Use of the GOES-R Split-Window Difference to Diagnose Deepening Low-Level Water Vapor

Abstract

The depth of boundary layer water vapor plays a critical role in convective cloud formation in the warm season, but numerical models often struggle with accurate predictions of above-surface moisture. Satellite retrievals of water vapor have been developed, but they are limited by the use of a model's first guess, instrument spectral resolution, horizontal footprint size, and vertical resolution. In 2016, Geostationary Operational Environmental Satellite-R (GOES-R), the first in a series of new-generation geostationary satellites, will be launched. Its Advanced Baseline Imager will provide unprecedented spectral, spatial, and temporal resolution. Among the bands are two centered at 10.35 and 12.3 mm. The brightness temperature difference between these bands is referred to as the split-window difference, and has been shown to provide information about atmospheric column water vapor. In this paper, the split-window difference is reexamined from the perspective of GOES-R and radiative transfer model simulations are used to better understand the factors controlling its value. It is shown that the simple split-window difference can provide useful information for forecasters about deepening low-level water vapor in a cloud-free environment.

It's not hot air: Using GOES‐16 infrared window bands to diagnose adjacent summertime air masses

“…Analysts conducting a cursory visual inspection of such a scene in the infrared window band at 12.3 μm independently of the 10.3 μm band may conclude there are few if any meaningful differences between them and the 3.9 μm band, especially at night. However, a band difference between the 10.3 and 12.3 μm bands, known as the “split window” difference (SWD), can enhance slight differences to corroborate the front seen in the 3.9 μm band and evince a low‐level moisture plume (Lindsey et al , ). Supporting Information Video S1(a) reveals the presence of a low‐level moisture plume for this case across southern Minnesota.…”

Applications of the 16 spectral bands on the Advanced Baseline Imager (ABI).

“…Absorption and re-emission of water vapor, particularly in the lower troposphere, slightly cools most cloud-free BTs in the 12.3 μm "Dirty Longwave Window" band compared to the other IR window bands. Subtraction of the 12.3 μm BT from the 10.3 μm BT yields the "split window difference" (SWD); a larger SWD (Lindsey et al 2014) will reflect areas of more water vapor in cloud-free areas. More on BT band differences are covered in section 4.…”

Observations of Lower Tropospheric Water Vapor Structures in GOES‐16 ABI Imagery

“…Some of the new spectral bands on the ABI allow for the generation of true color imagery (Miller et al, 2017, ), determination of cloud optical and microphysical properties (Heidinger et al, ), cloud macrophysical properties such as geometric thickness (Noh et al, ), and information about convection initiation and severity (Cintineo et al, ; Lindsey et al, ; Walker et al, ). ABI also provides the first geostationary‐based 1.38‐μm band and a unique new ability to characterize the spatially and temporally resolved distribution and evolution of cirrus in the full disk view of the sensor over a portion of the Western Hemisphere.…”

“…Another way that GOES‐16 data can be used to identify water vapor in the boundary layer is through the use of the so‐called split window difference (SWD), defined as values of Tb(10.35 μm)‐Tb(12.3 μm; e.g., Lindsey et al, ). Due to (1) enhanced absorption of upwelling energy, from the surface, by water vapor near 12.3 μm compared to near 10.35 μm and (2) the weighting functions of each band peaks near the surface (relatively clean atmospheric window bands), relatively small positive values of the SWD indicate where more water vapor existed in a vertical column, only in clear‐sky regions, during the daytime, when temperatures decrease with height.…”