Tropical Depression One-E forms in the East Pacific Ocean

April 24th, 2020 |

GOES-17 “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.35 µm) images [click to play animation | MP4]

GOES-17 “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.35 µm) images [click to play animation | MP4]

1-minute Mesoscale Domain Sector GOES-17 (GOES-West) “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.35 µm) images (above) showed the circulation of Tropical Invest 90E in the East Pacific Ocean on 24 April 2020. The low-level circulation center appeared to be located about 100 miles southwest of the 18 UTC surface analysis position.

GOES-17 Visible images with a plot of Deep-Layer Wind Shear from the CIMSS Tropical Cyclones site (below) indicated that Invest 90E was embedded within an environment of low shear — the National Hurricane Center gave the feature an 80% chance of further developing into a tropical depression within 48 hours.

GOES-17 “Red” Visible (0.64 µm) with a plot of Deep-Layer Wind Shear at 23 UTC images [click to enlarge]

GOES-17 “Red” Visible (0.64 µm) images, with a plot of Deep-Layer Wind Shear at 23 UTC [click to enlarge]

VIIRS True Color RGB and Infrared Window (11.45 µm) images from NOAA-20 and Suomi NPP as viewed using RealEarth (below) revealed tendrils of transverse banding along the western and northern periphery if the disturbance.

VIIRS True Color RGB and Infrared Window (11.45 µm) images from NOAA-20 and Suomi NPP [click to enlarge]

VIIRS True Color RGB and Infrared Window (11.45 µm) images from NOAA-20 and Suomi NPP [click to enlarge]

===== 25 April Update =====

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

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

GOES-17 Infrared images (above) showed the period when the disturbance became classified as Tropical Depression One-E at 15 UTC — making this the earliest tropical cyclone on record in the East Pacific basin during the satellite era.

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

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

GOES-17 Infrared images with plots of tropical surface analyses (above) indicated that TD One-E was situated just north of the Intertropical Convergence Zone (ITCZ). The MIMIC-TPW product (below) showed that the tropical depression was tapping moisture from the ITCZ and drawing it northward.

MIMIC Total Precipitable Water product [click to enlarge]

MIMIC Total Precipitable Water product [click to enlarge]

GOES-17 Visible images (below) revealed an exposed low-level circulation that was displaced north-northwest of the primary cluster of deep convection.

GOES-17 “Red” Visible (0.64 µm) images [click to play animation | MP4]

GOES-17 “Red” Visible (0.64 µm) images [click to play animation | MP4]

GOES-17 Scanning designed to reduce heating-caused data outages

April 24th, 2020 |

GOES-17 Upper Level Water Vapor (Band 8, 6.19 µm) Infrared Imagery, 0400-1620 (Click to animate)

NOAA/NESDIS has modified the GOES-17 Mode 6 scanning schedule during times of increased data-outages related to the faulty Loop Heat Pipe (LHP) mechanism (Blog Post 1, 2, 3 on that subject;  see also here) on GOES-17.  (The OSPO Notification is here).  Between 0600 and 1200 UTC, Full Disk scans are imaged every 15 minutes, rather than every 10;  the two flexible mesoscale sectors (including the one with a default location over Alaska) are scanned every 2 minutes, rather than every minute;  the GOES-17 ‘CONUS’ domain, also known as the PACUS domain, typically scanned every 5 minutes, is not scanned at all.  These modifications will be in place in 2020 from 9 April through 1 May, from 12 August through 1 September and from 14 October through 31 October.  Dates for 2021 (and beyond) have not yet been determined.  The ‘time-time’ chart for this modified scanning is shown below (figure source).

‘Time-Time’ chart for GOES-17 Scanning during Mode 3 Cooling operations. Cyan regions denote no ABI scanning activity, green regions are Meoscale sector scans, pink denotes the full disk scan. Other colors show navigation and calibration times. Note the lack of a 5-minute PACUS scan (Click to enlarge)

This change in scanning strategy mitigates heating-caused imagery losses because it reduces the amount thermal energy absorbed by the ABI when it is pointed towards a warm source (that is, Earth) instead of cold outer space.  By reducing the scanning periods, OSPO reduced (but did not eliminate) the span of time during which time data from many of the infrared channels of the ABI are unusable because of saturated sensors.

Note in the animation above how the time-step changes at 0600 UTC to every 15 minutes, and then changes back to every 10 minutes at 1200 UTC.  A slower animation from 0530 – 0630 UTC (link) shows that increment change more clearly.  Because the so-called CONUS scan does not happen, GOES-17 CONUS scan imagery is not available during this time window;  of course, data are available in the CONUS region via the every-15-minute Full Disk scans.

The image below, courtesy Mat Gunshor, CIMSS, (derived from this website) shows how this Mode 3 Cooling Operations reduces the window when data are unavailable.  The time span when data are unusable (highlighted by the green double-headed arrows) is shorter in 2020 as a result of this new scanning strategy.  Also, the peak Focal Plane Module (FPM) Temperature is reduced, which may have implications for the long-term health of the satellite.

Comparisons between GOES-16 and GOES-17 Low-Level water vapor infrared imagery (Band 10, 7.34 µm).  Julian day 104 from 2019 (left) and 2020 (right).  GOES-16 and -17 Full-Disk imagery at the end of the time series as shown.  Time series plots (bottom) show the Focal Plane Module (FPM) temperature (black) and the GOES-17 – GOES-16 brightness temperature difference (blue) for a region centered on the Equator equidistant between the two satellite sub-points.