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Deep convection in the Gulf of Lion is believed to be primarily driven by the mistral winds. However, our findings show that the seasonal atmospheric change provides roughly two-thirds of the buoyancy loss required for deep convection to occur for the year 2012 to 2013, with the mistral supplying the final third. Two NEMOMED12 ocean simulations of the Mediterranean Sea were run from 1 August 2012 to 31 July 2013, forced with two sets of atmospheric-forcing data from a RegIPSL coupled run within the Med-CORDEX framework. One set of atmospheric-forcing data was left unmodified, while the other was filtered to remove the signal of the mistral. The control simulation featured deep convection, while the seasonal simulation did not. A simple model was derived by relating the anomaly scale forcing (the difference between the control and seasonal runs) and the seasonal scale forcing to the ocean response through the stratification index. This simple model revealed that the mistral's effect on buoyancy loss depends more on its strength rather than its frequency or duration. The simple model also revealed that the seasonal cycle of the stratification index is equal to the net surface heat flux over the course of the year, with the stratification maximum and minimum occurring roughly at the fall and spring equinoxes.

We build three Long Short-Term Memory (LSTM) daily streamflow prediction models (deep learning networks) for 531 basins across the contiguous United States (CONUS), and compare their performance: (1) a LSTM post-processor trained on the U.S. National Water Model (NWM) outputs (LSTM_PP) as a target variable, (2) a LSTM post-processor trained on the NWM outputs and using atmospheric forcings (LSTM_PPA), and (3) a LSTM model trained on USGS average daily streamflow data and using atmospheric forcing (LSTM_A). We trained the LSTMs for the period 2004-2014 and evaluated on 1994-2002, and compared several performance metrics to the NWM reanalysis. Overall performance of the three LSTMs is similar, with median NSE scores of 0.73 (LSTM_PP), 0.75 (LSTM_PPA), and 0.74 (LSTM_A), and all three LSTMs outperform the NWM validation scores of 0.62. Additionally, LSTM_A outperforms LSTM_PP and LSTM_PPA in ungauged basins. While LSTM as a post-processor improves NWM predictions substantially, we achieved comparable performance with the LSTM trained without the NWM outputs (LSTM_A). Finally, we performed a sensitivity analysis to diagnose the land surface component of the NWM as the source of mass bias error and the channel router as a source of simulation timing error. This indicates that the NWM routing scheme should be considered a priority for NWM improvement.

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.

The daily life of the population is influenced by several phenomena, one of them, called tide, which consists of the variation in the level of the water bodies that surround the continents. Meteorological tide is defined as the difference between the observed tide and the tideastronomical effects are caused by two causes: variation in atmospheric pressure and exchange of air-sea momentum. During this phenomenon, the water body piles up along the coast, which may exceed its natural limit, reaching occupied and built-up areas causing negative impacts. In this way, the identification of a pattern of association of direction and intensity of winds, associated with events of meteorological tide, helps the decision making of the public power, with regard to coastal management, focused on precaution. This research aimed to determine the values ​​of the meteorological tide and its relationship with the intensity and direction of the incident winds in the period from 2014 to 2019 in the municipality of Itapoa / SC. More intense winds were observed between the months of January to March and in August and September, lower intensities between the months of April to July. The data showed that there is a low positive correlation between the meteorological tide and the meridional and zonal components of the wind, however the most significant is the meridional component. Data analysis and bibliographic review indicate that there is some relationship between atmospheric forcing (wind intensity and direction) and meteorological tide events.

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.

We explore the response of wintertime Arctic sea ice growth to strong cyclones and to large-scale circulation patterns on the daily scale using Earth system model output in phase 5 of the Coupled Model Intercomparison Project (CMIP5). A combined metrics ranking method selects three CMIP5 models that are successful in reproducing the wintertime Arctic dipole (AD) pattern. A cyclone identification method is applied to select strong cyclones in two subregions in the North Atlantic to examine their different impacts on sea ice growth. The total change of sea ice growth rate (SGR) is split into those respectively driven by the dynamic and thermodynamic atmospheric forcing. Three models reproduce the downward longwave radiation anomalies that generally match thermodynamic SGR anomalies in response to both strong cyclones and large-scale circulation patterns. For large-scale circulation patterns, the negative AD outweighs the positive Arctic Oscillation in thermodynamically inhibiting SGR in both impact area and magnitude. Despite the disagreement on the spatial distribution, the three CMIP5 models agree on the weaker response of dynamic SGR than thermodynamic SGR. As the Arctic warms, the thinner sea ice results in more ice production and smaller spatial heterogeneity of thickness, dampening the SGR response to the dynamic forcing. The higher temperature increases the specific heat of sea ice, thus dampening the SGR response to the thermodynamic forcing. In this way, the atmospheric forcing is projected to contribute less to change daily SGR in the future climate.

