Time scales of the Greenland freshwater anomaly in the subpolar North Atlantic

Author Posting. © American Meteorological Society, 2021. 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 Climate 34(22), (2021): 8971–8987, https://doi.org/10.1175/JCLI-D-20-0610.1.The impact of increasing Greenland freshwater discharge on the subpolar North Atlantic (SPNA) remains unknown as there are uncertainties associated with the time scales of the Greenland freshwater anomaly (GFWA) in the SPNA. Results from numerical simulations tracking GFWA and an analytical approach are employed to estimate the response time, suggesting that a decadal time scale (13 years) is required for the SPNA to adjust for increasing GFWA. Analytical solutions obtained for a long-lasting increase of freshwater discharge show a non-steady-state response of the SPNA with increasing content of the GFWA. In contrast, solutions for a short-lived pulse of freshwater demonstrate different responses of the SPNA with a rapid increase of freshwater in the domain followed by an exponential decay after the pulse has passed. The derived theoretical relation between time scales shows that residence time scales are time dependent for a non-steady-state case and asymptote the response time scale with time. The residence time of the GFWA deduced from Lagrangian experiments is close to and smaller than the response time, in agreement with the theory. The Lagrangian analysis shows dependence of the residence time on the entrance route of the GFWA and on the depth. The fraction of the GFWA exported through Davis Strait has limited impact on the interior basins, whereas the fraction entering the SPNA from the southwest Greenland shelf spreads into the interior regions. In both cases, the residence time of the GFWA increases with depth demonstrating long persistence of the freshwater anomaly in the subsurface layers.D. S. Dukhovskoy and E. P. Chassignet were funded by the DOE (Award DE-SC0014378) and HYCOM NOPP (Award N00014-19-1-2674). The HYCOM-CICE simulations were supported by a grant of computer time from the DoD High-Performance Computing Modernization Program at NRL SSC. G. Platov was funded by the RSF N19-17-00154. P. G. Myers was funded by an NSERC Discovery Grant (Grant RGPIN 04357). A. Proshutinsky was funded by FAMOS project (NSF Grant NSF 14-584)

Forest Protection and Permanence of Reduced Emissions

Tropical forests are essential for climate change mitigation. As awareness grows over the use of credits from reduced emissions from deforestation and forest degradation (REDD+) and other nature-based climate solutions within both voluntary and compliance carbon markets, key concerns about the long-term durability of the reductions, or their permanence, arise for countries, corporations, regulators and policy makers. The paper seeks to analyze an efficient means of distribution and application of different policy pathways to slow down and stop deforestation and explore the longevity of reductions via modeling. The impact of policies like REDD+ most likely will have a time limitation. At some point tropical nations will take more responsibility to protect forests. REDD+ should constitute an initial intervention that will help tropical nations shock to a zero-deforestation trajectory. To establish conditions of permanence, we conduct numerical analyses using a model based on a cellular automata algorithm that learns from historical deforestation patterns and other spatial features in the Brazilian state of Mato Grosso. The model simulates future deforestation, first applying policy to reduce deforestation and then relaxing the policy intervention. Our simulations show that policies that are successful in reducing deforestation and related emissions from business as usual may have long-term positive consequences on an avoided deforestation trajectory even after potential policy reversals. Some accumulated gains could be lost but sizable benefits will remain, assuring permanence of emissions reduction during the policy implementation and potentially even after policies are relaxed. Hence, permanence depends both on the probability of policy reversals and the risk of emissions rebounding. Our results are important for advancing the understanding around the unsettled debate on the permanence of avoided emissions. Further, this paper argues that as policies to prevent deforestation or reduce emissions otherwise are reversible, permanence should be understood and discussed in a probabilistic and time-dependent framework

Greenland freshwater pathways in the sub-Arctic Seas from model experiments with passive tracers

