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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.

An analysis of the observed Adriatic mean sea-level time series has been carried out in order to determine the primary causes of the changes documented during the last 50 years. Significant positive sea-level trend, related to climate change, was detected for all stations using the least-squares method and t-test. Rodionov’s regime shift index algorithm was used to detect the following three pronounced regime shifts: the 1989 shift lasting 7 years with a decrease of 4.37 cm in sea level, the 1996 shift lasting 13 years with an increase of 2.07 cm in sea level, and the 2009 shift lasting at least until 2018 with an increase of 5.3 cm in sea level. A relationship between sea-level data and North Atlantic Oscillation (NAO), mean sea-level pressure, and wind components has been explored using both monthly and yearly data and establishing significant correlation, most pronounced for the November-December-January-February (NDJF) season. Lastly, the observed regime shifts were further analysed by reviewing synoptic conditions. It was once again confirmed that all the climate shifts were related to pronounced changes of the NAO., U ovom radu su analizirani izmjereni nizovi podataka usrednjenih razina mora kako bi se utvrdili glavni razlozi promjene razine mora zabilježene u posljednjih 50 godina. Značajni pozitivan trend, povezan s klimatskim promjenama, uočen je na svim postajama koristeći metodu najmanjih kvadrata i t-test. Koristeći Rodionov algoritam za promjenu režima pronađene su tri značajne promjene: pad razine mora 1989. od 4.37 cm koji je trajao 7 godina, porast razine mora 1996. od 2.07 cm koji je trajao 13 godina te porast razine mora 2009. od 5.3 cm koji je trajao do barem 2018. Istražena je veza srednje razine mora sa srednjim tlakom na razini mora, Sjeverno-atlantskom oscilacijom te vjetra koristeći mjesečne i godišnje podatke. Ustanovljena je značajna korelacija, ponajviše za period studeni-prosinac-siječanj-veljača. Pronađene promjene režima su analizirane provjerom sinoptičkih uvjeta. Još jednom je potvrđeno da su sve promjene režima povezane sa izraženom promjenom Sjeverno-atlantske oscilacije.

International audience; The circulation and stratification in the shallow semi-enclosed bay of Paracas located downstream of the main upwelling cell off the Peruvian coast were studied during the summer season using a regional circulation model and in situ observations. A downscaling strategy based on a series of three embedded grids, from 10 km to 500 m resolution in the bay allows to take into account the influence of remote perturbations on the bay dynamics. Debiased surface winds from a high-resolution regional atmospheric model were used to force the model. The shortwave absorption depth was parameterized using satellite measurements of surface chlorophyll. Sensitivity experiments to the model forcing and parameterizations were performed to investigate the impact of the wind diurnal variability, tidal forcing, freshwater discharge from a nearby river and shortwave absorption depth on the bay stratification. Results show that: debiasing the wind intensity reduced the model cold bias in the bay and increase the stratification; a shallow shortwave absorption depth induced a cooling of the subsurface water, increasing the stratification; freshwater discharge from the Pisco river north of the bay increased slightly the stratification in the bay during days of weak wind. The high sensitivity of the bay stratification to the atmospheric forcing calls for the need to use more realistic wind forcing products. The circulation in the bay under strong (>5.5 m s-1) and weak (-1) winds was also examined. The summer circulation during strong upwelling-favorable wind conditions was characterized by northward surface currents transporting the bay surface waters outward and subsurface currents transporting cold deeper waters into the bay along its western shore. During weak wind conditions, the current is outward in the bottom layer and a surface southward current related to the poleward undercurrent flowing over the continental slope and shelf transported warm waters into the bay, generating a cyclonic circulation in the bay.

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.