Measurements of collocated fields of atmospheric forcing, surface waves, and mean and turbulent velocities associated with passage of Tropical Storm (TS) Barry over the U.S. Navy Tower R2 on the Georgia continental shelf are presented. A vertical-beam ADCP enables computation of directional surface wave spectra and hence of directional Stokes functions of depth and time, as well as mean (including tidal) and turbulent velocities throughout the water column. Full-depth turbulent velocity and backscatter structures observed during TS Barry are determined to be Langmuir supercells (LS). The LS appear in the present observations and in similar observations from a shallower site only when a surface growth rate g* exceeds a critical value, providing a means of predicting how deep an unstratified water column must be before LS will not be expected. When observed, LS structures at Tower R2 are less organized than archetypical LS structures: we suggest that this result is due primarily to smaller near-bottom growth rate in the deeper water column. Despite g* values above the critical value, and appropriate values of Langmuir and Rayleigh numbers, full-depth velocity/backscatter structures disappear completely for a time between the two wind maxima associated with the TS, as wind veers rapidly clockwise with eye passage to the west of Tower R2. From the observations, the most likely explanation for this hiatus is decreased wave breaking during the period of wind veering, reducing surface supply of “effective” vertical vorticity that dominates generation of Langmuir circulation (LC). This result has significant implications for LES modeling of LC.

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.

Significant summer land surface warming has been observed in the middle latitudes over East Asia, especially after the mid-1990s, which has evidently affected the East Asian weather and climate. Using multisource observations and reanalysis data during 1979–2013, this study explores the possible reasons for recent land surface warming over this region by considering atmospheric forcing and regional land–atmosphere interaction related to extratropical cyclones (ECs). Results show that there is a close relationship between land surface warming and weakened ECs over East Asia. Recent land surface warming was attributed to local atmospheric forcing and feedback of land–atmosphere interaction associated with weakened ECs. The abnormal large-scale circulation associated with anomalous ECs produced evident dynamic forcing on the land surface. Weakened ECs are usually accompanied by an abnormal high pressure system and anticyclonic circulation around Lake Baikal, which benefit the intensification of anomalous southerly wind in the rear of the anomalous anticyclone, leading to positive temperature advection and temperature increase over East Asia. Meanwhile, the anomalous adiabatic warming caused by abnormal descending motion associated with the anticyclonic anomaly also contributes to local warming. The feedback of local land–atmosphere interaction plays an important role in land surface warming. Weakened ECs increase both incident solar radiation and precipitation. The increased precipitation reduces the soil moisture and in turn weakens the surface evaporation and local cooling effect, resulting in land surface warming. Our findings are helpful for better understanding the mechanisms responsible for recent summer land surface warming over East Asia as well as its climatic effects.

The impacts of diurnal atmospheric forcing on the summer salinity change in the East China Sea are investigated using the Regional Ocean Modeling System, forced by the hourly and daily reanalysis of wind and insolation. The differences between the forcing of these two frequencies reveal a dipole pattern of salinity change with a positive salinity deviation (1–2 psu) offshore of the Yangtze River estuary, and a negative deviation (from −1 to −0.5 psu) along the Jiangsu Coast. Further dye tracking experiments confirm that diurnal forcing strengthened the northwestward longshore freshwater transport (NLFT) of the Yangtze River by 5.2 × 109 m3 and reduced the mean water age of 7 days. Sensitivity experiments using different forcing combinations suggest that the diurnal wind, that is, the land–sea breeze, is the key to developing the dipole pattern of salinity change and the NLFT. Through the experiment, the land–sea breeze induced a mean clockwise circulation offshore of the Yangtze River estuary. The above changes resulted from both the nonlinearity of wind stress averaging (i.e., the square nature of wind stress) and the baroclinic adjustment related to the diurnal salinity variation, which is directly connected to the diurnal swing of the Yangtze River front. The baroclinic adjustment generated a dipole pattern of vorticity changes offshore of the Yangtze River estuary and a coherent northwestward jet current strengthening the NLFT. These processes developed the summer dipole pattern of the salinity change.

The Southern Ocean (SO) surface wind stress is a major atmospheric forcing for driving the Antarctic Circumpolar Current and the global overturning circulation. Here the effects of wind fluctuations at different time scales on SO wind stress in 18 models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) are investigated. It is found that including wind fluctuations, especially on time scales associated with synoptic storms, in the stress calculation strongly enhances the mean strength, modulates the seasonal cycle, and significantly amplifies the trends of SO wind stress. In 11 out of the 18 CMIP5 models, the SO wind stress has strengthened significantly over the period of 1960–2005. Among them, the strengthening trend of SO wind stress in one CMIP5 model is due to the increase in the intensity of wind fluctuations, while in all the other 10 models the strengthening trend is due to the increasing strength of the mean westerly wind. These discrepancies in SO wind stress trend in CMIP5 models may explain some of the diverging behaviors in the model-simulated SO circulation. Our results suggest that to reduce the uncertainty in SO responses to wind stress changes in the coupled models, both the mean wind and wind fluctuations need to be better simulated.

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.

