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Bruno Buongiorno Nardelli

Abstract

A novel technique for the high-resolution interpolation of in situ sea surface salinity (SSS) observations is developed and tested. The method is based on an optimal interpolation (OI) algorithm that includes satellite sea surface temperature (SST) in the covariance estimation. The covariance function parameters (i.e., spatial, temporal, and thermal decorrelation scales) and the noise-to-signal ratio are determined empirically, by minimizing the root-mean-square error and mean error with respect to fully independent validation datasets. Both in situ observations and simulated data extracted from a numerical model output are used to run these tests. Different filters are applied to sea surface temperature data in order to remove the large-scale variability associated with air–sea interaction, because a high correlation between SST and SSS is expected only at small scales. In the tests performed on in situ observations, the lowest errors are obtained by selecting covariance decorrelation scales of 400 km, 6 days, and 2.75°C, respectively, a noise-to-signal ratio of 0.01 and filtering the scales longer than 1000 km in the SST time series. This results in a root-mean-square error of ~0.11 g kg−1 and a mean error of ~0.01 g kg−1, that is, reducing the errors by ~25% and ~60%, respectively, with respect to the first guess.

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Bruno Buongiorno Nardelli
and
Rosalia Santoleri

Abstract

Different methods for the extrapolation of vertical profiles from sea surface measurements have been tested on 14 yr of conductivity–temperature–depth (CTD) data collected within the Hawaii Ocean Time-series (HOT) program at A Long-Term Oligotrophic Habitat Assessment (ALOHA) station in the North Pacific Ocean. A new technique, called multivariate EOF reconstruction (mEOF-R), has been proposed. The mEOF-R technique is similar to the previously developed coupled pattern reconstruction (CPR) technique and relies on the availability of surface measurements and historical profiles of salinity, temperature, and steric heights. The method is based on the multivariate EOF analysis of the vertical profiles of the three parameters and on the assumption that only a few modes are needed to explain most of the variance/covariance of the fields. The performances of CPR, single EOF reconstruction (sEOF-R), and mEOF-R have been compared with the results of residual GEM techniques and with ad hoc climatologies, stressing the potential of each method in relation to the length of the time series used to train the models and to the accuracy expected from planned satellite missions for the measurement of surface salinity, sea level, and temperature. The mEOF-R method generally produces the most reliable estimates (in the worst cases comparable to the climatologies) and seems to be slightly less susceptible to errors in the surface input. Multivariate EOF analysis of HOT data also gave by itself interesting results, being able to discriminate the three major signals driving the temporal variability in the area.

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Bruno Buongiorno Nardelli
and
Rosalia Santoleri

Abstract

A method for the extrapolation of vertical profiles of temperature (and/or steric heights) from measurements of sea surface elevation and sea surface temperature has been developed and is described here. The technique, called coupled pattern reconstruction (CPR), is based on a multivariate analysis of the coupled variability of vertical profiles from historical hydrographic data and on the hypothesis that only few modes are needed to explain most of the covariance of the fields. Through a linear regression between the amplitudes of the coupled modes it is possible to reconstruct the first two modes by solving a simple linear system written for the surface values, which are supposed to be known. The CPR method has been applied and tested on 9 yr of conductivity– temperature–depth (CTD) measurements collected in the northern Mediterranean Sea during the Dynamiques des Flux de Matière en Mediterranée (DYFAMED) program (1994–2002). The first 6 yr were used as a training dataset, while the last 3 were set aside as independent test measurements. Results have demonstrated a substantial improvement in terms of absolute error with respect to an ad hoc climatology, and slightly worse performances compared to the most advanced technique found in literature, which consists of the single empirical orthogonal function reconstruction (sEOF-R) through a multivariate regression of the amplitudes, except for the very first meters. However, CPR is demonstrated to be much more robust and better performing with respect to sEOF-R when considering the errors associated with real measurements of sea surface elevation.

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Bruno Buongiorno Nardelli
,
Rosalia Santoleri
, and
Stefania Sparnocchia

Abstract

Transient mesoscale and submesoscale processes, such as small eddies and filaments, could play a fundamental role in the marine ecosystem, especially in oligotrophic seas like the Mediterranean. However, very little is known about the biological and physical dynamics characterizing such structures. In this work, the 8-km horizontal resolution data collected during the SYMPLEX 1998 survey are analyzed to describe the physical dynamics of small mesoscale features along the Atlantic–Ionian stream (western Ionian Sea). The data were optimally interpolated over a regular grid and used to compute the 3D ageostrophic circulation by solution of the Q-vector formulation of the omega equation. The relative importance of stratification, relative vorticity, and twisting terms in the Rossby–Ertel potential vorticity is thus examined along selected isopycnals, together with the associated vertical motions and vortex stretching. A surface cyclonic eddy ∼15 km of radius was observed near a meander of the Atlantic–Ionian stream. This small cyclone is characterized by high potential vorticity values similar to that of the meander, by a relative vorticity of 0.5f, and by vertical velocities of the order of 10–14 m d−1. A subduction process of ∼15 m d−1 was found in correspondence of the meander trough, giving rise to a deep cold anticyclone, while peak upward velocities reached the same order of magnitude at the trough.

