Taylor Moon , Joel Harper, Andreas Colliander, Alamgir Hossan, Neil Humphrey

The addition and refreezing of liquid water to Greenland's accumulation
area are increasingly important processes for assessing the ice sheet’s
present and future mass balance, but uncertain initial conditions, complex
infiltration physics, and limited field data pose challenges. Satellite-based
L-band radiometry offers a promising new tool for observing liquid water
in the firn layer, although further validation is needed. This paper
compares time series of liquid water amount (LWA) from three
percolation zone sites generated by two model-based and two
observation-based methods. LWA is a useful metric for quantifying firn
evolution, offering insights into meltwater processes and model
performance. LWA integrates the interplay of liquid water generation and
refreezing, which often occur simultaneously and repeatedly within firn
layers on diurnal, episodic, and seasonal scales. The four LWA records
showed average discrepancies of up to 62% nRMSE, reflecting
shortcomings inherent to each method. Better agreement between series
occurred after excluding the regional climate model record, lowering
nRMSE to 8%-13%. The agreement between L-band radiometry and
other LWA records inspires confidence in this observational tool for
advancing understanding of firn meltwater processes and serving as a
validation target for simulations of water generation, infiltration, and
refreezing in Greenland’s melting firn layer.