CPP-02. SeaIceRT: a python interface for a Delta-Eddington radiative transfer model

Abstract
Sunlight transmitted through snow and sea ice to the upper ocean plays an important role in regulating biological activity in Polar regions, determining the timing of initiations of algal and phytoplankton blooms. Measurements of under-ice photosynthetically active radiation (PAR) are available from field campaigns and from autonomous buoys. However, understanding of the spatial distribution and time evolution of PAR for larger regions and over longer time periods requires estimates of light transmission through snow and sea ice from radiative transfer models. Even intensive and observation rich field campaigns such as MOSAiC can only collect measurements from a limited number of measurement points over selected periods of time. Radiative transfer models can be used to "fill in" gaps in the under ice light field, enabling observations of the atmosphere, snow and ice characteristics, oceanography and biology collected at distributed locations to be combined. Here we present SeaIceRT, a python interface for the single column Delta-Eddington sea ice radiative transfer model from the Community Ice CodE (CICE) sea ice model used in the NCAR Community Earth System Model version 2 (CESM2). The python code provides a simple interface to the underlying FORTRAN radiative transfer model. Model parameters and forcing variables (ice thickness, snow depth and density, and melt pond depth) can be set and explored from an interactive environment such as ipython or Jupyter notebooks, as well as incorporated into python scripts to estimate under-ice light over periods of time, along transects or for grids for the Arctic Ocean. We demonstrate setting up and running the model for several transects collected during the MOSAiC cruise and for estimating phytoplankton bloom onset for the Arctic Ocean. We hope that the software package provides a framework for both simplifying and expanding access to these modelling tools. SeaIceRT is open source software. Documentation and code can be found at https://github.com/andypbarrett/seaice_radiative_transfer.