Cooperative Institute for Research in Environmental Sciences at the University of Colorado Boulder

Benjamin Green

Dr. Green is collaborating with Dr. Stan Benjamin and Dr. Chris Fairall (both of whom are also CIRES fellows associated with the Weather and Climate Dynamics division) and their colleagues at NOAA’s Earth System Research Laboratories (ESRL) to investigate numerical simulations of the Madden-Julian Oscillation (MJO). Specifically, the simulations couple the atmospheric Flow-following finite-volume Icosahedral Model (FIM) developed at ESRL to an icosahedral version of the HYbrid Coordinate Ocean Model (iHYCOM). The MJO is the primary cause of intraseasonal (30-60 day) variability in the tropical troposphere, and has been found to have impacts on weather across the globe on similar timescales. Therefore, it is believed that numerical weather prediction (NWP) models capable of adequately simulating the MJO will yield more accurate forecasts at longer lead times. This research will investigate the ability of the coupled FIM-iHYCOM model (hereafter “FIM”) to simulate the MJO by comparing month-long FIM hindcasts with observations taken during the Dynamics of the Madden-Julian Oscillation (DYNAMO) field campaign. Preliminary results indicate that FIM struggles to propagate the MJO signal eastward across the equatorial Indian Ocean and Maritime Continent. This deficiency is likely a consequence of the model inadequately resolving the thin layer of warm water in the top few meters of the ocean, as suggested by recent studies. The next step of the project will be to improve FIM’s representation of this so-called “diurnal warm layer” and thus hopefully yield more realistic MJO simulations. Concurrent research will also examine the sensitivity of the MJO to FIM’s parameterization of convection. Finally, we will determine if better MJO representation in FIM leads to more skillful forecasts globally – which if so would be of great significance, especially because the non-hydrostatic version of FIM (NIM) is being considered as a candidate for NOAA’s new operational global model.