Complex Empirical Orthogonal Function Research Articles

Extraction of persistent lagrangian coherent structures for the pollutant transport prediction in the Bay of Bengal

Lagrangian Coherent Structures (LCS) are the hidden fluid flow skeletons that provide meaningful information about the Lagrangian circulation. In this study, we computed the monthly climatological LCSs (cLCS) maps utilizing 24 years (1994–2017) of HYbrid Coordinate Ocean Model (HYCOM) currents and ECMWF re-analysis winds in the Bay of Bengal (BoB). The seasonal reversal of winds and associated reversal of currents makes the BoB dynamic. Therefore, we primarily aim to reveal the cLCSs associated with seasonal monsoon currents and mesoscale (eddies) processes over BoB. The simulated cLCS were augmented with the complex empirical orthogonal functions to confirm the dominant lagrangian transport pattern features better. The constructed cLCS patterns show a seasonal accumulation zone and the transport pattern of freshwater plumes along the coastal region of the BoB. We further validated with the satellite imagery of real-time oil spill dispersion and modelled oil spill trajectories that match well with the LCS patterns. In addition, the application of cLCSs to study the transport of hypothetical oil spills occurring at one of the active oil exploration sites (Krishna-Godavari basin) was described. Thus, demonstrated the accumulation zones in the BoB and confirmed that the persistent monthly cLCS maps are reasonably performing well for the trajectory prediction of pollutants such as oil spills. These maps will help to initiate mitigation measures in case of any occurrence of oil spills in the future.

Spatiotemporal Variations in Upper‐Ocean Salinity Over the North Pacific in 2004–2021

AbstractInterannual variations in upper ocean salinity in the North Pacific Ocean (NP) were examined comprehensively over a period of 18 years (2004–2021) with gridded data sets considering vertical profiles of salinity. The salinity in nearly half of the basin varied in phase with a slight lag, and the rest of the basin exhibited the opposite phase on a decadal scale. The average salinity above 400 dbar prominently increased in the eastern and western mid‐latitude regions from approximately 2010 to the latter half of the 2010s, and decreased in the central subarctic and subtropics during the same period. This spatial pattern was similar to that of temperature change. While the freshening in the subtropics was remarkably above 100 dbar, salinity changes in the subarctic were large even in the subsurface. The first mode of the complex empirical orthogonal function analysis indicated the eastward (westward) propagation of salinity anomalies in the subarctic (subtropics), that is, a clockwise shift. Salinity budget analysis revealed that the changes in the 2010s were mainly caused by geostrophic advection in zonal regions around 40°N and 20°N, and the eastern NP. Precipitation also contributed to freshening in the subtropics, but not in the central subarctic. The meridional migration of salinity fronts in the subarctic and subtropics induced by wind stress, which is meridional contraction of the subtropical gyre, contributed to freshening in the central NP. It is unclear whether salinification in the eastern and western regions inevitably synchronizes and should be further examined.

Predicting Surface Oscillations in Lake Superior from Normal Mode Dynamics

Abstract Satellite observation of sea surface height (SSH) may soon have sufficient accuracy and resolution to map geostrophic currents in Lake Superior. A dynamic atmosphere correction will be needed to remove SSH variance due to basinwide seiching. Here, the dynamics of rotating barotropic gravity modes are examined using numerical models and lake-level gauges. Gravity modes explain 94% of SSH variance in a general circulation model and evolve as forced, damped oscillators. These modes have significant SSH, but negligible kinetic energy (2 J m−2) and dissipation rates (0.01 mW m−2) relative to other motions in Lake Superior. Removing gravity modes from instantaneous SSH allows geostrophic currents to be accurately computed. Complex empirical orthogonal functions (CEOFs) from 50 years of data at eight lake-level gauges show patterns consistent with the first two gravity modes. The frequency spectra of these CEOFs are consistent with forced, damped oscillators with natural frequencies of 3.05 and 4.91 cycles per day (cpd) and decay time scales of 4.5 and 1.0 days. Modal amplitudes from the general circulation model and lake-level gauges are 80% coherent at 1 cpd, but only 50% coherent at 3 cpd, indicating that the atmospheric reanalysis used to force the general circulation model is not accurate at the high natural frequencies of the gravity modes. The results indicate that a dynamic atmosphere correction should combine modeled gravity modes below 1 cpd and observed mode-1 and mode-2 amplitudes (from lake-level gauges) at higher frequencies. An inverted barometer correction is also recommended to account for low-frequency atmospheric pressure gradients that do not project onto gravity modes.

