General interpretation « CIMSS Satellite Blog

Aurora Borealis seen on Suomi NPP VIIRS Day/Night Band imagery

May 9th, 2012

Suomi NPP VIIRS 0.7 µm Day/Night Band + 11.45 µm IR + "Fog/stratus product" images

An AWIPS comparison of Suomi NPP VIIRS 0.7 µm Day/Night Band (DNB), 11.45 µm IR, and IR brightness temperature difference “Fog/stratus product” images at 06:51 UTC on 09 May 2012 (above) revealed several ribbons of the aurora borealis (which showed up as bright west-to-east oriented features on the DNB image over Ontario and Quebec, Canada). Note that there was no correlation between these bright DNB aurora features and any high cloud features on the 11.45 µm IR image, or any low cloud or fog features on the legacy “fog/stratus product” image.

These aurora features would have been along the southern periphery of the auroral oval, which was expanding southward at that time according to images from the Space Weather Prediction Center (below).

Space Weather Prediction Center auroral oval product images

Photos of the aurora borealis were taken from Upsala, Ontario — located approximately halfway between Thunder Bay (station identifier CYQT) and Dryden (station identifier CYHD) — and posted on Spaceweather.com. These photos were taken about an hour prior to the VIIRS images shown above.

Posted in General interpretation, Suomi NPP, VIIRS | No Comments »

Undular bore over northeastern North Dakota and northwestern Minnesota

May 2nd, 2012

GOES-13 10.7 µm IR channel + 0.63 µm visible channel images (click image to play animation)

Surface outflow from dissipating convection over southern Manitoba, Canada during the pre-dawn hours on 02 May 2012 created an undular bore, which then propagated southeastward across northeastern North Dakota and northwestern Minnesota. AWIPS images of 4-km resolution GOES-13 10.7 µm IR channel data followed by 1-km resolution GOES-13 0.63 µm visible channel data after sunrise (above) showed the undular bore wave clouds. Surface winds associated with this convective outflow gusted to 30 knots in southern Manitoba at 12 UTC and 27 knots in northwestern Minnesota at 13 UTC.

POES AVHRR 12.0 µm IR image

An AWIPS image of 1-km resolution POES AVHRR 12.0 µm data (above) indicated that the wave cloud top IR brightness temperature was in the +2 to +3 C range. According to the 12 UTC rawinsonde data from International Falls, Minnesota (below), a temperature inversion located between 683 hPa and 693 hPa was likely acting to duct the undular bore as it moved southeastward.

International Falls, Minnesota rawinsonde data (12 UTC)

Posted in AVHRR, General interpretation, GOES-13, POES | No Comments »

Using VIIRS imagery for snow/ice vs cloud discrimination over Alaska, the Arctic Ocean, and the Bering Sea

April 26th, 2012

Suomi NPP VIIRS 0.64 µm visible channel + 1.61 µm near-IR channel images

AWIPS images of 1-km resolution Suomi NPP VIIRS 0.64 µm visible channel and 1.61 µm near-IR channel images (above) demonstrated the value of using the near-IR imagery to help discriminate between snow/ice (which appears darker on the near-IR image) and supercooled water droplet cloud features (which appear as brighter shades of white on the near-IR image) over northern Alaska and the Arctic Ocean on 23 April 2012. Numerous large leads (or cracks) in the Arctic Ocean sea ice are apparent on the visible channel image.

Many of the cloud features over the Arctic Ocean were thin and at a low altitude, so there was not a great deal of thermal contrast seen on the corresponding 11.45 µm IR image (below).

Suomi NPP VIIRS 1.61 µm near-IR channel + 11.45 µm IR channel images

Three days later (on 26 April 2012), a similar comparison of a Suomi NPP VIIRS 0.64 µm visible channel image with the corresponding 1.61 µm near-IR image (below) showed that much of the ice in the Bering Sea was beginning to break up (although a significant amount of land-fast ice remained along the western coastline of Alaska). The near-IR image also helped to highlight other interesting features along the far left edge of the satellite scene: aircraft contrails over Nunivak Island, and a thin trail of wave clouds extending downwind of St. Matthew Island.

Suomi NPP VIIRS 0.64 µm visible channel + 1.61 µm near-IR channel images

===========================================

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

An animation of 1-km resolution GOES-15 0.63 µm visible channel images (above; click image to play animation) showed the motion of the southern extent of the ice in the Bering Sea on 26 April. On the previous day, the sea ice had retreated northward from Saint George Island (station identifier PAPB), after a record-setting 79 consecutive days with sea ice. Farther to the north, the sea ice would remain at Saint Paul Island (station identifier PASN) into early May, also setting a new record for sea ice duration at that island.

A significant amount of sea ice motion could be seen on the GOES-15 visible images, due to strong surface winds over the southern Bering Sea on that day. In addition, the visible images revealed some interesting wave clouds immediately downwind of the higher terrain of some of the Aleutian Islands.

A better view of the southern extent of ice in the Bering Sea was available using a 1-km resolution NOAA-19 AVHRR false-color Red/Green/Blue (RGB) image (below). As with the GOES-15 images above, Saint Paul Island and Saint George Island are located near the center of the image.