Pub Date : 2020-08-10DOI: 10.1080/1755876X.2020.1771815
Matthew Martin, E. Rémy, B. Tranchant, Robert R. King, Eric Greiner, Craig Donlon
ABSTRACT Observing system experiments have been carried out with two operational ocean data assimilation systems to assess the impact of assimilating satellite sea surface salinity (SSS) data. The SSS data reduces the errors in tropical Pacific salinity by 4% and 8% in the Met Office and Mercator Ocean systems respectively with an impact down to about 50 m depth on average. Salinity errors were reduced by up to 30% in the tropical Atlantic in both systems. There were significant reductions in near-surface temperature and sea level anomaly errors in both the central tropical Pacific and Amazon outflow regions in the Met Office system. The experiment results and characteristics of the operational ocean forecasting systems lead to a new set of requirements for satellite salinity data. The product accuracy required to significantly improve real-time ocean analysis and forecasts should be less than 0.2 pss at a resolution of at least 50 km for daily products. Improvements to spatial resolution down to the order of 10 km would represent an even more significant breakthrough. To be assimilated in near-real time, products should be available within 24 h and estimates of the systematic and random components of the uncertainty should be provided with each measurement.
{"title":"Observation impact statement on satellite sea surface salinity data from two operational global ocean forecasting systems","authors":"Matthew Martin, E. Rémy, B. Tranchant, Robert R. King, Eric Greiner, Craig Donlon","doi":"10.1080/1755876X.2020.1771815","DOIUrl":"https://doi.org/10.1080/1755876X.2020.1771815","url":null,"abstract":"ABSTRACT Observing system experiments have been carried out with two operational ocean data assimilation systems to assess the impact of assimilating satellite sea surface salinity (SSS) data. The SSS data reduces the errors in tropical Pacific salinity by 4% and 8% in the Met Office and Mercator Ocean systems respectively with an impact down to about 50 m depth on average. Salinity errors were reduced by up to 30% in the tropical Atlantic in both systems. There were significant reductions in near-surface temperature and sea level anomaly errors in both the central tropical Pacific and Amazon outflow regions in the Met Office system. The experiment results and characteristics of the operational ocean forecasting systems lead to a new set of requirements for satellite salinity data. The product accuracy required to significantly improve real-time ocean analysis and forecasts should be less than 0.2 pss at a resolution of at least 50 km for daily products. Improvements to spatial resolution down to the order of 10 km would represent an even more significant breakthrough. To be assimilated in near-real time, products should be available within 24 h and estimates of the systematic and random components of the uncertainty should be provided with each measurement.","PeriodicalId":50105,"journal":{"name":"Journal of Operational Oceanography","volume":"13 2 1","pages":"87 - 103"},"PeriodicalIF":3.1,"publicationDate":"2020-08-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78035300","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-07-02DOI: 10.1080/1755876X.2019.1681873
Mahmoud Pirooznia, M. Raoofian Naeeni
ABSTRACT In this study, the collocation method accompanied with variance component estimation is used for least square adjustment of crossover observations in order to determine the effects of radial errors on the observations of satellite altimetry. The collocation is used for time series analysis of sea surface height observations both for predicting the possible missing observations in each cycle, and for approximating the observation of each cycle at crossover points. In addition, use is made of the variance component estimation to quantify the noise variance of observations and improve the least square evaluation of radial errors. For analysis of radial errors, two different approaches are followed, in the first approach, the radial errors are assumed to behave like a series of trigonometric function, the coefficients of which are unknowns which should be determined from observations. In the second approach, the values of radial errors, for ascending and descending passes are determined. Our results show the efficiency of collocation algorithm for highly accurate time series analysis of altimetry observations and moreover, they reveal the effectiveness of variance component estimation for true noise specification of observations which can significantly improve the results of least square adjustment. The outcome of this study can be used to calibration of altimeters. The numerical results indicate that the mean range biases of Topex/Poseidon, Jason 1-2 and ENVISAT in the six single and dual crossover points using the first and the second methods are about 0, 84, 33, 204 and 0, 98, 41, 286 mm, respectively.
