Mesoscale vortex in North Dakota

November 6th, 2018 |

One interesting aspect of this 06 November 2018 mesoscale vortex (which was embedded within a stratus cloud deck) was the fact that a signature of the feature was evident in imagery from 15 of the 16 ABI spectral bands on GOES-16 (below) — only the 6.2 µm Upper-level Water Vapor images lacked even a subtle signal. The appearance of the vortex on 1.37 µm Near-Infrared “Cirrus” imagery was possible because the atmospheric column was very dry over that region (MODIS Total Precipitable Water values of 2-4 mm or 0.08-0.16 inch, and 0.31 inch on the 12 UTC Aberdeen SD sounding), so there was very little attenuation of upwelling 1.37 µm radiation by middle/upper-tropospheric water vapor.

16-panel comparison of GOES-16 ABI spectral bands [click to play animation | MP4]

16-panel comparison of GOES-16 ABI spectral bands [click to play animation | MP4]

Closer views of GOES-16 “Red” Visible (0.64 µm), Near-Infrared “Snow/Ice” (1.61 µm) and Low-level Water Vapor (7.3 µm) images are shown below. The dry air aloft also shifted the altitude of the GOES-16 Water Vapor band weighting functions to lower altitudes — calculated using 12 UTC rawinsonde data from Aberdeen SD, the 7.3 µm Low-level Water Vapor weighting function peaked near 600 hPa, with significant contributions from as low as the 700 hPa level.

GOES-16

GOES-16 “Red” Visible (0.64 µm, left), Near-Infrared “Snow/Ice” (1.61 µm, center) and Low-level Water Vapor (7.3 µm, right) images [click to play animation | MP4]

A sequence of Terra/Aqua MODIS and NOAA-20/Suomi NPP VIIRS legacy “fog/stratus” Brightness Temperature Difference (BTD) images (below) indicated that the vortex formed about 40 miles northwest of Devils Lake (KDVL) sometime between 0438 UTC and 0805 UTC (10:38 PM and 2:05 AM local time). An AWIPS-1 version of the animation is available here.

Fog/sratus infrared Brightness Temperature Difference images from Terra/Aqua MODIS and NOAA-20/Suomi NPP VIIRS [click to enlarge | MP4]

Fog/sratus infrared Brightness Temperature Difference images from Terra/Aqua MODIS and NOAA-20/Suomi NPP VIIRS [click to enlarge | MP4]

The stratus clouds surrounding the vortex could be further characterized using a variety of GOES-16 channel difference and derived products as shown below.

GOES-16 Split Cloud Top Phase (11.2 - 8.4 µm) product [click to play animation | MP4]

GOES-16 Split Cloud Top Phase (11.2 – 8.4 µm) product [click to play animation | MP4]

The Split Cloud Top Phase (11.2 µm8.4 µm) product (above) allowed this feature to be followed during darkness and daylight. It initially became apparent in GOES-16 imagery near Devils Lake shortly after 11 UTC or 5 AM local time, then traveled southeastward to the southeastern corner of the state before beginning to lose definition after 20 UTC or 2 PM local time. Positive values of this infrared BTD product (shades of blue to cyan) highlight water droplet clouds, while negative BTD values (shades of violet) indicate clouds composed of ice crystals.

GOES-16 Cloud Particle Size Distribution product [click to play animation | MP4]

GOES-16 Cloud Particle Size Distribution product [click to play animation | MP4]

The Cloud Particle Size Distribution derived product (above) uses Visible and Near-Infrared bands, so is only created during daylight hours — and only for solar zenith angles of 65º or less, which meant only for a few hours over much of North Dakota with the low sun angle of early November. The product showed a tongue of smaller cloud-top particles (darker blue to violet enhancement) wrapping cyclonically into the center of the feature during the day.

GOES-16 Cloud Top Phase product [click to play animation | MP4]

GOES-16 Cloud Top Phase product [click to play animation | MP4]

The Cloud Top Phase product (above) indicated that the vortex and surrounding stratus cloud deck were composed of supercooled water droplets (lighter green enhancement).

