NOAA Stations Research Articles

Total water level prediction at continental scale: Coastal ocean

We demonstrate recent progress made in the simulation of total water level (TWL) at continental scale, using the coastal ocean of US East Coast/Gulf of Mexico coast as an example. A key difference between the continental-scale and small-scale modeling is that the former requires a more accurate vertical datum. Using a geoid-based datum (xGEOID20b), a satellite altimetry product, and a state-of-the-art 3D unstructured-grid model, we significantly improve the accuracy for TWL both near- and off-shore. The average root-mean-square error at all NOAA stations is 14 cm. The non-tidal signals are found to be sensitive to the representation of a large-scale current system near the boundary and extending the domain extent to accommodate this system improves these signals.

An Approach to Approximate Wave Height from Acoustic Tide Gauges

Abstract The demand for nearshore wave observations is increasing due to spatial gaps and the importance of observations for accurate models and better understanding of inundation processes. Here, we show how water level (WL) standard deviation (sigma, σ) measurements at three acoustic NOAA tide gauges that utilize an Aquatrak sensor [Duck, North Carolina, Bob Hall Pier (BHP) in Corpus Christi, Texas, and Lake Worth, Florida] can be used as a proxy for significant wave height (Hm0). Sigma-derived Hm0 is calibrated to best fit nearby wave observations and error is quantified through RMSE, normalized RMSE (NRMSE), bias, and a scatter index. At Duck and Lake Worth, a quadratic fit of sigma to nearby wave observations results in a R2 of 0.97 and 0.83, RMSE of 0.11 and 0.11 m, and NRMSE of 0.09 and 0.22, respectively. A linear fit between BHP sigma and Hm0 is best, resulting in R2 0.62, RMSE of 0.22, and NRMSE of 0.26. Regression fits deviate across NOAA stations and from the classic relationship of Hm0 = 4σ, indicating Hm0 cannot be accurately estimated with this approach at these Aquatrak sites. The dynamic water level (DWL = still WL ± 2σ) is calculated over the historic time series showing climatological and seasonal trends in the stations’ daily maximums. The historical DWL and sigma wave proxy could be calculated for many NOAA tide gauges dating back to 1996. These historical wave observations can be used to fill observational spatial gaps, validate models, and improve understanding of wave climates. Significance Statement There is a large spatial gap in nearshore real-time observational wave data that can provide critical information to researchers and resource managers regarding inundation and erosion, help validate coastal hydrodynamic models, and provide the maritime community with products that help ensure navigational safety. This study utilizes existing infrastructure to help fill the demand for nearshore wave observations by deriving a proxy for wave height at three sites. This work shows spatial variability in the regression fits across the sites, which should be explored at more stations in future work. Multidecadal length time series were also used at the sites to investigate climatological and seasonal trends that provide insight into wave climates and wave driven processes important for coastal flooding.

Modeling wave climates and wave energy attenuation in marsh terrace environments in the northern Gulf of Mexico

Marsh terracing is a coastal restoration technique that has been implemented in Louisiana and Texas for almost 30 years. Marsh terraces are segmented ridges of soil built in inland coastal ponds for the objectives of creating new marsh, disrupting fetch, and dissipating wind-driven wave energy, which causes marsh erosion. Despite widespread implementation, no numerical modeling studies have been conducted to understand the effect of terraces on wave climate in marsh environments. The objectives of this study were to: 1) simulate wave climates in marsh terrace fields using the Simulating WAves Nearshore (SWAN) model and evaluate the agreement between modeled and observed wave conditions and 2) assess the effectiveness of marsh terraces at reducing significant wave height by comparing wave climates in terraced sites with hypothetical unterraced sites. The SWAN model was used to simulate wind-waves at two terrace fields in coastal Louisiana. Model validation was performed using data collected with in situ wave instruments and wind data measured by NOAA stations located 25 km to the east and 62 km to the northeast of the study area. Results from this study modeled and measured small (0.03–0.14 m) and high–frequency waves (0.80–1.29 s) in the marsh terrace fields. Model validation revealed agreement between modeled and observed data, particularly for significant wave height and direction. Additionally, a comparison of wave climates in terraced and unterraced marsh environments indicated an average significant wave height reduction of 45% (min:18%, max: 84%) when terraces were present. Overall, the model was able to evaluate wave climates in marsh terrace fields and assess the effectiveness of this restoration technique in reducing significant wave height. The model's performance in this low energy and complex environment (shallow water, nonlinear shoreline, marsh fragmentated) is encouraging given the lack of research assessing wave parameters in marsh terrace environments.

