Comparison of Ocean Model and HF Radar Surface Currents

The Mississippi Sound (MS Sound) is an elongated, shallow lagoon-type or bar-built estuary with its major axis parallel to the Gulf of Mexico that extends east-west along the southern coasts of Mississippi and Alabama, from Lighthouse Point, Mississippi to the Dauphin Island and on its southern side the MS Sound is partly separated from the Gulf of Mexico by the Mississippi-Alabama barrier islands [1]. Knowing the pattern and variability of the surface currents in the MS Sound is significant as they affect hypoxia development, oil spill contamination, storm surge-induced flooding of the coastal areas, advection of freshwater plumes and the variability of salinity, which impacts habitat suitability of organisms such as the eastern oyster. Hence, it is important to aim for understanding the MS Sound circulation, and how it affects the ecology of the estuary. This study addresses one objective towards that goal by conducting a validation study of a regional model by comparing its output to surface currents measured by High Frequency Radar (HFR) systems. Coastal-based HFR stations measure the surface currents that move towards or away from the station, in different azimuthal and radial distance bins. These movements are termed radial currents. HFR networks combine the overlapping radial currents from two or more stations to estimate total horizontal surface currents [2]. In this study, a comparison has been made between the radial currents from HFR stations and those computed from the output of the Coupled Ocean Atmosphere Wave Sediment Transport (COAWST) modeling system [3]. For this study, the comparability of HFR derived radial surface currents from two HFR sites have been analyzed against model data from an application of COAWST to Mississippi Sound for a time period in 2019 [4]. The two 25 MHz CODAR Ocean Sensor HFR systems, located in the western MS Sound, measure radial surface currents and provide an hourly average. The model provides hourly output at 400-m horizontal resolution. Similarities and differences between model and in-situ data have been identified in the context of wind and tidal forcing in the MS Sound during that time period. This study will help validate the model surface currents in accordance with the observed high frequency radar currents, it will lead to insights into the causes of periods of lower model fidelity, and ultimately support improvements of the model. Further study can also be done comparing the radial currents from high frequency radar station with the output of other regional ocean models.