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Journal articleEscoubet CP, Hwang K-J, Toledo-Redondo S, et al., 2020,
Cluster and MMS simultaneous observations of magnetosheath high speed jets and their impact on the magnetopause
, Frontiers in Astronomy and Space Sciences, Vol: 6, Pages: 1-21, ISSN: 2296-987XWhen the supersonic solar wind encounters the Earth's magnetosphere a shock, called bow shock, is formed and the plasma is decelerated and thermalized in the magnetosheath downstream from the shock. Sometimes, however, due to discontinuities in the solar wind, bow shock ripples or ionized dust clouds carried by the solar wind, high speed jets (HSJs) are observed in the magnetosheath. These HSJs have typically a Vx component larger than 200 km s−1 and their dynamic pressure can be a few times the solar wind dynamic pressure. They are typically observed downstream from the quasi-parallel bow shock and have a typical size around one Earth radius (RE) in XGSE. We use a conjunction of Cluster and MMS, crossing simultaneously the magnetopause, to study the characteristics of these HSJs and their impact on the magnetopause. Over 1 h 15 min interval in the magnetosheath, Cluster observed 21 HSJs. During the same period, MMS observed 12 HSJs and entered the magnetosphere several times. A jet was observed simultaneously by both MMS and Cluster and it is very likely that they were two distinct HSJs. This shows that HSJs are not localized into small regions but could span a region larger than 10 RE, especially when the quasi-parallel shock is covering the entire dayside magnetosphere under radial IMF. During this period, two and six magnetopause crossings were observed, respectively, on Cluster and MMS with a significant angle between the observation and the expected normal deduced from models. The angles observed range between from 11° up to 114°. One inbound magnetopause crossing observed by Cluster (magnetopause moving out at 142 km s−1) was observed simultaneous to an outbound magnetopause crossing observed by MMS (magnetopause moving in at −83 km s−1), showing that the magnetopause can have multiple local indentation places, most likely independent from each other. Under the continuous impacts of HSJs, the magnetopause is deformed significan
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Journal articlePerrone D, D'Amicis R, De Marco R, et al., 2020,
Highly Alfvenic slow solar wind at 0.3 au during a solar minimum: Helios insights for Parker Solar Probe and Solar Orbiter
, Astronomy and Astrophysics: a European journal, Vol: 633, Pages: 1-7, ISSN: 0004-6361Alfvénic fluctuations in solar wind are an intrinsic property of fast streams, while slow intervals typically have a very low degree of Alfvénicity, with much more variable parameters. However, sometimes a slow wind can be highly Alfvénic. Here we compare three different regimes of solar wind, in terms of Alfvénic content and spectral properties, during a minimum phase of the solar activity and at 0.3 au. We show that fast and Alfvénic slow intervals share some common characteristics. This would suggest a similar solar origin, with the latter coming from over-expanded magnetic field lines, in agreement with observations at 1 au and at the maximum of the solar cycle. Due to the Alfvénic nature of the fluctuations in both fast and Alfvénic slow winds, we observe a well-defined correlation between the flow speed and the angle between magnetic field vector and radial direction. The high level of Alfvénicity is also responsible of intermittent enhancements (i.e. spikes), in plasma speed. Moreover, only for the Alfvénic intervals do we observe a break between the inertial range and large scales, on about the timescale typical of the Alfvénic fluctuations and where the magnetic fluctuations saturate, limited by the magnitude of the local magnetic field. In agreement with this, we recover a characteristic low-frequency 1/f scaling, as expected for fluctuations that are scale-independent. This work is directly relevant for the next solar missions, Parker Solar Probe and Solar Orbiter. One of the goals of these two missions is to study the origin and evolution of slow solar wind. In particular, Parker Solar Probe will give information about the Alfvénic slow wind in the unexplored region much closer to the Sun and Solar Orbiter will allow us to connect the observed physics to the source of the plasma.
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Journal articleWang R, Vasko IY, Mozer FS, et al., 2020,
Electrostatic Turbulence and Debye-scale Structures in Collisionless Shocks
, ASTROPHYSICAL JOURNAL LETTERS, Vol: 889, ISSN: 2041-8205- Author Web Link
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- Citations: 43
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Journal articleLiu Z, Wang L, Shi Q, et al., 2020,
Case Study of Solar Wind Suprathermal Electron Acceleration at the Earth's Bow Shock
, ASTROPHYSICAL JOURNAL LETTERS, Vol: 889, ISSN: 2041-8205- Author Web Link
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- Citations: 5
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Journal articleGryspeerdt E, Mülmenstädt J, Gettelman A, et al., 2020,
Surprising similarities in model and observational aerosol radiative forcing estimates
, Atmospheric Chemistry and Physics, Vol: 20, Pages: 613-623, ISSN: 1680-7316The radiative forcing from aerosols (particularly through their interaction with clouds) remains one of the mostuncertain components of the human forcing of the climate. Observation-based studies have typically found a smaller aerosoleffective radiative forcing than in model simulations and were given preferential weighting in the IPCC AR5 report. With theirown sources of uncertainty, it is not clear that observation-based estimates are more reliable. Understanding the source of the model-observational difference is thus vital to reduce uncertainty in the impact of aerosols on the climate.These reported discrepancies arise from the different methods of separating the components of aerosol forcing used in modeland observational studies. Applying the observational decomposition to global climate model output, the two different linesof evidence are surprisingly similar, with a much better agreement on the magnitude of aerosol impacts on cloud properties.Cloud adjustments remain a significant source of uncertainty, particularly for ice clouds. However, they are consistent with the uncertainty from observation-based methods, with the liquid water path adjustment usually enhancing the Twomey effectby less than 50%. Depending on different sets of assumptions, this work suggests that model and observation-based estimatescould be more equally weighted in future synthesis studies.
