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Abstract: The long-term variability of the physical and biochemical structure of oxic and suboxic layers in the Black Sea was studied using a one-dimensional coupled hydrophysical and biogeochemical model. The focus was on the correlation between atmospheric forcing (2 m air temperature and dew point temperature, surface level pressure, surface wind) affected by the North Atlantic Oscillation in and the regional responses. The quality of model performance was demonstrated using observed vertical and temporal distribution of biogeochemical variables. It was shown that during 1960–2000, the long-term variability of simulated winter-mean SST in the Black Sea correlated reasonably well with the variability of 2 m air temperature. Furthermore, the thermal state of the upper ocean impacted largely on the variability of biogeochemical variables, such as oxygen, nitrate and phytoplankton concentration. The tele-connection between North Atlantic Oscillation and Black Sea biogeochemistry was manifested in a different way for the specific time-interval 1960–2000; the corresponding regime shifts were thus associated with the large scale forcing. One such extreme event occurred in 1976 leading to a pronounced shift in the oxygen and hydrogen sulfide state. [Copyright &y& Elsevier]

Abstract: At Aveiro lagoon (Portuguese northwest coast) bivalve contamination with diarrhoetic shellfish poisoning toxins (DSTs), okadaic acid (OA) and dinophysistoxin-2 (DTX2), is a recurrent annual phenomenon seriously affecting seafood safety. The influence of meteorological parameters was studied to understand accumulation of DSTs in mussels, related to the blooming of the causative toxic microalgae, belonging to genus Dinophysis. Two simplified models were useful in predicting the accumulation of DSTs in blue mussels from this lagoon. Either the May river drainage or the rainfall accumulated from January through May could adequately predict the severity of OA accumulated from predation upon Dinophysis acuminata during June/July. In both cases a linear relationship was obtained, with correlation coefficients of 0.85 or greater. Winds with a west direction favour coastal concentration of Dinophysis acuta in Aveiro region. Both OA and DTX2 contamination increased exponentially in September/October with the cumulative number of days with W-wind orientation in the preceding August (correlation coefficients greater than 0.92). This relationship was attributed to the quadratic effect of wind stress on surface currents. August is a transitional month, when the continental runoff effect upon Dinophysis acuminata can still be observed and Dinophysis acuta advection may be promoted by westerly winds occurring in July. The frequency of periods with northerly winds in July can halt accumulation of toxins derived from Dinophysis acuta. [Copyright &y& Elsevier]

Among the numerous processes that govern the functioning of a lake ecosystem, the regime of dissolved oxygen (DO) is of primary importance. The DO content is strongly affected by the temperature regime, mixing conditions and by the duration of the ice-covered period. These are formed due to atmospheric forcing and are, therefore, subject to variations in regional climate. Despite the large amount of data revealing the physical effect on the biological and chemical regimes in lakes, there is still insufficient understanding, both qualitative and quantitative, of how a lake ecosystem would be affected by changes in the lake temperature and mixing conditions due to changes in the atmospheric forcing. Below, the study of shallow lakes' response to climatic changes using the coupled FLake FLakeEco modelling system is presented. The results obtained reveal the extreme vulnerability of the lakes' ecosystems to changes in atmospheric forcing. In 'future' climate the permanent existence of potentially dangerous anaerobic zones in shallow lakes is expected. The projected decreased oxygen concentrations are caused by: (1) the reduced oxygen flux from the atmosphere to the lakes due to increased temperature; and (2) strengthened density stratification of the water columns which would prevent aeration of the near-bottom layers. [ABSTRACT FROM AUTHOR]

In this paper we present new data from ship-based measurements and two-year observations from moorings in the Laptev Sea along with Russian historical data. The observations from the Laptev Sea in 2007 indicate that the bottom water temperatures on the mid-shelf increased by more than 3°C compared to the long-term mean as a consequence of the unusually high summertime surface water temperatures. Such a distinct increase in near-bottom temperatures has not been observed before. Remnants of the relatively warm bottom water occupied the mid-shelf from September 2007 until April 2008. Strong polynya activity during March to May 2007 caused more summertime open water and therefore warmer sea surface temperatures in the Laptev Sea. During the ice-free period in August and September 2007, the prevailing cyclonic atmospheric circulation deflected the freshwater plume of the River Lena to the east, which increased the salinity on the mid-shelf north of the Lena Delta. The resulting weaker density stratification allowed more vertical mixing of the water column during storms in late September and early October, leading to the observed warming of the near-bottom layer in the still ice-free Laptev Sea. In summer and autumn 2008, when the density stratification was stronger and sea surface temperatures were close to the long-term mean, no near-bottom water warming was observed. Warmer water temperatures near the seabed may also impact the stability of the shelf's submarine permafrost. [ABSTRACT FROM AUTHOR]

Considerable interannual differences were observed in river water and sea-ice meltwater inventory values derived from δ18O and salinity data in the Eurasian Basin along the continental margin of the Laptev Sea in the summers of 1993 and 1995, and in the summers of 2005 and 2006 during Nansen and Amundsen Basins Observational system (NABOS) expeditions. The annually different pattern in river and sea-ice meltwater inventories remain closely linked for all of the years studied, which indicates that source regions and transport mechanisms for both river water and sea-ice formation are largely similar over the relatively shallow Laptev Sea Shelf. A simple Ekman trajectory model for surface Lagrangian particles based solely on wind forcing can explain the main features observed between years with significantly different wind patterns and vorticities, and can also explain differences in river water distributions observed for years with a generally similar offshore wind setting. An index based on this simplified trajectory model is rather similar to the vorticity index, but reflects the hydrology on the shelf better for distinctive years. This index is not correlated with the Arctic Oscillation, but rather with a local mode of oscillation, which controls the outflow and distribution of the Eurasian Basin major freshwater source on an annual timescale. [ABSTRACT FROM AUTHOR]