To mitigate temporal aliasing effects in monthly mean global gravity fields from the GRACE and GRACE‐FO satellite tandem missions, both tidal and non‐tidal background models describing high‐frequency mass variability in atmosphere and oceans are needed. To quantify tides in the atmosphere, we exploit the higher spatial (31 km) and temporal (1 hr) resolution provided by the latest atmospheric ECMWF reanalysis, ERA5. The oceanic response to atmospheric tides is subsequently modeled with the general ocean circulation model MPIOM (in a recently revised TP10L40 configuration that includes the feedback of self‐attraction and loading to the momentum equations and has an improved bathymetry around Antarctica) as well as the shallow water model TiME (employing a much higher spatial resolution and more elaborate tidal dissipation than MPIOM). Both ocean models consider jointly the effects of atmospheric pressure variations and surface wind stress. We present the characteristics of 16 waves beating at frequencies in the 1–6 cpd band and find that TiME typically outperforms the corresponding results from MPIOM and also FES2014b as measured from comparisons with tide gauge data. Moreover, we note improvements in GRACE‐FO laser ranging interferometer range‐acceleration pre‐fit residuals when employing the ocean tide solutions from TiME, in particular, for the S1 spectral line with most notable improvements around Australia, India, and the northern part of South America., Plain Language Summary: In addition to many rather slow processes such as the melting of glaciers, rapid mass redistribution related to the weather also measurably affect the Earth's gravity field. The ability of monitoring liquid freshwater changes within the Earth system from the satellite gravity missions GRACE (2002–2017) and GRACE‐FO (since 2018) relies on accurate background models of mass variability in atmosphere and oceans for both tidal and non‐tidal processes. Atmospheric tides are primarily excited in the middle atmosphere by solar energy absorption at periods of 24 hr and its overtones. We find additional tidal signatures in the atmosphere excited by periodic deformations of both crust and sea‐surface of the Earth. We thus introduce here a new data set for the atmospheric tides and their corresponding oceanic response that features both more waves and higher accuracy than other background models previously used for the processing of GRACE and GRACE‐FO satellite gravimetry data., Key Points: Sixteen relevant tidal lines identified in hourly data from ERA5 atmospheric reanalysis. Dedicated simulations with a high‐resolution global hydrodynamic model to simulate ocean tides with atmospheric influence. New tidal models reduce pre‐fit residuals in GRACE‐FO Laser Ranging Interferometer data., Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659, https://pypi.org/project/cdsapi/, https://mpimet.mpg.de/en/science/models/mpi-esm/mpiom, https://doi.org/10.5067/graod-1bg06

A long simulation over the period 1901–2010 with an eddy-permitting ocean circulation model is used to study the variability of the upper layer circulation in the North Ionian Gyre (NIG) in the Eastern Mediterranean Sea (EMed). The model is driven by the atmospheric forcing from the twentieth century reanalysis data set ERA-20C, ensuring a consistent performance of the model over the entire simulation period. The main modes of variability known in the EMed, in particular the decadal reversals of the NIG upper layer circulation observed since the late 1980s are well reproduced. We find that the simulated NIG upper layer circulation prior to the observational period is characterized by long-lasting cyclonic phases with weak variability during years 1910–1940 and 1960–1985, while in the in-between period (1940–1960) quasi-decadal NIG circulation reversals occur with similar characteristics to those observed in the recent decades. Our simulation indicates that the NIG upper layer circulation is rather prone to the cyclonic mode with occasional kicks to the anticyclonic mode. The coherent variability of the NIG upper layer circulation mode and of the Adriatic Deep Water (AdDW) outflow implies that atmospheric forcing triggering strong AdDW formation is required to kick the NIG into an anticyclonic circulation 1–2 years later. A sensitivity experiment mimicking a cold winter event over the Adriatic Sea supports this hypothesis. Our simulation shows that it is the multi-decadal variability of the salinity in the Adriatic Sea that leads to periods where low salinity prevents strong AdDW formation events. This explains the absence of quasi-decadal NIG reversals during 1910–1940 and 1960–1985.

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.

South China Sea Operational Oceanography Forecasting System (SCSOFS) had been constructed 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 recent comprehensive updates of the configurations of the physical model and data assimilation scheme in order to improve SCSOFS forecasting skills. It highlights three of the most sensitive updates, including sea surface atmospheric forcing method, tracers advection discrete scheme, and modification of data assimilation scheme. Inter-comparison and accuracy assessment among five versions during the whole upgrading processes are performed by employing OceanPredict 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 known as 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.

Understanding water level (WL) fluctuations in river deltas is of importance for managing water resources and minimizing the impacts of floods and droughts. Here, we demonstrate the competing effects of atmospheric and oceanic forcing on multi-timescale variability and changes in the Pearl River Delta (PRD) WLs in southern China, using 52 years (1961–2012) of in-situ observations at 13 hydrological stations. PRD WL presents significant seasonal to decadal variations, with large amplitudes upstream related to strong variability of southern China rainfall, and with relatively small amplitudes at the coastal stations determined by sea level (SL) fluctuations of the northern South China Sea. We find that the strengths of atmospheric and oceanic forcing in PRD are not mutually independent, leading to a distinct contrast of WL–forcing relationships at upstream and coastal stations. In the transition zone, because of counteracts of atmospheric and oceanic forcing, no robust relationships are identified between WL and either of the forcing. We further show that in the drought season of the warm ENSO and PDO epochs, the effect of atmospheric (oceanic) forcing on PRD WL is largely enhanced (weakened), due to increased southern China rainfall and negative SL anomalies. Over the observation period, WL significantly decreased at upstream stations, by up to 28–42 mm/year for flood season, contrasting with the upward trends of