When subjecting ocean models to atmospheric forcing, the models exhibits two types of variability—a response to the external forcing (hereafter referred to as signal) and inherently generated (internal, intrinsic, unprovoked, chaotic) variations (hereafter referred to as noise). Based on an ensemble of simulations with an identical atmospherically forced oceanic model that differ only in the initial conditions at different times, the signal-to-noise ratio of the atmospherically forced oceanic model is determined. In the large scales, the variability of the model output is mainly induced by the external forcing and the proportion of the internal variability is small, so the signal-to-noise ratio is large. For smaller scales, the influence of the external forcing weakens and the influence of the internal variability strengthens, so the signal-to-noise ratio becomes less and less. Thus, the external forcing is dominant for large scales, while most of the variability is internally generated for small scales.

Using the depth (z) and density (ϱ) frameworks, we analyze local contributions to AMOC variability in a 900‐year simulation with the AWI climate model. Both frameworks reveal a consistent interdecadal variability; however, the correlation between their maxima deteriorates on year‐to‐year scales. We demonstrate the utility of analyzing the spatial patterns of sinking and diapycnal transformations through depth levels and isopycnals. The success of this analysis relies on the spatial binning of these maps which is especially crucial for the maps of vertical velocities which appear to be too noisy in the main regions of upwelling and downwelling because of stepwise bottom topography. Furthermore, we show that the AMOC responds to fast (annual or faster) fluctuations in atmospheric forcing associated with the NAO. This response is more obvious in the ϱ than in the z framework. In contrast, the link between AMOC and deep water production south of Greenland is found for slower fluctuations and is consistent between the frameworks.

The subtropical northeastern Pacific (SNEP) acts as a bridge conveying information between the North and tropical Pacific. While most studies have investigated the SNEP sea surface temperature (SST...

NSEP/NCAR reanalysis data for the period of 1948–2017 were used for description of the long-term variability of the hydro-meteorological parameters in the Caspian Sea (surface air temperature, sea surface temperature, wind, relative and specific humidity, precipitation rate, precipitable water). Linear trends and polynomial approximations of these parameters are presented. The latter show the nonlinear nature and periodicity of the parameters’ variability. Three time spans of 10–25 years duration with multidirectional trends of hydrometeorological parameters have been identified. The switch of wind regimes occurred 10–12 years earlier than the change of thermal and humidity regimes, which suggests the leading role of the long-term variations of the large-scale atmospheric forcing in the variability of hydrometeorological parameters in the Caspian Sea.

The response of snowpack to a +2°C global warming relative to the present climate was estimated in Hokkaido, Japan, using a physical snowpack model driven by dynamically downscaled (DDS) data, after model evaluation. The evaluation revealed that the snowpack model successfully reproduced the height of snow cover (HS), snow water equivalent (SWE) and snow-covered days (SCDs), but had a moderate bias in the thickness ratios of melt form (MF) and hoar category (HC). The DDS-forced simulation predicted that the seasonal-maximum HS and SWE would decrease by 30–40% in the southwestern and eastern parts of Hokkaido due to a large decrease in snowfall during the accumulation period, and that the HS and SWE in the north would decrease, albeit not significantly due to uncertain atmospheric forcing. The number of SCDs in Hokkaido was predicted to decline by ~30 d. Additionally, ~50% of snowpack thickness during a season would be MF in most areas, whereas HC would be

Stochastic variability of internal atmospheric modes, known as teleconnection patterns, drives large-scale patterns of low-frequency SST variability in the extratropics. To investigate how the decadal component of this stochastically driven variability in the South and North Pacific affects the tropical Pacific and contributes to the observed basinwide pattern of decadal variability, a suite of climate model experiments was conducted. In these experiments, the models are forced with constant surface heat flux anomalies associated with the decadal component of the dominant atmospheric modes, particularly the Pacific–South American (PSA) and North Pacific Oscillation (NPO) patterns. Both the PSA and NPO modes induce basinwide SST anomalies in the tropical Pacific and beyond that resemble the observed interdecadal Pacific oscillation. The subtropical SST anomalies forced by the PSA and NPO modes propagate to the equatorial Pacific mainly through the wind–evaporation–SST feedback. This atmospheric bridge is stronger from the South Pacific than the North Pacific due to the northward displacement of the intertropical convergence zone and the associated northward advection of momentum anomalies. The equatorial ocean dynamics is also more strongly influenced by atmospheric circulation changes induced by the PSA mode than the NPO mode. In the PSA experiment, persistent and zonally coherent wind stress curl anomalies over the South Pacific affect the zonal mean depth of the equatorial thermocline and weaken the equatorial SST anomalies resulting from the atmospheric bridge. This oceanic adjustment serves as a delayed negative feedback and may be important for setting the time scales of tropical Pacific decadal variability.

