scholarly journals On the Role of Temperature and Salinity Data Assimilation to Constrain a Coupled Physical–Biogeochemical Model in the Baltic Sea

2016 ◽  
Vol 46 (3) ◽  
pp. 713-729 ◽  
Author(s):  
Weiwei Fu
Keyword(s):  
Data Assimilation ◽  
Baltic Sea ◽  
Mixed Layer ◽  
Biogeochemical Model ◽  
The Baltic Sea ◽  
Physical Data ◽  
Salinity Data ◽  
The Mean ◽  
The Baltic

AbstractA three-dimensional variational data assimilation (3DVAR) method is implemented in a coupled physical–biogeochemical (CPB) model in the Baltic Sea. This study carries out a 10-yr assimilation experiment with satellite sea surface temperature (SST) and observed in situ temperature (T) and salinity (S) profiles. The impact of the assimilation is assessed with the focus on how the biogeochemical model responds to the improved hydrodynamics. The assimilation of temperature and salinity data yields considerable improvements in the physical model. On a basin scale, the mean bias of SST, T, S, and mixed layer depth (MLD) is decreased by 0.18°C (57%), 0.31°C (49%), 0.34 psu (43%), and 1.8 m (43%), respectively. More importantly, the biogeochemical simulation is improved in response to the physical data assimilation. Compared with in situ observations, the mean biases of chlorophyll a (Chl), dissolved inorganic nitrogen (DIN) and phosphorus (DIP) are decreased by 0.09 mg m−3 (15.5%), 0.19 mmol m−3 (9%), and 0.15 mmol m−3 (23%). Physical data assimilation also improves the simulated variability of Chl, DIN, and DIP and their correlations with observation. Compared with satellite observations, the mean bias of surface chlorophyll is reduced by 0.10–0.32 mg m−3 especially in the Skagerrak–Kattegat area and Bornholm basin. The decrease of total Chl change is caused by different mechanisms for winter and summer. While the deepened mixed layer acts as a dilution factor in winter, strengthened stratification agrees well with the decrease of chlorophyll in summer. In the vertical, relatively large changes of DIN and DIP occur below 60 m, which corresponds to the mean permanent halocline depth (~60–80 m) of the Baltic Sea.

scholarly journals A 20-year reanalysis experiment in the Baltic Sea using three-dimensional variational (3DVAR) method

Ocean Science ◽  
2012 ◽  
Vol 8 (5) ◽  
pp. 827-844 ◽  
Author(s):  
W. Fu ◽  
J. She ◽  
M. Dobrynin
Keyword(s):  
Baltic Sea ◽  
Mixed Layer ◽  
Tide Gauge ◽  
Mixed Layer Depth ◽  
Three Dimensional ◽  
Stable Model ◽  
Layer Depth ◽  
The Baltic Sea ◽  
The Mean ◽  
The Baltic

Abstract. A 20-year retrospective reanalysis of the ocean state in the Baltic Sea is constructed by assimilating available historical temperature and salinity profiles into an operational numerical model with three-dimensional variational (3DVAR) method. To determine the accuracy of the reanalysis, the authors present a series of comparisons to independent observations on a monthly mean basis. In the reanalysis, temperature (T) and salinity (S) fit better with independent measurements than the free run at different depths. Overall, the mean biases of temperature and salinity for the 20 year period are reduced by 0.32 °C and 0.34 psu, respectively. Similarly, the mean root mean square error (RMSE) is decreased by 0.35 °C for temperature and 0.3 psu for salinity compared to the free run. The modeled sea surface temperature, which is mainly controlled by the weather forcing, shows the least improvements due to sparse in situ observations. Deep layers, on the other hand, witness significant and stable model error improvements. In particular, the salinity related to saline water intrusions into the Baltic Proper is largely improved in the reanalysis. The major inflow events such as in 1993 and 2003 are captured more accurately as the model salinity in the bottom layer is increased by 2–3 psu. Compared to independent sea level at 14 tide gauge stations, the correlation between model and observation is increased by 2%–5%, while the RMSE is generally reduced by 10 cm. It is found that the reduction of RMSE comes mainly from the reduction of mean bias. In addition, the changes in density induced by the assimilation of T/S contribute little to the barotropic transport in the shallow Danish Transition zone. The mixed layer depth exhibits strong seasonal variations in the Baltic Sea. The basin-averaged value is about 10 m in summer and 30 m in winter. By comparison, the assimilation induces a change of 20 m to the mixed layer depth in deep waters and wintertime, whereas small changes of about 2 m occur in summer and shallow waters. It is related to the strong heating in summer and the dominant role of the surface forcing in shallow water, which largely offset the effect of the assimilation.

