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While it is known that sea surface temperature (SST) variability in the subtropical northeastern Pacific (SNEP) can be forced by wintertime atmospheric variability, the region over which atmospheric variability plays the significant driving role remains to be elucidated. Based on observational data during 1900–2014 and a first-order autoregressive model, we show that SNEP SST variability is dominantly forced by wintertime atmospheric variability over the North Pacific, slightly north of the SNEP. Atmospheric variability south of the SNEP, however, does not play the dominant driving role because of atmospheric barotropic response that partially offsets baroclinic Gill response over the ocean surface. Further, by decomposing North Pacific atmospheric variability into tropical Pacific (TP)-forced and non-TP-forced components using a tropical Pacific pacemaker experiment, we find that the leading modes in the two components comparably contribute to forcing SNEP SST in the historical record. Further analyses show that their contribution is unstable on decadal timescales, with stronger forcing effect from TP-forced Aleutian Low (AL) variability before the 1930s and after the 1980s. Such non-stationary forcing effect is primarily attributed to the relative amplitude between TP-forced AL and non-TP-forced atmospheric variability, which would affect the predictability of SNEP SST variability. [ABSTRACT FROM AUTHOR]

The dependence of the large-scale structure of oceanographic fields on short-term variations in atmospheric forcing (AF) at the ocean surface has been studied. Estimates of this dependence were obtained by comparing the results of two numerical experiments with the NEMO model in the ORCA1 configuration used as a computational core in the data assimilation system at the Hydrometeorological Center of Russia. The experiments similar in all other respects differed only in the discreteness of the AF data: 3–24 hours in the main experiment and 1 month in the experiment with time-averaged AF. Large-scale characteristics were compared: kinetic energy averaged over large regions, Atlantic Meridional Overturning Circulation, meridional heat transport, mixed layer depth, and sea ice volume. It has been shown that neglecting high-frequency AF variability can significantly distort the long-term evolution of oceanographic fields reproduced by ocean models and thereby affect the quality of model forecasts. [ABSTRACT FROM AUTHOR]

The bidirectional mass exchange between the Marmara Sea and the Aegean Sea provides one part of the critical hydrodynamic links between the Black Sea and the Mediterranean Sea. In this study, we examined exchange in the Dardanelles based on a 3-D numerical model simulation covering an 11-year period under realistic atmospheric forcing. The model includes the Black Sea, the Marmara Sea, and a part of the Aegean Sea to include the remote effects of basin dynamics. The main features as one-, two-, and three-layered flow structures are successfully reproduced by the model in comparison to earlier observations. It is found that the strait is subject to submaximal exchange by only one control near the Nara Pass. According to long-term modeling results, most variability occurs on synoptic time scales, and wind stress has a dominant role in those variations. The seasonal and interannual variability of exchange flow is relatively low and displays a close relationship with freshwater input to the Black Sea. [ABSTRACT FROM AUTHOR]

The unprecedented North Pacific marine heatwave (known as the Blob) in 2013/14 winter has attracted many research interests, considering its dramatic impacts on the ecosystem and regional climate. Meanwhile, the summertime Blob events have also emerged in recent decades. In this study, we identified four Blob events in the summer of 2014, 2015, 2019, and 2020 during the Satellite Era. Here we show diversity existed in the formation of summer Blob events. The atmospheric forcing responsible for the Blob is the weakened North Pacific subtropical high (NPSH), which contributes significantly to the Blob in 2019 via anomalous shortwave radiation. However, the atmospheric forcing alone cannot fully explain all the Blob events, especially the one in 2020 when the weakened NPSH is absent. Other than the weakened NPSH, the preceding spring sea surface temperature (SST) warm anomalies in the northeast Pacific can persist into the following summer due to anomalous mixed layer heat content and significantly contribute to the Blob. A binary linear regression model considering both the SST persistence and the NPSH is constructed, successfully reproducing the observed Blob variation for the period 1982–2020 (r = 0.76, p < 0.001). The model improves the ability to capture the warm peaks in all four summer Blob events, which either single factor cannot fully depict. [ABSTRACT FROM AUTHOR]

