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Water Vapor imagery sensing the surface of Hawai’i

By Scott Bachmeier •

GOES-18 Upper-level Water Vapor (6.2 µm, upper left), Mid-level Water Vapor (6.9 µm, upper right), Lower-level Water Vapor (7.3 µm, lower left) and “Clean” Infrared Window (10.3 µm, lower right) [click to play animated GIF | MP4]

GOES-18 (GOES-West) Upper-level Water Vapor (6.2 µm), Mid-level Water Vapor (6.9 µm), Lower-level Water Vapor (7.3 µm) and “Clean” Infrared Window (10.3 µm) images (above) revealed the diurnal cycle of nighttime cooling and daytime warming at the summits of Mauna Kea and Mauna Loa on the Big Island of Hawai’i on 10 January 2023. In addition, a hot thermal signature (darker red to black pixels) was evident in the 10.3 µm imagery due to ongoing volcanic activity at Kilauea. This case is another example which helps to underscore the fact that Water Vapor spectral bands are essentially Infrared bands, which — in the absence of clouds — essentially sense the mean temperature of a layer (or layers) of moisture within the troposphere.

The presence of very dry air within most of the middle/upper troposphere over Hawai’i on 10 January had the effect of shifting the water vapor weighting functions to lower altitudes, as seen on plots for the 3 ABI Water Vapor bands calculated using 12 UTC rawinsonde data from Hilo PHTO (below). This allowed thermal radiation from the higher terrain to pass upward — with minimal attenuation — through what little high-altitude moisture was present and reach the 7.3 µm / 6.9 µm / 6.2 µm detectors on GOES-18.

Plots of weighting functions for GOES-18 Water Vapor spectral bands 08 (light brown), 09 (cyan) and 10 (dark brown), calculated using Hilo (PHTO) rawnsonde data at 1200 UTC on 10 January 2023 [click to enlarge]

Categories: General interpretation, GOES-18