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

Severe Tropical Cyclone Ita

April 10th, 2014
MTSAT-2 10.8 µm IR channel images (click to play animation)

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

McIDAS images of MTSAT-2 10.8 µm IR channel data (above; click image to play animation) showed the development of a distinct eye associated with Intense Cyclone Ita (23P) as it moved southwestward across the Coral Sea toward the coast of Queensland, Australia on 10-11 April 2014. Cyclone Ita exhibited a period of rapid intensification (Advanced Dvorak Technique plot) early on 10 April, reaching Category 4 intensity (JTWC advisory) on the Saffir-Simpson scale (or a Category 5 on the Australian intensity scale: BOM advisory). Ita had been moving through an environment with weak deep layer wind shear and over warm sea surface temperatures, which aided in its intensification.

A timely overpass of a Metop polar-orbiting satellite provided ASCAT surface scatterometer winds at 11:26 UTC, as seen on an image from the CIMSS Tropical Cyclones site (below).

MTSAT-1 10.8 IR image with Metop ASCAT surface scatterometer winds

MTSAT-1 10.8 IR image with Metop ASCAT surface scatterometer winds

The structure of the eye of Ita was nicely displayed on a TRMM satellite TMI 85 GHz microwave image at 14:32 UTC (below).

TRMM TMI 85 GHz microwave image

TRMM TMI 85 GHz microwave image

A McIDAS-V image comparison of Suomi NPP VIIRS 11.45 µm IR and 0.7 µm Day/Night Band data at 14:58 UTC (below; courtesy of William Straka, SSEC/CIMSS) showed great detail of the eye and surrounding eyewall region of Ita.

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

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

The first available early-morning MTSAT-2 0.675 µm visible channel image at 20:32 UTC (below) revealed a convective tower within the northeastern portion of the eyewall region, with a distinct overshooting top (10-11 April animation of MTSAT-2 visible images).

MTSAT-2 0.675 µm visible channel image

MTSAT-2 0.675 µm visible channel image

The MTSAT InfraRed/Water Vapor difference product (below; click image to play animation) indicated that overshooting tops were likely around a large area surrounding the core of Ita.

MTSAT IR/WV Difference product (click to play animation)

MTSAT IR/WV Difference product (click to play animation)

===== 11 April Update =====

A TRMM satellite TMI 85 GHz microwave image at 05:23 UTC showed that Ita had a double-eyewall structure as it was close to making landfall, indicating that the cyclone was undergoing an eyewall replacement cycle — this suggests that Ita was in a weakening phase as it made landfall.

TRMM TMI 85 GHz microwave image

TRMM TMI 85 GHz microwave image

Tehuano wind event

April 8th, 2014
GOES-13 0.63 µm visible channel images (click to play animation)

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

As we have seen a number of times during the Winter 2013/2014 season, another strong Tehuano wind event occurred on 08 April 2014. McIDAS images of GOES-13 0.63 µm visible channel data (above; click image to play animation) showed distinct arc clouds marking the leading edge of 2 pulses of gap winds emerging southward over the Gulf of Tehuantepec. The second (later) pulse of gap winds appeared to be stronger, and transported plumes of blowing dust to the south.

A timely overpass of a Metop polar-orbiting satellite provided ASCAT surface scaterometer winds which showed the fanning out of the Tehuano flow at 16:20 UTC (below). An advisory for the development of Storm Force winds had been issued by the NOAA Ocean Prediction Center for the Gulf of Tehuantepec.

GOES-13 10.7 µm IR image with Metop ASCAT surface scatterometer winds

GOES-13 10.7 µm IR image with Metop ASCAT surface scatterometer winds

MADIS 1-hour interval satellite winds (below; click image to play animation) tracked the velocity of the arc cloud and dust plumes during the day, which were moving at speeds up to 30 knots.

GOES-13 10.7 µm IR images with MADIS 1-hour satellite winds (click to play animation)

GOES-13 10.7 µm IR images with MADIS 1-hour satellite winds (click to play animation)

Past cases of well-defined Tehuano wind events can be found here.

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.