Measuring tropospheric gravity waves over stratocumulus cloud decks

Tropospheric internal gravity waves, often originating from jets, fronts, or deep convection, leave subtle but discernible imprints on the vast stratocumulus decks that cover subtropical oceans. These waves represent a non-negligible, yet poorly quantified, interaction between the free atmosphere and the marine boundary layer. This presentation introduces a robust, twopass methodology using 2D continuous wavelet transforms (CWT) on geostationary satellite imagery (GOES-16) to objectively detect, track, and characterize these wave packets. The core of our framework is its ability to precisely separate the intrinsic wave propagation signal from the dominant, large-scale advective flow of the cloud field.

Our method quantifies the primary physical signature of these waves: the modulation of cloudtop brightness caused by vertical displacements at the boundary layer inversion. By tracking these propagating brightness patterns, our algorithm identifies individual wave packets as dynamically evolving objects and measures their physical properties, including wavelength, propagation speed, and direction. To validate the method, we generate synthetic satellite imagery by superimposing the signatures of hypothetical wave fields (with known properties such as wavelength, speed, and direction) onto realistic, advected cloud scenes. This process allows us to confirm the method's ability to faithfully retrieve the initial parameters and to characterize its measurement uncertainties.

We then apply this validated methodology to a real-world case study from 12 October 2023 over the Southeast Pacific. The analysis successfully isolates a coherent wave packet with a ~150 km wavelength and tracks its dynamic evolution.

Potential applications are numerous, including the construction of wave climatologies, the study of wave-cloud interactions, the analysis of their role in organizing shallow convection, and the assessment of their long-range predictability. The tool, made available as open-source software, is intended to facilitate a systematic exploration of these key, yet often hidden, components of the climate system.