Split Window Difference fields over the Ocean

August 20th, 2019 |

GOES-17 ABI Split Window Difference (10.3 – 12.3) at 0100 UTC on 20 August 2019 (Click to enlarge)

The Split Window Difference field (10.3 µm – 12.3 µm), shown above in the south Pacific around Samoa and American Samoa (Leone is on the island of Tutuila just west of 170º W Longitude; Fitiuta is on the island of Ta’u just east of 170º W Longitude), can be used to estimate the horizontal distribution of water vapor. The Split Window Difference can give a good estimate of moisture distribution in the atmosphere over the ocean where conventional moisture measurements are limited. The image above shows greater values (3.5 – 4 K, in yellow and orange) over the northern part of the image and smaller values (2-3 K, in yellow and blue) over the southern part of the image, divided by a band of cloudiness that passes through 20º S, 170º W.

NOAA-20 overflew this region at 0056 UTC, and NUCAPS profiles were available, as shown below.

GOES-17 ABI Split Window Difference (10.3 – 12.3) at 0100 UTC on 20 August 2019 along with NUCAPS Sounding locations (Click to enlarge)

The animation below steps through soundings at different locations. Total precipitable water as determined from the sounding is indicated. In the region where the Split Window Difference field was around 4 K, precipitable water values were in the 1.5-1.7″ range; in regions where the Split Window Difference was closer to 2 K, precipitable water values were closer to 0.5-0.75″.

NUCAPS Vertical Profiles at different locations, as noted. (Click to animate)

Microwave-only data, shown below from the MIMIC website, shows a sharp gradient at 20º S, 170º W.

MIMIC Total Precipitable Water, 0000 UTC on 20 August 2019 (Click to enlarge)

At ~1200 UTC, when NUCAPS again passed over this region, profiles could again be used to discern gradients in total precipitable water.  At that time, however, the Split Window Difference field was not computed because warming of the Advanced Baseline Imager (ABI) associated with the sub-optimal performance of the Loop Heat Pipe meant that Band 15 data were not available.  (Baseline Level 2 Products, such as total precipitable water, are also unavailable from GOES-17 because of the Loop Heat Pipe issue) The Split Window Difference field could be computed from Himawari-8 data however.

Swan Lake Fire in Alaska

August 17th, 2019 |

GOES-17

GOES-17 “Red” Visible (0.64 µm) and Shortwave Infrared (3.9 µm) images [click to play animation | MP4]

1-minute Mesoscale Domain Sector GOES-17 (GOES-West) “Red” Visible (0.64 µm) and Shortwave Infrared (3.9 µm) images (above) revealed thick smoke and a pronounced thermal anomaly (hot pixels, darker black) associated with the Swan Lake Fire on the Kenai Peninsula in south-central Alaska on 17 August 2019. Later in the day, a few pyrocumulus jumps could be seen in Visible imagery over the fire source region, as fire behavior increased (another day when pyrocumulus jumps were apparent with this fire was 30 June, during a period when southerly winds were transporting dense smoke to the Anchorage area).

Strong northerly-northwesterly winds were transporting smoke from the Swan Lake Fire southward across the Kenai Peninsula and the Seward area — a time series of surface report data from Seward (below) showed that this smoke had reduced the visibility to less than 1 mile by 03 UTC (7 PM local time). South-central Alaska was experiencing drought conditions, which had worsened from the preceding week; the strong winds on this day acted to dry fuels even further, leading to a re-invigoration of the long-lived fire.

Time series of surface reports from Seward, Alaska [click to enlarge]

Time series of surface report data from Seward, Alaska [click to enlarge]

Seward Airport webcam image at 2358 UTC [click to enlarge]

Seward Airport webcam image at 2358 UTC [click to enlarge]

The PM2.5 Air Quality Index reached 427 at Cooper Landing, and 358 farther downwind at Seward (below).

Air Quality Index at Copper Landing and Seward [click to enlarge]

Air Quality Index at Copper Landing and Seward [click to enlarge]

The southward transport of smoke across the Seward area and out over the adjacent offshore waters of the Gulf of Alaska was evident in VIIRS True Color Red-Green-Blue (RGB) images from NOAA-20 and Suomi NPP, as viewed using RealEarth (below).

