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Ocean Surface Topography from Space
Strait and Inter-Ocean Transport Estimation Using Altimetry SSH and Gravimetry OBP
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Y. Tony Song
(California Institute of Technology - JPL)

Jun-Yi Guo
(Ohio State University)
C.K. Shum
(Ohio State University)
Raden Dwi Susanto
(Lamont-Doherty Earth Observatory of Columbia University)


Strait and inter-ocean transport are of fundamental interest to physical oceanography [Whitehead, 1989; Killworth, 1995; Godfrey, 1996] and ocean climate considerations [Hansen et al., 2001; Gordon et al., 2003], but are poorly understood and difficult to measure because long-term direct measurements of strait circulation is an expensive alternative and their implementation remains logistically challenging. We hypothesize that the magnitude and variability of strait transport varies with sea-surface height (SSH) and ocean bottom pressure (OBP) gradients between two inter-connected oceans. The combined 15-year TP/Jason-1 and other altimetry data has been the great resource of ocean surface topography, and the Gravity Recovery and Climate Experiment (GRACE) mission has been delivering temporal gravity data for five years with some oceanographic applications [e.g., Chambers et al., 2004; Song and Zlotniki, 2004; 2007; Zlotnicki et al., 2006]. Now it is the perfect time to combine the altimetry and gravimetry data for a better estimate of inter-ocean transport, based on the three years time series of Indonesian throughflow (ITF) measurements from the INSTANT program [Sprintall et al. 2004; Gordon et al, 1999], ongoing-projects measuring the throughflows in the Luzon, Mindoro, Karimata and Makassar Straits [Susanto and Gordon, 2005], and modelling support from a high-resolution global model with a terrain-following coordinate system for better resolving the strait geometry.

Recently, we have developed a theoretical method by combining the "geostrophic control" formula of Garrett and Toulany [1982] and the "hydraulic control" theory of Whitehead et al. [1974]--allowing the use of SSH and OBP variables for estimating inter-ocean transport and separating the transport into surface and bottom fluxes [Song, 2006], providing a potential use of satellite measurements for operational applications. The problem of strait and inter-ocean transport estimation has not been studied in the previous OSTST program. Here we break new ground by combining satellite and in-situ observations with analytical and numerical models for the challenging problem. Based on the previous studies and the INSTANT-related measurements, we are:

  1. Developing a methodology allowing a better use of satellite SSH and OBP data for studying strait circulation and inter-ocean transport.
  2. Deriving a proxy of inter-ocean exchange/throughflow products by combining satellite data with in-situ measurements and model simulations.
  3. Focusing on two case-studies for a better understanding the controlling mechanisms of the Indonesian throughflow and the sea-ice/glacier melting and resulting freshwater fluxes effect on the Denmark Strait overflow.

This research will result in: (1) an improved understanding of Indonesian throughflow and Denmark Strait overflow; (2) an innovative methodology for utilizing satellite SSH and OBP; and (3) a demonstration of using future higher-resolution satellite data from OSTM and GRACE follow-on missions. The project addresses the research themes of the OSTST: (1) To support studies in physical oceanography utilizing Jason/OSTM mission data, as well as the combined 15-year TP/Jason data, jointly with other satellite (ERS-1/-2, ENVISAT, GFO) and in situ data and/or models, in support of both basic research and operational applications; and (2) to investigate the use of gravity mission data with altimeter data for improving the understanding of the mean ocean circulation.

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