In this paper, temporal variability and trends of sea ice in the Kara Sea and their correlations with local atmospheric forcing have been quantified and analyzed based on NSDIC SIC dataset and ECMWF ERA-Interim dataset from 1979 to 2017. The sea ice starts to melt in early May and becomes fully frozen at the end of December. The ice melting process is much slower than freezing process. Since 2005, the lowest coverage has been nearly to be 5%, meaning the extensive ice-free condition in summer. The EOF1 patterns of SIC anomaly coincide well with the spatial patterns of trends of SIC. In winter, the whole domain almost remains unchanged and the declining trends are less than −5%/decade but with two high-value regions between −5 and −15%/decade in northwest and southwest. In summer, the sea ice area, extent and relative concentration have been declining significantly with SIC exceeding −15%/decade in the northern part. The decreasing SIC condition is closely sensitive to air temperature over sea surface with correlation coefficients between 0.5 and 1 in the whole domain. Winter accumulative temperature can significantly determine the ice regime in the following melt-freeze period. Correlation coefficients between winter accumulative temperature and melt-freeze sea ice anomaly index, duration of melt-freeze period can up to be −0.85 and 0.77, respectively. Since 2005, the summer sea ice anomaly index becomes closely related to meridional wind with correlation coefficient approaching 0.72. This sea ice motion becomes more sensitive and easily driven by the meridional strong winds when in lower SIC conditions due to the less internal ice stresses.

Temperature Variability of the Baltic Sea Since 1850 and Attribution to Atmospheric Forcing Variables

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.

The Hudson Bay Complex is the outlet for many Canadian rivers, receiving roughly 900 km3/year of river runoff. Historically, studies found a consistent cyclonic flow year-round in Hudson Bay, due to the geostrophic boundary current induced by river discharge and cyclonic wind forcing that was supported by available observations at that time. Using a high-resolution ocean general circulation model, we show that in summer, the mean circulation is not cyclonic but consists of multiple small cyclonic and anticyclonic features, with the mean flow directed through the center of the bay. Absolute Dynamic Topography and velocity observations also show this seasonal flow pattern. We find that this summer circulation is driven by geostrophic currents, generated by steric height gradients, which are induced by increased river discharge during the spring freshet, and reinforced by anticyclonic seasonal wind patterns.

Sea surface temperature (SST) from four Nucleus for European Modelling of the Ocean (NEMO) model simulations is analyzed to study the bulk flux parameterization to compute SST over the Hudson Bay C...

Deep oceanic convection occurs in few locations around the globe. One such location is found in the Labrador Sea where dense waters can subside to depths in excess of 2km below the surface. The weak stratification preconditions the water column for deep convection, triggered by wintertime surface cooling associated with high wind speed events. The convected water brings with it dissolved gases, such as Carbon Dioxide, which are in constant flux between ocean and atmosphere. It is thought that this process of turbulent boundary layer interactions coupled with deep convection is responsible for mixing these gases into the deep ocean, making the ocean the largest sink of anthropogenic carbon.The convective overturning process depends on the temperature and salinity profiles which, together dictate density and thus the static stability of the water column. We have adapted a widely used one-dimensional mixed-layer model, referred to as PWP, to include a parameterization of the air-sea flux of gases such as Oxygen and Carbon Dioxide. The model is forced with surface meteorological fields from the ERA5 reanalysis as well as the higher resolution operational reanalysis from the ECMWF.With the model, we investigate the sensitivity of deep-water formation and the vertical profile of these gases to various atmospheric forcing scenarios. Overturning in the Labrador Sea is most active during the winter months when heat flux out of the ocean is at its maximum. It is found that overturning is far more sensitive to thermal forcing than it is to freshwater forcing within the range of forcings typical to the Labrador Sea. We explore the impact of this sensitivity, including the dependence of the atmospheric forcing on modes of climate variability such as the NAO, has on the role that the Labrador Sea plays as a marine sink for anthropogenic carbon.

Even before the introduction of the term “Marine Heat Wave” (MHW) and its statistical definition in global-scale studies, the scientific community had studied and recorded potentially harmful impacts of persistent conditions of warm surface layers and highly stratified water columns on the marine ecosystem. The main triggers for MHWs are yet not well understood and the current knowledge is mainly based on mass mortalities linked to temperature anomalies. EM-MHeatWaves is an interdisciplinary, collaborative, DAAD/IKYDA funded research project that investigates the atmospheric forcing, oceanic circulation and ecosystem response of MHWs in the Eastern Mediterranean Sea over the past 35 years. Two universities (Justus-Liebig-University Giessen, University of the Aegean) and one research center (Hellenic Centre for Marine Research) re-examine the definition of MHWs with emphasis on the Eastern Mediterranean by applying a holistic approach that includes reverse-engineering using model data and reanalysis covering the period 1985 to 2014. We focus on the Eastern Mediterranean because of the high sensitivity of the basin’s ecosystem to atmospheric and marine warming events, the invasion of tropical alien (Lessepsian) species, the characteristic oceanic circulation with the Eastern Mediterranean Transient events, the exchange with the Black Sea through the Turkish Strait System as well as the coastal upwelling areas. In order to study the spatiotemporal characteristics of Eastern Mediterranean MHWs we work towards a better understanding of the oceanographic processes as well as of the compounding character of the atmospheric contribution. Based on the response of marine biogeochemical cycles (depletion of subsurface oxygen levels, observed changes in the mixed layer and chlorophyll maxima depths, nutrient stoichiometries, carbon uptake and sequestration rates) and their impacts on ecosystems (i.e. shifts in planktonic and benthic community regimes, mass mortality events, disease outbreaks, etc.), triggered by the rise of ocean temperatures, we study the statistical characteristics of the oceanic temperatures and assess the corresponding ocean circulation, the synchronous and lagged contribution of the large scale atmospheric circulation. We further study the signature of these extreme Mediterranean MHW events in future projections from model runs with respect to duration, severity and spatial extent and compare them to reanalysis. EM-MHeatWaves aims at strengthening the partnership between the German and Greek institutions by conducting joint research at a high scientific level.

