UNDERSTANDING PASSIVE MICROWAVE VARIABILITY OVER QUEEN MAUD LAND IN THE CONTEXT OF INCREASING MASS BALANCE

A. Colliander^1,2, N. Schlegel³, A. Hossan², C. Walker⁴, J. Harper⁵, J. Lemmetyinen¹, A. Riihelä¹

¹Finnish Meteorological Institute, ²Jet Propulsion Laboratory, California Institute of Technology, ³NOAA/OAR Geophysical Fluid Dynamics Laboratory, ⁴Woods Hole Oceanographic Institution, ⁵University of Montana

The Queen Maud Land (QML) sector of East Antarctica hosts a complex system of grounded ice sheet and fringing ice shelves that play a central role in regulating ice discharge to the Southern Ocean. Ice sheet evolution in this region is governed by interactions between atmospheric forcing, katabatic winds, and underlying bedrock topography, resulting in spatially variable accumulation and flow regimes. The bordering ice shelves act as buttresses that stabilize inland ice dynamics but are sensitive to oceanic heat intrusions, changing sea-ice conditions, and episodic seasonal surface melt. Such melt and refreezing processes enhance firn compaction, weaken surface integrity, and may precondition ice shelves for hydrofracture under future warming. Notably, QML currently exhibits an increasing mass balance trend, in contrast to many other sectors of the Antarctic Ice Sheet, motivating this investigation.

Multi-frequency passive microwave observations provide a unique means to probe the structure and dynamics of snow, firn, and ice, capturing both contemporary and long-term signals. Lower frequencies can penetrate hundreds of meters, potentially reaching the ice–ocean interface beneath ice shelves, while higher frequencies are sensitive to near-surface processes. Together, these complementary sensitivities allow monitoring of meltwater evolution, firn compaction, and subsurface changes in ice-shelf integrity, as well as the structural and thermal properties shaped by decades to millennia of snow accumulation.

Snow, firn, and ice were represented using the Glacier Energy and Mass Balance model (GEMB), which simulates surface mass balance from meteorological inputs and provides firn profiles of temperature, density, and liquid water content (LWC). Microwave brightness temperatures (TB) were simulated with the Microwave Emission Model of Layered Snowpacks (MEMLS) at 1.4–36.5 GHz, using GEMB-derived layer properties (thickness, temperature, density, grain size, LWC), including ice layers formed through densification. We employed L-band (1.4 GHz) TB observations from the SMAP radiometer (6 AM/PM equatorial crossing, 40° incidence angle, 38 km native resolution, ~1000 km swath), complemented by AMSR2 data at 6.9–89 GHz (1:30 AM/PM crossing, 55° incidence angle, ~1900 km swath), with footprints from ~41 km (6.9 GHz) to ~5 km (89 GHz). Both datasets provide at least twice-daily coverage of QML since 2012.

Together, the TB observations, GEMB simulations, and MEMLS modelling provide an integrated picture of snow, firn, and ice evolution across QML. We will present analyses of grounded ice-sheet structure, spatial patterns of surface and subsurface temperature, fresh snow accumulation, ice-shelf surface melt signals and their structural impacts, and residuals between observed and modelled TB. Radiometric modelling offers a powerful tool to constrain firn structure and melt processes in regions lacking in situ data. By combining passive microwave observations with firn models, we aim to improve calibration, initialization, and the reliability of projections of QML mass balance.