TY  - JOUR
A1  - Steffen, Will
A1  - Röckstrom, Johan
A1  - Richardson, Katherine
A1  - Lenton, Timothy M.
A1  - Folke, Carl
A1  - Liverman, Diana
A1  - Summerhayes, Colin P.
A1  - Barnosky, Anthony D.
A1  - Cornell, Sarah E.
A1  - Crucifix, Michel
A1  - Donges, Jonathan
A1  - Fetzer, Ingo
A1  - Lade, Steven J.
A1  - Scheffer, Marten
A1  - Winkelmann, Ricarda
A1  - Schellnhuber, Hans Joachim
T1  - Trajectories of the Earth System in the Anthropocene
JF  - Proceedings of the National Academy of Sciences of the United States of America
N2  - We explore the risk that self-reinforcing feedbacks could push the Earth System toward a planetary threshold that, if crossed, could prevent stabilization of the climate at intermediate temperature rises and cause continued warming on a "Hothouse Earth" pathway even as human emissions are reduced. Crossing the threshold would lead to a much higher global average temperature than any interglacial in the past 1.2 million years and to sea levels significantly higher than at any time in the Holocene. We examine the evidence that such a threshold might exist and where it might be. If the threshold is crossed, the resulting trajectory would likely cause serious disruptions to ecosystems, society, and economies. Collective human action is required to steer the Earth System away from a potential threshold and stabilize it in a habitable interglacial-like state. Such action entails stewardship of the entire Earth System-biosphere, climate, and societies-and could include decarbonization of the global economy, enhancement of biosphere carbon sinks, behavioral changes, technological innovations, new governance arrangements, and transformed social values.
KW  - Earth System trajectories
KW  - climate change
KW  - Anthropocene
KW  - biosphere feedbacks
KW  - tipping elements
Y1  - 2018
U6  - https://doi.org/10.1073/pnas.1810141115
SN  - 0027-8424
VL  - 115
IS  - 33
SP  - 8252
EP  - 8259
PB  - National Acad. of Sciences
CY  - Washington
ER  - 
TY  - JOUR
A1  - Reese, Ronja
A1  - Winkelmann, Ricarda
A1  - Gudmundsson, Gudmundur Hilmar
T1  - Grounding-line flux formula applied as a flux condition in numerical simulations fails for buttressed Antarctic ice streams
JF  - The Cryosphere : TC ; an interactive open access journal of the European Geosciences Union
N2  - Currently, several large-scale ice-flow models impose a condition on ice flux across grounding lines using an analytically motivated parameterisation of grounding-line flux. It has been suggested that employing this analytical expression alleviates the need for highly resolved computational domains around grounding lines of marine ice sheets. While the analytical flux formula is expected to be accurate in an unbuttressed flow-line setting, its validity has hitherto not been assessed for complex and realistic geometries such as those of the Antarctic Ice Sheet. Here the accuracy of this analytical flux formula is tested against an optimised ice flow model that uses a highly resolved computational mesh around the Antarctic grounding lines. We find that when applied to the Antarctic Ice Sheet the analytical expression provides inaccurate estimates of ice fluxes for almost all grounding lines. Furthermore, in many instances direct application of the analytical formula gives rise to unphysical complex-valued ice fluxes. We conclude that grounding lines of the Antarctic Ice Sheet are, in general, too highly buttressed for the analytical parameterisation to be of practical value for the calculation of grounding-line fluxes.
Y1  - 2018
U6  - https://doi.org/10.5194/tc-12-3229-2018
SN  - 1994-0416
SN  - 1994-0424
VL  - 12
IS  - 10
SP  - 3229
EP  - 3242
PB  - Copernicus
CY  - Göttingen
ER  - 
TY  - JOUR
A1  - Ni, Binbin
A1  - Cao, Xing
A1  - Shprits, Yuri
A1  - Summers, Danny
A1  - Gu, Xudong
A1  - Fu, Song
A1  - Lou, Yuequn
T1  - Hot Plasma Effects on the Cyclotron-Resonant Pitch-Angle Scattering Rates of Radiation Belt Electrons Due to EMIC Waves
JF  - Geophysical research letters
N2  - To investigate the hot plasma effects on the cyclotron-resonant interactions between electromagnetic ion cyclotron (EMIC) waves and radiation belt electrons in a realistic magnetospheric environment, calculations of the wave-induced bounce-averaged pitch angle diffusion coefficients are performed using both the cold and hot plasma dispersion relations. The results demonstrate that the hot plasma effects have a pronounced influence on the electron pitch angle scattering rates due to all three EMIC emission bands (H+, He+, and O+) when the hot plasma dispersion relation deviates significantly from the cold plasma approximation. For a given wave spectrum, the modification of the dispersion relation by hot anisotropic protons can strongly increase the minimum resonant energy for electrons interacting with O+ band EMIC waves, while the minimum resonant energies for H+ and He+ bands are not greatly affected. For H+ band EMIC waves, inclusion of hot protons tends to weaken the pitch angle scattering efficiency of >5MeV electrons. The most crucial differences introduced by the hot plasma effects occur for >3MeV electron scattering rates by He+ band EMIC waves. Mainly due to the changes of resonant frequency and wave group velocity when the hot protons are included, the difference in scattering rates can be up to an order of magnitude, showing a strong dependence on both electron energy and equatorial pitch angle. Our study confirms the importance of including hot plasma effects in modeling the scattering of ultra-relativistic radiation belt electrons by EMIC waves.