Radiales del Mediterráneo, RADMED-TRES, SI

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

Summary: The internally generated variability in the climate system, which is unrelated to any external factors, can be conceptualized as “noise”. This noise is a constitutive element of high-dimensional nonlinear models of such systems. In a three-layer nested simulation, which is forced by climatological (periodic) atmospheric forcing and includes an (almost) global model, a West-Pacific model, and South China Sea (SCS) model, we demonstrate that such “noise” builds also ocean models. They generate variability by themselves without an external forcing. The “noise” generation intensifies with higher resolution, which favors macroturbulence. Keywords: “Noise”, Internal variability, South China Sea, Eddies, Model resolution

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.

Purpose. The paper purpose is to assess quality of meteorological information for the Azov–Black Sea basin derived from the ERA-Interim reanalysis (the European Centre for Medium-Range Weather Forecasts), and to examine possibility of using the obtained data for presetting atmospheric forcing in the numerical hydrodynamic model of the Black and Azov seas. ERA-Interim. Methods and Results. The analysis is based on comparison of the annual average fields with the measurement data on the atmospheric circulation parameters represented in hydrometeorological atlases. The most significant discrepancies between the ERA-Interim fields and the data of climatic arrays are noted and, consequently, the discrepancy-related potential errors arising in reproducing water circulation in the indicated seas are considered. Conclusions. The comparative analysis showed that, for a number of the parameters, the reanalysis data were in qualitative agreement with the measurements. The highest discrepancies (up to 70%) were revealed in the precipitation field nearby the Caucasian coast in autumn. Such an error in the boundary conditions can negatively affect both the sea surface salinity distribution in the numerical modeling and, therefore, reproduction of thermohaline circulation in this region of the sea. A significant error in the results of numerical modeling can also be induced by the discrepancies in the wind fields. In the ERA-Interim data, the wind speed module is generally understated by 7% over the whole Black Sea in a spring-summer period, and by 20–25% in the Azov Sea throughout a year. The direction of the resultant wind is the most distorted in summer, whereas in winter, the deviations are significant only in the southeastern part of the Black Sea. The best agreement is observed between the temperature and air humidity fields, and the climatic arrays’ data: the discrepancies between the values of these parameters are minimal.

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...

The COupled Snowpack and Ice surface energy and mass balance model in PYthon (COSIPY) was employed to investigate the relationship between the variability and sensitivity of the mass balance record of the Halji glacier, in the Himalayas, north-western Nepal, over a 40 year period since October 1981 to atmospheric drivers. COSIPY was forced with the atmospheric reanalysis dataset ERA5-Land that has been statistically downscaled to the location of an automatic weather station at the Halji glacier. Glacier mass balance simulations with air temperature and precipitation perturbations were executed and teleconnections investigated. For the mass-balance years 1982 to 2019, a mean annual glacier-wide climatic mass balance of -0.48 meters water equivalent per year (mw.e./a) with large interannual variability (standard deviation 0.71mw.e./a) was simulated. This variability is dominated by temperature and precipitation patterns. The Halji glacier is mostly sensitive to summer temperature and monsoon-related precipitation perturbations, which is reflected in a strong correlation with albedo. According to the simulations, the climate sensitivity with respect to either positive or negative air temperature and precipitation changes is nonlinear: A mean temperature increase (decrease) of 1K would result in a change of the glacier-wide climatic mass balance of −1.43mw.e./a ( 0.99mw.e./a) while a precipitation increase (decrease) of 10 % would cause a change of 0.45mw.e./a ( −0.59mw.e./a). Out of 22 circulation and monsoon indexes, only the Webster and Yang Monsoon index and Polar/Eurasia index provide significant correlations with the glacier-wide climatic mass balance. Based on the strong dependency of the climatic mass balance from summer season conditions, we conclude that the snow–albedo feedback in summer is crucial for the Halji glacier. This finding is also reflected in the correlation of albedo with the Webster and Yang Monsoon index.

