Ice Remaining on the Great Lakes

April 16th, 2014

Suomi/NPP VIIRS Day Night Band imagery, 0740 UTC on 16 April 2014 [Click to enlarge]

Suomi/NPP VIIRS Day Night Band imagery, 0740 UTC on 16 April 2014 [Click to enlarge]

Mostly clear skies over the Great Lakes and a near-Full Moon allowed the Suomi NPP VIIRS Day/Night Band (DNB) imager to record the remaining extent of ice on the five Great Lakes with remarkable clarity at night.

Portions of Georgian Bay (Lake Huron), Green Bay (Lake Michigan) and southeastern Lake Superior continue to be ice-covered. Ice also remains in eastern Lake Erie, over northeastern Lake Michigan, and in parts of Lake Huron. Lake Ontario and Lake St. Clair are ice-free.

Daytime VIIRS DNB image (19:23 UTC on 15 April) and Nighttime VIIRS DNB image (07:40 UTC on 16 April)

Daytime VIIRS DNB image (19:23 UTC on 15 April) and Nighttime VIIRS DNB image (07:40 UTC on 16 April)

Taking a closer look at Lake Superior (above), it is interesting to compare the previous daytime VIIRS DNB image (at 19:23 UTC on 15 April) with the subsequent nighttime DNB image about 17 hours later (at 07:40 UTC on 16 April):

(1)  You can ascertain changes in the ice motion and areal coverage, even at night

(2) The later 16 April image showed that far northern portions of the Lake Superior ice had become snow-covered (exhibiting a brighter white appearance), after a weak disturbance brought small bands of lake-effect snow over that area (GOES-13 10.7 µm IR image animation). Even though the MODIS Sea Surface Temperature product showed that SST values over the open waters of northern Lake Superior were only in the low 30′s F, surface reports on the GOES-13 IR image animation indicated that the air moving across those waters in the wake of the weak disturbance was significantly colder. This fresh snow cover could have an impact on the ice melting rate in those areas.

Grassland fires in Kansas

April 12th, 2014
GOES-13 3.9 µm shortwave IR images (click to play animation)

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

Numerous grassland fires began to burn across parts of eastern Kansas (and also extreme northeastern Oklahoma) during the afternoon hours on 11 April 2014. AWIPS images of 4-km resolution GOES-13 3.9 µm shortwave IR channel data (above; click image to play animation) showed that many of these fires continued to burn into the overnight hours — the largest and most intense fire “hot spot” (black to yellow to red color enhancment) was seen northwest of Emporia, Kansas (station identifier KEMP) at 06:40 UTC or 1:40 AM local time, which exhibited an IR brightness temperature of 40º C. Smoke from these fires reduced the surface visibility as low as 2 miles at Manhattan (KMHK) and 4 miles at Topeka (KTOP). However, as high cirrus clouds began to move over the region later in the night and toward dawn, identification of the fire hot spots on GOES imagery became more difficult.

A comparison of 1-km resolution Suomi NPP VIIRS 3.74 µm and 4-km resolution GOES-13 3.9 µm shortwave IR images just after 07 UTC or 2 AM local time (below) demonstrated the advantage of higher spatial resolution for detecting not only the locations of many of the smaller fire hot spots, but also for providing a more accurate value of the intensity of the larger, hotter fires; in this case, the highest IR brightness temperature of the larger fire northwest of Emporia on the VIIRS image was 50.5º C (red color enhancement), compared to only 22.5º C (darker black color enhancement) on the GOES-13 image.

Suomi NPP VIIRS 3.74 µm and GOES-13 3.9 µm shortwave IR images

Suomi NPP VIIRS 3.74 µm and GOES-13 3.9 µm shortwave IR images

Since these fires were burning at night, they also exhibited bright signatures on the 0.7 µm Suomi NPP VIIRS Day/Night Band (DNB) image; lights from cities and towns also appeared as bright spots on the DNB image, but a comparison with the corresponding VIIRS 3.74 µm shortwave IR image helped to identify which could be attributed to actively burning fires (below).

