Lunar Eclipse Effects on VIIRS Day/Night Band Imagery

April 15th, 2014
Suomi NPP VIIRS Day Night Band images, times as indicated

Suomi NPP VIIRS Day Night Band images, times as indicated

A Total Lunar Eclipse occurred over North America early in the morning of 15 April 2014. The resultant lack of lunar illumination had a profound impact on the “visible image at night” quality of the VIIRS 0.7 µm Day/Night Band imagery during the Suomi NPP satellite overpass at around 0800 UTC over the midsection of the United States. The animation above shows excellent illumination from the Full Moon at 0619 UTC (2:19 AM Eastern time) along the East Coast, and also at 0940 UTC (2:40 AM Pacific time) along the West Coast; however, the image at 0800 UTC (3:00 AM Central time), in the middle of eclipse totality, resembles Day/Night Band images seen during a New Moon. The three images can also be combined into a collage, as shown below, to illustrate the changes in the Day/Night band that occur as lunar intensity changes.

Collage of three successive Suomi NPP VIIRS Day Night Band images, times as indicated

Collage of three successive Suomi NPP VIIRS Day Night Band images, times as indicated

A comparison of three similar Day/Night Band images from the day before is here.

Even though the 08:00 UTC VIIRS Day/Night Band image exhibited a comparatively dull and “washed-out” appearance (due to very little illumination from eclipsed moonlight), there were still features of interest that could be seen. For example, a closer look over the southeastern US using the 0.7 µm Day/Night Band and 11.45 µm IR channel images (below) showed the effect of lightning activity associated with a pre-cold-frontal squall line over the Florida panhandle and the adjacent offshore waters of the Gulf of Mexico: a pair of long, narrow bright streaks (caused by cloud illumination from intense lightning activity as the sensor was rapidly scanning from northwest to southeast), abruptly followed by dark black streaks that eventually faded away. These dark black streaks represent post-saturation “recovery periods” after the sensor scanned the extremely bright cloud features. Incidentally, the coldest 11.45 µm IR brightness temperature over the Florida panhandle was -80º C (very near the area of dense cloud-to-ground lightning strikes).

Suomi NPP VIIRS 0.7 µm Day/Night Band and 11.45 µm IR channel images, with surface frontal analysis and 1-hour cloud-to-ground lightning strikes

Suomi NPP VIIRS 0.7 µm Day/Night Band and 11.45 µm IR channel images, with surface frontal analysis and 1-hour cloud-to-ground lightning strikes

Convectively-generated mesospheric airglow waves over Texas

April 4th, 2014
GOES-13 10.7 µm IR channel images (click to play animation)

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

AWIPS images of 4-km resolution GOES-13 (GOES-East) 10.7 µm IR channel images with overlays of cloud-to-ground lightning strikes and surface frontal positions (above; click image to play animation) showed the explosive development of a thunderstorm just ahead of a cold frontal boundary that was moving southeastward across southern Texas during the overnight hours on 04 April 2014 (06 UTC surface analysis). This relatively small thunderstorm was very active in terms of lightning production, and eventually produced hail of 1.0 to 1.75 inches in diameter and damaging winds (SPC storm reports) as it approached the coast of Texas. Cloud-top IR temperatures were as cold as -73º C on the GOES-13 images.

A 1-km resolution POES AVHRR 12.0 µm IR image at 08:41 UTC or 3:41 AM local time (below) exhibited cloud-top IR brightness temperatures as cold as -79º C. Overlays on the IR image include cloud-to-ground lightning strikes around the time of the IR image, along with the eventual reports of hail that this storm produced about an hour later. South of the thunderstorm, the banded signatre of a pre-frontal lower-tropospheric undular bore could also be seen across deep south Texas.

POES AVHRR 12.0 µm IR channel image, with cloud-to-ground lightning strikes and hail reports

POES AVHRR 12.0 µm IR channel image, with cloud-to-ground lightning strikes and hail reports

A comparison of 1-km resolution Suomi NPP VIIRS 11.45 µm IR and 0.7 µm Day/Night Band images at 08:05 UTC or 3:05 AM local time (below) showed an “enhanced-V” signature associated with the thunderstorm, with very cold IR brightness temperatures of -86º C at the vertex of the enhanced-V. The Day/Night Band (DNB) image also showed a number of very bright “streaks” near McMullen, Texas (station identifier KNMT), a signature of portions of the cloud which were illuminated by intense lightning activity. The blurred signatures of bright city lights could even be seen through the clouds. Also, note on the DNB image the presence of curved bands off the Texas coast, over the Gulf of Mexico: what could those be?

