Multi-model attribution of upper-ocean temperature changes using an isothermal approach

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Sensitivity of Arctic warming to sea ice concentration

We examine the sensitivity of Arctic amplification (AA) to background sea ice concentration (SIC) under greenhouse warming by analyzing the data sets of the historical and Representative Concentration Pathway 8.5 runs of the Coupled Model Intercomparison Project Phase 5. To determine whether the sensitivity of AA for a given radiative forcing depends on background SIC state, we examine the relationship between the AA trend and mean SIC on moving 30 year windows from 1960 to 2100. It is found that the annual mean AA trend varies depending on the mean SIC condition. In particular, some models show a highly variable AA trend in relation to the mean SIC clearly. In these models, the AA trend tends to increase until the mean SIC reaches a critical level (i.e., 20-30%), and the maximum AA trend is almost 3 to 5 times larger than the trend in the early stage of global warming (i.e., 50-60%, 60-70%). However, the AA trend tends to decrease after that. Further analysis shows that the sensitivity of AA trend to mean SIC condition is closely related to the feedback processes associated with summer surface albedo and winter turbulent heat flux in the Arctic Ocean.1111Ysciescopu

Consistency and discrepancy in the atmospheric response to Arctic sea-ice loss across climate models

This is the author accepted manuscript. The final version is available from Springer Nature via the DOI in this recordThe decline of Arctic sea ice is an integral part of anthropogenic climate change. Sea-ice loss is already having a significant impact on Arctic communities and ecosystems. Its role as a cause of climate changes outside of the Arctic has also attracted much scientific interest. Evidence is mounting that Arctic sea-ice loss can affect weather and climate throughout the Northern Hemisphere. The remote impacts of Arctic sea-ice loss can only be properly represented using models that simulate interactions among the ocean, sea ice, land and atmosphere. A synthesis of six such experiments with different models shows consistent hemispheric-wide atmospheric warming, strongest in the mid-to-high-latitude lower troposphere; an intensification of the wintertime Aleutian Low and, in most cases, the Siberian High; a weakening of the Icelandic Low; and a reduction in strength and southward shift of the mid-latitude westerly winds in winter. The atmospheric circulation response seems to be sensitive to the magnitude and geographic pattern of sea-ice loss and, in some cases, to the background climate state. However, it is unclear whether current-generation climate models respond too weakly to sea-ice change. We advocate for coordinated experiments that use different models and observational constraints to quantify the climate response to Arctic sea-ice loss.J.A.S. and R.B. were funded by the Natural Environment Research Council (NE/P006760/1). C.D. acknowledges the National Science Foundation (NSF), which sponsors the National Center for Atmospheric Research. D.M.S. was supported by the Met Office Hadley Centre Climate Programme (GA01101) and the APPLICATE project, which is funded by the European Union’s Horizon 2020 programme. X.Z. was supported by the NSF (ARC#1023592). P.J.K. and K.E.M. were supported by the Canadian Sea Ice and Snow Evolution Network, which is funded by the Natural Science and Engineering Research Council of Canada. T.O. was funded by Environment and Climate Change Canada (GCXE17S038). L.S. was supported by the National Oceanic and Atmospheric Administration’s Climate Program Office

Inter-model diversity in jet stream changes and its relation to Arctic climate in CMIP5

We examined how coupled general circulation models (CGCMs) simulate changes in the jet stream differently under greenhouse warming, and how this intermodel diversity is related to the simulated Arctic climate changes by analyzing the simulation of the Coupled Model Intercomparison Project Phase 5. Although the jet stream in the multi-model ensemble mean shifts poleward, a considerable diversity exists among the 34 CGCMs. We found that inter-model differences in zonal wind responses, especially in terms of meridional shift of the midlatitude jet, are highly dependent on Arctic surface warming and lower stratospheric cooling. Specifically, the midlatitude jet tends to shift relatively equatorward (poleward) in the models with stronger (weaker) Arctic surface warming, whereas the jet tends to shift relatively poleward (equatorward) in the models with stronger (weaker) Arctic lower stratospheric cooling.1156sciescopu

Pacific Decadal Oscillation and its relation to the extratropical atmospheric variation in CMIP5

It is investigated how the simulated Pacific Decadal Oscillation (PDO) differs among various coupled general circulation models (CGCMs), and how it is related to the simulated atmospheric variation in the North Pacific. The dataset of the historical runs of the 26 CGCMs reported to the Coupled Model Intercomparison Project Phase 5 are used. It is shown that the differences in the PDO pattern among 26 CGCMs are closely related to diverse displacements of the simulated Aleutian Low (AL), that is, the PDO pattern is highly dependent on longitudinal and latitudinal position of the anomalous AL associated with the PDO (PDO-related AL; AL(PDO)). In addition, it is demonstrated that in the models that have the southward shift of the AL(PDO), the North Pacific sea surface temperature anomalies (SSTAs) associated with the PDO tend to modulate the atmospheric circulation strongly, implying strong two-way feedback between ocean and atmosphere. Therefore, this gives relatively strong persistency of the PDO. It is also found that the PDO in these models is highly correlated with the variation of the Kuroshio Extension current, implying that ocean dynamical processes play an important role in developing SSTAs.X11118sciescopu

Multi-model attribution of upper-ocean temperature changes using an isothermal approach

Both air-sea heat exchanges and changes in ocean advection have contributed to observed upper-ocean warming most evident in the late-twentieth century. However, it is predominantly via changes in air-ea heat fluxes that human-induced climate forcings, such as increasing greenhouse gases, and other natural factors such as volcanic aerosols, have influenced global ocean heat content. The present study builds on previous work using two different indicators of upper-ocean temperature changes for the detection of both anthropogenic and natural external climate forcings. Using simulations from phase 5 of the Coupled Model Intercomparison Project, we compare mean temperatures above a fixed isotherm with the more widely adopted approach of using a fixed depth. We present the first multi-model ensemble detection and attribution analysis using the fixed isotherm approach to robustly detect both anthropogenic and natural external influences on upper-ocean temperatures. Although contributions from multidecadal natural variability cannot be fully removed, both the large multi-model ensemble size and properties of the isotherm analysis reduce internal variability of the ocean, resulting in better observation-model comparison of temperature changes since the 1950s. We further show that the high temporal resolution afforded by the isotherm analysis is required to detect natural external influences such as volcanic cooling events in the upper-ocean because the radiative effect of volcanic forcings is short-lived.111Nsciescopu

Quartz Resonator for Simultaneous Measurement of Changes in Mass and Electrical Impedance during Protein Adsorption

A novel quartz resonator has been developed for the synchronized measurement of changes in mass and electrical impedance during the adsorption of various concentrations of bovine serum albumin (BSA). The top platinum surface of the quartz crystal was used as the working electrode and real-time Fourier transform analysis was conducted to obtain time-resolved electrochemical impedance spectra. The change in mass due to the BSA adsorption was calculated from the change in the frequency of the quartz resonator. These simultaneous measurements of mass and electrical impedance were used to determine not only the kinetics of protein adsorption but also the morphological changes in the adsorbed layer, which were confirmed with atomic force microscopy. (C) 2013 The Electrochemical Society. All rights reserved.open1122sciescopu