VIIRS True Color RGB images from NOAA-20 and Suomi NPP [click to enlarge]

VIIRS True Color RGB images from NOAA-20 and Suomi NPP [click to enlarge]

GOES-17 ABI Temperature Data Quality Flags (TDQF) thresholds update

August 8th, 2019 |

Top: Thumbnails of GOES-17 and GOES-16 ABI Band 12 (9.6 µm) on August 1, 2019. Bottom: Time series of GOES-17 minus GOES-16 brightness temperature for a region located between the two satellites. Also plotted is the GOES-17 Focal Plane Temperature. The reduced duration of the GOES-17 data to be flagged is highlighted. [click to enlarge]

As of 19:45 UTC on August 8, 2019, the new Look-Up-Table (LUT) went into operations for use in the GOES-17 ABI Temperature Data Quality Flags (TDQF). These hotter thresholds are possible due to the recent implementation of the Predictive Calibration algorithm.  Note that the image also includes the percent good (and conditionally usable) values (flagged 0 or 1) for both GOES-16 and GOES-17 ABI. Recall there are 5 Data Quality Flags for ABI data:

  • DQF:percent_good_pixel_qf = 1.f ;
  • DQF:percent_conditionally_usable_pixel_qf = 0.f ;
  • DQF:percent_out_of_range_pixel_qf = 0.f ;
  • DQF:percent_no_value_pixel_qf = 0.f ;
  • DQF:percent_focal_plane_temperature_threshold_exceeded_qf = 0.f

The last one, DQF:percent_focal_plane_temperature_threshold_exceeded_qf, reports what percentage of the images pixels are warmer than the threshold value. Note that the thresholds on both the increasing and decreasing temperatures are also reported in the meta-data.

Near realtime brightness temperature comparisons between GOES-16 and GOES-17, as well as historical comparisons for a region centered on the equator and half way between the two satellites.

From the NOAA Notification:

Product(s) or Data Impacted: GOES-17 ABI auxiliary field change

Date/Time of Initial Impact: August 8, 2019 1945 UTC

Details/Specifics of Change:

The GOES-17 ABI Temperature Data Quality Flags (TDQF) thresholds for the thermal bands have been updated to the values in the table below.  This update will make utilizing the TDQF more effective for flagging saturated data caused by the GOES-17 ABI cooling system anomaly. There will be no impacts to distribution caused by this update.

Table of updated Temperature Quality Data Flag thresholds [click to enlarge]

Table of updated Temperature Quality Data Flag thresholds [click to enlarge]

Tropical Depression Flossie near Hawai’i

August 5th, 2019 |

GOES-17

GOES-17 “Red” Visible (0.64 µm), “Clean” Infrared Window (10.35 µm) and Upper-level Water Vapor (6.2 µm) images [click to play animation | MP4]

An animation that cycles through GOES-17 (GOES-West) “Red” Visible (0.64 µm), “Clean” Infrared Window (10.35 µm) and Upper-level Water Vapor (6.2 µm) images (above) showed Tropical Depression Flossie just northeast of Hawai’i on 05 August 2019. Note that (1) the exposed low-level circulation center (LLCC) was very apparent in the visible imagery, (2) deep convection offset to the east/northeast of the LLCC exhibited cloud-top infrared brightness temperatures as cold as -83ºC , and (3) a series of gravity waves were propagating westward away from the convection, moving toward Hawai’i.

GOES-15 Infrared imagery and deep-layer wind shear data from the CIMSS Tropical Cyclones site (below) showed that the tropical cyclone was in an environment of strong shear, which was responsible for the displacement between the exposed LLCC and the convection. In addition to the wind shear, the weakening trend of the system was also due to its motion over cold Sea Surface Temperatures and low Ocean Heat Content.

GOES-15 Infrared Window (10.7 µm) images, with contours and streamlines of deep-layer wind shear [click to enlarge]

GOES-15 Infrared Window (10.7 µm) images, with contours and streamlines of deep-layer wind shear at 18 UTC [click to enlarge]