A comparison of simulations of the global ocean circulation with the NEMO/SI3 model with two types of atmospheric forcing (DFS5.2 and CFSR/CDAS), as well as with two grid resolutions (1° and 0.25°) is presented. The objective of such comparison is to substantiate a choice of a source of data on atmospheric forcing and a grid resolution for use in an operational system for the ocean state diagnosing and forecasting. It is shown that all considered simulations reproduce main large-scale ocean characteristics. The CFSR/CDAS merged meteorological dataset, which provides better agreement with actual data, is quite suitable for specifying atmospheric forcing in retrospective and operational applications of the NEMO/SI3 model, including its use as a computational core in the data assimilation system within the framework of the analysis–forecast–analysis sequential assimilation scheme. [ABSTRACT FROM AUTHOR]

Water level measurements at four sub-basins of a highly dissipative coastal lagoon were used to study variability at tidal and subtidal scales and to determine whether atmospheric forcing influenced variations in water level at tidal scales. The amplitude of the main astronomic constituents, which were diurnal, attenuated quickly to <5% by the second sub-basin. The attenuation was represented well by an analytical solution that described a damped wave. The semidiurnal constituent with a period of 12 h (S2), however, decreased to 50% of the lagoon's entrance amplitude and then increased to 60% by the fourth sub-basin. Reproduction of this S2 behavior by the analytical model required unrealistically low signal attenuation, much lower than for the other semidiurnal constituent (12.42 h, M2). This behavior suggested that the S2 amplification was non-gravitational and related to semidiurnal atmospheric forcing, which was dominated by barometric pressure. Such suggestion was confirmed by coherence and wavelet coherence analysis and by the fact that the largest overtide was related to the interaction between S2, instead of M2, and the diurnal constituent. This study documents that a highly dissipative coastal lagoon becomes forced semidiurnally by barometric pressure toward its head. Subtidal water levels were studied with empirical orthogonal functions, revealing 2 modes that explained ~85% of the variance. Mode 1 was related to northerly winds ('Nortes') and mode 2 was linked to the Trade winds that dominate the region. [ABSTRACT FROM AUTHOR]

Meteotsunamis are long waves generated by displacement of a water body due to atmospheric pressure disturbances that have similar spatial and temporal characteristics to landslide tsunamis. NAMI DANCE that solves the nonlinear shallow water equations is a widely used numerical model to simulate tsunami waves generated by seismic origin. Several validation studies showed that it is highly capable of representing the generation, propagation and nearshore amplification processes of tsunami waves, including inundation at complex topography and basin resonance. The new module of NAMI DANCE that uses the atmospheric pressure and wind forcing as the other inputs to simulate meteotsunami events is developed. In this paper, the analytical solution for the generation of ocean waves due to the propagating atmospheric pressure disturbance is obtained. The new version of the code called NAMI DANCE SUITE is validated by comparing its results with those from analytical solutions on the flat bathymetry. It is also shown that the governing equations for long wave generation by atmospheric pressure disturbances in narrow bays and channels can be written similar to the 1D case studied for tsunami generation and how it is integrated into the numerical model. The analytical solution of the linear shallow water model is defined, and results are compared with numerical solutions. A rectangular shaped flat bathymetry is used as the test domain to model the generation and propagation of ocean waves and the development of Proudman resonance due to moving atmospheric pressure disturbances. The simulation results with different ratios of pressure speed to ocean wave speed (Froude numbers) considering sub-critical, critical and super-critical conditions are presented. Fairly well agreements between analytical solutions and numerical solutions are obtained. Additionally, basins with triangular (lateral) and stepwise shelf (longitudinal) cross sections on different slopes are tested. The amplitudes of generated waves at different time steps in each simulation are presented with discussions considering the channel characteristics. These simulations present the capability of NAMI DANCE SUITE to model the effects of bathymetric conditions such as shelf slope and local bathymetry on wave amplification due to moving atmospheric pressure disturbances. [ABSTRACT FROM AUTHOR]

