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Barry Ma

Senior Oceanographer





Department Affiliation

Ocean Physics


B.S., 1988

M.S. Physical Oceanography, US Naval Postgraduate School, 1998

Ph.D. Oceanography, University of Washington, 2004


2000-present and while at APL-UW

The surface mixed layer heat budget from mooring observations in the central Indian Ocean during Madden–Julian Oscillation events

Chi, N.-H., R.-C. Lien, E.A. D'Asaro, and B.B. Ma, "The surface mixed layer heat budget from mooring observations in the central Indian Ocean during Madden–Julian Oscillation events," J. Geophys. Res., 119, 4638-4652, doi:10.1002/2014JC010192, 2014.

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1 Jul 2014

The oceanic surface mixed layer heat budget in the central equatorial Indian Ocean is calculated from observations at two mooring sites (0°S 79°E and 1.5°S 79°E) during three active and calm phases of Madden–Julian Oscillation (MJO) events between September 2011 and January 2012. At both mooring locations, the surface mixed layer is generally heated during MJO calm phases. During MJO active phases at both mooring locations, the surface mixed layer is always cooled by the net surface heat flux and also sometimes by the turbulent heat flux at the bottom of the surface mixed layer. The turbulent heat flux at the bottom of the surface mixed layer, however, varies greatly among different MJO active phases and between the two mooring locations. A barrier layer exerts control on the turbulent heat flux at the base of the surface mixed layer; we quantify this barrier layer strength by a "barrier layer potential energy," which depends on the thickness of the barrier layer, the thickness of the surface mixed layer, and the density stratification across the isothermal layer. During one observed MJO active phase, a strong turbulent heat flux into the mixed layer was diagnosed, despite the presence of a 10–20 m thick barrier layer. This was due to the strong shear across the barrier layer driven by the westerly winds, which provided sufficient available kinetic energy to erode the barrier layer. To better simulate and predict net surface heat fluxes and the MJO, models must estimate the oceanic barrier layer potential energy, background shear, stratification, and surface forcing accurately.

Large-amplitude internal solitary waves observed in the northern South China Sea: Properties and energetics

Lien, R.-C., F. Henyey, B. Ma, and Y.J. Yang, "Large-amplitude internal solitary waves observed in the northern South China Sea: Properties and energetics," J. Phys. Oceanogr., 44, 1095-1115, doi:10.1175/JPO-D-13-088.1, 2014.

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1 Apr 2014

Five large-amplitude internal solitary waves (ISWs) propagating westward on the upper continental slope in the northern South China Sea were observed in May–June 2011 with nearly full-depth measurements of velocity, temperature, salinity, and density. As they shoaled, at least three waves reached the convective breaking limit: along-wave current velocity exceeded the wave propagation speed C. Vertical overturns of ~100 m were observed within the wave cores; estimated turbulent kinetic energy was up to 1.5 x 10-4 W kg-1. In the cores and at the pycnocline, the gradient Richardson number was mostly <0.25. The maximum ISW vertical displacement was 173 m, 38% of the water depth. The normalized maximum vertical displacement was ~0.4 for three convective breaking ISWs, in agreement with laboratory results for shoaling ISWs. Observed ISWs had greater available potential energy (APE) than kinetic energy (KE). For one of the largest observed ISWs, the total wave energy per unit meter along the wave crest E was 553 MJ m-1, more than three orders of magnitude greater than that observed on the Oregon Shelf. Pressure work contributed 77% and advection contributed 23% of the energy flux. The energy flux nearly equaled CE. The Dubriel–Jacotin–Long model with and without a background shear predicts neither the observed APE > KE nor the subsurface maximum of the along-wave velocity for shoaling ISWs, but does simulate the total energy and the wave shape. Including the background shear in the model results in the formation of a surface trapped core.