A thermistor-string-based Snow and Ice Mass Balance Apparatus (SIMBA) was deployed in an Arctic lake Orajärvi in northern Finland (67.36°N, 26.83°E) during winter seasons 2011/2012 - 2019/2020. The snow depth and ice thickness (total and separately for congelation ice and granular ice) were retrieved from SIMBA temperature measurements. The average maximum ice thickness was 72 cm with a standard deviation of 10 cm. The interannual variability of lake ice composition was large. In the past 3 ice seasons, the granular ice dominated the total ice thickness. For example, granular ice accounted 80% of the total ice thickness in May 2020. A high-resolution thermodynamic snow/ice model was applied to simulate ice mass balance, with special attention to the lake ice composition. Local weather station data and ECMWF reanalysis products were used as model forcing. The increase of granular ice formation is a result of more snow precipitation during the ice season, increased variability of seasonal air temperature, and a warming trend. The observed snow thickness on land showed a high correlation with snow-ice thickness on top of lake ice. The relationships between the ratio of snow-ice to total ice thickness and the large-scale atmospheric circulation indexes were investigated. Precipitation and, consequently, snow ice thickness on Lake Orajärvi correlated with the phase of the Pacific Decadal Oscillation, which is in line with previous results for precipitation and ice conditions in northern Finland, but an eventual causal teleconnection still requires further studies.

Interseasonal forecasting of El Niño Southern Oscillation (ENSO), which is traditionally based on data of tropical sea surface temperatures (SST), is in high demand due to the impacts of ENSO on regional climatic conditions around the world as well as the global climate. Improvements in the quality of data in recent decades have led to the active use of statistical ENSO models, which compete with physical models in predictive power. The main disadvantage of statistical forecasts is the pronounced seasonal growth of uncertainty when predicting the upcoming summer-fall ENSO conditions from winter-spring months (so called the spring predictability barrier (SPB)). Recent studies show that Pacific atmospheric circulation anomalies in winter-spring may have a long-term impact on the summer tropical climate via the SST footprint. Here, we infer an index based on sea level pressure (SLP) data from February-March in a single area surrounding Hawaii, and show that this area is the most informative part of the large SLP pattern initiating the SST footprinting mechanism. We define the Hawaiian index (HI) as the mean SLP anomalies in the region (130N-190N, 1500W-1600W) averaged over February-March and demonstrate that the statistical AR model of the Niño 3.4 index taking the HI as a forcing is better in the Bayesian sense and delivers significantly better multimonth predictions. In fact, the HI forcing in the model substantially lowers the SPB and hence increases the predictability of the whole June-May ENSO cycle for forecasts starting in spring. Thus, we can recommend that modelers test the HI as an additional predictor in statistical ENSO models.This research was supported by the Russian Science Foundation (Contract 19-42-04121)

The Adriatic basin is narrow and elongated with numerous islands and surrounded in many parts by steep orography. Therefore ocean models of the Adriatic Sea should benefit from high-resolution atmospheric forcing that could properly account for orographic variations. We compare the results of long-term hindcasts obtained by using three different atmospheric reanalyses with different spatial resolutions. The CROCO ocean model (formerly ROMS_AGRIF) was configured on a relatively coarse 4 km grid, which we consider fine enough to observe the effects of different forcing resolutions, but still coarse enough that we were able to run multiple simulations in a manageable time. Initial and open boundary conditions were provided by CMEMS Mediterranean Sea Physics Reanalysis, and the model includes 36 freshwater sources. A thorough analysis of several run configurations revealed that spatial resolution should not be the primary criteria in choosing the right forcing, as atmospheric models can be subject to significant biases. These tend to strongly influence the results and sometimes even cause circulation reversals. Here we present the main differences between the runs and also evaluate each of them by comparing the results with satellite observations of sea surface temperature.

