Derived Motion Winds near the surface with a strong East Coast Storm

March 2nd, 2018 |

GOES-16 ABI Band 10 (Low-Level Water Vapor, 7.3 µm) Infrared Imagery, 0507-1757 UTC on 2 March 2018 (Click to animate)

The evolution of a very strong Nor’easter on the East Coast of the United States for the twelve hours ending at ~1800 UTC on 2 March 2018 is shown above. During this time period, the storm produced winds that shut down schools and Government in the Nation’s Capitol (and elsewhere), with High Wind Warnings widespread from North Carolina to Massachusetts (Link, from this site). Significant Coastal Flooding is likely in New England with this storm.

One of the Level 2 Products produced with GOES-R Series Satellite (GOES-16 and soon, GOES-17) data are Derived Motion Wind Vectors at various levels. The images below show winds of up to 70 knots (!!) at or below 900 hPa over the Chesapeake Bay between 1627 and 1657 UTC on 2 March. Observations (bottom) show numerous surface gusts exceeding 50 knots in the region during that time.

GOES-16 ABI Band 10 (Low-Level Water Vapor, 7.3 µm) Infrared Imagery, 1627 and 1657 UTC on 2 March 2018, with Derived Motion Winds in excess of 50 knots at ~1000 hPa (red) and ~900 hPa (Magenta) plotted (Click to enlarge)

GOES-16 ABI Band 2 (“Red” Visible, 0.64 µm) Visible Imagery, 1502, 1602 and 1702 UTC on 2 March 2018, with surface observations plotted in green (Click to enlarge)

 

When Water Vapor Channels are Window Channels

January 2nd, 2018 |

GOES-16 Low-Level Water Vapor Imagery (7.3 µm), 1322 UTC on 2 January 2017 (Click to enlarge)

The very cold and dry airmass over the eastern half of the United States during early January 2018 is mostly devoid of water vapor, a gas that, when present, absorbs certain wavelengths of radiation that is emitted from the surface (or low clouds). That absorbed energy is then re-emitted from higher (colder) levels. Typically, surface features over the eastern United States are therefore not apparent. When water vapor amounts in the atmosphere are small, however, surface information can escape directly to space, much in the same way as occurs with (for example) the Clean Window channel (10.3 µm) on GOES-16 (water vapor does not absorb energy with a wavelength of 10.3 µm). The low-level water vapor (7.3 µm) image above, from near sunrise on 2 January 2018, shows many surface features over North and South Carolina, Kentucky, Tennessee and southern Illinois. The features are mostly lakes and rivers that are markedly warmer than adjacent land. (In fact, Kentucky Lake and Lake Barkely in southwest Kentucky are also visible in the 6.9 µm imagery!)

Weighting Functions from 1200 UTC on 2 January for Davenport IA (left), Lincoln IL (center) and Greensboro NC (right) for 6.2 µm (Green), 6.95 µm (blue) and 7.3 µm (magenta), that is, the upper-, mid- and lower-level water vapor channels, respectively, on ABI. Peak pressures for the individual weighting functions are noted, as are Total Precipitable Water values at the station (Click to enlarge)

GOES-16 Weighting Functions (Click here ) describe the location in the atmosphere from which the GOES-16 Channel is detecting energy.  The upper-level (6.2 µm) and mid-level (6.95 µm) weighting functions show information originating from above the surface.  Much surface information is available at Greensboro, with smaller proportional amounts at Davenport and Lincoln.

The “Cirrus” Channel on GOES-16’s ABI (Band 4, 1.38 µm) also occupies a spot in the electromagnetic spectrum where water vapor absorption is strong.  Thus, reflected solar radiation from the surface is rarely viewed at this wavelength.  The toggle below, between the ‘Veggie’ Channel (0.86 µm) and the Cirrus Channel (1.38 µm) shows that some surface features — for example, lakes in North Carolina — are present in the Cirrus Channel.

ABI Band 3 (0.86 µm) and ABI Band 4 (1.38 µm) (That is, Veggie and Cirrus channels) at 1502 UTC on 2 January 2018 (Click to enlarge)

Whenever the atmosphere is exceptionally dry, and skies are clear, check the water vapor channels on ABI to see if surface features can be viewed. A few examples of sensing surface features using water vapor imagery from the previous generation of GOES can be seen here.

GOES-16 water vapor imagery: wave structures within a dry slot

March 8th, 2017 |

GOES-16 Water Vapor images: 6.2 µm (top), 6.9 µm (middle) and 7.4 µm (bottom) [click to play animation]

GOES-16 Water Vapor images: 6.2 µm (top), 6.9 µm (middle) and 7.4 µm (bottom) [click to play animation]

** The GOES-16 data posted on this page are preliminary, non-operational data and are undergoing testing. **

(Hat tip to T.J. Turnage, NWS Grand Rapids, for alerting us to this case): A variety of mesoscale wave structures were seen in NOAA GOES-16 Lower-Tropospheric Water Vapor (7.3 µm) and Middle-Tropospheric Water Vapor 6.9 µm images (above; also available as an MP4 animation) within a dry slot along the southern periphery of a trough associated with a large and intense mid-latitude cyclone centered over Hudson Bay, Canada on 08 March 2017. Beneath this dry slot, wind gusts exceeded 60 mph across southern portions of Minnesota, Wisconsin and Lower Michigan as momentum aloft was mixed downward to the surface.