scholarly journals A 20-yr reanalysis Experiment in the Baltic Sea Using three Dimensional Variational (3DVAR) method

2012 ◽  
Vol 9 (3) ◽  
pp. 1933-1971
Author(s):  
W. Fu ◽  
J. She ◽  
M. Dobrynin
Keyword(s):  
Baltic Sea ◽  
Mixed Layer ◽  
Mixed Layer Depth ◽  
Three Dimensional ◽  
Model Error ◽  
Layer Depth ◽  
The Baltic Sea ◽  
Baltic Proper ◽  
The Mean ◽  
The Baltic

Abstract. A 20-year retrospective reanalysis of the ocean state in the Baltic Sea is constructed using three dimensional variational (3DVAR) data assimilation combining an operational numerical model with available historical temperature (T) and salinity (S) profiles. To determine the accuracy of the reanalysis, the authors present a series of comparisons with independent observations on a monthly mean basis. The performance of the assimilation in deep/shallow waters is investigated. With assimilation, temperature and salinity in the reanalysis fit better than the free run with independent measurements at different depths. Overall, the mean biases of temperature and salinity are reduced by 0.32 °C and 0.34 psu, respectively. Similarly, the mean root mean square error (RMSE) of the reanalysis is decreased by 0.35 °C and 0.3 psu compared to the free run. In space, the model error is inhomogeneous and strongly steered by the model error dynamics. Seasonally varying error of the modeled sea surface temperature is mainly controlled by the weather forcing, and shows the least improvements due to sparse observations. Deep layers, on the other hand, witness significant and stable model error improvements. In particular, the salinity related to saline water intrusions into the Baltic Proper is largely improved in the reanalysis. The major inflow events such as in 1993 and 2003 are captured more accurately in the reanalysis as the model salinity in the bottom layer is increased by 2–3 psu. Sea level is also improved due to an improved density field. The correlation between model and observation is increased by 2 %–5 %, and the RMSE is generally reduced by 10 cm in the reanalysis compared to the free run. The reduction of RMSE is mainly due to the reduction of mean bias. Assimilation of T/S contributes little to the barotropic transport in the shallow Danish Transition zone. The mixed layer depth exhibits strong seasonal variations in the Baltic Sea. The basin-averaged value is about 10 m in summer and 30 m in winter. In addition, assimilation of T/S profiles results in changes of about 20 m for the mixed layer depth in the Baltic Proper region in winter. Comparisons of mixed layer depth show that the assimilation induces more changes in deep water of winter time whereas the mixed layer depth is changed only about 2 m in summer time and shallow waters. One reason could be that the effect of the assimilation is counterbalanced by the effect of heating in summer and the dominant role of the surface forcing in shallow water. The significant impact in deep waters suggests that the T/S assimilation mainly adjusts the baroclinic transport by redistributing the density field.

scholarly journals In-Situ Evaluation of the Protectivity of Coatings Applied to Metal Cultural Artefacts Using Non-Destructive Electrochemical Measurements

2021 ◽  
Vol 2 (1) ◽  
pp. 120-132
Author(s):  
Douglas J. Mills ◽  
Katarzyna Schaefer ◽  
Tomasz Wityk
Keyword(s):  
Baltic Sea ◽  
Electrochemical Noise ◽  
Organic Coating ◽  
Noise Measurement ◽  
The Baltic Sea ◽  
Coating Type ◽  
The Baltic ◽  
Non Destructive ◽  
Electrolytic Resistance

