The Subseasonal Experiment (SubX): A Multimodel Subseasonal Prediction Experiment

Abstract

The Subseasonal Experiment (SubX) is a multimodel subseasonal prediction experiment designed around operational requirements with the goal of improving subseasonal forecasts. Seven global models have produced 17 years of retrospective (re)forecasts and more than a year of weekly real-time forecasts. The reforecasts and forecasts are archived at the Data Library of the International Research Institute for Climate and Society, Columbia University, providing a comprehensive database for research on subseasonal to seasonal predictability and predictions. The SubX models show skill for temperature and precipitation 3 weeks ahead of time in specific regions. The SubX multimodel ensemble mean is more skillful than any individual model overall. Skill in simulating the Madden–Julian oscillation (MJO) and the North Atlantic Oscillation (NAO), two sources of subseasonal predictability, is also evaluated, with skillful predictions of the MJO 4 weeks in advance and of the NAO 2 weeks in advance. SubX is also able to make useful contributions to operational forecast guidance at the Climate Prediction Center. Additionally, SubX provides information on the potential for extreme precipitation associated with tropical cyclones, which can help emergency management and aid organizations to plan for disasters.

MJO Propagation Processes and Mean Biases in the SubX and S2S Reforecasts

“…Compared to the previous version (CY40R1) of the ECMWF system (Kim, ), RMM skill is increased about 2–3 days in CY43R3. Overall, SubX models have skill comparable to S2S models (Janiga et al, ; Lim et al, ; Pegion et al, ; Vitart, ). As demonstrated in many studies, RMM skill is greater for forecasts with initially strong MJO and lower for initially weak MJO events (not shown).…”

Subseasonal to Seasonal Prediction of Weather to Climate with Application to Tropical Cyclones

“…The renewed interest in S2S forecasting led to the development of the Subseasonal Experiment (SubX) project in the United States, which has created an additional multimodel database of subseasonal forecasts and reforecasts from seven North American models (Pegion et al, ). While similar in form to the S2S database and also archived in the IRI Data Library, SubX differs from S2S in several respects.…”

“…Identifying suitable compromises and trade‐offs in forecast system design is a challenge under practical constraints for operational activities (costs, priorities, and timeliness) and demands further research (Takaya, ). A step forward was taken by SubX which strove toward a common protocol, but where hindcast ensembles were still often compromised in terms of ensemble size (Pegion et al, ).…”

GEOS‐S2S Version 2: The GMAO High‐Resolution Coupled Model and Assimilation System for Seasonal Prediction

“…GEOS‐S2S forecasts are also routinely included in various other national and international multimodel ensembles including the multimodel forecast products at the International Research Institute for Climate and Society of Columbia University GMAO's involvement in such projects enables rigorous evaluations of the system's forecast skill and model biases and allows the quantification of GEOS‐S2S system performance relative to that of other state‐of‐the‐art systems. The suite of GEOS‐S2S‐1 forecasts was expanded for Version 2, to include near‐real‐time weekly initialized forecasts at the subseasonal time scale, thereby facilitating GMAO's participation in NOAA's experimental subseasonal multimodel ensemble project (Pegion et al, ).…”