Black Sea Mixed Layer Sensitivity to Various Wind and Thermal Forcing Products on Climatological Time Scales*

2005 ◽  
Vol 18 (24) ◽  
pp. 5266-5293 ◽  
Author(s):  
A. Birol Kara ◽  
Harley E. Hurlburt ◽  
Alan J. Wallcraft ◽  
Mark A. Bourassa
Keyword(s):  
Black Sea ◽  
Wind Forcing ◽  
Sea Surface ◽  
The Black Sea ◽  
Atmospheric Forcing ◽  
Coastal Regions ◽  
Thermal Forcing ◽  
Model Simulations ◽  
Vector Correlation ◽  
Surface Circulation

Abstract This study describes atmospheric forcing parameters constructed from different global climatologies, applied to the Black Sea, and investigates the sensitivity of Hybrid Coordinate Ocean Model (HYCOM) simulations to these products. Significant discussion is devoted to construction of these parameters before using them in the eddy-resolving (≈3.2-km resolution) HYCOM simulations. The main goal is to answer how the model dynamics can be substantially affected by different atmospheric forcing products in the Black Sea. Eight wind forcing products are used: four obtained from observation-based climatologies, including one based on measurements from the SeaWinds scatterometer on the Quick Scatterometer (QuikSCAT) satellite, and the rest formed from operational model products. Thermal forcing parameters, including solar radiation, are formed from two operational models: the European Centre for Medium-Range Weather Forecasts (ECMWF) and the Fleet Numerical Meteorology and Oceanography Center (FNMOC) Navy Operational Global Atmospheric Prediction System (NOGAPS). Climatologically forced Black Sea HYCOM simulations (without ocean data assimilation) are then performed to assess the accuracy and sensitivity of the model sea surface temperature (SST) and sea surface circulation to these wind and thermal forcing products. Results demonstrate that the model-simulated SST structure is quite sensitive to the wind and thermal forcing products, especially near coastal regions. Despite this sensitivity, several robust features are found in the model SST in comparison to a monthly 9.3-km-resolution satellite-based Pathfinder SST climatology. Annual mean HYCOM SST usually agreed to within ≈±0.2° of the climatology in the interior of the Black Sea for any of the wind and thermal forcing products used. The fine-resolution (0.25° × 0.25°) wind forcing from the scatterometer data along with thermal forcing from NOGAPS gave the best SST simulation with a basin-averaged rms difference value of 1.21°C, especially improving model results near coastal regions. Specifically, atmospherically forced model simulations with no assimilation of any ocean data suggest that the basin-averaged rms SST differences with respect to the Pathfinder SST climatology can vary from 1.21° to 2.15°C depending on the wind and thermal forcing product. The latter rms SST difference value is obtained when using wind forcing from the National Centers for Environmental Prediction (NCEP), a product that has a too-coarse grid resolution of 1.875° × 1.875° for a small ocean basin such as the Black Sea. This paper also highlights the importance of using high-frequency (hybrid) wind forcing as opposed to monthly mean wind forcing in the model simulations. Finally, there are large variations in the annual mean surface circulation simulated using the different wind sets, with general agreement between those forced by the model-based products (vector correlation is usually >0.7). Three of the observation-based climatologies generally yield unrealistic circulation features and currents that are too weak.

A New Solar Radiation Penetration Scheme for Use in Ocean Mixed Layer Studies: An Application to the Black Sea Using a Fine-Resolution Hybrid Coordinate Ocean Model (HYCOM)*

2005 ◽  
Vol 35 (1) ◽  
pp. 13-32 ◽  
Author(s):  
A. Birol Kara ◽  
Alan J. Wallcraft ◽  
Harley E. Hurlburt
Keyword(s):  
Solar Radiation ◽  
Optical Depth ◽  
Black Sea ◽  
Ocean Circulation ◽  
Mixed Layer ◽  
Ocean Model ◽  
The Black Sea ◽  
Atmospheric Forcing ◽  
Model Simulations ◽  
Hybrid Coordinate Ocean Model