Abstract: The Mediterranean basin features a semi-enclosed sea, where interactions and feedbacks between the atmosphere and the Sea at various temporal and spatial scales play a predominant role in the regional climate. This study analyzes the Mediterranean Sea response in sensitivity experiments conducted by driving the NEMO-MED12 oceanic model in perpetual mode with various atmospheric forcings, all produced by the WRF non-hydrostatic mesoscale atmospheric model, but differing by their resolutions: two horizontal resolutions (20km at basin scale and 6.7km in the North-Western [NWE] area) and two temporal resolutions (daily and three-hourly). The atmospheric fields available from August 1998 to July 1999 are in good agreement with estimates derived from satellite data. The heat budget of the Mediterranean Sea represents an heat loss of 5W/m2 and the annual freshwater budget is −1.04m, in agreement with climatologies. An increase in the spatial resolution in the NWE area modifies the modeled circulation from −10% to +15% for the SST, from −30% to +50% for the SSS, from −10% to +30% for the MLD and from −10% to +30% for the EKE in surface. The increase in the wind speed with a better chanelling by the land orography enhances in particular the oceanic convection process in the NWE area. On the other hand, the increase in the temporal resolution reduces the convection process, because of the diurnal restratification of the oceanic upper layer. It also reduces the surface parameters high-frequency variability, whereas it increases the EKE values in surface, due to the rapid response to the wind. [Copyright &y& Elsevier]

The article presents a study on the winter-mean sea surface temperature's (SST) long-term variability in Black and Aegean Seas and its correlation with several atmospheric forcing. It states that satellite and reanalysis data from 1982 to 2004 were used examine the correlation with the atmospheric forcing which include surface air temperature (SAT). Results show that SST variability is correlated with the SAT variability while SAT is correlated with the meridional component of the surface wind.

Abstract: We develop, calibrate and test a dataset intended to drive global ocean hindcasts simulations of the last five decades. This dataset provides surface meteorological variables needed to estimate air-sea fluxes and is built from 6-hourly surface atmospheric state variables of ERA40. We first compare the raw fields of ERA40 to the CORE.v1 dataset of , used here as a reference, and discuss our choice to use daily radiative fluxes and monthly precipitation products extracted from satellite data rather than their ERA40 counterparts. Both datasets lead to excessively high global imbalances of heat and freshwater fluxes when tested with a prescribed climatological sea surface temperature. After identifying unrealistic time discontinuities (induced by changes in the nature of assimilated observations) and obvious global and regional biases in ERA40 fields (by comparison to high quality observations), we propose a set of corrections. Tropical surface air humidity is decreased from 1979 onward, representation of Arctic surface air temperature is improved using recent observations and the wind is globally increased. These corrections lead to a significant decrease of the excessive positive global imbalance of heat. Radiation and precipitation fields are then submitted to a small adjustment (in zonal mean) that yields a near-zero global imbalance of heat and freshwater. A set of 47-year-long simulations is carried out with the coarse-resolution (2°×2°) version of the NEMO OGCM to assess the sensitivity of the model to the proposed corrections. Model results show that each of the proposed correction contributes to improve the representation of central features of the global ocean circulation. [Copyright &y& Elsevier]

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

Abstract: High, small-scale SST variability (6 °C over 5–10 km) observed South of Martha''s Vineyard during the low-wind component of the Coupled Boundary Layers Air–Sea Transfer (CBLAST-Low) oceanographic field program in August 2003 is investigated using the Navy Coastal Ocean Model (NCOM), with atmospheric forcing provided by the Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS®). 1 [1] COAMPS® is a registered trademark of the Naval Research Laboratory. The ocean model includes tidal boundary forcing by the eight major tidal constituents, which is superimposed on the non-tidal lateral boundary conditions obtained from the 1/8° global NCOM real-time hindcast. The simulation is conducted with a high-resolution, 200-m grid, with bathymetry from the NGDC 3-arc-second Coastal Relief Model. The COAMPS fields, tidal forcing and NCOM results are evaluated with the CBLAST-Low observations and previous results. Both the simulation and observation analyses reveal that SST variability south of Martha''s Vineyard is significant on August 18 and 25 and is strongly related to the cooling events on August 17 to 18 and August 24 to 25. The northeast winds passing through Muskeget Channel generate sharp horizontal SST gradients on August 18 by accelerating the westward transport of cold water from the cold, tidally-mixed Nantucket Shoals and by wind-induced upwelling and surface-cooling-induced vertical mixing. The mechanism of SST change on August 25 is differentiated from the change on August 18 by the northwest winds being unfavorable to the westward transport of cold water. The SST cooling on August 25 is mainly caused by local vertical mixing induced by heat lost. [Copyright &y& Elsevier]

Abstract: The relationship between various atmospheric variables at the sea surface and climatological monthly means of sea surface temperature (SST) is investigated over the global ocean. The goal is to quantify the change in SST that results solely from variations in a particular atmospheric variable. This is accomplished using a series of numerical simulations from an atmospherically-forced ocean general circulation model (OGCM). It is first demonstrated that SST variations at all latitudes are generally strongly and positively correlated with increases in near-surface air temperature, and vapor mixing ratio and net shortwave radiation at the sea surface, while they are often moderately and negatively correlated with increases in near-surface wind speed. There is only a weak and negative relationship between variations in SST and those in net longwave radiation at the sea surface. Variations in the net shortwave radiation and vapor mixing ratio are found to have more influence in driving the seasonal cycle of SST than other atmospheric variables. Global averages of slope values from the least squares fit indicate that a 1°C change in air temperature results in ≈0.2°C change in SST. Similarly, a 1gkg−1 change in vapor mixing ratio gives ≈0.4°C change in SST, and 10Wm−2 change in shortwave (longwave) radiation results in ≈0.13°C (≈0.07°C) change in SST. All these values vary regionally, and are neither constant nor in the same direction everywhere. In addition, some atmospheric variables are already correlated to each other. Therefore, a fractional factorial design which involves the joint effects of all atmospheric variables on SST at the same time is further applied. Results from the factorial design are somewhat consistent with the simple linear regression analysis, in that a 2°C increase in air temperature can typically give an increase in SST, generally ranging between 0.5 and 0.8°C over the global ocean. [Copyright &y& Elsevier]