Suomi NPP VIIRS 11.45 µm IR channel and 0.7 µm Day/Night Band images, with overlays of positive and negative cloud-to-ground lightning strikes

Suomi NPP VIIRS 11.45 µm IR channel and 0.7 µm Day/Night Band images, with overlays of positive and negative cloud-to-ground lightning strikes

A larger-scale view of the VIIRS IR and Day/Night Band images (below) revealed a remarkably large pattern of concentric mesospheric airglow waves (reference) propagating radially outward away from the region where the thunderstorm had explosively developed and penetrated the tropopause about an hour earlier. Unlike the cloud bands associated with the lower-tropospheric undular bore in deep south Texas, there was no signature of these mesospheric airglow waves on the VIIRS IR image.

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

A Skew-T / Log-p plot of the 12 UTC rawinsonde data from Corpus Christi, Texas (below) indicated that the coldest temperature above the tropopause was around -71º C — so the -86º C IR brightness temperature seen on the VIIRS IR image suggests a vigorous thunderstorm overshooting top which penetrated the tropopause and ascended a significant distance into the lower stratosphere. Such a vigorous overshooting top likely triggered the upward-propagating mesospheric airglow waves. The sounding profile also showed how unstable the airmass was ahead of the advancing cold front: the Lifted Index was -11.6º C, and the Convective Available Potential Energy (CAPE, which is labelled on the sounding analysis as “POSITIVE ENERGY ABV LFC”) of 4218 J/kg. Such high convective instability would allow a thunderstorm updraft to reach a high upward vertical velocity.

Plot of 12 UTC Corpus Christi, Texas rawinsonde data

Plot of 12 UTC Corpus Christi, Texas rawinsonde data

10-km resolution GOES-13 sounder Cloud Top Height derived prodcut images (below) indicated maximum thunderstorm top values of 44,230 feet (brightest white color enhancement), which was around the altitude of the tropopause level on the Corpus Christi rawinsonde data.

GOES-13 sounder Cloud Top Height derived product images

GOES-13 sounder Cloud Top Height derived product images

For additional information and images of this mesospheric airglow wave event, see the CIRA/RAMMB VIIRS Imagery and Visualization Team blog.

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.

Severe thunderstorms over the Gulf of Mexico

March 6th, 2014
Suomi NPP VIIRS 11.45 µm IR channel and 0.7 µm Day/Night Band images (with CG lightning strikes)

Suomi NPP VIIRS 11.45 µm IR channel and 0.7 µm Day/Night Band images (with CG lightning strikes)

A night-time AWIPS image comparison of Suomi NPP VIIRS 11.45 µm IR and 0.7 µm Day/Night Band data (above) showed a large mesoscale convective system (MCS) over the Gulf of Mexico at 07:08 UTC (2:08 AM local time) on 06 March 2014. On the IR image, brightness temperatures were as cold as -80º C on the far southern end of the storm, which had developed in the warm sector of a developing area of low pressure (surface frontal analysis). The Day/Night Band image revealed: (1) numerous bright west-to-east oriented “lightning streaks” caused by intense lightning activity illuminating the MCS cloud and cloud top — note that there were over 1300 cloud-to-ground (CG) lightning strikes detected in a 15-minute period, and (2) arc-shaped mesospheric airglow waves propagating northward and northeastward away from the region of vigorous overshooting tops at the southern end of the MCS.

A comparison of the 375-meter resolution Suomi NPP VIIRS 11.45 µm IR image with a 4-km resolution GOES-13 10.7 µm IR image (below) showed that the higher spatial resolution of the VIIRS data provided much clearer view of the various cloud structures along with a better depiction of the values of the cloud-top IR brightness temperatures.

Suomi NPP VIIRS 11.45 µm IR and GOES-13 10.7 µm IR channel images

Suomi NPP VIIRS 11.45 µm IR and GOES-13 10.7 µm IR channel images

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

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

GOES-13 10.7 µm IR channel images (above; click image to play animation) showed the evolution of the MCS as it continued to move eastward toward Florida. A squall line developed along the leading edge of the MCS, which played a role in producing a few tornadoes and areas of damaging winds over the southern half of the Florida peninsula (below).

Plot of SPC storm reports

Plot of SPC storm reports