Gravity waves over the Gulf of Mexico and Florida

January 22nd, 2020 |

GOES-16 Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images, with pilot reports of turbulence [click to play animation | MP4]

GOES-16 Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images, with pilot reports of turbulence [click to play animation | MP4]

GOES-16 (GOES-East) Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images (above) showed a packet of gravity waves over the eastern Gulf of Mexico and southern Florida on 22 January 2020. Later time in the time period, there were isolated pilot reports of moderate turbulence in the vicinity of the waves (though it’s uncertain whether the gravity waves were directly responsible).

What caused these gravity waves to form and slowly propagate southeastward is also uncertain — earning this example its place in the “What the heck is this?” blog category. The SPC Mesoscale Analysis at 07 UTC (below) did show weak convergence of 300 hPa ageostrophic winds (dark blue oval) in the entrance region of a secondary jet streak “J” over the Gulf of Mexico — this convergence could have played a role in the gravity wave development.

SPC Mesoscale Analysis valid at 07 UTC, showing 300 hPa height, isotachs and ageostrophic winds [click to enlarge]

SPC Mesoscale Analysis valid at 07 UTC, showing 300 hPa height, isotachs and ageostrophic winds [click to enlarge]

GOES-16 Derived Motion Winds (calculated using 6.9 µm imagery) in the vicinity of the gravity waves (below) had velocities in the 50-60 knot range at pressure levels of 370-380 hPa (0916 UTC).

GOES-16 Water Vapor (6.2 um) Derived Motion Winds [click to enlarge]

GOES-16 Water Vapor (6.9 µm) Derived Motion Winds [click to enlarge]

Also of note was the fact that the surface of Florida was sensed by Low-level Water Vapor imagery (below). With an unseasonably cold, dry air mass moving southward over the peninsula, the 7.3 µm water vapor weighting function was shifted to lower altitudes — this allowed the thermal contrast between relatively cool land surfaces and the surrounding warmer water to be seen in the 7.3 µm imagery.

GOES-16 Low-level (7.3 µm) Water Vapor images, with pilot reports of turbulence [click to play animation | MP4]

GOES-16 Low-level (7.3 µm) Water Vapor images, with pilot reports of turbulence [click to play animation | MP4]

At Key West, Florida the Total Precipitable Water value of 0.3 inch calculated from 12 UTC rawinsonde data (below) was a new record for the date/time (the previous record minimum value was 0.36 inch).

Climatology of Total Precipitable Water for the Key West, Florida rawinsonde site [click to enlarge]

Climatology of Total Precipitable Water for the Key West, Florida rawinsonde site [click to enlarge]

MIRS Ice Concentration Products over the Great Lakes

January 20th, 2020 |

MIRS Lake Ice Concentration (as a percentage) from NOAA-20 ATMS at 0735 UTC on 19 January 2020 (Click to enlarge)

CIMSS is now providing via LDM MIRS Lake Ice Products over the Great Lakes. These data are created using the Community Satellite Processing Package (CSPP) Software and NOAA-20/Suomi-NPP ATMS data downlinked at the Direct Broadcast Antennas in Madison WI. Imagery is shown above from 0735 UTC on 19 January 2020; the image below is from 0717 UTC on 20 January 2020, from NOAA-20, about 24 hours later, and then from 0808 UTC on 20 January 2020, from Suomi NPP (although it is labeled as NOAA-20). A great benefit of these microwave products is that they are not affected by persistent cloud cover that is common over the Great Lakes in winter.

MIRS Lake Ice Concentration (as a percentage) from NOAA-20 ATMS at 0717 UTC on 20 January 2020 (Click to enlarge)

MIRS Lake Ice Concentration (as a percentage) from NOAA-20 ATMS at 0806 UTC on 20 January 2020 (Click to enlarge)

Ice concentration estimates from microwave are very strongly influenced by view angle. Make certain in your comparisons (if you are trying to ascertain changes in lake ice coverage during Lake-Effect Snow events, for example) that you understand this! If the footprint sizes are similar, a comparison to different passes is valid; if the footprint sizes differ, the effects of view angle must be considered. Orbital paths can be viewed here (NOAA-20 it passed right over Lake Erie at 0722 UTC on 20 January; Suomi-NPP passed over Duluth at 0812 UTC on 20 January). In the two examples above, note how ice cover estimates differ over Lake Ontario. In the later example, from ATMS on Suomi-NPP, Lake Ontario is far closer to the limb; the ATMS footprint is much larger and the estimate of lake ice concentration is affected. This toggle compares the VIIRS Day Night band image to the ATMS observations; Lake Ontario is close to the limb for NPP’s pass over western Lake Superior at this time.

For instructions on how to access these data, please contact the blogpost author. Many thanks to Kathy Strabala and Lee Cronce, CIMSS, for their work in making these data available. Click here for short video explaining MIRS Ice Concentration).

