@article {arango_4d-var_2023,
	title = {4D-Var data assimilation in a nested model of the Mid-Atlantic Bight},
	journal = {Ocean Modelling},
	volume = {184},
	year = {2023},
	pages = {102201},
	abstract = {The Regional Ocean Modeling System (ROMS) 4-dimensional variational (4D-Var) data assimilation platform has been extended to include nested grid configurations using both one-way and two-way nesting strategies. The efficacy of this new ROMS utility is demonstrated in a model comprising three nested grids with horizontal refinement and configured for the Mid-Atlantic Bight. The three nested grids have a horizontal resolution ranging from \~{}7 km to \~{}0.8 km thereby capturing circulation regimes that span the Gulf Stream western boundary current, through the mesoscale eddy field, and down to the rapidly evolving and energetic submesoscale. These circulation regimes represent a challenge for any data assimilation system, and the nested 4D-Var system was found to perform well across the range of resolved space and time scales. The observational data used to constrain the ocean state estimates come from a wide range of remote sensing, in situ, and mobile platforms, along with the U.S. National Science Foundation{\textquoteright}s Ocean Observatories Initiative Pioneer Array. Several aspects of the system performance are explored and described here, including the fit of the model to the observations, the influence of data assimilation on the wave number spectra at the submesoscale, and the downscaling and upscaling of information captured by the observations.},
	keywords = {4D-Var, Data assimilation, Mid-Atlantic Bight, Nested grids, Pioneer Array},
	issn = {1463-5003},
	doi = {10.1016/j.ocemod.2023.102201},
	url = {https://www.sciencedirect.com/science/article/pii/S1463500323000422},
	author = {Arango, Hernan G. and Levin, Julia and Wilkin, John and Moore, Andrew M.}
}
@article {wilkin_data-assimilative_2022,
	title = {A data-assimilative model reanalysis of the U.S. Mid Atlantic Bight and Gulf of Maine: Configuration and comparison to observations and global ocean models},
	journal = {Progress in Oceanography},
	volume = {209},
	year = {2022},
	pages = {102919},
	abstract = {A 15-year reanalysis (2007{\textendash}2021) of circulation in the coastal ocean and adjacent deep sea of the northeast U.S. continental shelf is described. The analysis uses the Regional Ocean Modeling System (ROMS) and four-dimensional variational (4D-Var) data assimilation (DA) of observations from in situ platforms, coastal radars, and satellites. The reanalysis downscales open boundary information from the Copernicus Marine Environmental Monitoring Service (CMEMS) global analysis. The dynamic model is forced by regional meteorological analyses, observed daily river discharges, and harmonic tides that augment the open boundary conditions. A complementary analysis of the mean seasonal cycle of regional circulation, also computed using ROMS 4D-Var but with climatological mean observations and forcing, is used to reduce biases in the CMEMS boundary data and to provide a dynamically and kinematically constrained Mean Dynamic Topography to use in conjunction with the assimilation of satellite altimeter sea level anomaly observations. The configuration of ROMS 4D-Var used is described, presenting details of the comprehensive suite of observations assembled, data pre-processing and quality control procedures, and background and observation error hypotheses. Control variables of the DA are the initial conditions, surface forcing, and boundary conditions of a sequence of non-overlapping 3-day analysis cycles. Comparisons to a non-assimilative version of the same ROMS model configuration show the added skill brought by assimilation of local observations. The improvement that downscaling with assimilation achieves over ocean state estimates from CMEMS and the U.S. Naval Research Laboratory Global Ocean Forecast System (GOFS) is demonstrated by the reduction in residuals of the DA, and by comparison to independent (unassimilated) observations. Wherever data volumes allow, skill assessments are made with the respect to anomalies from the mean seasonal cycle to emphasize performance at the ocean mesoscale. To highlight the utility of the analysis to inform studies related to coastal sea level variability and marine ecosystems, comparisons are made to unassimilated coastal sea level gauges and novel observations from sensors on fishing gear. The assimilation of coastal satellite altimetry data produces coastal sea level results that are coherent with observations across all time scales from interannual to tidal, while bias and correlation metrics show that bottom temperatures in regions of commercial fishing activity in the Mid-Atlantic Bight and the Gulf of Maine are modeled well.},
