Northward propagation of the subseasonal variability over the eastern Pacific warm pool

Abstract

Previous studies suggest that easterly vertical shear of summer mean flow could be a key factor in the northward propagation of the subseasonal variability (SSV) over the Asian monsoon region (e.g., Jiang et al., 2004). Analysis indicates that this same mechanism may also be dictating propagation features over the eastern Pacific (EPAC). Consistent with the presence of local easterly vertical wind shear, northward propagation of the SSV is also evident over the EPAC with a phase speed of about 0.6 deg day-1. Moreover, similar to its counterpart in the Indian Ocean, the northward propagating SSV over this region is also characterized by positive anomalies of equivalent barotropic vorticity and lower-tropospheric specific humidity, and planetary boundary layer (PBL) convergence, to the north of the convection center. Thus, the present study provides another independent example of the essential role that easterly vertical wind shear may be playing in regulating the meridional migration of the SSV. Copyright 2008 by the American Geophysical Union.