Detection of low clouds on “Cirrus band” imagery

October 29th, 2017 |

GOES-16 Visible (0.64 µm, top), Cirrus (1.37 µm, middle) and Infrared Window (10.3 µm, bottom) images [click to play animation]

GOES-16 Visible (0.64 µm, top), Cirrus (1.37 µm, middle) and Infrared Window (10.3 µm, bottom) images [click to play animation]

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

The ABI “Cirrus” (1.37 µm) band is centered in a strong water vapor absorption spectral region — therefore it does not routinely sense the lower troposphere, where there is usually substantial amounts of water vapor. Hence, its main application is the detection of higher-altitude cirrus cloud features.

However, in areas of the atmosphere characterized by low amounts of total precipitable water, the Cirrus band can sense clouds (and other features, such as blowing dust) in the lower troposphere. Such was the case on 29 October 2017, when a ribbon of dry air resided over the northern Gulf of Mexico in the wake of a strong cold frontal passage; low-level stratocumulus clouds were very apparent on GOES-16 Cirrus band images (above). Also of note: cloud features associated with Tropical Storm Philippe could be seen east of Florida.

The three GOES-16 Water Vapor bands (Upper-level 6.2 µm, Mid-level 6.9 µm and Lower-level 7.3 µm) highlighted the pocket of dry air that was moving across the northern Gulf of Mexico on that day (below).

GOES-16 Upper-level Water Vapor (6.2 µm, top), Mid-level Water Vapor (6.9 µm, middle) and Lower-level Water Vapor (7.3 µm, bottom) images [click to play animation]

GOES-16 Upper-level Water Vapor (6.2 µm, top), Mid-level Water Vapor (6.9 µm, middle) and Lower-level Water Vapor (7.3 µm, bottom) images [click to play animation]

The MODIS instrument on Terra and Aqua has a 1.37 µm Cirrus band as well; 1619 UTC Terra images (below) also revealed the stratocumulus clouds (especially those over the northeastern Gulf, where the driest air resided). Conversely, note how the low cloud features of Philippe were not seen on the Cirrus image, since abundant moisture within the tropical air mass east of Florida attenuated 1.37 µm wavelength radiation originating from the lower atmosphere.

In addition, the VIIRS instrument — on Suomi NPP, and the upcoming JPSS series — has a 1.37 µm Cirrus band.

Terra MODIS visible (0.65 µm), Cirrus (1.375 µm) and Infrared Window (11.0 µm) images [click to enlarge]

Terra MODIS visible (0.65 µm), Cirrus (1.375 µm) and Infrared Window (11.0 µm) images [click to enlarge]

Hourly images of the MIMIC Total Precipitable Water product (below) showed the ribbon of very dry air (TPW values less than 10 mm or 0.4 inch) sinking southward over the northern Gulf of Mexico. This TPW product uses microwave data from POES, Metop and Suomi NPP satellites (description).

http://cimss.ssec.wisc.edu/goes/blog/wp-content/uploads/2017/10/tpw_17z.png

MIMIC Total Precipitable Water images [click to play animation]

Heavy rain in Florida

October 26th, 2017 |

Aided in part by precipitation associated with Hurricane Irma, some areas of Florida have received record rainfall during the June-October 2017 period:

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

GOES-16 Visible (0.64 µm, left), Near-Infrared

GOES-16 Visible (0.64 µm, left), Near-Infrared “Vegetation” (0.86 µm, center) and Near-Infrared “Snow/Ice” (1.61 µm, right) images [click to play animation]

A comparison of GOES-16 “Red” Visible (0.64 µm), Near-Infrared “Vegetation” (0.86 µm) and Near-Infrared “Snow/Ice” (1.61 µm) images (above) showed that water was a strong absorber of radiation at 0.86 µm and 1.61 µm wavelengths — therefore wet ground, rivers, lakes and the oceans appeared dark in those images. This makes those two GOES-16 ABI spectral bands useful for identifying areas of flooding.

Two areas in Florida are noteworthy on the images: the St. Johns River in the northeast part of the state (where Moderate Flooding had been occurring), and parts of South Florida (which had just received an additional 1-5 inches of rain on  the previous day).

A closer look at those 2 areas using Terra MODIS Visible (0.65 µm) and Near-Infrared “:Snow/Ice” (1.61 µm) images are shown below.

Terra MODIS Visible (0.65 µm) and Near-Infrared :Snow/Ice

Terra MODIS Visible (0.65 µm) and Near-Infrared :Snow/Ice” (1.61 µm) images, showing central and northeastern Florida [click to enlarge]

Terra MODIS Visible (0.65 µm) and Near-Infrared :Snow/Ice" (1.61 µm) images, showing southern Florida [click to enlarge]

Terra MODIS Visible (0.65 µm) and Near-Infrared :Snow/Ice” (1.61 µm) images, showing southern Florida [click to enlarge]

In stark contrast to the periods of heavy rain, a strong cold front brought clear skies and very dry air over Florida, as seen in MIMIC Total Precipitble Water product (below).