Added: A consequence of the relatively poor resolution of ATMS (compared to, say, AMSR-2 on GCOM) is that a footprint in the Great Lakes will often not be over only water or over only land. A mixed surface (land and water within the ATMS footprint) means that the ice concentration algorithm will struggle to interpret the signal and reach the right solution. Best resolution from ATMS occurs near the sub-satellite point (from 15-50 km, depending on the frequency), and that’s where this product give the best information. (Thanks to Chris Grassotti, NOAA/CISESS for this information)

Eruption of Mount Shishaldin in Alaska

January 19th, 2020 |

Topography along with Suomi NPP VIIRS Shortwave Infrared (3.74 µm) and Infrared Window (11.45 µm) images at 1323 UTC [click to enlarge]

Topography along with Suomi NPP VIIRS Shortwave Infrared (3.74 µm) and Infrared Window (11.45 µm) images at 1323 UTC [click to enlarge]

Following two days of increasing seismicity, Mount Shishaldin began a period of more intense eruptive activity around 0930 UTC on 19 January 2020 — a comparison of topography along with Suomi NPP VIIRS Shortwave Infrared (3.74 µm) and Infrared Window (11.45 µm) images at 1323 UTC (above) displayed a distinct thermal anomaly (cluster of red 3.74 µm pixels) and a volcanic cloud moving east-southeastward.

Comparisons of Shortwave Infrared and Infrared Window images from Suomi NPP VIIRS and GOES-17 ABI (below) revealed a parallax shift that is inherent with geostationary imagery at high latitudes.

Comparison of Shortwave Infrared images from Suomi NPP VIIRS (3.74 um) and GOES-17 ABI (3.9 um) [click to enlarge]

Comparison of Shortwave Infrared images from Suomi NPP VIIRS (3.74 µm) and GOES-17 ABI (3.9 µm) [click to enlarge]

Comparison of Infrared Window images from Suomi NPP VIIRS (11.45 µm) and GOES-17 ABI (10.35 µm) [click to enlarge]

Comparison of Infrared Window images from Suomi NPP VIIRS (11.45 µm) and GOES-17 ABI (10.35 µm) [click to enlarge]

A toggle between GOES-17 parallax correction vectors and magnitudes for cloud top heights of 15,000 feet (4.5 km) and 30,000 feet (9.1 km) are shown below —  the amount of northwestward volcanic cloud displacement between the Suomi NPP and GOES-17 Infrared images roughly matched the 16 km (or 10 mile) value for a 15,000 foot cloud top in that region of the Full Disk. Later advisories listed the maximum ash height at 20,000-30,0000 feet.

GOES-17 parallax correction vectors (green) and magnitudes (km, red) [click to enlarge]

GOES-17 parallax correction vectors (green) and magnitudes (km, red) [click to enlarge]

1-minute Mesoscale Domain Sector GOES-17 (GOES-West) Split Cloud Top Phase (11.2 – 8.4 µm) images (below) displayed an increasing volcanic ash signal (negative values, darker blue to violet enhancement) beginning around 01 UTC on 20 January. Some light ash fall was reported at False Pass, Alaska.

GOES-17 Split Cloud Top Phase (11.2 - 8.4 um) images [click to play animation | MP4]

GOES-17 Split Cloud Top Phase (11.2 – 8.4 µm) images [click to play animation | MP4]

10-minute images of GOES-17 radiometrially retreived Ash Height from the NOAA/CIMSS Volcanic Cloud monitoring site (below) indicated that the bulk of the ash plume existed within the 2-6 km altitude range.

GOES-17 Ash Height product [click to play animation | MP4]

GOES-17 Ash Height product [click to play animation | MP4]

In corresponding GOES-17 False Color Red-Green-Blue (RGB) images (below), the volcanic plume exhibited shades of red/magenta/pink — the characteristic signature of an ash-laden cloud.

GOES-17 False Color RGB [click to play animation | MP4]

GOES-17 False Color RGB [click to play animation | MP4]

Tropical Cyclone Tino in the South Pacific Ocean

January 16th, 2020 |

Himawari-8

Himawari-8 “Clean” Infrared Window (10.4 µm) images [click to play animation | MP4]

JMA Himawari-8 “Clean” Infrared Window (10.4 µm) images (above) showed the development of Tropical Cyclone Tino in the South Pacific Ocean on 16 January 2020. Tino was moving southeast toward the island nation of Fiji. Convection around the tropical cyclone exhibited extensive cloud-top infrared brightness temperatures (IRBTs) of -90ºC and colder (shades of yellow embedded within the dark purple enhancement), including a few red -100ºC pixels at 1630 UTC.

Plots of rawinsonde data from Fiji (below) showed a tropopause around 100 hPa, where the temperature was around -85ºC — so the tropical overshooting tops with IRBTs in the -90 to -100ºC range were extending into the stratosphere.

Plots of rawinsonde data from Fiji [click to enlarge]

Plots of rawinsonde data from Nandi, Fiji [click to enlarge]

Plots of deep-layer wind shear from the CIMSS Tropical Cyclones site (below) indicated that Tino gradually intensified within a narrow zone of light shear.

Plots of deep-layer wind shear [click to enlarge]

Plots of deep-layer wind shear [click to enlarge]

===== 17 January Update =====

GOES-17

GOES-17 “Clean” Infrared Window (10.35 µm) images [click to play animation | MP4]

A GOES-17 (GOES-West) Mesoscale Domain Sector was positioned over Tropical Cyclone Tino on 17 January, providing images at 1-minute intervals — “Clean” Infrared Window (10.35 µm) images (above) showed the continued development of convective bursts, which at times exhibited IRBT values as cold as -100ºC (red pixels on the coldest portion of the enhancement).