Subseasonal features of the Asian summer monsoon in the NCEP climate forecast system

The operational climate forecast system (CFS) of the US National Centers for Environmental Prediction provides climate predictions over the world, and CFS products are becoming an important source of information for regional climate predictions in many Asian countries where monsoon climate dominates.Recent studies have shown that, on monthly-to-seasonal time-scales, the CFS is highly skillful in simulating and predicting the variability of the Asian monsoon.The higher-frequency variability of the Asian summer monsoon in the CFS is analyzed, using output from a version with a spectral triangular truncation of 126 waves in horizontal and 64 sigma layers in vertical, focusing on synoptic, quasi-biweekly, and intraseasonal time-scales.The onset processes of different regional monsoon components were investigated within Asia.Although the CFS generally overestimates variability of monsoon on these time-scales, it successfully captures many major features of the variance patterns, especially for the synoptic time-scale.The CFS also captures the timing of summer monsoon onsets over India and the Indo-China Peninsula.However, it encounters difficulties in simulating the onset of the South China Sea monsoon.The success and failure of the CFS in simulating the onset of monsoon precipitation can also be seen from the associated features of simulated atmospheric circulation processes.Overall, the CFS is capable of simulating the synoptic-to-intraseasonal variability of the Asian summer monsoon with skills.As for seasonal-to-interannual time-scales shown previously, the model is expected to possess a potential for skillful predictions of the high-frequency variability of the Asian monsoon.