The recent 3-day weekend was a 3-night extravaganza for Aurora enthusiasts with an active Aurora Borealis lighting up the sky for 3 nights in a row.  The VIIRS (Visible Infrared Imaging Radiometer Suite) Day Night Band Sensor flying on the Suomi-NPP and NOAA-20 polar-orbiting satellites captured stunning snapshots of the celestial phenomena during each North America overpass.  

Auroras are visible signatures of disturbances in Earth’s magnetosphere that occur when the solar wind interacts with Earth’s magnetic field during geomagnetic storms and substorms. They typically flow between 100 to 500 km above Earth’s surface. Polar-orbiting satellites fly at an altitude of 824 km (512 miles) and are perfectly situated to observe and monitor the Aurora Borealis in the Northern Hemisphere or Aurora Australis in the Southern Hemisphere.

Uniquely sensitive to low levels of visible light at night, VIIRS Day Night Band is the only satellite sensor able to detect and display the Aurora. The DNB is sensitive to radiation in wavelengths between 0.5 – 0.9 µm, which covers much of the visible and some near-infrared wavelengths. The images appear monochromatic because they are a combination of all energy within the entire bandwidth, meaning we can’t separate out the “green” or “red” parts of the data to see vibrant colors that citizen science photographers capture from below. Thousands of Northern Lights pictures were shared on social media over the weekend. Here are just a few …

Day Night Band images from North America satellite overpasses are available via the VIIRS Imagery Viewer , a 7-day archive — refreshed daily — for all 22 VIIRS channels, usually within 60 minutes of being acquired onboard the spacecraft. Current and archived VIIRS images over the continental USA are also available on the VIIRS TODAY website. As future JPSS VIIRS satellites join the fleet, that data will also be available on these sites.

Of note: the JPSS-2 (NOAA-21) satellite is scheduled for launch on November 1st, 2022.

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Overlapping 1-minute Mesoscale Domain Sectors provided 30-second GOES-18 (GOES-West) Fire Temperature RGB images, along with GOES-17 Fire Detection and Characterization Algorithm (FDCA) products (above) — which showed thermal signatures of the larger Ross Fork Fire and the smaller Wildhorse Fire in southern Idaho on 04 September 2022. The Wildhorse Fire caused a closure of US Highway 20, just west of Hill City, for a period of 12 hours.

The #wildhorsefire has closed US- 20 near Pine Turnoff. The fire is currently about 20-25 miles west of #fairfield #Idaho #idwx pic.twitter.com/CIftSoHZdM

— NWS Boise (@NWSBoise) September 5, 2022

The Ross Fork Fire burned very hot, with Shortwave Infrared (3.9 µm) infrared brightness temperatures reaching 137.88ºC (the saturation temperature of GOES-18 ABI Band 7 detectors). For those hottest fire pixels, occasionally FDCA parameters (Fire Temperature, Fire Power, Fire Area and Fire Mask) were generated and displayable via AWIPS cursor sampling (below).

Note, however, that FDCA parameters were not displayable in AWIPS for Cloudy Fires (fires with partial obscuration by pyrocumulus clouds and/or optically-thick smoke) or for Saturated Fires (below). Part of this issue is related to the fact that the peak GOES-18 3.9 µm temperature (137.88ºC) was slightly lower than the peak 3.9 µm value for GOES-16/-17 (138.71ºC).

 

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GOES-18 (GOES-West) Day Land Cloud Fire RGB and Shortwave Infrared (3.9 µm) images along with GOES-17 Fire Power and Fire Temperature products (above) displayed characteristics associated with the Cedar Creek Fire in Oregon on 02 September 2022. The peak 3.9 µm infrared brightness temperature reached 137.88ºC, with Fire Power values exceeding 2000 MW and Fire Temperature values exceeding 1200 K. The Fire Power and Fire Temperature products are components of the Fire Detection and Characterization Algorithm (FDCA).

GOES-18 True Color RGB images created using CSPP GeoSphere (below) showed the large smoke plume produced by this wildfire, which spread north-northeastward across Washington State during the day.

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GOES-R Satellites include GOES-16 (the present GOES-East), GOES-17 and GOES-18 (both scanning as GOES-West), and GOES-U, which will become GOES-19 after achieving geostationary orbit after launch (scheduled to occur in 2024). The follow-on to the GOES-R Series is GeoXo (Geostationary Extended Observations), with a launch planned in the 2030s. The GeoXo Imager, GXI, will improve on capability of GOES-R’s Advanced Baseline Imager (ABI). (See this announcement for development of the instrument) One of the channels that might be on this new imager will take observations at/around 5.1 µm. Why was this band chosen? And which present-day instruments can give observations at/near that wavelength to demonstrate that band’s utility?

The Cross-Track Infrared Sounder (CrIS) on NOAA-20 and Suomi-NPP is a Fourier transform spectrometer that provides 2000+ observations in 3 different wavelength ranges: Shortwave infrared (SWIR, 3.92- 4.64 ?m), mid-wave infrared (MWIR, 5.71-8.26 µm) and longwave infrared (LWIR, 9.14-15.38 µm). The toggle above compares 5.71 µm and 7.3 µm observations (wavenumbers 1755 and 1370) from five CrIS granules on 15 August 2022. Note how much warmer the 5.71 µm brightness temperatures are compared to the 7.3 µm brightness temperatures over northeast Mississippi (for example). The shorter wavelength observation are viewing features closer to the boundary layer.

A toggle of GOES-16 imagery and derived products for the same time is shown below. Strong instability (via the Derived Stability Lifted Index) and moisture (from the TPW field) are indicated in a region where the upper troposphere is dry (the 1200 UTC sounding on 15 August at Jackson MS shows considerable mid-level instability, although the SPC Outlook for that day showed only General Thunder.)

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This paper (from the AMS Annual Meeting in 2021) explored some of the issues in using 5.1 µm. A strength of observations at this wavelength is that it lies in a region where absorption (and therefore cooling in the observations) by CO₂ is minimal, and where absorption by water vapor in increasing (absorption by water vapor is much stronger for wavelengths between 5.5 µm and 7.5 µm)

This poster from the Collective Madison Meeting of the American Meteorological Society (in 2022) includes weighting function figures for 5.1 µm in various atmospheres, as shown below. In all atmospheres, a significant portion of the signal is coming from the surface. Compare these weighting functions to, for example, the 7.3 µm (“Low-level Water Vapor”, Band 10) for Tropical and US Standard atmospheres: very little surface information is present in observations at 7.3 µm. (See also the CIMSS weighting function website for ABI channels) The conclusion: observations at 5.1 µm can give more information about the water vapor distribution in the boundary layer than present-day water vapor channels on ABI. (See also this paper by Miller et al.)

The IASI instrument on MetopB/MetopC does take observations at 5.1 µm. Stay tuned for a blog post using those observations. Thanks to Mat Gunshor, CIMSS, and Tim Schmit, NOAA/STAR, for enlightening discussions about the 5.1 µm observations.

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GeoXo is also slated to carry a hyperspectral sounder (GXS). Sounders give far more complete assessments of the state of the atmosphere than an imager, even an advanced one like GXI!

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