A prototype system for observing the Atlantic Meridional Overturning Circulation - scientific basis, measurement and risk mitigation strategies, and first results

The Atlantic Meridional Overturning Circulation (MOC) carries up to one quarter of the global northward heat transport in the Subtropical North Atlantic. A system monitoring the strength of the MOC volume transport has been operating since April 2004. The core of this system is an array of moored sensors measuring density, bottom pressure and ocean currents. A strategy to mitigate risks of possible partial failures of the array is presented, relying on backup and complementary measurements. The MOC is decomposed into five components, making use of the continuous moored observations, and of cable measurements across the Straits of Florida, and wind stress data. The components compensate for each other, indicating that the system is working reliably. The year-long average strength of the MOC is 18.7±5.6 Sv, with wind-driven and density-inferred transports contributing equally to the variability. Numerical simulations suggest that the surprisingly fast density changes at the western boundary are partially linked to westward propagating planetary wave

Measurement of the B0s Lifetime in the Flavor-Specific Decay Channel B0s→D−sμ+νX

We present an updated measurement of the B0s lifetime using the semileptonic decays B0s→D−sμ+νX, with D−s→ϕπ− and ϕ→K+K− (and the charge conjugate process). This measurement uses the full Tevatron Run II sample of proton-antiproton collisions at s√=1.96  TeV, comprising an integrated luminosity of 10.4  fb−1. We find a flavor-specific lifetime τfs(B0s)=1.479±0.010(stat)±0.021(syst)  ps. This technique is also used to determine the B0 lifetime using the analogous B0→D−μ+νX decay with D−→ϕπ− and ϕ→K+K−, yielding τ(B0)=1.534±0.019(stat)±0.021(syst)  ps. Both measurements are consistent with the current world averages, and the B0s lifetime measurement is one of the most precise to date. Taking advantage of the cancellation of systematic uncertainties, we determine the lifetime ratio τfs(B0s)/τ(B0)=0.964±0.013(stat)±0.007(syst)

Using Argo data to investigate the Meridional Overturning Circulation in the North Atlantic

Author Posting. © The Author(s), 2009. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part I: Oceanographic Research Papers 57 (2010): 29-36, doi:10.1016/j.dsr.2009.10.003.Using a variety of oceanographic data, including direct volume transports in the Florida 19 Strait, and Argo float profiles and drift velocities at 24 and 36N in the North Atlantic, inverse calculations are presented in which the net meridional transport, 20 down to a depth of approximately 1600 m, is estimated at both latitudes for a five year period 2003-2007. The upper ocean is divided into 7 layers using neutral density, and mass conservation constraints have been applied to a closed box bounded by these latitudes, including the Florida Strait. Ekman layer transports have been included in the top-most layer, and the inverse calculation has solved for changes from the initial reference velocities, Ekman and Florida Strait transports, given a priori estimates on the accuracy of each of these quantities. Solutions with and without transformations due to Mediterranean Water (MW) formation are made. Our results indicate that 1) time-averaged transport estimates derived from Argo have significant less eddy noise than individual hydrographic sections, 2) Argo drift velocities provide information to the inverse solution for the ocean interior, and 3) comparison of the total integrated interior mass transports in the thermocline waters for the period 2003-2007 with the previous estimates based on trans-ocean hydrographic sections shows that the Meridional Overturning Circulation has not significantly changed since 1957.TJ would like to acknowledge support from NSF Grant OCE-0241354 and NOAA/CICOR grant NA17RJ1223

Performance of an Operating High Energy Physics Data Grid: D0SAR-Grid

The D0 experiment at Fermilab's Tevatron will record several petabytes of data over the next five years in pursuing the goals of understanding nature and searching for the origin of mass. Computing resources required to analyze these data far exceed capabilities of any one institution. Moreover, the widely scattered geographical distribution of D0 collaborators poses further serious difficulties for optimal use of human and computing resources. These difficulties will exacerbate in future high energy physics experiments, like the LHC. The computing grid has long been recognized as a solution to these problems. This technology is being made a more immediate reality to end users in D0 by developing a grid in the D0 Southern Analysis Region (D0SAR), D0SAR-Grid, using all available resources within it and a home-grown local task manager, McFarm. We will present the architecture in which the D0SAR-Grid is implemented, the use of technology and the functionality of the grid, and the experience from operating the grid in simulation, reprocessing and data analyses for a currently running HEP experiment.Comment: 3 pages, no figures, conference proceedings of DPF04 tal