{"title":"The application of least-square collocation and variance component estimation in crossover analysis of satellite altimetry observations and altimeter calibration","authors":"Mahmoud Pirooznia, M. Raoofian Naeeni","doi":"10.1080/1755876X.2019.1681873","DOIUrl":"https://doi.org/10.1080/1755876X.2019.1681873","url":null,"abstract":"ABSTRACT In this study, the collocation method accompanied with variance component estimation is used for least square adjustment of crossover observations in order to determine the effects of radial errors on the observations of satellite altimetry. The collocation is used for time series analysis of sea surface height observations both for predicting the possible missing observations in each cycle, and for approximating the observation of each cycle at crossover points. In addition, use is made of the variance component estimation to quantify the noise variance of observations and improve the least square evaluation of radial errors. For analysis of radial errors, two different approaches are followed, in the first approach, the radial errors are assumed to behave like a series of trigonometric function, the coefficients of which are unknowns which should be determined from observations. In the second approach, the values of radial errors, for ascending and descending passes are determined. Our results show the efficiency of collocation algorithm for highly accurate time series analysis of altimetry observations and moreover, they reveal the effectiveness of variance component estimation for true noise specification of observations which can significantly improve the results of least square adjustment. The outcome of this study can be used to calibration of altimeters. The numerical results indicate that the mean range biases of Topex/Poseidon, Jason 1-2 and ENVISAT in the six single and dual crossover points using the first and the second methods are about 0, 84, 33, 204 and 0, 98, 41, 286 mm, respectively.","PeriodicalId":50105,"journal":{"name":"Journal of Operational Oceanography","volume":"43 1","pages":"100 - 120"},"PeriodicalIF":3.1,"publicationDate":"2020-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88863971","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-07-02DOI: 10.1080/1755876X.2019.1658567
Tanuja Nigam, K. Prakash, V. Pant
ABSTRACT The Regional Ocean Modelling System (ROMS) is utilised to estimate the cyclone-induced mixing and cooling associated with two tropical cyclones, namely Phet and Nilofar over the Arabian Sea (AS). Numerical experiments were carried out with realistic and idealistic oceanic conditions to assess the impact of oceanic initial condition and stratification on the interaction of upper ocean with the tropical cyclones in the AS. The model simulated profiles of temperature and baroclinic kinetic energy are analysed to examine the post-cyclonic cooling and vertical distribution of inertial kinetic energy which interacts with the upper-ocean stratification. Following the cyclone-induced upwelling, the inertial mixing acts to deepen the mixed layer depth (MLD) up to 50 and 100 m from its initial values of 15 and 22 m for the Phet and Nilofar, respectively. The analysis suggests that the combined effect of higher maximum sustained winds and slower translational speed of Nilofar cyclone leads to the excessive cooling (by 1.5°C) of the sea surface as compared to Phet. A decrement in the magnitude of cooling is observed when oceanic initial stratification was altered. The available baroclinic velocity shear at different depths found to modulate the magnitude of upper-ocean cooling in different model experiments.