Abstract: There are two ways of external forcing of the lower ionosphere, the region below an altitude of about 100km: (1) From above, which is directly or indirectly of solar origin. (2) From below, which is directly or indirectly of atmospheric origin. The external forcing of solar origin consists of two general factors – solar ionizing radiation variability and space weather. The solar ionization variability consist mainly from the 11-year solar cycle, the 27-day solar rotation and solar flares, strong flares being very important phenomenon in the daytime lower ionosphere due to the enormous increase of the solar X-ray flux resulting in temporal terminating of MF and partly LF and HF radio wave propagation due to heavy absorption of radio waves. Monitoring of the sudden ionospheric disturbances (SIDs – effects of solar flares in the lower ionosphere) served in the past as an important tool of monitoring the solar activity and its impacts on the ionosphere. Space weather effects on the lower ionosphere consist of many different but often inter-related phenomena, which govern the lower ionosphere variability at high latitudes, particularly at night. The most important space weather phenomenon for the lower ionosphere is strong geomagnetic storms, which affect substantially both the high- and mid-latitude lower ionosphere. As for forcing from below, it is caused mainly by waves in the neutral atmosphere, i.e. planetary, tidal, gravity and infrasonic waves. The most important and most studied waves are planetary and gravity waves. Another channel of the troposphere coupling to the lower ionosphere is through lightning-related processes leading to sprites, blue jets etc. and their ionospheric counterparts. These phenomena occur on very short time scales. The external forcing of the lower ionosphere has observationally been studied using predominantly ground-based methods exploiting in various ways the radio wave propagation, and by sporadic rocket soundings. All the above phenomena are briefly mentioned and some of them are treated in more detail. [Copyright &y& Elsevier]

Abstract: Coordinated Ocean-ice Reference Experiments (COREs) are presented as a tool to explore the behaviour of global ocean-ice models under forcing from a common atmospheric dataset. We highlight issues arising when designing coupled global ocean and sea ice experiments, such as difficulties formulating a consistent forcing methodology and experimental protocol. Particular focus is given to the hydrological forcing, the details of which are key to realizing simulations with stable meridional overturning circulations. The atmospheric forcing from [Large, W., Yeager, S., 2004. Diurnal to decadal global forcing for ocean and sea-ice models: the data sets and flux climatologies. NCAR Technical Note: NCAR/TN-460+STR. CGD Division of the National Center for Atmospheric Research] was developed for coupled-ocean and sea ice models. We found it to be suitable for our purposes, even though its evaluation originally focussed more on the ocean than on the sea-ice. Simulations with this atmospheric forcing are presented from seven global ocean-ice models using the CORE-I design (repeating annual cycle of atmospheric forcing for 500 years). These simulations test the hypothesis that global ocean-ice models run under the same atmospheric state produce qualitatively similar simulations. The validity of this hypothesis is shown to depend on the chosen diagnostic. The CORE simulations provide feedback to the fidelity of the atmospheric forcing and model configuration, with identification of biases promoting avenues for forcing dataset and/or model development. [Copyright &y& Elsevier]

Abstract: Bulk heat flux parameterization is an increasingly popular technique for forcing non-coupled ocean models. If sea surface temperature (SST) from the model is colder (warmer) than observed, then the net heat flux will be higher (lower) than observed; thus, bulk parameterizations tend to keep model SST close to observational SST on long time scales. However, bulk parameterizations imply neither strong damping of SST variability nor strong relaxation to near-surface (e.g., at 10 m) air temperature (T a). This is demonstrated using SST simulations from a 0.72°×0.72° cos(lat) (longitude×latitude) resolution global HYbrid Coordinate Ocean Model (HYCOM) that does not include assimilation of any SST data or explicit relaxation to any SST climatology, but does use bulk heat fluxes. Results are discussed when climatological wind and thermal atmospheric forcing for HYCOM are constructed from three different archived numerical weather prediction (NWP) products: (1) the European Centre for Medium-Range Weather Forecasts (ECMWF) 15-year Re-Analysis during 1979–1993 (ERA-15), (2) ECMWF 40-year Re-Analysis (ERA-40) during 1979–2002, and (3) the Common Ocean Reference Experiment Corrected Normal Year forcing version 1.0 (CORE-CNY) based on the National Centers for Environmental Prediction (NCEP) re-analysis which spans 1948–2002. To investigate the implications of the bulk heat flux approach as relaxation to SST and T a, HYCOM SST simulations are used to demonstrate that model SST errors with respect to the National Oceanic Atmospheric Administration (NOAA) SST climatology do not look like T a −SST fields from NWP products. Such a result is confirmed for all simulations forced with ERA-15, ERA-40 and CORE-CNY, separately. Overall, global averages of mean HYCOM SST error are 0.2 °C (1.5 °C), 0.4 °C (1.7 °C) and 0.6 °C (2.3 °C) with respect to NOAA SST (NWP T a) climatology when the model uses atmospheric forcing from ERA-15, ERA-40 and CORE-CNY, respectively. [Copyright &y& Elsevier]

