The role of mindanao dome in the variability of the Pacific North equatorial current bifurcation

Abstract

The Mindanao Dome (MD) features prominent oceanic variability and is located geographically close to the bifurcation latitude Y (b) of the Pacific North Equatorial Current. In this study, the role of the MD in the variability of Y (b) is examined with 20 years of satellite altimetric sea surface height (SSH) data and a 1.5-layer linear Rossby wave model. It is shown that the seasonal variations of surface Y (b) are related to not only the SSH fluctuations near the bifurcation point (bifurcation box; 125A degrees-130A degrees E, 12A degrees-15A degrees N) but also those outstanding in the MD region (MD box; 127A degrees-132A degrees E, 6A degrees-9A degrees N). The impact of the MD SSH changes is significant when the bifurcation point stays at southerly latitudes during February-September, which hinders (delays) the southward leap (northward retreat) of Y (b) in April-May (July-August) and thus leads to the asymmetry of the mean Y (b) seasonal cycle (with a positive skewness of gamma = +0.64). Such asymmetry also shows year-to-year variations depending on yearly mean Y (b) value. A southerly yearly mean Y (b) involves larger contribution of the MD and thus causes larger asymmetry of Y (b) seasonal cycle. At interannual and longer timescales, the MD acts to amplify the fluctuations of the bifurcation. It is responsible for about 20 % of the total low-frequency Y (b) variances and plays an important role in the 0.12A degrees A year(-1) southward trend of Y (b) in the past two decades. The impact of the MD on Y (b) changes is becoming increasingly significant at various timescales such as the bifurcation point migrating southward in recent years.