Similarities and Differences in the Earth’s Water Variations Signal Provided by Grace and AMSR-E Observations Using Maximum Covariance Analysis at Various Land Cover Data Backgrounds

ABSTRACT The study presents a compatibility analysis of gravimetric observations with passive microwave observations. Monitoring the variability of soil water content is one of the essential issues in climate-related research. Total water storage changes (ΔTWS) observed by Gravity Recovery and Climate Experiment (GRACE), enables the creation of many applications in hydrological monitoring. Soil moisture (SM) is a critical variable in hydrological studies. Advanced Microwave Scanning Radiometer (AMSR-E) satellite products provided unique observations on this variable in near-daily time resolutions. The study used maximum covariance analysis (MCA) to extract principal components for ΔTWS and SM signals. The analysis was carried out for the global area, dividing the discussion into individual continents. The amplitudes of gravimetric and microwave signals were computed via the complex empirical orthogonal function (EOF) and the complex conjugate EOF* to determine the regions for detailed comparison. Similarities and differences in signal convergence results were compared with land cover data describing soil conditions, vegetation cover, urbanization status, and cultivated land. Convergence was determined using Pearson correlation coefficients and cross-correlation. In order to compare ΔTWS and SM in individual seasons, ΔTWS observations were normalized. Results show that naturally forested areas and large open spaces used for agriculture support the compatibility between GRACE and AMSRE observations and are characterized by a good Pearson correlation coefficient >0.8. Subpolar regions with permafrost present constraints for AMSR-E observations and have little convergence with GRACE observations.

Diurnal Variability of Ocean Temperature Off Pt. Sal, Central California

AbstractDiurnal‐band temperature (DU‐T) variability is investigated over 30 days from measures of temperature over the vertical obtained by 78 moorings deployed in the Santa Monica Basin near Pt. Sal (PS), California. DU‐T variability accounts for 3.6%–23% of the total variability. Vertical empirical orthogonal function mode‐1 DU‐T variability accounts for an average of 86% of the total vertical DU‐T variability at each mooring, is greatest north of PS where its vertical structure is baroclinic, and weakest south of PS where its vertical structure is surface intensified. Spatial complex empirical orthogonal function mode‐1 DU‐T accounts for 73% of the total DU‐T over the region, reveals an onshore baroclinic DU‐T propagation of ∼0.5 m/s, and a previously observed equatorward baroclinic DU‐T propagation of ∼1.9 m/s along the coast north of PS. Dominant vertical mode‐1 diurnal‐band baroclinic velocity (DU‐w) variability at each mooring exhibits a two‐layer structure that is 180° out of phase with maxima near the surface and the bottom, and resembles the DU‐T propagation. DU‐T variability mechanisms include wind‐forced deepening of the surface mixed layer, inertial motions, upwelling, and barotropic and baroclinic tides. Among these concomitant diurnal mechanisms, wind‐driven inertial motions are likely the primary mechanism influencing DU‐T variability during upwelling‐favorable conditions owing to coherence between observed DU‐w and the predicted inertial response to wind‐forcing. Further, spatial mode‐1 DU‐T is correlated and coherent with spatial mode‐1 DU‐w and diurnal wind‐forcing. In addition to describing predominant DU‐T variability patterns, these findings have important implications regarding spatial patterns in biological recruitment, transport, and settlement.

