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Conference paperNowack P, Ong QYE, Braesicke P, et al., 2019,
Machine learning parameterizations for ozone in climate sensitivity simulations
, Kurzfassungen der Meteorologentagung DACH -
Journal articleMalik A, Nowack PJ, Haigh JD, et al., 2019,
Tropical Pacific Climate Variability under Solar Geoengineering: Impacts on ENSO Extremes
<jats:p>Abstract. Many modelling studies suggest that the El Niño Southern Oscillation (ENSO), in interaction with the tropical Pacific background climate, will change under rising atmospheric greenhouse gas concentrations. Solar geoengineering (reducing the solar flux from outer space) has been proposed as a means to counteract anthropogenic greenhouse-induced changes in climate. Effectiveness of solar geoengineering is uncertain. Robust results are particularly difficult to obtain for ENSO because existing geoengineering simulations are too short (typically ~ 50 years) to detect statistically significant changes in the highly variable tropical Pacific background climate. We here present results from a 1000-year sunshade geoengineering simulation, G1, carried out with the coupled atmosphere-ocean general circulation model HadCM3L. In agreement with previous studies, reducing the shortwave solar flux more than compensates the warming in the tropical Pacific that develops in the 4×CO2 scenario: we observe an overcooling of 0.3 °C (5 %) and 0.23-mm day−1 (5 %) reduction in mean rainfall relative to preindustrial conditions in the G1 simulation. This is due to the different latitudinal distributions of the shortwave (solar) and longwave (CO2) forcings.The location of the Intertropical Convergence Zone (ITCZ) located north of equator in the tropical Pacific, which moved 7.5° southwards under 4×CO2, is also restored to its preindustrial location. However, other aspects of the tropical Pacific mean climate are not reset as effectively. Relative to preindustrial conditions, in G1 the zonal wind stress, zonal sea surface temperature (SST) gradient, and meridional SST gradient are reduced by 10 %, 11 %, and 9 %, respectively, and the Pacific Walker Circulation (PWC) is consistently weakened. The overall amplitude of ENSO strengthens by 5–8 %, but there is a 65 % reduct
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Journal articleThompson DWJ, Ceppi P, Li Y, 2019,
A robust constraint on the temperature and height of the extratropical tropopause
, Journal of Climate, Vol: 32, Pages: 273-287, ISSN: 0894-8755In a recent study, the authors hypothesize that the Clausius–Clapeyron relation provides a strong constraint on the temperature of the extratropical tropopause and hence the depth of mixing by extratropical eddies. The hypothesis is a generalization of the fixed-anvil temperature hypothesis to the global atmospheric circulation. It posits that the depth of robust mixing by extratropical eddies is limited by radiative cooling by water vapor—and hence saturation vapor pressures—in areas of sinking motion. The hypothesis implies that 1) radiative cooling by water vapor constrains the vertical structure and amplitude of extratropical dynamics and 2) the extratropical tropopause should remain at roughly the same temperature and lift under global warming. Here the authors test the hypothesis in numerical simulations run on an aquaplanet general circulation model (GCM) and a coupled atmosphere–ocean GCM (AOGCM). The extratropical cloud-top height, wave driving, and lapse-rate tropopause all shift upward but remain at roughly the same temperature when the aquaplanet GCM is forced by uniform surface warming of +4 K and when the AOGCM is forced by RCP8.5 scenario emissions. “Locking” simulations run on the aquaplanet GCM further reveal that 1) holding the water vapor concentrations input into the radiation code fixed while increasing surface temperatures strongly constrains the rise in the extratropical tropopause, whereas 2) increasing the water vapor concentrations input into the radiation code while holding surface temperatures fixed leads to robust rises in the extratropical tropopause. Together, the results suggest that roughly invariant extratropical tropopause temperatures constitutes an additional “robust response” of the climate system to global warming.
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Journal articlePapini E, Franci L, Landi S, et al., 2019,
Can Hall Magnetohydrodynamics Explain Plasma Turbulence at Sub-ion Scales?
