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.

Fix for GOES-13 Sounder Pixel Drop-outs

March 24th, 2014
GOES-13 Sounder 10.7 µm imagery without and with Processing Software changes (click to enlarge)

GOES-13 Sounder 10.7 µm imagery without and with Processing Software changes (click to enlarge)

The GOES-13 (GOES-East) Sounder instrument has been experiencing data anomalies that manifest themselves as missing pixels (link, link). These errors occurred because of slight fluctuations in the speed of the sounder filter wheel, resulting in a time offset. Processing software expects the data to be present at a certain time, but because of the filter wheel speed fluctuations, data were not present when expected. All 19 spectral bands on the GOES-13 Sounder were affected.

Missing data can now be reclaimed using a modified version of the SPS (Sensor Processing System), the ground software that makes the GVAR data stream. GOES Engineers have been testing this software change. The test software modifications properly handle the slight differences in the timing of the data. As of this time, a date has not been slated for operational implementation by NOAA NESDIS.

An example with all 19 bands of the GOES-13 Sounder is shown below, with the current pixel drop-outs (top) and after the software changes were applied (bottom) as part of off-line testing (image toggle).

GOES-13 Sounder imagery (all 19 bands) [click to enlarge]

GOES-13 Sounder imagery (all 19 bands) [click to enlarge]

GOES-13 Sounder imagery (all 19 bands) produced with new processing software [click to enlarge]

GOES-13 Sounder imagery (all 19 bands) produced with new processing software [click to enlarge]

Strong storm off the coast of California

February 28th, 2014
GOES-15 6.5 µm water vapor channel images (click to play animation)

GOES-15 6.5 µm water vapor channel images (click to play animation)

McIDAS images of 4-km resolution GOES-15 6.5 µm water vapor channel data (above; click image to play animation; also available as an MP4 animation) showed the development of a strong and rapidly-occluding storm off the coast of California during the 27 February28 February 2014 period.

An AWIPS image of 17:30 UTC GOES-15 water vapor channel data with overlays of 17:28 UTC Metop ASCAT surface scatterometer winds and the 18:00 UTC tropical surface analysis (below) showed satellite-sensed surface winds as strong as 51 knots in the southwestern quadrant of the storm.

GOES-15 6.5 µm water vapor channel image with ASCAT surface scatterometer winds and surface analysis

GOES-15 6.5 µm water vapor channel image with ASCAT surface scatterometer winds and surface analysis

Greater detail in the storm structure could be seen in 1-km resolution MODIS 6.7 µm water vapor channel images at 10:32 UTC and 21:40 UTC (below).

MODIS 6.7 µm water vapor channel images

MODIS 6.7 µm water vapor channel images

One indication of the strength of the storm was the high amounts of GOES-15 sounder Total Column Ozone associated with the circulation (below; click image to play animation), which reached levels as high as 440-450 Dobson Units (lighter red color enhancement). Such high levels of total column ozone are also often associated with potential vorticity anomalies and a dramatically lowered tropopause — in this case, the GFS40 model indicated the the dynamic tropopause (taken to be the pressure of the PV1.5 surface) was as below the 480 hPa pressure level at 18:00 UTC. It is interesting to note that there was a pilot report of moderate turbulence at 36,000 feet, along the sharp western gradient of the total column ozone (and the sharp gradient of the PV1.5 pressure) — the pilot noted that the turbulene lasted for 10 minutes.

GOES-15 sounder Total Column Ozone product (click to play animation)

GOES-15 sounder Total Column Ozone product (click to play animation)

A comparison of 375-meter resolution Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images at 22:08 UTC (below) revealed a few convective elements offshore which exhibited cloud-top IR brightness temperatures as cold as -50º C (yellow color enhancement), with a few cloud-to-ground lightning strikes being detected.

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images (with cloud-to-ground lightning strikes)

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images (with cloud-to-ground lightning strikes)

===== 01 March Update =====

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 comparison of Suomi NPP VIIRS 0.7 µm Day/Night Band (DNB) and 11.45 µm IR channel images at 10:22 UTC or 2:22 AM local time on 01 March (above) revealed the presence of numerous arc-shaped mesospheric airglow waves in the western semicircle of the storm circulation on the DNB image — note that there was no corresponding wave signature on the IR image.

These vertically-propagating mesospheric airglow waves were likely generated by the 140-knot jet streak that was moving southward around the rear side of the storm  (below).

Suomi NPP VIIRS 0.7 µm Day/Night Band image with NAM 250 hPa winds and isotachs

Suomi NPP VIIRS 0.7 µm Day/Night Band image with NAM 250 hPa winds and isotachs