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A well-known exception to rising sea surface temperatures (SST) across the globe is the subpolar North Atlantic, where SST has been declining at a rate of 0.39 ( $$\pm$$ 0.23) K century−1 during the 1900–2017 period. This cold blob has been hypothesized to result from a slowdown of the Atlantic Meridional Overturning Circulation (AMOC). Here, observation-based evidence is used to suggest that local atmospheric forcing can also contribute to the century-long cooling trend. Specifically, a 100-year SST trend simulated by an idealized ocean model forced by historical atmospheric forcing over the cold blob region matches 92% ( $$\pm$$ 77%) of the observed cooling trend. The data-driven simulations suggest that 54% ( $$\pm$$ 77%) of the observed cooling trend is the direct result of increased heat loss from the ocean induced by the overlying atmosphere, while the remaining 38% is due to strengthened local convection. An analysis of surface wind eddy kinetic energy suggests that the atmosphere-induced cooling may be linked to a northward migration of the jet stream, which exposes the subpolar North Atlantic to intensified storminess.

In August 2018, a remarkable polynya was observed off the north coast of Greenland, a perennial ice zone where thick sea ice cover persists. In order to investigate the formation process of this polynya, satellite observations, a coupled ice-ocean model, ocean profiling data, and atmosphere reanalysis data were applied. We found that the thinnest sea ice cover in August since 1978 (mean value of 1.1 m, compared to the average value of 2.8 m during 1978−2017) and the modest southerly wind caused by a positive North Atlantic Oscillation (mean value of 0.82, compared to the climatological value of −0.02) were responsible for the formation and maintenance of this polynya. The opening mechanism of this polynya differs from the one formed in February 2018 in the same area caused by persistent anomalously high wind. Sea ice drift patterns have become more responsive to the atmospheric forcing due to thinning of sea ice cover in this region.

Meteorological tsunamis (meteotsunamis) are defined as anomalous long-period (2 to 120 min) sea-level oscillations resulting from atmospheric forcing. In the current version of the Global Historical Tsunami Database covering almost 4000 years and including about 2500 tsunamis and tsunami-like events, meteotsunamis constitute a very small fraction of all events (4.1%). In the twenty-first century, when digital instruments for sea-level recording became widely available, identified meteotsunamis still only constitute 5.8% of all catalogued tsunami events. At the same time, there are many regions (Great Lakes, northeastern Gulf of Mexico, US East coast, southern Britain, Balearic Islands, Adriatic Sea, Yellow Sea, south-west coast of Japan, south-east coast of Brazil), where meteotsunamis dominate over all the other types of tsunamigenic events. Cataloguing of meteotsunami events, as reported in mass media, and described in scientific publications, faces the problems of their correct parameterization within the adopted format of the tsunami database. This format was developed in the late 1980s primarily for parameterization of seismogenic tsunamis, which at that time constituted more than 90% of the database’s content. As a result, most of the meteotsunamis included in the database lack some basic parameters, such as time of origin, location of source as well as run-up heights. The present paper addresses these issues and discusses the ways for their possible resolution. Several well-known cases of recent meteotsunamis are considered from the standpoint of their parameterization and hazard assessment.

The relative contributions of atmospheric fluctuations on 6 h−2 d, 2−8 d, and 8 d−1 month time scales to the changes in the air−sea fluxes, the SO circulation, and Antarctic sea ice are investigated. It was found that the imposed forcing variability on the three time scales creates a significant increase in wind power input, and hence an increase of about 50%, 97%, and 5% of eddy kinetic energy relative to the simulation driven by monthly forcing, respectively. Also, SO circulation and the strength of the upper cell of meridional overturning circulation become strengthened. These results indicate more dominant effects of atmospheric variability on the 2−8 d time scale on the SO circulation. Meanwhile, the 6 h−2 d (2−8 d) atmospheric variability causes an increase in the total sea-ice extent, area, and volume, by about 33%, 30%, and 19% (17%, 20%, and 25%), respectively, relative to those in the experiment forced by monthly atmospheric variables. Such significant sea-ice increases are caused by a cooler ocean surface and stronger sea-ice transports owing to the enhanced heat losses and air-ice stresses induced by the atmospheric variability at 6 h−2 d and 2−8 d, while the effects of the variability at 8 d−1 month are rather weak. The influences of atmospheric variability found here mainly result from wind fluctuations. Our findings in this study indicate the importance of properly resolving high-frequency atmospheric variability in modeling studies.

Using a high-resolution precipitation dataset, the present study detected that the mountainous area of central China (MACA) is a hotspot of ENSO’s impact on the summer rainfall variability. Further analysis suggests that both ENSO and atmospheric forcing make contributions to the summer rainfall variability in MACA. The dominant rainfall-related SST mode features as a seasonal transition from an El Nino-like warming in the preceding winter to a La Nina-like cooling in the following autumn, and it explains about 29% of the total variance of the rainfall during 1951–2018. It indicates that ENSO with a rapid phase transition is responsible for inducing summer rainfall anomalies in MACA. Besides, an upper-level circumglobal wave mode in the Northern Hemisphere during summer also explains about 29% of the summer rainfall variance. Contributions of both the SST and the atmospheric modes have experienced interdecadal changes. The influence of the SST mode gradually increases and plays a dominant role in the recent decades, suggesting that ENSO with a rapid phase transition becomes more important for rainfall prediction in MACA.

