Transverse banding: a signature of potential turbulence

July 20th, 2016

GOES-13 Infrared Window (10.7 um) images, pilot reports of turbulence, Turbulence AIRMET boundaries [click to play animation]

GOES-13 Infrared Window (10.7 um) images, pilot reports of turbulence, Turbulence AIRMET boundaries [click to play animation]

GOES-13 (GOES-East) Infrared Window (10.7 µm) images (above) showed the formation of tendrils of transverse banding along the northern semicircle of  decaying mesoscale convective systems as they moved eastward across Nebraska and Iowa on 19 July 2016. Pilot reports of turbulence are plotted on the images, along with Turbulence AIRMET polygons issued at 0800 UTC and 1400 UTC. Most of the pilot reports of turbulence were in the Light to Moderate category, although there was one report of Moderate to Severe intensity at 1612 UTC over eastern Iowa.

The corresponding GOES-13 Water Vapor (6.5 µm) images (below) perhaps highlighted the transverse banding features a bit better at times, since the weighting function for that spectral band generally peaks in the middle to upper troposphere where the transverse banding cloud features existed.

GOES-13 Water Vapor (6.5 um) images, pilot reports of turbulence, Turbulence AIRMET boundaries [click to play animation]

GOES-13 Water Vapor (6.5 um) images, pilot reports of turbulence, Turbulence AIRMET boundaries [click to play animation]

A sequence of Infrared Window images from POES AVHRR (10.8 µm) and Suomi NPP VIIRS (11.45 µm) (below) showed a higher-resolution view of the initial formation of transverse banding during the 0411 to 1008 UTC time period.

Infrared Window images from POES AVHRR (10.8 µm) and Suomi NPP VIIRS (11.45 µm) [click to enlarge]

Infrared Window images from POES AVHRR (10.8 µm) and Suomi NPP VIIRS (11.45 µm) [click to enlarge]

Shown below are two other types of satellite imagery that can be helpful for identifying the areal extent of transverse banding cloud features: the Suomi NPP VIIRS Day/Night Band (0.7 µm), and the MODIS Cirrus band (1.37 µm). A similar Cirrus band will be part of the ABI instrument on GOES-R.

Suomi NPP VIIRS Infrared Window (11.45 µm) and Day/Night Band (0.7 µm) images [click to enlarge]

Suomi NPP VIIRS Infrared Window (11.45 µm) and Day/Night Band (0.7 µm) images [click to enlarge]

Terra MODIS Infrared Window (11.0 µm) and Cirrus (1.37 µm) images [click to enlarge]

Terra MODIS Infrared Window (11.0 µm) and Cirrus (1.37 µm) images [click to enlarge]

Mesoscale Convective System in the Upper Midwest

July 6th, 2016

GOES-13 Infrared Window (10.7 um) images, with SPC storm reports [click to play animation]

GOES-13 Infrared Window (10.7 µm) images, with SPC storm reports [click to play animation]

GOES-13 (GOES-East) 4-km resolution Infrared Window (10.7 µm) images (above) showed the development of a large Mesoscale Convective System (MCS) which produced tornadoes, large hail, and damaging winds (SPC storm reports | NWS La Crosse summary) as it propagated southeastward across the Upper Midwest during the evening and overnight hours of 05 July06 July 2016.

A sequence of 1-km resolution Terra/Aqua MODIS (11.0 µm), 1-km resolution POES AVHRR (12.0 µm) and 375-meter resolution Suomi NPP VIIRS (11.45 µm) Infrared images (below) showed better details of such features as overshooting tops, some of which exhibited IR brightness temperature values as cold as -78º C on MODIS, -81º C on AVHRR and -86º C on VIIRS.

Infrared MODIS (11.0 um), AVHRR (12.0 um) and VIIRS (11.45 um) images, with SPC storm reports [click to play animation]

Infrared MODIS (11.0 µm), AVHRR (12.0 µm) and VIIRS (11.45 µm) images, with SPC storm reports [click to play animation]

A comparison of Suomi NPP VIIRS Infrared Window (11.45 µm) and Day/Night Band (0.7 µm) images at 0852 UTC or 3:52 am local time (below) showed the MCS as its core was centered over northern Illinois. Note how the tall, dense cloud mass blocked the view of nearly all city lights over a large area — including the normally very large and very bright lights of the Chicago metroplex. With almost no illumination from the Moon (which was in its Waxing Crescent phase, at 1% of Full), only the faint light of airglow helped to illuminate some cloud features over the northern portion of the satellite scene. In addition, numerous bright white streaks were seen in the Day/Night Band image along the leading (southern) edge of the MCS, due to cloud illumination from intense lightning activity; one lone lightning streak was evident in Wisconsin, whose intensity was bright enough to saturate the Day/Night Band detectors (hence the long “post-saturation recovery” streak as the sensor continued scanning toward the southeast).