The accuracy of land surface hydrological simulations using an offline land surface model (LSM) depends largely on the quality of the atmospheric forcing data. In this study, Global Land Data Assimilation System (GLDAS) forcing data and the newly developed China Meteorological Administration Land Data Assimilation System (CLDAS) forcing data are used to drive the Noah LSM with multiple parameterizations (Noah-MP) and to explore how the newly developed CLDAS forcing data improve land surface hydrological simulations over mainland China. The monthly soil moisture (SM) and evapotranspiration (ET) simulations are then compared and evaluated against observations. The results show that the Noah-MP driven by the CLDAS forcing data (referred to as CLDAS_Noah-MP) significantly improves the simulations in most cases over mainland China and its eight river basins. CLDAS_Noah-MP increases the correlation coefficient (R) values from 0.451 to 0.534 for the SM simulations at a depth range of 0–ss10 cm in mainland China, especially in the eastern monsoon area such as the Huang-Huai-Hai Plain, the southern Yangtze River basin, and the Zhujiang River basin. Moreover, the root-mean-square error is reduced from 0.078 to 0.068 m3 m−3 for the SM simulations, and from 12.9 to 11.4 mm month−1 for the ET simulations over mainland China, especially in the southern Yangtze River basin and Zhujiang River basin. This study demonstrates that, by merging more in situ and remote sensing observations in regional atmospheric forcing data, offline LSM simulations can better simulate regional-scale land surface hydrological processes. [ABSTRACT FROM AUTHOR]

The sea level variabilities, especially the atmosphere-driven sea level variabilities, which are different in studies on diverse areas and timescales, need to be further documented in the Bohai Bay. Coastal sea level data and coincident meteorological data collected hourly at two observation stations (E1 and E2) in the Bohai Bay, which is a typical semi-enclosed coastal sea in China, are analyzed for the period from 19 August 2014 to 18 November 2014. The sub-sampled low-pass (<0.8 cpd) sea levels (SLSLs) at E1 and E2 are almost the same as each other, while the winds are not. On the whole, SLSLs at E1 and E2 are dominantly influenced by the across-shore wind; in detail, the dominant wind orientation at E1 is 65° measured clockwise from north, and SLSL at E2 is significantly influenced by the sub-sampled wind (SW) at 55°. Regression of SLSL onto the corresponding SW in dominant orientation and the atmospheric pressure is used to predict SLSL, which make the frequency of occurrences when the predicted total sea level is within 0.15 m from the observed values increase to 66.03% and 58.08% at E1 and E2 from original 36.71% and 34.80% without using it, respectively. The results indicate that for the prediction of the total sea level variability in the coastal shallow waters, the SLSL influenced by the atmospheric forcing, including local wind and atmospheric pressure, can be predicted using the multivariable linear regression model. [ABSTRACT FROM AUTHOR]

Although atmospheric reanalyses are an extremely valuable tool to study the climate of polar regions, they suffer from large uncertainties in these data-poor areas. In this work, we examine how Antarctic sea ice biases in an ocean-sea ice model are related to these forcing uncertainties. Three experiments are conducted in which the NEMO-LIM model is driven by different atmospheric forcing sets. The minimum ice extent, the ice motion and the ice thickness are sensitive to the reanalysis chosen to drive the model, while the wintertime ice extent and inner pack concentrations are barely affected. The analysis of sea ice concentration budgets allows identifying the processes leading to differences between the experiments, and also indicates that large and similar errors compared to observations are present in all three cases. Our assessment of the influence of forcing inaccuracies on the simulated Antarctic sea ice allows disentangling two types of model biases: the ones that can be reduced thanks to better atmospheric forcings, and those that would require improvements of the physics of the ice or ocean model. [ABSTRACT FROM AUTHOR]

