[AOS21-07] Causal Mechanism of Sea Level Rise in the South Pacific Ocean
★Invited Papers
Keywords:Sea level rise, Decadal change, Ocean circulation, Adjoint model, State estimation, Data assimilation
Sea level in the South Pacific Ocean east of New Zealand has, over the past two and a half decades, increased faster than the rate of global mean sea level rise (Figure). The excess increase in regional sea level has been associated with spin-up of the subtropical gyre, accompanied by deepening isopycnals and strengthening circulation. Here, in conjunction with satellite and in situ observations, we examine the causal mechanism of this change using the latest ocean state estimate of the Consortium for Estimating the Circulation and Climate of the Ocean (ECCO), Version 4 Release 4 (http://ecco-group.org).
The study identifies the mechanism responsible for the relative sea level rise by expanding the fluctuation into contributions from different forcings using the model's adjoint. Specifically, instead of a forcing directly over the region, we find trends in zonal wind stress east of where the sea level rise takes place causing the observed variation. The remote forcing drives low frequency planetary waves that propagate west across the basin. The islands of New Zealand arrest the propagation and limit the meridional extent of the variation.
The investigation illustrates the utility of ECCO's tools and products in identifying processes controlling the ocean. The ECCO estimate combines nearly all extant observations with a state-of-the-art general circulation model, providing a complete description of the ocean. The study highlights elements of this synthesis with an emphasis on the efficacy of the model's adjoint in analyzing the ocean, besides its use in assimilating data.
The study identifies the mechanism responsible for the relative sea level rise by expanding the fluctuation into contributions from different forcings using the model's adjoint. Specifically, instead of a forcing directly over the region, we find trends in zonal wind stress east of where the sea level rise takes place causing the observed variation. The remote forcing drives low frequency planetary waves that propagate west across the basin. The islands of New Zealand arrest the propagation and limit the meridional extent of the variation.
The investigation illustrates the utility of ECCO's tools and products in identifying processes controlling the ocean. The ECCO estimate combines nearly all extant observations with a state-of-the-art general circulation model, providing a complete description of the ocean. The study highlights elements of this synthesis with an emphasis on the efficacy of the model's adjoint in analyzing the ocean, besides its use in assimilating data.