Numerical study of rotating convection with bi-directional temperature gradients

In this work, we report results from three-dimensional numerical simulations of convection in a rotating cylindrical annulus with mean temperature gradients present along the radial and vertical directions. The simulations have been performed in OpenFOAM (Open-source Field Operation And Manipulation). The bi-directional temperature gradient is achieved by imposing uniform heat flux in a thin circular strip at the outer periphery of the bottom surface, and a uniform temperature at the entire inner cylindrical surface. The study has been carried out for a particular Rayleigh number, Ra = 4.76×108, and a range of Taylor numbers, Ta = 6.5×108–2.7×109. The Ra value is chosen so that some qualitative comparison could be done with available experimental data. A laminar flow solver has been used to perform the computations in a rotating frame of reference. Complex empirical orthogonal function analysis has been carried out for the velocity and temperature fields. The contour maps of the radial velocity field in the r−θ plane clearly show the existence of mode 4 and 4 AV (amplitude vacillation) baroclinic waves at low values of Ta, which break down into eddies as Ta increases. The mean temperature field in the r–z plane supports the existence of Convective Columnar Plumes (CCP) on the outer edge, which interacts with the baroclinic waves, aiding in the transport of heat in the system. The fluctuations in CCP disintegrate into smaller-scale structures at the highest Ta. Quantification of turbulent fluxes shows the effectiveness of the heat transport at Ta∼O(108), as compared to Ta∼O(109). Our results clearly demonstrate the role of waves, plumes, and eddies on heat transport in the presence of bi-directional temperature gradients.

Revisiting the zonally asymmetric extratropical circulation of the Southern Hemisphere spring using complex empirical orthogonal functions

Revisiting the zonally asymmetric extratropical circulation of the Southern Hemisphere spring using complex empirical orthogonal functions

Surface circulation in the Gulf of Thailand from remotely sensed observations: seasonal and interannual timescales

Abstract. The Gulf of Thailand (GoT), a shallow semi-enclosed basin located in the western equatorial Pacific, undergoes much wind variabilities on both seasonal and interannual timescales that produce complex surface circulation. The local Ekman pumping modifies sea level in the northern GoT, while remote wind forcing influences sea level variability at the GoT western boundary, potentially through the coastal trapped Kelvin waves. The importance of the Ekman current on ageostrophic current is also important; the stronger influence of the Ekman current is found toward the southern part of the GoT. The GoT circulation reverses its direction seasonally following the monsoon wind reversal which is well-captured by the most dominant complex empirical orthogonal function explaining 28 % of the total circulation variance. During the monsoon transition, a strong meridional current along the western boundary that connects to the flow at the GoT southeastern entrance is observed. This implies high exchange between the GoT and the South China Sea and thus modification of the GoT water. On the interannual timescale, the GoT circulation is directly impacted by both the El Niño–Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD). Interestingly, the two climate modes have different spatial influences on the GoT circulation. The IOD dominates the interannual current along the GoT western boundary and the southern boundary of the observing domain (8∘ N), while the ENSO correlates with that in the interior. The results highlight the complex circulation pattern as being contributed by different dynamics over each region of the GoT.

Seasonal Variability of the Ocean Circulation in Queen Charlotte Strait, British Columbia

ABSTRACT Queen Charlotte Strait (QCST) is a large marine area separating northern Vancouver Island from the British Columbia mainland. Although it is an important waterway connecting Queen Charlotte Sound with Johnstone Strait and eventually the Strait of Georgia, complex dynamics in QCST, including tides, surface winds, river runoffs, and coastal currents, are yet understudied. In this numerical study, a high-resolution (up to approximately 10 m in the horizontal) model was developed for QCST and adjacent areas to investigate the circulation in the strait, using the unstructured grid, Finite-Volume, primitive equation Community Ocean Model (FVCOM). Two operational larger-scale models force the FVCOM model: the Coastal Ice Ocean Prediction System for the West coast (CIOPS-W) at the open ocean (one-way nesting), and the High-Resolution Deterministic Prediction System (HRDPS) at surface boundaries. Prevailing winds over QCST are southeasterly in winter and northwesterly in summer and the model demonstrated the capacity to reproduce the ocean circulation regimes in both seasons of 2019. Complex empirical orthogonal function (CEOF) and correlation analyses determined that surface winds play a dominant role on the variability of residual flow in QCST in the winter, while river runoffs strongly influence the variability during the summer. The analyses highlight that QCST is a complex estuarine system with significant seasonal variability rather than just a simple conduit between Queen Charlotte Sound and the Strait of Georgia.

