Hurricane Force low pressure system off the US East Coast

April 1st, 2020 |

GOES-16 “Red” Visible (0.64 µm), Mid-level Water Vapor (6.9 µm) and Air Mass RGB images [click to play animation | MP4]

GOES-16 “Red” Visible (0.64 µm), Mid-level Water Vapor (6.9 µm) and Air Mass RGB images [click to play animation | MP4]

A sequence of GOES-16 (GOES-East) “Red” Visible (0.64 µm), Mid-level Water Vapor (6.9 µm) and Air Mass Red-Green-Blue (RGB) mages (above) showed an occluding Hurricane Force low pressure system (surface analyses) off the US East Coast on 01 April 2020. In the Air Mass RGB images, darker red areas just south of the storm center indicated the presence of higher amounts of total column ozone, brought about by a lowering tropopause — RAP40 model fields of the PV1.5 pressure (representing the height of the “dynamic tropopause”) suggested that the tropopause had descended below the 500 hPa pressure level later in the day.

The hurricane-force winds at the surface were creating seas as high as 33 feet. The milky/hazy signature of a highly-agitated sea surface + sea spray — immediately south of the convection around the core of the storm — was evident in GOES-16 True Color RGB images, created using Geo2Grid (below).

GOES-16 True Color RGB images [click to play animation | MP4]

GOES-16 True Color RGB images [click to play animation | MP4]

GOES-16 Visible images with an overlay of GLM Flash Extent Density (below) revealed that lightning activity gradually decreased within convection surrounding the core of the low during the day.

GOES-16 “Red” Visible (0.64 µm), Mid-level Water Vapor (6.9 µm) and Air Mass RGB images [click to play animation | MP4]

GOES-16 “Red” Visible (0.64 µm) images with an overlay of GLM Flash Extent Density [click to play animation | MP4]

As the storm was becoming organized near the Southeast US coast during the preceding overnight hours, a toggle between Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images at 0627 UTC (below) showed widespread mesospheric airglow waves in the Day/Night Band — these waves were likely generated by the approach of an upper-tropospheric jet streak.

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

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

Addition information about this event is available on the Satellite Liaison Blog.

High-altitude waves over the Arctic

March 27th, 2020 |

GOES-17

GOES-17 “Ozone” (9.61 µm) images, with rawinsonde sites plotted in yellow [click to play animation | MP4]

GOES-17 (GOES-West) “Ozone” (9.61 µm) images (above) revealed waves propagating northwestward over northern Alaska, northern Yukon and the adjacent Beaufort Sea during the pre-dawn hours on 27 March 2020. That area was too illuminated by either aurora borealis or the rising sun — so Suomi NPP VIIRS Day/Night Band (0.7 µm) imagery could not confirm the presence of mesospheric airglow waves (see this blog post for some examples).

A plot of the GOES-17 “Ozone” spectral band weighting function — calculated using 12 UTC rawinsonde data from Fairbanks, Alaska — showed a peak contribution from within the stratosphere at the 39 hPa pressure level, corresponding to an altitude around 21 km (below).

Plot of GOES-17

Plot of GOES-17 “Ozone” (9.61 um) weighting function, calculated using 12 UTC rawinsonde data from Fairbanks, Alaska [click to enlarge]

The curious aspect of these waves was their northwestward propagation — rawinsonde data from 3 sites across the region (below) indicated that the winds aloft within the upper troposphere and throughout the stratosphere were strong northwesterly, which meant the waves were moving against the ambient flow. Lacking a coherent, science-based explanation for these wave features, this blog post earns its place in the “What the heck is this?” category.

Plots of rawinsonde data from Fairbanks, Alaska [click to enlarge]

Plots of rawinsonde data from Fairbanks, Alaska [click to enlarge]

Plots of rawinsonde data from Utqiagvik (formerly Barrow), Alaska [click to enlarge]

Plots of rawinsonde data from Utqiagvik (formerly Barrow), Alaska [click to enlarge]

Plots of rawinsonde data from Inuvik, Northwest Territories [click to enlarge]

Plots of rawinsonde data from Inuvik, Northwest Territories [click to enlarge]

Lake Erie mesovortex, and an undular bore over the Dakotas

March 24th, 2020 |

GOES-16

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

Two interesting small-scale features were seen in GOES-16 (GOES-East) imagery on 24 March 2020. First of all, 1-minute Mesoscale Domain Sector “Red” Visible (0.64 µm) images (above) showed a mesovortex that was migrating west-northwestward across Lake Erie during the day. This feature had a diameter of around 10 miles — such a small-scale circulation was not captured by Metop-A ASCAT surface scatterometer data.

During the preceding overnight hours, an early signature of the mesovortex was evident in Suomi NPP VIIRS Shortwave Infrared (3.74 µm) and “Fog product” Brightness Temperature Difference (BTD) images at 0806 UTC (below).

Suomi NPP VIIRS Shortwave Infrared (3.74 µm) and "Fog product" Brightness Temperature Difference (BTD) images [click to enlarge]

Suomi NPP VIIRS Shortwave Infrared (3.74 µm) and “Fog product” Brightness Temperature Difference (BTD) images [click to enlarge]

The second feature of interest was a pre-cold-frontal undular bore that was moving eastward across the Dakotas, as seen in Day Cloud Phase Distinction Red-Green-Blue (RGB) images (below).

GOES-16 Day Cloud Phase Distinction RGB images [click to play animation | MP4]

GOES-16 Day Cloud Phase Distinction RGB images [click to play animation | MP4]

The effect of snow cover on boundary layer cloud development

March 15th, 2020 |

GOES-16 Snow/Cloud Discrimination RGB images [click to play animation]

GOES-16 Snow/Cloud Discrimination RGB images, with hourly plots of surface wind barbs (knots) [click to play animation]

GOES-16 (GOES-East) “Snow/Cloud Discrimination” Red-Green-Blue (RGB) images (above) revealed a west-to-east oriented band of fresh snow cover (1-4 inches, shades of red) across central Illinois on 15 March 2020. With a low-level northeasterly flow of cold air across the region, boundary layer cumulus clouds began to develop as solar heating warmed the surface — but this cloud development was suppressed over deeper portions of the snow cover. These RGB images use “Red” Visible (0.64 µm) data as the Red component, and Near-Infrared “Snow/Ice” (1.61 µm) data as the Green and Blue components; bare ground appears as shades of cyan, with supercooled water droplet clouds appearing as brighter shades of white.

A sequence of VIIRS Snow/Cloud Discrimination RGB images from NOAA-20 and Suomi NPP (below) showed a closer look at the band of snow cover and its effect on modulating the afternoon development of cumulus clouds.

VIIRS Snow/Cloud Discrimination RGB images from NOAA-20 and Suomi NPP [click to enlarge]

VIIRS Snow/Cloud Discrimination RGB images from NOAA-20 and Suomi NPP [click to enlarge]

A 30-meter resolution Landsat-8 False Color RGB image viewed using RealEarth (below) provided a detailed view of the band of snow cover (shades of cyan) at 1622 UTC.

Landsat-8 False Color RGB image, with and without labels [click to enlarge]

Landsat-8 False Color RGB image, with and without labels [click to enlarge]