Baroclinic Coupling Improves Depth‐Integrated Modeling of Coastal Sea Level Variations Around Puerto Rico and the U.S. Virgin Islands

Abstract

This study applies a baroclinic‐coupled depth‐integrated modeling system to the North Atlantic Ocean, where an unstructured mesh is used to focus resolution down to ∼30 m along the coasts of Puerto Rico and the U.S. Virgin Islands. Ocean baroclinicity is incorporated through one‐way coupling from operational data‐assimilated Global Ocean Forecasting System 3.1 temperature and salinity fields at just 12% additional computational time. The main objectives are to provide a comprehensive analysis of observed and modeled coastal sea levels (spanning from seasonal to supertidal variations) in Puerto Rico and the U.S. Virgin Islands during 2017 and to evaluate the associated model performance with and without baroclinic coupling at 14 National Oceanic and Atmospheric Administration/National Ocean Service tide gauges deployed in the region. It is found that baroclinic coupling increases modeled energy across the entire frequency spectrum, which is more commensurate with observations. In particular, density‐driven effects such as the seasonal cycle and sea level setdown due to trailing cold wakes from passing hurricanes are largely reproduced. Supertidal shelf‐resonant seiching at one to two cycles per hour is observed and modeled at a number of locations, where excitation of these modes is often promoted by the baroclinic coupling. Baroclinicity improves the yearlong model skill at every tide gauge, where the mean total skill is increased from 87% to 93% accuracy (54% to 85% for the nontidal residual). In September 2017 during Hurricanes Irma and Maria, baroclinicity increases model skill at 10 out of 14 tide gauges even when the barotropic mode is adjusted to have no mean offset from the observations.

U.S. IOOS Coastal and Ocean Modeling Testbed: Hurricane‐Induced Winds, Waves, and Surge for Deep Ocean, Reef‐Fringed Islands in the Caribbean

“…Observations at the CARICOOS San Juan buoy documented these dynamics, with ocean temperature dropping almost 5°, and an increase in salinity from 35.5 to 37.3 psu (Chardon‐Maldonado et al, ). Since Hurricane Irma passed to the north of the Puerto Rican shelf over deep water, setdown in the water level was not observed in the study region for this storm (Pringle et al, ).…”

“…Thus, depending on the storm track SLOSH‐FW may erroneously compute wind‐driven surge in the open ocean adjacent to narrow‐shelved island environments. Note that the post storm drawdown in the water level data can be attributed to vertical mixing and cold water upwelling due to the passage of Hurricane Maria over the Puerto Rican shelf, which was reproduced when incorporating baroclinicity into ADCIRC (Pringle et al, ). Observations at the CARICOOS San Juan buoy documented these dynamics, with ocean temperature dropping almost 5°, and an increase in salinity from 35.5 to 37.3 psu (Chardon‐Maldonado et al, ).…”

“…Second, heavy rainfall causing flooding was critical in Hurricane Maria (Pasch et al, ), thus coupling coastal models to hydrological models (e.g., Silva‐Araya et al, ) and identifying areas susceptible to rain‐induced flooding, coastal flooding, or a combination of both (Bilskie & Hagen, ), is an important step going forward. Last, the density structure of the ocean accounts for a reasonably large proportion of sea level variability in the Caribbean, and incorporating baroclinicity through coupling to data‐assimilated global ocean models (e.g., GOFS 3.1; Metzger et al, ) has been shown to improve depth‐integrated model skill in comparison to coastal sea level observations around PR and USVI (Pringle et al, ).…”

“…In these sections coastal water levels simulated by ADCIRC are compared to observations at NOAA/NOS tide gauges and USGS rapid deployments (Figure and Table ). A mean sea level offset accounting for the effects of baroclinicity not represented in the calculation (Pringle et al, ) is used to postprocess modeled water levels for comparison to observations. This is calculated independently at each tide gauge based on the water level using the time period in between Hurricanes Irma and Maria and ranged between 0.10 and 0.14 m at an average of 0.11 m. Also, wave conditions simulated by SWAN are compared with observations made at the CARICOOS wave buoys.…”

Impacts of Tropical Cyclones on the Caribbean Under Future Climate Conditions

“…Pringle et al. (2019) developed a depth‐integrated model, which accounts for the effects of the oceanographic processes on the free surface and depth‐integrated currents. This was achieved by means of one‐way coupling ADvanced CIRCulation + Simulating WAves Near Shore (ADCIRC + SWAN; Dietrich et al.…”