Subseasonal Forecasting with an Icosahedral, Vertically Quasi-Lagrangian Coupled Model: Systematic Errors and Deterministic/Probabilistic Forecast Skill

Shan Sun
  23 Mar, Noon, in 2155

The FIM-iHYCOM coupled model has been running real-time for NOAA’s Subseasonal Experiment (SubX) since July 2017. It couples the atmospheric Flow-following finite volume Icosahedral Model (FIM) to an icosahedral version of the Hybrid Coordinate Ocean Model (HYCOM). This coupled model is unique in terms of its grid structure: in the horizontal, both atmospheric and ocean model operate on a common icosahedral mesh, eliminating the need for a flux interpolator; in the vertical, both models use an adaptive ALE (Arbitrary Lagrangian-Eulerian)coordinate. FIM uses GFS physics package, with an option of Grell-Freitas scale aware convective parameterization.

For SubX, FIM-iHYCOM initializes four time-lagged ensemble members around each Wednesday, and integrates for 32 days. Preliminary results from the multi-year hindcasts indicate that both deterministic and probabilistic forecast skill of week-3-4 from FIM-iHYCOM are comparable to those of the operational model CFSv2. Moreover, we will discuss model skills in simulating Madden-Julian Oscillation index, blocking frequency and sudden stratospheric warming events.