A high-resolution Arctic Ocean-Finite Volume Community Ocean Model (AO-FVCOM) and observational current data from 14 mooring stations in Bering Strait and surrounding regions between 1990 and 2015 were used to study the seasonal and in-terannual variability of Bering Strait throughflow (BST). AO-FVCOM represented the BST with a climatological northward flux of 1.06Sv, which was close to the observational mean of 0.94 + 0.26Sv. From the model results, the strongest volume flux was in summer, approximately 45% larger than that in winter. Interannual variability of BST was also indicated in the model results, and the maximum and minimum annual mean transports are in 2007 and 2012, respectively. AO-FVCOM showed larger differences from the observations in 2000, 2002, and 2015 than in other years, which may be related to the limitation of atmospheric forcing for the model. According to the driving mechanisms of BST, sea level difference (SLD) across the strait dominates the northward volume transport, and local wind is also important in forcing the seasonal variability of the BST and SLD patterns to change the BST indirectly.

An open and fundamental issue in climate dynamics is the origin of multidecadal variability in the climate system. Resolving this issue is essential for adequate attribution of human-induced climate change. The purpose of this paper is to provide a perspective on multidecadal variability from the analysis of observations and results from model simulations. Data from the instrumental record indicate the existence of large-scale coherent patterns of multidecadal variability in sea surface temperature. Combined with long time series of proxy data, these results provide ample evidence for the existence of multidecadal sea surface temperature variations. Results of a hierarchy of climate models have provided several mechanisms of this variability, ranging from pure atmospheric forcing, via internal ocean processes to coupled ocean-atmosphere interactions. An important problem is that current state-of-the-art climate models underestimate multidecadal variability. We argue that these models miss important processes in their representation of ocean eddies and focus on a robust mechanism of multidecadal variability which is found in multi-century simulations with climate models having a strongly eddying ocean component.

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 (

Based on our previous study (Yu et al., Clim Dyn 49:1139–1156, 2017), this paper further investigates the interdecadal change in the relationship between the Kuroshio Extension (KE; 27°–37°N, 140°–158°E) and the East Asian summer monsoon (EASM) in the late 1980s. The summer KE sea surface temperature anomalies (SSTAs) show a significant positive relationship with the EASM over the period 1968–1987 (P1), but a significant negative connection with the EASM between 1991 and 2010 (P2). This interdecadal change in the KE–EASM relationship can be interpreted by considering the difference in the relationships of summer KE SSTAs with the East Asian subtropical westerly jet (EASWJ) and western North Pacific subtropical high (WNPSH) during the two periods. During P1, summertime KE SST warming is significantly related to the strengthened EASWJ and WNPSH, but it has close relationships with the weakened and northward-moving EASWJ and WNPSH during P2. These anomalous EASWJ and WNPSH associated with the summertime KE SST warming in P1 (P2) then favors increased (reduced) rainfall over the Yangtze River Valley that corresponds to a strong (weak) EASM, thereby leading to the significant positive (negative) KE–EASM relationship during this period. This change in the relationships of summer KE SSTAs with the EASWJ and WNPSH may be attributed to the increased KE SST variability associated with an enhanced Pacific Decadal Oscillation (PDO) in summer during P2, which is most probably induced by the stronger North Pacific Oscillation (NPO)-like atmospheric forcing, especially its southern pole (SP), in the preceding spring during this period. The spring NPO-like SP forces the KE SSTAs and PDO more directly during the following summer and can thus have been a better precursor for the following EASM than the full NPO-like dipole after the late 1980s.

The influence of high-frequency atmospheric forcing on the formation of a well-mixed summer warm water column in the central Bohai Sea is investigated comparing model simulations driven by daily surface forcing and those using monthly forcing data. In the absence of high-frequency atmospheric forcing, numerical simulations have repeatedly failed to reproduce this vertically uniform column of warm water measured over the past 35 years. However, high-frequency surface forcing is found to strongly influence the structure and distribution of the well-mixed warm water column, and simulations are in good agreement with observations. Results show that high frequency forcing enhances vertical mixing over the central bank, intensifies downward heat transport, and homogenizes the water column to form the Bohai central warm column. Evidence presented shows that high frequency forcing plays a dominant role in the formation of the well-mixed warm water column in summer, even without the effects of tidal and surface wave mixing. The present study thus provides a practical and rational way of further improving the performance of oceanic simulations in the Bohai Sea and can be used to adjust parameterization schemes of ocean models.

