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Analyzing History to Project and Manage the Future.

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Project log

Nickitas Georgas
added a research item
The project had the following objectives: 1) To address the paucity of physical environmental data during Long Island Sound’s (LIS) observed warming trend and accompanying fisheries shift by running a hindcast of the LIS circulation using the New York Harbor Observing and Prediction System (NYHOPS), an operational, comprehensive, high-resolution, three-dimensional, numerical model. 2) To explore and understand climate-forced links between the physical and ecological environment of the Sound by studying the statistical correlations of historic ecological data (mainly fish trawl survey data) to the physical environmental data from the NYHOPS model with a goal to explain the recent ecological regime changes and, 3) To project the impacts of climate change and variability on the Sound’s ecosystem and its living marine resources, by forcing NYHOPS with Intergovernmental Panel for Climate Change (IPCC)-class global climate models.
Justin Schulte
added a research item
Possible mechanisms behind the longevity of intense Long Island Sound (LIS) water temperature events are examined using an event-based approach. By decomposing a LIS surface water temperature time series into negative and positive events, it is revealed that the most intense LIS water temperature 10 event in the 1979-2013 period occurred around 2012, coinciding with the 2012 ocean heat wave across the mid-Atlantic Bight. The LIS events are related to a ridge-trough dipole pattern whose strength and evolution can be measured using a dipole index. The dipole index was shown to be strongly correlated with LIS water temperature anomalies, explaining close to 64% of cool-season LIS water temperature variability. Consistently, a major dipole pattern event coincided with the intense 2012 LIS warm event. 15 A composite analysis revealed that long-lived intense LIS water temperature events are associated with tropical sea surface temperature (SST) patterns. The onset and mature phases of LIS cold events were shown to coincide with central Pacific El Niño events, whereas the termination of LIS cold events was shown to possibly coincide with canonical El Niño events or El Niño events that are a mixture of eastern and central Pacific El Niño flavors. The mature phase of LIS warm events was shown to be associated 20 with negative SST anomalies across the central equatorial Pacific, though the results were not found to be robust. The dipole pattern was also shown to be related to tropical SST patterns and fluctuations in central Pacific SST anomalies were shown to evolve coherently with the dipole pattern and the strongly related East Pacific/North Pacific pattern on decadal time scales. The results from this study have important implications for seasonal and decadal prediction of the LIS thermal system. 25 Ocean Sci. Discuss., https://doi.
Justin Schulte
added a research item
Climate indicators related to Long Island Sound (LIS) water and air temperature variability were investigated. The Pacific decadal oscillation (PDO) and east Pacific/North Pacific (EP/NP) patterns are found to be strongly correlated with LIS air temperature anomalies during most seasons, especially during the winter. Additionally, the winter EP/NP index is strongly correlated with subsequent spring and summer LIS water temperature anomalies, potentially rendering the EP/NP index useful in extended LIS water temperature outlooks. Such lagged relationships are found to be related largely to the decorrelation time scale of seasonal water temperature anomalies. The atmospheric circulation pattern associated with anomalous LIS water temperature conditions is consistent with atmospheric Rossby wave trains emanating from the western equatorial Pacific. The EP/NP index has a characteristic time scale of approximately 5 to 10 years and such fluctuations are termed the quasi-decadal mode, the mode identified as varying coherently with LIS air and water temperature anomalies. Apparent PDO and EP/NP regime shifts in 1997 are found to coincide with a LIS water temperature regime shift. This result suggests that not all LIS warming experienced during recent decades is solely due to anthropogenic causes but rather is to some extent a result of natural variability. The results from this study provide a useful framework for both seasonal and decadal prediction of LIS water temperature variability.