	keywords = {Bottom temperature, Climatology, Coastal circulation, Data assimilation, Gulf of Maine, Mid Atlantic Bight, Numerical modeling, Sea level},
	issn = {0079-6611},
	doi = {10.1016/j.pocean.2022.102919},
	url = {https://www.sciencedirect.com/science/article/pii/S0079661122001781},
	author = {Wilkin, John and Levin, Julia and Moore, Andrew and Arango, Hernan and L{\'o}pez, Alexander and Hunter, Elias}
}
@article {RN195,
	title = {Observation impacts on the Mid-Atlantic Bight front and cross-shelf transport in 4D-Var ocean state estimates: Part II {\textemdash} The Pioneer Array},
	journal = {Ocean Modelling},
	volume = {157},
	year = {2021},
	pages = {101731},
	type = {Journal Article},
	abstract = {The Regional Ocean Modeling System (ROMS) 4-dimensional variational (4D-Var) data assimilation system was used to compute ocean state estimates of the Mid-Atlantic Bight (MAB). A three-level nested grid configuration was employed with horizontal resolution successively enhanced from 7 km down to 800 m at the innermost nest. This captures the dynamics on space- and time-scales ranging from the Gulf Stream western boundary current down to the rapidly evolving and energetic sub-mesoscale circulation. This is a companion study to Levin et al. (2020) which examined the overall impacts of the entire observing system on shelf-break exchange. This follow-on study specifically focuseson the impact of the in situ elements of the ocean observing system on the 4D-Var analyses. The particular focus here is on the Pioneer Array, a high-density observing system in the MAB designed to measure the multi-scale nature of shelf-break exchange processes. Building on Levin et al. (2020), it is found that the relative impact of observations from different components of the Pioneer Array depends on the scales of motion that are resolved by each nested grid. This is in apparent agreement with the linear theory of geostrophic adjustment despite the O(1) Rossby number. The synergy between the observations from different observing platforms has also been quantified by comparing the observation impacts with the sensitivity of the 4D-Var analyses to changes in the observing array. It is found that while some observations do not have a significant direct impact on the analyses, they nevertheless provide essential information about the presence of circulation features, corroborating that measured by other sensors. Thus, the individual parts of the observing system can borrow strength from each other. Finally, the contribution of each component of the observing system to the expected error in the 4D-Var analyses was also quantified, where the critical role played by the Pioneer Array moorings in resolving the sub-mesoscale circulation is again highlighted.},
	keywords = {Mid-Atlantic Bight, Observation impact, Observation sensitivity, Pioneer Array, ROMS 4D-Var},
	doi = {10.1016/j.ocemod.2020.101731},
	url = {https://app.dimensions.ai/details/publication/pub.1132944594},
	author = {Levin, Julia and Arango, Hernan G. and Laughlin, Bruce and Hunter, Elias and Wilkin, John and Moore, Andrew M.}
}
@article {RN196,
	title = {Observation impacts on the Mid-Atlantic Bight front and cross-shelf transport in 4D-Var ocean state estimates: Part I {\textemdash} Multiplatform analysis},
	journal = {Ocean Modelling},
	volume = {156},
	year = {2020},
	pages = {101721},
	type = {Journal Article},