Electrochemical Noise Measurement (ENM) and DC electrolytic resistance measurement (ERM) can be used to assess the level of protectiveness provided by an organic coating (paint or varnish) to the underlying metal. These techniques also have applicability to the thinner, transparent type of coatings used to protect archaeological artefacts. Two studies are presented here demonstrating how ERM and ENM techniques can be applied in artefact preservation. The similarity of the techniques, both of which are a measure of resistance, means results can be considered to be analogous. The first study investigated the use of ERM to determine the protection levels provided by typical coatings in order to develop a database of coating type and application for objects, for specific environments. The second study used ENM to evaluate coatings which had been applied to historic artefacts recovered from shipwrecks in the Baltic Sea and displayed inside the museum or kept in the museum store area. The studies showed the usefulness of both techniques for determining the level of protection of a coating and how a better performing coating can be specified if a pre-existing coating on an artefact has been found to be unsuitable.

scholarly journals Assessment of a physical-biogeochemical coupled model system for operational service in the Baltic Sea

Ocean Science ◽  
2012 ◽  
Vol 8 (4) ◽  
pp. 683-701 ◽  
Author(s):  
Z. Wan ◽  
J. She ◽  
M. Maar ◽  
L. Jonasson ◽  
J. Baasch-Larsen
Keyword(s):  
Baltic Sea ◽  
Inorganic Nitrogen ◽  
Biogeochemical Model ◽  
Observation Data ◽  
Model Assessment ◽  
Model Errors ◽  
The Baltic Sea ◽  
Statistical Measures ◽  
The Baltic ◽  
Operational Service

Abstract. Thanks to the abundant observation data, we are able to deploy the traditional point-to-point comparison and statistical measures in combination with a comprehensive model validation scheme to assess the skills of the biogeochemical model ERGOM in providing an operational service for the Baltic Sea. The model assessment concludes that the operational products can resolve the main observed seasonal features for phytoplankton biomass, dissolved inorganic nitrogen, dissolved inorganic phosphorus and dissolved oxygen in euphotic layers as well as their vertical profiles. This assessment reflects that the model errors of the operational system at the current stage are mainly caused by insufficient light penetration, excessive organic particle export downward, insufficient regional adaptation and some from improper initialization. This study highlights the importance of applying multiple schemes in order to assess model skills rigidly and identify main causes for major model errors.

scholarly journals Evaluation of Sentinel-3A OLCI Products Derived Using the Case-2 Regional CoastColour Processor over the Baltic Sea

Sensors ◽  
2019 ◽  
Vol 19 (16) ◽  
pp. 3609 ◽  
Author(s):  
Kyryliuk ◽  
Kratzer
Keyword(s):  
Remote Sensing ◽  
Baltic Sea ◽  
Attenuation Coefficient ◽  
Secchi Depth ◽  
Local Algorithm ◽  
The Baltic Sea ◽  
In Situ Data ◽  
The Baltic ◽  
Level 2

