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Ocean Surface Topography from Space
Interannual variability and decadal change of upwelling and heat redistribution over the Indian Ocean: effects of climate modes


Weiqing Han - (University Of Colorado, Boulder)

  Dr. Aixue Hu
(University Of Colorado, Boulder)

Compelling evidence from bservational and modeling studies shows that the Indian Ocean (IO) has had large impacts on global and regional climate in the 20th century. Due to this importance, extensive research has been carried out in the past decade to explore IO variability, with most focusing on the sea surface temperature (SST). Studies on upwelling and upper-ocean heat content (HC) are much limited. Yet, their variations are of paramount importance for regulating climate. In particular, the relative roles played by climate modes in causing interannual variability and decadal change of the west and east IO upwelling have not been quantified, and effects of the upwelling variability on the spatial patterns of upper-ocean HC are not well understood. While few recent studies suggested that a significant portion of heat associated with the surface warming hiatus since 2003 is transported into the IO from the Pacific via the Indonesian Throughflow (ITF), how this extra heat is distributed over the IO and affects the spatial patterns of HC remains is unclear.

The overall goal of the proposed research is to utilize the Jason-series mission data and the ~20-year multiple satellite altimeter data, other satellite data, in situ observations combined with model experiments and application of recently developed advanced statistic tools, to provide a thorough investigation on the roles played by climate modes in causing interannual variability and decadal change of the IO upwelling and heat redistribution. Our main period of interest is 1993-2016, when satellite altimeter data are available. Results for this period will also be analyzed in a longer-term context from 1960-present using available thermosteric sea level data, other in situ observations, reanalysis products and existing ocean model outputs, in order to understand the robustness of the interannual variability and decadal change. Specific objectives are to:

  1. conduct observational analyses using Bayesian Dynamical Linear Model and other statistic tools to explore the interannual variability and decadal change of the west and east IO upwelling, their connections, and roles in determining the basin-scale HC patterns in the upper IO; assess the effects of climate modes on the upwelling and HC patterns;
  2. perform model experiments to quantify the effects of each climate mode in causing interannual variability of the west and east IO upwelling and HC patterns, and develop an in-depth understanding of the processes involved;
  3. examine the decadal change of upwelling and upper-ocean HC patterns induced by climate modes, and explore the associated processes;
  4. investigate where the heat carried by the ITF during the surface warming hiatus is stored, understand the relevant processes for heat redistribution, and estimate the effect of Interdecadal Pacific Oscillation (IPO) in causing this heat export into the IO.

Because sea level represents an integral effect of surface and subsurface processes (e.g., heating), and due to the inadequate spatial-temporal coverage of in situ observations in the subsurface, the 23-yr long satellite altimeter data are crucial for the proposed investigation on upwelling and heat redistribution. The proposed research directly contributes to the goal of the OSTST because utilizing the Jason-series and multiple satellite altimetry data for basic research to advance Earth sciences constitutes an important component. The project also contributes to the goal of the CLIVAR East and West IO Upwelling Research Initiatives, which aim to address the emerging urgency to better understand the IO upwelling towards sustainable development in these regions. The project is a collaborative effort between the University of Colorado (W. Han) and the National Center for Atmospheric Research (NCAR; G. Meehl and A. Hu).

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