Using the GOES-13 (GOES-East) Sounder water vapor bands as a proxy for the three ABI water vapor bands, weighting functions calculated using 12 UTC rawinsonde data from Chanhassen, Minnesota (below) showed a dramatic downward shift in the weighting function curves (compared to a US Standard Atmosphere) — this meant that the 3 water vapor bands were sensing radiation from layers much closer to the surface on 08 March (where the strong winds could interact with terrain and cause standing waves to form). It is interesting to note that the outline of the southern part of Lake Michigan could be seen on GOES-16 Lower-Tropospheric Water Vapor (7.3 µm) imagery (animated GIF | MP4 animation) — the signal of the thermal contrast between the lake water (MODIS SST values in the upper 30s to low 40s F) and the adjacent land surfaces (MODIS LST values in the middle 50s to low 60s F) was “bleeding up” through what little water vapor was present aloft.

GOES-13 Sounder water vapor weighting functions: 12 UTC Chanhassen, Minnesota sounding vs US Standard Atmosphere [click to enlarge]

GOES-13 Sounder water vapor weighting functions: 12 UTC Chanhassen, Minnesota sounding vs US Standard Atmosphere [click to enlarge]

A comparison of GOES-16 Visible (0.64 µm) and Middle/Lower-Level Water Vapor images (below; also available as an MP4 animation) showed that these water vapor wave structures were forming in cloud-free air — this is a signature of the potential for low-altitude turbulence.

GOES-16 images: 0.64 µm Visible (top), 6.9 µm Water Vapor (middle) and 7.4 µm Water Vapor (bottom) [click to play animation]

GOES-16 images: 0.64 µm Visible (top), 6.9 µm Water Vapor (middle) and 7.4 µm Water Vapor (bottom) [click to play animation]

In fact, there were widespread pilot reports of moderate turbulence within the dry slot (below), with a few isolated reports of severe to even extreme turbulence in eastern Wisconsin and southern Lower Michigan.

GOES-13 Water Vapor (6.5 µm) images, with pilot reports of turbulence [click to play animation]

GOES-13 Water Vapor (6.5 µm) images, with pilot reports of turbulence [click to play animation]

2 West Pacific storms, as seen using 3 Himawari-8 water vapor bands

March 19th, 2016 |

Himawari-8 Water Vapor images: 6.2 µm (top), 6.9 µm (middle), and 7.3 µm (bottom) - [click to play MP4 animation]

Himawari-8 Water Vapor images: 6.2 µm (top), 6.9 µm (middle), and 7.3 µm (bottom) – [click to play MP4 animation]

The Himawari-8 AHI instrument has 3 water vapor bands, centered at 6.2 µm, 6.9 µm, and 7.3 µm. Images of these 3 water vapor bands (above; also available as a large 126 Mbyte animated GIF) showed the intensification of a mid-latitude cyclone as it moved east of Japan during the 17-19 March 2016 period. Surface analyses of this storm produced by the Ocean Prediction Center are shown below.

West Pacific surface analyses [click to play animation]

West Pacific surface analyses [click to play animation]

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Himawari-8 Water Wapor images: 7.3 µm (left), 6.9 µm (center), and 6.2 µm (right) - [click to play MP4 animation]

Himawari-8 Water Wapor images: 7.3 µm (left), 6.9 µm (center), and 6.2 µm (right) – [click to play MP4 animation]

Several days earlier (during 14-16 March), another storm just off the coast of Japan rapidly intensified to hurricane force as it moved north-northeastward toward the southern tip of the Kamchatka Peninsula. A comparison of the three Himawari-8 AHI water vapor bands (above; also available as a large 109 Mbyte animated GIF) depicted varying aspects of the storm evolution. The corresponding Ocean Prediction Center surface analyses are shown below.

West Pacific surface analyses [click to play animation]West Pacific surface analyses [click to play animation]

West Pacific surface analyses [click to play animation]

The GOES-R ABI instrument will have nearly identical water vapor bands; plots of their weighting functions (below, from this site) show that each of these 3 spectral bands senses radiation from different layers of the atmosphere. This example assumes a typical cold mid-latitude winter temperature/moisture vertical profile, with a satellite view angle (or “zenith angle”) of 45 degrees.

GOES-R ABI water vapor band weighting function plots

GOES-R ABI water vapor band weighting function plots