{"title":"An assessment of the impact of oceanic initial conditions on the interaction of upper ocean with the tropical cyclones in the Arabian Sea","authors":"Tanuja Nigam, K. Prakash, V. Pant","doi":"10.1080/1755876X.2019.1658567","DOIUrl":"https://doi.org/10.1080/1755876X.2019.1658567","url":null,"abstract":"ABSTRACT The Regional Ocean Modelling System (ROMS) is utilised to estimate the cyclone-induced mixing and cooling associated with two tropical cyclones, namely Phet and Nilofar over the Arabian Sea (AS). Numerical experiments were carried out with realistic and idealistic oceanic conditions to assess the impact of oceanic initial condition and stratification on the interaction of upper ocean with the tropical cyclones in the AS. The model simulated profiles of temperature and baroclinic kinetic energy are analysed to examine the post-cyclonic cooling and vertical distribution of inertial kinetic energy which interacts with the upper-ocean stratification. Following the cyclone-induced upwelling, the inertial mixing acts to deepen the mixed layer depth (MLD) up to 50 and 100 m from its initial values of 15 and 22 m for the Phet and Nilofar, respectively. The analysis suggests that the combined effect of higher maximum sustained winds and slower translational speed of Nilofar cyclone leads to the excessive cooling (by 1.5°C) of the sea surface as compared to Phet. A decrement in the magnitude of cooling is observed when oceanic initial stratification was altered. The available baroclinic velocity shear at different depths found to modulate the magnitude of upper-ocean cooling in different model experiments.","PeriodicalId":50105,"journal":{"name":"Journal of Operational Oceanography","volume":"15 1","pages":"121 - 137"},"PeriodicalIF":3.1,"publicationDate":"2020-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90333446","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-07-02DOI: 10.1080/1755876X.2019.1606691
S. J. Prasad, P. A. Francis, T. B. Balakrishnan Nair, S. Shenoi, T. Vijayalakshmi
ABSTRACT Simulated ocean currents from ocean circulation models along with the surface winds are generally used to force an oil spill trajectory model. Ocean circulation is a key factor in determining the drift of the spilled marine pollutants. The simulations of the drift pattern of spilled oil, when forced by the ocean currents from two ocean models, are presented here. Merchant Vessel (MV) Rak sunk at 72.4865°E, 18.7715°N, on 4 August 2011. As per the information from Indian Coast Guard, approximately 122.5 tons of fuel oil was spilled from the vessel from 5 August 2011 to 12 August 2011. An oil spill trajectory model, General NOAA Operational Modeling Environment (GNOME), was used to simulate the oil drift pattern from MV Rak from 1000 hours of 5 August 2011 to 1300 hours of 12 August 2011. GNOME was forced with winds from European Centre for Medium Range Weather Forecast (ECMWF) and ocean currents from Indian Ocean Forecasting System (INDOFOS) and High-resolution Operational Ocean Forecasting and reanalysis System (HOOFS). We found that the oil drift pattern obtained when forced with ocean currents from HOOFS was in better agreement with the actual track, compared to the one obtained while using INDOFOS currents.
{"title":"Oil spill trajectory prediction with high-resolution ocean currents","authors":"S. J. Prasad, P. A. Francis, T. B. Balakrishnan Nair, S. Shenoi, T. Vijayalakshmi","doi":"10.1080/1755876X.2019.1606691","DOIUrl":"https://doi.org/10.1080/1755876X.2019.1606691","url":null,"abstract":"ABSTRACT Simulated ocean currents from ocean circulation models along with the surface winds are generally used to force an oil spill trajectory model. Ocean circulation is a key factor in determining the drift of the spilled marine pollutants. The simulations of the drift pattern of spilled oil, when forced by the ocean currents from two ocean models, are presented here. Merchant Vessel (MV) Rak sunk at 72.4865°E, 18.7715°N, on 4 August 2011. As per the information from Indian Coast Guard, approximately 122.5 tons of fuel oil was spilled from the vessel from 5 August 2011 to 12 August 2011. An oil spill trajectory model, General NOAA Operational Modeling Environment (GNOME), was used to simulate the oil drift pattern from MV Rak from 1000 hours of 5 August 2011 to 1300 hours of 12 August 2011. GNOME was forced with winds from European Centre for Medium Range Weather Forecast (ECMWF) and ocean currents from Indian Ocean Forecasting System (INDOFOS) and High-resolution Operational Ocean Forecasting and reanalysis System (HOOFS). We found that the oil drift pattern obtained when forced with ocean currents from HOOFS was in better agreement with the actual track, compared to the one obtained while using INDOFOS currents.","PeriodicalId":50105,"journal":{"name":"Journal of Operational Oceanography","volume":"177 1","pages":"84 - 99"},"PeriodicalIF":3.1,"publicationDate":"2020-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79929193","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-06-16DOI: 10.1080/1755876X.2020.1780757
C. Meinen, Ryan H. Smith, Rigoberto F. García
ABSTRACT For 30+ years, submarine cable voltage measurements have been a critical measurement system used to produce a highly valuable time series of daily Florida Current volume transport at 27°N in the Florida Straits. However, the high cost associated with replacing the measurement system, should the existing telecommunications cable break, represents a significant vulnerability to the continuation of this important transport time series. Six years of data from tide gauges near the ends of the cable at 27°N have been used to test the potential of a paired tide gauge system to replace the cable in the event of a future problem. Validations against the daily cable observations, and against snapshot transport estimates from ship sections, suggest that the tide gauges do represent a viable replacement, however, the accuracy of the transports determined from the tide gauges is lower than for the cable observations (2.7 Sv vs. 1.7 Sv, respectively). The tide gauges capture roughly 55% of the total variance observed by the cable. The correlation between the cable data and the tide gauge differences is fairly constant (r ≈ 0.75) after low-pass filtering the data at periods from 3 to 365 days, illustrating a lack of coherence sensitivity to those time scales.