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Journal articleZelinka MD, Myers TA, McCoy DT, et al., 2020,
Causes of higher climate sensitivity in CMIP6 models
, Geophysical Research Letters, Vol: 47, ISSN: 0094-8276Equilibrium climate sensitivity, the global surface temperature response to CO urn:x-wiley:grl:media:grl60047:grl60047-math-0001 doubling, has been persistently uncertain. Recent consensus places it likely within 1.5–4.5 K. Global climate models (GCMs), which attempt to represent all relevant physical processes, provide the most direct means of estimating climate sensitivity via CO urn:x-wiley:grl:media:grl60047:grl60047-math-0002 quadrupling experiments. Here we show that the closely related effective climate sensitivity has increased substantially in Coupled Model Intercomparison Project phase 6 (CMIP6), with values spanning 1.8–5.6 K across 27 GCMs and exceeding 4.5 K in 10 of them. This (statistically insignificant) increase is primarily due to stronger positive cloud feedbacks from decreasing extratropical low cloud coverage and albedo. Both of these are tied to the physical representation of clouds which in CMIP6 models lead to weaker responses of extratropical low cloud cover and water content to unforced variations in surface temperature. Establishing the plausibility of these higher sensitivity models is imperative given their implied societal ramifications.
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Journal articleGingell I, Schwartz SJ, Eastwood JP, et al., 2020,
Statistics of reconnecting current sheets in the transition region of earth's bow shock
, Journal of Geophysical Research: Space Physics, Vol: 125, Pages: 1-14, ISSN: 2169-9380We have conducted a comprehensive survey of burst mode observations of Earth's bow shock by the Magnetospheric Multiscale mission to identify and characterize current sheets associated with collisionless shocks, with a focus on those containing fast electron outflows, a likely signature of magnetic reconnection. The survey demonstrates that these thin current sheets are observed within the transition region of approximately 40% of shocks within the burst mode data set of Magnetospheric Multiscale. With only small apparent bias toward quasi‐parallel shock orientations and high Alfvén Mach numbers, the results suggest that reconnection at shocks is a universal process, occurring across all shock orientations and Mach numbers. On examining the distributions of current sheet properties, we find no correlation between distance from the shock, sheet width, or electron jet speed, though the relationship between electron and ion jet speed supports expectations of electron‐only reconnection in the region. Furthermore, we find that robust heating statistics are not separable from background fluctuations, and thus, the primary consequence of reconnection at shocks is in relaxing the topology of the disordered magnetic field in the transition region.
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Journal articleHanson ELM, Agapitov OV, Mozer FS, et al., 2020,
Terrestrial Bow Shock Parameters From MMS Measurements: Dependence on Upstream and Downstream Time Ranges
, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 125, ISSN: 2169-9380- Author Web Link
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- Citations: 3
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Journal articleVihma T, Graversen R, Chen L, et al., 2020,
Effects of the tropospheric large-scale circulation on European winter temperatures during the period of amplified Arctic warming
, INTERNATIONAL JOURNAL OF CLIMATOLOGY, Vol: 40, Pages: 509-529, ISSN: 0899-8418- Cite
- Citations: 48
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Journal articleWolf G, Czaja A, Brayshaw DJ, et al., 2020,
Connection between Sea Surface Anomalies and Atmospheric Quasi-Stationary Waves
, JOURNAL OF CLIMATE, Vol: 33, Pages: 201-212, ISSN: 0894-8755- Author Web Link
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- Citations: 6
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Journal articleReid J, Cargill PJ, Hood AW, et al., 2020,
Coronal energy release by MHD avalanches: Heating mechanisms
, Astronomy and Astrophysics: a European journal, Vol: 633, Pages: 1-16, ISSN: 0004-6361The plasma heating associated with an avalanche involving three twisted magnetic threads within a coronal loop is investigated using three-dimensional magnetohydrodynamic simulations. The avalanche is triggered by the kink instability of one thread, with the others being engulfed as a consequence. The heating as a function of both time and location along the strands is evaluated. It is shown to be bursty at all times but to have no preferred spatial location. While there appears to be a level of “background” heating, this is shown to be comprised of individual, small heating events. A comparison between viscous and resistive (Ohmic) heating demonstrates that the strongest heating events are largely associated with the Ohmic heating that arises when the current exceeds a critical value. Viscous heating is largely (but not entirely) associated with smaller events. Ohmic heating dominates viscous heating only at the time of the initial kink instability. It is also demonstrated that a variety of viscous models lead to similar heating rates, suggesting that the system adjusts to dissipate the same amount of energy.