This paper addresses the impact of atmospheric variability on ocean circulation in tidal and non-tidal basins. The data are generated by an unstructured-grid numerical model resolving the dynamics in the coastal area, as well as in the straits connecting the North Sea and Baltic Sea. The model response to atmospheric forcing in different frequency intervals is quantified. The results demonstrate that the effects of the two mechanical drivers, tides and wind, are not additive, yet non-linear interactions play an important role. There is a tendency for tidally and wind-driven circulations to be coupled, in particular in the coastal areas and straits. High-frequency atmospheric variability tends to amplify the mean circulation and modify the exchange between the North and the Baltic Sea. The ocean response to different frequency ranges in the wind forcing is area-selective depending on specific local dynamics. The work done by wind on the oceanic circulation depends strongly upon whether the regional circulation is tidally or predominantly wind-driven. It has been demonstrated that the atmospheric variability affects the spring-neap variability very strongly.

High resolution hybrid atmospheric water budget over the South Asian monsoon region is examined. The regional characteristics, variability, regional controlling factors and the interrelations of the atmospheric water budget components are investigated. The surface evapotranspiration was created using the High Resolution Land Data Assimilation System (HRLDAS) with the satellite-observed rainfall and vegetation fraction. HRLDAS evapotranspiration shows significant similarity with in situ observations and MODIS satellite-observed evapotranspiration. Result highlights the fundamental importance of evapotranspiration over northwest and southeast India on atmospheric water balance. The investigation shows that the surface net radiation controls the annual evapotranspiration over those regions, where the surface evapotranspiration is lower than 550 mm. The rainfall and evapotranspiration show a linear relation over the low-rainfall regions (

A series of meteotsunamis hit a few locations in the Mediterranean and Black Seas during 22– 27 June 2014. Meteot- sunamis were particularly numerous on 25 and 26 June in the Adriatic Sea, where at least six harbours and bays were stricken by ˇ powerful waves: strongest events occurred in Vela Luka (Korcula Island), a known meteotsunami hot-spot, where waves reached ˇ height of *3 m, and in Rijeka dubrovacka Bay, where strong *5 m/s currents accompanied *2.5 m high waves. Inten- sification of high-frequency sea level activity was observed at both the eastern and western Adriatic tide gauge stations, with maximum recorded wave heights reaching *68 cm (Ortona, Italy). A series of individual air pressure disturbances characterized by pronounced rates of air pressure change (up to 2.4 hPa/5 min), limited spatial extent (*50 km) and high temporal variability, propagated over the Adriatic on 2 days in question. Numerical hydrodynamic model SCHISM forced by measured and idealised air pressure distur- bances was utilised to reproduce the observed Adriatic sea level response. Several important conclusions were reached: (1) meteotsunamis occurring at various parts of the coast were gen- erated by different atmospheric air pressure disturbances ; (2) topographic influence can be removed from sea level spectra by computing spectral signal- to-background ratios ; the result, being related to the external forcing, resembles atmospheric pressure spectra ; (3) sea response is strongly dependant on details of atmospheric forcing ; and (4) over complex bathymetries, like the middle and south Adriatic ones, numerous effects, including Proudman resonance, edge waves, strong topographical enhance- ment and refractions on the islands placed on the pathway of atmospheric disturbances should be taken into account to fully understand meteotsunami generation and dynamics. An in- depth numerical study is planned to supplement the latter conclusion and to quantify contribution of each process.

The Community Land Model version 3.5 is driven by an observation-based meteorological dataset to simulate soil moisture over China for the period 1951–2008. A method for identifying the patterns of interannual variability that arise from slow (potentially predictable) and intraseasonal (unpredictable) variability is also applied; this allows identification of the sources of the predictability of seasonal soil moisture in China, during March–April–May (MAM), June–July–August (JJA), September–October–November (SON) and December–January–February (DJF). The potential predictability (slow-to-total) of the soil moisture above 1 m is high, with lowest value of 0.76 in JJA and highest value of 0.94 in DJF. The spatial distribution of the potential predictability comprises a northwest–southeast gradient, with a minimum center over East China and a maximum center over the northwest. The most important source of predictability is from the soil moisture persistence, which generally accounts for more than 50 % of the variability in soil moisture. The SSTs in the Indian Ocean, the North Atlantic and the eastern tropical Pacific Oceans are also identified as important sources of variability in the soil moisture, during MAM, JJA and SON/DJF, respectively. In addition, prolonged linear trends in each season are an important source. Using the slow principal component time series as predictands, a statistical scheme for the seasonal forecasting of soil moisture across China is developed. The prediction skills, in terms of the percentage of explained variance for the verification period (1992–2008), are 59, 51, 62 and 77 % during MAM–DJF, respectively. This is considerably higher than a normal grid prediction scheme.

