Planetary Boundary Layers in Atmospheres, Oceans, and Ice on Earth and Moons

Coordinators: Baylor Fox-Kemper, Daria Halkides, Brad Marston, and Fiamma Straneo

Scientific Advisors: Stephen Belcher, Julie Castillo-Rogez, Carter Ohlmann, and Jim McWilliams

The exchange of energy, mass, and other important quantities across interfaces is a fundamental physical problem spanning all of the natural sciences. Boundary and interfacial layers often exert controlling influence on these exchanges. Interfacial and boundary layers are often characterized by a change of phase, and through spray, bubbles, melting/freezing, and other vigorous mixing or forcing, the coexistence of multiple phases can become important. This program will focus on key questions that illustrate the generality of the interaction phenomenon and facilitate the synthesis of ideas and techniques from different disciplines. Below, we present some of the key questions, broken down into broad areas.

  • Oceans: How important are surface waves in driving turbulence in the boundary layer? Are the wave-averaged equations optimal for modeling upper ocean turbulence, given the wealth of recent observations? On large scales atmospheric variability tends to drive the ocean: does this persist down into the mesoscales (<100 km) and beyond
    What roles do submesoscale motions play in air-sea exchange?
  • Atmospheres: What physics controls the formation and evolution of boundary layer clouds? To what extent are supersaturation, cloud seeding, and nucleation perturbed by anthropogenic emissions? What sets the direction, intensity, and climate change sensitivity of "atmospheric rivers"--the major source of extratropical precipitation? How can fundamental physics (e.g., thermodynamic formulations, conservation principles, statistical physics) be brought to bear on improving the representation of cloud and precipitation biases? Over complex land surfaces, such as vegetated and urban landscapes, how capable are our theory and models of simulating conditions and dispersal, especially for stable boundary layers?
  • Ice: As sea ice ages and roughens, how does it influence the atmospheric and oceanic turbulence nearby? What are the appropriate equations to govern the behavior of sea ice on various scales? How does the melting of ice shelves occur as a boundary layer process? How do exchanges of energy and freshwater occur at the ends of glaciers that feed into fjords in Greenland (and possibly also in a future Antarctic)?
  • Climate: How important are the varied processes within these boundary layers in determining the mean climate state? In determining the sensitivity of climate to perturbations? Which regions in the world are still poorly represented by existing boundary layer theory? What processes are endemic to those regions, and how are they to be understood?
  • Planetary Sciences: Are the equilibrium wind waves of Titan similar to those on Earth? Are the formulations of terrestrial wave models and wave physics sufficient to capture these extraterrestrial waves? What consequences do the ice-covered oceans of Europa, Enceladus, and possibly Ceres have for these bodies' exchanges and budgets of energy? For the stability of their ice cover? For life on these moons?