An analysis of Atlantic Water in the Arctic Ocean using the Arctic Subpolar Gyre State Estimate and observations

Submitted in partial fulfillment of the requirements for the degree of Master of Science in Physical Oceanography at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2020.The Atlantic Water (AW) Layer in the Arctic Subpolar gyre sTate Estimate (ASTE), a regional, medium-resolution coupled ocean-sea ice state estimate, is analyzed for the first time using bounding isopycnals. A surge of AW, marked by rapid increases in mean AW Layer potential temperature and AW Layer thickness, begins two years into the state estimate (2004) and traverses the Arctic Ocean along boundary current pathways at approximately 2 cm/s. The surge also alters AW flow direction and speed including a significant reversal in flow direction along the Lomonosov Ridge. The surge results in a new quasi-steady AW flow from 2010 through the end of the state estimate period in 2017. The time-mean AW circulation during this time period indicates a significant amount of AW spreads over the Lomonosov Ridge rather than directly returning along the ridge to Fram Strait. A three-layer depiction of ASTE’s overturning circulation within the AO indicates AW is converted to colder, fresher Surface Layer water at a faster rate than is transformed to Bottom Water (1.2 Sv vs. 0.4 Sv). Observed AW properties compared to ASTE output indicate increasing misfit during the simulated period with ASTE’s AW Layer generally being warmer and thicker than in observations.This research was funded via the United States Navy’s Civilian Institution Program with the MIT/WHOI Joint Program (JP). The thesis supervisor’s participation in this project was supported by National Science Foundation-Grant #PLR-1603660 and by Office of Naval Research-Grant #N000141612381. This project, specifically ASTE developed by Dr. An T. Nguyen, is also supported by National Science Foundation-Grant #PLR-1603903

An analysis of Atlantic water in the Arctic Ocean using the Arctic subpolar gyre state estimate and observations

© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Grabon, J. S., Toole, J. M., Nguyen, A. T., & Krishfield, R. A. An analysis of Atlantic water in the Arctic Ocean using the Arctic subpolar gyre state estimate and observations. Progress in Oceanography, 198, (2021): 102685, https://doi.org/10.1016/j.pocean.2021.102685.The Atlantic Water (AW) Layer in the Arctic Subpolar gyre sTate Estimate Release 1 (ASTE R1), a data-constrained, regional, medium-resolution coupled ocean-sea ice model, is analyzed for the period 2004–2017 in combination with available hydrographic data. The study, focusing on AW defined as the waters between two bounding isopycnals, examines the time-average, mean seasonal cycle and interannual variability of AW Layer properties and circulation. A surge of AW, marked by rapid increases in mean AW Layer potential temperature and AW Layer thickness, begins two years into the state estimate and traverses the Arctic Ocean along boundary current pathways at a speed of 1–2 cm/s. The surge also alters AW circulation, including a reversal in flow direction along the Lomonosov Ridge, resulting in a new quasi-steady AW circulation from 2010 through the end of the state estimate period. The time-mean AW circulation during this latter time period indicates that a significant amount of AW spreads over the Lomonosov Ridge rather than directly returning along the ridge to Fram Strait. A three-layer depiction of the time-averaged ASTE R1 overturning circulation within the Arctic Ocean reveals that more AW is converted to colder, fresher Surface Layer water than is transformed to Deep and Bottom Water (1.2 Sv vs. 0.4 Sv). ASTE R1 also exhibits an increase in the volume of AW over the study period at a rate of 1.4 Sv, with near compensating decrease in Deep and Bottom Water volume. Observed AW properties compared to ASTE R1 output reveal increasing misfit during the simulated period with the ASTE R1 AW Layer generally being warmer and thicker than in observations.This work is based on the dissertation of the lead author submitted in partial requirement of a M.S. degree from the Massachusetts Institute of Technology/Woods Hole Oceanographic Institution Joint Program in Oceanography. The lead author’s participation was funded by the United States Navy’s Civilian Institution (CIVINS) Program. The contributions to this study by the junior authors were supported by the National Science Foundation (JMT and RAK grant PLR-1603660; ATN grant NSF-OPP-1603903)

Airborne Lidar Observations of the Transition Zone Between the Convective Boundary Layer and Free Atmosphere During the International H2O Project (IHOP) in 2002