Response of the invasive Alliaria petiolata to extreme temperatures and drought

AbstractAlliaria petiolata, a strict biennial in North America, can have an annual alternating high abundance of rosettes and flowering plants. We monitored changes in abundance of rosettes and flowering plants in permanent plots (2004–2014). Three times during our study, the alternating yearly cycle was not observed (2007–2008, 2008–2009, and 2013–2014). We concluded stochastic extreme climate events (ECEs), deviating from long‐term climatic data norms (10th or 90th percentile), likely caused negative organism responses. Long‐term data from a local NOAA station located 25 km from our study site included monthly data (1) total precipitation, (2) number of days with >0.13 cm precipitation, and (3) mean and minimum temperatures. September 2007 met the criteria for ECEs for all monthly variables. We first observed A. petiolata on our study site in 1988, and by the early 1990s, it was abundant. To determine whether September 2007 significantly differed from other September (1984–2014), we used six variables related to drought: (1) total precipitation, (2) number of days with precipitation, (3) number of contiguous days without precipitation, (4) mean monthly temperature, (5) mean maximum daily temperature, and (6) the number of days with temperatures >30°C. The first two variables likely increase plant stress as they decrease, whereas stress declines as the remaining variables decrease. We used the six variables to generate a principal component analysis (PCA) biplot. Axes 1 and 2 accounted for 74.3% of the variance. Record‐breaking minimum temperatures (ECEs) for January (2009) and February–March (2014) likely reduced rosette abundance and disrupted reestablishment of alternating high abundance of rosettes and flowering plants. Our data suggest that a single ECE variable, minimum temperature, and multiple ECE variables related to drought likely had negative effects on A. petiolata.

Net community production and calcification from 7 years of NOAA Station Papa Mooring measurements

AbstractSeven years of near‐continuous observations from the Ocean Station Papa (OSP) surface mooring were used to evaluate drivers of marine carbon cycling in the eastern subarctic Pacific. Processes contributing to mixed layer carbon inventory changes throughout each deployment year were quantitatively assessed using a time‐dependent mass balance approach in which total alkalinity and dissolved inorganic carbon were used as tracers. By using two mixed layer carbon tracers, it was possible to isolate the influences of net community production (NCP) and calcification. Our results indicate that the annual NCP at OSP is 2 ± 1 mol C m−2 yr−1 and the annual calcification is 0.3 ± 0.3 mol C m−2 yr−1. Piecing together evidence for potentially significant dissolved organic carbon cycling in this region, we estimate a particulate inorganic carbon to particulate organic carbon ratio between 0.15 and 0.25. This is at least double the global average, adding to the growing evidence that calcifying organisms play an important role in carbon export at this location. These results, coupled with significant seasonality in the NCP, suggest that carbon cycling near OSP may be more complex than previously thought and highlight the importance of continuous observations for robust assessments of biogeochemical cycling.

Integer ambiguity validation in high accuracy GNSS positioning

Carrier phase observations are required for high-accuracy positioning with Global Navigation Satellite Systems. This requires that the correct number of whole carrier cycles in each observation (integer ambiguity) is determined. The existing methods have been shown to perform differently depending on the observables. Subsequently, the ratio test used for ambiguity validation was developed further including combining it with the integer aperture concept. The key challenges in using the ratio test are the existence of biases in float solutions and stochastic dependence between the two elements of the ratio. The current methods either make assumptions of independence and nonexistence of biases or use simulations together with the bias-free assumption. We propose a new method taking into account both challenges which result in an unknown distribution of the ratio test statistic. A doubly non-central F distribution (DNCF) is proposed for the determination of threshold. The cumulative distribution function (CDF) of DNCF over-bounds the CDF of ratio test statistic distribution in case there is a bias in the float solution and a correlation between the two elements of the ratio. The Precise Point Positioning (PPP) method with products from CNES and measurement data from 10 NOAA stations are used to verify the proposed method. The test results show that the proposed method improves the performance of ambiguity resolution achieving a lower rate of wrong fixing than current state of the art.