Author Posting. © American Geophysical Union, 2016. 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: Oceans 121 (2016): 877–907, doi:10.1002/2015JC011290.Accelerating since the early 1990s, the Greenland Ice Sheet mass loss exerts a significant impact on thermohaline processes in the sub-Arctic seas. Surplus freshwater discharge from Greenland since the 1990s, comparable in volume to the amount of freshwater present during the Great Salinity Anomaly events, could spread and accumulate in the sub-Arctic seas, influencing convective processes there. However, hydrographic observations in the Labrador Sea and the Nordic Seas, where the Greenland freshening signal might be expected to propagate, do not show a persistent freshening in the upper ocean during last two decades. This raises the question of where the surplus Greenland freshwater has propagated. In order to investigate the fate, pathways, and propagation rate of Greenland meltwater in the sub-Arctic seas, several numerical experiments using a passive tracer to track the spreading of Greenland freshwater have been conducted as a part of the Forum for Arctic Ocean Modeling and Observational Synthesis effort. The models show that Greenland freshwater propagates and accumulates in the sub-Arctic seas, although the models disagree on the amount of tracer propagation into the convective regions. Results highlight the differences in simulated physical mechanisms at play in different models and underscore the continued importance of intercomparison studies. It is estimated that surplus Greenland freshwater flux should have caused a salinity decrease by 0.06–0.08 in the sub-Arctic seas in contradiction with the recently observed salinification (by 0.15–0.2) in the region. It is surmised that the increasing salinity of Atlantic Water has obscured the freshening signal.NSERC. Grant Numbers RGPIN 227438-09, RGPIN 04357 and RGPCC 433898; RFBR. Grant Number 13-05-00480, 14-05-00730, and 15-05-02457; NSF Grant Number: PLR-0804010, PLR-1313614, and PLR-12037202016-07-2

Theory of phase-locking in generalized hybrid Josephson junction arrays

A recently proposed scheme for the analytical treatment of the dynamics of two-dimensional hybrid Josephson junction arrays is extended to a class of generalized hybrid arrays with ''horizontal'' shunts involving a capacitive as well as an inductive component. This class of arrays is of special interest, because the internal cell coupling has been shown numerically to favor in-phase synchronization for certain parameter values. As a result, we derive limits on the circuit design parameters for realizing this state. In addition, we obtain formulas for the flux-dependent frequency including flux-induced switching processes between the in-phase and anti-phase oscillation regime. The treatment covers unloaded arrays as well as arrays shunted via an external load.Comment: 24 pages, REVTeX, 5 Postscript figures, Subm. to Phys. Rev.

Forest protection and permanence of reduced emissions

Tropical forests are essential for climate change mitigation. With growing interest over the use of credits from reducing emissions from deforestation and forest degradation (REDD+) and other natural climate solutions within both voluntary and compliance carbon markets, key concerns about the long-term durability of the reductions, or their permanence, arise for countries, corporations, regulators, and policy makers. This paper seeks to analyze the longevity of emissions reductions from different policies to slow down and stop deforestation. To establish conditions of permanence, we conduct numerical analyses using a model based on a cellular automata algorithm that learns from historical deforestation patterns and other spatial features in the Brazilian state of Mato Grosso. First, we simulate increased law enforcement to curb deforestation at a jurisdictional scale from 2025 to 2034, followed by potential policy rollbacks from 2035 to 2050. Second, we consider alternative scenarios to avoid potentially legal deforestation coupled with reforestation. We find spatial and path dependence – a successful policy intervention may permanently change the deforestation trajectory even after potential policy reversals. Hence, permanence depends both on the probability of policy reversals and the risk of emissions overshooting. Our results are important for advancing the understanding around the unsettled debate on the permanence of avoided emissions. Further, this paper argues that as policies to prevent deforestation or reduce emissions otherwise are reversible, permanence should be understood and discussed in a probabilistic and time-dependent framework

Численное моделирование современного состояния вод и морского льда Северного Ледовитого океана

The paper presents results of numerical simulation of variability of the sea ice area and water circulation in the Arctic Ocean performed with use of the atmosphere reanalysis data for the period from middle of the last century to the present time. The model results reflect the ocean responses to changes of the atmosphere circulation regimes that manifests in changes of trajectories of waters coming into the Arctic Ocean from the Pacific and Atlantic oceans. The model results show influence of the Pacific and Atlantic waters on distribution and thickness of the Arctic ice. В работе представлены результаты численного моделирования изменчивости площади морского льда и циркуляции вод Северного Ледовитого океана с использованием данных реанализа атмосферы. Результаты моделирования отражают реакцию океана на смену режимов циркуляции атмосферы, что проявляется в изменении траектории движения вод, поступающих в Арктический бассейн из Тихого и Атлантического океанов. Показано влияние тихоокеанских и атлантических вод на распределение и толщину арктического льда.

