Publications

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2019
Subramanian, AC, Balmaseda MA, Centurioni L, Chattopadhyay R, Cornuelle BD, DeMott C, Flatau M, Fujii Y, Giglio D, Gille ST, Hamill TM, Hendon H, Hoteit I, Kumar A, Lee JH, Lucas AJ, Mahadevan A, Matsueda M, Nam S, Paturi S, Penny SG, Rydbeck A, Sun R, Takaya Y, Tandon A, Todd RE, Vitart F, Yuan DL, Zhang CD.  2019.  Ocean observations to improve our understanding, modeling, and forecasting of subseasonal-to-seasonal variability. Frontiers in Marine Science. 6   10.3389/fmars.2019.00427   AbstractWebsite

Subseasonal-to-seasonal (S2S) forecasts have the potential to provide advance information about weather and climate events. The high heat capacity of water means that the subsurface ocean stores and re-releases heat (and other properties) and is an important source of information for S2S forecasts. However, the subsurface ocean is challenging to observe, because it cannot be measured by satellite. Subsurface ocean observing systems relevant for understanding, modeling, and forecasting on S2S timescales will continue to evolve with the improvement in technological capabilities. The community must focus on designing and implementing low-cost, high-value surface and subsurface ocean observations, and developing forecasting system capable of extracting their observation potential in forecast applications. S2S forecasts will benefit significantly from higher spatio-temporal resolution data in regions that are sources of predictability on these timescales (coastal, tropical, and polar regions). While ENSO has been a driving force for the design of the current observing system, the subseasonal time scales present new observational requirements. Advanced observation technologies such as autonomous surface and subsurface profiling devices as well as satellites that observe the ocean-atmosphere interface simultaneously can lead to breakthroughs in coupled data assimilation (CDA) and coupled initialization for S2S forecasts.

2015
Lien, RC, Ma B, Lee CM, Sanford TB, Mensah V, Centurioni LR, Cornuelle BD, Gopalakrishnan G, Gordon AL, Chang MH, Jayne SR, Yang YJ.  2015.  The Kuroshio and Luzon undercurrent east of Luzon Island. Oceanography. 28:54-63.   10.5670/oceanog.2015.81   AbstractWebsite

Current structure, transport, and water mass properties of the northward-flowing Kuroshio and the southward-flowing Luzon Undercurrent (LU) were observed for nearly one year, June 8, 2012-June 4, 2013, across the Kuroshio path at 18.75 degrees N. Observations were made from four platforms: an array of six subsurface ADCP moorings, two Seagliders, fivepressure inverted echo sounders (PIES), and five horizontal electric field (HEF) sensors, providing the most detailed time series of the Kuroshio and Luzon Undercurrent water properties to date. Ocean state estimates of the western boundary current system were performed using the MIT general circulation model-four-dimensional variational assimilation (MITgcm-4D-Var) system. Prominent Kuroshio features from observations are simulated well by the numerical model. Annual mean Kuroshio transport, averaged over all platforms, is similar to 16 Sv with a standard deviation similar to 4 Sv. Kuroshio and LU transports and water mass pathways east of Luzon are revealed by Seaglider measurements. In a layer above the salinity maximum associated with North Pacific Tropical Water (NPTW), Kuroshio transport is similar to 7 Sv and contains North Equatorial Current (NEC) and Western Philippine Sea (WPS) waters, with an insignificant amount of South China Sea water on the shallow western flank. In an intermediate layer containing the core of the NPTW, Kuroshio transport is similar to 10 Sv, consisting mostly of NEC water. In the lower layer of the Kuroshio, transport is similar to 1.5 Sv of mostly North Pacific Intermediate Water (NPIW) as a part of WPS waters. Annual mean Luzon Undercurrent southward transport integrated to 1,000 m depth is similar to 2.7 Sv with a standard deviation similar to 2 Sv, carrying solely WPS waters below the salinity minimum of the NPIW. The transport of the western boundary current integrated over the full ocean depth east of Luzon Island is similar to 14 +/- 4.5 Sv. Sources of the water masses in the Kuroshio and Luzon Undercurrent are confirmed qualitatively by the numerical model.

2011
Skarsoulis, EK, Cornuelle BD, Dzieciuch MA.  2011.  Second-Order Sensitivity of Acoustic Travel Times to Sound Speed Perturbations. Acta Acustica United with Acustica. 97:533-543.   10.3813/aaa.918434   AbstractWebsite

The second-order sensitivity of finite-frequency acoustic travel times to sound speed perturbations in range-independent environments is studied. Using the notion of peak arrivals and the normal-mode representation of the Green's function first- and second-order perturbation expressions are derived for the travel times in terms of the underlying perturbations in the Green's function and finally in the sound speed profile. The resulting theoretical expressions are numerically validated. Assuming small and local perturbations the non-linear effects appear to be strongest for sound speed perturbations taking place close to the lower turning depths of the corresponding eigenrays. At the upper turning depths - in the case of temperate propagation conditions - the effects are much weaker due to the larger sound speed gradients. The magnitude of the second-order sensitivity of travel times relative to the first-order sensitivity can be used to obtain an estimate for the limits of linearity.