Abstract A 1/25° × 1/25° cos(lat) (longitude × latitude) (≈3.2-km resolution) eddy-resolving Hybrid Coordinate Ocean Model (HYCOM) is introduced for the Black Sea and used to examine the effects of ocean turbidity on upper-ocean circulation features including sea surface height and mixed layer depth (MLD) on annual mean climatological time scales. The model is a primitive equation model with a K-profile parameterization (KPP) mixed layer submodel. It uses a hybrid vertical coordinate that combines the advantages of isopycnal, σ, and z-level coordinates in optimally simulating coastal and open-ocean circulation features. This model approach is applied to the Black Sea for the first time. HYCOM uses a newly developed time-varying solar penetration scheme that treats attenuation as a continuous quantity. This scheme includes two bands of solar radiation penetration, one that is needed in the top 10 m of the water column and another that penetrates to greater depths depending on the turbidity. Thus, it is suitable for any ocean general circulation model that has fine vertical resolution near the surface. With this scheme, the optical depth–dependent attenuation of subsurface heating in HYCOM is given by monthly mean fields for the attenuation of photosynthetically active radiation (kPAR) during 1997–2001. These satellite-based climatological kPAR fields are derived from Sea-Viewing Wide Field-of-View Sensor (SeaWiFS) data for the spectral diffuse attenuation coefficient at 490 nm (k490) and have been processed to have the smoothly varying and continuous coverage necessary for use in the Black Sea model applications. HYCOM simulations are driven by two sets of high-frequency climatological forcing, but no assimilation of ocean data is then used to demonstrate the importance of including spatial and temporal varying attenuation depths for the annual mean prediction of upper-ocean quantities in the Black Sea, which is very turbid (kPAR > 0.15 m−1, in general). Results are reported from three model simulations driven by each atmospheric forcing set using different values for the kPAR. A constant solar-attenuation optical depth of ≈17 m (clear water assumption), as opposed to using spatially and temporally varying attenuation depths, changes the surface circulation, especially in the eastern Black Sea. Unrealistic sub–mixed layer heating in the former results in weaker stratification at the base of the mixed layer and a deeper MLD than observed. As a result, the deep MLD off Sinop (at around 42.5°N, 35.5°E) weakens the surface currents regardless of the atmospheric forcing used in the model simulations. Using the SeaWiFS-based monthly turbidity climatology gives a shallower MLD with much stronger stratification at the base and much better agreement with observations. Because of the high Black Sea turbidity, the simulation with all solar radiation absorbed at the surface case gives results similar to the simulations using turbidity from SeaWiFS in the annual means, the aspect of the results investigated in this paper.

Role of suspended matter in controlling beryllium-7 (7Be) in the Black Sea surface layer

2021 ◽  
pp. 103513
Author(s):  
Dmitrii A. Kremenchutskii ◽  
Gennady F. Batrakov ◽  
Illarion I. Dovhyi ◽  
Yury A. Sapozhnikov
Keyword(s):  
Surface Layer ◽  
Black Sea ◽  
Suspended Matter ◽  
Sea Surface ◽  
The Black Sea

scholarly journals Long term trends in the sea surface temperature of the Black Sea

Ocean Science ◽  
2010 ◽  
Vol 6 (2) ◽  
pp. 491-501 ◽  
Author(s):  
G. I. Shapiro ◽  
D. L. Aleynik ◽  
L. D. Mee
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Black Sea ◽  
Sea Surface ◽  
The Black Sea ◽  
The North ◽  
Sst Variability ◽  
Long Term Trends ◽  
Cooling Trend

Abstract. There is growing understanding that recent deterioration of the Black Sea ecosystem was partly due to changes in the marine physical environment. This study uses high resolution 0.25° climatology to analyze sea surface temperature variability over the 20th century in two contrasting regions of the sea. Results show that the deep Black Sea was cooling during the first three quarters of the century and was warming in the last 15–20 years; on aggregate there was a statistically significant cooling trend. The SST variability over the Western shelf was more volatile and it does not show statistically significant trends. The cooling of the deep Black Sea is at variance with the general trend in the North Atlantic and may be related to the decrease of westerly winds over the Black Sea, and a greater influence of the Siberian anticyclone. The timing of the changeover from cooling to warming coincides with the regime shift in the Black Sea ecosystem.

scholarly journals Drivers, mechanisms and long-term variability of seasonal hypoxia on the Black Sea northwestern shelf – is there any recovery after eutrophication?

2013 ◽  
Vol 10 (6) ◽  
pp. 3943-3962 ◽  
Author(s):  
A. Capet ◽  
J.-M. Beckers ◽  
M. Grégoire
Keyword(s):  
Organic Matter ◽  
Spatial Distribution ◽  
Interannual Variability ◽  
Black Sea ◽  
Sea Surface ◽  
The Black Sea ◽  
Northwestern Shelf ◽  
Bottom Waters ◽  
Seasonal Hypoxia ◽  
Bottom Hypoxia

