Subseasonal Forecasting with an Icosahedral, Vertically Quasi-Lagrangian Coupled Model. Part I: Model Overview and Evaluation of Systematic Errors

Details

• Journal Title:
  Monthly Weather Review
• Personal Author:
  Sun, Shan ; Bleck, Rainer ; Benjamin, Stanley G. ; Green, Benjamin W. ; Grell, Georg A.
• NOAA Program & Office:
  OAR (Oceanic and Atmospheric Research) ; GSL (Global Systems Laboratory) ; ESRL (Earth System Research Laboratory) ; CIRES (Cooperative Institute for Research in Environmental Sciences)
• Description:
  The atmospheric hydrostatic Flow-Following Icosahedral Model (FIM), developed for medium-range weather prediction, provides a unique three-dimensional grid structure-a quasi-uniform icosahedral horizontal grid and an adaptive quasi-Lagrangian vertical coordinate. To extend the FIM framework to subseasonal time scales, an icosahedral-grid rendition of the Hybrid Coordinate Ocean Model (iHYCOM) was developed and coupled to FIM. By sharing a common horizontal mesh, air-sea fluxes between the two models are conserved locally and globally. Both models use similar adaptive hybrid vertical coordinates. Another unique aspect of the coupled model (referred to as FIM-iHYCOM) is the use of the Grell-Freitas scale-aware convective scheme in the atmosphere. A multiyear retrospective study is necessary to demonstrate the potential usefulness and allow for immediate bias correction of a subseasonal prediction model. In these two articles, results are shown based on a 16-yr period of hindcasts from FIM-iHYCOM, which has been providing real-time forecasts out to a lead time of 4 weeks for NOAA's Subseasonal Experiment (SubX) starting July 2017. Part I provides an overview of FIM-iHYCOM and compares its systematic errors at subseasonal time scales to those of NOAA's operational Climate Forecast System version 2 (CFSv2). Part II uses bias-corrected hindcasts to assess both deterministic and probabilistic subseasonal skill of FIM-iHYCOM. FIM-iHYCOM has smaller biases than CFSv2 for some fields (including precipitation) and comparable biases for other fields (including sea surface temperature). FIM-iHYCOM also has less drift in bias between weeks 1 and 4 than CFSv2. The unique grid structure and physics suite of FIM-iHYCOM is expected to add diversity to multimodel ensemble forecasts at subseasonal time scales in SubX.
• Source:
  Monthly Weather Review, 146(5), 1601-1617.
• DOI:
  https://doi.org/10.1175/mwr-d-18-0006.1
• Document Type:
  Journal Article
• Funding:
  Grant no. NA17OAR4320101
• Rights Information:
  Other
• Compliance:
  Submitted
• Main Document Checksum:
  urn:sha-512:a4608288ab72c6ad73af26bd390972ee8b7301e888e4a9e07371fe2278c45d72bb5f98b30f41a88aaa8a4ab0cc1eb8d8453b5b6166f839acab3b199cc718a492
• Download URL:
  https://repository.library.noaa.gov/view/noaa/21876/noaa_21876_DS1.pdf
• File Type:
  [PDF - 6.90 MB ]