High-resolution Imagery of Stratus along the West Coast

October 10th, 2014 |
Suomi NPP 0.7 µm Day Night Band imagery at 0907 and 1048 UTC over central California with surface observations of ceilings and visibilities (click to enlarge)

Suomi NPP 0.7 µm Day Night Band imagery at 0907 and 1048 UTC over central California with surface observations of ceilings and visibilities (click to enlarge)

The Suomi NPP VIIRS Day Night Band during a Full (or near-Full) Moon yields striking visible imagery at night because of abundant reflected lunar illumination. Sequential orbits along the west coast of the Pacific on the morning of 10 October showed the penetration of coastal stratus and fog inland at two times (click here for the images above without the surface observations). A similar case study from 9 October is shown here. The slow inland penetration of stratus/fog is captured by the scenes: tendrils of fog extend up small valleys along the edge of the Salinas Valley, for example, and the fog extends farther down the valley at 1048 UTC. Similar expansion of fog occurs over Sonoma Valley north of San Francisco Bay.

Careful inspection of the imagery shows parallel lines along the western edge at 0907 UTC and along the eastern edge at 1048 UTC. In addition, city lights and topographic features are displaced somewhat along the eastern edge of the 1048 UTC image. These are all artifacts of the VIIRS instrument viewing geometry (that is, parallax) and post-processing that is necessary near the edges to maintain high-resolution imagery there.

A toggle between the corresponding VIIRS 11.45 µm – 3.74 µm infrared brightness temperature difference images (commonly referred to as the “fog/stratus product”), below, similarly shows gradual expansion of water-based clouds between 0907 and 1048 UTC. There are also image features, color enhanced as black, that suggest very thin cirrus is moving over the coast. These clouds are thin enough that they cannot be discerned in the Day Night Band imagery, but their presence nevertheless inhibits the detection of low clouds in places, such as over the southernmost part of the Salinas Valley at 1048 UTC.

Suomi NPP Brightness Temperature Difference (11.45 µm - 3.74 µm) Imagery at 0907 and 1048 UTC over central California (click to enlarge)

Suomi NPP Brightness Temperature Difference (11.45 µm – 3.74 µm) Imagery at 0907 and 1048 UTC over central California (click to enlarge)

Suomi NPP 0.7 µm visible Day Night Band imagery at 0907 and 1048 UTC over Washington State with surface observations of ceilings and visibilities (click to enlarge)

Suomi NPP 0.7 µm visible Day Night Band imagery at 0907 and 1048 UTC over Washington State with surface observations of ceilings and visibilities (click to enlarge)

The image toggle above shows similar features over Washington State. Fog/stratus tendrils move up river valleys in the ~90 minutes between the two polar-orbiting satellite passes, and areas of fog increase in size. (click here for the same images without observations). Because the first image is very near the edge of the VIIRS instrument scan swath, there is also a shift in city lights and some geographic features, again an artifact of scanning geometry (parallax) and the post-processing to maintain high-resolution imagery at the scan edges.

Suomi NPP Brightness Temperature Difference (11.45 µm - 3.74 µm) Imagery at 0907 and 1048 UTC over Washington State (click to enlarge)

Suomi NPP Brightness Temperature Difference (11.45 µm – 3.74 µm) Imagery at 0907 and 1048 UTC over Washington State (click to enlarge)

The IR brightness temperature difference product over Washington, above, also shows evidence of a slow increase in the areal coverage of fog/stratus near the coast. The effects of limb brightening are also present in the first image. When a satellite scans near the edge of its domain, the path from the point on the Earth to the satellite traverses more of the upper atmosphere, and a colder sensed temperature results. This effect is wavelength-dependent. For example, at one point (47º N, 125º W) in the stratus (with fairly uniform temperature) off the west coast of the Washington, in the stratus (which should have a fairly constant temperature), brightness temperatures were about 1º C cooler in 11.35 µm imagery, but closer to 2.5º C cooler in the 3.74 µm imagery. Hence, the brightness temperature difference signal is larger at 0906 UTC.

Both brightness temperature difference fields show signals over dry land that are related to emissivity differences in the soils. These occur over central Washington, above and over Nevada in the images centered over California.

“Blood Moon” total lunar eclipse, and a selenelion

October 8th, 2014 |

A “Blood Moon” total lunar eclipse occurred between 09:15 UTC and 12:34 UTC on 08 October 2014. One effect of this eclipse can be seen in a comparison of nighttime “during eclipse” and “after eclipse” Suomi NPP VIIRS 0.7 µm Day/Night Band images (above). The 11:33 UTC “during eclipse” Day/Night Band image appears somewhat dim and washed out, due to limited illumination by only red sunlight being refracted by the Earth’s atmosphere into the eclipse shadow. Less than 2 hours later, the 13:14 UTC Day/Night Band image appears much more bright with crisp cloud feature details, due to an abundance of illumination from the Full Moon.

A few hours after sunrise in North America, a portion of the Moon was captured on the GOES-13 (GOES-East) 0.63 µm visible channel image at 16:30 UTC (below). Note how the edges of the Moon appear slightly jagged, caused by the fact that it was moving (setting) behind the Earth as the GOES-13 imager instrument was scanning horizontally step-wise from north to south. In addition, at the point where the edge of the Moon meets the edge of the Earth, there is a “lensing effect” where the Earth’s atmosphere is refracting light from the Moon and creating the illusion of a curved wedge of dark space that is visible within the atmosphere.