Abstract: Ocean circulation influences nearly all aspects of the marine ecosystem. This study describes the water circulation patterns on time scales from hours to years across Torres Strait and adjacent gulfs and seas, including the north of the Great Barrier Reef. The tridimensional circulation model incorporated realistic atmospheric and oceanographic forcing, including winds, waves, tides, and large-scale regional circulation taken from global model outputs. Simulations covered a hindcast period of 8 years (i.e. 01/03/1997–31/12/2004), allowing the tidal, seasonal, and interannual flow characteristics to be investigated. Results indicated that the most energetic current patterns in Torres Strait were strongly dominated by the barotropic tide and its spring-neap cycle. However, longer-term flow through the strait was mainly controlled by prevailing winds. A dominant westward drift developed in summer over the southeasterly trade winds season, which then weakened and reversed in winter over the northwesterly monsoon winds season. The seasonal flow through Torres Strait was strongly connected to the circulation in the north of the Great Barrier Reef, but showed little connectivity with the coastal circulation in the Gulf of Papua. Interannual variability in Torres Strait was highest during the monsoon period, reflecting variability in wind forcing including the timing of the monsoon. The characteristics of the circulation were also discussed in relation to fine sediment transport. Turbidity level in Torres Strait is expected to peak at the end of the monsoon, while it is likely to be at a low at the end of the trade season, eventually leading to a critically low bottom light level which constitutes a severe risk of seagrass dieback. [Copyright &y& Elsevier]

Abstract: The surface salinity response to changes of various external forcings and model parameters is investigated in a regional 1/3° configuration of the NEMO-OPA model implemented over the eastern North-Atlantic subtropical Ocean. Fourteen realistic climatological simulations are run. By default, neither relaxation to climatological surface salinity nor temperature is included. Forcing fields and parameters expected to impact the surface salinity are modified. These include: the wind stress, the surface temperature, wind speed and relative humidity entering the bulk calculation for sensible and latent heat fluxes, the precipitation, the data specified at open boundaries, the lateral viscosity operator, the salt lateral diffusivity, the vertical mixing scheme, the on/off switch of the double diffusion parameterization, the river runoffs and the SSS/SST restoring terms. The SSS standard deviation over this ensemble of model simulations is of the order of 0.1psu, which is also the order of the annual cycle of the surface salinity field in this area. In this experimental framework, the wind stress is found to have the largest impact on the model SSS, both in terms of mean field and annual variability. The sensitivity to the precipitation, atmospheric temperature, open boundary external data, and to the relaxation to climatological SSS and SST, is also significant. Of all the model parameterizations, the lateral salt diffusivity is the one associated to the strongest surface salinity model response. This work allows the identification of the main sources of error for model surface salinity. It paves the way for a more comprehensive investigation of SSS model error statistics, which is needed for future data assimilation experiments motivated by the close launch of the new SSS-observing SMOS and Aquarius satellite missions. [Copyright &y& Elsevier]

Ice cover persistence in the lower reaches of the Nemunas River has decreased during the last 150 yr. The variation in the river freeze- and break-up dates is related to climatic variables. The significance of the negative break-up trend exceeds that of the positive freeze-up trend. Low-frequency large-scale atmospheric circulation patterns such as the North Atlantic Oscillation and Arctic Oscillation (NAO/AO) appear to have more influence on the break-up date than on the freeze-up date. Different classification methods applied to the atmospheric patterns prevailing in the early freeze-up events reveal similar results; however, differences arising between classifications are attributable to non-persistent and high frequency patterns. [ABSTRACT FROM AUTHOR]

Abstract: A nearshore wave, tide and current prediction system was demonstrated during the MREA04 Trial in the Portuguese coastal waters near Pinheiro da Cruz during the early spring of 2004. Daily forecasts of regional scale wave and tidal information and nearshore waves and currents were generated in DIOPS utilizing a suite of regional and nearshore models forced with data from meteorological and oceanographic production centers. A limited beach experiment was conducted with three Nortek current meters deployed in the surf zone and a video imagery system to generate 10-min time exposures used to identify the locations of wave breaking. In this study, Delft3D, a coastal hydrodynamic modeling system, capable of simulating hydrodynamic processes due to waves, tides, rivers, winds and coastal currents, is used to predict the nearshore wave and longshore currents near Pinheiro da Cruz. The nearshore bathymetry used in this study was based on LIDAR data collected in February 2000. Delft3D shows mixed results when compared with the measured wave height and nearshore currents. Improved Delft3D results can be achieved in the future if migrating sand bars can be measured and included in the modeling. [Copyright &y& Elsevier]

Abstract: A comparative analysis was conducted on climate variability in four sub-arctic seas: the Sea of Okhotsk, the Bering Sea shelf, the Labrador Sea, and the Barents Sea. Based on data from the NCEP/NCAR reanalysis, the focus was on air–sea interactions, which influence ice cover, ocean currents, mixing, and stratification on sub-seasonal to decadal time scales. The seasonal cycles of the area-weighted averages of sea-level pressure (SLP), surface air temperature (SAT) and heat fluxes show remarkable similarity among the four sub-arctic seas. With respect to variation in climate, all four seas experience changes of comparable magnitude on interannual to interdecadal time scales, but with different timing. Since 2000 warm SAT anomalies were found during most of the year in three of the four sub-arctic seas, with the exception of the Sea of Okhotsk. A seesaw (out of phase) pattern in winter SAT anomalies between the Labrador and the Barents Sea in the Atlantic sector is observed during the past 50 years before 2000; a similar type of co-variability between the Sea of Okhotsk and the Bering Sea shelf in the Pacific is only evident since 1970s. Recent positive anomalies of net heat flux are more prominent in winter and spring in the Pacific sectors, and in summer in the Atlantic sectors. There is a reduced magnitude in wind mixing in the Sea of Okhotsk since 1980, in the Barents Sea since 2000, and in early spring/late winter in the Bering Sea shelf since 1995. Reduced sea-ice areas are seen over three out of four (except the Sea of Okhotsk) sub-arctic seas in recent decades, particularly after 2000 based on combined in situ and satellite observations (HadISST). This analysis provides context for the pan-regional synthesis of the linkages between climate and marine ecosystems. [Copyright &y& Elsevier]

