Hydrography and Circulation West of Sardinia in June 2014

Knoll, Michaela; Borrione, Ines; Fiekas, Heinz-Volker; Funk, A; Hemming, Michael; Kaiser, Jan; Onken, Reiner; Queste, Bastien Y.; Russo, Aniello

doi:10.5194/os-2017-45

Cited by 5 publications

(5 citation statements)

References 15 publications

(44 reference statements)

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“…The rich dataset collected during the REP14-MED campaign is used for this purpose. REP14-MED took place in June 2014 off the western coast of Sardinia (Onken et al, 2018;Knoll et al, 2017). Two RVs tracked in parallel a 100× 100 km 2 area during a 20-day period, providing dense CTD sampling with a 10 km separation and continuous towed CTD measurements for limited periods of time.…”

Section: Introductionmentioning

confidence: 99%

Dense CTD survey versus glider fleet sampling: comparing data assimilation performance in a regional ocean model west of Sardinia

Hernández-Lasheras

Mourre

2018

Ocean Sci.

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Abstract. The REP14-MED sea trial carried out off the west coast of Sardinia in June 2014 provided a rich set of observations from both ship-based conductivity–temperature–depth (CTD) probes and a fleet of underwater gliders. We present the results of several simulations assimilating data either from CTDs or from different subsets of glider data, including up to eight vehicles, in addition to satellite sea level anomalies, surface temperature and Argo profiles. The Western Mediterranean OPerational forcasting system (WMOP) regional ocean model is used with a local multi-model ensemble optimal interpolation scheme to recursively ingest both lower-resolution large-scale and dense local observations over the whole sea trial duration. Results show the capacity of the system to ingest both types of data, leading to improvements in the representation of all assimilated variables. These improvements persist during the 3-day periods separating two analyses. At the same time, the system presents some limitations in properly representing the smaller-scale structures, which are smoothed out by the model error covariances provided by the ensemble. An evaluation of the forecasts using independent measurements from shipborne CTDs and a towed ScanFish deployed at the end of the sea trial shows that the simulations assimilating initial CTD data reduce the error by 39 % on average with respect to the simulation without data assimilation. In the glider-data-assimilative experiments, the forecast error is reduced as the number of vehicles increases. The simulation assimilating CTDs outperforms the simulations assimilating data from one to four gliders. A fleet of eight gliders provides similar performance to the 10 km spaced CTD initialization survey in these experiments, with an overall 40 % model error reduction capacity with respect to the simulation without data assimilation when comparing against independent campaign observations.

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Section: Introductionmentioning

confidence: 99%

Dense CTD survey versus glider fleet sampling: comparing data assimilation performance in a regional ocean model west of Sardinia

Hernández-Lasheras

Mourre

2018

Ocean Sci.

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“…In the latter, the skill score decreased at a faster rate than in the global domain which indicated the reduced predictability in the more energetic regions. Ten years later in the framework of GODAE (Global Ocean Data Assimilation Experiment; Bell et al, 2009), Lellouche et al (2013) computed the skill score of the sea level anomaly forecast for different setups of the MERCA- TOR global model against persistence. They demonstrated that for most regions the skill score was positive, except for the North Atlantic, the Mediterranean Sea, and Antarctica.…”

Section: Discussionmentioning

confidence: 99%

Forecast skill score assessment of a relocatable ocean prediction system, using a simplified objective analysis method

Onken

2017

Ocean Sci.

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Abstract. A relocatable ocean prediction system (ROPS) was employed to an observational data set which was collected in June 2014 in the waters to the west of Sardinia (western Mediterranean) in the framework of the REP14-MED experiment. The observational data, comprising more than 6000 temperature and salinity profiles from a fleet of underwater gliders and shipborne probes, were assimilated in the Regional Ocean Modeling System (ROMS), which is the heart of ROPS, and verified against independent observations from ScanFish tows by means of the forecast skill score as defined by Murphy (1993). A simplified objective analysis (OA) method was utilised for assimilation, taking account of only those profiles which were located within a predetermined time window W . As a result of a sensitivity study, the highest skill score was obtained for a correlation length scale C = 12.5 km, W = 24 h, and r = 1, where r is the ratio between the error of the observations and the background error, both for temperature and salinity. Additional ROPS runs showed that (i) the skill score of assimilation runs was mostly higher than the score of a control run without assimilation, (i) the skill score increased with increasing forecast range, and (iii) the skill score for temperature was higher than the score for salinity in the majority of cases. Further on, it is demonstrated that the vast number of observations can be managed by the applied OA method without data reduction, enabling timely operational forecasts even on a commercially available personal computer or a laptop.

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“…exists (Knoll et al, 2017). SST increased by up to 0.6 • C between 19 and 20 March, and continued to increase intermittently to a maximum of 14.3 • C on 5 April (total increase of 1 • C over the deployment period).…”

Section: Development Of a Spring Bloommentioning

confidence: 95%

Net community production in the northwestern Mediterranean Sea from glider and buoy measurements

Hemming

Kaiser

Boutin³

et al. 2022

Preprint

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Abstract. The Mediterranean Sea comprises just 0.8 % of the global oceanic surface, yet considering its size, it is regarded as a disproportionately large sink for anthropogenic carbon due to its physical and biogeochemical characteristics. An underwater glider mission was carried out in March–April 2016 close to the BOUSSOLE and DyFAMed time series moorings in the northwestern Mediterranean Sea. The glider deployment served as a test of a prototype ion-sensitive field-effect transistor pH sensor. Dissolved oxygen (O2) concentrations and optical backscatter were also observed by the glider and increased between 19 March and 1 April, along with pH. These changes indicated the start of a phytoplankton spring bloom, following a period of intense mixing. Concurrent measurements of CO2 fugacity and O2 concentrations at the BOUSSOLE mooring buoy showed fluctuations, in qualitative agreement with the pattern of glider measurements. Mean net community production rates (N) were estimated from glider and buoy measurements of dissolved O2 and inorganic carbon (DIC) concentrations. Glider and buoy DIC concentrations were derived from a salinity-based total alkalinity parameterisation, glider pH, and buoy CO2 fugacity. The spatial coverage of glider data allowed calculating advective O2 and DIC fluxes. Mean N estimates for the euphotic zone between 10 March and 3 April were (−17 ± 35) for glider O2, (44 ± 94) for glider DIC, (17 ± 35) for buoy O2 and (49 ± 86) mmol m–2 d–1 for buoy DIC, all indicating net metabolic balance over these 25 days. However, these 25 days were actually split into a period of net DIC increase and O2 decrease between 10 and 19 March and a period of net DIC decrease and O2 increase between 19 March and 3 April. The latter period is interpreted as the onset of the spring bloom. The regression coefficients between O2 and DIC-based N estimates were 0.25 ± 0.08 for the glider data and 0.54 ± 0.06 for the buoy, significantly lower than the canonical metabolic quotient of 1.45 ± 0.15. This study shows the added value of co-locating a profiling glider with moored time series buoys, but also demonstrates limitations in achievable precision.

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Hydrography and Circulation West of Sardinia in June 2014

Cited by 5 publications

References 15 publications

Dense CTD survey versus glider fleet sampling: comparing data assimilation performance in a regional ocean model west of Sardinia

Dense CTD survey versus glider fleet sampling: comparing data assimilation performance in a regional ocean model west of Sardinia

Forecast skill score assessment of a relocatable ocean prediction system, using a simplified objective analysis method

Net community production in the northwestern Mediterranean Sea from glider and buoy measurements

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