Abstract
Abstract. We explore the feasibility of an observation operator producing passive microwave brightness temperatures for sea ice at a frequency of 6.9 GHz. We investigate the influence of simplifying assumptions for the representation of sea ice vertical properties on the simulation of microwave brightness temperatures. We do so in a one-dimensional setup, using a complex 1D thermodynamic sea ice model and a 1D microwave emission model. We find that realistic brightness temperatures can be simulated in cold conditions from a simplified linear temperature profile and a simplified salinity profile as a function of depth in the ice. These realistic brightness temperatures can be obtained based on profiles interpolated to as few as five layers. Most of the uncertainty resulting from the simplifications is introduced by the simplification of the salinity profiles. In warm conditions, the simplified salinity profiles lead to brine volume fractions that are too high in the subsurface layer. To overcome this limitation, we suggest using a constant brightness temperature for the ice during warm conditions and treating melt ponds as water surfaces. Finally, in our setup, we cannot assess the effect of wet snow properties. As periods of snow with intermediate moisture content, typically occurring in spring and fall, locally last for less than a month, our approach allows one to estimate realistic brightness temperatures at 6.9 GHz from climate model output for most of the year.
Highlights
Sea ice concentration products are retrieved from passive microwave brightness temperatures measured by satellites and come with a non-negligible uncertainty (Ivanova et al, 2015; Tonboe et al, 2016; Lavergne et al, 2019)
As most general circulation models (GCMs) do not explicitly represent the time evolution of vertical profiles of temperature and salinity in the ice and snow, we investigate the effect of simplified temperature and salinity profiles on the simulation of brightness temperatures
With the help of a one-dimensional thermodynamic sea ice model and a one-dimensional emission model, we investigated if realistic sea ice brightness temperatures can be simulated based on GCM output at a frequency of 6.9 GHz with vertical polarization
Summary
Sea ice concentration products are retrieved from passive microwave brightness temperatures measured by satellites and come with a non-negligible uncertainty (Ivanova et al, 2015; Tonboe et al, 2016; Lavergne et al, 2019). This observational uncertainty hinders reliable climate model initialization (Bunzel et al, 2016) and model evaluation (Notz et al, 2013). It hinders a robust extrapolation of the future sea ice evolution based on current observations. Niederdrenk and Notz (2018) showed that the observational uncertainty in sea ice concentration translates into uncertainty in the sensitivity of sea ice to changes in global-mean air temperature and leads to uncertainty in the temperature at which an icefree Arctic in summer can be expected
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