, ASTROPHYSICAL JOURNAL, Vol: 870, ISSN: 0004-637X -
Journal articleTong Y, Vasko IY, Pulupa M, et al., 2019,
Whistler Wave Generation by Halo Electrons in the Solar Wind
, ASTROPHYSICAL JOURNAL LETTERS, Vol: 870, ISSN: 2041-8205- Author Web Link
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- Citations: 50
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Journal articleVerdini A, Grappin R, Montagud-Camps V, et al., 2019,
Numerical simulations of high cross-helicity turbulence from 0.2 to 1 AU
, NUOVO CIMENTO C-COLLOQUIA AND COMMUNICATIONS IN PHYSICS, Vol: 42, ISSN: 2037-4909 -
Journal articleDiaz-Aguado MF, Bonnell JW, Bale SD, et al., 2019,
Experimental Investigation of Total Photoemission Yield from New Satellite Surface Materials
, JOURNAL OF SPACECRAFT AND ROCKETS, Vol: 56, Pages: 248-258, ISSN: 0022-4650- Author Web Link
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- Citations: 7
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Journal articlePapini E, Franci L, Landi S, et al., 2019,
Statistics of magnetic reconnection and turbulence in Hall-MHD and hybrid-PIC simulations
, NUOVO CIMENTO C-COLLOQUIA AND COMMUNICATIONS IN PHYSICS, Vol: 42, ISSN: 2037-4909 -
Journal articleLandi S, Franci L, Papini E, et al., 2019,
Spectral anisotropies in high resolution three-dimensional simulations
, NUOVO CIMENTO C-COLLOQUIA AND COMMUNICATIONS IN PHYSICS, Vol: 42, ISSN: 2037-4909 -
Journal articleMin S-K, Kim Y-H, Park I-H, et al., 2019,
ANTHROPOGENIC CONTRIBUTION TO THE 2017 EARLIEST SUMMER ONSET IN SOUTH KOREA
, BULLETIN OF THE AMERICAN METEOROLOGICAL SOCIETY, Vol: 100, Pages: S73-S77, ISSN: 0003-0007 -
Conference paperPudney M, King S, Horbury T, et al., 2019,
SOLAR ORBITER STRATEGIES FOR EMC CONTROL AND VERIFICATION
, ESA Workshop on Aerospace EMC (Aerospace EMC), Publisher: IEEE- Author Web Link
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- Citations: 7
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Book chapterDougherty M, Christensen U, Cao H, et al., 2019,
Saturn's Magnetic Field and Dynamo
, Saturn in the 21st Century, Editors: Baines, Flasar, Krupp, Stallard, Publisher: Cambridge University Press, Pages: 69-96, ISBN: 978-1-107-10677-2 -
Conference paperBrown P, Auster U, Bergman JES, et al., 2019,
MEETING THE MAGNETIC EMC CHALLENGES FOR THE IN-SITU FIELD MEASUREMENTS ON THE JUICE MISSION
, ESA Workshop on Aerospace EMC (Aerospace EMC), Publisher: IEEE- Author Web Link
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- Citations: 5
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Journal articleTorbert RB, Burch JL, Phan TD, et al., 2018,
Electron-scale dynamics of the diffusion region during symmetric magnetic reconnection in space.
, Science, Vol: 362, Pages: 1391-1395Magnetic reconnection is an energy conversion process that occurs in many astrophysical contexts including Earth's magnetosphere, where the process can be investigated in situ by spacecraft. On 11 July 2017, the four Magnetospheric Multiscale spacecraft encountered a reconnection site in Earth's magnetotail, where reconnection involves symmetric inflow conditions. The electron-scale plasma measurements revealed (i) super-Alfvénic electron jets reaching 15,000 kilometers per second; (ii) electron meandering motion and acceleration by the electric field, producing multiple crescent-shaped structures in the velocity distributions; and (iii) the spatial dimensions of the electron diffusion region with an aspect ratio of 0.1 to 0.2, consistent with fast reconnection. The well-structured multiple layers of electron populations indicate that the dominant electron dynamics are mostly laminar, despite the presence of turbulence near the reconnection site.
