Coastal Dynamics Observed from a Mobile Air-Sea Interaction Platform David G. Ortiz-Suslow * , Kimberley Huguenard † , Nathan J. M. Laxague * , Neil J. Williams * , Darek Bogucki † , and Brian K. Haus * * Rosensteil School of Marine and Atmospheric Science 4600 Rickenbacker Cswy, Miami, FL 33149 † Texas A&M University at Corpus Christi 6300 Ocean Dr, Corpus Christi, TX 78412 Abstract—A mobile air-sea interaction platform has been developed in order to quantify the spatial and temporal vari- ability of wind-wave-current coupling in coastal and estuarine environments. University of Miami’s Surface Physics Experi- mental Catamaran (SPEC) is outfitted with both atmospheric and oceanographic instruments, as well as an on-board, real- time data acquisition system. SPEC has a custom-designed bow mounting plate that provides a rigid platform for securing sensors away from the vessel’s already minimal superstructure. This versatile platform provides the high temporal resolution of conventional moorings and towers coupled with the spatial resolution necessary to capture the complex dynamics of near shore processes. The SPEC was deployed as part of a coastal field campaign that took place along Northwest Florida’s Gulf Coast region during the month of December 2013. As part of this effort, the dynamics near a river plume’s frontal edge were investigated using both SPEC-mounted instrumentation as well as other SPEC-deployed sensors. Observations revealed internal bores (or propagating hydraulic jumps) traveling away from the plume front. These findings have significant implications for the coastal transport of surface material (e.g., oil) across large distances far from the original source. I. I NTRODUCTION The flux of momentum, heat, and material across the air- sea interface is a critical component of various near-surface processes, such as wind-wave growth and dissipation, near- surface mixing, and gas transfer (e.g., [23], [30]). The need for global, atmosphere-ocean coupled models motivated past studies to investigate air-sea fluxes in the open ocean (or depth-unlimited) regimes [4]. As a result, the empirical pa- rameterizations developed to generalize the degree of air-sea interaction have built-in assumptions that are only valid over a relatively restrictive set of criterion (see [31], [1], and [6]). The convergence of processes in a depth-limited environment remains under-explored and further observations are required to characterize the role wave shoaling, strong current gradients, and significant horizontal stratification have on the dynamics of the air-sea interface (e.g., [18], [25]). Towers [26], buoys [30], and wind-wave tanks [2] have all been used successfully for measuring fluxes at the air-sea interface. Generally, these previous observations have either occurred or been applicable in an open-ocean regime. In coastal waters the high degree of spatial-temporal variability in the wave, current, and wind fields suggest that mobile platforms could be a viable complement to traditional ob- servation methods [18]. For example, [3] showcased high frequency wind, wave, and current data collected from a mid- sized research vessel outfitted with a custom air-sea interaction instrument package. The goal of their work was to investigate wind-wave coupling in shoaling wave conditions. In a similar vein, the University of Miami developed the Surface Physics Experimental Catamaran (SPEC) as a mobile and agile air- sea interaction vessel for studies within the inner-shelf and coastal waterways. The SPEC can function as a stand-alone platform, as well as a means of deploying and recovering various Lagrangian and Eulerian sensors; this versatility makes the SPEC well-suited for sampling a wide variety of coastal processes. During December 2013, the Consortium for Advanced Research on Transport of Hydrocarbon in the Environment (CARTHE) conducted the field campaign, Surfzone Coastal Oil Pathways Experiment (SCOPE), with the primary aim of understanding the cross-shore transport of surface material (e.g., oil) from the inner-shelf to the beach. The experiment site (see next section) was situated near a tidal inlet-estuary system, which was observed to play a significant role in both the along- and across-shore transport. During the ebb stage of the tide, less dense, riverine water can flow into the coastal region as a river plume with the leading edge of this water mass being known as the plume front. Simultaneous, high res- olution measurements of winds, water surface elevation, and currents (near-surface and at depth) are necessary for building a complete picture of the underlying dynamics in these highly turbulent regions. To this end, the SPEC was deployed to sample this frontal region throughout this campaign. On December 17th, an internal bore was observed outside of the the plume front and propagating westward (away from the plume). These observations were made in nearly quiescent ocean-atmosphere conditions (i.e., there was little to no wind or wave action). Using both SPEC-mounted sensors as well as two SPEC-deployed profilers, the hydrographic and turbulent characteristics of the bore were quantified. Presented here is a detailed description of the design and instrumentation of the SPEC as well as a sub-set of the December 17th data collected during the field campaign, which highlights the experimental capabilities of this platform.