Despite distinct geographic distributions of top-of-the-atmosphere radiative forcing, anthropogenic greenhouse gases and aerosols have been found to produce similar patterns of climate response in atmosphere-and-ocean coupled climate model simulations. Understanding surface energy flux changes, a crucial pathway by which atmospheric forcing is communicated to the ocean, is a vital bridge to explaining the similar full atmosphere-and-ocean responses to these disparate forcings. Here we analyze the fast, atmosphere-driven change in surface energy flux caused by present-day greenhouse gases vs aerosols to elucidate its role in shaping the subsequent slow, coupled response. We find that the surface energy flux response patterns achieve roughly two-thirds of the anti-correlation seen in the fully coupled response, driven by Rossby waves excited by symmetric changes to the land–sea contrast. Our results suggest that atmosphere and land surface processes are capable of achieving substantial within-hemisphere homogenization in the climate response to disparate forcers on fast, societally-relevant timescales., Anthropogenic aerosol and greenhouse gas concentrations are spatially uncorrelated, but the climate response to each shows a similar spatial pattern. Here the authors show that two-thirds of the spatial similarity in the full response manifests through fast-acting atmosphere and land surface processes alone.

Decadal climate variability in the southern Indian Ocean has great influences on southern African climate through modulation of atmospheric circulation. Although many efforts have been made to understanding physical mechanisms, predictability of the decadal climate variability, in particular, the internally generated variability independent from external atmospheric forcing, remains poorly understood. This study investigates predictability of the decadal climate variability in the southern Indian Ocean using a coupled general circulation model, called SINTEX-F. The ensemble members of the decadal reforecast experiments were initialized with a simple sea surface temperature (SST) nudging scheme. The observed positive and negative peaks during late 1990s and late 2000s are well reproduced in the reforecast experiments initiated from 1994 and 1999, respectively. The experiments initiated from 1994 successfully capture warm SST and high sea level pressure anomalies propagating from the South Atlantic to the southern Indian Ocean. Also, the other experiments initiated from 1999 skillfully predict phase change from a positive to negative peak. These results suggest that the SST-nudging initialization has the essence to capture the predictability of the internally generated decadal climate variability in the southern Indian Ocean.

The East Sea (Japan Sea), a small marginal sea in the northwestern Pacific, is ventilated deeply down to the bottom and sensitive to changing surface conditions. Addressing the response of this marginal sea to the hydrological cycle and atmospheric forcing would be helpful for better understanding present and future environmental changes in oceans at the global and regional scales. Here, we present an analysis of observations revealing a slowdown of the long-term deepening in water boundaries associated with changes of water formation rate. Our results indicate that bottom (central) water formation has been enhanced (reduced) with more (less) oxygen supply to the bottom (central) layer since the 2000s. This paper presents a new projection that allows a three-layered deep structure, which retains bottom water, at least until 2040, contrasting previous results. This projection considers recent increase of slope convections mainly due to the salt supply via air-sea freshwater exchange and sea ice formation and decrease of open-ocean convections evidenced by reduced mixed layer depth in the northern East Sea, resulting in more bottom water and less central water formations. Such vigorous changes in water formation and ventilation provide certain implications on future climate changes.

The mean and variability of the Atlantic meridional overturning circulation (AMOC), as represented in six ocean reanalysis products, are analyzed over the period 1960–2007. Particular focus is on multi-decadal trends and interannual variability at 26.5°N and 45°N. For four of the six reanalysis products, corresponding reference simulations obtained from the same models and forcing datasets but without the imposition of subsurface data constraints are included for comparison. An emphasis is placed on identifying general characteristics of the reanalysis representation of AMOC relative to their reference simulations without subsurface data constraints. The AMOC as simulated in these two sets are presented in the context of results from the Coordinated Ocean-ice Reference Experiments phase II (CORE-II) effort, wherein a common interannually varying atmospheric forcing data set was used to force a large and diverse set of global ocean-ice models. Relative to the reference simulations and CORE-II forced model simulations it is shown that (1) the reanalysis products tend to have greater AMOC mean strength and enhanced variance and (2) the reanalysis products are less consistent in their year-to-year AMOC changes. We also find that relative to the reference simulations (but not the CORE-II forced model simulations) the reanalysis products tend to have enhanced multi-decadal trends (from 1975–1995 to 1995–2007) in the mid to high latitudes of the northern hemisphere.

Interannual-to-decadal variability and trends of sea level in the South China Sea (SCS) are studied using altimetric data during 1993–2012 and reconstructed sea level data from 1950–2009. The interannual variability shows a strong seasonality. Surface wind anomalies associated with El Nino-Southern Oscillation explain the sea-level anomaly pattern in the interior SCS, while Rossby waves radiated from the eastern boundary dominate the sea-level variability in the eastern SCS. Decadal variability of sea level in the SCS follows that in the western tropical Pacific, with large variance found west of Luzon Island. Local atmospheric forcing makes a negative contribution to decadal variability in the central SCS, and Rossby waves radiated from the eastern boundary appear to be important. During 1993–2012, decadal sea level averaged in the SCS is significantly correlated with the Pacific Decadal Oscillation (PDO) (r = −0.96). The decadal variability associated with the PDO accounts for most part of sea-level trends in the SCS in the last two decades.