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.

Sinking particles are a critical conduit for the export of organic material from surface waters to the deep ocean. Despite their importance in oceanic carbon cycling, little is known about the biotic composition and seasonal variability of sinking particles reaching abyssal depths. Herein, sinking particle flux data, collected in the deep Ierapetra Basin for a three-year period (June 2010 to June 2013), have been examined at the light of atmospheric and oceanographic parameters and main mass components (lithogenic, opal, carbonates, nitrogen, and organic carbon), stable isotopes of particulate organic carbon (POC) and source-specific lipid biomarkers. Our aim is to improve the current understanding of the dynamics of particle fluxes and the linkages between atmospheric dynamics and ocean biogeochemistry shaping the export of organic matter in the deep Eastern Mediterranean Sea. Overall, particle fluxes showed seasonality and interannual variability over the studied period. POC fluxes peaked in spring April–May 2012 (12.2 mg m−2 d−1) related with extreme atmospheric forcing. Summer export was approximately fourfold higher than mean wintertime, fall and springtime (except for the episodic event of spring 2012), fueling efficient organic carbon sequestration. Lipid biomarkers indicate a high relative contribution of natural and anthropogenic, marine- and land-derived POC during both spring (April–May) and summer (June–July) reaching the deep-sea floor. Moreover, our results highlight that both seasonal and episodic pulses are crucial for POC export, while the coupling of extreme weather events and atmospheric deposition can trigger the influx of both marine labile carbon and anthropogenic compounds to the deep Levantine Sea. Finally, the comparison of time series data of sinking particulate flux with the corresponding biogeochemical parameters data previously reported for surface sediment samples from the deep-sea shed light on the benthic–pelagic coupling in the study area. Thus, this study underscores that accounting the seasonal and episodic pulses of organic carbon into the deep sea is critical in modeling the depth and intensity of natural and anthropogenic POC sequestration, and for a better understanding of the global carbon cycle.

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.

The density and salinity of High Salinity Shelf Water, a key component of Antarctic Bottom Water emanating from the Ross Sea, are intensified by brine rejection induced by ice formation within the Terra Nova Bay (TNB) polynya. Ocean mooring data from 2007, meteorological observations from automatic weather stations and a satellite-derived history of the opening of TNB polynya delineate variability in water column salinity linked to atmospheric forcing, with a period on the order of 10 days. Lagged correlation analysis indicates that on average salinity response lags the polynya opening by 2 days and the wind forcing by 5 days. We find stronger correlations of salinity with the wind during March through May and with the polynya open-water fraction during June through October, with decreasing lags in the latter period. A one-dimensional mixed-layer model incorporating thermodynamic ice formation captures the oscillations in salinity. A process study shows that the variability in the polynya open-water fraction governs the final salinity attained by the model as well as the salinity cycling. Variability in surface heat fluxes modulates that effect. Our work suggests that there is a more complex relationship between salinity, the polynya open-water fraction, and atmospheric forcing than previously suggested.

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.

