APL-UW Home

Jobs
About
Campus Map
Contact
Privacy
Intranet

Melissa Moulton

Research Scientist/Engineer Senior

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's recent research includes studying strong, offshore-directed jets known as rip currents which can carry pollutants, larvae, and heat from the shoreline to the inner shelf and are hazardous to swimmers. Her work seeks to improve understanding and prediction of rip currents using field observations and numerical simulations. (http://www.whoi.edu/oceanus/feature/the-riddle-of-rip-currents) In addition, Dr. Moulton is investigating inner shelf processes using airborne remote sensing, drifters, 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

Extremely low frequency (0.1 to 1.0 mHz) surf zone currents

Elgar, S., B. Raubenheimer, D.B. Clark, and M. Moulton, "Extremely low frequency (0.1 to 1.0 mHz) surf zone currents," Geophys. Res. Lett., 46, 1531-1536, doi:10.1029/2018GL081106, 2019.

More Info

2 Jan 2019

Low‐frequency surf zone eddies disperse material between the shoreline and the continental shelf, and velocity fluctuations with frequencies as low as a few mHz have been observed previously on several beaches. Here spectral estimates of surf zone currents are extended to an order of magnitude lower frequency, resolving an extremely low frequency peak of approximately 0.5 mHz that is observed for a range of beaches and wave conditions. The magnitude of the 0.5‐mHz peak increases with increasing wave energy and with spatial inhomogeneity of bathymetry or currents. The 0.5‐mHz peak may indicate the frequency for which nonlinear energy transfers from higher‐frequency, smaller‐scale motions are balanced by dissipative processes and thus may be the low‐frequency limit of the hypothesized 2‐D cascade of energy from breaking waves to lower frequency motions.

Comparison of rip current hazard likelihood forecasts with observed rip current speeds

Moulton, M., G. Dusek, S. Elgar, and B. Raubenheimer, "Comparison of rip current hazard likelihood forecasts with observed rip current speeds," Wea. Forecasting, 32, 1659-1666, doi:10.1175/WAF-D-17-0076.1, 2017.

More Info

1 Aug 2017

Although rip currents are a major hazard for beachgoers, the relationship between the danger to swimmers and the physical properties of rip current circulation is not well understood. Here, the relationship between statistical model estimates of hazardous rip current likelihood and in situ velocity observations is assessed. The statistical model is part of a forecasting system that is being made operational by the National Weather Service to predict rip current hazard likelihood as a function of wave conditions and water level. The temporal variability of rip current speeds (offshore-directed currents) observed on an energetic sandy beach is correlated with the hindcasted hazard likelihood for a wide range of conditions. High likelihoods and rip current speeds occurred for low water levels, nearly shore-normal wave angles, and moderate or larger wave heights. The relationship between modeled hazard likelihood and the frequency with which rip current speeds exceeded a threshold was assessed for a range of threshold speeds. The frequency of occurrence of high (threshold exceeding) rip current speeds is consistent with the modeled probability of hazard, with a maximum Brier skill score of 0.65 for a threshold speed of 0.23 m s-1, and skill scores greater than 0.60 for threshold speeds between 0.15 and 0.30 m s-1. The results suggest that rip current speed may be an effective proxy for hazard level and that speeds greater than ~0.2 m s-1 may be hazardous to swimmers.

Rip currents and alongshore flows in single channels dredged in the surf zone

Moulten, M., S. Elgar, B. Raubenheimer, J.C. Warner, and N. Kumar, "Rip currents and alongshore flows in single channels dredged in the surf zone," J. Geophys. Res. Oceans, 122, doi:10.1002/2016JC012222, 2017.

More Info

8 May 2017

To investigate the dynamics of flows near nonuniform bathymetry, single channels (on average 30 m wide and 1.5 m deep) were dredged across the surf zone at five different times, and the subsequent evolution of currents and morphology was observed for a range of wave and tidal conditions. In addition, circulation was simulated with the numerical modeling system COAWST, initialized with the observed incident waves and channel bathymetry, and with an extended set of wave conditions and channel geometries. The simulated flows are consistent with alongshore flows and rip-current circulation patterns observed in the surf zone. Near the offshore-directed flows that develop in the channel, the dominant terms in modeled momentum balances are wave-breaking accelerations, pressure gradients, advection, and the vortex force. The balances vary spatially, and are sensitive to wave conditions and the channel geometry. The observed and modeled maximum offshore-directed flow speeds are correlated with a parameter based on the alongshore gradient in breaking-wave-driven-setup across the nonuniform bathymetry (a function of wave height and angle, water depths in the channel and on the sandbar, and a breaking threshold) and the breaking-wave-driven alongshore flow speed. The offshore-directed flow speed increases with dissipation on the bar and reaches a maximum (when the surf zone is saturated) set by the vertical scale of the bathymetric variability.

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
Close

 

Close