Atmosphere-ocean interactions are known to dominate seasonal to decadal sea level variability in the southeastern North Sea. In this study an atmospheric proxy for the observed sea level variability in the German Bight is introduced. Monthly mean sea level (MSL) time series from 13 tide gauges located in the German Bight and one virtual station record are evaluated in comparison to sea level pressure fields over the North Atlantic and Europe. A quasi-linear relationship between MSL in the German Bight and sea level pressure over Scandinavia and the Iberian Peninsula is found. This relationship is used (1) to evaluate the atmospheric contribution to MSL variability in hindcast experiments over the period from 1871-2008 with data from the twentieth century reanalysis v2 (20CRv2), (2) to isolate the high frequency meteorological variability of MSL from longer-term changes, (3) to derive ensemble projections of the atmospheric contribution to MSL until 2100 with eight different coupled global atmosphere-ocean models (AOGCM's) under the A1B emission scenario and (4) two additional projections for one AOGCM (ECHAM5/MPI-OM) under the B1 and A2 emission scenarios. The hindcast produces a reasonable good reconstruction explaining approximately 80 % of the observed MSL variability over the period from 1871 to 2008. Observational features such as the divergent seasonal trend development in the second half of the twentieth century, i.e. larger trends from January to March compared to the rest of the year, and regional variations along the German North Sea coastline in trends and variability are well described. For the period from 1961 to 1990 the Kolmogorov-Smirnow test is used to evaluate the ability of the eight AOGCMs to reproduce the observed statistical properties of MSL variations. All models are able to reproduce the statistical distribution of atmospheric MSL. For the target year 2100 the models point to a slight increase in the atmospheric component of MSL with generally larger changes during winter months (October-March). Largest MSL changes in the order of ~5-6 cm are found for the high emission scenario A2, whereas the moderate B1 and intermediate A1B scenarios lead to moderate changes in the order of ~3 cm. All models point to an increasing atmospheric contribution to MSL in the German Bight, but the uncertainties are considerable, i.e. model and scenario uncertainties are in the same order of magnitude. [ABSTRACT FROM AUTHOR]

For the purpose of coastal planning and management, especially under changing climatic conditions, enhanced knowledge about the evolution of extreme sea levels in the past, present, and future is required. This paper presents statistical analyses of high seasonal water level percentiles of 13 tide gauges in the German Bight, spanning over a period of up to 109 years throughout the twentieth and twenty-first centuries. Seasonal and annual high percentile time series of water levels were investigated in comparison to the mean sea level (MSL) for changes on seasonal, inter-annual, and decadal timescales. While throughout the first half of the twentieth century extreme water levels generally followed changes in MSL, during the second half of the century, linear extreme sea level trends exceeded those in MSL in the order of 9-64 cm per century. The largest, although insignificant, contribution to the magnitude of these trends occurs in the winter season (January to March), while smaller but, due to the generally lower atmospheric variability, significant changes are observed during spring (April to June). The observed multi-decadal trends are generally in good agreement with multi-decadal trends in the corresponding percentiles of local zonal surface winds. Only small parts of the trends remain unexplained. It is suggested that these remaining trends result from modifications in the local tidal regime. For the aspects of coastal planning, the findings clarify that in the German Bight, in addition to changes in MSL, potential changes in storminess and in the tidal regime significantly contribute to the development of extreme water levels. Since these factors have influenced the characteristic of extremes throughout the recent past, they also have to be taken into account when estimating design water levels for, e.g., dikes (in a warming climate) under changing greenhouse gas emissions. [ABSTRACT FROM AUTHOR]