Speaking of sunrise, an interesting aspect of this lunar eclipse was that it was a rare “selenelion”, when the rising sun in the east could be seen at the same time as the non-eclipsed portion of the setting moon in the west (Space.com article). This selenelion was captured at 12:03 UTC or 7:03 am local time by the east-looking and west-looking rooftop cameras on the Space Science and Engineering Center building (below; image captures courtesy of John Lalande, SSEC).

Super Typhoon Vongfong in the West Pacific Ocean

October 7th, 2014 |
Advanced Dvorak Technique plot for Typhoon Vongfong

Advanced Dvorak Technique plot for Typhoon Vongfong

Beginning shortly before 00 UTC on 07 October 2014, Typhoon Vongfong began a period of rapid intensification, as shown on a plot of the Advanced Dvorak Technique (ADT) intensity estimate (above). The peak ADT intensity late in the day was 146 knots. On the other hand, the CIMSS Satellite Consensus or SATCON indicated a peak intensity of 156 knots around that time.

MTSAT-2 10.8 µm IR channel images beginning during the period of rapid intensification on 07 October and extending into 08 October (below; click image to play animation; also available as an MP4 animation) revealed the formation of a very large and well-defined eye. There were large portions of the eyewall which exhibited cloud-top IR brightness temperatures of -80º C and colder (purple color enhancement).

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

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

A large-scale view and a close-up view of the eye of Vongfong using Suomi NPP VIIRS 0.7 µm Day/Night Band and 11.45 µm IR channel images at 16:59 UTC or 1:59 am local time are shown below (courtesy of William Straka, SSEC). Due to an abundance of reflected light from a Full Moon, these examples demonstrate the “visible image at night” capability of the VIIRS Day/Night Band.

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

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

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

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

In a comparison of a MTSAT-2 10.8 µm IR image with the corresponding DMSP SSMIS 85 GHz microwave image around 22:47 UTC (below), there was evidence of the formation of a larger secondary eyewall surrounding the primary eyewall (which can signal the beginning of an eyewall replacement cycle). Using the microwave data, the diameter of the eye was determined to be 60.59 km.

MTSAT-2 10.8 um IR image and DMSP SSMIS 85 GHz microwave image

MTSAT-2 10.8 um IR image and DMSP SSMIS 85 GHz microwave image

As the morning sun began to illuminate Super Typhoon Vongfong around 21:32 UTC, an MTSAT-2 0.675 µm visible channel image (below) provided a stunning view of the eye of the intense tropical cyclone. An animation of subsequent MTSAT-2 visible images revealed the presence of mesovortices within the eye.

MTSAT-2 0.675 µm visible channel image

MTSAT-2 0.675 µm visible channel image

08 October Update: A large-scale view and a close-up view of the eye of Super Typhoon Vongfong using Suomi NPP VIIRS 0.7 µm Day/Night Band and 11.45 µm IR channel images at 16:40 UTC or 1:40 am local time on 08 October are shown below (courtesy of William Straka, SSEC).

Suomi NPP VIIRS 0.7 µm Daqy/Night Band and 11.45 µm IR channel images

Suomi NPP VIIRS 0.7 µm Daqy/Night Band and 11.45 µm IR channel images

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

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

11 October Update: A large-scale view and a close-up view of the eye of a weakened Vongfong (as it passed near the island of Okinawa) using Suomi NPP VIIRS 0.7 µm Day/Night Band and 11.45 µm IR channel images at 17:18 UTC on 11 October are shown below (courtesy of William Straka, SSEC).

Suomi NPP VIIRS 0.7 µm Daqy/Night Band and 11.45 µm IR channel images

Suomi NPP VIIRS 0.7 µm Daqy/Night Band and 11.45 µm IR channel images

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

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

Additional satellite images of Super Typhoon Vongfong can be found on the Satellite Liaison Blog.

GOES-15 RSO Testing

October 7th, 2014 |
GOES-15 10.7 µm infrared channel imagery in Sitka Sector (click to enlarge)

GOES-15 10.7 µm infrared channel imagery in Sitka Sector (click to enlarge)

NOAA/NESDIS placed GOES-15 in Rapid Scan Operations (RSO) mode for several hours on 7 October 2014 (link) to test RSO capabilities over different sectors of the Pacific Ocean. RSO Capabilities over the Pacific were possible in the 1990s; the testing yesterday showed they could be done again. Three sectors were scanned. The Sitka sector, above (centered near the Island of Sitka), can monitor the eastern Gulf of Alaska and western North America. The other sectors were over Hawaii (below, the Hawaii Sector) and over the western Gulf of Alaska and parts of the Bering Sea (bottom, the TPARC Sector, which sector overlaps a THORPEX experiment site).

GOES-15 10.7 µm infrared channel imagery in Hawaii Sector (click to enlarge)

GOES-15 10.7 µm infrared channel imagery in Hawaii Sector (click to enlarge)

GOES-15 10.7 µm infrared channel imagery in TPARC Sector (click to enlarge)

GOES-15 10.7 µm infrared channel imagery in TPARC Sector (click to enlarge)

NESDIS is investigating why these RSO data did not flow into AWIPS as intended.

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Update, 15 October 2014.

A second RSO Test occurred on 15 October (Link). Data from this successful RSO test were available in AWIPS during this test. GOES-15 scanning strategies are shown here. The Hawaii sector is shown here. Data available over the Hawaii sector from 1930 to 2030 UTC on 15 October are shown below.

GOES-15 10.7 µm infrared channel imagery in Hawaii Sector (click to animate)

GOES-15 10.7 µm infrared channel imagery in Hawaii Sector (click to animate)