Abstract: Satellite, in situ and reanalysis data for the period of 1950–2005 were used to study the long-term variability of sea surface temperature (SST) in the Black Sea and its connection with the major large-scale atmospheric forcing (air temperature, surface wind and North Atlantic Oscillation — NAO). In contrast to the quasi-regular decadal oscillations of the SST typical for the Northern Atlantic, the pattern of long-term SST variability in the Black Sea is better described as an intermittent periods of SST increase/decrees with the duration of approximately 6–10 years and short (1–2 years) and quite abrupt transitions between them. Confirmed is a known fact of existence of the two major surface wind regimes over the Black Sea i.e., Southern–Western (SW) and Northern–Eastern (NE) and new details on the correlations between the zonal and meridional wind components in each regime are added. A new important finding is that the switch between two regimes occurs quite abruptly at values of NAO index slightly less then zero. It was shown that in weak to moderate positive NAO situation the SW wind regime prevail and wind components are well correlated with the NAO index. The long-term variability of winter-mean SST in the Black Sea is reasonably well correlated with the variability of surface air temperature (SAT), which in turn is highly correlated with the meridional component of surface wind. It is shown that strengthening/weakening of the Southern wind or weakening/strengthening of the Northern wind cause SAT and SST increase/decrease. Finally, a conceptual diagram of NAO impact on the meridional component of the surface wind, SAT and SST is presented. [Copyright &y& Elsevier]

Abstract: The spatial and temporal evolution of the beta-emitting, anthropogenic radionuclide Technetium-99 (99Tc) in the North and Norwegian Seas have been simulated with a regional isopycnic Ocean General Circulation Model (OGCM), forced with realistic, daily averaged atmospheric forcing fields for the period 1975 to 2003. The main source of this soluble radionuclide is the reprocessing plants at Sellafield in the Irish Sea and La Hague on the French coast in the English Channel. The radioactive contaminants follow the general ocean circulation in the area, and are eventually transported northwards along the Norwegian coast heading towards the Arctic Ocean. Comparison with observational time series from two stations along the coast of Norway shows that the model fairly realistically captures both the amplitude and the temporal trend of 99Tc from Sellafield and La Hague. To isolate the effect of changes in the ocean circulation and mixing on the released tracers, idealized tracers with a clock attribution are included for both sources. These idealized tracers measure the age along the pathways of the tracers from the two sources. The age from the Sellafield-derived tracer at the island Hillesøy on the northern coast of Norway is found to be in the range 5–8 years, which is slightly older than previous estimates of the related concept of transit time. A complex pattern of variability is identified, with local and regional atmospheric forcing influencing both the northward tracer flux and the time elapsed since the tracer left the source. [Copyright &y& Elsevier]

Abstract: Within the framework of several local and international programs, a quasi-operational ocean-forecasting system for the Southeastern Mediterranean Sea has been established and evaluated through a series of preoperational tests. The Princeton Ocean Model (POM) is used for simulating and predicting the hydrodynamics while the Wave Model (WAM) is used for predicting surface waves. Both models were set up to allow varying resolution and multiple nesting. In addition, POM was set up to be easily relocatable to allow rapid deployment of the model for any region of interest within the Mediterranean Sea. A common requirement for both models is the need for atmospheric forcing. Both models require time varying wind or wind stress. In addition, the hydrodynamic model requires initial conditions as well as time dependent surface heat fluxes, fresh water flux, and lateral boundary conditions at the open boundaries. Several sources of atmospheric forcing have been assessed based on their availability and their impact on the quality of the ocean models'' forecasts. The various sources include operational forecast centers, other research centers, as well as running an in-house regional atmospheric model. For surface waves, higher spatial and temporal resolution of the winds plays a central role in improving the forecasts in terms of significant wave height and the timing of various high wave events. For the hydrodynamics, using the predicted wind stress and heat fluxes directly from an atmospheric model can potentially produce short range ocean forecasts that are nearly as good as hindcasts forced with gridded atmospheric analyses. Finally, a high-resolution, nested version of the model has shown to be stable under a variety of forcing conditions and time scales, thus indicating the robustness of the selected nesting strategy. For the southeastern corner of the Mediterranean, at forecast lead times of up to 4 days the high-resolution model shows improved skill over the coarser resolution driving model when compared to satellite derived sea surface temperatures. Most of the error appears to be due to the analysis error inherent in the initial conditions. [Copyright &y& Elsevier]

Abstract: The Gulf of Finland is an elongated estuary located in the north-eastern extremity of the Baltic Sea. This semi-enclosed sea-area is subject to heavy sea traffic, and is one of the main risk areas for oil accidents in the Baltic. The continuous development and validation of operational particle drift and oil-spill forecasting systems is thus seen to be essential for this sea-area. Here, the results of a three-day drift experiment in May 2003 are discussed. The field studies were performed using GPS-positioned surface floating buoys. The aim of this paper is to evaluate how well models can reproduce the drift of these buoys. Model simulations, both in forecast and hindcast modes, were carried out by three different 3D hydrodynamic models, the results of which are evaluated by comparing the calculated drifts with observations. These models were forced by HIRLAM (High Resolution Limited Area Model) and ECMWF (European Centre for Medium-Range Weather Forecasts) meteorological forecast fields. The simulated drift of the buoys showed a good agreement with observations even when, during the study period, a rapidly-changing wind situation was observed to affect the investigation area; in this situation the winds turned about 100 degrees in half an hour. In such a case it is a very complicated task to forecast the drifters'' routes: there is a need to regularly update the meteorological forcing fields and to use these regularly-updated fields throughout the simulations. It is furthermore recommended that forecasts should be made using several circulation models and several meteorological forecasts, in order to get an overview of the accuracy of the forecasted drifts and related differences in between the forecasts. [Copyright &y& Elsevier]