In this study, the Level-2 products of the Ocean and Land Colour Instrument (OLCI) data on Sentinel-3A are derived using the Case-2 Regional CoastColour (C2RCC) processor for the SentiNel Application Platform (SNAP) whilst adjusting the specific scatter of Total Suspended Matter (TSM) for the Baltic Sea in order to improve TSM retrieval. The remote sensing product “kd_z90max” (i.e., the depth of the water column from which 90% of the water-leaving irradiance are derived) from C2RCC-SNAP showed a good correlation with in situ Secchi depth (SD). Additionally, a regional in-water algorithm was applied to derive SD from the attenuation coefficient Kd(489) using a local algorithm. Furthermore, a regional in-water relationship between particle scatter and bench turbidity was applied to generate turbidity from the remote sensing product “iop_bpart” (i.e., the scattering coefficient of marine particles at 443 nm). The spectral shape of the remote sensing reflectance (Rrs) data extracted from match-up stations was evaluated against reflectance data measured in situ by a tethered Attenuation Coefficient Sensor (TACCS) radiometer. The L2 products were evaluated against in situ data from several dedicated validation campaigns (2016–2018) in the NW Baltic proper. All derived L2 in-water products were statistically compared to in situ data and the results were also compared to results for MERIS validation from the literature and the current S3 Level-2 Water (L2W) standard processor from EUMETSAT. The Chl-a product showed a substantial improvement (MNB 21%, RMSE 88%, APD 96%, n = 27) compared to concentrations derived from the Medium Resolution Imaging Spectrometer (MERIS), with a strong underestimation of higher values. TSM performed within an error comparable to MERIS data with a mean normalized bias (MNB) 25%, root-mean square error (RMSE) 73%, average absolute percentage difference (APD) 63% n = 23). Coloured Dissolved Organic Matter (CDOM) absorption retrieval has also improved substantially when using the product “iop_adg” (i.e., the sum of organic detritus and Gelbstoff absorption at 443 nm) as a proxy (MNB 8%, RMSE 56%, APD 54%, n = 18). The local SD (MNB 6%, RMSE 62%, APD 60%, n = 35) and turbidity (MNB 3%, RMSE 35%, APD 34%, n = 29) algorithms showed very good agreement with in situ data. We recommend the use of the SNAP C2RCC with regionally adjusted TSM-specific scatter for water product retrieval as well as the regional turbidity algorithm for Baltic Sea monitoring. Besides documenting the evaluation of the C2RCC processor, this paper may also act as a handbook on the validation of Ocean Colour data.

scholarly journals Nutrient transports in the Baltic Sea – results from a 30-year physical–biogeochemical reanalysis

2017 ◽  
Vol 14 (8) ◽  
pp. 2113-2131 ◽  
Author(s):  
Ye Liu ◽  
H. E. Markus Meier ◽  
Kari Eilola
Keyword(s):  
Baltic Sea ◽  
Cross Sections ◽  
Ocean Model ◽  
Optimal Interpolation ◽  
Nutrient Concentrations ◽  
Biogeochemical Model ◽  
The Baltic Sea ◽  
Gulf Of Riga ◽  
Baltic Proper ◽  
The Baltic

Abstract. Long-term oxygen and nutrient transports in the Baltic Sea are reconstructed using the Swedish Coastal and Ocean Biogeochemical model (SCOBI) coupled to the Rossby Centre Ocean model (RCO). Two simulations with and without data assimilation covering the period 1970–1999 are carried out. Here, the weakly coupled scheme with the Ensemble Optimal Interpolation (EnOI) method is adopted to assimilate observed profiles in the reanalysis system. The reanalysis shows considerable improvement in the simulation of both oxygen and nutrient concentrations relative to the free run. Further, the results suggest that the assimilation of biogeochemical observations has a significant effect on the simulation of the oxygen-dependent dynamics of biogeochemical cycles. From the reanalysis, nutrient transports between sub-basins, between the coastal zone and the open sea, and across latitudinal and longitudinal cross sections are calculated. Further, the spatial distributions of regions with nutrient import or export are examined. Our results emphasize the important role of the Baltic proper for the entire Baltic Sea, with large net transport (export minus import) of nutrients from the Baltic proper into the surrounding sub-basins (except the net phosphorus import from the Gulf of Riga and the net nitrogen import from the Gulf of Riga and Danish Straits). In agreement with previous studies, we found that the Bothnian Sea imports large amounts of phosphorus from the Baltic proper that are retained in this sub-basin. For the calculation of sub-basin budgets, the location of the lateral borders of the sub-basins is crucial, because net transports may change sign with the location of the border. Although the overall transport patterns resemble the results of previous studies, our calculated estimates differ in detail considerably.

scholarly journals Sensitivity of oxygen dynamics in the water column of the Baltic Sea to external forcing

Ocean Science ◽  
2010 ◽  
Vol 6 (2) ◽  
pp. 461-474 ◽  
Author(s):  
S. Miladinova ◽  
A. Stips
Keyword(s):  
Baltic Sea ◽  
Transport Model ◽  
Meteorological Data ◽  
Biogeochemical Model ◽  
Physical Factors ◽  
Observation Data ◽  
Intermediate Water ◽  
The Baltic Sea ◽  
The Baltic ◽  
Oxygen Dynamics

