A First Global View of Sub‐Millimeter Radiances From the Arctic Weather Satellite

Abstract The Arctic Weather Satellite (AWS) from the European Space Agency is a small satellite launched in August 2024 carrying a microwave radiometer for atmospheric sounding. AWS features the first satellite‐borne sub‐millimeter wavelength (>300 GHz) channels for operational meteorology. This “sub‐mm” band is more sensitive to scattering from ice clouds than traditional microwave frequencies and opens up new possibilities for measuring ice clouds and constraining their representations in atmospheric models. For example, 325 GHz radiances are roughly three times more sensitive to frozen water path than 183 GHz radiances. This letter explores how well sub‐mm radiances are currently modeled by state‐of‐the‐art radiative transfer simulators. It also highlights the novel information about ice clouds that can be exploited using these radiative transfer simulators, in the context of weather forecasting and physics‐based retrievals.