Las fluctuaciones de la Temperatura Superficial del Mar (TSM) impactan sobre las variaciones del clima en una amplia variedad de escalas espacio-temporales y pueden afectar a los ecosistemas marinos tanto en áreas costeras, como en el océano abierto y profundo. El objetivo de esta tesis es analizar las tendencias de largo plazo y variabilidad interanual de las Anomalías de la Temperatura Superficial del Mar (ATSM) en los océanos alrededor de Sudamérica, con foco en la Plataforma Patagónica (PP) del Mar Argentino e identificar los mecanismos físicos que pueden explicar estas fluctuaciones observadas en el periodo 1982-2017. Los resultados encontrados muestran dos áreas de tendencias estadísticamente significativas en la PP: un área de calentamiento entre los 42° y 45°S (PPN), y otra de enfriamiento entre los 49° y 52°S (PPS). La tasa de calentamiento encontrada es de 0.15± 0.01°C década−1, y la de enfriamiento es de -0.12 ± 0.01°C década−1. Para ambas regiones, las tendencias observadas corresponden en forma casi exclusiva a los cambios registrados en los últimos 10 años del período de estudio. Los cambios observados de la ATSM fueron estudiados en conexión con el forzante atmosférico local. Para el período 1982-2007 el viento meridional explica el 30 % de la varianza total en PPN y PPS en escalas de tiempo interanuales. Durante el lapso 2008-2017, la ATSM en PPN está correlacionada negativa y significativamente con el viento zonal local; mientras que en PPS, con el viento meridional. Se estudiaron los modos principales de variabilidad de la ATSM en conjunto con los posibles forzantes remotos de estas variaciones, a través de una descomposición en valores singulares. La covariabilidad entre la ATSM y la presión a nivel del mar se puede explicar a través de dos modos principales que explican alrededor del 90% de la covariabilidad interanual. De esta manera, se logró describir a la covariabilidad interanual de la ATSM a partir de dos esquemas de circulación acoplados entre la atmósfera y el océano, en la región alrededor de Sudamérica. Finalmente, se analizaron los efectos de las variaciones de la ATSM en el desarrollo del bloom fitoplanctónico en la PP, estimado a partir de datos de clorofila satelital (CSAT). En la región PPN las variaciones de ATSM, asociadas con la estratificación vertical, se relacionan indirectamente con la CSAT. Se observa que en períodos de ATSM positivas, la intensa estratificación vertical de la columna de agua limita la llegada de los nutrientes hacia la superficie y se registran anomalías negativas de CSAT. En la región PPS, en cambio, este mecanismo podría beneficiar a las comunidades fitoplanctónicas, cuyo crecimiento se encuentra limitado por la disponibilidad de luz y la intensa mezcla vertical. The fluctuations of the Sea Surface Temperature (SST) can impact on climate varia- tions on a wide variety of spatio-temporal scales. In addition, variations in the SST could affect the distribution of marine ecosystems in coastal areas, in the open ocean and in the deep ocean. The objective of this thesis is to analyze the long-term trends and interannual variability of SST anomalies (SSTa) on the Patagonian Shelf (PS) of the Argentinean Sea and the adjacent open ocean, and the identification of the physical mechanisms that can explain these trends and interannual fluctuations for the period 1982-2017. Our results show two areas of statistically significant trends on the PS: one area of warming (positive trend) delimited between 42-45 S (Northern PS, ie NPS), and another area of cooling (negative trend) delimited between 49-52 S (Southern PS, ie SPS). Bet- ween 1982 and 2017, warming rate is 0.15 0.01°C decade and the cooling rate is -0.12 +0.01°C decade. For both regions, the observed trends correspond almost exclusively to changes registered in the last 10 years of the period of study. The observed variability of SSTa is studied in connection with atmospheric forcing (zonal and meridional wind components, wind speed, wind curl and heat fluxes). During 1982-2007, the local meridional wind explains 30% of the total variance at NPS and SPS on interannual time scales. During 2008-2017, the SSTa at NPS is significantly anticorre lated with the local zonal wind, while the SSTa at SPS is significantly anticorrelated with meridional wind. The leading covariability patterns of SSTa and remote atmospheric forcing were as- sesed by a Singular Value Decomposition (SVD) methodology. The covariability between SSTa and sea level pressure can be described by the first two leading patterns which ex- plain about 90% of the interannual covariability. Hence, the interannual covariability of the SSTa around southern South America can be characterized by two ocean-atmosphere coupled circulation schemes. We analyzed the phytoplankton bloom development on the PS through satellite-based chlorophyll concentration (Chl-a), and its relation with observed SSTa variations. At NPS, SSTa and vertical stratification is significantly anticorrelated with Chl-a. During periods of positive SSTa, the vertical stratification of the water column increases and limits the supply of nutrients from subsurface to the surface which leads to a decrease in Chl-a. On the other hand, at SPS this mechanism could benefit phytoplankton communities whose growth is limited by the light availability and intense vertical mixing. Fil: Risaro, Daniela Belén. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.

The extent to which the ongoing decline in Arctic sea ice affects mid-latitude climate has received great attention and polarised opinions. The basic issue is whether the inter-annual variability in Arctic sea ice is the cause of, or the response to, variability in mid-latitude atmospheric circulation. A recent paper by Mori et al. (M19) claims to have reconciled previous conflicting studies by showing that a consistent mid-latitude climate response to inter-annual sea-ice anomalies can be identified in both the ERA-Interim reanalysis, taken as observations, and in an ensemble of atmosphere-only (AMIP) climate model simulations. We here demonstrate that such a conclusion cannot be drawn, due to issues with the interpretation of the maximum covariance analysis performed. After applying the M19 approach to the output from a simple statistical model, we conclude that a predominant atmospheric forcing of the sea-ice variability, rather than the converse, is the most plausible explanation of the results presented in M19.