{"title":"Evaluating pressure gauges as a potential future replacement for electromagnetic cable observations of the Florida Current transport at 27°N","authors":"C. Meinen, Ryan H. Smith, Rigoberto F. García","doi":"10.1080/1755876X.2020.1780757","DOIUrl":"https://doi.org/10.1080/1755876X.2020.1780757","url":null,"abstract":"ABSTRACT For 30+ years, submarine cable voltage measurements have been a critical measurement system used to produce a highly valuable time series of daily Florida Current volume transport at 27°N in the Florida Straits. However, the high cost associated with replacing the measurement system, should the existing telecommunications cable break, represents a significant vulnerability to the continuation of this important transport time series. Six years of data from tide gauges near the ends of the cable at 27°N have been used to test the potential of a paired tide gauge system to replace the cable in the event of a future problem. Validations against the daily cable observations, and against snapshot transport estimates from ship sections, suggest that the tide gauges do represent a viable replacement, however, the accuracy of the transports determined from the tide gauges is lower than for the cable observations (2.7 Sv vs. 1.7 Sv, respectively). The tide gauges capture roughly 55% of the total variance observed by the cable. The correlation between the cable data and the tide gauge differences is fairly constant (r ≈ 0.75) after low-pass filtering the data at periods from 3 to 365 days, illustrating a lack of coherence sensitivity to those time scales.","PeriodicalId":50105,"journal":{"name":"Journal of Operational Oceanography","volume":"76 1","pages":"166 - 176"},"PeriodicalIF":3.1,"publicationDate":"2020-06-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79503419","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-06-02DOI: 10.1080/1755876X.2020.1771811
P. G. Remya, T. Rabi Ranjan, P. Sirisha, R. Harikumar, T. M. Balakrishnan Nair
ABSTRACT Present study aims at the development of the Indian Ocean wave forecasting system for wind waves using WAVEWATCH-III wave model and a detailed validation of the same to ensure the model reliability for operational use. WAVEWATCH-III model has a multi-grid approach with resolution varying from 100 km (global grid) to 4 km (coastal grid), and is driven by the 10 m wind, produced by the ECMWF meteorological model. Two different observation data sets, provided by a network of buoys and Jason-2 altimeter, have been used for the evaluationof the model skill. The reliability of the wave model is tested separately for deep and for coastal waters, and reliable (correlation > 0.8 and Scatter Index < 30%) performance is found for both areas for the year 2016. A spatial validation using the satellite data also supported the reliability of the forecast in the IO. Verification during the extreme conditions also showed an accurate performance of the model in predicting the wave heights with correlation >0.9 and Scatter Index < 20%. The overall analysis endorses the model reliability over the IO, making this model very suitable, and hence it could be used for the operational forecasting purpose and other maritime services.