The mechanisms of coupled model bias in seasonal ENSO phase locking are investigated using versions 1.0 and 1.3 of the CSIRO–BOM ACCESS coupled model (hereafter, ACCESS1.0 and ACCESS1.3, respectively). The two ACCESS coupled models are mostly similar in construction except for some differences, the most notable of which are in the cloud and land surface schemes used in the models. ACCESS1.0 simulates a realistic seasonal phase locking, with the ENSO variability peaking in December as in observations. On the other hand, the simulated ENSO variability in ACCESS1.3 peaks in March, a bias shown to be shared by many other CMIP5 models. To explore the mechanisms of this model bias, we contrast the atmosphere–ocean feedbacks associated with ENSO in both ACCESS model simulations and also compare the key feedbacks with those in other CMIP5 models. We find evidence that the ENSO phase locking bias in ACCESS1.3 is primarily caused by incorrect simulations of the shortwave feedback and the thermocline feedback in this model. The bias in the shortwave feedback is brought about by unrealistic SST–cloud interactions leading to a positive cloud feedback bias that is largest around March, in contrast to the strongest negative cloud feedback found in ACCESS1.0 simulations and observations at that time. The positive cloud feedback bias in ACCESS1.3 is the result of a dominant role played by the low-level clouds in its modeled SST–cloud interactions in the tropical eastern Pacific. Two factors appear to contribute to the dominance of low-level clouds in ACCESS1.3: the occurrence of a stronger mean descending motion bias and, to a lesser extent, a larger mean SST cold bias during March–April in ACCESS1.3 than in ACCESS1.0. A similar association is found between the positive cloud feedback bias and the biases in spring-time mean descending motion and SST for a group of CMIP5 models that show a seasonal phase locking bias similar to ACCESS1.3. Significant differences are also found between the thermocline feedbacks simulated by ACCESS1.0 and ACCESS1.3 that appear to reinforce the seasonal ENSO phase locking bias in the latter model. We discuss a mechanism by which the thermocline feedback differences could arise from atmospheric forcing differences in the two models.

Our understanding of the spatio-temporal variability of sensible and latent heat fluxes over land has advanced slowly due to the absence of long-term measurements. To help address this, we produced a long-term heat flux dataset by using a land-surface model driven using observation-based atmospheric forcing. We then corrected the dataset using net radiation observations, and validated the corrected dataset using multiple-source measurements. The results indicate that the corrected dataset represents the variability of these two heat fluxes well on various time scales. Based on the dataset, analyses show that, during 1951–2008, sensible heat flux decreased significantly over China, with a linear trend of $$-$$ 0.04 W m $$^{-2}$$ year $$^{-1}$$ , while latent heat flux increased at 0.02 W m $$^{-2}$$ year $$^{-1}$$ . Regionally, the trends appeared more significant in north-east China, south-west China, and the Tibetan Plateau. On average, the Tibetan Plateau showed the maximum sensible heat flux, especially over the south-west region, with averages $$>$$ 100 W m $$^{-2}$$ . Meanwhile, higher latent heat fluxes mainly covered the Yangtze-Huaihe river basin and southward, with averages $$>$$ 70 W m $$^{-2}$$ . Regarding the response of heat fluxes to soil moisture, the variations of sensible and latent fluxes were more sensitive to soil moisture over dry regions (arid and semi-arid soil moisture zones), while the stronger anomalies for both fluxes occurred over wet regions (semi-humid and humid soil moisture zones).

The present study documents the atmosphere–ocean interaction in interannual variations over the South China Sea (SCS). The atmosphere–ocean relationship displays remarkable seasonality and regionality, with an atmospheric forcing dominant in the northern and central SCS during the local warm season, and an oceanic forcing in the northern SCS during the local cold season. During April–June, the atmospheric impact on the sea surface temperature (SST) change is characterized by a prominent cloud-radiation effect in the central SCS, a wind-evaporation effect in the central and southern SCS, and a wind-driven oceanic effect along the west coast. During November–January, regional convection responds to the SST forcing in the northern SCS through modulation of the low-level convergence and atmospheric stability. Evaluation of the precipitation–SST and precipitation–SST tendency correlation in 24 selected models from CMIP5 indicates that the simulated atmosphere–ocean relationship varies widely among the models. Most models have the worst performance in spring. On average, the models simulate better the atmospheric forcing than the oceanic forcing. Improvements are needed for many models before they can be used to understand the regional atmosphere–ocean interactions in the SCS region.

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.

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.

Previous studies suggested that the wintertime SST in the North Pacific that are generated by the concurrent North Pacific Oscillation (NPO) are able to force El Nino during subsequent winter via the so-called ‘seasonal footprinting mechanism’ (SFM). We examine how the NPO effectively generates the El Nino via the SFM in the observations and models. The occurrence ratio for El Nino under conditions of NPO forcing during the previous winters is about 41 % for the period of 61 years (1949–2009), indicating that the atmospheric forcing from the mid-latitudes through the SFM does not always trigger an El Nino. We observed certain favorable conditions under which the SFM may effectively induce El Nino. We directly compared these observations with two cases: when the wintertime NPO leads to El Nino during the following winter through the SFM, and when the wintertime NPO is not followed by El Nino. Our analysis demonstrates that the spatial structures of the NPO, associated wind speed and net heat flux in the northeast Pacific, differ between the two cases. Such differences determine the existence of a footprint SST in the northeastern Pacific during the late spring and summer, which plays a key role in initiating the El Nino via the projection of westerly wind stress anomalies onto the equatorial Pacific during the same seasons. By conducting linear baroclinic model experiments, it is found that the positions of La Nina SST forcing during the previous winter are able to modify the spatial structures of the NPO, which produces favorable conditions for the El Nino during subsequent winter via the SFM.