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Chunxue Yang
,
Francesca Elisa Leonelli
,
Salvatore Marullo
,
Vincenzo Artale
,
Helen Beggs
,
Bruno Buongiorno Nardelli
,
Toshio M. Chin
,
Vincenzo De Toma
,
Simon Good
,
Boyin Huang
,
Christopher J. Merchant
,
Toshiyuki Sakurai
,
Rosalia Santoleri
,
Jorge Vazquez-Cuervo
,
Huai-Min Zhang
, and
Andrea Pisano

Abstract

A joint effort between the Copernicus Climate Change Service (C3S) and the Group for High Resolution Sea Surface Temperature (GHRSST) has been dedicated to an intercomparison study of eight global gap-free sea surface temperature (SST) products to assess their accurate representation of the SST relevant to climate analysis. In general, all SST products show consistent spatial patterns and temporal variability during the overlapping time period (2003–18). The main differences between each product are located in the western boundary current and Antarctic Circumpolar Current regions. Linear trends display consistent SST spatial patterns among all products and exhibit a strong warming trend from 2012 to 2018 with the Pacific Ocean basin as the main contributor. The SST discrepancy between all SST products is very small compared to the significant warming trend. Spatial power spectral density shows that the interpolation into 1° spatial resolution has negligible impacts on our results. The global mean SST time series reveals larger differences among all SST products during the early period of the satellite era (1982–2002) when there were fewer observations, indicating that the observation frequency is the main constraint of the SST climatology. The maturity matrix scores, which present the maturity of each product in terms of documentation, storage, and dissemination but not the scientific quality, demonstrate that ESA-CCI and OSTIA SST are well documented for users’ convenience. Improvements could be made for MGDSST and BoM SST. Finally, we have recommended that these SST products can be used for fundamental climate applications and climate studies (e.g., El Niño).

Open access
Chunxue Yang
,
Chiara Cagnazzo
,
Vincenzo Artale
,
Bruno Buongiorno Nardelli
,
Carlo Buontempo
,
Jacopo Busatto
,
Luca Caporaso
,
Claudia Cesarini
,
Irene Cionni
,
John Coll
,
Bas Crezee
,
Paolo Cristofanelli
,
Vincenzo de Toma
,
Yassmin Hesham Essa
,
Veronika Eyring
,
Federico Fierli
,
Luke Grant
,
Birgit Hassler
,
Martin Hirschi
,
Philippe Huybrechts
,
Eva Le Merle
,
Francesca Elisa Leonelli
,
Xia Lin
,
Fabio Madonna
,
Evan Mason
,
François Massonnet
,
Marta Marcos
,
Salvatore Marullo
,
Benjamin Müller
,
Andre Obregon
,
Emanuele Organelli
,
Artur Palacz
,
Ananda Pascual
,
Andrea Pisano
,
Davide Putero
,
Arun Rana
,
Antonio Sánchez-Román
,
Sonia I. Seneviratne
,
Federico Serva
,
Andrea Storto
,
Wim Thiery
,
Peter Throne
,
Lander Van Tricht
,
Yoni Verhaegen
,
Gianluca Volpe
, and
Rosalia Santoleri

Abstract

If climate services are to lead to effective use of climate information in decision-making to enable the transition to a climate-smart, climate-ready world, then the question of trust in the products and services is of paramount importance. The Copernicus Climate Change Service (C3S) has been actively grappling with how to build such trust: provision of demonstrably independent assessments of the quality of products, which was deemed an important element in such trust-building processes. C3S provides access to essential climate variables (ECVs) from multiple sources to a broad set of users ranging from scientists to private companies and decision-makers. Here we outline the approach ­undertaken to coherently assess the quality of a suite of observation- and reanalysis-based ECV products covering the atmosphere, ocean, land, and cryosphere. The assessment is based on four pillars: basic data checks, maturity of the datasets, fitness for purpose (scientific use cases and climate studies), and guidance to users. It is undertaken independently by scientific experts and presented alongside the datasets in a fully traceable, replicable, and transparent manner. The methodology deployed is detailed, and example assessments are given. These independent scientific quality assessments are intended to guide users to ensure they use tools and datasets that are fit for purpose to answer their specific needs rather than simply use the first product they alight on. This is the first such effort to develop and apply an assessment framework consistently to all ECVs. Lessons learned and future perspectives are outlined to potentially improve future assessment activities and thus climate services.

Open access