Séminaire

While the underlying theory behind polar feedback mechanisms has been known for a long time, current climate models still struggle to capture observed rates of sea ice decline and ice sheet mass.  This may be explained, at least in part, by a historical lack of observational constraints the roles clouds and snowfall play in modulating polar processes.  Satellite observations collected in the last decade have shed new light on these processes and are revealing that atmospheric reanalyses and global climate models exhibit significant biases in several key energy and water fluxes that influence ice-sheet dynamics and, ultimately, project onto global sea level rise.  Reconstructions of polar energy balance from these modern satellite observations also reveal a troubling gap in our ability to observe key properties of the polar environment.  Far-infrared radiation (that occurring at wavelengths longer than 15 microns) makes up 60% of the thermal emission from the Arctic and nearly half of Earth’s emission, globally.  Remarkably, however, while far-infrared spectra have been collected from every planet in the solar system, Earth’s far-infrared emission spectrum has never been systematically documented.  These measurements could offer powerful new insights into the key processes at work in the rapidly changing Arctic.  This presentation will also describe a new satellite mission concept aimed at addressing this critical observational gap.  The Polar Radiant Energy in the Far-InfaRed Experiment (PREFIRE) utilizes two CubeSats in asynchronous orbits to systematically document the spectral variation of thermal emission across the mid- and far-infrared (5 – 45 microns) throughout the Arctic.  We anticipate that PREFIRE measurements will reveal changes in the full spectrum of Arctic radiant energy associated with processes that operate on scales ranging from sub-daily to seasonal.  By distinguishing the unique spectral fingerprints of changes in temperature, water vapor, clouds, and surface melt processes, PREFIRE will help untangle the complex time-varying errors in model physics responsible for the large spread in simulations of the Arctic energy budget.

sylvain.mailler@lmd.polytechnique.fr