Explicitly determined sea ice emissivity and emission temperature over the Arctic for surface‐sensitive microwave channels

• Published in: Quarterly journal of the Royal Meteorological Society Vol. 149; no. 754; pp. 2011 - 2030
• Main Authors: Kang, Eui‐Jong, Sohn, Byung‐Ju, Tonboe, Rasmus Tage, Noh, Young‐Chan, Kwon, In‐Hyuk, Kim, Sang‐Woo, Maturilli, Marion, Kim, Hyun‐Cheol, Liu, Chao
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01.07.2023; Wiley Subscription Services, Inc; Royal Meteorological Society
• Subjects: 1-D Var retrieval; 1D‐Var retrieval; Arctic sea ice; Arctic winter sea ice; Arctic zone; Atmospheric temperature; Boundary conditions; Channels; Data assimilation; Data collection; Emissions; Emissivity; emitting layer temperature; emitting layer temperatures; Growth models; Ice; Ice environments; Lower troposphere; microwave temperature sounding; Radiative transfer; Salinity; Sea ice; Sea ice temperatures; Snow; Snow and ice; snow and sea ice model; Soundings; Temperature; Troposphere; Weather forecasting; Arctic region
• ISSN: 0035-9009; 1477-870X
• DOI: 10.1002/qj.4492

Data assimilation of satellite microwave measurements is one of the important keys to improving weather forecasting over the Arctic region. However, the use of surface‐sensitive microwave‐sounding channel measurements for data assimilation or retrieval has been limited, especially during winter, due to the poorly constrained sea ice emissivity. In this study, aiming at more use of those channel measurements in the data assimilation, we propose an explicit method for specifying the surface radiative boundary conditions (namely emissivity and emitting layer temperature of snow and ice). These were explicitly determined with a radiative transfer model for snow and ice and with snow/ice physical parameters (i.e. snow/ice depths and vertical distributions of temperature, density, salinity, and grain size) simulated from the thermodynamically driven snow/ice growth model. We conducted 1D‐Var experiments in order to examine whether this approach can help to use the surface‐sensitive microwave temperature channel measurements over the Arctic sea ice region for data assimilation. Results show that (1) the surface‐sensitive microwave channels can be used in the 1D‐Var retrieval, and (2) the specification of the radiative boundary condition at the surface using the snow/sea ice emission model can significantly improve the atmospheric temperature retrieval, especially in the lower troposphere (500 hPa to surface). The successful retrieval suggests that useful information can be extracted from surface‐sensitive microwave‐sounding channel radiances over sea ice surfaces through the explicit determination of snow/ice emissivity and emitting layer temperature. This article proposes an explicit method for estimating multi‐spectral emissivities and associated emission temperatures for microwave window and temperature‐sounding channels in the wintertime Arctic sea ice region, with information and constraints from the thermodynamic growth model and radiative transfer model for snow and ice. Subsequently, through the application of this method along the trajectory of the MOSAiC expedition from 1 December 2019 to 31 March 2020, we successfully demonstrated that the explicit method is capable of describing the surface boundary conditions necessary for the atmospheric radiative transfer calculation. These results not only provide a solid foundation for microwave data assimilation but also open a door to the atmosphere–snow/ice–ocean coupled data assimilation.