Stratocumulus Brightness Changes and Texture-Tracked Wind Divergence: A Decades-Long Observatory for Internal Gravity Waves

Low clouds over the dark subtropical oceans are well studied for their outsized radiative importance to the Earth’s mean energy budget. However, their same strong bright-above-dark contrast also presents a unique opportunity as an observing system for fundamentally mysterious mesoscale (100s of km) internal gravity (or buoyancy) waves in the atmosphere. These waves are ubiquitously discernable in satellite animations, rippling across the not-quite-opaque cloud decks, but have not been well measured objectively. The eye just sees wavy patterns of light and dark, but now a quantiative picture can be built up using Particle Image Velocimetry or Optical Flow to estimate the motions of texture elements. The divergence of that wind field is well correlated to the rate of change of brighness, consistent with vertical motions of the cloud PBL top, and the quantitative relationship provides powerful constraints on wave-cloud interactions in stratocumulus decks, as well confidence in both observables drawn from the data.

The newly funded project described here will quantify these visual signatures, using only geostationary satellite imagery, in three prongs: intensively in rich high-resolution datasets to engage with field campaigns, extensively from samples spanning basins and seasons and decades, and collaboratively through the production of freely available datasets.