The East Asia-western North Pacific boreal summer intraseasonal oscillation simulated in GAMIL 1.1.1

We evaluate the performance of GAMIL1.1.1 in a 27-year forced simulation of the summerintraseasonal oscillation (ISO) over East Asia (EA)-western North Pacific (WNP). The assessmentis based on two measures: climatological ISO (CISO) and transient ISO (TISO). CISO is the ISOcomponent that is phase-locked to the annual cycle and describes seasonal march. TISO is theISO component that varies year by year.The model reasonably captures many observed features of the ISO, including the stepwise northwardadvance of the rain belt of CISO, the dominant periodicities of TISO in both the South ChinaSea-Philippine Sea (SCS-PS) and the Yangtze River Basin (YRB), the northward propagation of 30--50-dayTISO and the westward propagation of the 12--25-day TISO mode over the SCS-PS, and the zonal propagatingfeatures of three major TISO modes over the YRB. However, the model has notable deficiencies. Theseinclude the early onset of the South China Sea monsoon associated with CISO, too fast northwardpropagation of CISO from 20^oN to 40^oN and the absence of the CISO signal south of 10^oN,the deficient eastward propagation of the 30--50-day TISO mode and the absence of a southward propagationin the YRB TISO modes.The authors found that the deficiencies in the ISO simulation are closely related to the model's biases inthe mean states, suggesting that the improvement of the model mean state is crucial for realisticsimulation of the intraseasonal variation.