A fairly undeveloped barrier island along the mid-Atlantic coast, Onslow Beach, was exposed to two differing, yet sequential meteorological events in the fall of 2008. The response of the barrier island differed significantly enough to warrant investigation into the causes of aberrant overwash locations. Tropical Storm Hanna generated high significant wave heights for a short period of time and caused overwash events along the southern portion of Onslow Beach. The Nor'easter and subsequent wind shift after TS Hanna generated significant wave heights that were lower than during TS Hanna, yet more locations of overwash were recorded along the beach. Data from NOAA wave buoys and a nearshore deployed AWAC were analyzed to understand the underlying physics behind the recorded differences in barrier island response. These data were also used to validate a coupled hydrodynamic (ADCIRC) and waves (SWAN) model to investigate the alongshore variability. Low frequency variability, on the order of days, and tidal timing of shoreward high significant wave heights contributed to the recorded variability. [ABSTRACT FROM AUTHOR]

The persistence barrier of sea surface temperature anomalies (SSTAs) in the North Pacific was investigated and compared with the ENSO spring persistence barrier. The results show that SSTAs in the central western North Pacific (CWNP) have a persistence barrier in summer: the persistence of SSTAs in the CWNP shows a significant decline in summer regardless of the starting month. Mechanisms of the summer persistence barrier in the CWNP are different from those of the spring persistence barrier of SSTAs in the central and eastern equatorial Pacific. The phase locking of SSTAs to the annual cycle does not explain the CWNP summer persistence barrier. Remote ENSO forcing has little linear influence on the CWNP summer persistence barrier, compared with local upper-ocean process and atmospheric forcing in the North Pacific. Starting in wintertime, SSTAs extend down to the deep winter mixed layer then become sequestered beneath the shallow summer mixed layer, which is decoupled from the surface layer. Thus, wintertime SSTAs do not persist through the following summer. Starting in summertime, persistence of summer SSTAs until autumn can be explained by the atmospheric forcing through a positive SSTAs-cloud/radiation feedback mechanism because the shallow summertime mixed layer is decoupled from the temperature anomalies at depth, then the following autumn-winter-spring, SSTAs persist. Thus, summer SSTAs in the CWNP have a long persistence, showing a significant decline in the following summer. In this way, SSTAs in the CWNP show a persistence barrier in summer regardless of the starting month. [ABSTRACT FROM AUTHOR]

The ability of the SMARA storm surge numerical prediction system to reproduce local effects in estuarine and coastal winds was recently improved by considering one-way coupling of the air–sea momentum exchange through the wave stress, and best forecasting practices for downscaling. The inclusion of long period atmospheric pressure forcing in tide and tide/surge calculations corrected a systematic error in the surge, produced by the South Atlantic Ocean quasi-stationary pressure patterns. The maximum forecast range for the storm surge at Buenos Aires provided by the real-time use of water level observations is approximately 12 h. The best available water level prediction is the 6-h forecast (nowcast) based on the closest water level observations. The 24-h forecast from the numerical models slightly improves this nowcast. Although the numerical forecast accuracy degrades after the first 48 h, the improvement to the full range observation-based prediction is maintained at the inner Río de la Plata area and extends to the first 3 days at the intermediate navigation channels. [ABSTRACT FROM AUTHOR]

Ocean response to atmospheric forcing in the CZ ocean model is analyzed. The results show that Nino 3 index from the CZ ocean model driven by linear composite of biennial, ENSO and even annual time scale wind stress anomalies is consistent well with composite of responding two or three components of observed Nino 3 index during the El Nino period while the La Nina phenomena cannot be reproduced by the linear composite. It implies that linear response process for ocean response to atmospheric forcing is dominated during the El Nino period while nonlinear response might be main process during the La Nina period. Simulated results also suggest that optimal response frequency of the CZ ocean model is the frequency lower than annual variability and ocean response to the atmospheric forcing with annual time scale can give rise to incorrect signal-errors in the simulated SSTA field. [ABSTRACT FROM AUTHOR]