Suomi NPP VIIRS 0.7 µm Day/Night Band and 3.74 µm shortwave IR images

Suomi NPP VIIRS 0.7 µm Day/Night Band and 3.74 µm shortwave IR images

As mentioned above, high cirrus clouds moving over the region later in the night made fire hot spot identification more difficult on the 4-km resolution GOES-13 shortwave IR imagery. However, a 1-km resolution POES AVHRR 3.74 µm shortwave IR image at 11:50 UTC or 6:50 AM local time (below) was able to detect a number of fire hot spots (darker black pixels) through the cirrus cloud features.

POES AVHRR 3.74 µm shortwave IR image

POES AVHRR 3.74 µm shortwave IR image

Rapidly intensifying mid-latitude cyclone off the East Coast of the US

March 26th, 2014
Composite of GOES-15 (GOES-West) and GOES-13 (GOES-East) 6.5 µm water vapor channel images (click to play animation)

Composite of GOES-15 (GOES-West) and GOES-13 (GOES-East) 6.5 µm water vapor channel images (click to play animation)

AWIPS images of a composite of 4-km resolution GOES-15 (GOES-West) and GOES-13 (GOES-East) 6.5 µm water vapor channel data (above; click image to play animation) showed the development of a large mid-latitude cyclone off the East Coast of the US on 26 March 2014. This cyclone underwent rapid intensification as it moved northeastward, with the storm’s central pressure deepening 43 hPa in 24 hours and reaching a minimum value of 955 hPa (which was lower than the 960 hPa minimum central pressure of the March 1993 “Storm of the Century”). Wind gusts in excess of 100 mph were observed both on offshore buoys (44027) and at coastal sites: as the storm approached the Canadian Maritimes, Wreckhouse in Newfoundland experienced an all-time record maximum wind gust of 116 mph (186 km/hour).

A closer view of the storm’s evolution on GOES-13 6.5 µm water vapor channel imagery with overlays of buoy reports, cloud-to-ground lightning strikes, and analyzed surface pressure and surface fronts is shown below.

GOES-13 6.5 µm water vapor channel images (click to play animation)

GOES-13 6.5 µm water vapor channel images (click to play animation)

McIDAS images of 1-km resolution GOES-13 0.63 µm visible channel data (below; click image to play animation) revealed greater detail in the cloud structures near the center of the storm circulation. The appearance of dual vortices can be seen, with the northernmost vortex appearing to be the dominant one associated with the true storm center.

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

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

A night-time view of the storm as it was beginning to intensify off the coast of Virginia at 05:56 UTC or 12:56 AM Eastern Time is seen in a comparison of Suomi NPP VIIRS 0.7 µm Day/Night Band (DNB) and 11.45 µm IR channel images (below). The bright white streaks appearing offshore on the DNB image are portions of the cloud illuminated by intense lightning — and there were a number of cloud-to-ground lightning strikes detected in the vicinity of these DNB lightning streaks.

Suomi NPP VIIRS 0.7 µm Day/Night Band and 11.45 µm IR channel images at 05:56 UTC

Suomi NPP VIIRS 0.7 µm Day/Night Band and 11.45 µm IR channel images at 05:56 UTC

As the period of rapid intensification continued off the eastern coast of the US, the GOES-13 sounder Total column Ozone product (animation) depicted very high values (400-450 Dobson Units, shades of red) just south of the storm center at 09:00 UTC, which was a signature of a potential vorticity anomaly (a lowering of the dynamic tropopause caused by an intrusion of dry, ozone-rich stratospheric air into the upper and middle troposphere). According to the GFS40 model, the height of the dynamic tropopause (taken to be the pressure of the PV1.5 surface) had descended to around the 450 hPa level at 06 UTC. The image comparison below shows that this pocket of high ozone was co-located with a pocket of dry middle-tropospheric air on the water vapor imagery, which became even drier with time to the point that it exhibited a light orange color enhancement around 12 UTC on the closer-view GOES-13 6.5 µm water vapor channel image animation seen above.

GOES sounder Total Column Ozone product and GOES imager 6.5 µm water vapor channel data

GOES sounder Total Column Ozone product and GOES imager 6.5 µm water vapor channel data

MODIS 0.65 µm visible channel, 11.0 µm IR channel, and 6.7 µm water vapor channel images at 15:40 UTC

MODIS 0.65 µm visible channel, 11.0 µm IR channel, and 6.7 µm water vapor channel images at 15:40 UTC

Daytime views of the storm structure were provided by comparisons of 1-km resolution MODIS 0.65 µm visible channel, 11.0 µm IR channel, and 6.7 µm water vapor channel images at 15:40 UTC or 10:40 AM Eastern Time (above) and 17:19 UTC or 12:19 PM Eastern Time (below).