The aim of the work is to study the mechanisms of the Black Sea mesoscale variability based on an analysis of Lorenz energy cycles calculated from the density and currents velocity obtained by the results of three numerical experiments. An eddy-resolving z-model with a horizontal resolution of 1.6 km was used. Three experiments were carried out with different atmospheric forcing: 1) - climatic data; 2) - SKIRON data for 2011; 3) – SKIRON data for 2016. The mean current kinetic energy MKE, the eddy kinetic energy EKE, the mean available potential energy MPE, the eddy available potential energy EPE and the rates of energy conversion, generation and dissipation were considered in detail.For all experiments the generation and dissipation rates of the MKE and EKE are close to each other, so the kinetic energy from wind dissipated inside the sea. A buoyancy work (described by the conversion between the MPE and MKE) increase the MKE. The EKE was increasing due to the energy transport from the mean current into eddies and the transport from the EPE to the EKE for all experiments. It is shown that these two energy fluxes were comparable in the experiment 1, while the ratio between of them has changed almost six times in the experiments 2 and 3. The c(MKE, EKE) prevailed in 2011, but the c(EPE, EKE) dominated in 2016.The maps analysis of the EKE spatial distribution showed that its maximum in the climatic field was located above a continental slope and in areas of the biggest mesoscale eddies. The mesoscale variability of the climatic circulation was due to the influence of both baroclinic and barotropic instability. The zones of the EKE maximum were located in the abyssal part of the sea in the experiments 2 and 3. EKE was increasing in 2011 mainly due to the inflow from the mean current through barotropic instability. The growth of EKE in 2016 was due to conversion of EPE induced by baroclinic instability.The difference in the EKE variability by the results of climatic and real forcing experiments is associated with the wind forcing. The contribution of the wind stress work to MKE was decreased for the experiments 2 and 3, so as a result, it was observed weakening in the mean current, intensive stream meandering and generation of mesoscale eddies not only in the coastal zones but also in the abyssal part of the sea. Thus, the Black Sea mesoscale variability is determined by barotropic instability or by the combined contribution of barotropic and baroclinic instability processes under intense wind action. The mesoscale variability is due to baroclinic instability under weak wind action.The reported study was funded by RFBR and Government of the Sevastopol according to the research project No 18-45-920019 and the state task No. 0555-2021-0004.

Translation of atmospheric forcing variability into the ocean interior via ocean ventilation is an important aspect of transient climate change. On a seasonal timescale in the subtropics, this translation is mediated by a so‐called “Demon” that prevents access to all except late‐winter mixed‐layer water. Here, we use an eddy‐permitting numerical circulation model to investigate a similar process operating on longer (interannual) timescales in the subpolar North Atlantic. We find that variations in atmospheric forcing are mediated in their translation to the ocean interior, with year‐to‐year changes in the late‐winter mixed layer depth being the critical factor. The signature of persistent strong atmospheric forcing driving deep mixed layers is preferentially ventilated to the interior when the forcing is ceased. Susceptibility to this effect depends on the location and density of subduction — with the rate at which newly ventilated water escapes its region of subduction being the crucial factor. Plain Language Summary Water that leaves the ocean's surface boundary layer — where water is in direct contact with the overlying atmosphere — to be transported into the subsurface, is said to be “ventilated” (the name arising from the abundance of oxygen in newly ventilated water). The ventilation process, which carries implications for the ocean storage of climate‐relevant substances such as carbon dioxide, occurs only at certain times and under certain conditions. In describing a mechanism for the selective nature of ventilation over the seasonal cycle, Henry Stommel imagined a Demon sitting at the base of the surface boundary layer, granting access only to parcels of water that meet certain characteristics (namely their speed of “escape”). Thus, “Stommel's Demon” was born. Here, we investigate this same process as it operates in more northerly regions and on longer timescales. In so doing we give birth to a new “interannual Demon”, and describe its characteristics.

To improve Antarctic sea-ice simulations and estimations, an ensemble-based Data Assimilation System for the Southern Ocean (DASSO) was developed based on a regional sea ice–ocean coupled model, which assimilates sea-ice thickness (SIT) together with sea-ice concentration (SIC) derived from satellites. To validate the performance of DASSO, experiments were conducted from 15 April to 14 October 2016. Generally, assimilating SIC and SIT can suppress the overestimation of sea ice in the model-free run. Besides considering uncertainties in the operational atmospheric forcing data, a covariance inflation procedure in data assimilation further improves the simulation of Antarctic sea ice, especially SIT. The results demonstrate the effectiveness of assimilating sea-ice observations in reconstructing the state of Antarctic sea ice, but also highlight the necessity of more reasonable error estimation for the background as well as the observation.

South China Sea Operational Oceanography Forecasting System (SCSOFS) had been built up and operated in National Marine Environmental Forecasting Center of China to provide daily updated hydrodynamic forecasting in SCS for the future 5 days since 2013. This paper presents comprehensive updates had been conducted to the configurations of the physical model and data assimilation scheme in order to improve SCSOFS forecasting skills in recent years. It highlights three of the most sensitive updates, sea surface atmospheric forcing method, tracers advection discrete scheme, and modification of data assimilation scheme. Scientific inter-comparison and accuracy assessment among five versions during the whole upgrading processes are performed by employing Global Ocean Data Assimilation Experiment OceanView Inter-comparison and Validation Task Team Class4 metrics. The results indicate that remarkable improvements have been achieved in SCSOFSv2 with respect to the original version SCSOFSv1. Domain averaged monthly mean root mean square errors decrease from 1.21 °C to 0.52 °C for sea surface temperature, from 21.6 cm to 8.5 cm for sea level anomaly, respectively.

