IndoArchipel

Background

The western tropical Pacific represents an area with strong interannual and decadal sea level variations. While the changes in the open ocean are basically understood in terms of wind-driven redistributions of upper-ocean waters associated with major climate modes (ENSO, PDO), much less is known about the modification of these signals in the Indonesian Archipelago and the marginal seas and shelf areas of southeast Asia, i.e., about the relative role of remote and local forcing mechanisms. Projections of future trends in these areas are hampered since present climate models do not resolve the complex flow structures of the boundary currents and flows through the narrow passages, and are thus lacking potentially important processes, e.g., for connecting the changes in the western Pacific with the Indian Ocean, and for a realistic propagation of deep ocean changes onto the shelf areas and coastal waters.

Objectives

• Provide a regionally refined characterization of the sea level variability along the continental shelf and marginal seas of southern and southeastern Asia, including a mechanistic interpretation of local and remote forcing effects associated with the main climate modes of the Indo-Pacific (ENSO, IOD, PDO, and possibly, the SAM).
• Provide regionally refined projections of the range of future sea level changes to be expected from the possible trends in the atmospheric conditions as simulated in 21st-century climate scenarios.

Methods

• Global ocean modelling with very high (1/20°) resolution over the tropical Indian and western Pacific region (two-way nesting using a ¼°-base model).
• Multi-decadal hindcast simulations using new atmospheric reanalysis products with much enhanced spatial resolution, in conjunction with a novel formulation of the surface boundary fluxes that provides for essential air-sea feedbacks missing in traditional bulk formulations.
• Assessment of the mechanisms of sea level variability with the help of sensitivity experiments aimed at isolating the effect of individual forcing agents.
• Regionally-refined projection of possible future evolutions building on atmospheric trend scenarios from climate studies, complemented by ‘what if’-experiments addressing the effects of possible changes in other drivers, such as increased melting rates of Greenland and Antarctic ice sheets.