{"title":"Indian Ocean wave forecasting system for wind waves: development and its validation","authors":"P. G. Remya, T. Rabi Ranjan, P. Sirisha, R. Harikumar, T. M. Balakrishnan Nair","doi":"10.1080/1755876X.2020.1771811","DOIUrl":"https://doi.org/10.1080/1755876X.2020.1771811","url":null,"abstract":"ABSTRACT Present study aims at the development of the Indian Ocean wave forecasting system for wind waves using WAVEWATCH-III wave model and a detailed validation of the same to ensure the model reliability for operational use. WAVEWATCH-III model has a multi-grid approach with resolution varying from 100 km (global grid) to 4 km (coastal grid), and is driven by the 10 m wind, produced by the ECMWF meteorological model. Two different observation data sets, provided by a network of buoys and Jason-2 altimeter, have been used for the evaluationof the model skill. The reliability of the wave model is tested separately for deep and for coastal waters, and reliable (correlation > 0.8 and Scatter Index < 30%) performance is found for both areas for the year 2016. A spatial validation using the satellite data also supported the reliability of the forecast in the IO. Verification during the extreme conditions also showed an accurate performance of the model in predicting the wave heights with correlation >0.9 and Scatter Index < 20%. The overall analysis endorses the model reliability over the IO, making this model very suitable, and hence it could be used for the operational forecasting purpose and other maritime services.","PeriodicalId":50105,"journal":{"name":"Journal of Operational Oceanography","volume":"134 1","pages":"1 - 16"},"PeriodicalIF":3.1,"publicationDate":"2020-06-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85257698","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-03-23DOI: 10.1080/1755876X.2020.1743049
Ana Paula Morais Krelling, A. Gangopadhyay, I. D. da Silveira, Felipe Vilela‐Silva
ABSTRACT Key elements of a Feature-oriented regional modelling system (FORMS) in the Western Equatorial Atlantic (1°–11°S) are developed for possible application in an operational forecast system as well as in process-oriented studies. This equatorial margin region is dominated by the northwestward flowing near surface North Brazil Undercurrent (NBUC) and the southeastward Deep Western Boundary Current (DWBC). Specifically, we investigate the genesis of a subsurface frontal meander of the NBUC, centred at about 4°S, 36.5°W, called the Potiguar Eddy (PE). The Feature Models (FMs) of NBUC and DWBC are first developed from observed velocity data, with temperature calculated through the thermal wind equation, and salinity from climatology. Two numerical experiments were then set up for the process study, (i) a realistic NBUC + DWBC experiment, with maximum depth of 5500 m, and (ii) a NBUC-only experiment, with maximum depth limited to 1500 m. Results conclude that the PE can be generated by a velocity field containing only the NBUC, and the DWBC – induced vertical shear seems to play a part on the eddy’s baroclinic characteristics (vertical extent and strength). This study highlights the potential of applicability of FORMS for operational forecasts and for process studies in similar regions of the world ocean where currents and topography interact to create permanent and/or semi-permanent eddies.
{"title":"Development of a feature-oriented regional modelling system for the North Brazil Undercurrent region (1°–11°S) and its application to a process study on the genesis of the Potiguar Eddy","authors":"Ana Paula Morais Krelling, A. Gangopadhyay, I. D. da Silveira, Felipe Vilela‐Silva","doi":"10.1080/1755876X.2020.1743049","DOIUrl":"https://doi.org/10.1080/1755876X.2020.1743049","url":null,"abstract":"ABSTRACT Key elements of a Feature-oriented regional modelling system (FORMS) in the Western Equatorial Atlantic (1°–11°S) are developed for possible application in an operational forecast system as well as in process-oriented studies. This equatorial margin region is dominated by the northwestward flowing near surface North Brazil Undercurrent (NBUC) and the southeastward Deep Western Boundary Current (DWBC). Specifically, we investigate the genesis of a subsurface frontal meander of the NBUC, centred at about 4°S, 36.5°W, called the Potiguar Eddy (PE). The Feature Models (FMs) of NBUC and DWBC are first developed from observed velocity data, with temperature calculated through the thermal wind equation, and salinity from climatology. Two numerical experiments were then set up for the process study, (i) a realistic NBUC + DWBC experiment, with maximum depth of 5500 m, and (ii) a NBUC-only experiment, with maximum depth limited to 1500 m. Results conclude that the PE can be generated by a velocity field containing only the NBUC, and the DWBC – induced vertical shear seems to play a part on the eddy’s baroclinic characteristics (vertical extent and strength). This study highlights the potential of applicability of FORMS for operational forecasts and for process studies in similar regions of the world ocean where currents and topography interact to create permanent and/or semi-permanent eddies.","PeriodicalId":50105,"journal":{"name":"Journal of Operational Oceanography","volume":"88 1","pages":"69 - 86"},"PeriodicalIF":3.1,"publicationDate":"2020-03-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/1755876X.2020.1743049","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"72417266","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-03-14DOI: 10.1080/1755876X.2020.1738121