Abstract. The Black Sea northwestern shelf (NWS) is a shallow eutrophic area in which the seasonal stratification of the water column isolates the bottom waters from the atmosphere. This prevents ventilation from counterbalancing the large consumption of oxygen due to respiration in the bottom waters and in the sediments, and sets the stage for the development of seasonal hypoxia. A three-dimensional (3-D) coupled physical–biogeochemical model is used to investigate the dynamics of bottom hypoxia in the Black Sea NWS, first at seasonal and then at interannual scales (1981–2009), and to differentiate its driving factors (climatic versus eutrophication). Model skills are evaluated by a quantitative comparison of the model results to 14 123 in situ oxygen measurements available in the NOAA World Ocean and the Black Sea Commission databases, using different error metrics. This validation exercise shows that the model is able to represent the seasonal and interannual variability of the oxygen concentration and of the occurrence of hypoxia, as well as the spatial distribution of oxygen-depleted waters. During the period 1981–2009, each year exhibits seasonal bottom hypoxia at the end of summer. This phenomenon essentially covers the northern part of the NWS – which receives large inputs of nutrients from the Danube, Dniester and Dnieper rivers – and extends, during the years of severe hypoxia, towards the Romanian bay of Constanta. An index H which merges the aspects of the spatial and temporal extension of the hypoxic event is proposed to quantify, for each year, the intensity of hypoxia as an environmental stressor. In order to explain the interannual variability of H and to disentangle its drivers, we analyze the long time series of model results by means of a stepwise multiple linear regression. This statistical model gives a general relationship that links the intensity of hypoxia to eutrophication and climate-related variables. A total of 82% of the interannual variability of H is explained by the combination of four predictors: the annual riverine nitrate load (N), the sea surface temperature in the month preceding stratification (Ts), the amount of semi-labile organic matter accumulated in the sediments (C) and the sea surface temperature during late summer (Tf). Partial regression indicates that the climatic impact on hypoxia is almost as important as that of eutrophication. Accumulation of organic matter in the sediments introduces an important inertia in the recovery process after eutrophication, with a typical timescale of 9.3 yr. Seasonal fluctuations and the heterogeneous spatial distribution complicate the monitoring of bottom hypoxia, leading to contradictory conclusions when the interpretation is done from different sets of data. In particular, it appears that the recovery reported in the literature after 1995 was overestimated due to the use of observations concentrated in areas and months not typically affected by hypoxia. This stresses the urgent need for a dedicated monitoring effort in the Black Sea NWS focused on the areas and months concerned by recurrent hypoxic events.

scholarly journals An operational implementation of the GHER model for the Black Sea, with SST and CTD data assimilation

2009 ◽  
Vol 6 (2) ◽  
pp. 1895-1911 ◽  
Author(s):  
L. Vandenbulcke ◽  
A. Capet ◽  
J. M. Beckers ◽  
M. Grégoire ◽  
S. Besiktepe
Keyword(s):  
Black Sea ◽  
Initial Conditions ◽  
Sea Surface ◽  
The Black Sea ◽  
Marmara Sea ◽  
Reduced Rank ◽  
Data Transfers ◽  
Time Required ◽  
Assimilation Scheme

Abstract. In this article, we describe the first operational implementation of the GHER hydrodynamic model. This happened onboard the research vessel "Alliance", in the context of the Turkish Straits System 2008 campaign, which aimed at the real-time characterization of the Marmara Sea and (south-western) Black Sea. The model performed badly at first, mainly because of poor initial conditions. Hence, as the model includes a reduced-rank extended Kalman filter assimilation scheme, after a hindcast where sea surface temperature and temperature and salinity profiles were assimilated, the model yielded realistic forecasts. Furthermore, the time required to run a one-day simulation (about 5 min of simulation, or 10 min with pre-processing and data transfers included) is very limited and thus operational use of the model is possible.

The new Black Sea Reanalysis System within CMEMS

2021 ◽  
Author(s):  
Leonardo Lima ◽  
Stefania Angela Ciliberti ◽  
Ali Aydogdu ◽  
Romain Escudier ◽  
Simona Masina ◽  
...  
Keyword(s):  
Data Assimilation ◽  
Sea Level ◽  
Black Sea ◽  
General Circulation ◽  
Circulation Model ◽  
Sea Surface Height ◽  
Sea Surface ◽  
The Black Sea ◽  
Freshwater Flux ◽  
Sea Level Anomaly

