12A.4
An assessment of the Forecast Capability for BSISO by the NCEP Operational Global Forecast Systems
Mingyue Chen, NOAA/NWS/NCEP/CPC, Camp Springs, MD; and W. Wang and A. Kumar
The northward propagating boreal summer intraseasonal oscillation (BSISO) is the dominant mode of intraseasonal variability over the Asian monsoon region. Previous studies have shown that both intrinsic atmospheric dynamics and air-sea coupling can result in the northward propagation of the BSISO. This study examines the impacts of the treatment of ocean surface on the representation of the BSISO in three National Centers for Environmental Prediction (NCEP) models, including: (1) the NCEP uncoupled atmospheric global forecast system model version 2003 (GFS03); (2) the NCEP coupled climate forecast system model (CFS03) which consists of GFS03 as its atmospheric component and an oceanic component; and (3) the NCEP operational uncoupled atmospheric global forecast system (GFSOP) which has been upgraded with new physics package. Atmospheric initial conditions are from the frozen NCEP reanalysis 2 for GFS03 and CFS03, and from the real-time NCEP global data assimilation system for GFSOP. Both GFS03 and GFSOP are atmosphere-only models and comparison between them will indicate the effects of the improvements in the atmospheric model and atmospheric initial conditions. The CFS03 is different from GFS03 only in its inclusion of the air-sea interaction, and comparison between them will represent the impacts of the air-sea coupling. The results from the composite of strong northward propagation events during 2005-2007 show that both uncoupled atmospheric global forecast systems (GFSOP and GFS03) are able to forecast northward propagation of BSISO from equatorial Indian Ocean but with weaker amplitude and slower speed. No clear improvement is obtained in GFSOP compared to GFS03. The coupled forecast system (CFS03) is capable of forecasting the northward propagation of BSISO with more reasonable amplitude and propagation speed. The propagation in both observation and in CFS03 is associated with the leading anomalies of latent heat flux, solar radiation, and SST. Our results indicate that both atmospheric intrinsic dynamics and air-sea coupling are responsible for the maintenance of the northward propagation of the BSISO.
Session 12A, Coupled ocean-atmosphere interactions and their contribution to climate variability on all time scales: Part 1
Thursday, 15 January 2009, 8:30 AM-9:45 AM, Room 128A
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