N2O as a tracer of mixing stratospheric and tropospheric air based on CARIBIC data with applications for CO2

Stratosphere–troposphere exchange (STE) affects distributions of trace gases, with ozone (O3) and CO being commonly used to study mixing process in the UTLS (Upper Troposphere and Lower Stratosphere) region. Here we explore the application of N2O as a tracer of stratosphere to troposphere flux for CO2 and its isotopes, using N2O and CO2 mixing ratios including a set of CO2 isotope data for CARIBIC aircraft samples and NOAA-Carbon Cycle flask samples. A frequency distribution of CARIBIC N2O data (mostly UTLS at mid- and high-latitudes) reveals a narrow distribution around a tropospheric maximum at nearly the same N2O mixing ratio as the distribution peak for the station Mauna Loa (MLO) however with a skewing due to STE. We demonstrate that upper-tropospheric and STE-affected air can be distinguished using a threshold value based on the N2O distribution width at MLO. A comparison with the use of O3 is given. N2O is discussed to be a robust and linear (season and latitude independent) tracer of STE mixing proportions. We propose that CARIBIC data coupled with CO2 isotopic data published for the stratosphere and data of NOAA stations can be used as a frame of reference for δ18O(CO2) and Δ17O(CO2) STE fluxes. The Δ17O(CO2) flux is of particular interest as it is thought to constrain estimates of biosphere productivity, atmospheric oxygen cycle and global gross CO2 fluxes. CARBIC data can also help tracing STE flux by deep stratospheric intrusions and a data analysis is given for the Walliguan (WLG) observatory on the Tibetan Plateau.

Analysis of <sup>13</sup>C and <sup>18</sup>O isotope data of CO<sub>2</sub> in CARIBIC aircraft samples as tracers of upper troposphere/lower stratosphere mixing and the global carbon cycle

Abstract. The project CARIBIC (http://caribic-atmospheric.com) aims to study atmospheric chemistry and transport by regularly measuring many compounds in the free troposphere and the upper troposphere/lowermost stratosphere (UT/LMS) by using passenger aircraft. Here we present CO2 concentrations and isotope results, and analyze the data together with supporting trace gas data. 509 CARIBIC-2 samples (highest precision and accuracy δ13C(CO2) and δ18O(CO2) data) from June 2007 until March 2009, together with CARIBIC-1 samples (flights between November 1999 and April 2002, 350 samples in total, 270 for NH, mostly δ13C(CO2) data) give a fairly extensive, unique data set for the NH free troposphere and the UT/LMS region. Total uncertainty of the data is the same as reported for the global monitoring program by NOAA-ESRL. To compare data from different years a de-trending is applied. In the UT/LMS region δ13C(CO2), δ18O(CO2) and CO2 are found to correlate well with stratospheric tracers, in particular N2O; δ18O(CO2) appears to be a useful, hitherto unused, tracer of atmospheric transport in the UT/LMS region and also inter-hemispheric mixing. By filtering out the LMS data (based on N2O distributions), the isotope variations for the free and upper troposphere are obtained. These variations have only small latitudinal gradients, if any, and are in good agreement with the data of selected NOAA stations in NH tropics. Correlations between δ13C(CO2) and CO2 are observed both within single flight(s) covering long distances and during certain seasons. The overall variability in de-trended δ13C(CO2) and CO2 for CARIBIC-1 and CARIBIC-2 are similar and are generally in agreement, which underscores agreement between high and low resolution sampling. Based on all correlations, we infer that the CO2 distribution in the NH troposphere along CARIBIC flight routes is chiefly regulated by uplift and pole-wards transport of tropical air up to approximately 50° N. The main reason for variability of signals in the troposphere (which is larger for the higher resolution sampling during CARIBIC-2) is mixing of different tropospheric air masses affected by different CO2 sources and sinks. The effect of stratospheric flux appears to be limited. All in all it is demonstrated that CARIBIC produced new important and reliable data sets for little explored regions of the atmosphere. A logical next step will be global scale modeling of 13C and especially 18O, which is linked to the hydrological cycle.

