Observed Decadal Sea-Level Variations Over the Tropical Indo-Pacific Basin: Association with and Indicators for Varying Walker Cells and Climate Modes
Event: 2017 Ocean Surface Topography Science Team Meeting
Session: Science II: Large Scale Ocean Circulation Variability and Change
Presentation type: Type Oral
Satellite observed sea surface height (SSH) over the tropical Indo-Pacific basin exhibits distinct spatial patterns of decadal variations since the 1990s: During some periods (e.g., 1998-2002), SSH rises in the maritime continent region that resides in the warm pool and hosts multitude coasts and Islands, and falls in the central-eastern Pacific and west Indian Ocean; during some other periods (e.g., 1993-1997), the SSH pattern reverses. In-situ based upper 700m thermosteric sea level shows evident decadal sea level variations since the 1960s, and can represent the overall pattern detected by satellite observations during their overlapping period. The distinct sea level patterns over both the tropical Pacific and Indian Oceans are largely driven by zonal surface winds associated with the Pacific and Indian Walker Cell (WCs), which vary on decadal timescales (periods of one to few decades) but the two do not always co-vary. Using a Bayesian Dynamic Linear Model (DLM), we explore the causes for the WCs’ variability since the 1960s. During northern winter (Nov-Apr), decadal variability of ENSO plays a vital role in determining both the Pacific and Indian WCs, with El Nino–like conditions reducing warm pool convection and weakening the WCs, and the two WCs co-vary. During summer (May-Oct), while the Pacific WC is still determined by decadal variability of ENSO, the Indian WC is associated with decadal variations of ENSO, Indian Ocean Dipole (IOD), Indian summer monsoon convection and tropical Indian Ocean SST, with monsoon convection having the largest effect since the 1990s. The complex causes for the Indian WC during summer result in its poor co-variability with the Pacific WC for the summer season. These results indicate that decadal sea level patterns over the tropical Indo-Pacific basin are direct consequences of, and thus may serve as indicators for, decadal climate variability.