Sea level trends and interannual variability at Antalya and Mentes tide gauges are investigated during the 1985–2001 period, quantifying the roles of atmospheric, steric and local land motion contributions. Tide gauge sea level measurements, temperature/salinity climatologies and GPS data are used in the analyses and the results are compared with the output of a barotropic model forced by atmospheric pressure and wind. The overall sea level trends at two tide gauges collocated with GPS are in the range of 5.5 to 7.9 mm/yr during the study period, but showing different behaviour in the sub-periods 1985–1993 and 1993–2001 due to variations in the contributing factors both in space and time. After the removal of the atmospheric forcing and steric contribution from sea level records, the resulting trends vary between 1.9 to 4.5 mm/yr in Antalya and −1.2 to −11.6 mm/yr in Mentes depending on the period considered. Vertical land movement estimated from GPS data seems to explain the high positive residual trend in Antalya during the whole period. On the other hand, the source of the highly negative sea level trend of about −14 mm/yr in Mentes during 1985–1993 could not be resolved with the available datasets. Interannual variability of wind and atmospheric pressure appear to dominate the sea level at both tide gauges during the study period. Atmospheric and steric contributions together account for ∼50% of the total sea level variance at interannual time scales. Mass induced sea level variations which were not considered in this study may help to close the sea level trend budgets as well as to better explain the interannual sea level variance.

Super typhoon Durian struck the central Philippines on November 30, 2006 and southern coast of Vietnam on December 5, 2006. The reported maximum wind exceeded 250 km/h, and the central pressure was 904 hPa during the peak of the system. The typhoon brought colossal damage, both in terms of lives and in terms of properties to the Philippines and Vietnam while Thailand and Malaysia were slightly affected. The energy from the high-velocity wind and central pressure drop resulted in the generation of storm surges along the coastal region of the Philippines including its surrounding islands as well as parts of southern Vietnam. In this paper, a numerical 2D model is used to study the oceanic response to the atmospheric forcing by 2006 super typhoon Durian in the coastal regions of the Philippines and Vietnam. The initial study of this model aims to provide some useful insights before it could be used as a coastal disaster prediction system in the region of South China Sea (SCS). The atmospheric forcing for the 2D model, which includes the pressure gradient and the wind field, is generated by an empirical asymmetrical storm model. The simulated results of storm surges due to typhoon Durian at two locations lie in the range of observed data/estimates published by the Joint Typhoon Warning Centre (JTWC).

Based on station observations, The European Centre for Medium-Range Weather Forecasts reanalysis (ERA40), the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis and Princeton University’s global meteorological forcing data set (Princeton), four atmospheric forcing fields were constructed for use in driving the Community Land Model version 3.5 (CLM3.5). Simulated soil moisture content throughout the period 1951–2000 in the Yellow River basin was validated via comparison with corresponding observations in the upper, middle, and lower reaches. The results show that CLM3.5 is capable of reproducing not only the characteristics of intra-annual and annual variations of soil moisture, but also long-term variation trends, with different statistical significance in the correlations between the observations and simulations from different forcing fields in various reaches. The simulations modeled with station-based atmospheric forcing fields are the most consistent with observed soil moisture, and the simulations based on the Princeton data set are the second best, on average. The simulations from ERA40 and NCEP/NCAR are close to each other in quality, but comparatively worse to the other sources of forcing information that were evaluated. Regionally, simulations are most consistent with observations in the lower reaches and less so in the upper reaches, with the middle reaches in between. In addition, the soil moisture simulated by CLM3.5 is systematically greater than the observations in the Yellow River basin. Comparisons between the simulations by CLM3.5 and CLM3.0 indicate that simulation errors are primarily caused by deficiencies within CLM3.5 and are also associated with the quality of atmospheric forcing field applied.

A finite element model for solving ocean circulation forced by winds and atmospheric heat fluxes is presented. It is vertically integrated 1 1/2 layer model which solves the motion and continuity hydrodynamic equations coupled with the advection-diffusion transport equation for temperature. A space-time Petrov-Galerkin formulation is used to minimize the undesirable numerical spurious oscillation effects of unresolved boundary layers solution of classical Galerkin method. The model is employed to simulate the circulation of the eastern South Pacific Ocean represented by a mesh covering the area between the equator and 30ºS and between the 70ºW to 100ºW. Monthly climatological data are used to determine the wind and heat fluxes forcing functions of the model. The model simulates the main features of observed sea surface temperature (SST) pattern during the summer months showing the upwelling along the coastal boundary with currents oriented northwestward and the presence of southward flows and warm water intrusion in offshore side. The calculated SST fields are compared with the mean observed SST showing that the coastal processes and the interaction with the equatorial band are physically better resolved.