This article belongs to the Section Earth Sciences and Geography., The Mediterranean Sea, strategically situated across a dynamic frontier line that separates two regions with different climates (Europe and North Africa), has been the focus of attention of many studies dealing with its thermohaline circulation, deep water formation processes or heat and freshwater budgets. Large-scale atmospheric forcing has been found to play an important role in these topics and attention has been renewed in climatic indices that can be used as a proxy for atmospheric variability. Among them, the North Atlantic oscillation, the East Atlantic or the East Atlantic–West Russia patterns have been widely addressed but much less attention has been devoted to a Mediterranean mode, the Mediterranean oscillation. This overview summarizes the recent advances that have been achieved in the understanding of these climatic indices and their influence on the functioning of the Mediterranean from a physical point of view. The important role of the Mediterranean oscillation is emphasized and the most relevant aspects of the other indices are revisited and discussed., Most of the work used for this review article was carried out for the authors in the frame of the P07-RNM-02938 and P12-RNM-01412 Junta de Andalucía Spanish-funded projects.

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.

Climate change has major implications for a wide range of natural processes and phenomena, with precipitation patterns particularly sensitive to changes in atmospheric forcing. The arid and...

This work was funded by the Saudi ARAMCO-KAUST Marine Environmental Observatory (SAKMEO) and the KAUST Office of Sponsored Research (OSR) under the Collaborative Research Grant (CRG) program (Grant # URF/1/2979-01-01). The authors would like to thank Dr. Hari Dasari for providing the atmospheric forcing, and Dr. Nikolaos Zarokanellos and Michel Campbell for valuable advices on various technical issues with the gliders. The authors are also grateful for the NASA Jet Propulsion Laboratory Our Ocean group for providing the G1SST dataset.

Climate warming is expected to change the functioning of regional seas substantially. However, it is still an open question how the global climate processes will affect in the future the regional seas, their wave climate, changes in the storm surges and, consequently, the coastal erosion, flooding risks, and coastal communities. In this study, we perform a detailed analysis of the wave climate of the Baltic Sea and the Caspian Sea based on the multi-mission satellite altimetry data in 1990 – 2017. The dataset of significant wave heights (SWH) from ten satellites was cross-validated against regional in situ buoy and echosounder measurements. In the Caspian Sea, due to the limited availability of the in-situ measurements, the satellite data were validated with visual wave measurements. After correction for systematic differences, the visual observations showed excellent correspondence with monthly averaged satellite data with a typical root mean square difference of 0.06 m. Even though several satellite pairs (ENVISAT/JASON-1, SARAL/JASON-2, ERS-1/TOPEX) exhibit substantial mutual temporal drift, and calm wave conditions are ignored, the overall picture is very consistent. The averaged over the whole basin annual mean SWH in the Baltic Sea shows an increase of 0.005 m/yr but no significant trend is detected in the Caspian Sea.Interestingly, in both Baltic and Caspian seas, changes in the average SWH exhibit a strong spatial pattern. In the Baltic Sea, a meridional pattern is detected: an increase in the central and western parts of the sea and a decrease in the eastern part. This pattern has a timescale of ~13 yr. We also found a faster-varying region in the Baltic Proper where trends in the wave heights experience abrupt changes with a timescale of 3 years and show a strong relation to changes in the North Atlantic Oscillation. In the Caspian Sea, the wave height decreased by 0.019 ± 0.007 m/yr in the eastern segment of the central basin and by 0.04 ± 0.04 m/yr in the western segment of the southern basin when the other parts showed an increase of wave heights. These changes can be explained by an increase in the frequency of westerly winds at the expense of southerly winds. Analysing the changes in the atmospheric forcing we found that there is a cyclic behaviour with a timescale of ~12 years which result in abrupt changes in the wave climate every 12 years, causing the trends in different regions to reverse its sign.We demonstrate that the impact on the coast and coastal community is caused by a complex chain of events, starting from changes in the wind direction due to large-scale atmospheric variability and atmospheric teleconnections, which create abrupt shifts in the wave climate of regional seas. We discuss that regional seas have a different response to the changing climate compared to the open ocean condition, which can lead to accelerated coastal erosion and a higher risk of flooding.

On-set of spring stratification is one of the physical factors that influence the productivity of the continental shelves. Atmospheric convective mixing determines the on-set of spring stratification. This is particularly important in seasonally stratified shelf seas, where stratification constrain nutrient injection to the water column. Higher productivity in stratified period relies on intermittent diapycnal mixing events. Thus, the on-set and intensity of stratification is important for the functioning of the shelf-sea ecosystem. In this study, we investigate on-set of stratification, and its relation with the atmospheric conditions as well as imprints of sub-mesoscale features. We use high resolution in-situ measurements from 10 glider deployments, spanning over 18 months in the central North Sea. Focusing on two consecutive winters, we present year to year variability in the timing and intensity of stratification. An early initiation of stratification is observed in 2018/2019, which is also intense compared to the previous year of 2017/2018. We find that reduced wind stress and net air-sea heat fluxes result in an early on-set of stratification in 2018/2019. In February 2019, intermittent increases in chlorophyll are observed, corresponding to a minimum in sea-to-air heat loss. Similarly, in 2019 an earlier spring bloom is observed. We investigate this period with NEMO model outputs at 7km resolution (AMM7) and show a similar response, emphasizing the influence of atmospheric variability on dynamics of the shelf-sea.