A hybrid deep learning model for predicting the Kuroshio path south of Japan

At present, many prediction models based on deep learning methods have been widely used in ocean prediction with satisfactory results. However, few deep learning models are used to predict the Kuroshio path south of Japan. In this study, a hybrid deep learning prediction model is constructed based on the long short-term memory (LSTM) neural network, combined with the complex empirical orthogonal function (CEOF) and bivariate empirical mode decomposition (BEMD), called CEOF-BEMD-LSTM. We train the model by using a 50-year (1958-2007) long time series of daily mean positions of the Kuroshio path south of Japan extracted from a regional ocean reanalysis dataset. During the test period of 15 years (2008-2022) by using daily altimetry dataset, our model shows a good performance for the Kuroshio path prediction with the lead time of 120 days, with 0.44° root-mean-square error (RMSE) and 0.75 anomaly correlation coefficient (ACC). This model also has good prediction skill score (SS). Moreover, the CEOF-BEMD-LSTM model successfully hindcasts the formation of the latest Kuroshio large meander since the summer of 2017. Predictions of the Kuroshio path for the coming 120 days (from January1 to April 30, 2023) indicate that the Kuroshio will continue to remain in the state of the large meander. Besides, predictor(s) of the Kuroshio path south of Japan need to be sought and added in future research.

The Impact of Inherited Morphology on Sandbar Migration During Mild Wave Seasons

AbstractSandbars are ubiquitous morphologic features found in the nearshore environment throughout the world, yet predictive capabilities of their evolution remain limited. In order to provide new insights on the relevant processes controlling sandbar morphodynamics, this study uses a 41‐year record of 637 monthly cross‐shore profiles from Duck, North Carolina, USA, to derive complex empirical orthogonal functions representative of the two dominant modes of sandbar migrations: offshore and onshore propagation. Interference of these two modes produces commonly observed sandbar states. While mild wave energies are traditionally assumed to drive onshore sandbar migration, the offshore mode is repeatedly seen to dominate sandbar migration in mild wave seasons following anomalously high late‐winter wave energy and when the inherited morphology is composed of a single bar or terrace, as opposed to a more common two‐bar state. A data‐derived conceptual model is presented synthesizing the effect of antecedent morphology and wave climate chronology on interannual trends in net offshore sandbar migration.

Slow Slip Detectability in Seafloor Pressure Records Offshore Alaska

AbstractIn subduction zones worldwide, seafloor pressure data are used to observe tectonic deformation, particularly from megathrust earthquakes and slow slip events (SSEs). However, such measurements are also sensitive to oceanographic circulation‐generated pressures over a range of frequencies that conflate with tectonic signals of interest. Using seafloor pressure and temperature data from the Alaska Amphibious Community Seismic Experiment, and sea surface height data from satellite altimetry, we evaluate the efficacy of various seasonal and oceanographic pressure signal proxy corrections and conduct synthetic tests to determine their impact on the timing and amplitude prediction of ramp‐like signals typical of SSEs. We find that subtracting out the first mode of the complex empirical orthogonal functions of the pressure records on either the shelf or slope yields signal root‐mean‐square error (RMS) reductions up to 73% or 80%, respectively. Additional correction with proxies that exploit the depth‐dependent spatial coherence of pressure records provides cumulative variance reductions up to 83% and 93%, respectively. Our detectability tests show that the timing and amplitude of synthetic SSE‐like ramps can be well constrained for ramp amplitudes ≥4 cm on the shelf and ≥2 cm on the slope, using a fully automated detector. The principal limits on detectability are residual abrupt changes in pressure that occur as part of the transition to and from summer to winter conditions but are not adequately characterized by our seasonal corrections, as well as the inability to properly account for instrumental drift, which is not readily separated from the seasonal signal.

