Butterfly: a Satellite Mission to Transform our Understanding of the Contribution of Air-Sea Fluxes to Weather and Climate

The ocean, the largest reservoir of heat and water on Earth, exchanges heat and moisture with the atmosphere through turbulent fluxes at the air–sea interface. These fluxes impact atmospheric and oceanic variability, thereby modifying weather and climate, including precipitation patterns, terrestrial water availability, floods and droughts, and extreme events such as terrestrial and marine heatwaves. Some of the largest fluxes occur over Western Boundary Currents (WBCs) when dry, cold continental air is carried over these large warm currents by midlatitude westerlies. The high wind speeds and large air–sea temperature and humidity differences result in large sensible and latent heat fluxes which affect lower atmosphere temperature and humidity. However, not only are the magnitudes of these fluxes are important, but their spatial gradients as well. This is true even in regions outside the WBCs: small-scale (~25 km) sea surface temperature variations associated with ocean fronts and eddies are ubiquitous in the world ocean. Recent evidence indicates that large-scale atmospheric circulation depends on air–sea interaction processes that are directly mediated by small-scale fluxes.

In this talk I will discuss Butterfly, a to-be-proposed NASA Earth Venture Mission. Butterfly’s 2-year, single satellite mission is designed to deliver estimates of global air–sea turbulent heat and moisture fluxes at the <25-km spatial resolution and <15% net uncertainty. Accurate global 25-km flux measurements are needed to improve our knowledge of air–sea interaction processes and how they impact weather and climate model prediction. Butterfly is the first satellite mission to focus specifically on air–sea fluxes. It carries a single passive microwave instrument and will be placed in a high inclination orbit with a swath width of 640 km with 91% global coverage achieved in 2 days. Butterfly science questions include understanding the degree to which these fields of high-resolution turbulent heat and moisture fluxes influence midlatitude storm evolution. In addition, the error characteristics of Butterfly measurements will enable developers of satellite-based global ocean turbulent heat and moisture flux products to balance these contributions to the energy and water cycles to within 5%. Pathways that are being explored for improvements in resolution will be discussed.