Mode 6 Testing with GOES-17

September 25th, 2018 |

GOES-17 11.2 µm (Infrared Window Channel) Full Disk Images, 0915 – 1510 UTC on 25 September. Note the cadence change at 1300 UTC: every 15 minutes before 1300 UTC, every ten minutes after (Click to animate)

GOES-17 imagery shown here is preliminary and non-operational.

The default scanning strategy for the Advanced Baseline Imager on GOES-16 is Mode 3, also known as Flex Mode.  In Mode 3, there are 2 Mesoscale Sectors scanned every minute, a CONUS sector scanned every 5 minutes, and a Full Disk image scanned every 15 minutes.  GOES-17 is undergoing Mode 6 scanning, starting today, and proceeding into early October.  In Mode 6, there will continue to be two Mesoscale sectors scanned every minute, and a CONUS sector scanned every 5 minutes.  However, Full Disk imagery will be scanned every 10 minutes, rather than every 15.  6 Full Disk images each hour would align GOES-17 (and GOES-16, when and if this becomes operational) with default Full Disk imagery scanning on Himawari.

The animation of Full-Disk imagery above, showing Band 14 (11.2 µm), the window channel, on GOES-17, shows that Mode 6 scanning — every 10 minutes — started at 1300 UTC on 25 September.  Prior to that time, Mode 3 scanning — every 15 minutes — was occurring. GOES-16 Scanning remains Mode 3.

Added: Simultaneous GOES-16/GOES-17 Mode 4 (Continuous Full Disk — the highest data rate from the ABI) testing is planned for 1 October 2018.

NUCAPS views Saharan Air over the Atlantic

September 20th, 2018 |

Saharan Air Layer Analysis over the Tropical Atlantic, 0600 UTC on 20 September 2018 (Click to enlarge)

There have been many episodes of Saharan Air over the tropical Atlantic within the past months, and another episode is in progress on 20 September. The Saharan Air Layer (SAL) analysis, above, from the CIMSS Tropical Weather website (Direct Link), shows dry air north and east of the Caribbean. The Clean Window ABI Band 13 (10.3 µm) Full-Disk ABI infrared imagery, below, from 0500 UTC, overlain with NUCAPS sounding points, shows where data were available from that morning overpass of Suomi NPP.

GOES-16 ABI 10.3 µm Infrared Imagery at 0500 UTC along with NUCAPS Sounding Points at approximately the same time (Click to enlarge)

The stepping animation below shows NUCAPS Soundings at a selection of points that starts north of the Saharan Air Layer and ends up within the SAL. The underlying figure is the Dust RGB from AWIPS, an RGB that combines the Split Window Difference (12.3 µm -10.3 µm; Red Component), Split Cloud Top Phase Brightness Temperature Difference (11.2 µm – 8.5 µm; Green Component) and 10.3 µm Infrared Imagery (Blue Component). Typically, regions with dust as might accompany a SAL have a pink tinge. The soundings are annotated to include Total Precipitable Water measurements, and mid-level Relative humidity. NUCAPS soundings identify the region where the SAL is present.

Dust RGB at 0433 UTC north and east of the Caribbean, and NUCAPS Soundings at selected points along a transect (Click to enlarge)

The SAL air continued its movement west during the day on 20 September.  The toggle below shows the Dust RGB, ABI Band 3 (0.86 µm) and the Baseline Aerosol Detection Product (in blue) at about the same time as the afternoon NUCAPS Sounding overpass (from Suomi NPP).  Suomi NPP overflew the eastern half of the SAL air (the overpass from NOAA-20 was more centered on the SAL air approaching the Caribbean, but NOAA-20 NUCAPS soundings are not yet in AWIPS;  they should be by the end of the year).

GOES-16 ABI Dust RGB, “Veggie Band” (Near-Infrared at 0.86 µm), and Baseline Aerosol Detection Product (Blue points), 1615 UTC on 20 September 2018 (Click to enlarge)

NUCAPS Soundings at 3 points (North of the SAL, within the SAL, and south of the SAL), below, show much different thermodynamics within the SAL.

