The Arctic Weather Satellite, introducing a new wavelength range for ice hydrometeor retrievals

Abstract. The first cloud property retrievals based on operational sub-millimetre measurements are presented, making use of the channels between 89 and 325 GHz of the Arctic Weather Satellite (AWS). The main quantities of the dataset are frozen water path (FWP) and the associated mass-weighted mean altitudes and particle sizes. In this first version, results are restricted to latitudes between 60° S and 60° N. The retrievals are based on detailed simulations of instrument observations. The actual inversion is made by a quantile regression neural network, and case-specific uncertainty estimates are provided.

Retrievals performed on simulations suggest that retrieved FWP values are essentially unbiased across a wide dynamic range, from 10 kg m^-2 down to 40 g m^-2. The associated mass-weighted mean altitude is also essentially unbiased for the entire relevant range of 2 km to 12 km. The particle size estimates, however, show a slight bias for sizes other than 400 μm. Comparisons with other datasets provide strong indications that these results also extend to retrievals from real observations; for example, local and zonal means match those of existing radar/lidar-based retrieval products.

The accuracy in FWP should be unprecedented among estimates based on passive satellite data, thanks to the new sensitivity afforded by sub-millimetre channels. The dataset complements cloud radar observations by providing a significantly broader spatial coverage. There is also potential to create a climate-relevant dataset, as the retrievals are directly applicable to the EPS-Sterna constellation, continuing the AWS observations up to 2045.