GCM Simulation of the Northward Propagating Intraseasonal Oscillation in the South Asian Summer Monsoon Region
谱模式SAMIL对南亚季风区大气季节内振荡向北传播的模拟

The northward propagating intraseasonal oscillation(ISO) in the South Asian summer monsoon region simulated by general circulation model SAMIL developed in the State Key Laboratory for Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics(LASG),Institute of Atmospheric Physics(IAP),Chinese Academy of Sciences is examined and compared with that from NCEP reanalysis data.SAMIL simulates this oscillation with comparable strength in the South Asia region,and northward propagation of this oscillation from the equator is also simulated though the propagation is slightly slower than that from observations.The simulated northward propagating ISO shows similar vertical structure to observations.The vorticity and the specific humidity fields are obviously meridionally asymmetric with the positive vorticity and specific humidity anomalies lying over the north of the ISO convective center.The maximum ascending motion and convergence in the planetary boundary layer also lie over the north of the ISO convection center.Reasonable simulation of this meridional asymmetric structure leads to well simulation of the northward propagating ISO for the SAMIL model.Key factors associated with the good performance in simulating northward propagating ISO are the reasonable simulations of summer wind fields in South Asian and distribution of specific humidity in the planetary boundary layer.Meanwhile,the modeling result also suggests that the vertical structure of summer winds in South Asian plays a key role in the northward propagation of ISO there,which is consistent with previous studies.