Observation of Southward Shift of the North Pacific Intertropical Convergence Zone

Abstract:

One of the major feature of tropical precipitation is the seasonal movement of the Inter-Tropical Convergence Zone (ITCZ). Linear trend analyses of observational rainfall data show global trend patterns of opposite changes near the ITC regions. High-resolution monthly oceanic rainfall data derived from microwave observations by the Remote Sensing Systems are examined to characterize the trend and variability of the North Pacific Inter-tropical Convergence Zone (ITCZ) for the period 1988–2012. Position of the ITCZ is defined as the centroid of rain band between 15°N and equator for each longitude. The climatology captures the seasonal cycle of meridional migration of the ITCZ. The North Pacific ITCZ location shows significant southward shift of 0.3–0.5° decade^–1 in the annual mean and in all seasons except for northern spring with El Niño-Southern Oscillation signal removed. Empirical orthogonal function analyses of the ITCZ position anomalies in the northern summer and autumn indicates a distinct difference in the ITCZ long-term variability between the western North Pacific and the eastern North Pacific, with more pronounced southward shift in the western North Pacific. The technique is applied to other rainfall data sets to characterize the temporal and spatial variability of the ITCZ movements.