MODIS 0.65 µm visible channel, 11.0 µm IR channel, and 6.7 µm water vapor channel images at 17:19 UTC

MODIS 0.65 µm visible channel, 11.0 µm IR channel, and 6.7 µm water vapor channel images at 17:19 UTC

A comparison of 375-meter resolution (projected onto a 1-km AWIPS grid) Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images at 17:19 UTC or 12:19 PM Eastern Time is shown below.

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images at 17:19 UTC

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images at 17:19 UTC

SSEC RealEarth comparison of GOES-13 IR and Suomi NPP VIIRS true-color RGB images

SSEC RealEarth comparison of GOES-13 IR and Suomi NPP VIIRS true-color RGB images

The images above demonstrate using the SSEC RealEarth web map server to compare GOES-13 IR and Suomi NPP VIIRS true-color Red/Green/Blue (RGB) images of the storm, zooming in on the true-color image for more detail of dual vortex cloud features near the circulation center. The GOES IR image showed the impressively large size of the overall cloud structure associated with the mid-latitude cyclone.

The large size of the cyclone is also apparent in the VIIRS 1.38 µm imagery shown here. This wavelength highlights ice crystals — that is, high clouds — within the storm.

Additional details and satellite images of this storm can be found on the GOES-R and JPSS Satellite Liaison Blog.

Suomi NPP VIIRS Sea Surface Temperature product flowing into AWIPS

March 21st, 2014
Suomi NPP Sea Surface Temperature product, 0727 UTC 21 March 2014

Suomi NPP Sea Surface Temperature product, 0727 UTC 21 March 2014

Suomi NPP VIIRS data are being used to compute sea-surface temperature (SST), and those fields are now being input into AWIPS for evaluation. The Suomi NPP images as displayed in AWIPS are labeled as MODIS SSTs (this was done to speed the injection process into AWIPS; however, note that the labels on VIIRS images for this blog post were modified to display the correct satellite source). Even though the labels are the same (both MODIS and VIIRS products are labeled “MODIS Sea Sfc Temperature” in AWIPS), the data sources are different, and the user can learn to identify the data being used.

A user can match the time of the image to overpass times for the Aqua, Terra or Suomi NPP satellites. Overlaying a different Suomi NPP image, for example 11.45 µm IR brightness temperature, below, that covers the same geographic region will also tell the user which data source — from VIIRS or MODIS — is being used to construct the SST product.

VIIRS-based SSTs and 11.45 µm IR brightness temperatures (click to enlarge)

VIIRS-based SSTs and 11.45 µm IR brightness temperatures (click to enlarge)

A MODIS-based SST from approximately the same time is shown below. The VIIRS swath is much wider than the MODIS swath. This will always be true.

MODIS and VIIRS-based SSTs at ~0805 UTC 20 February 2014 (click to enlarge)

MODIS and VIIRS-based SSTs at ~0730 UTC 21 March 2014 (click to enlarge)

Values for MODIS SSTs and VIIRS SSTs are similar. In general, the cloud-clearing with Suomi NPP VIIRS is more accurate, meaning there are more clear pixels with the Suomi NPP data and therefore more SST pixels. Note in particular differences in the strong temperature gradient along the edges of the Gulf Stream where MODIS algorithms mistakenly flag pixels as cloudy.

[Added: This animation cycles through the SSTs and the Window Channel IR images from both VIIRS and MODIS]

2 days earlier, a nighttime/daytime Suomi NPP VIIRS SST comparison on 19 March — magnified to provide a closer look at the Gulf of Mexico (below) — revealed intricate structure associated with the Loop Curent (the large darker red feature, with SST values around 80º F), as well as other small-scale eddys in the surrounding Gulf waters.

Suomi NPP VIIRS SST images at 08:03 UTC and 19:27 UTC on 19 March

Suomi NPP VIIRS SST images at 08:03 UTC and 19:27 UTC on 19 March