Understanding Water Level Changes in the Great Lakes by an ICA-Based Merging of Multi-Mission Altimetry Measurements

Accurately monitoring spatio-temporal changes in lake water levels is important for studying the impacts of climate change on freshwater resources, and for predicting natural hazards. In this study, we applied multi-mission radar satellite altimetry data from the Laurentian Great Lakes, North America to optimally reconstruct multi-decadal lake-wide spatio-temporal changes of water level. We used the results to study physical processes such as teleconnections of El Niño and southern oscillation (ENSO) episodes over approximately the past three-and-a-half decades (1985–2018). First, we assessed three reconstruction methods, namely the standard empirical orthogonal function (EOF), complex EOF (CEOF), and complex independent component analysis (CICA), to model the lake-wide changes of water level. The performance of these techniques was evaluated using in-situ gauge data, after correcting the Glacial Isostatic Adjustment (GIA) process using a contemporary GIA forward model. While altimeter-measured water level was much less affected by GIA, the averaged gauge-measured water level was found to have increased up to 14 cm over the three decades. Our results indicate that the CICA-reconstructed 35-year lake level was more accurate than the other two techniques. The correlation coefficients between the CICA reconstruction and the in situ water-level data were 0.96, 0.99, 0.97, 0.97, and 0.95, for Lake Superior, Lake Michigan, Lake Huron, Lake Erie, and Lake Ontario, respectively; ~7% higher than the original altimetry data. The root mean squares of errors (RMSE) were 6.07 cm, 4.89 cm, 9.27 cm, 7.71 cm, and 9.88 cm, respectively, for each of the lakes, and ~44% less than differencing with the original altimetry data. Furthermore, the CICA results indicated that the water-level changes in the Great Lakes were significantly correlated with ENSO, with correlation coefficients of 0.5–0.8. The lake levels were ~25 cm higher (~30 cm lower) than normal during EI Niño (La Niña) events.

Antarctica ice-mass variations on interannual timescale: Coastal Dipole and propagating transports

The target is the non-secular, non-seasonal, interannual ice-mass redistribution over the Antarctica continent, as observed by the satellite mission GRACE (Gravity Recovery and Climate Experiment) for the period from 2002 to 2016. We employ the empirical orthogonal function (EOF) and complex EOF (CEOF) methods on the GRACE monthly time-variable gravity in the form of the mascon data. We find three separate phenomena on different timescales that are hitherto unreported: (i) EOF Mode 1 represents an interannual standing “seesaw” pattern largely concentrates along the coast, which we refer to as the Antarctica Coastal Dipole (ACD), with turnarounds coincident with ENSO events, relative to precipitation anomalies, whereas Mode 2-3 both correlate with the Antarctica Oscillation (AAO); (ii) the leading CEOF Mode shows two different propagating waves, one is the Eastward Propagation (EP) with the periodicity of ∼4.7 years most evident in the East Antarctica, may be induced by the Antarctica Circumpolar Wave; (iii) another is a Westward Propagation (WP) with ∼2 years periodicity in the West Antarctica that mainly travels from the Ronnie Ice Shelf to the Ross Ice Shelf, may relate to AAO.

Analysis of Interannual and Seasonal Nearshore Bar Behaviour Observed from Decadal Optical Satellite Data in the Curonian Spit, Baltic Sea