Abstract. A 1-D biogeochemical/physical model of marine systems has been applied to study the oxygen cycle in four stations of different sub-basins of the Baltic Sea, namely, in the Gotland Deep, Bornholm, Arkona and Fladen. The model consists of the biogeochemical model of Neumann et al. (2002) coupled with the 1-D General Ocean Turbulence Model (GOTM). The model has been forced with meteorological data from the ECMWF reanalysis project for the period 1998–2003, producing a six year hindcast which is validated with datasets from the Baltic Environmental Database (BED) for the same period. The vertical profiles of temperature and salinity are relaxed towards both profiles provided by 3-D simulations of General Estuarine Transport Model (GETM) and observed profiles from BED. Modifications in the parameterisation of the air-sea oxygen fluxes have led to a significant improvement of the model results in the surface and intermediate water layers. The largest mismatch with observations is found in simulating the oxygen dynamics in the Baltic Sea bottom waters. The model results demonstrate the good capability of the model to predict the time-evolution of the physical and biogeochemical variables at all different stations. Comparative analysis of the modelled oxygen concentrations with respect to observation data is performed to distinguish the relative importance of several factors on the seasonal, interannual and long-term variations of oxygen. It is found that natural physical factors, like the magnitude of the vertical turbulent mixing, wind speed and the variation of temperature and salinity fields are the major factors controlling the oxygen dynamics in the Baltic Sea. The influence of limiting nutrients is less pronounced, at least under the nutrient flux parameterisation assumed in the model.

CLOUDINESS IN THE POLISH COASTAL ZONE OF THE BALTIC SEA AND CONDITIONS FOR RECREATION

2017 ◽  
Vol 45 ◽  
pp. 51-63
Author(s):  
Czesław Koźmiński ◽  
Bożena Michalska
Keyword(s):  
Baltic Sea ◽  
Coastal Zone ◽  
Temporal Variations ◽  
The Baltic Sea ◽  
Summer Half ◽  
The Mean ◽  
Bioclimatic Conditions ◽  
The Baltic ◽  
Time Specific

Purpose. Determination of size, variability and gradient of cloudiness on the Polish coast of the Baltic sea during the summer half-year and identification of zones with variable suitability for recreation due to cloudiness. Method. The research is based on daily values of cloudiness in the warm half-year (April-September) recorded on a scale from 0 to 8 octants, obtained from six meteorological stations located on the Polish coast of the Baltic sea during the period 2000–2016. Methods of linear regression were used in the analysis of temporal variations of cumulative monthly deviations in cloudiness for consecutive years from the mean multiannual value. In terms of recreational suitability, days were categorised into four classes according to cloudiness. Three zones of varying conditions for recreation were identified. Results. The essential characteristic of cloudiness on the Polish coast of the Baltic sea is very high variability from one day to another and the resulting change in the value of solar radiation, which, consequently affects bioclimatic stimuli. Cumulative deviations of monthly cloudiness values from the mean multiannual value show a decrease in cloudiness in April, June and July, and an increase in the remaining months of the warm half-year. It is possible to distinguish three periods regarding increased frequency of clear and moderately clear weather lasting continuously for at least 3 and 5 days on the coastal zone in summer. The Polish coast of the Baltic sea is marked by three zones of varying conditions for recreation due to cloudiness in the summer – moderately favourable, favourable and very favourable. Research and conclusion limitations. Lack of access to time-specific results of cloudiness measurement. Practical implications. The results obtained in the course of this research may be used by individuals as well as the organizers of their stays, and for the purpose of characterisation of bioclimatic conditions of the coast. Originality. In view of the recent climatic changes recorded over the last 30 years, the present research demonstrates the current cloudiness level on the Polish coast of the Baltic sea. Type of research. Presentation of the results of empirical research.

Sign in / Sign up

Export Citation Format

Share Document