Nickitas Georgas
added a research item
The eastern North American sea level pressure dipole (ENA) pattern is a recently identified teleconnection pattern that has been shown to influence mid-Atlantic United States (U.S.) streamflow variability. Because the pattern was only recently identified, its impacts on U.S. precipitation and estuaries on daily to seasonal timescales is unknown. Thus, this paper presents the first seasonal investigation of ENA relationships with global atmospheric fields, U.S. precipitation, and mid-Atlantic estuarine salinity. We show that the ENA pattern explains up to 25–36% of precipitation variability across Texas and the western U.S. We also show that, for the Northeast U.S., the ENA pattern explains up to 65% of precipitation variability, contrasting with previous work showing how well-known climate indices can only explain a modest amount of precipitation variability. The strongest ENA-precipitation relationships are in the spring and fall. The relationships between the ENA pattern and precipitation across remote regions reflect the upper-atmospheric Rossby wave pattern associated with the ENA pattern that varies seasonally. The El-Nino/Southern Oscillation (ENSO) is related to the spring ENA pattern, indicating that extended outlooks of the ENA pattern may be possible. We also show that the ENA index is strongly correlated with salinity and vertical haline stratification across coastal portions of the mid-Atlantic Bight so that hypoxia forecasts based on the ENA index may be possible. Statistical connections between vertical salinity gradient and ENSO were identified at lags of up two years, further highlighting the potential for extended hypoxia outlooks. The strong connection between anomalies for precipitation and mid-Atlantic Bight salinity suggests that the ENA pattern may be useful at an interdisciplinary level for better understanding historical regional climate variability and future impacts of climate change on regional precipitation and the health of estuaries.
Nickitas Georgas
added a research item
  The Generalized Watershed Loading Functions (GWLF) model and its ArcView interface (AVGWLF) were used to estimate and examine the components of the total nitrogen (TN) nonpoint source (NPS) load generated within New York and Connecticut (CT) watersheds surrounding Long Island Sound (LIS, the Sound). The majority of data used as model inputs were generally available from online sources, and the work involved an overall calibration to streamflow and TN data in accordance with generic guidelines recommended in the GWLF manual. The GWLF model performance for three calibration and two validation watersheds in CT was compared with results of a detailed model, Hydrological Simulation Program in Fortran, developed in a previous study. The results of the application illustrate the usefulness of the relatively simpler, less parameter-intensive GWLF model in performing exploratory loading analysis in preparation for adaptive nutrient management in the LIS watersheds. The presented methodology is valuable for identification of priority watersheds for NPS pollution reduction and also for planning-level evaluation of best management practices to achieve the desired reductions. It is estimated that ground-water base flow may be the largest pathway for NPS TN to the Sound, contributing about 54% of the total NPS TN load, a finding with significant implications for LIS total maximum daily load reduction scenarios. In addition to ground water, septic systems are estimated to contribute about 17% of the total load, with the remaining TN load being mostly runoff from urban (17%), agricultural (5%), and low impact (e.g., forest) areas (6%).
Nickitas Georgas
added 3 research items
This article presents the results and validation of a comprehensive, multi-decadal, hindcast simulation performed using the New York Harbor Observing and Prediction System´s (NYHOPS) three-dimensional hydrodynamic model. Meteorological forcing was based on three-hourly gridded data from the North American Regional Reanalysis of the US National Centers for Environmental Prediction. Distributed hydrologic forcing was based on daily United States Geologic Survey records. Offshore boundary conditions for NYHOPS at the Mid-Atlantic Bight shelf break included hourly subtidal water levels from a larger-scale model ran for the same period, tides, and temperature and salinity profiles based on the Simple Ocean Data Assimilation datasets. The NYHOPS model's application to hindcast total water level and 3D water temperature and salinity conditions in its region over three decades was validated against observations from multiple agencies. Average indices of agreement were: 0.93 for storm surge (9 cm RMSE, 90% of errors less than 15 cm), 0.99 for water temperature (1.1 • C RMSE, 99% of errors less than 3 • C), and 0.86 for salinity (1.8 psu RMSE, 96% of errors less than 3.5 psu). The model's skill in simulating bottom water temperature, validated against historic data from the Long Island Sound bottom trawl survey, did not drift over the years, a significant and encouraging finding for multi-decadal model applications used to identify climatic trends, such as the warming presented here. However, the validation reveals residual biases in some areas such as small tributaries that receive urban discharges from the NYC drainage network. With regard to the validation of storm surge at coastal stations, both the considerable strengths and remaining limitations of the use of North American Regional Reanalysis (NARR) to force such a model application are discussed.