Modulation of Kuroshio transport by mesoscale eddies at the Luzon Strait entrance

Lien, R.-C., B. Ma, Y.-H. Cheng, C.-R. Ho, B. Qiu, C.M. Lee, and M.-H. Chang, "Modulation of Kuroshio transport by mesoscale eddies at the Luzon Strait entrance," J. Geophys. Res., 119, 2129-2142, doi:10.1002/2013JC009548, 2014.

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1 Apr 2014

Measurements of Kuroshio Current velocity at the entrance to Luzon Strait along 18.75°N were made with an array of six moorings during June 2012 to June 2013. Strong positive relative vorticity of the order of the planetary vorticity f was observed on the western flank of the Kuroshio in the upper 150 m. On the eastern flank, the negative vorticity observed was about an order of magnitude smaller than f. Kuroshio transport near its origin is computed from direct measurements for the first time. Kuroshio transport has an annual mean of 15 Sv with a standard deviation of 3 Sv. It is modulated strongly by impinging westward propagating eddies, which are identified by an improved eddy detection method and tracked back to the interior ocean. Eight Kuroshio transport anomalies >5 Sv are identified; seven are explained by the westward propagating eddies. Cyclonic (anticyclonic) eddies decrease (increase) the zonal sea level anomaly (SLA) slope and reduce (enhance) Kuroshio transport. Large transport anomalies of >10 Sv within O(10 days) are associated with the pairs of cyclonic and anticyclonic eddies. The observed Kuroshio transport was strongly correlated with the SLA slope (correlation = 0.9). Analysis of SLA slope data at the entrance to Luzon Strait over the period 1992–2013 reveals a seasonal cycle with a positive anomaly (i.e., an enhanced Kuroshio transport) in winter and spring and a negative anomaly in summer and fall. Eddy induced vorticity near the Kuroshio has a similar seasonal cycle, suggesting that seasonal variation of the Kuroshio transport near its origin is modulated by the seasonal variation of the impinging mesoscale eddies.

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The variability of internal tides in the Northern South China Sea

Ma, B.B., R.-C. Lien, and D.S. Ko, "The variability of internal tides in the Northern South China Sea," J. Oceanogr., 69, 619-630, doi:10.1007/s10872-013-0198-0, 2013.

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1 Oct 2013

An array of three bottom-mounted ADCP moorings was deployed on the prevailing propagation path of strong internal tides for nearly 1 year across the continental slope in the northern South China Sea. These velocity measurements are used to study the intra-annual variability of diurnal and semidiurnal internal tidal energy in the region. A numerical model, the Luzon Strait Ocean Nowcast/Forecast System developed at the U.S. Naval Research Laboratory that covers the northern South China Sea and the Kuroshio, is used to interpret the observed variation of internal tidal energy on the Dongsha slope. Internal tides are generated primarily at the two submarine ridges in the Luzon Strait. At the western ridge generation site, the westward energy flux of the diurnal internal tide is sensitive to the stratification and isopycnal slope associated with the Kuroshio. The horizontal shear at the Kuroshio front does not modify the propagation path of either diurnal or semidiurnal tides because the relative vorticity of the Kuroshio in Luzon Strait is not strong enough to increase the effective inertial frequency to the intrinsic frequency of the internal tides. The variation of internal tidal energy on the continental slope and Dongsha plateau can be attributed to the variation in tidal beam propagation in the northern South China Sea.

Internal tides on the East China Sea continental slope

Lien, R.-C., T.B. Sanford, S. Jan, M.-H. Chang, and B.B. Ma, "Internal tides on the East China Sea continental slope," J. Mar. Res., 71, 151-186, doi:10.1357/002224013807343461, 2013.