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Journal articleMatteini L, Stansby D, Horbury TS, et al., 2018,
On the 1/f spectrum in the solar wind and its connection with magnetic compressibility
, Letters of the Astrophysical Journal, Vol: 869, ISSN: 2041-8205We discuss properties of Alfvénic fluctuations with large amplitude in plasmas characterized by low magnetic field compression. We note that in such systems power laws cannot develop with arbitrarily steep slopes at large scales, i.e., when $| \delta {\boldsymbol{B}}| $ becomes of the order of the background field $| {\boldsymbol{B}}| $. In such systems there is a scale l 0 at which the spectrum has to break due to the condition of weak compressibility. A very good example of this dynamics is offered by solar wind fluctuations in Alfvénic fast streams, characterized by the property of constant field magnitude. We show here that the distribution of $\delta B=| \delta {\boldsymbol{B}}| $ in the fast wind displays a strong cutoff at $\delta B/| {\boldsymbol{B}}| \lesssim 2$, as expected for fluctuations bounded on a sphere of radius $B=| {\boldsymbol{B}}| $. This is also associated with a saturation of the rms of the fluctuations at large scales and introduces a specific length l 0, above which the amplitude of the fluctuations becomes independent on the scale l. Consistent with that, the power spectrum at l > l 0 is characterized by a −1 spectral slope, as expected for fluctuations that are scale-independent. Moreover, we show that the spectral break between the 1/f and inertial range in solar wind spectra indeed corresponds to the scale l 0 at which $\langle \delta B/B\rangle \sim 1$. Such a simple model provides a possible alternative explanation of magnetic spectra observed in interplanetary space, also pointing out the inconsistency for a plasma to simultaneously maintain $| {\boldsymbol{B}}| \sim \mathrm{const}.$ at arbitrarily large scales and satisfy a Kolmogorov scaling.
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Journal articleHattermann FF, Wortmann M, Liersch S, et al., 2018,
Simulation of flood hazard and risk in the Danube basin with the Future Danube Model
, Climate Services, Vol: 12, Pages: 14-26, ISSN: 2405-8807Major river and flash flood events have accumulated in Central and Eastern Europe over the last decade reminding the public as well as the insurance sector that climate related risks are likely to become even more damaging and prevalent as climate patterns change. However, information about current and future hydro-climatic extremes is often not available. The Future Danube Model (FDM) is an end-user driven multi-hazard and risk model suite for the Danube region that has been developed to provide climate services related to perils such as heavy precipitation, heat waves, floods, and droughts under recent and scenario conditions. As a result, it provides spatially consistent information on extreme events and natural resources throughout the entire Danube catchment. It can be used to quantify climate risks, to support the implementation of the EU framework directives, for climate informed urban and land use planning, water resources management, and for climate proofing of large scale infrastructural planning including cost benefit analysis. The model suite consists of five individual and exchangeable modules: a weather and climate module, a hydrological module, a risk module, an adaptation module, and a web-based visualization module. They are linked in such a way that output from one module can either be used standalone or fed into subsequent modules. The utility of the tool has been tested by experts and stakeholders. The results show that more and more intense hydrological extremes are likely to occur under climate scenario conditions, e.g. higher order floods may occur more frequently.
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Journal articleEggington J, Mejnertsen L, Desai R, et al., 2018,
Forging links in Earth's plasma environment
, Astronomy and Geophysics, Vol: 59, Pages: 6.26-6.28, ISSN: 1366-8781 -
Journal articleHesse M, Norgren C, Tenfjord P, et al., 2018,
On the role of separatrix instabilities in heating the reconnection outflow region
, Physics of Plasmas, Vol: 25, ISSN: 1070-664XA study of the role microinstabilities at the reconnection separatrix can play in heating the electrons during the transition from inflow to outflow is being presented. We find that very strong flow shears at the separatrix layer lead to counterstreaming electron distributions in the region around the separatrix, which become unstable to a beam-type instability. Similar to what has been seen in earlier research, the ensuing instability leads to the formation of propagating electrostatic solitons. We show here that this region of strong electrostatic turbulence is the predominant electron heating site when transiting from inflow to outflow. The heating is the result of heating generated by electrostatic turbulence driven by overlapping beams, and its macroscopic effect is a quasi-viscous contribution to the overall electron energy balance. We suggest that instabilities at the separatrix can play a key role in the overall electron energy balance in magnetic reconnection.