M. Viitak, P. Avilez-Valente, A. Bio, L. Bastos, I. Iglesias
ABSTRACT The available wind datasets can be exploited to support the setup of accurate wave models, able to reproduce and forecast extreme event scenarios. It is of utmost importance in the actual context of climate change. This study focuses on evaluating the performance of a numerical wave model, using different wind datasets, helping to create a tool to assess coastal risks, and further on to support the future implementation of reliable warning systems based on numerical models. The numerical model SWAN was implemented, configured and validated for the NW Iberian Peninsula coast, as a test case region. A period of two months, from December 2013 to January 2014, was simulated due to the winter storms that crossed the area. Six distinct wind datasets were selected to test their suitability in regional wave modelling. The results were validated against several sets of wave buoy data, considering wave parameters such as significant wave height, mean wave period and peak direction. The implemented wave model configuration allowed the representation of the wave evolution with relatively good accuracy. All the wind datasets were able to produce reasonably good wave condition estimates. The dataset that best represented the wave properties varied from one wave parameter to another, but the most reliable for the selected region was the reanalysis product generated at the European Centre for Medium-Range Weather Forecasts.
{"title":"Evaluating wind datasets for wave hindcasting in the NW Iberian Peninsula coast","authors":"M. Viitak, P. Avilez-Valente, A. Bio, L. Bastos, I. Iglesias","doi":"10.1080/1755876X.2020.1738121","DOIUrl":"https://doi.org/10.1080/1755876X.2020.1738121","url":null,"abstract":"ABSTRACT The available wind datasets can be exploited to support the setup of accurate wave models, able to reproduce and forecast extreme event scenarios. It is of utmost importance in the actual context of climate change. This study focuses on evaluating the performance of a numerical wave model, using different wind datasets, helping to create a tool to assess coastal risks, and further on to support the future implementation of reliable warning systems based on numerical models. The numerical model SWAN was implemented, configured and validated for the NW Iberian Peninsula coast, as a test case region. A period of two months, from December 2013 to January 2014, was simulated due to the winter storms that crossed the area. Six distinct wind datasets were selected to test their suitability in regional wave modelling. The results were validated against several sets of wave buoy data, considering wave parameters such as significant wave height, mean wave period and peak direction. The implemented wave model configuration allowed the representation of the wave evolution with relatively good accuracy. All the wind datasets were able to produce reasonably good wave condition estimates. The dataset that best represented the wave properties varied from one wave parameter to another, but the most reliable for the selected region was the reanalysis product generated at the European Centre for Medium-Range Weather Forecasts.","PeriodicalId":50105,"journal":{"name":"Journal of Operational Oceanography","volume":"8 1","pages":"152 - 165"},"PeriodicalIF":3.1,"publicationDate":"2020-03-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80448107","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-03-11DOI: 10.1080/1755876X.2020.1737344
J. Noble, Tirumalesh Keesari
ABSTRACT An environmental isotope study was conducted to assess the cause for the freshening of seawater observed in the Mahim Bay, Mumbai, India after a storm event during the southwest monsoon period. Water samples were collected from the various locations of the coastal water and the suspected inland water sources such as rain, river and groundwater and analysed for major ion species and stable isotopes (δ18O and δ2H). Dissolved radon (222Rn) in the coastal water was monitored in-situ. Field monitoring survey in the coastal water indicated lower electrical conductivity (1,730 μS/cm) near Mahim Mosque compared to the surrounding shelf waters. Relatively high excess 222Rn activities (up to 55 Bq/m3) were observed in the Mahim Bay, even after 13 days of seawater freshening event. Based on the hydrochemical and isotope results, various prevailing hypotheses on the occurrence of low salinity water in the Mahim Bay were tested. It is inferred that the low salinity coastal water was associated with groundwater discharge occurring in the Mahim Bay and in the Mithi River and were unlikely due to the overflow of Vihar and Powai Lakes in the catchment of Mithi River and surface runoff because of the rain/storm events. Temporal variations of electrical conductivity and stable isotopic composition of coastal water in the Mahim Bay showed that the groundwater inputs were decreasing after the storm event. 222Rn was found to be a useful tracer for distinguishing the subsurface flow of water to the coastal system.