Long-term observations of nearshore bar behaviour are a vital component of coastal monitoring, management, and prediction. Optical satellite remote sensing enables the possibility of such observations over large spatial areas, but its full potential remains unexploited. This study assessed alongshore variability in cross-shore nearshore bar behaviour on a wave-dominated multi-bar coast of the Curonian Spit (south-eastern Baltic Sea) between 2011 and 2021, using satellite-derived bar data. Nearshore bars were extracted from a time series of PlanetScope and RapidEye satellite images with an automated GIS-based algorithm, previously proposed by the study authors. The cross-shore behaviour of a multiple bar system was analysed by adapting traditional bathymetry-based analysis techniques to satellite-derived data that included bar crestlines and images of multi-scale Relative Bathymetric Position Index (RBPI). The analysis was performed on 1071 shore-perpendicular transects. Multi-bar onshore and offshore migration rates were quantified on interannual and seasonal timescales. The results show that, on an interannual timescale, bars migrated offshore at rates up to 9.7 m/month, while the rates of onshore migration reached up to 11 m/month. During the months of low wave energy, bars moved offshore at rates up to 6.2 m/month, and during the months of high wave energy, up to 12.9 m/month. However onshore migration rates, during the months of low and high wave energy, reached up to 7.0 and 13.4 m/month, respectively. A complex empirical orthogonal function (CEOF) analysis was performed on RBPI-derived cross-shore profiles, and cyclic offshore directed bar behaviour was examined. For the first time, the net offshore migration (NOM) cycle with bar cycle return periods of 1.8 to 13.5 years was investigated on the south-eastern Baltic Sea coast. Bar cycle return periods increased and rates of bar cross-shore migration decreased from north to south along the Curonian Spit. Similar nearshore bar behaviour regions were identified using clustering analysis based on quantified temporal and morphological characteristics of the bars. Factors controlling alongshore variability in bar cross-shore behaviour were determined. The study results suggest that small alongshore variations in nearshore hydrodynamics, caused by the local wave climate and its interplay with the shoreline orientation, determine the morphological and temporal variability of the multi-bar system in the Curonian Spit.

On the Relationship Between Tropical Instability Waves and Intraseasonal Equatorial Kelvin Waves in the Pacific From Satellite Observations (1993–2018)

Intraseasonal Kelvin waves (IKWs) and Tropical Instability Waves (TIWs) are essential components of the tropical Pacific coupled climate variability. While downwelling IKWs are precursors of ENSO (e.g., the El Niño Southern Oscillation), TIWs contribute to its asymmetry by mixing more/less warm off-equatorial and cold tongue waters during La Niña/El Niño. Theoretical studies and a few observational case studies also suggest that TIWs and IKWs can interact non-linearly. However, owing to the chaotic nature of TIWs, observational evidence that such a process occurs consistently has not been established thus far. Here, we document for the first time their interaction from satellite observations over a period spanning almost 30 years (1993–2018). From complex empirical orthogonal functions analysis and sea level decomposition into meridional modes, we evidence that a substantial share (∼42%) of the variance of TIWs-induced intraseasonal sea level anomalies are associated with IKWs activity. We show that non-linear dynamical heating (NDH) in the Eastern equatorial Pacific associated with this intraseasonal mode can be as large as that for interannual time scales. Implications for understanding the eastern tropical Pacific heat budget and ENSO variability are discussed.

Spatial and temporal evolution of drought characteristics across the Yellow River basin

Drought disasters restrict economic and social development. Understanding the evolution of the spatiotemporal characteristics of drought plays a vital role in basin risk response and management. Complex empirical orthogonal function analysis is widely used in meteorological research and is an important tool for studying the spatial-temporal distribution structure of arid fields. This research aims to take the Yellow River Basin (YRB) as an example, separate the temporal and spatial distribution structure of drought based on the CEOF method, and explore the abrupt changes, trends, and periodic characteristics of different temporal and spatial distribution patterns. In addition, the cross-wavelet analysis reveals the lagging correlation relationship between the distribution pattern of the arid field in the basin and the Southern Oscillation factor. Results indicated that: (1) there are three typical spatial and temporal distribution patterns (full basin type, southeast-northwest reversed type and east-west reversed type) of the interannual scale drought in the YRB; (2) interannual drought evolution have obvious spatial propagation characteristics. (3) There are correlations between the three types and the Southern Oscillation on the temporal-frequency scale, and there is a time lag of 1-2a with the Southern Oscillation factor.