GOES-16 Cloud Top Height product [click to play animation | MP4]

GOES-16 Cloud Top Height product [click to play animation | MP4]

The Cloud Top Height product (above) showed that the vortex and surrounding stratus clouds had tops generally in the 12,000-14,000 feet range (darker shades of blue).

Terra and Aqua MODIS Visible (0.65 µm), Cirrus (1.37 µm), Snow/Ice (1.61 µm) and Infrared Window (11.0 µm) at 1816 UTC and 1955 UTC [click to enlarge | MP4]

Terra and Aqua MODIS Visible (0.65 µm), Cirrus (1.37 µm), Snow/Ice (1.61 µm) and Infrared Window (11.0 µm) at 1816 UTC and 1955 UTC [click to enlarge | MP4]

Comparisons of Terra and Aqua MODIS Visible (0.65 µm), Cirrus (1.37 µm), Snow/Ice (1.61 µm) and Infrared Window (11.0 µm) at 1816 UTC and 1955 UTC are shown above — and comparisons of VIIRS Visible (0.64 µm), Snow/Ice (1.61 µm) and Infrared Window (11.45 µm) images from Suomi NPP at 1841 UTC and 2020 UTC along with NOAA-20 (incorrectly labeled as Suomi NPP) at 1941 UTC are shown below. Infrared Window brightness temperatures from both MODIS and VIIRS were in the -20º to -25ºC range (cyan to light blue enhancement) within and adjacent to the vortex.

Suomi NPP VIIRS Visible (0.64 µm), Snow/Ice (1.61 µm) and Infrared Window (11.45 µm) images at 1841 UTC, 1941 UTC and 2020 UTC [click to enlarge | MP4]

Suomi NPP VIIRS Visible (0.64 µm), Snow/Ice (1.61 µm) and Infrared Window (11.45 µm) images at 1841 UTC, 1941 UTC and 2020 UTC [click to enlarge | MP4]

A closer view was provided by a sequence of True Color and False Color Red-Green-Blue (RGB) images from Terra/Aqua MODIS and Suomi NPP VIIRS as visualized using RealEarth (below).

True Color and False Color RGB images from Terra/Aqua MODIS and Suomi NPP VIIRS [click to play animation]

True Color and False Color RGB images from Terra/Aqua MODIS and Suomi NPP VIIRS [click to play animation]

The mesoscale vortex — whose diameter was only about 20-30 miles — formed within cyclonic boundary layer flow about 100 miles south of an advancing cold front (below).

Terra MODIS Visible (0.65 µm) image with aurface analysis of pressure and fronts [click to enlarge]

Terra MODIS Visible (0.65 µm) image with aurface analysis of pressure and fronts [click to enlarge]

One potential forcing mechanism could have been a lobe of 700 hPa vorticity which was about 30 miles upstream of the vortex at 12 UTC and 18 UTC, according to the NAM12 model (below).

GOES-16 Split Cloud Top Phase (11.2 - 8.4 µm) product at 1202 and 1802 UTC, with overlays of NAM12 700 hPa vorticity [click to enlarge]

GOES-16 Split Cloud Top Phase (11.2 – 8.4 µm) product at 1202 and 1802 UTC, with overlays of NAM12 model 700 hPa vorticity [click to enlarge]

[Note: AWIPS color enhancements that differ from the defaults were used for some of the GOES-16 images and products shown here, to better highlight the subtle vortex feature]

Blowing dust in the Arabian Sea

November 3rd, 2018 |

Sequence of daily True Color RGB images from Terra MODIS, Aqua MODIS and Suomi NPP VIIRS, covering the period 01-03 November [click to play animation]

Sequence of daily True Color RGB images from Terra MODIS, Aqua MODIS and Suomi NPP VIIRS, covering the period 01-03 November [click to play animation]

Strong winds across southern Iran and Pakistan were lofting plumes of blowing sand/dust offshore over the Gulf of Oman and the Arabian Sea during 01 November, 02 November and 03 November 2018 — a sequence of daily composites of True Color Red-Green-Blue (RGB) images from Terra MODIS, Aqua MODIS and Suomi NPP VIIRS from RealEarth (above) showed the increase in dust transport during that 3-day period.