Suomi NPP VIIRS Infrared Window (11.45 um) and Day/Night Band (0.7 um) images [click to enlarge]

Suomi NPP VIIRS Infrared Window (11.45 µm) and Day/Night Band (0.7 µm) images [click to enlarge]

A few hours earlier at 0339 UTC, the CLAVR-x POES AVHRR Cloud Top Height product (below) showed areas with height values of 16-17 km (lighter cyan color enhancement) — the large amount of water and ice particles contained within such tall clouds was therefore able to effectively block the view of city lights on the VIIRS Day/Night Band image. Note that a Cloud Top Height product will be available from the ABI instrument on GOES-R.

POES AVHRR Cloud Top Height product and Infrared (12.0 um) image [click to enlarge]

POES AVHRR Cloud Top Height product and Infrared (12.0 µm) image [click to enlarge]

First full day of Summer: snow in the Brooks Range of Alaska

June 22nd, 2016

GOES-15 Water Vapor (6.5 µm) images [click to play animation]

GOES-15 Water Vapor (6.5 µm) images [click to play animation]

GOES-15 (GOES-West) Water Vapor (6.5 µm) images (above) showed the southeastward migration of an upper-level low across the North Slope and the eastern Brooks Range of Alaska during the 21 June – 22 June 2016 period. A potential vorticity (PV) anomaly was associated with this disturbance, which brought the dynamic tropopause — taken to be the pressure of the PV 1.5 surface — downward to below the 600 hPa pressure level over northern Alaska. Several inches of snow were forecast to fall in higher elevations of the eastern portion of the Brooks Range.

With the very large satellite viewing angle (or “zenith angle”) associated with GOES-15 imagery over Alaska  — which turns out to be 73.8 degrees for Fairbanks — the altitude of the peak of the Imager 6.5 µm water vapor weighting function (below) was shifted to higher altitudes (in this case, calculated using rawinsonde data from 12 UTC on 22 June, near the 300 hPa pressure level).

GOES-15 Imager water vapor (Band 3, 6.5 µm) weighting function [click to enlarge]

GOES-15 Imager water vapor (Band 3, 6.5 µm) weighting function [click to enlarge]

The ABI instrument on GOES-R will have 3 water vapor bands, roughly comparable to the 3 water vapor bands on the GOES-15 Sounder — the weighting functions for those 3 GOES-15 Sounder water vapor bands (calculated using the same Fairbanks rawinsonde data) are shown below. Assuming a similar spatial resolution as the Imager, the GOES-15 Sounder bands 11 (7.0 µm, green) and 12 (7.4 µm, red) would have allowed better sampling and visualization of the lower-altitude portion of this particular storm system. The 3 ABI water vapor bands are nearly identical to those on the Himawari-8 AHI instrument; an example of AHI water vapor imagery over part of Alaska can be seen here.

GOES-15 Sounder water vapor weighting function plots [click to enlarge]

GOES-15 Sounder water vapor weighting function plots [click to enlarge]

As the system departed and the clouds began to dissipate on 22 June, GOES-13 Visible (0.63 µm) images (below) did indeed show evidence of bright white snow-covered terrain on the northern slopes and highest elevations of the Brooks Range.

GOES-15 Visible (0.63 µm) images [click to play animation]

GOES-15 Visible (0.63 µm) images [click to play animation]

A sequence of 1-km resolution POES AVHRR Visible (0.86 µm) images (below) showed a view of the storm during the 21-22 June period, along with the resultant snow cover on 22 June. However, the snow quickly began to melt as the surface air temperature rebounded into the 50’s and 60’s F at some locations.

