The stable atmospheric boundary layer over snow‐covered sea ice: Model evaluation with fine‐scale ISOBAR18 observations. (26th May 2022)

• Record Type: Journal Article
• Authors: Lorenz, T.; Mayer, S.; Kral, S. T.; Suomi, I.; Steeneveld, G.‐J.; Holtslag, A. A. M.
• Is Part Of: Quarterly journal of the Royal Meteorological Society. Volume 148:Number 745(2022)
• Page Start: 2031
• Page End: 2046
• Publication Date: 2022-05-26
• Subjects: ISOBAR -- numerical weather prediction -- sea ice -- single‐column model -- stable boundary layer -- UAS measurements; Meteorology -- Periodicals; 551.5
• DOI: 10.1002/qj.4293
• Languages: English
• ISSNs: 0035-9009

Abstract

Abstract: A realistic representation of the stable atmospheric boundary layer in numerical weather prediction (NWP) and climate models is still a challenge. We study the evolution of a stable boundary layer over snow‐covered sea ice in Bothnian Bay during wintertime in 2018. We perform high‐resolution model experiments with the Weather Research and Forecasting model in its single‐column model configuration and its default mesoscale configuration to assess which physical processes are essential to predict near‐surface variables correctly. We evaluate our model runs against the unique observational dataset collected during ISOBAR18, which combines novel, upper‐air measurements by an uncrewed aircraft system with wind lidar, sodar, and conventional meteorological mast data. By analysing surface fluxes in the single‐column model, we demonstrate how the atmospheric cooling at the ground can be modelled more realistically than in the mesoscale set‐up. We show that surface albedo and sea‐ice thickness are essential for the surface energy balance in the model, and we demonstrate how the surface fluxes in the mesoscale downscaling with default settings are subject to strong biases. We also show that the ERA5 reanalysis is not capable of representing the observed surface meteorology in the stable atmospheric boundary layer. Our study illustrates the importance of surface albedo and sea‐ice thickness for NWP models. Though a seasonal snow albedo is already in use in many NWP settings, the routine inclusion of sea‐ice thickness, in particular, would be a great step forward for weather forecasts and regional climate simulations. Abstract : This study highlights the delicate balance of processes involved in the simulation of a stable atmospheric boundary layer, observed during the ISOBAR18 field campaign over snow‐covered sea ice in Bothnian Bay (photograph by Kristine Flacké Haualand). Our results demonstrate the challenges that mesoscale atmospheric models face when representing stable boundary layers and stress the importance of accurate sea‐ice albedo, concentration, and thickness for numerical weather prediction and regional climate simulations.