Abstract: The seasonal cycles of some atmospheric parameters at Cochin (southwest coast of India) have been studied with a specific emphasis on the role played by them in forcing the seasonal sea level. Equatorward along-shore wind stress as well as equatorward volume transport by coastal currents along the Indian peninsula could play an important role in the sea level low during the premonsoon and southwest monsoon seasons. During postmonsoon season, along-shore wind stress plays no major role in the high sea level whereas this could be due to the poleward volume transport by the coastal along-shore currents. Atmospheric pressure and river discharge do not seem to influence much the sea level during the southwest monsoon period, even though the river discharge during that period is considerable. The sea level was minimal during the southwest monsoon season, when the river discharge was at its annual maximum. The difference between the seasonal march of observed and pressure corrected sea level (CSL) was not significant for the study region. Harmonic analysis of the climatological data on the various parameters revealed that air temperature is the only parameter with a dominance of the semi-annual over the annual cycle. Cross-shore wind stress indicated strong interannual variability whereas relative density showed strong seasonal variability. The climatological seasonal cycles of CSL at eight other tide gauge stations along the west coast of the Indian subcontinent are also examined, to assess the role of various forcings on the seasonal sea level cycle. The signatures of El Nino-Southern Oscillation (ENSO) phenomenon could be seen in some of the parameters (SST, air temperature, atmospheric pressure, along-shore wind stress, relative density and sea level). The signature of ENSO was particularly strong in the case of atmospheric pressure followed by relative density, the variance accounted by the relationship being 47% and 16%, respectively. [Copyright &y& Elsevier]

The response of the Antarctic circumpolar circulation to wind stress variability is studied in a simple model of the Southern Ocean. The model consists of a zonally reentrant channel with mid-ocean barrier, forced by surface heat flux and stochastic wind stress. The MITgcm code is used to solve for temperature, sea level, and the velocity field.The channel transport responds actively to the stochastic wind forcing through the excitation of several eigenmodes. The fundamental basin mode is excited, which has a period of about 20 days. However, the response is dominated by a topographic mode with a period of 3 days. This barotropic mode is related primarily to topographic Rossby waves propagating on the submarine sill, and Kelvin waves propagating westward on the southern boundary. The mode shares characteristics with numerical predictions of normal modes in the Southern Ocean, as well as with recently observed modes of variability around Antarctica, with periods between 1 and 2 days. These results show that both topographic normal modes and Rossby basin modes can play a role in the adjustment of the ACC to high-frequency wind stress variability.The presence of the resonance in the system leads to interesting phase behavior between the wind stress forcing and the ocean transport: for a considerable frequency range, the transport seems to lead the wind stress variability. This shows that the classical notion of transport passively lagging wind forcing is inadequate when eigenmodes are excited. [Copyright &y& Elsevier]

Abstract: The present study of temporal and spatial variations of shore-fast ice in the Kara Sea includes utilization of aircraft observations by the Arctic and Antarctic Research Institute (AARI) from 1953 to 1990, and surface brightness temperature from SSM/I from 1987 to 2001. Analyses of a time series of spatially distributed SSM/I brightness temperatures provide estimates of the shore-fast ice extent. The present work shows spatial distributions of frequencies of shore-fast ice coverage in the Kara Sea for each month, and it gives a time series of its area. The fast ice extent in early spring typically reaches a stable configuration, which falls into one of two different categories (modes) with significantly different area. The smaller of these two modes tends to appear with increased frequency since 1980. This gives, for this period, a negative trend in fast ice area during spring. There is a correlation above 0.5 between the average winter temperature and maximum ice thickness anomalies and fast ice area. Analysis of surface wind data and sea level pressure indicates that wind during winter controls much of the shore-fast ice development. Specially strong westerly and southwesterly winds tend to give a smaller fast ice extent than otherwise. Variations in river discharge tend only to have an observable effect on the ice at the river mouths. [Copyright &y& Elsevier]

Mean temporal circulation at Ormen Lange (OL) off mid-Norway is strongly dominated by the Norwegian Atlantic Current. Tidal effects are weak. Observed events of short peak value in current speed along with peak in temperature close to the seabed at the shelf slope may be driven by strong pressure gradients. That is, strong atmospheric low pressures and/or internal pressure fronts between warmer Atlantic Water (AW) and colder Norwegian Sea Water (NSW). Along the shelf slope at OL there may be steepening of the isopycnals, separating AW and NSW, due to wind generated downwelling and strong Ekman veering during storms or approaching internal density fronts. During such events the density surfaces tend to undershoot their equilibrium level, and as the forcing weakens, the suppressed water may run up along the shelf slope. In this run up phase, peak values in the velocities are often found.Since the atmospheric forcing may be a major forcing mechanism behind the observed events, we have performed a numerical study of the sensitivity of near bottom velocities at OL to the pathway of low pressure disturbances and the strength and the radii of them.The results indicate how depth dependent currents at different locations respond to varying atmospheric forcing, with highest currents close to the surface, time delay of response at greater depths and highest impact of storms passing further out in the Nordic Seas than immediately over OL. [Copyright &y& Elsevier]