POES AVHRR Visible (0.86 µm) images [click to play animation]

POES AVHRR Visible (0.86 µm) images [click to play animation]

The increase in fresh snow cover along the northern slopes and the highest elevations of the central and northeastern Brooks Range — most notably from Anaktuvuk Pass to Fort Yukon to Sagwon — was evident in a comparison of Suomi NPP VIIRS true-color Red/Green/Blue (RGB) images from 17 June and 22 June, as viewed using RealEarth (below). The actual time of the satellite overpass on 22 June was 2134 UTC.

Suomi NPP VIIRS true-color RGB images, 17 June and 22 June [click to enlarge]

Suomi NPP VIIRS true-color RGB images, 17 June and 22 June [click to enlarge]

25-year anniversary of the 1991 Mount Pinatubo eruption

June 15th, 2016

GMS-4 Infrared Window (11.5 µm) images [click to play animation]

GMS-4 Infrared Window (11.5 µm) images [click to play animation]

During the first 2 weeks of June 1991 the Mount Pinatubo volcano on the island of Luzon in the Philippines began to produce a series of eruptions, culminating in the climactic eruption beginning at 0227 UTC on 15 June. An animation of 5-km resolution GMS-4 Infrared Window (11.5 µm) images (above) spans the period from 1831 UTC on 12 June to 1831 UTC on 16 June, and showed the very large volcanic cloud following the 15 June eruption (the animation pauses at the 0230 UTC image on 15 June — just after the time of the major eruption). Also evident in the imagery was the westward movement of what became Category 3 Typhoon Yunya (known locally in the Philippines as Diding) toward Luzon. A larger-scale version of the animation is available here.

A closer view of the GMS-4 Infrared Window (11.5 µm) images (below) revealed interesting characteristics of the volcanic plume which penetrated the tropopause (which was at an air temperature of around -83º C, according to nearby rawinsonde reports) during the 3-8 hours following the onset of the 0227 UTC eruption. Note the initial appearance of a small area of very warm IR cloud-top IR brightness temperatures (-21.6º C at 0631 UTC, and -25.7º C at 0730 UTC) which then blossomed outward and became a westward-moving stratospheric plume that was notably warmer than the majority of the cold volcanic cloud canopy (which exhibited IR brightness temperatures in the -80º to -90º C range, denoted by the violet to yellow color enhancement).

GMS-4 Infrared Window (11.5 µm) images [click to enlarge]

GMS-4 Infrared Window (11.5 µm) images [click to enlarge]

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NOAA-10 AVHRR Infrared Window (10.8 µm), Visible (0.91 µm) and Shortwave Infrared (3.7 µm) images [click to enlarge]

NOAA-10 AVHRR Infrared Window (10.8 µm), Visible (0.91 µm) and Shortwave Infrared (3.7 µm) images [click to enlarge]

A higher-resolution (1.1-km) view of the post-eruption cloud was provided by NOAA-10 AVHRR images at 1034 UTC on 15 June (above). Even though it was just past sunset over the Philippines, the narrow stratospheric plume could be seen towering above the canopy of the main volcanic cloud (the plume was at a high enough altitude — estimated at a maximum of 40 km (reference 1 | reference 2) — to still be illuminated by sunlight). The summit of Pinatubo is located 8.7 miles/14 km west-southwest of what was then Clark Air Force Base (station identifier RPLC). On the 10.8 µm Infrared Window image, cloud-top gravity waves could be seen propagating radially outward from the overshooting top located above the volcano (which exhibited a minimum IR brightness temperature of -86º C, violet color enhancement). Note the much warmer IR brightness temperatures (as warm as -31º C, green color enhancement) associated with the stratospheric plume just off the west coast of Luzon. A closer view is available here.

About 10 hours prior to the climactic eruption, a volcanic ash cloud from one of the earlier eruptions was captured by NOAA-10 AVHRR images at 2329 UTC on 14 June (below). Around this same time it can be seen that Yunya was making landfall as a minimal-intensity typhoon along the eastern coast of Luzon. A closer view is available here.

NOAA-10 AVHRR Infrared Window (10.8 µm), Visible (0.91 µm) and Shortwave Infrared (3.7 µm) images [click to enlarge]

NOAA-10 AVHRR Infrared Window (10.8 µm), Visible (0.91 µm) and Shortwave Infrared (3.7 µm) images [click to enlarge]