The present and future system for measuring the Atlantic meridional overturning circulation and heat transport

of the global combined atmosphere-ocean heat flux and so is important for the mean climate of the Atlantic sector of the Northern Hemisphere. This meridional heat flux is accomplished by both the Atlantic Meridional Overturning Circulation (AMOC) and by basin-wide horizontal gyre circulations. In the North Atlantic subtropical latitudes the AMOC dominates the meridional heat flux, while in subpolar latitudes and in the subtropical South Atlantic the gyre circulations are also important. Climate models suggest the AMOC will slow over the coming decades as the earth warms, causing widespread cooling in the Northern hemisphere and additional sea-level rise. Monitoring systems for selected components of the AMOC have been in place in some areas for decades, nevertheless the present observational network provides only a partial view of the AMOC, and does not unambiguously resolve the full variability of the circulation. Additional observations, building on existing measurements, are required to more completely quantify the Atlantic meridional heat transport. A basin-wide monitoring array along 26.5°N has been continuously measuring the strength and vertical structure of the AMOC and meridional heat transport since March 31, 2004. The array has demonstrated its ability to observe the AMOC variability at that latitude and also a variety of surprising variability that will require substantially longer time series to understand fully. Here we propose monitoring the Atlantic meridional heat transport throughout the Atlantic at selected critical latitudes that have already been identified as regions of interest for the study of deep water formation and the strength of the subpolar gyre, transport variability of the Deep Western Boundary Current (DWBC) as well as the upper limb of the AMOC, and inter-ocean and intrabasin exchanges with the ultimate goal of determining regional and global controls for the AMOC in the North and South Atlantic Oceans. These new arrays will continuously measure the full depth, basin-wide or choke-point circulation and heat transport at a number of latitudes, to establish the dynamics and variability at each latitude and then their meridional connectivity. Modeling studies indicate that adaptations of the 26.5°N type of array may provide successful AMOC monitoring at other latitudes. However, further analysis and the development of new technologies will be needed to optimize cost effective systems for providing long term monitoring and data recovery at climate time scales. These arrays will provide benchmark observations of the AMOC that are fundamental for assimilation, initialization, and the verification of coupled hindcast/forecast climate models

Mixing and entrainment in the Red Sea outflow plume. Part I : plume structure

Author Posting. © American Meteorological Society, 2005. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 35 (2005): 569–583, doi:10.1175/JPO2679.1.When the salty and heavy water of the Red Sea exits from the Strait of Bab el Mandeb, it continues downslope into the Gulf of Aden mainly along two channels. The 130-km-long “Northern Channel” (NC) is topographically confined and is typically only 5 km wide. In it, the Red Sea plume shows unanticipated patterns of vertical structure, turbulent mixing, and entrainment. Above the seafloor a 25–120-m-thick weakly stratified layer shows little dilution along the channel. Hence this bottom layer undergoes only weak entrainment. In contrast, a 35–285-m-thick interfacial layer shows stronger entrainment and is shown in a companion paper to undergo vigorous turbulent mixing. It is thus the interface that exhibits the bulk of entrainment of the Red Sea plume in the NC. The interfacial layer also carries most of the overall plume transport, increasingly so with downstream distance. The “Southern Channel” (SC) is wider than the NC and is accessed from the latter by a sill about 33 m above the floor of the NC. Entrainment into the bottom layer of the SC is diagnosed to be strong near the entry into the SC such that the near-bottom density and salinity are smaller in the SC than in the NC at the same distance from Bab el Mandeb. In comparison with winter conditions, the authors encountered weaker outflow with shallower equilibration depths during the summer cruise. Bulk Froude numbers computed for the whole plume varied within the range 0.2–1. Local maxima occurred in relatively steep channel sections and coincided with locations of significant entrainment.The Red Sea Outflow Experiment was funded by the National Science Foundation under Contracts OCE-9819506 and OCE-9818464. Additional support was provided to the “Climate Process Team Gravity Currents” under OCE-0336799

Measurement of the top quark mass in the lepton+jets channel using the ideogram method

This is the publisher's version, also available electronically from http://journals.aps.org/prd/abstract/10.1103/PhysRevD.75.092001

Lifetime Difference and CP-Violating Phase in the B(0)(s)System

This is the publisher's version, also available electronically from http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.98.121801