	abstract = {The Regional Ocean Modeling System (ROMS) 4-dimensional variational (4D-Var) data assimilation system was used to compute ocean state estimates of the Mid-Atlantic Bight (MAB). A three-level nested grid configuration was employed with horizontal resolution successively enhanced from 7 km down to 800 m at the innermost nest. This captures the dynamics on space- and time-scales ranging from the Gulf Stream western boundary current down to the rapidly evolving and energetic sub-mesoscale circulation. This is a companion study to Levin et al. (2020) which examined the overall impacts of the entire observing system on shelf-break exchange. This follow-on study specifically focuseson the impact of the in situ elements of the ocean observing system on the 4D-Var analyses. The particular focus here is on the Pioneer Array, a high-density observing system in the MAB designed to measure the multi-scale nature of shelf-break exchange processes. Building on Levin et al. (2020), it is found that the relative impact of observations from different components of the Pioneer Array depends on the scales of motion that are resolved by each nested grid. This is in apparent agreement with the linear theory of geostrophic adjustment despite the O(1) Rossby number. The synergy between the observations from different observing platforms has also been quantified by comparing the observation impacts with the sensitivity of the 4D-Var analyses to changes in the observing array. It is found that while some observations do not have a significant direct impact on the analyses, they nevertheless provide essential information about the presence of circulation features, corroborating that measured by other sensors. Thus, the individual parts of the observing system can borrow strength from each other. Finally, the contribution of each component of the observing system to the expected error in the 4D-Var analyses was also quantified, where the critical role played by the Pioneer Array moorings in resolving the sub-mesoscale circulation is again highlighted.},
	keywords = {Mid-Atlantic Bight, Observation impact, Observation sensitivity, Pioneer Array, ROMS 4D-Var},
	doi = {10.1016/j.ocemod.2020.101721},
	url = {https://app.dimensions.ai/details/publication/pub.1132245849},
	author = {Levin, Julia and Arango, Hernan G. and Laughlin, Bruce and Hunter, Elias and Wilkin, John and Moore, Andrew M.}
}
@article {RN81,
	title = {Satellite detection of an unusual intrusion of salty slope water into a marginal sea: Using SMAP to monitor Gulf of Maine inflows},
	journal = {Remote Sensing of Environment},
	volume = {217},
	year = {2018},
	pages = {550-561},
	type = {Journal Article},
	abstract = {Satellite salinity from the Soil Moisture Active Passive (SMAP) mission and in situ observations are used to diagnose the source of a significant increase in warm and salty surface water entering the Gulf of Maine (GoM) in the winter of 2017{\textendash}2018. SMAP salinity anomaly data indicate that this event was related to a salty feature that moved along the northwestern Atlantic shelf break from near the Grand Banks southwest towards the GoM over eight months before entering the Gulf in December 2017 to January 2018. Satellite altimetry, sea surface salinity, and sea surface temperature data suggest that, before entering the GoM, the salty feature interacted with Gulf Stream meanders and eddies several times, helping to sustain the water mass. It is likely that feature interactions with a warm Gulf Stream meander took place in the fall of 2017, helping to advect high salinity water onto the shelf and then into the GoM as a surface trapped feature in late fall 2017. According to satellite salinity data, this episode led to significant salinification (about 1 psu) in the northeastern GoM. Interior GoM buoy salinity data agree in showing four months of increased GoM salinity of the upper 50 m starting in November 2017. Buoy T/S analyses characterize this surface inflow as modified warm Atlantic slope water, typically seen only below 100 m and previously unobserved at the surface in the 15-year buoy record. This new salty water circulated cyclonically along the GoM coastline and mixed into the deeper Gulf through February 2018. Its intrusion may have also enhanced the cyclonic winter circulation in the Gulf. GoM surface salinity anomalies ended abruptly in early March 2018 coincident with the occurrence of a bomb cyclone and its associated strong upper ocean mixing.

},
	keywords = {Gulf of Maine, satellite salinity, Sea level, Temperature},
	issn = {0034-4257},
	doi = {10.1016/j.rse.2018.09.004},
	url = {http://www.sciencedirect.com/science/article/pii/S0034425718304152},
	author = {Grodsky, Semyon A. and Vandemark, Douglas and Feng, Hui and Levin, Julia}
}
