Observing Processes impacting The Sea Ice Mass balance from In Situ Measurements - SATellite validation

The Arctic sea ice is not only an indicator of climate change, it is also a major player in the climate system.So there is a real challenge to improve our forecasting capabilities. Climate models agree that Arctic summer pack ice may disappear, but observations indicate that this is occurring at a rate substantially faster than that of simulations, despite the progress made over the last years. There are also wide disparities between the models. Documenting and analyzing processes of exchange (heat, fresh water, momentum) at the ocean-ice-atmosphere interface in the Arctic is therefore particularly important to better understand the evolution of the ice pack on the one hand, but also to better parameterize these exchanges to improve the predictive capability of climate models. Some processes are not yet taken into account by climate models such as the ability of swells propagating from the marginal ice zone (MIZ) to fracture an increasingly thin and fragile ice pack, and in doing so to affect ocean-ice ocean-atmosphere heat flux.

Perhaps more so than the detailed representation of processes, the lack of an accurate knowledge of the very background state of the ice pack (the current ice volume) is being pointed out as a major hindrance for accurate climate prediction. Precise measurement of ice thickness from space is therefore a key issue. While constantly improving, the remote sensing of ice thickness struggles in reducing uncertainties inherent to the method, which is based on freeboard measurement (chiefly uncertainties in snow load and ice density). In this context, the acquisition of in situ observations in the Arctic sea ice is a major need. These are critical not only to analyze and understand the processes involved, to ultimately improve their parameterization in climate models, but they also remain crucial for validating satellite observations (for Ku-band radar altimetry and L-band radiometry missions in particular).

The acquisition of year-round in situ measurements in such inhospitable regions requires autonomous vectors. We have developed an autonomous buoy ’Ice-T’ (for ’Ice Thickness’) dedicated to the study of the ice mass balance. The buoy provides as well real-time transmitted heave spectra measurements in sea ice. This project aims to pursue the acquisition of an uninterrupted time series of observations initiated in 2011 along the transpolar drift, between the North Pole, where the buoy is deployed, and Fram strait and beyond as the buoy often continues its drift in the MIZ along Greenland.

New technological developments are envisioned here: (1) the inclusion of a miniature radar for direct snow height measurement, a poorly known parameter and a major source of error for the remote sensing of ice thickness ; (2) In addition we plan to include salinity measurements in the sea ice, in particular at the snow-ice interface, observations which could be important for improving freeboard measurements in the Ku-band frequency, as the presence of saline snow layer impacts the location of the main radar scattering horizon. The observations that we propose to acquire will be used both to validate satellite observations and to investigate a variety of processes at the ocean-ice-atmosphere interface.