Renellys C. Perez

Temporal variability of the meridional overturning circulation at 34.5 S: Results from two pilot boundary arrays in the South Atlantic

Data from two boundary arrays deployed along 34.5°S are combined to produce the first continuous in situ time series observations of the basin-wide meridional overturning circulation (MOC) in the South Atlantic. Daily estimates of the MOC between March 2009 and December 2010 range between 3 Sv and 39 Sv (1 Sv = 106 m3 s−1) after a 10 day low-pass filter is applied. Much of the variability in this ∼20 month record occurs at periods shorter than 100 days. Approximately two-thirds of the MOC variability is due to changes in the geostrophic (baroclinic plus barotropic) volume transport, with the remainder associated with the direct wind-forced Ekman transport. When low-pass filtered to match previously published analyses in the North Atlantic, the observed temporal standard deviation at 34.5°S matches or somewhat exceeds that observed by time series observations at 16°N, 26.5°N, and 41°N. For periods shorter than 20 days the basin-wide MOC variations are most strongly influenced by Ekman flows, while at periods between 20 and 90 days the geostrophic flows tend to exert slightly more control over the total transport variability of the MOC. The geostrophic shear variations are roughly equally controlled by density variations on the western and eastern boundaries at all time scales captured in the record. The observed time-mean MOC vertical structure and temporal variability agree well with the limited independent observations available for confirmation.

Induction doses of interferon‐α‐2a in combination with ribavirin and/or amantadine for the treatment of chronic hepatitis C in non‐responders to interferon monotherapy: a randomized trial

Summary.  The benefit of the triple therapy (interferon + amantadine + ribavirim) is still unknown. The efficacy of induction doses of interferon‐α‐2a monotherapy or in combination with ribavirin and/or amantadine was evaluated in interferon non‐responders with chronic hepatitis C. A total of 378 patients were randomized. All the groups received the same doses and duration of interferon‐α‐2a: (i) interferon 9 MUI/day for 4 weeks and then 3 MUI/3 t.i.w. for 44 weeks (n = 53); (ii) interferon in combination with amantadine 100 mg twice daily for 48 weeks (n = 111); (iii) interferon in combination with ribavirin 1000–1200 mg (n = 106); (iv) interferon in combination with amantadine and ribavirin (n = 108). Baseline parameters were similar in the four groups. Sustained virological and biochemical responses were 13%, 6%, 18% and 22% respectively. No significant differences were found between double ribavirin arm vs triple therapy, but the difference was significant between interferon–amantadine (P = 0.008) and triple therapy (P = 0.0005). Hence, the induction doses of interferon in combination with ribavirin or ribavirin plus amantadine showed encouraging results in patients with chronic hepatitis C who were resistant to interferon. However, triple therapy is not superior to double.

Basin‐Wide Oceanographic Array Bridges the South Atlantic

The meridional overturning circulation (MOC) is a global system of surface, intermediate, and deep ocean currents. The MOC connects the surface layer of the ocean and the atmosphere with the huge reservoir of the deep sea and is the primary mechanism for transporting heat, freshwater, and carbon between ocean basins. Climate models show that past changes in the strength of the MOC were linked to historical climate variations. Further research suggests that the MOC will continue to modulate climate change scenarios on time scales ranging from decades to centuries [Latif et al., 2006].

Geostrophic Velocity Measurement Techniques for the Meridional Overturning Circulation and Meridional Heat Transport in the South Atlantic

Two ocean general circulation models are used to test the ability of geostrophic velocity measurement systems to observe the meridional overturning circulation (MOC) and meridional heat transport (MHT) in the South Atlantic. Model sampling experiments are conducted at five latitudes (between 158 and 34.58S) spanning the range of extratropical current regimes in the South Atlantic. Two methods of estimating geopotential height anomalies and geostrophic velocities are tested, simulating dynamic height moorings (T‐S array) and current and pressure recording inverted echo sounders (CPIES) deployed within the models. The T‐S array accurately reproduces the MOC variability with a slight preference for higher latitudes, while the CPIES array has skill only at higherlatitudesresulting fromthe increasedgeopotential height anomalysignal. Whether direct model velocities or geostrophic velocities are used, MHT and the MOC are strongly correlated, and successful reconstruction of MHT only occurs when there is skill in the MOC reconstructions. The geopotential height anomaly signal is concentrated near the boundariesalong 34.58S, suggesting that this is an advantageous latitude for deployment of an in situ array. Four reduced arrays that build upon the sites from two existing pilot arrays along 34.58S were examined. For these realistically sized arrays, the MOC and MHT reconstructions from the T‐S and CPIES arrays have comparable skill, and an array of approximately 20 instruments can be effectively used to reproduce the temporal evolution and vertical structure of the MOC and MHT.

