklahoma, Texas, and adjacent states) on 05 March 2015. According to NOHRSC, morning snow depths (contour map | numerical snow depth values) were generally in the 2-4 inch range, with some sites reporting 5 inches on the ground.

The narrow snow band in Kansas went through the Witchita area; a 15-meter resolution Landsat-8 0.59 µm panochromatic visible image from the SSEC RealEarth web map server (below) provided a very detailed view of the snow cover in that area.

Landsat-8 0.59 µm panochromatic visible image (with and without Google Maps labels)

Landsat-8 0.59 µm panochromatic visible image (with and without Google Maps labels)

Eruption of the Villarrica volcano in central Chile

March 3rd, 2015 |
Suomi NPP VIIRS 0.7 µm Day/Night Band, 1.6 µm near-IR, 3.9 µm shortwave IR, and 11.45 µm longwave IR images

Suomi NPP VIIRS 0.7 µm Day/Night Band, 1.6 µm near-IR, 3.9 µm shortwave IR, and 11.45 µm longwave IR images

There was an explosive eruption of the Villarrica volcano in central Chile on the morning of 03 March 2015; the Buenos Aires VAAC issued their first volcanic ash advisory based upon initial detection on 06:38 UTC GOES-13 imagery, although media report and blog sources indicated that the eruption started closer to 06:00 UTC (3 am local time). A comparison of 06:07 UTC Suomi NPP VIIRS 0.7 µm Day/Night Band (DNB), 1.6 µm near-IR, 3.9 µm shortwave IR, and 11.45 µm longwave IR images (above; courtesy of William Straka, SSEC) revealed a bright glow on the DNB and near IR images, with a pronounced “hot spot” evident on the shortwave IR (yellow to orange pixels; the hottest shortwave IR brightness temperature was over 600 K!) and even the longwave IR (darker black pixels) images. The DNB image was particularly striking, with nearby clouds and surface features being illuminated by the eruption.

MODIS and GOES-13 multispectral false-color Red/Green/Blue (RGB) images from the NOAA/CIMSS Volcanic Cloud Monitoring site (below; click image to play animation) showed that there was detection of a thermal anomaly or “hot spot” (indicated by a red box) as early as 04:20 UTC (MODIS) and 05:45 UTC (GOES-13); the volcanic cloud filament — which was estimated to be at an altitude of 30,000 feet — could be seen drifting to the southeast following the eruption.

MODIS and GOES-13 false-color RGB images (click to play animation)

MODIS and GOES-13 false-color RGB images (click to play animation)

On GOES-13 10.7 µm IR channel images (below; click image to play animation), the volcanic cloud initially exhibited an IR brightness temperature as cold as -42ºC  (green color enhancement), but the cloud filament quickly became very diffuse and difficult to identify on the IR images by 09:38 UTC.

GOES-13 10.7 µm IR images (click to play animation)

GOES-13 10.7 µm IR images (click to play animation)

The 12 UTC rawinsonde profiles from Puerto Montt, Chile (station identifier SCTE) on 02 March and 03 March are shown below. On the 02 March profile, the -42º C temperature was at an altitude around 9400 meters or 30,800 feet; on the 03 March profile, -42º C was around 9100 meters or 29,900 feet.

Puerto Montt, Chile 12 UTC rawinsonde profiles on 02 March and 03 March

Puerto Montt, Chile 12 UTC rawinsonde profiles on 02 March and 03 March

On GOES-13 3.9 µm shortwave IR images (below; click image to play animation) a “hot spot” (black to yellow to red color enhancement) was seen for several hours after the initial eruption. The highest shortwave IR brightness temperature observed by GOES-13 was 340.8 K — much lower than than the >600 K observed with the higher spatial resolution Suomi NPP VIIRS instrument.

GOES-13 3.9 µm shortwave IR channel images (click to play animation)

GOES-13 3.9 µm shortwave IR channel images (click to play animation)