A comparison of True Color RGB images from Terra MODIS, NOAA-20 VIIRS, Suomi NPP VIIRS and Aqua MODIS on 03 November is shown below.

Comparison of True Color RGB images from Terra MODIS, NOAA-20 VIIRS, Suomi NPP VIIRS and Aqua MODIS on 03 November [click to play animation]

Comparison of True Color RGB images from Terra MODIS, NOAA-20 VIIRS, Suomi NPP VIIRS and Aqua MODIS on 03 November [click to play animation]

Metop-A and Metop-B ASCAT data (source) showed surface wind speeds in the 20-25 knot range emerging from the coast where plumes of blowing dust were located (below).

Meop ASCAT surface scatteromete winds [click to enlarge]

Meop ASCAT surface scatteromete winds [click to enlarge]

EUMETSAT Meteosat-11 High Resolution Visible (0.8 µm) images from 02 November and 03 November (below) showed the daily evolution of the dust plumes.

Meteosat-11 Visible (0.8 µm) images [click to play animation | MP4]

Meteosat-11 Visible (0.8 µm) images on 02 November [click to play animation | MP4]

Meteosat-11 Visible (0.8 µm) images on 03 November [click to play animation | MP4]

Meteosat-11 Visible (0.8 µm) images on 03 November [click to play animation | MP4]

Above-Anvil Cirrus Plume (AACP) over Argentina

November 3rd, 2018 |

An Above-Anvil Cirrus Plume (AACP) was observed over northern Argentina on 03 November 2018 during the RELAMPAGO-CACTI field experiment — radar indicated that the plume was 2-3 km above the top of the main thunderstorm anvil. A comparison of GOES-16 (GOES-East) “Red” Visible (0.64 µm), Near-Infrared “Snow/Ice” (1.61 µm) and “Clean” Infrared Window (10.3 µm) images (below) showed that the plume exhibited a colder appearance compared to the underlying anvil (which is explained by the temperature profile from 12 UTC Cordoba rawinsonde data). GOES-16 was actually scanning the AACP at 14:38:41 UTC — very close to the time of the radar image. The plume-producing thunderstorm was located south of Cordoba (identifier SACO).

GOES-16 "Red" Visible (0.64 µm), Near-Infrared "Snow/Ice" (1.61 µm) and "Clean" Infrared Window (10.3 µm) images [click to enlarge]

GOES-16 “Red” Visible (0.64 µm), Near-Infrared “Snow/Ice” (1.61 µm) and “Clean” Infrared Window (10.3 µm) images [click to enlarge]

Animations of GOES-16 Visible vs Snow/Ice and Visible vs Infrared are shown below. The southern storm also produced a smaller AACP at 1445 UTC.

GOES-16 "Red" Visible (0.64 µm), Near-Infrared "Snow/Ice" (1.61 µm) images [click to play animation | MP4]

GOES-16 “Red” Visible (0.64 µm) and Near-Infrared “Snow/Ice” (1.61 µm) images [click to play animation | MP4]

GOES-16 "Red" Visible (0.64 µm) and "Clean" Infrared Window (10.3 µm) images [click to play animation | MP4]

GOES-16 “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.3 µm) images [click to play animation | MP4]

Views of the convection across that region were provided by Terra MODIS (1457 UTC), Aqua MODIS (1736 UTC), Suomi NPP VIIRS (1742 UTC) and NOAA-20 VIIRS (1832 UTC) True Color Red-Green-Blue (RGB) images from RealEarth (below)True Color RGB images from Terra MODIS (1457 UTC), Aqua MODIS (1736 UTC), Suomi NPP VIIRS (1742 UTC) and NOAA-20 VIIRS (1832 UTC) [click to enlarge]