A series of tsunami-like waves of non-seismic origin struck several southern European countries during the period of 23 to 27 June 2014. The event caused considerable damage from Spain to Ukraine. Here, we show that these waves were long-period ocean oscillations known as meteorological tsunamis which are generated by intense small-scale air pressure disturbances. An unique atmospheric synoptic pattern was tracked propagating eastward over the Mediterranean and the Black seas in synchrony with onset times of observed tsunami waves. This pattern favoured generation and propagation of atmospheric gravity waves that induced pronounced tsunami-like waves through the Proudman resonance mechanism. This is the first documented case of a chain of destructive meteorological tsunamis occurring over a distance of thousands of kilometres. Our findings further demonstrate that these events represent potentially dangerous regional phenomena and should be included in tsunami warning systems.

Storm-related sea level variations 1958–2002 along the North Sea coast from a high-resolution numerical hindcast are investigated and compared to the results of earlier studies. Considerable variations were found from year to year and over the entire period. The large-scale pattern of these variations is consistent with that derived from previous studies, while the magnitudes of the long-term trends differ. The latter is attributed to different analysis periods, improvements in the atmospheric forcing, and the enhanced spatial resolution of the numerical simulation. It is shown that the different analysis periods, in particular, represent an issue as the increase in storm-related sea levels was found to be weaker over the last few years that have not been included in earlier studies. These changes are consistent with observed changes of the storm climate over the North Sea. It is also shown that observed and hindcast trends may differ significantly. While the latter are in agreement with observed changes in the storm climate, it may be concluded that observed sea level changes along the North Sea coast comprise a considerable fraction that cannot be attributed to changes in the large-scale atmospheric circulation.

During the storm event 29–31 October 2000 long regular trains of residual sea-level oscillations with period about 6 h occurred in the North Sea area. Crest-to-trough heights up to 0.8 m were observed along the western coast of Norway. Model simulations show that these oscillations were mainly due to spatial and temporal variations in the atmospheric forcing and were not the result of nonlinear tide–surge interaction. The oscillations propagated northwards along the Norwegian coast and the signal was amplified in some fjords in agreement with predictions by high-resolution regional models. In Skagerrak in the north eastern North Sea the main storm-surge signal appeared as amplitude-modulated oscillations with period about 12 h and crest-to-trough height up to 1.5 m. Here the tide–surge interaction contributed up to about 20% of the peak surge. On the coast of Scotland and in the southern part of the North Sea nonlinear effects produced oscillations with 6-h period at some stations.

Hydrodynamic and sediment transport measurements from instrumentation deployed during a 54-day winter period at two sites on the Louisiana inner shelf are presented. Strong extratropical storms, with wind speeds of 7.8 to 15.1 m s–1, were the dominant forcing mechanism during the study. These typically caused mean oscillatory flows and shear velocities about 33% higher than fair weather (averaging 12.3 and 3.2 cm s–1 at the landward site, and 11.4 and 2.7 cm s–1 at the seaward site, respectively). These responses were coupled with mean near-bottom currents more than twice as strong as during fair weather (10.3 and 7.5 cm s–1 at the landward and seaward sites, respectively). These flowed in approximately the same direction as the veering wind, causing a net offshore transport of fine sand. Weak storms were responsible for little sediment transport whereas during fair weather, onshore sand transport of approximately 25–75% of the storm values appears to have occurred. This contradicts previous predictions of negligible fair-weather sediment movement on this inner shelf.

The present study investigates the features of the surface latent heat flux (LHF) anomalies and their related variables over the tropical Pacific during two types of El Nino-Southern Oscillation (ENSO) events and seeks a possible candidate for the main contributions to the LHF anomalies. During El Nino Modoki and canonical El Nino events, the LHFs show positive anomalies over the equatorial central Pacific and in the areas immediately south of the equatorial eastern Pacific. In addition, the largest magnitudes and widest ranges of positive LHF anomalies for both types of events occur during their mature stages rather than during their developing or decaying phases. Analyses show that the positive LHF anomalies associated with both events are largely affected by the positive sea-air humidity difference anomalies. However, the negative surface wind speed anomalies associated with the canonical El Nino events clearly contribute to the decreases in the positive LHF anomalies over the central Pacific and in the area immediately north of the equatorial eastern Pacific due to the presence of westerly and northerly anomalies, respectively. Moreover, over the equatorial central Pacific and in the area immediately south of the eastern Pacific, the LHF anomalies are mainly influenced by oceanic variables during both types of ENSO events, indicating an atmospheric response to oceanic forcing. In contrast, outside of the area spanning 10° north and south of the equator in the tropical Pacific and with the exception of the southeastern region, the LHF anomalies are greatly influenced by atmospheric variables, suggesting an oceanic response to atmospheric forcing. Distinct differences exist during the mature event phase, with oceanic forcing dominating the equatorial central Pacific during El Nino Modoki events and the area immediately south of the equatorial eastern Pacific during canonical El Nino events. In addition, both types of ENSO events suggest the increasing influence of oceanic forcing over the equatorial eastern Pacific during ENSO event evolutions.

