@article {RN242,
	title = {The impact of remote sensing observations on cross-shelf transport estimates from 4D-Var analyses of the Mid-Atlantic Bight},
	journal = {Advances in Space Research},
	volume = {68},
	number = {2},
	year = {2021},
	pages = {553-570},
	type = {Journal Article},
	abstract = {This paper explores the impact of the individual components of a coastal ocean observing system on estimates of the circulation derived from a state-of-the-art analysis and forecast system for the Mid-Atlantic Bight and Gulf of Maine. The foundation of these activities is the Regional Ocean Modeling System 4-dimensional variational (4D-Var) data assimilation platform, which is run in support of the Mid-Atlantic Regional Association Coastal Ocean Observing System as part of the U.S. Integrated Ocean Observing System. The specific focus of this study is on the impact of remote sensing observations from both space- and land-based platforms on estimates of cross-shelf transport in the vicinity of the National Science Foundation Ocean Observatories Initiative Pioneer array. Sea surface temperature (SST) and sea surface height (SSH) were found to have, on average, a similar impact on the transport estimates. However, during a typical 3-day 4D-Var assimilation cycle, approximately two orders of magnitude more observations of SST than SSH are used in the model, and closer analysis shows that each altimeter measurement has approximately 50 times more impact on the transport estimates than an individual SST observation. This highlights the value of altimetry data for ocean state estimation, and the significance of expanding the altimeter constellation. The observations that are most impactful of all are in situ measurements of temperature and salinity, which have typically 3{\textendash}4 times more impact than an individual SSH datum. A robust geographical distribution of the observation impacts emerges across a range of transport metrics which results from the combined influence of space-time dynamical interpolation and error covariance information within the 4D-Var system. The observation impact calculations suggest that High Frequency (HF) radar estimates of surface currents have relatively little direct influence on cross-shelf transport estimates. However, quantification of the sensitivity of these same estimates to changes in the observing system indicate that HF radar observations indirectly provide important information. This is understood in the current system by appealing to the idea of borrowing strength from the field of statistics in which some observations (satellite remote sensing in the case considered here) can borrow strength from other, seemingly less important observations.},
	keywords = {4D-Var, Mid Atlantic Bight, Observation impact},
	issn = {0273-1177},
	doi = {10.1016/j.asr.2019.09.012},
	author = {Levin, J. and Arango, H. G. and Laughlin, B. and Wilkin, J. and Moore, A. M.}
}
@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.}
}
