Significance of cyclonic SubTropical Oceanic Rings of Magnitude (STORM) eddies for the carbon budget of the euphotic layer in the subtropical northeast Atlantic

Author Posting. © American Geophysical Union, 2003. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 108, C12 (2003): 3383, doi:10.1029/2003JC001884.The interannual and seasonal variability of cyclonic eddies budded from the Azores Current during the period 1993–1999 in the northeast subtropical Atlantic region (20°N–34°N; 19°W–35°W) was studied by using TOPEX/Poseidon and ERS-1/2 altimeter images, the operational ocean mesoscale forecasting system SOPRANE, and a mesoscale eddies automatic detection system. Seventeen cyclonic eddies were detected and monitored for time periods ranging from 50 to 360 days. They were characterized by mean westward velocity, amplitude, diameter, and eccentricity of about 2 km d−1, 8 cm, 187 km and 0.7, respectively. The generation of cyclonic eddies was subjected to an important interannual variability, especially in 1995 when the activity of cyclonic eddies in the northeast Atlantic was more intense and associated with parallel changes in the eddy energy of the Azores Current. Seventy-five percent of the mesoscale features were generated throughout the October–February period. Significant relationships were found between the seasonal NAO index and both the annual eddy kinetic and potential energy in the Azores Current region and also the total annual area occupied by STORM eddies, calculated with a 1-year phase lag. The outcome of this study was used to estimate the contribution of STORM eddies to the organic carbon deficit measured in the northeast subtropical Atlantic. On average, these eddies accounted for <1% of the net community production in the region.This work has been done by CLS under contract (98.87.064.00.470.29.25) with SHOM/ CMO. This study was funded by the European Commission under the CANIGO contract MAS3CT960060 and CICYT. B. Mouriño was supported by a FPU fellowship from the Ministerio de Educacio´n y Cultura (Spain)

Global high-resolution mapping of ocean circulation from TOPEX/Poseidon and ERS-1 and -2

International audienceThis study focuses on the improved estimation of mesoscale surface ocean circulation obtained by merging TOPEX/Poseidon (T/P) and ERS-1 and -2 altimeter measurements between October 1992 and May 1998. Once carefully intercalibrated and homogenized, these data are merged through an advanced global objective analysis method that allows us to correct for residual long wavelength errors and uses realistic correlation scales of ocean dynamics. The high-resolution (0.25°×0.25°) merged T/P+ERS-1 and -2 sea level anomaly maps provide more homogeneous and reduced mapping errors than either individual data set and more realistic sea level and geostrophic velocity statistics than T/P data alone. Furthermore, the merged T/P+ERS-1 and -2 maps yield eddy kinetic energy (EKE) levels 30% higher than maps of T/P alone. They also permit realistic global estimates of east and north components of EKE and their seasonal variations, to study EKE sources better. A comparison of velocity statistics with World Ocean Circulation Experiment surface drifters in the North Atlantic shows very good agreement. Comparison with contemporary current meter data in various oceanic regimes also produces comparable levels of energy and similar ratios of northward and eastward energy, showing that the maps are suitable to studying anisotropy. The T/P+ERS zonal and meridional components of the mapped currents usually present comparable rms variability, even though the variability in the Atlantic is more isotropic than that in the Pacific, which exhibits strong zonal changes. The EKE map presents a very detailed description, presumably never before achieved at a global scale. Pronounced seasonal changes of the EKE are found in many regions, notably the northeastern Pacific, the northeastern and northwestern Atlantic, the tropical oceans, and the zonally extended bands centered near 20°S in the Indian and western Pacific Oceans and at 20°N in the northwestern Pacific

Modeling the structure and variability of the southern Benguela upwelling using QuikSCAT wind forcing

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Impact of atmospheric coastal jet off central Chile on sea surface temperature from satellite observations (2000-2007)

International audienceThe coast of central Chile is characterized by intermittent low-level along-shore southerly wind periods, called coastal jets (CJs). In this study, we take advantage of long-term satellite data to document the CJs characteristics over 2000-2007 and investigate its impact on upwelling. The CJ structure has a core some 100 km from the shore and a cross-shore scale of ∼160 km, and it usually lasts for several days (3-10). Its period of occurrence ranges from weekly to a few months. On the basis of covariance analyses between wind stress and sea surface temperature (SST) anomalies, it is found that CJ activity is seasonally phase locked with SST, with a peak season in August-October. The statistically dominant forcing mechanisms of the SST cooling during CJ event is a combination of seaward advection of temperature resulting from Ekman transport, air-sea heat exchange, and Ekman-driven coastal divergence. However, case studies of two events suggest a significant sensitivity of the dominant upwelling forcing mechanisms to the background conditions. For instance, the upward Ekman pumping associated with cyclonic wind stress curl is enhanced for the event with the CJ located more to the south. Although there are limitations associated with both the formulation of the heat budget and the data sets, the results illustrate the complexity of the upwelling forcing mechanisms in this region and the need for realistic high-resolution forcing fluxes. A CJ activity index is also proposed that takes into account the coastal upwelling variability, which can be used for teleconnection studies