We examine the upper ocean thermohaline structure in the southeast Indian Ocean and its temporal variability based on XBT/XCTD observations from four cruises across the Southern Ocean from Fremantle, Australia to Prydz Bay, Antarctica. The transects were occupied in March 1998, November 1998, March 2000 and March 2002. Three major fronts—the subtropical front, subantarctic front and polar front—are clearly identified from our surveys and compared with earlier studies. Particularly, two polar fronts, separated by a few degrees of latitude, appear southeast the Kerguelen Plateau. The primary polar front is characterized by a strong horizontal thermal gradient extending deep in the water column, while the secondary polar front is identified by the 2°C isotherm at Tmin depth and has a relatively shallow frontal expression. Dynamic height across the Antarctic Circumpolar Current (ACC) was calculated for the transects in 2000 and 2002. With a negligible yearly variation in the total transport across the ACC, the higher sample density in 2002 reveals more detailed structure of the ACC: two jets associated with the SAF and primary polar front are embedded within the broad ACC.We find a strong temporal variation in the upper ocean thermal structure in the polar ocean southeast the Kerguelen Plateau. The depths of the mixed layer and Tmin layer increase over time. The mixed layer temperature decreases while the Tmin temperature increases during the same period. In addition, we see an increase from 1998 to 2002 in the length of the ice-free period prior to each XBT/XCTD sampling and surface wind forcing, calculated as the friction velocity cubed during the ice-free period. Our analysis suggests that the longer the ocean is exposed to the atmosphere and the stronger the wind stirring, the more enhanced is the turbulent mixing. This results in a greater mixed layer depth and more entrainment of colder water from the Tmin layer to the mixed layer. This surface forcing also enhances internal diffusive processes that mix the Tmin water with the warmer waters above and below the Tmin layer. The surface forcing is apparently dominant in determining the upper ocean thermal structure in this polar region. [Copyright &y& Elsevier]

In this study, we compare two 1-D mixing parameterizations developed by Gaspar et al. [J. Geophys. Res. C95 (C9) (1990) 16179] (G90) and Large et al. [Rev. Geophys. 32 (1994) 363] (L94), respectively. Both models are tested against drifting Marisonde bouys deployed in the Bay of Biscay during PRECOCE experiment (1997–1998) [Mariette, V., Ratsivalaka, C., Verbe´que V., Leborgne, E., 1999. CAMPAGNE PREOCOCE (PREdiction du comportement des Couches superficielles de l'Oce´an le long des Coˆtes Europe´ennes, Tomes 1, 2 and 3, Rapport EPSHOM/CMO/RE/NP 11 du 31 mai 1999]. Periods of stabilizing and destabilizing conditions are successively examined by using both realistic and schematic dynamical and thermodynamical air–sea fluxes. Schematic conditions applied over one diurnal cycle evidence the relative performance of G90 and L94 parameterizations as a function of surface inputs and stratification. The results obtained from these schematic cases are used to compare the results obtained by G90 and L94 over periods of 2 to 10 weeks along three Marisonde buoy trajectories. The ability of both models to simulate the seasonal thermocline formation in Spring as well as its destruction in Fall is discussed. If the nonlocal parameterization used by L94 is taken in its complete form (including the diapycnal mixing), it allows the mixed-layer deepening in Fall in a more satisfactory way than the local parameterization used by G90. The results obtained in Spring by both models are debatable. [Copyright &y& Elsevier]

Abstract A three-dimensional hydrodynamic model has been used to analyse temporally and spatially resolved circulation patterns in the Baltic Sea with special emphasis on drifting particles representing larval fish. The main purpose of this study was (i) to investigate potential drift patterns of larval fish, (ii) to identify its intra- and inter-annual variability for time periods based on the timing of spawning and (iii) to analyse its seasonal and spatial variability in dependence of the atmospheric forcing conditions. For the time period 1979–1998 temporally and spatially resolved simulated flow fields were used to describe the potential drift from the centre of main reproductive effort of Baltic cod (Gadus morhua ). The results of the model runs demonstrate a general change in circulation pattern from retention during a first decade (1979–1988) to dispersion in the following decade (1989–1998). This increase in dispersion was related to an increase in the variability of the local wind forcing conditions over the Baltic. The more frequent occurrence of dispersion in spring of the recent decade was accompanied by a strong decay in biomass of one of the main larval fish feeding component in the central basin, the calanoid copepod Pseudocalanus elongatus . Larger dispersion of this prey organism may have affected the spatial overlap and thus the contact rates between predator and prey. Hence, this may have resulted in a food limitation for early life stages of Baltic cod and potentially contributed to the pronounced shift in cod peak spawning time from spring to late summer. Early life stages of cod originating from late spawning fish, benefited from a stronger dispersion in late summer and autumn, into shallow coastal areas with higher calanoid abundance. [ABSTRACT FROM AUTHOR]

Abstract Oceanic inflow is estimated to contribute more than 90% of the nutrient input into the North Sea. Variability in the volume, chemical properties, biological content and source of the inflowing water is thus likely to have a considerable effect on North Sea ecosystems. Changes seen in the plankton, and in particular Calanus finmarchicus and Calanus helgolandicus , over the last 40 years as measured by the Continuous Plankton Recorder survey, allow clear periods to be identified that appear to be associated with variability in inflow. Monthly estimates of inflow and outflow across a section between Orkney and Utsira in Norway as well as netflow (sum of Baltic outflow, runoff and Channel inflow), have been derived from runs of the NORWECOM model for two integrated depth intervals: surface to 150 m and >150 m. A comparison is made between the physical model output and plankton results for the period 1958–99. Distinct plankton periods that appear to reflect changing inflow events are discussed in relation to hydrometeorological and earlier plankton studies over approximately the last 100 years. [ABSTRACT FROM AUTHOR]

This project examines the role of local atmospheric forcing during the transition from relatively cold wintertime to relatively warmer springtime temperatures in the northern Middle Atlantic Bight (MAB) region during 1965–1973. A one-dimensional water column model is run for eight consecutive winter seasons with local surface heat flux used as the only external forcing. Historical data from the Nantucket Light Ship, along with modeled radiation estimates for New York and Boston are used for the heat flux calculations. Two model simulations were made for each winter season, allowing for both a qualitative and quantitative comparison of model output with observed regional temperature variability and with observed temperature changes measured at Nantucket Lightship (NLS). Interannual variability (IAV) in local atmospheric heat flux during wintertime is shown to be a dominant factor in determining springtime temperature conditions during the study period. However, the residuals from a regression analysis suggest that advective processes may have contributed to the observed temperature variability, although it is believed that the advective influence is secondary to local surface heat flux in the northern MAB for this study period. [Copyright &y& Elsevier]