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1 Jan 2013

Strong semidiurnal internal tides are observed on the continental slope of the East China Sea (ECS) using an array of subsurface moorings and EM-APEX floats. A Princeton Ocean Model (POM) is used to simulate the effects of stratification profiles on the generation and propagation of M2 internal tides; model simulations are compared with observations. On the ECS continental slope northeast of Taiwan, the semidiurnal barotropic tidal current flows nearly perpendicular to the shelf break and continental slope, favoring the generation of internal tides. Both the critical slope analysis and numerical model results suggest multiple generation sites on the continental slope, shelf break and around North MienHua Canyon. Unique high-wavenumber semidiurnal internal tides with a dominant vertical scale of ~100 m are found on the continental slope. The high-wavenumber semidiurnal internal tides appear in a form of spatially coherent shear layers across the ECS slope. They propagate vertically both upward and downward. Patches of strong energy and shear at a typical vertical scale of O(50 m) are present at the intersections of the upward and downward propagating high-wavenumber internal tides. The strong shear of high-wavenumber semidiurnal tides could play an important role in triggering shear instability on the ECS slope. The semidiurnal internal tidal energy flux, primarily in low wavenumbers, on the ECS slope, exhibits strong temporal and spatial variations. The observed depth integrated energy flux is 3.0–10.7 kW m-1, mostly seaward from the continental shelf/slope. The POM model predicts similar seaward energy fluxes at a slightly weaker magnitude, 1.0–7.2 kW m-1. The difference may be due to the absence of mesoscale processes in the model, e.g., the Kuroshio Current and eddies, the assumed horizontally uniform stratification profiles, insufficient model resolution for the abrupt canyon bathymetry, and the lack of the other major semidiurnal tidal constituent, S2, in the model. On the ECS slope, the total energy in the internal wave continuum, between 0.3 cph (beyond semidiurnal tidal harmonics) and the buoyancy frequency, is 6-13 times that of the Garrett–Munk model, presumably as a result of the energy cascade from strong inertial waves and internal tides in the region.

Very large subaqueous sand dunes on the upper continental slope in the South China Sea generated by episodic, shoaling deep-water internal solitary waves

Reeder, D.B., B.B. Ma, and Y.J. Yang, "Very large subaqueous sand dunes on the upper continental slope in the South China Sea generated by episodic, shoaling deep-water internal solitary waves," Mar. Geol., 279, 12-18, doi:10.1016/j.margeo.2010.10.009, 2011.

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15 Jan 2011

Very large subaqueous sand dunes were discovered on the upper continental slope of the northern South China Sea. The dunes were observed along a single 40 km long transect southeast of 21.93N, 117.53E on the upper continental slope in water depths of 160 m to 600 m. The sand dunes are composed of fine to medium sand, with amplitudes exceeding 16 m and crest-to-crest wavelengths exceeding 350 m. The dunes' apparent formation mechanism is the world's largest observed internal solitary waves which generate from tidal forcing on the Luzon Ridge on the east side of the South China Sea, propagate west across the deep basin with amplitudes regularly exceeding 100 m, and dissipate extremely large amounts of energy via turbulent interaction with the continental slope, suspending and redistributing the bottom sediment. While subaqueous dunes are found in many locations throughout the world's oceans and coastal zones, these particular dunes appear to be unique for two principal reasons: their location on the upper continental slope (away from the influence of shallow-water tidal forcing, deep basin bottom currents and topographically-amplified canyon flows), and their distinctive formation mechanism (approximately 60 episodic, extremely energetic, large amplitude events each lunar cycle).

Vertical arrival structure of shipping noise in deep water channels

Li, Z., L.M. Zurk, and B. Ma, "Vertical arrival structure of shipping noise in deep water channels," In Proceedings, MTS/IEEE OCEANS 2010, Seattle, 20-23 September, doi:10.1109/OCEANS.2010.5664539 (MTS/IEEE, 2010).

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20 Sep 2010

In passive sonar systems, knowledge of low-frequency shipping noise is significant for target detection performance. However, an accurate model for the shipping noise structure is difficult to obtain, because of the varying distributions of ships and complicated underwater environment. This work characterizes low-frequency distant shipping noise observed in deep water environments as a function of receiver depth and vertical arrival structure placed below the conjugate depth.