A global surface drifter data set at hourly resolution

The surface drifting buoys, or drifters, of the Global Drifter Program (GDP) are predominantly tracked by the Argos positioning system, providing drifter locations with O(100 m) errors at nonuniform temporal intervals, with an average interval of 1.2 h since January 2005. This data set is thus a rich and global source of information on high-frequency and small-scale oceanic processes, yet is still relatively understudied because of the challenges associated with its large size and sampling characteristics. A methodology is described to produce a new high-resolution global data set since 2005, consisting of drifter locations and velocities estimated at hourly intervals, along with their respective errors. Locations and velocities are obtained by modeling locally in time trajectories as a first-order polynomial with coefficients obtained by maximizing a likelihood function. This function is derived by modeling the Argos location errors with t location-scale probability distribution functions. The methodology is motivated by analyzing 82 drifters tracked contemporaneously by Argos and by the Global Positioning System, where the latter is assumed to provide true locations. A global spectral analysis of the velocity variance from the new data set reveals a sharply defined ridge of energy closely following the inertial frequency as a function of latitude, distinct energy peaks near diurnal and semidiurnal frequencies, as well as higher-frequency peaks located near tidal harmonics as well as near replicates of the inertial frequency. Compared to the spectra that can be obtained using the standard 6-hourly GDP product, the new data set contains up to 100% more spectral energy at some latitudes.

Fulfilling Observing System Implementation Requirements with the Global Drifter Array

AbstractThe Global Ocean Observing System (GOOS) requirements for in situ surface temperature and velocity measurements call for observations at 5° × 5° resolution. A key component of the GOOS that measures these essential climate variables is the global array of surface drifters. In this study, statistical observing system sampling experiments are performed to evaluate how many drifters are required to achieve the GOOS requirements, both with and without the presence of a completed global tropical moored buoy array at 5°S–5°N. The statistics for these simulations are derived from the evolution of the actual global drifter array. It is concluded that drifters should be deployed within the near-equatorial band even though that band is also in principle covered by the tropical moored array, as the benefits of not doing so are marginal. It is also concluded that an optimal design half-life for the drifters is ~450 days, neglecting external sources of death, such as running aground or being picked up. Finally...

A Generalized Method for Estimating the Structure of the Equatorial Atlantic Cold Tongue: Application to Drifter Observations

A generalized method is developed to determine the position of the Atlantic northern cold tongue front across its zonal extent from satellite sea surface temperature (SST) data. Previous approaches estimated the frontal position subjectively or individually, calling for a more objective technique that is suitable for large datasets. The developed methodology is based on a median frontal SST, and associated positional uncertainties are on the order of 0.38 latitude for the period 1998‐2011. Frontal characteristics are generally consistent with tropical instability waves (TIWs) and interannual variations are large. Application to drifter observations shows how the new methodology can be used to better understand circulation features near the northern cold tongue front. A drifter pair deployed on the eastern side of a passing TIW crest north of the frontrevealedthatthetrajectoriesofthedrifterswereclearlyinfluencedbytheshapeofthefrontandtheydid not cross the front, but rather stayed close together about 2.58 north of the front. In a more complete analysis using all available drifters near the Atlantic northern cold tongue front, only about 12% of the trajectories crossed the front. Analyses in an along- and cross-frontal frame of reference complement isopycnal coordinate mapping, and tropical Atlantic drifter velocities averaged in frontal coordinates indicate a broadened shear zone between the northern branch of the South Equatorial Current and North Equatorial Countercurrent as well as meridional convergence near the front.

Simultaneous pancreas-kidney transplant compared with kidney transplant in type I diabetic patients with end-stage renal disease.

IN OUR SECTIONS, diabetic nephropathy as a result of diabetes mellitus type I is the etiology of terminal renal insufficiency in 6% of patients on a dialysis program and in 8.7% of kidney transplant patients. This group of patients can benefit from a combined pancreas-kidney transplant (PKT), rather than an isolated kidney transplant (KT). This type of transplant eliminates the need for dialysis and therapy with insulin, as well as stabilizes retinopathy, neuropathy, and diabetic nephropathy. The aim of this article is to compare the results of PKT with those of isolated KT in patients with terminal renal insufficiency secondary to mellitus diabetes type I, assessing the number of rejections, kidney graft function, kidney and pancreas graft survival and patient survival during the first 2 posttransplant years.

Role of Mixed Layer Dynamics in Tropical North Atlantic Interannual Sea Surface Temperature Variability

AbstractThis study examines the causes of observed sea surface temperature (SST) anomalies in the tropical North Atlantic between 1982 and 2015. The emphasis is on the boreal winter and spring seasons, when tropical Atlantic SSTs project strongly onto the Atlantic meridional mode (AMM). Results from a composite analysis of satellite and reanalysis data show important forcing of SST anomalies by wind-driven changes in mixed layer depth and shortwave radiation between 5° and 10°N, in addition to the well-known positive wind–evaporation–SST and shortwave radiation–SST feedbacks between 5° and 20°N. Anomalous surface winds also drive pronounced thermocline depth anomalies of opposite signs in the eastern equatorial Atlantic and intertropical convergence zone (ITCZ; 2°–8°N). A major new finding is that there is strong event-to-event variability in the impact of thermocline depth on SST in the ITCZ region, in contrast to the more consistent relationship in the eastern equatorial Atlantic. Much stronger anomalie...

Measuring the Atlantic Meridional Overturning Circulation

The Atlantic meridional overturning circulation (AMOC) plays a crucial role in redistributing heat and salt throughout the global oceans. Achieving a more complete understanding of the behavior of the AMOC system requires a comprehensive observational network that spans the entire Atlantic basin. This article describes several different types of observational systems that are used by scientists of the National Oceanographic and Atmospheric Administration and their partners at other national and international institutions to study the complex nature of the AMOC. The article also highlights several emerging technologies that will aid AMOC studies in the future.