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Ananda Pascual
and
Damià Gomis

Abstract

An extension of the use of altimetric data aimed at inferring the vertical structure of the geostrophic velocity field (and thereby to compute transports) is explored. The method is based on the assumption that altimetry provides a reliable measure of dynamic height (DH), and on the fact that DH and the density field can both be expressed in terms of the DH empirical orthogonal functions (EOFs). It is then argued that when altimetry is complemented by surface density data, it is possible to determine the amplitudes of the two leading EOFs of the mass field, which altogether usually account for a large percentage of the field variance.

The method is tested in the western Mediterranean, where historical databases contain enough data as to compute statistically significant EOFs. Results indicate that with altimetric data alone (i.e., DH in the tests), the EOF-based method can estimate the actual velocity field with an uncertainty of about 60% (in terms of total transport). However, if surface density is also available, estimates have an uncertainty of only 20%. Limitations of the method such as the underlying statistical assumptions, data errors, and the assumed equivalence between altimetry and DH are also discussed.

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Evan Mason
,
Ananda Pascual
, and
James C. McWilliams
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Evan Mason
,
Ananda Pascual
, and
James C. McWilliams

Abstract

This paper presents a software tool that enables the identification and automated tracking of oceanic eddies observed with satellite altimetry in user-specified regions throughout the global ocean. As input, the code requires sequential maps of sea level anomalies such as those provided by Archiving, Validation, and Interpretation of Satellite Oceanographic (AVISO) data. Outputs take the form of (i) data files containing eddy properties, including position, radius, amplitude, and azimuthal (geostrophic) speed; and (ii) sequential image maps showing sea surface height maps with active eddy centers and tracks overlaid. The results given are from a demonstration in the Canary Basin region of the northeast Atlantic and are comparable with a published global eddy track database. Some discrepancies between the two datasets include eddy radius magnitude, and the distributions of eddy births and deaths. The discrepancies may be related to differences in the eddy identification methods, and also possibly to differences in the smoothing of the sea surface height maps. The code is written in Python and is made freely available under a GNU license (http://www.imedea.uib.es/users/emason/py-eddy-tracker/).

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Ananda Pascual
,
Christine Boone
,
Gilles Larnicol
, and
Pierre-Yves Le Traon

Abstract

The timeliness of satellite altimeter measurements has a significant effect on their value for operational oceanography. In this paper, an Observing System Experiment (OSE) approach is used to assess the quality of real-time altimeter products, a key issue for robust monitoring and forecasting of the ocean state. In addition, the effect of two improved geophysical corrections and the number of missions that are combined in the altimeter products are also analyzed. The improved tidal and atmospheric corrections have a significant effect in coastal areas (0–100 km from the shore), and a comparison with tide gauge observations shows a slightly better agreement with the gridded delayed-time sea level anomalies (SLAs) with two altimeters [Jason-1 and European Remote Sensing Satellite-2 (ERS-2)/Envisat] using the new geophysical corrections (mean square differences in percent of tide gauge variance of 35.3%) than those with four missions [Jason-1, ERS/Envisat, Ocean Topography Experiment (TOPEX)/Poseidoninterlaced, and Geosat Follow-On] but using the old corrections (36.7%). In the deep ocean, however, the correction improvements have little influence. The performance of fast delivery products versus delayed-time data is compared using independent in situ data (tide gauge and drifter data). It clearly highlights the degradation of real-time SLA maps versus the delayed-time SLA maps: four altimeters are needed in real time to get the similar quality performance as two altimeters in delayed time (sea level error misfit around 36%, and zonal and meridional velocity estimation errors of 27% and 33%, respectively). This study proves that the continuous improvement of geophysical corrections is very important, and that it is essential to stay above a minimum threshold of four available altimetric missions to capture the main space and time oceanic scales in fast delivery products.

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Ananda Pascual
,
Damià Gomis
,
Robert L. Haney
, and
Simón Ruiz

Abstract

The quasigeostrophic geopotential tendency and omega equations are integrated to examine the dynamics of an upper-ocean coastal meander sampled during an intensive survey in the Palamós Canyon (northwestern Mediterranean Sea). Results for dynamic height tendency reveal that the meander is not growing or decaying but is propagating downstream at a velocity of about 4 km day−1. This propagation speed implies a problem of synopticity in the field observations, which is solved through a data relocation scheme. The station relocation has important consequences on the magnitude of crucial dynamical variables such as the vertical velocity: maximum values of 20 m day−1 before the relocation reduce to 10 m day−1 after the relocation. The impact of bottom boundary conditions in the solution of the omega equation is also analyzed. Results indicate that for the stratification encountered during the survey, effects of topographic forcing are negligible above approximately 300 m.

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Amala Mahadevan
,
Ananda Pascual
,
Daniel L. Rudnick
,
Simón Ruiz
,
Joaquín Tintoré
, and
Eric D’Asaro
Free access
Bartolomé Garau
,
Simón Ruiz
,
Weifeng G. Zhang
,
Ananda Pascual
,
Emma Heslop
,
John Kerfoot
, and
Joaquín Tintoré

Abstract

In this work a new methodology is proposed to correct the thermal lag error in data from unpumped CTD sensors installed on Slocum gliders. The advantage of the new approach is twofold: first, it takes into account the variable speed of the glider; and second, it can be applied to CTD profiles from an autonomous platform either with or without a reference cast. The proposed methodology finds values for four correction parameters that minimize the area between two temperature–salinity curves given by two CTD profiles. A field experiment with a Slocum glider and a standard CTD was conducted to test the method. Thermal lag–induced salinity error of about 0.3 psu was found and successfully corrected.

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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