The impact of high-frequency atmospheric forcing on the Yellow Sea (YS) circulation with emphasis on the Yellow Sea Warm Current (YSWC) was investigated by comparing model simulations with and with...

During the past decades, the aquaculture industry has developed rapidly, due to drop in wild fish catch. Water quality variables play a major role in aquaculture operations specifically, seawater temperature has a major impact on the metabolism of the fish species and therefore on the growth rate too. Since the fish farming business relies on the growth rate of the species to plan and operate the farm, seawater temperature becomes crucial information. With the availability of hydrodynamic modelling tools and global ocean information source such as Copernicus Marine Environment Monitoring Service, seawater temperature can be simulated for practically any coasts with a dynamic downscaling approach. But the simulated data needs to be assessed for uncertainties for enabling informed decision making using such model predictions. In this paper, a coastal 3D hydrodynamic model aiming at simulating seawater temperature is developed for the southern Aegean Sea, Greece using the Delft3D Flexible Mesh modelling tool. Seawater temperature is impacted by atmospheric forces; therefore, uncertainties are assessed for seawater temperature using ensemble atmospheric forcing functions of the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5. Spatial analysis of the uncertainty indicates regions of different seawater temperature behavior within the model domain. The seasonal behavior of the vertical temperature gradient suggests that farms need to adapt different operational strategies in different seasons to make the best use of the seawater temperature. The application of Copernicus Marine Environment Monitoring Service data along with ECMWF ERA5 ensemble atmospheric forcing members proves to be beneficial in analyzing the uncertainties both in spatial and vertical gradient of seawater temperature.

This article belongs to the Section Earth Sciences and Geography. The Mediterranean Sea, strategically situated across a dynamic frontier line that separates two regions with different climates (Europe and North Africa), has been the focus of attention of many studies dealing with its thermohaline circulation, deep water formation processes or heat and freshwater budgets. Large-scale atmospheric forcing has been found to play an important role in these topics and attention has been renewed in climatic indices that can be used as a proxy for atmospheric variability. Among them, the North Atlantic oscillation, the East Atlantic or the East Atlantic–West Russia patterns have been widely addressed but much less attention has been devoted to a Mediterranean mode, the Mediterranean oscillation. This overview summarizes the recent advances that have been achieved in the understanding of these climatic indices and their influence on the functioning of the Mediterranean from a physical point of view. The important role of the Mediterranean oscillation is emphasized and the most relevant aspects of the other indices are revisited and discussed. Most of the work used for this review article was carried out for the authors in the frame of the P07-RNM-02938 and P12-RNM-01412 Junta de Andalucía Spanish-funded projects.

This chapter covers our current understanding and recent advances in the study of Earth's ionosphere during magnetic storms and substorms with a special focus on electrodynamics and its consequences in the past 14 years. In particular, the focus is on the new awareness of looking at the magnetosphere, ionosphere, and thermosphere (M-I-T) as a whole system that has brought us to the next level of understanding. Both ground-based observations and the new space-based observations from magnetospheric missions are expanding rapidly. More and more compelling science questions cannot be addressed and resolved without combining simultaneous multiple observations in the ionosphere, plasmasphere, and magnetosphere in order to establish a consistent understanding of the system. Models have greatly improved mostly by coupling different regions and different species. New models can reproduce system phenomena that involve M-I-T coupling and help us elucidate the underlying processes within the coupled systems. Our future challenges will involve (1) cross-scale system and scale interactions; (2) the whole geospace modeling concept, including lower atmospheric forcing; (3) multiday forecasting capability.

This article reports the results of three field campaigns conducted in Lake Issyk-Kul in 2015, 2016, and 2017. During the campaigns, CTD profiling and water sampling were performed at 34 locations all over the lake. A total of 75 CTD profiles were obtained. Some biogeochemical and thermohaline parameters at the lake surface were also mapped at high horizontal resolution along the ship's track. In addition, thermistor chains were deployed at three mooring stations in the eastern littoral region of the lake, yielding 147-day-long records of temperature data. The measurements revealed that – while the thermal state of the active layer, as well as some biogeochemical characteristics, were subject to significant interannual variability mediated by atmospheric forcing – the haline structure of the entire lake was remarkably stable at the interannual scale. Our data do not confirm the reports of progressive warming of the deep Issyk-Kul waters as suggested in some previous publications. However, they do indicate a positive trend of salinity in the lake's interior over the last 3 decades. A noteworthy newly found feature is a weak but persistent salinity maximum below the thermocline at a depth of 70–120 m, from where salinity slightly decreased downwards. The data from the moored thermistor chains support the previously published hypothesis about the significant role of the submerged ancient riverbeds on the eastern shelf in advecting littoral waters into the deep portion of the lake during differential cooling period. We hypothesize that the less saline littoral water penetrating into the deep layers due to this mechanism is responsible for the abovementioned features of salinity profile, and we substantiate this hypothesis by estimates based on simple model assumptions.