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Journal articleGuo RL, Yao ZH, Sergis N, et al., 2018,
Reconnection Acceleration in Saturn's Dayside Magnetodisk: A Multicase Study with Cassini
, ASTROPHYSICAL JOURNAL LETTERS, Vol: 868, ISSN: 2041-8205 -
Journal articleRichardson TB, Forster PM, Andrews T, et al., 2018,
Drivers of Precipitation Change: An Energetic Understanding
, Journal of Climate, Vol: 31, Pages: 9641-9657, ISSN: 0894-8755The response of the hydrological cycle to climate forcings can be understood within the atmospheric energy budget framework. In this study precipitation and energy budget responses to five forcing agents are analyzed using 10 climate models from the Precipitation Driver Response Model Intercomparison Project (PDRMIP). Precipitation changes are split into a forcing-dependent fast response and a temperature-driven hydrological sensitivity. Globally, when normalized by top-of-atmosphere (TOA) forcing, fast precipitation changes are most sensitive to strongly absorbing drivers (CO2, black carbon). However, over land fast precipitation changes are most sensitive to weakly absorbing drivers (sulfate, solar) and are linked to rapid circulation changes. Despite this, land-mean fast responses to CO2 and black carbon exhibit more intermodel spread. Globally, the hydrological sensitivity is consistent across forcings, mainly associated with increased longwave cooling, which is highly correlated with intermodel spread. The land-mean hydrological sensitivity is weaker, consistent with limited moisture availability. The PDRMIP results are used to construct a simple model for land-mean and sea-mean precipitation change based on sea surface temperature change and TOA forcing. The model matches well with CMIP5 ensemble mean historical and future projections, and is used to understand the contributions of different drivers. During the twentieth century, temperature-driven intensification of land-mean precipitation has been masked by fast precipitation responses to anthropogenic sulfate and volcanic forcing, consistent with the small observed trend. However, as projected sulfate forcing decreases, and warming continues, land-mean precipitation is expected to increase more rapidly, and may become clearly observable by the mid-twenty-first century.
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Journal articleJohlander A, Vaivads A, Khotyaintsev YV, et al., 2018,
Shock ripples observed by the MMS spacecraft: ion reflection and dispersive properties
, PLASMA PHYSICS AND CONTROLLED FUSION, Vol: 60, ISSN: 0741-3335- Author Web Link
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- Citations: 21
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Journal articleKrupp N, Roussos E, Kollmann P, et al., 2018,
Energetic Neutral and Charged Particle Measurements in the Inner Saturnian Magnetosphere During the Grand Finale Orbits of Cassini 2016/2017
, GEOPHYSICAL RESEARCH LETTERS, Vol: 45, Pages: 10847-10854, ISSN: 0094-8276 -
Book chapterDougherty M, Buratti BJ, Seidelmann PK, et al., 2018,
Enceladus as an active world: History and discovery. In Enceladus and the Icy
, Enceladus and the Icy Moons of Saturn, Editors: Schenk, Clark, Howett, Verbiscer, Waite, Publisher: University of Arizona Press, Pages: 3-16, ISBN: 9780816537075Dougherty M. K., Buratti B. J., Seidelmann P. K., and Spencer J. R. (2018) Enceladus as an active world: History and discovery. In Enceladus and the Icy Moons of Saturn (P. M. Schenk et al., eds.), pp. 3–16. Univ. of Arizona, Tucson, DOI: ...
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Journal articleStansby D, Salem C, Matteini L, et al., 2018,
A new inner heliosphere proton parameter dataset from the Helios mission
, Solar Physics, Vol: 293, ISSN: 0038-0938In the near future, Parker Solar Probe and Solar Orbiter will provide the first comprehensive in-situ measurements of the solar wind in the inner heliosphere since the Helios mission in the 1970s. We describe a reprocessing of the original Helios ion distribution functions to provide reliable and reproducible data to characterise the proton core population of the solar wind in the inner heliosphere. A systematic fitting of bi-Maxwellian distribution functions was performed to the raw Helios ion distribution function data to extract the proton core number density, velocity, and temperatures parallel and perpendicular to the magnetic field. We present radial trends of these derived proton parameters, forming a benchmark to which new measurements in the inner heliosphere will be compared. The new dataset has been made openly available for other researchers to use, along with the source code used to generate it.