Airborne, light detection and ranging (lidar) backscatter observations of the convective boundary layer from the International H2O Project (IHOP) in 2002 are analysed to study the structure of the transition zone; the backscatter gradient between the convective boundary layer and free atmosphere. A newmathematical algorithm is developed and used to extract high-resolution (15 m) transition-zone boundaries from 6,500 km (flight legs) of airborne observations.The cospectra of transition-zone boundaries and its thickness indicate that thickness changes occur from boundaries moving in opposite directions (vertically) at small wavelengths (1 km) both boundaries move coherently, with the lower boundary changing altitude more rapidly. Daily probability distributions of the transition-zone thickness are positively skewed with a mode of 60 m. The structure of the transition zone shows no dependence on the “overall” Richardson number, unlike the entrainment zone. This study provides the first quantitative characterization of the structure of the instantaneous transition zone, a contribution towards an improved understanding of convective boundary-layer entrainment

First studies of final focus quadrupoles vibrations of the z lattice of FCC-ee

International audienceThe proposed FCC-ee machine is a high-energy, high-intensity and high-precision lepton collider which will require to reduce as much as possible the differential motions of its two beams at the interaction points. In this prospect, the vibration impacts of the quadrupoles in the region close to the interaction point are investigated. Considering the z-pole optics design and its dedicated optics simulation under MAD-X, the present paper describes the integration of the dynamics aspects (vibrations mitigation) to render the modelling more realistic towards operation. This simulation is based on the "particle tracking" mode. In this prospect, dynamic characteristics of the designed mechanical assembly are estimated according to an analysis in finite element models. Required transfer functions and realistic temporal sequences along the assembly are thus created and they can be implemented as inputs to the optical simulations to verify that this assembly allows the expected beam parameters. The obtained results on a dedicated cantilever mock-up are presented and the last optics simulations are discussed

First studies of final focus quadrupoles vibrations of the z lattice of FCC-ee

International audienceThe proposed FCC-ee machine is a high-energy, high-intensity and high-precision lepton collider which will require to reduce as much as possible the differential motions of its two beams at the interaction points. In this prospect, the vibration impacts of the quadrupoles in the region close to the interaction point are investigated. Considering the z-pole optics design and its dedicated optics simulation under MAD-X, the present paper describes the integration of the dynamics aspects (vibrations mitigation) to render the modelling more realistic towards operation. This simulation is based on the "particle tracking" mode. In this prospect, dynamic characteristics of the designed mechanical assembly are estimated according to an analysis in finite element models. Required transfer functions and realistic temporal sequences along the assembly are thus created and they can be implemented as inputs to the optical simulations to verify that this assembly allows the expected beam parameters. The obtained results on a dedicated cantilever mock-up are presented and the last optics simulations are discussed

Influence of vibratory effects on the beam parameters of SuperKEKB

International audienceSuperKEKB is an asymmetrical lepton collider with a circumference of 3 016 meters, which collides 7 GeV electrons with 4 GeV positrons. To optimize the luminosity, which recently reached a world record of 4.71 10^34 cm-2 s-1, all the undesirable effects on beam parameters must be analyzed in detail, especially close to the interaction point where the Belle II detector is operated. The presented study investigates the influence of mechanical vibration on the luminosity. For this purpose, four seismic sensors (Guralp 6T) were installed and collect data 24 hours a day, two on the ground and another two located on the supports of the two cantilevered cryostats, inside which the last focusing magnets on both sides of the interaction point (the most critical for vibrations) are mounted. The luminosity is measured thanks to the LumiBelle2 fast luminosity monitor, which is based on diamond detectors installed in both beam lines. Vibration-induced disturbances in the luminosity frequency spectrum are investigated for several types of perturbations, in particular the ones resulting from ground motion amplified by the dynamical behavior of the cryostat, as well as also from external vibrations sources

Influence of vibratory effects on the beam parameters of SuperKEKB

International audienceSuperKEKB is an asymmetrical lepton collider with a circumference of 3 016 meters, which collides 7 GeV electrons with 4 GeV positrons. To optimize the luminosity, which recently reached a world record of 4.71 10^34 cm-2 s-1, all the undesirable effects on beam parameters must be analyzed in detail, especially close to the interaction point where the Belle II detector is operated. The presented study investigates the influence of mechanical vibration on the luminosity. For this purpose, four seismic sensors (Guralp 6T) were installed and collect data 24 hours a day, two on the ground and another two located on the supports of the two cantilevered cryostats, inside which the last focusing magnets on both sides of the interaction point (the most critical for vibrations) are mounted. The luminosity is measured thanks to the LumiBelle2 fast luminosity monitor, which is based on diamond detectors installed in both beam lines. Vibration-induced disturbances in the luminosity frequency spectrum are investigated for several types of perturbations, in particular the ones resulting from ground motion amplified by the dynamical behavior of the cryostat, as well as also from external vibrations sources