This study used National Center for Environmental Prediction (NCEP) reanalysis data to confirm that the variance of sea surface temperature (SST) in the South China Sea (SCS) has pronounced intraseasonal oscillations characterized by quasi-standing waves; and was aimed to document how intraseasonal time scale SST formed and developed in the SCS. The results derived from the composite analysis indicated the existence of a local low-level atmospheric dynamic forcing system over the SCS. The main formation mechanism of SST intraseasonal oscillation is the low-level rotational atmospheric circulation forcing over the SCS on intraseasonal time scales and the solar radiation variations caused by cloud amount changes.

The effect of the atmosphere on the Earth's rotation can be computed by twodifferent but fundamentally equivalent approaches. The more commonly used is the so-called angular momentum approach, and the second is the torque approach. Their physicalmeanings are recalled, and numerical results from the two are intercompared, concentrating on the lowest periods of a few days or shorter. The indirect effect of the atmosphereon the Earth rotation due to atmospheric forcing on the ocean is also described based on both static and dynamic oceanic models.Results are discussed for the equatorial components and for the highest frequencies.

The most plausible scenarios for seasonal to interannual variabilities and their possible causes are investigated for the Tsushima Current system passing through the Japan Sea. The study is based on the north and south two-box model across the polar front in an idealized upper ocean of the Japan Sea. The boxes are connected by lateral diffusive heat transport and cooled by atmospheric forcing at the annual mean state. The south box, i.e. the Tsushima Current region, only interacts with the outside warmer box in the East China Sea and has an eastward thermal-driven current originating in the outside box. The magnitude of this current depends on the strength of the thermal gradient between the north and south boxes; the inflow of warm waters can therefore be maintained by net heat loss through the sea-surface. I call such a thermal-driven inflow process a "Cooling-Induced Current" system in the present study. Under periodical heat forcing, the perturbation response of the model to water temperature fields and inflow transport were examined. It is shown that the lateral diffusion time across the polar front (over a period of 10 years) is crucial to the interannual modeled response. An analysis of the seasonal heat budget suggests that the heat transported into the Japan Sea from the East China Sea in summer is stored mainly within the Tsushima Current region and contributes to heat loss by the sea-surface cooling in winter.

The paper discusses the results of numerical experiments on response of the Black Sea to the ‘real’ (mean monthly) atmospheric forcing. A new version of the multi-layer quasi-isopycnic model is applied which does not use the rigid-lid approximation and allows for a salt flux through the sea surface. Ways of obtaining quantitative agreement between the calculated data due only to the external forcing, without invokingin situ temperature/salinity observations are suggested.

Based on measurements, taken during a 40-day period in autumn 1993, of air pressure, wind and water levels at the southern and northern ends of the Bosphorus, an analysis of the water level variation is per formed. The water level difference governs the state of flow through the Bosphorus, and during times of high water level difference the lower layer may block. The water level difference is calculated with an average er ror of 5 cm. The northeasterly wind, slightly dominated by the easterly component, is found to exert a large contribution to the water level difference, whereas the air pressure exerts a net contribution mainly through a phase difference between the response at the northern and southern ends of the Bosphorus. The results are utilised in a calculation of water level differences based on a 2-year time series of air pressure, wind speed and direction. A lower layer blocking frequency of 13% is obtained, in accordance with other works.

The paper discusses the data derived from a numerical experiment on the ocean’s response (between the equator and 64°N) to the seasonal variability of the atmospheric forcing (wind and heat flux through the ocean surface). A multilayer (7 layers) non-linear model is used incorporating the upper mixed layer interacting with the internal layers in the regimes of entraining and subduction. The restructuring of the layer composition, the currents and temperature variability, as well as the alternation of the entrainment and subduction regimes are analysed.

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.

A three dimensional boundary fitted coordinate hydrodynamic model for simulation of ocean currents is briefly described. The model is tested on simple test cases with tidal and atmospheric forcing and the results are compared with analytical solutions. Finally, the two-dimensional version of the model is applied for simulating tidal and storm surge elevation and currents on the Norwegian continental shelf. The simulation is carried out both for a coarse and fine grid. The simulated sea elevation and currents are compared with observations and model results from the operational model at the Norwegian Meteorological Institute.

Although the surface seiches of Lake Constance have been observed as early as 1549 and received serious scientific attention since 1893 in the classical work of Forel, they have only recently been investigated by modern hydrodynamical methods. It is the goal of this report to critically compare theoretical predictions of the periods and form of seiches with recent and historical observations as well as to examine the mechanisms of generation of these surface oscillations by means of applying measured atmospheric forcing in Lake Constance to a theoretical model. In the first part of this work, we review the findings of a large number of previous investigations, while the second part consists of a verification analysis of the model predictions of seiches. In the final part, we present a theory, predictions and observations of the excitation of seiches by arbitrary wind and barometric pressure gradient forcing.