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Melissa Moulton

Research Scientist/Engineer Principal

Affiliate Assistant Professor, Civil and Environmental Engineering

Email

mmoulton@apl.washington.edu

Phone

206-221-7623

Research Interests

Coastal and Nearshore Processes, Environmental Fluid Mechanics, Remote Sensing, Beach Hazard Prediction

Biosketch

Dr. Moulton is a coastal physical oceanographer who studies the dynamics and impacts of rip currents, coastal storms, and inner shelf processes using remote sensing, in situ observations, laboratory experiments, and numerical models.

Education

B.A. Physics, Amherst College, 2009

Ph.D. Physical Oceanography, MIT/WHOI Joint Program, 2016

Publications

2000-present and while at APL-UW

Internal bore evolution across the shelf near Pt. Sal CA interpreted as a gravity current

Spydell, M.S., and 15 others including C. Chickadel, M. Moulton, and J. Thomson, "Internal bore evolution across the shelf near Pt. Sal CA interpreted as a gravity current," J. Phys. Oceanogr., 51, 3629-3650, doi:10.1175/JPO-D-21-0095.1, 2021.

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11 Nov 2021

Off the central California coast near Pt. Sal, a large amplitude internal bore was observed for 20 h over 10 km cross-shore, or 100 m to 10 m water depth (D), and 30 km alongcoast by remote sensing, 39 in situ moorings, ship surveys, and drifters. The bore is associated with steep isotherm displacements representing a significant fraction of D. Observations were used to estimate bore arrival time tB, thickness h, and bore and non-bore (ambient) temperature difference ΔT, leading to reduced gravity g'. Bore speeds c, estimated from mapped tB, varied from 0.25 m s-1 to 0.1 m s-1 from D = 50 m to D = 10 m. The h varied from 5 to 35 m, generally decreased with D, and varied regionally alongisobath. The bore ΔT varied from 0.75 to 2.15°C. Bore evolution was interpreted from the perspective of a two-layer gravity current. Gravity current speeds U, estimated from the local bore h and g compared well to observed bore speeds throughout its cross-shore propagation. Linear internal wave speeds based on various stratification estimates result in larger errors. On average bore thickness h = D/2, with regional variation, suggesting energy saturation. From 50–10 m depths, observed bore speeds compared well to saturated gravity current speeds and energetics that depend only on water depth and shelf-wide mean g'. This suggests that this internal bore is the internal wave analogue to a saturated surfzone surface gravity bore. Alongcoast variations in pre-bore stratification explain variations in bore properties. Near Pt. Sal, bore Doppler shifting by barotropic currents is observed.

Modeled three-dimensional currents and eddies on an alongshore-variable barred beach

Baker, C.M., M. Moulton, B. Raubenheimer, S. Elgar, and N. Kumar, "Modeled three-dimensional currents and eddies on an alongshore-variable barred beach," J. Geophys. Res., 126, doi:10.1029/2020JC016899, 2021.

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1 Jul 2021

Circulation in the nearshore region, which is critical for material transport along the coast and between the surf zone and the inner shelf, includes strong vortical motions. The horizontal length scales and vertical structure associated with vortical motions are not well documented on alongshore-variable beaches. Here, a three-dimensional phase-resolving numerical model, Simulating WAves till SHore (SWASH), is compared with surfzone waves and flows on a barred beach, and is used to investigate surfzone eddies. Model simulations with measured bathymetry reproduce trends in the mean surfzone circulation patterns, including alongshore currents and rip current circulation cells observed for offshore wave heights from 0.5 to 2.0 m and incident wave directions from 0 to 15° relative to shore normal. The length scales of simulated eddies, quantified using the alongshore wavenumber spectra of vertical vorticity, suggest that increasing wave directional spread intensifies small-scale eddies (O(10) m). Simulations with bathymetric variability ranging from alongshore uniform to highly alongshore variable indicate that large-scale eddies (O(100) m) may be enhanced by surfzone bathymetric variability, whereas small-scale eddies (O(10) m) are less dependent on bathymetric variability. The simulated vertical dependence of the magnitude and mean length scale (centroid) of the alongshore wavenumber spectra of vertical vorticity and very low-frequency (f ≈ 0.005 Hz) currents is weak in the outer surf zone, and decreases toward the shoreline. The vertical dependence in the simulations may be affected by the vertical structure of turbulence, mean shear, and bottom boundary layer dynamics.

Warm and cool nearshore plumes connecting the surf zone to the inner shelf

Moulton, M., C.C. Chickadel, and J. Thomson, "Warm and cool nearshore plumes connecting the surf zone to the inner shelf," Geophys. Res. Lett., 48, doi:10.1029/2020GL091675, 2021.

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28 May 2021

Cross‐shore transport of larvae, pollutants, and sediment between the surf zone and the inner shelf is important for coastal water quality and ecosystems. Rip currents are known to be a dominant pathway for exchange, but the effects of horizontal temperature and salinity gradients are not well understood. Airborne visible and infrared imaging performed on the California coast shows warm and cool plumes driven by rip currents in the surf zone and extending onto the shelf, with temperature differences of approximately 1°C. The airborne imagery and modeled temperatures and tracers indicate that warm plumes exhibit more lateral spreading and transport material in a buoyant near‐surface layer, whereas cool plumes move offshore in a subsurface layer. The average cross‐shore extent of warm plumes at the surface is approximately one surfzone width larger than for cool plumes. Future work may explore the sensitivity of nearshore plumes to density patterns, wave forcing, and bathymetry.

More Publications

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
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