<p>Ocean reanalyses are becoming increasingly important to reconstruct and provide an overview of the ocean state from the past to the present-day. These products require advanced scientific methods and techniques to produce a more accurate ocean representation. In the scope of the Copernicus Marine Environment Monitoring Service (CMEMS), a new Black Sea (BS) reanalysis, BS-REA (BSE3R1 system), has been produced by using an advanced variational data assimilation method to combine the best available observations with a state-of-the-art ocean general circulation model. The hydrodynamical model is based on Nucleus for European Modeling of the Ocean (NEMO, v3.6), implemented for the BS domain with horizontal resolution of 1/27° x 1/36°, and 31 unevenly distributed vertical levels. NEMO is forced by atmospheric surface fluxes computed via bulk formulation and forced by ECMWF ERA5 atmospheric reanalysis product. At the surface, the model temperature is relaxed to daily objective analysis fields of sea surface temperature from CMEMS SST TAC. The exchange with Mediterranean Sea is simulated through relaxation of the temperature and salinity near Bosporus toward a monthly climatology computed from a high-resolution multi-year simulation, and the barotropic Bosporus Strait transport is corrected to balance the variations of the freshwater flux and the sea surface height measured by multi-satellite altimetry observations. A 3D-Var ocean data assimilation scheme (OceanVar) is used to assimilate sea level anomaly along-track observations from CMEMS SL TAC and available in situ vertical profiles of temperature and salinity from both SeaDataNet and CMEMS INS TAC products. Comparisons against the previous Black Sea reanalysis (BSE2R2 system) show important improvements for temperature and salinity, such that errors have significantly decreased (about 50%). Temperature fields present a continuous warming in the layer between 25-150 m, within which there is the presence of the Black Sea Cold Intermediate Layer (CIL). SST exhibits a positive bias and relatively higher root mean square error (RMSE) values are present in the summer season. Spatial maps of sea level anomaly reveal the largest RMSE close to the shelf areas, which are related to the mesoscale activity along the Rim current. The BS-REA catalogue includes daily and monthly means for 3D temperature, salinity, and currents and 2D sea surface height, bottom temperature, mixed layer fields, from Jan 1993 to Dec 2019.  The BSE3R1 system has produced very accurate estimates which makes it very suitable for assessing more realistic climate trends and indicators for important ocean properties.</p>

scholarly journals Evaluating the impact of atmospheric forcing and air–sea coupling on near-coastal regional ocean prediction

Ocean Science ◽  
2019 ◽  
Vol 15 (3) ◽  
pp. 761-778 ◽  
Author(s):  
Huw W. Lewis ◽  
John Siddorn ◽  
Juan Manuel Castillo Sanchez ◽  
Jon Petch ◽  
John M. Edwards ◽  
...  
Keyword(s):  
Heat Budget ◽  
Global Scale ◽  
Ocean Model ◽  
Surface Heat ◽  
Wind Forcing ◽  
Sea Surface ◽  
Atmospheric Forcing ◽  
Convective Scale ◽  
The Impact ◽  
Surface Heat Budget

Abstract. Atmospheric forcing applied as ocean model boundary conditions can have a critical impact on the quality of ocean forecasts. This paper assesses the sensitivity of an eddy-resolving (1.5 km resolution) regional ocean model of the north-west European Shelf (NWS) to the choice of atmospheric forcing and atmosphere–ocean coupling. The analysis is focused on a month-long simulation experiment for July 2014 and evaluation of simulated sea surface temperature (SST) in a shallow near-coastal region to the south-west of the UK (Celtic Sea and western English Channel). Observations of the ocean and atmosphere are used to evaluate model results, with a particular focus on the L4 ocean buoy from the Western Channel Observatory as a rare example of co-located data above and below the sea surface. The impacts of differences in the atmospheric forcing are illustrated by comparing results from an ocean model run in forcing mode using operational global-scale numerical weather prediction (NWP) data with an ocean model run forced by a convective-scale regional atmosphere model. The value of dynamically representing feedbacks between the atmosphere and ocean state is assessed via the use of these model components within a fully coupled ocean–wave–atmosphere system. Simulated SSTs show considerable sensitivity to atmospheric forcing and to the impact of model coupling in near-coastal areas. A warm ocean bias relative to in situ observations in the simulation forced by global-scale NWP (0.7 K in the model domain) is shown to be reduced (to 0.4 K) via the use of the 1.5 km resolution regional atmospheric forcing. When simulated in coupled mode, this bias is further reduced (by 0.2 K). Results demonstrate much greater variability of both the surface heat budget terms and the near-surface winds in the convective-scale atmosphere model data, as might be expected. Assessment of the surface heat budget and wind forcing over the ocean is challenging due to a scarcity of observations. However, it can be demonstrated that the wind speed over the ocean simulated by the convective-scale atmosphere did not agree as well with the limited number of observations as the global-scale NWP data did. Further partially coupled experiments are discussed to better understand why the degraded wind forcing does not detrimentally impact on SST results.

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