True Color RGB images from Terra MODIS (1457 UTC), Aqua MODIS (1736 UTC), Suomi NPP VIIRS (1742 UTC) and NOAA-20 VIIRS (1832 UTC) [click to enlarge]

Fog/stratus dissipation in southern Louisiana

October 30th, 2018 |

GOES-16

GOES-16 “Red” Visible (0.64 µm) images [click to play animation | MP4]

The topic of a conversation on Twitter, GOES-16 (GOES-East) “Red” Visible (0.64 µm) images (above) revealed curious circular areas of fog/stratus dissipation across southern Louisiana on the morning of 30 October 2018. — making it a natural candidate for the “What the heck is this?” blog category.

GOES-16 GEOCAT Low IFR Probability and Fog/Low Stratus Depth products (below) indicated that this fog and low stratus had been increasing in coverage and spreading northward across Louisiana during the preceding nighttime hours (VIIRS fog/stratus Brightness Temperature Difference images) — and the fog/stratus was relatively shallow, only having a depth of about 300 feet or less. In fact, if you look closely at the Visible animation above, a few small spots of slightly brighter cloud can be seen in the vicinity of Baton Rouge KBTR which are tall objects (such as refinery stacks, and even the State Capitol building) protruding above the fog/stratus and acting as an obstacle to their flow.

GOES-16 Low Instrument Flight Rules (IFR) Probability [click to play animation | MP4]

GOES-16 Low Instrument Flight Rules (IFR) Probability [click to play animation | MP4]

GOES-16 Fog/Low Stratus Depth product [click to play animation | MP4]

GOES-16 Fog/Low Stratus Depth product [click to play animation | MP4]

A sequence of 4-panel comparisons of GOES-16 “Blue” Visible (0.47 µm), “Red” Visible (0.64 µm) and Near-Infrared “Vegetation” (0.86 µm) images with Near-Infrared “Snow/Ice” (1.61 µm), Near-Infrared “Cloud Particle Size” (2.24 µm) and Shortwave Infrared (3.9 µm) images (below) showed no indication of any substantial differences between the cloud material within the circular features and the adjacent fog/stratus. The largest “outer rings” of the dissipating fog/stratus areas had a small amount of vertical extent, which cast a shadow that was best seen in the Near-Infrared 0.86 µm and 1.61 µm images.

4-panel comparisons of GOES-16

Sequence of 4-panel comparisons of GOES-16 “Blue” Visible (0.47 µm), “Red” Visible (0.64 µm), Near-Infrared “Vegetation” (0.86 µm), “Snow/Ice” (1.61 µm), and “Cloud Particle Size” (2.24 µm), and Shortwave Infrared (3.9 µm) images [click to play animation | MP4]

The most plausible explanation for the circular dissipation features turned out to be fires that were set in sugar cane fields following harvest — particulates in the smoke could have “seeded” the fog/stratus cloud layer, either changing the particle size distribution or making the cloud more susceptible to faster dissipation after sunrise due to solar heating of black carbon nuclei within the cloud droplets.  An Aqua MODIS Shortwave Infrared (3.7 µm) image from the previous afternoon (below) did reveal a number of small thermal anomalies or fire “hot spots” (yellow to red pixels) across the region at 1909 UTC (2:09 PM local time).

Aqua MODIS Shortwave Infrared (3.7 µm) image [click to enlarge]

Aqua MODIS Shortwave Infrared (3.7 µm) image [click to enlarge]

Similarly, GOES-16 Shortwave Infrared images on 29 October (below) also showed signatures of widespread small and generally short-lived fires (darker black pixels) across southern Louisiana. Surface winds were very light across that area (KARA | KPTN | KNBG | KMSY | KNEW), minimizing smoke dispersion from any fires.

GOES-16 Shortwave Infrared (3.9 µm) images [click to play animation | MP4]

GOES-16 Shortwave Infrared (3.9 µm) images [click to play animation | MP4]