Assessing spatio-temporal variability of firn volume scattering over Greenland with satellite altimeters

Abstract. In recent decades, satellite radar altimetry has been widely used to assess volume changes over the Greenland Ice Sheet. Especially, melt events result in drastic changes in volume scattering of firn, which induces a pronounced change in parameters derived from radar altimetry. Due to the recent and increasingly frequent melt events over Greenland, the impacts of these events on the firn condition i.e. formation of ice lenses and reduction of firn air content, need to be better understood. This study therefore exploits the ability of long-term CryoSat-2 data in indicating changes in firn volume scattering, in order to assess the spatio-temporal firn condition variations in Greenland. More specifically, this study utilises the leading edge width (LeW) parameter derived from CryoSat-2 Low Resolution Mode, which has been proven to be the parameter most sensitive to changes in volume scattering, and assesses its variation between January 2011 and August 2021. With a combined analysis of remote sensing observations, in situ observations and outputs from regional climate models, our study demonstrates that the LeW drop induced by extreme melt events in the interior of Greenland experiences a gradual recovery, which can potentially be explained by new snow deposition. However, in many high-elevation regions of Greenland where firn layers were originally dry, due to the recently recurring extensive melt, the firn volume scattering does not fully recover to the original state before the 2012 melt, indicating a long-lived increase in Greenland’s firn density in a changing climate. Finally, our study also confirms the capability of using radar altimeter data to monitor changes in volume scattering properties of firn in the long-term.