On The Relationship Between Magnetic Cancellation and UV Burst Formation

Burst-like events with signatures in the UV are often observed co-spatial to strong line-of-sight photospheric magnetic fields. Several authors, for example, have noted the spatial relationship between Ellerman bombs (EBs) and Moving Magnetic Features (MMFs), regions of flux which disconnect from a sunspot or pore before propagating away in the moat flow and often displaying evidence of cancellation. In this article, data collected by the Solar Dynamics Observatory's Helioseismic and Magnetic Imager and Atmospheric Imaging Assembly are analysed in an attempt to understand the potential links between such cancellation and UV burst formation. Two MMFs from AR 11579, three bi-poles from AR 11765, and six bi-poles (four of which were co-spatial to IRIS bursts) in AR 11850 were identified for analysis. All of these cancellation features were found to have lifetimes of the order hours and cancellation rates of the order 10^14-10^15 Mx s^-1. H-alpha line wing data from the Dunn Solar Telescope's Interferometric BIdimensional Spectrometer were also available for AR 11579 facilitating a discussion of links between MMFs and EBs. Using an algebraic model of photospheric magnetic reconnection, the measured cancellation rates are then used to ascertain estimates of certain quantities (such as up-flow speeds, jet extents, and potential energy releases) which compared reasonably to the properties of EBs reported within the literature. Our results suggest that cancellation rates of the order measured here are capable of supplying enough energy to drive certain UV bursts (including EBs), however, they are not a guaranteeing condition for burst formation

Thermal effect of bainitic transformation in tube steels during accelerated cooling

An original laboratory bench, which allows for modeling technological rates of cooling of hot-rolled sheets in the process of controlled thermomechanical processing (TMCP) has been designed. Samples cut from an industrial sheet of 06G2MB type pipe steel used in production of large diameter pipes with strength grade X80 have been used. Time dependencies of the actual temperature at initial cooling rates of 100 – 500 K / s have been obtained. All processing modes resulted in almost identical structures mainly formed due to the bainitic transformation. The dispersion of structures decreased with the increase of the cooling rate. Thermotechnical calculations were carried out assuming that the temperature equalization over the sample thickness was instant. The times of transformation amounted to 1 – 9 s. Most of the transformation at all cooling modes occurred in conditions close to the isothermal one. The athermal nature of the bainitic transformation in TMCP was recorded. Within the observed interval of cooling rates, the temperature at the starting point of the bainitic transformation was 660 – 730°C. The heat effect approximately was equal to 120 kJ / kg, which is twice larger than the thermal effect of the martensite transformation for low-carbon steels. This fact suggests that the kinetics of the bainitic transformation is largely determined by the energy of the slowest process, namely, the re-arrangement of carbon atoms in the austenite occurring parallelly to the shear transformation of FCC lattice into BCC one. It is assumed that energy contribution of the redistribution process of carbon atoms (if their amount is small) to the thermal effect of the bainitic transformation is comparable, at least, to the energy effect of the shear lattice rearrangement. © 2018, Institute for Metals Superplasticity Problems of Russian Academy of Sciences. All rights reserved.Благодарности/Acknowledgements. Работа выпол-нена на  оборудовании ОАО «Аусферр». Работа выпол-нена в  рамках государственного задания ФАНО России, тема «Структура» (”Structure“), номер госрегистрации 0120146333. Авторы выражают признательность за со-действие программе поддержки ведущих университетов РФ в целях повышения их конкурентоспособности № 211 Правительства РФ №02.А03.21.0006./The study was performed on the equipment from OAO “Ausferr”. The study was performed within the framework of the state assignment from the Federal Agency for Scientific Organizations of Russian Federation, theme “Structure”, registration number 0120146333. The authors express their gratitud

Numerical simulations of the current state of waters and sea ice in the Arctic Ocean

The paper presents results of numerical simulation of variability of the sea ice area and water circulation in the Arctic Ocean performed with use of the atmosphere reanalysis data for the period from middle of the last century to the present time. The model results reflect the ocean responses to changes of the atmosphere circulation regimes that manifests in changes of trajectories of waters coming into the Arctic Ocean from the Pacific and Atlantic oceans. The model results show influence of the Pacific and Atlantic waters on distribution and thickness of the Arctic ice