Y1  - 2018
U6  - https://doi.org/10.1002/2017GL076028
SN  - 0094-8276
SN  - 1944-8007
VL  - 45
IS  - 1
SP  - 21
EP  - 30
PB  - American Geophysical Union
CY  - Washington
ER  - 
TY  - JOUR
A1  - Shprits, Yuri
A1  - Menietti, J. D.
A1  - Drozdov, Alexander
A1  - Horne, Richard B.
A1  - Woodfield, Emma E.
A1  - Groene, J. B.
A1  - de Soria-Santacruz, M.
A1  - Averkamp, T. F.
A1  - Garrett, H.
A1  - Paranicas, C.
A1  - Gurnett, Don A.
T1  - Strong whistler mode waves observed in the vicinity of Jupiter’s moons
JF  - Nature Communications
N2  - Understanding of wave environments is critical for the understanding of how particles are accelerated and lost in space. This study shows that in the vicinity of Europa and Ganymede, that respectively have induced and internal magnetic fields, chorus wave power is significantly increased. The observed enhancements are persistent and exceed median values of wave activity by up to 6 orders of magnitude for Ganymede. Produced waves may have a pronounced effect on the acceleration and loss of particles in the Jovian magnetosphere and other astrophysical objects. The generated waves are capable of significantly modifying the energetic particle environment, accelerating particles to very high energies, or producing depletions in phase space density. Observations of Jupiter’s magnetosphere provide a unique opportunity to observe how objects with an internal magnetic field can interact with particles trapped in magnetic fields of larger scale objects.
Y1  - 2018
U6  - https://doi.org/10.1038/s41467-018-05431-x
SN  - 2041-1723
VL  - 9
PB  - Nature Publ. Group
CY  - London
ER  - 
TY  - JOUR
A1  - Kim, Kyung-Chan
A1  - Shprits, Yuri
T1  - Survey of the Favorable Conditions for Magnetosonic Wave Excitation
JF  - Journal of geophysical research : Space physics
N2  - The ratio of the proton ring velocity (VR) to the local Alfven speed (VA), in addition to proton ring distributions, plays a key factor in the excitation of magnetosonic waves at frequencies between the proton cyclotron frequency fcp and the lower hybrid resonance frequency fLHR in the Earth's magnetosphere. Here we investigate whether there is a statistically significant relationship between occurrences of proton rings and magnetosonic waves both outside and inside the plasmapause using particle and wave data from Van Allen Probe-A during the time period of October 2012 to December 2015. We also perform a statistical survey of the ratio of the ring energy (ER, corresponding to VR) to the Alfven energy (EA, corresponding to VA) to determine the favorable conditions under which magnetosonic waves in each of two frequency bands (fcp < f ≤ 0.5 fLHR and 0.5 fLHR < f < fLHR) can be excited. The results show that the magnetosonic waves in both frequency bands occur around the postnoon (12–18 magnetic local time, MLT) sector outside the plasmapause when ER is comparable to or lower than EA, and those in lower-frequency bands (fcp < f ≤ 0.5 fLHR) occur around the postnoon sector inside the plasmapause when ER/EA > ~9. However, there is one discrepancy between occurrences of proton rings and magnetosonic waves in low-frequency bands around the prenoon sector (6–12 MLT) outside the plasmapause, which suggests either that the waves may have propagated during active time from the postnoon sector after being excited during quiet time, or they may have locally excited in the prenoon sector during active time.
Y1  - 2018
U6  - https://doi.org/10.1002/2017JA024865
SN  - 2169-9380
SN  - 2169-9402
VL  - 123
IS  - 1
SP  - 400
EP  - 413
PB  - American Geophysical Union
CY  - Washington
ER  - 
TY  - JOUR
A1  - Woodfield, Emma E.
A1  - Horne, Richard B.
A1  - Glauert, S. A.
A1  - Menietti, J. D.
A1  - Shprits, Yuri
A1  - Kurth, William S.
T1  - Formation of electron radiation belts at Saturn by Z-mode wave acceleration
JF  - Nature Communications
N2  - At Saturn electrons are trapped in the planet’s magnetic field and accelerated to relativistic energies to form the radiation belts, but how this dramatic increase in electron energy occurs is still unknown. Until now the mechanism of radial diffusion has been assumed but we show here that in-situ acceleration through wave particle interactions, which initial studies dismissed as ineffectual at Saturn, is in fact a vital part of the energetic particle dynamics there. We present evidence from numerical simulations based on Cassini spacecraft data that a particular plasma wave, known as Z-mode, accelerates electrons to MeV energies inside 4 RS (1 RS = 60,330 km) through a Doppler shifted cyclotron resonant interaction. Our results show that the Z-mode waves observed are not oblique as previously assumed and are much better accelerators than O-mode waves, resulting in an electron energy spectrum that closely approaches observed values without any transport effects included.
Y1  - 2018
U6  - https://doi.org/10.1038/s41467-018-07549-4
SN  - 2041-1723
VL  - 9
PB  - Nature Publ. Group
CY  - London
ER  -