MIMIC Total Precipitable Water product [click to enlarge]

MIMIC Total Precipitable Water product [click to enlarge]

This dry air evoked enthusiasm in least one South Florida resident:


Super Typhoon Lan in the West Pacific

October 21st, 2017 |

Advanced Dvorak Technique (ADT) plot for Typhoon Lan [click to enlarge]

Advanced Dvorak Technique (ADT) plot for Typhoon Lan [click to enlarge]

A plot of the Advanced Dvorak Technique for Typhoon Lan (above) showed that the tropical cyclone underwent a period of rapid intensification during the 00-12 UTC period on 20 October 2017.

A 24-hour animation of Himawari-8 rapid-scan (2.5 minute interval) Infrared Window (10.4 µm) images (below) revealed the development of a very large eye during the 20 October/06 UTC to 21 October/06 UTC period.

Himawari-8 Infrared Window (10.4 µm) images [click to play MP4 animation]

Himawari-8 Infrared Window (10.4 µm) images [click to play MP4 animation]

A nighttime comparison of Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images at 1700 UTC or 2:00 AM kocal time (below; courtesy of William Straka, CIMSS/SSEC) provided a good visualization of the “stadium effect” — an eye that was more narrow at the surface, with a larger diameter at higher altitudes. A packet of mesospheric airglow waves (reference) was also evident on the Day/Night Band image, propagating south-southeastward away from the eye.

Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (10.4 µm) images [click to enlarge]

Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (10.4 µm) images [click to enlarge]

A 2-panel comparison of Himawari-8 Visible (0.64 µm) and Infrared Window (11.45 µm) images (below) showed the eye of Lan after it attained Super Typhoon status at 18 UTC on 20 October. Mesovortices could  be seen within the eye on the rapid-scan images.

Himawari-8 Visible (0.64 µm, left) and Infrared Window (10.4 µm, right) images [click to play MP4 animation]

Himawari-8 Visible (0.64 µm, left) and Infrared Window (10.4 µm, right) images [click to play MP4 animation]

A large amount of moisture was associated with this tropical cyclone, as depicted by hourly images of the MIMIC Total Precipitable Water product (below) — note the large area with TPW values of 70 mm or greater (light violet color enhancement).

MIMIC Total Precipitable Water product [click to play animation]

MIMIC Total Precipitable Water product [click to play animation]

A TPW value of 72.5 mm (2.87 inches) was derived from the Minamidaitojima, Japan rawinsonde data at 12 UTC on 21 October (below). Minamidaitojima is the largest island in the Daito Islands group southeast of Okinawa, Japan  — this station was just to the northeast of Lan around 12 UTC.

Rawinsonde data from Minamidaitojima, Japan [click to enlarge]

Rawinsonde data from Minamidaitojima, Japan [click to enlarge]

Tropical Storm Nate forms near Nicaragua

October 5th, 2017 |

GOES-16 ABI Band 2 Visible (0.64 µm) Imagery, 1127 – 1324 UTC on 5 October 2017 (Click to animate)

GOES-16 Visible Imagery, above, shows convection (imagery at 1-minute intervals) surrounding Tropical Storm Nate, just onshore in northeastern Nicaragua.

GOES-16 ABI “Clean Window” Infrared (10.3 µm) Imagery, 4 October 2017 at 2300 UTC through 1130 UTC on 5 October 2017 (Click to animate)

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

The Tropical Depression (#16) in the western Caribbean Sea has strengthened to become a minimal Tropical Storm, acquiring the name Nate. The animation from GOES-16, above, shows disorganized convection over the entire basin, stretching into the Pacific Ocean south of central America. (The sheared remains of Pacific Tropical Storm Ramon are also present south of Mexico). The animation below, from 0000-1300 UTC on 5 October 2017, shows the mid-level Water Vapor Infrared Imagery (6.95 µm) from GOES-16. Convection develops over the center of Nate, over Nicaragua, at the end of the animation.

GOES-16 ABI “Mid-Level Water Vapor” Infrared (6.95 µm) Imagery, 0000-1300 UTC on 5 October 2017 (Click to animate)

Microwave Imagery, below, from SSMI/S at around 1000 UTC on 5 October, (from this site) suggests that Nate is centered very near the coast of Nicaragua. Nate is forecast to move north into the Gulf of Mexico; its path through the northwest Caribbean suggests strengthening is possible if Nate remains far enough from land. Very warm water is present in the northwest Caribbean; that warmth extends to great depth as shown by this plot of Oceanic Heat Content; that warmth extends into the central Gulf of Mexico.

85 GHz Brightness Temperatures, 1000 UTC on 5 October 2017 (Click to enlarge)

Nate formed at a time when the Moon was Full. Thus, Suomi NPP Day Night Band Visible Imagery showed excellent illumination. The image below is from 0627 UTC on 5 October.

Suomi NPP Day Night Band Visible (0.7 µm) Imagery, 0627 UTC on 5 October 2017 (Click to enlarge)

Total Precipitable Water in advance of Nate is plentiful, as shown in the loop below (from this site). There is dry air over the continental United States, however, associated with a strong High Pressure System. Easterly winds south of that system are apparent in Scatterometer winds from early in the morning on 5 October.

MIMIC Morphed Total Precipitable Water, 1200 UTC 4 October – 1100 UTC 5 October 2017 (Click to enlarge)