Decadal changes in atmospheric CO 2 concentration and δ 13C over two seas and two oceans: Italy to New Zealand

Continuous measurements of the CO 2 concentration were repeatedly carried out from 1996 to 2007 between Italy and New Zealand by means of a Siemens Ultramat 5E analyzer assembled for shipboard use. Along the ship routes discrete air samples were collected from 1998 to 2005 using four-litre Pyrex flasks. The δ 13C of the CO 2 from the flask air samples was measured according to well-established techniques. The decadal changes of these two variables can now be evaluated from these results. Large variations of the CO 2 concentration were normally recorded in the Mediterranean and the Red Sea. Completely different trends of the CO 2 concentration were observed in the Red Sea (30° N to about 13° N) between 2007 (a marked southward decrease) and 2005 and 2003 when a marked southward increase is apparent, at least between 23° and 13° N. A further difference among different expeditions is related to the decrease or increase of the CO 2 concentration in the Gulf of Aden. The backward trajectories of the air masses help to explain, at least partially, these differences. In the Indian Ocean and Southern Ocean a decrease of a few ppmv of the CO 2 concentration takes place from Cape Guardafui (Northern Somaliland) to southern New Zealand, particularly during 2005 and 2007. The yearly rate of increase of the CO 2 concentration between 1996 and 2007 for the Indian Ocean is of about 1.9 ppmv yr −1, in excellent agreement with the NOAA/CMDL measurements carried out during the same period at Mahé Isld. (Indian Ocean) and Cape Grim (Tasmania). The δ 13C results obtained from the CO 2 of flask samples collected in the Mediterranean show the effect of anthropogenic emissions, though this is considerably smaller than expected. This inconsistency may be related to the large terrestrial biospheric sink of CO 2 in the Northern Hemisphere. The results obtained from the Red Sea are quite variable through time and space, particularly in its southern section; their interpretation is not easy. The Indian Ocean and the Southern Ocean show rather homogeneous δ 13C results even though a variable carbon isotope shift can be calculated from period/cruise to period/cruise. In the case of the Indian Ocean the mean δ 13C value from the flask air samples collected in 2005 is −8.29‰ and the calculated rate of the carbon isotope shift between 1998 and 2005 is −0.034‰ yr −1, considerably larger than that calculated at the closest NOAA station (Mahé Isld.) of −0.026‰ yr −1. This discrepancy may be, at least partially, caused by the small number of measurements carried out at sea. However, the atmosphere over the Indian Ocean is less affected by anthropogenic emissions than in other areas.

Long-term and recent changes in southern Lake Michigan water quality with implications for present trophic status

Southern Lake Michigan has changed in response to alterations in nutrients and invasive species. NOAA and EPA monitoring results are used to examine those changes. NOAA provides detailed seasonal resolution, but limited spatial coverage, whereas the EPA provides more spatial coverage, but limited seasonal resolution. We compare changes in total phosphorus (TP), silica, nitrate plus nitrite, and chlorophyll concentrations from before and after the invasion by the quagga mussel ( Dreissena rostriformis bugensis). Although TP at NOAA stations was consistently higher than at EPA stations, both confirm declines in spring and summer surface mixed layer (SML) conditions. Chlorophyll differed at EPA and NOAA stations before quagga mussel invasion, but not after the invasion. Spring chlorophyll decreased at NOAA stations after the invasion, but summer conditions did not change at either set of stations. Pre-invasion silica at NOAA stations was slightly higher than at EPA stations, and the lake's Si reservoir increased over the study period. Basin-scale spring Si increased gradually, whereas summer SML Si increased dramatically after 2003, likely reflecting reduced diatom production. Basin-scale nitrate increased significantly from pre- to post-invasion in both spring and summer. Summer nitrate utilization declined drastically in recent years, likely reflecting reduced phytoplankton production. TP loads decreased; however, the timing of changes in chlorophyll and Si and nitrate utilization suggest the recent increase in dreissenid filtering dramatically reduced spring phytoplankton abundance and production across the entire southern basin. The offshore pelagic zone of the historically mesotrophic southern Lake Michigan is now similar to oligotrophic Lake Superior.