{"title":"Freshening of seawater in the Mahim Bay, Mumbai, India: Insight from an environmental isotope study","authors":"J. Noble, Tirumalesh Keesari","doi":"10.1080/1755876X.2020.1737344","DOIUrl":"https://doi.org/10.1080/1755876X.2020.1737344","url":null,"abstract":"ABSTRACT An environmental isotope study was conducted to assess the cause for the freshening of seawater observed in the Mahim Bay, Mumbai, India after a storm event during the southwest monsoon period. Water samples were collected from the various locations of the coastal water and the suspected inland water sources such as rain, river and groundwater and analysed for major ion species and stable isotopes (δ18O and δ2H). Dissolved radon (222Rn) in the coastal water was monitored in-situ. Field monitoring survey in the coastal water indicated lower electrical conductivity (1,730 μS/cm) near Mahim Mosque compared to the surrounding shelf waters. Relatively high excess 222Rn activities (up to 55 Bq/m3) were observed in the Mahim Bay, even after 13 days of seawater freshening event. Based on the hydrochemical and isotope results, various prevailing hypotheses on the occurrence of low salinity water in the Mahim Bay were tested. It is inferred that the low salinity coastal water was associated with groundwater discharge occurring in the Mahim Bay and in the Mithi River and were unlikely due to the overflow of Vihar and Powai Lakes in the catchment of Mithi River and surface runoff because of the rain/storm events. Temporal variations of electrical conductivity and stable isotopic composition of coastal water in the Mahim Bay showed that the groundwater inputs were decreasing after the storm event. 222Rn was found to be a useful tracer for distinguishing the subsurface flow of water to the coastal system.","PeriodicalId":50105,"journal":{"name":"Journal of Operational Oceanography","volume":"39 1","pages":"129 - 141"},"PeriodicalIF":3.1,"publicationDate":"2020-03-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90598944","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-03-09DOI: 10.1080/1755876X.2021.1872229
T. Tamtare, D. Dumont, C. Chavanne
ABSTRACT The importance of explicitly resolving the Stokes drift in ocean surface drift modelling is demonstrated by comparing four models with 58,612 observational data points obtained from undrogued drifting buoys in the Estuary and Gulf of St. Lawrence, Canada. Drift model inputs are obtained from regional atmosphere and ocean circulation, and spectral wave models. The control drift model considers near-surface currents provided by the top grid cell of the ocean circulation model, which is 5-m thick, and a correction term proportional to the near-surface wind. The three other drift models account for the unresolved near-surface current shear by extrapolating the near-surface currents to the surface assuming Ekman dynamics. Two of these models consider explicitly the Stokes drift, with and without a wind correction term. Proposed models reduce the mean separation distance between observed and predicted trajectories by 34–40% relative to the control model, on average, for forecast times ranging from 3 to 72 h. The best improvement with respect to all metrics used is, however, obtained for the model that takes into account the near-surface shear correction and the Stokes drift, without any wind correction term (skill score of 0.93 after 3 h and 0.81 after 72 h).
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