Distant shipping noise is examined using a Monte Carlo simulation based on statistics derived from the Historical Temporal Shipping (HITS) database. Source levels and source depths of ships are assigned depending on the ship classification. The complex pressure field radiated from each interferer is computed using a normal mode propagation model, and the predicted values are summed coherently at each receiver location. Parameters for the ocean channel are chosen in agreement with the experimental observations, and sensitivity to exact parameters of the bottom sediment is explored. The depth dependence of the simulated shipping noise is in agreement with published experimental measurements. A Vertical Line Array (VLA) is used to produce vertical beams that isolate the surface interference from nearby targets. Simulation results quantifying the beamformer output as a function of ocean environment, receiver aperture, and frequency are presented for both conventional and adaptive beamformers.

The results suggest a favorable detection performance of a target in the presence of distant shipping interferers and wind noise, by adaptive beamforming using diagonal loading with white noise gain constraint techniques.

Rain-induced turbulence and air-sea gas transfer

Zappa, C.J., D.T. Ho, W.R. McGillis, M.L. Banner, J.W.H. Dacey, L.F. Bliven, B. Ma, and J. Nystuen, "Rain-induced turbulence and air-sea gas transfer," J. Geophys. Res., 114, doi:10.1029/2008JC005008, 2009.

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9 Jul 2009

Results from a rain and gas exchange experiment (Bio2 RainX III) at the Biosphere 2 Center demonstrate that turbulence controls the enhancement of the air-sea gas transfer rate (or velocity) k during rainfall, even though profiles of the turbulent dissipation rate E are strongly influenced by near-surface stratification. The gas transfer rate scales with E1/2 for a range of rain rates with broad drop size distributions. The hydrodynamic measurements elucidate the mechanisms responsible for the rain-enhanced k results using SF6 tracer evasion and active controlled flux technique. High-resolution k and turbulence results highlight the causal relationship between rainfall, turbulence, stratification, and air-sea gas exchange. Profiles of beneath the air-sea interface during rainfall, measured for the first time during a gas exchange experiment, yielded discrete values as high as 10-2 W kg-1. Stratification modifies and traps the turbulence near the surface, affecting the enhancement of the transfer velocity and also diminishing the vertical mixing of mass transported to the air-water interface. Although the kinetic energy flux is an integral measure of the turbulent input to the system during rain events, E is the most robust response to all the modifications and transformations to the turbulent state that follows. The Craig-Banner turbulence model, modified for rain instead of breaking wave turbulence, successfully predicts the near-surface dissipation profile at the onset of the rain event before stratification plays a dominant role. This result is important for predictive modeling of k as it allows inferring the surface value of E fundamental to gas transfer.

Prediction of underwater sound levels from rain and wind

Ma, B.B., J.A. Nystuen, and R.-C. Lien, "Prediction of underwater sound levels from rain and wind," J. Acoust. Soc. Am., 117, 3555-3565, 2005.

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1 Jun 2005

Wind and rain generated ambient sound from the ocean surface represents the background baseline of ocean noise. Understanding these ambient sounds under different conditions will facilitate other scientific studies. For example, measurement of the processes producing the sound, assessment of sonar performance, and helping to understand the influence of anthropogenic generated noise on marine mammals. About 90 buoy-months of ocean ambient sound data have been collected using Acoustic Rain Gauges in different open-ocean locations in the Tropical Pacific Ocean. Distinct ambient sound spectra for various rainfall rates and wind speeds are identified through a series of discrimination processes. Five divisions of the sound spectra associated with different sound generating mechanisms can be predicted using wind speed and rainfall rate as input variables. The ambient sound data collected from the Intertropical Convergence Zone are used to construct the prediction algorithms, and are tested on the data from the Western Pacific Warm Pool. This physically based semi-empirical model predicts the ambient sound spectra (0.5–50 kHz) at rainfall rates from 2–200 mm/h and wind speeds from 2 to 14 m/s.

Acoustics Air-Sea Interaction & Remote Sensing Center for Environmental & Information Systems Center for Industrial & Medical Ultrasound Electronic & Photonic Systems Ocean Engineering Ocean Physics Polar Science Center