Integrated Hydrodynamic Modeling and Frequency Analysis for Predicting 1% Storm Surge

Abstract This paper presents a method of integrating hydrodynamic modeling with frequency analysis to predict a 100-year storm surge in the coastal waters of Pensacola Bay, Florida. The ADCIRC hydrodynamic model was applied to Pensacola Bay, and was calibrated by using observations of water levels from the storm surge of Hurricane Ivan in 2004. The calibrated hydrodynamic model was used to predict extreme flood areas in Pensacola Bay, and was based on the frequency analysis of annual maximum water levels at the NOAA station in the Bay. The water levels of a 100-year return period at the NOAA station were obtained from frequency analysis, and further used to derive a synthetic storm-surge hydrograph at the ocean boundary. Under the gravity forcing as specified in 100-year boundary storm surge hydrograph, hydrodynamic modeling was conducted to predict spatial distributions of maximum water levels in the bay. The model prediction of a water level of 3.2 m at the NOAA station matches well with that from the f...

Interannual variability and sensitivity study of the ocean circulation and thermohaline structure in Prince William Sound, Alaska

The interannual variability and sensitivity of ocean circulation and the thermocline structure of Prince William Sound, Alaska were examined using a 3D circulation model. A 4-year (1995–1998) simulation compared well with field observations of circulation and monthly mean sea surface temperature at NOAA Station 46060. Seasonal circulation regimes were characterized by an anticyclonic gyre in the central sound in January–April, and a strong cyclonic gyre in the central sound in September to December, while summer was the transition period of the two circulation regimes. The size, position and strength of the gyres and thermohaline depth in the central sound showed small interannual variability. Freshwater displayed a very strong seasonal cycle in the sound with minimum in April–May and maximum in October with a spatial distribution of more in the northwest sound and less in the other areas. The simulated freshwater thickness in the whole sound showed up to 20% interannual variability related to wind. The numerical oil spill drift experiments also showed a large interannual variability of possible oil spill trajectories. Sensitivity studies showed the relative importance of each model forcing: (1) wind has more impact on the surface circulation and mixed layer depth. Without wind, the surface current became weaker and the thermocline became shallower; (2) tidal current is a major current in the sound and important to surface and bottom mixing. Without tide, the thermocline depth became shallower; (3) the magnitude of the Alaska coastal current (ACC) inflow determined the outflow current through Montague Strait. Doubled ACC inflow could change the cyclonic circulation pattern in October in case of normal or less ACC inflow into a northward jet with a small accompanying anticyclonic gyre and strongly flush the west sound in addition to the central sound. Also, double ACC inflow would increase the mix-layer depth significantly; and (4) the surface T, S restoring is critical to maintain T, S seasonal cycle and surface circulation patterns. Salinity was the most important factor determining the central sound circulation patterns.

Evaporation and Evapotranspiration under Climate Change in New England

Methods to estimate and generate free‐surface evaporation Ep and potential evapotranspiration Et monthly time series are presented. Results are applied to the Quabbin and Wachusett water‐supply reservoirs, which serve the Boston metropolitan area, and the Connecticut and Ware River basin watersheds, using historic (1950–80) climate data from several NOAA stations located in New England. The Ep and Et time series are perturbed using climate‐change scenarios of several general circulation models (GCMs) to investigate the sensitivity of both time series to doubled atmospheric CO2; Ep and Et are also perturbed by +2°C and +4°C monthly temperature rises. The sensitivity of Et to a potential climate‐change‐induced vegetation‐canopy resistance is also examined.