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Journal articleInai Y, Fujita R, Machida T, et al., 2018,
Seasonal characteristics of chemical and dynamical transports into the extratropical upper troposphere/lower stratosphere
<jats:p>Abstract. To investigate the seasonal characteristics of chemical tracer distributions in the extratropical upper troposphere and lower stratosphere (ExUTLS) as well as stratosphere–troposphere exchange processes, mixing fractions of air masses originating in the stratosphere, tropical troposphere, mid-latitude lower troposphere (LT), and high-latitude LT in the ExUTLS are estimated using 90-day backward trajectories calculated with European Centre For Medium-Range Weather Forecasts (ECMWF) ERA-Interim data as the meteorological input. Time-series of chemical tracers obtained from ground-based and airborne observations are incorporated into the estimated mixing fractions, thus reconstructing spatiotemporal distributions of chemical tracers in the ExUTLS. The reconstructed tracer distributions are analysed with the mixing fractions and the stratospheric age of air (AoA) estimated using a 10-year backward trajectory. The reconstructed distributions of CO and CO2 in the ExUTLS are affected primarily by tropospheric air masses because of the short chemical lifetime of the former and large seasonal variations in the troposphere of the latter. Distributions of CH4, N2O, and SF6 are controlled primarily by seasonally varying air masses transported from the stratosphere. For CH4 and N2O distributions, air masses transported via the deep branch of the Brewer–Dobson circulation are particularly important. This interpretation is qualitatively and quantitatively supported by the estimated spatiotemporal distributions of AoA. </jats:p>
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Journal articleYao ZH, Radioti A, Grodent D, et al., 2018,
Recurrent Magnetic Dipolarization at Saturn: Revealed by Cassini
, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 123, Pages: 8502-8517, ISSN: 2169-9380 -
Journal articleSorba AM, Achilleos NA, Guio P, et al., 2018,
The Periodic Flapping and Breathing of Saturn's Magnetodisk During Equinox
, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 123, Pages: 8292-8316, ISSN: 2169-9380 -
Journal articleHwang KJ, Sibeck DG, Burch JL, et al., 2018,
Small-scale flux transfer events formed in the reconnection exhaust region between two X lines
, Journal of Geophysical Research: Space Physics, Vol: 123, Pages: 8473-8488, ISSN: 2169-9380We report MMS observations of the ion-scale flux transfer events (FTEs) that may involve two main X lines and tearing instability between the two X lines. The four spacecraft detected multiple isolated regions with enhanced magnetic field strength and bipolar Bn signatures normal to the nominal magnetopause, indicating FTEs. The currents within the FTEs flow mostly parallel to B, and the magnetic tension force is balanced by the total pressure gradient force. During these events, the plasma bulk flow velocity was directed southward. Detailed analysis of the magnetic and electric field and plasma moments variations suggests that the FTEs were initially embedded within the exhaust region north of an X line but were later located southward/downstream of a subsequent X line. The cross sections of the individual FTEs are in the range of ~2.5–6.8 ion inertial lengths. The observations suggest the formation of multiple secondary FTEs. The presence of an X line in the exhaust region southward of a second X line results from the southward drift of an old X line and the reformation of a new X line. The current layer between the two X lines is unstable to the tearing instability, generating multiple ion-scale flux-rope-type secondary islands.
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Journal articleSchwartz SJ, Avanov L, Turner D, et al., 2018,
Ion kinetics in a hot flow anomaly: MMS observations
, Geophysical Research Letters, Vol: 45, Pages: 11520-11529, ISSN: 0094-8276Hot Flow Anomalies (HFAs) are transients observed at planetary bow shocks, formed by the shock interaction with a convected interplanetary current sheet. The primary interpretation relies on reflected ions channeled upstream along the current sheet. The short duration of HFAs has made direct observations of this process difficult. We employ high resolution measurements by NASA's Magnetospheric Multiscale Mission to probe the ion microphysics within a HFA. Magnetospheric Multiscale Mission data reveal a smoothly varying internal density and pressure, which increase toward the trailing edge of the HFA, sweeping up particles trapped within the current sheet. We find remnants of reflected or other backstreaming ions traveling along the current sheet, but most of these are not fast enough to out-run the incident current sheet convection. Despite the high level of internal turbulence, incident and backstreaming ions appear to couple gyro-kinetically in a coherent manner.
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Journal articleTong Y, Vasko I, Mozer FS, et al., 2018,
Simultaneous Multispacecraft Probing of Electron Phase Space Holes
, GEOPHYSICAL RESEARCH LETTERS, Vol: 45, Pages: 11513-11519, ISSN: 0094-8276- Author Web Link
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- Citations: 31
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