We examine the first in situ velocity data collected on the shelf of Southern Brazil. The mooring station with two current meters was deployed at 32°41′S, 51°27′W on March 4, 1997, and recovered on August 2, 1997. Also analyzed are wind data for the same period obtained at a nearby coastal meteorological station. The observed velocity series can be interpreted as a sum of highly variable flow correlated with local wind stress and a “residual” mean current flowing northward along the shore at a few centimetres per second. In winter, the currents observed in the bulk of the water column exhibited a dramatic decrease in magnitude, as compared to the remainder of the series, although there was no similar decay of winds. We hypothesize that this is due to the impact of very stable salinity controlled winter stratification in a narrow subsurface layer because of enhanced river discharges that effectively isolates the deeper layers from atmospheric forcing. The frequency band corresponding to the periods from 2 to 10 days, presumably associated with meteorological forcing, dominated the velocity spectrum. The tidal currents were weak and predominantly diurnal. [Copyright &y& Elsevier]

TELEMAC-2D, a two-dimensional depth-averaged finite element flow model, has been chosen for modelling the hydrodynamics of the Patos Lagoon during the 1998 El Nin˜o event. The model is initially calibrated against measurements carried out between 20 and 29/10/98, and good agreement is achieved between measured and predicted longitudinal velocities. Model validation is carried out by comparing measurements and predictions for one reference station in the estuarine area for the period between 23/05 and 06/06/98. Results indicate an excellent agreement between measurements and predictions, and the model is considered calibrated and validated for the Patos Lagoon hydrodynamics.A study of the Patos Lagoon hydrodynamics under the El Nin˜o extreme conditions shows that the local and non-local wind effects associated with the freshwater discharge at the top of the lagoon promote longitudinal and lateral set-up/set-down mechanisms that influence the circulation. Results indicate that velocities in the lagoon and estuary during the extreme conditions observed in the El Nin˜o period are much stronger than the normal periods.The response of the Patos Lagoon entrance to the local and non-local forcing is studied for the first time in terms of the inflow and outflow of water in the system. Results indicate that during the 1998 El Nin˜o event the non-local forcing dominated, promoting exchanges that represent around 7% of the lagoon initial volume in the simulation. Strong freshwater discharges at the top of the lagoon combined with pressure gradients due to changes in elevation generated by the local and non-local wind favours the predominant seawards flow at the mouth, with outflows in the order of 5000 m3 s−1. The strong outflow observed during the El Nin˜o extreme flow conditions generates huge plumes of freshwater into the adjacent coastal area. [Copyright &y& Elsevier]

The structure of the wind-induced exchange between Indian River Bay, Delaware and the adjacent continental shelf is examined based on current measurements made at the Indian River Inlet which represents the only conduit of exchange between the bay and the coastal ocean. Local wind measurements and sea levels from stations located along the open coast and in the interior of the bay are also obtained. Coastal sea level fluctuations are coherent with winds over periodicities of 2–10 days, with the highest response corresponding to winds aligned along two bands, one broadly centered around the general orientation of the Middle Atlantic Bight coastline between New Jersey and Virginia (040°T), and the other narrowly focused on the direction perpendicular to the local coastline (090°T). Currents in the inlet are also highly coherent with the wind along these two directions, but the high coherence is limited to time scales between 2 and 5 days. Within those time scales the currents in the inlet show largely depth-independent fluctuations which are highly coherent and in quadrature phase with the coastal sea level fluctuations, indicating that the subtidal exchanges in those time scales are principally accomplished by the remote wind effects on the shelf through the impingement of coastal sea level fluctuations at the entrance to the inlet. This coastal pumping effect produces unidirectional inflow throughout the water column under coastal set-up conditions, and outflow occurs under coastal set-down conditions. There is indication that a weaker, but still significant mode of bi-directional exchange also exists in the inlet, with currents in the upper layer fluctuating in opposite directions relative to those in the lower layer. [Copyright &y& Elsevier]

The interannual variability of the Mediterranean (MED) circulation from 1979 to 1993 is studied with a 1°/8×1°/8×1°/8 resolution OGCM. The surface forcing used is 6 hourly ECMWF (European Center for Medium Range Weather Forecast) reanalysis data. Two different periods in the surface forcing and model variability are identified during 1981–1993: the first, Period I (1981–1987) and the second, Period II (1988–1993). Changes in the model response between the two periods are driven by corresponding differences in the surface forcing, which presumably are a result of the decadal scale changes of the Northern Hemisphere (NH) atmospheric regimes, related to the intensification of North Atlantic Oscillation (NAO) at the end of the 1980s.During the second period (1988–1993), the Mediterranean circulation reveals an overall weakening of the kinetic energy in the Western Mediterranean (WMED) basin and significant changes in the structure of circulation in the Eastern basin. In the latter region, the anticyclonic activity increases in the southern Ionian and in the southern area of the mid-Mediterranean Jet. These anticyclonic eddies, present during different years of Period II with variable intensity, have an important impact on the transport of Modified Atlantic Waters (MAW) and Levantine Intermediate Waters (LIW) in the Eastern Mediterranean (EMED). This change of the circulation modified the salinity and the amount of Levantine Intermediate Waters transported towards the Aegean Sea and the Adriatic Sea, which are important factors for deep water formation processes there. These model results are in good agreement with available observational results. The deep water formation event observed in the Aegean Sea [Science 271 (1996) 333] is produced by the model, but at a shallower depth. We interpret this event as the result of circulation changes between Period I and Period II and anomalous surface atmospheric forcing over the Aegean Sea. [Copyright &y& Elsevier]