NUCAPS Profiles at ~1600 UTC on 20 September 2018 at three locations as noted (Click to enlarge)

NOAA’s G-IV flew through this outbreak, deploying dropsondes to sample the event. The path of the aircraft (with the dropsonde locations) is here. Sonde #26, below, in the heart of the SAL, is shown below, with a nearby NOAA-20 NUCAPS sounding. (Flight path and Sonde imagery courtesy Chris Barnet, STC/NOAA) Refer to the caption for details.  Recall that the Dropsonde shows values at a point.  The NUCAPS profile is sampling a volume that is approximately a 50-km cylinder!  There is nevertheless excellent agreement.

Dropsonde #26 data (raw data in light grey; values averaged into the 100 NUCAPS vertical layers in black); GFS sounding in magenta. NUCAPS Microwave-only sounding in green; NUCAPS Microwave and infrared retrieval (as might be seen in AWIPS) in Red. Time offset from the Dropsonde is noted (Click to enlarge)

SAL outbreaks cause a significant deterioration in air quality over the Caribbean. The image below, courtesy Ernesto Rodriguez, SOO for the National Weather Service office in San Juan, Puerto Rico, compares Air Quality before and during a SAL outbreak in July, and during the current outbreak.

The view outside of the National Weather Service office in San Juan on 20 September and 13 July 2018 (during SAL outbreaks) and on 12 July 2018 (before a SAL outbreak). Imagery courtesy Ernesto Rodriguez, NWS SJU.

Stereoscopic View of Tropical Storm Gordon in the Gulf of Mexico

September 4th, 2018 |

GOES-16 (left) and GOES-17 (right) Visible (0.64 µm) imagery on 4 September 2018, starting at 1132 UTC (Click to play mp4 animation)

GOES-17 Data shown here are preliminary and non-operational!

Stereoscopic views (using GOES-16 and — preliminary and non-operational — GOES-17 Visible (0.64 µm) imagery) of strengthening Tropical Storm Gordon are shown above. The stereoscopic view shows an initially sheared storm, with the surface circulation apparent becoming somewhat less sheared as convection redevelops over the surface center. (To view in three dimensions: cross your eyes until 3 equal images are apparent, and focus on the image in the center). This animation will be updated periodically as more GOES-17 data become available. (Click here for animated gif)

For more information on this storm, consult the National Hurricane Center website, or the CIMSS Tropical Weather Website.

Why Mesoscale Sectors Matter: Hurricane Norman

August 30th, 2018 |

GOES-16 Mesoscale Sectors over Hurricane Norman (left) and a tropical wave (right), along with a CONUS image

Pacific Hurricane Norman, a potent storm with sustained winds of 150 mph, exists outside of GOES-16’s CONUS (Contiguous United States) domain. In fact, on 30 August 2018, both GOES-16 Meso sectors were placed over the tropics to provide 1-minute imagery of tropical systems, both Norman over the Pacific, and a strong tropical easterly wave over the Atlantic and Caribbean. The toggle above shows the two positions (using visible imagery at 0.64 µm) along with the CONUS domain (using the clean window, band 13 at 10.3 µm).

The Mesoscale Sector allows 1-minute imagery over Norman. Otherwise, full-disk imagery with a time cadence of every 15 minutes would be used. The hour-long animation, below, shows the evolution of the storm and its environment.

GOES-16 ABI Band 2 Visible (0.64 µm) imagery, 2016-2115 UTC (Click to enlarge)

A closer view of the eye, below, (Click to play animated gif), shows a well-developed eye with embedded low clouds. Because Norman is near 120 W, the view angle is oblique and only the western edge of the eyewall can be viewed.

GOES-16 ABI Band 2 Visible (0.64 µm) imagery, 2016-2115 UTC (Click to animate)

Norman appears to be at the northern edge of deep tropical moisture, based on the toggle below of GOES-16 Clear Sky Total Precipitable Water and the GOES-16 infrared Low-Level Water Vapor image (7.34 µm). The projected path of Norman is mostly Westward so the storm will remain within deep tropical moisture for the next several days. It is forecast to remain a strong hurricane.

GOES-16 ABI Clear-Sky Total Precipitable Water toggled with GOES-16 Infrared Low-Level Water Vapor (7.34 µm) in cloudy skies, 2000 UTC on 30 August 2018 (Click to enlarge)

For more information on Norman, please consult the website of the National Hurricane Center or the SSEC/CIMSS Tropical Weather Website.