Spatiotemporal variability and driving factors of ground-level summertime ozone pollution over eastern China

Ground-level ozone is detrimental to human and vegetation health. The ground-level ozone concentration in China has been increasing in recent years. It is necessary to take actions to mitigate ozone pollution. Identifying the variability of ozone concentration is significant for developing an optimal mitigation strategy. In this study, complex empirical orthogonal functions (CEOFs) are used to analyze the spatial-temporal variability in the summertime surface ozone distribution over eastern China during 2015–2017. The first CEOF explains 50% of the ozone variance and represents anthropogenic sources over the North China, with an O3 exceedance period of 7–9 days (maximum daily 8-h average (MDA8) O3 more than 160 μg m−3). The second CEOF indicates a north-south dipole pattern of ozone fluctuation over eastern China. This pattern is mainly subject to the north-south movement of the subtropical high over eastern China and is ultimately modulated by the Philippine Sea Anticyclone Anomaly (PSAA). Our results suggest that policymakers should take weather patterns and interactions between different regions into consideration when designing a strategy to meet O3 air quality objectives.

Seafloor Geodetic Pressure Measurements to Detect Shallow Slow Slip Events: Methods to Remove Contributions From Ocean Water

AbstractShallow slow slip events (SSEs) provide a mechanism for strain release in the shallow part of subduction zones, with fundamental implications for fault mechanics and tsunami hazards. Despite their importance, SSEs are challenging to monitor. They occur under the ocean far from land‐based GPS stations, and while seafloor pressure sensors can detect SSE vertical seafloor movements, the measured bottom pressure includes “ocean noise” signals from pressure variations within the water column. Seeking to improve techniques to remove ocean noise, a pilot study offshore Oregon collected seafloor pressure and near‐bottom current measurements at four sites from April to November 2017. Three methods were applied to reduce ocean noise: 1) subtract a reference pressure, 2) apply complex empirical orthogonal function analysis to pressure measurements, and 3) combine pressure and current measurements with optimal interpolation (OI). All three methods are established techniques from either geodesy or oceanography. Each method produced residual standard deviation, σ < 1 hPa. No SSE was detected during this study. For illustration purposes synthetic SSEs of 2 cm amplitude and 7‐days duration were added and detected, one at a time at different spots. Because currents are unaffected by a SSE, the combination of currents and pressures with the dynamical constraint of geostrophy in OI reduced the false interpretation of the synthetic SSEs as oceanic. OI produced the most reliable detection. Future seafloor geodesy field projects should consider adding current sensors and using OI methods to reduce ocean noise and to reveal tectonic signals.

Weather-Driven Coastal Dynamics in a Tide-Dominated Area: Cases from Spring 2016 along the West Coast of Korea

Kim, B.-J.; Lee, D.E.; Ro, Y.-J., and Jeong, K.-Y., 2021. Weather-driven coastal dynamics in a tide-dominated area: Cases from Spring 2016 along the west coast of Korea. Journal of Coastal Research, 37(3), 494–505. Coconut Creek (Florida), ISSN 0749-0208.Analyses of current dynamics recorded using multilayer current meters in Spring 2016 (15 April–17 May, 32 d) at two stations near Kkotji Beach in Anmyeon-do, Yellow Sea, Korea, are presented. Harmonic analysis is applied to identify tidal characteristics in the study area. A slightly rotational current pattern is detected at ST01, while oscillations predominantly in north–south orientation are detected at ST02. Nontidal residual currents and the concurrent surface atmosphere data are analyzed together. Residual currents converge (diverge) between ST01 and ST02 following the increase (decrease) in thickness between two stations. Using advanced statistical methods, the spatial patterns of such dynamic events are shown with their association with surface atmosphere. Complex correlation analysis reveals that residual currents are significantly correlated with abrupt surface wind fluctuations associated with extratropical cyclones. The characteristics of residual currents and surface wind vectors are further analyzed, using complex empirical orthogonal functions (CEOF). The first residual current mode (R1) accounts for 46.8% of the total variation, while the second mode (R2) accounts for 24.9%. R1 represents a wind-induced component in the longshore direction, while R2 represents a bottom-driven component in the opposite direction. Both the modes correlate significantly with the first wind mode (W1, longshore wind), which leads the associated residual current modes by a few hours. Spectral analysis indicates that the two significant periods of surface wind and residual current modes are well matched to each other, exhibiting cycles of 1.6 and 4 days.