S. Guinehut

On the Use of Satellite Altimeter Data in Argo Quality Control

Abstract Satellite altimeter measurements are used to check the quality of the Argo profiling floats time series. The method compares collocated sea level anomalies from altimeter measurements and dynamic height anomalies calculated from Argo temperature and salinity profiles for each Argo float time series. Different kinds of anomalies (sensor drift, bias, spikes, etc.) have been identified on some real-time but also delayed-mode Argo floats. About 4% of the floats should probably not be used until they are carefully checked and reprocessed by the principal investigators (PIs). The method appears to be very complementary to the existing quality control checks performed in real time or delayed mode. It could also be used to quantify the impact of the adjustments made in delayed mode on the pressure, temperature, and salinity fields.

Design of an array of profiling floats in the North Atlantic from model simulations

This study aims to analyze the contribution of different profiling float arrays to the description of the 3-D large-scale thermohaline fields. It uses outputs and profiling float simulations derived from a primitive equation model of the North Atlantic Ocean. An optimal interpolation method is used to reconstruct the large-scale and low-frequency variability of the temperature and salinity fields at different depths from various sets of simulated temperature and salinity profiles. Both the covariance function and noise-to-signal ratio are derived from the analysis of the model fields. The differences between the reconstructed fields and the reference (model) fields are then analyzed. As expected, the results are sensitive to the a priori definition of the large-scale and low-frequency reference field. They show, however, that a 3j array with a 10-day cycle (Argo ‘‘nominal’’ resolution) can retrieve most of the variance of the large-scale and low-frequency temperature and salinity signals as observed by a 1/3j primitive equation model. The comparison between Eulerian and Lagrangian arrays shows only a slight deterioration in the results due to the spatial dispersion of the floats and due to the loss of 20 of them which left the model domain during the experiment. D 2002 Elsevier Science B.V. All rights reserved.

Assessing the impact of observations on ocean forecasts and reanalyses: Part 1, Global studies

Under GODAE OceanView the operational ocean modelling community has developed a suite of global ocean forecast, reanalysis and analysis systems. Each system has a critical dependence on ocean observations – routinely assimilating observations of in-situ temperature and salinity, and satellite sea-level anomaly and sea surface temperature. This paper demonstrates the value and impact of ocean observations to three global eddy-permitting forecast systems, one global eddy-permitting model-independent analysis system, one eddy-resolving reanalysis system, and two seasonal prediction systems. All systems have been used to assess the impact of Argo profiles, including scenarios with no Argo data, and a degraded Argo array – unanimously concluding that Argo is a critical data set – the most critical for seasonal prediction, and as critical as satellite altimetry for eddy-permitting applications. Most systems show that TAO data are as important as Argo in the tropical Pacific, and that XBT data have an impact that is comparable to other data types in the vicinity of XBT transects. It is clear that no currently available data type is redundant. On the contrary, the components of the global ocean observing system complement each other remarkably well, providing sufficient information to monitor and forecast the global ocean.

Net primary production in the Gulf Stream sustained by quasi‐geostrophic vertical exchanges

We analyze 12 years of mesoscale vertical motion derived from an observation-based product in the top 1000 m of the North West Atlantic Ocean. Vertical velocities (O(10 m d−1)) associated with Gulf Stream instabilities consist of alternating cells of upwelling and downwelling. Here we show that the magnitude of the vertical motions decays exponentially southward with an e-folding length scale that is informative on the dynamics of the system. We further investigate the impact of the vertical supply of nutrients about phytoplankton growth with a conceptual model incorporating the mean effect of nutrient distribution, quasi-geostrophic dynamics, and Ekman suction/pumping. Results confirm that the mean effect of mesoscale vertical velocity variability alone can sustain observed levels of net primary production in the immediate vicinity of the Gulf Stream, while other mechanisms, including horizontal advection and submesoscale dynamics, need to be considered when moving toward the subtropical gyre.