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Journal articleCao Y, Wellbrock A, Coates AJ, et al., 2020,
Field‐aligned photoelectron energy peaks at high altitude and on the nightside of titan
, Journal of Geophysical Research: Planets, Vol: 125, Pages: 1-13, ISSN: 2169-9097The ionization of N urn:x-wiley:jgre:media:jgre21272:jgre21272-math-0001 by strong solar He II 30.4‐nm photons produces distinctive spectral peaks near 24.1 eV in Titan's upper atmosphere, which have been observed by the Electron Spectrometer (ELS) as part of the Cassini Plasma Spectrometer. The ELS observations reveal that, in addition to the dayside, photoelectron peaks were also detected on the deep nightside where photoionization is switched off, as well as at sufficiently high altitudes where the ambient neutral density is low. These photoelectron peaks are unlikely to be produced locally but instead must be contributed by transport along the magnetic field lines from their dayside source regions. In this study, we present a statistical survey of all photoelectron peaks identified with an automatic finite impulse response algorithm based on the available ELS data accumulated during 56 Titan flybys. The spatial distribution of photoelectron peaks indicates that most photoelectrons detected at an altitude above 4,000 km and a solar zenith angle above 100° are field aligned, which is consistent with the scenario of photoelectron transport along the magnetic field lines. Our analysis also reveals the presence of a photoelectron gap in the deep nightside ionosphere where almost no photoelectrons were detected. It appears to be very difficult for photoelectrons to travel to this region, and such a feature may not be driven by the changes in the orientation between the solar and corotation wakes.
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Conference paperHeyns M, Lotz S, Gaunt CT, 2020,
Probabilistic Analysis of Power Network Susceptibility to GICs
, International Conference on Probabilistic Methods Applied to Power Systems (PMAPS), Publisher: IEEE, ISSN: 2642-6730 -
Conference paperOyedokun D, Heyns M, Cilliers P, et al., 2020,
Frequency Components of Geomagnetically Induced Currents for Power System Modelling
, International SAUPEC/RobMech/PRASA Conference, Publisher: IEEE, Pages: 824-829- Author Web Link
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- Citations: 23
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Journal articleKlein KG, Martinovic M, Stansby D, et al., 2019,
Linear Stability in the Inner Heliosphere: <i>Helios</i> Re-evaluated
, ASTROPHYSICAL JOURNAL, Vol: 887, ISSN: 0004-637X- Author Web Link
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- Citations: 15
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Journal articleMuelmenstaedt J, Gryspeerdt E, Salzmann M, et al., 2019,
Separating radiative forcing by aerosol-cloud interactions and rapid cloud adjustments in the ECHAM-HAMMOZ aerosol-climate model using the method of partial radiative perturbations
, Atmospheric Chemistry and Physics, Vol: 19, Pages: 15415-15429, ISSN: 1680-7316Using the method of offline radiative transfer modeling within the partial radiative perturbation (PRP) approach, the effective radiative forcing by aerosol–cloud interactions (ERFaci) in the ECHAM–HAMMOZ aerosol climate model is decomposed into a radiative forcing by anthropogenic cloud droplet number change and adjustments of the liquid water path and cloud fraction. The simulated radiative forcing by anthropogenic cloud droplet number change and liquid water path adjustment are of approximately equal magnitude at −0.52 and −0.53 W m−2, respectively, while the cloud-fraction adjustment is somewhat weaker at −0.31 W m−2 (constituting 38 %, 39 %, and 23 % of the total ERFaci, respectively); geographically, all three ERFaci components in the simulation peak over China, the subtropical eastern ocean boundaries, the northern Atlantic and Pacific oceans, Europe, and eastern North America (in order of prominence). Spatial correlations indicate that the temporal-mean liquid water path adjustment is proportional to the temporal-mean radiative forcing, while the relationship between cloud-fraction adjustment and radiative forcing is less direct. While the estimate of warm-cloud ERFaci is relatively insensitive to the treatment of ice and mixed-phase cloud overlying warm cloud, there are indications that more restrictive treatments of ice in the column result in a low bias in the estimated magnitude of the liquid water path adjustment and a high bias in the estimated magnitude of the droplet number forcing. Since the present work is the first PRP decomposition of the aerosol effective radiative forcing into radiative forcing and rapid cloud adjustments, idealized experiments are conducted to provide evidence that the PRP results are accurate. The experiments show that using low-frequency (daily or monthly) time-averaged model output of the cloud property fields underestimates the ERF
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Journal articleMcComas DJ, Christian ER, Cohen CMS, et al., 2019,
Probing the energetic particle environment near the Sun
, NATURE, Vol: 576, Pages: 223-+, ISSN: 0028-0836- Author Web Link
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- Citations: 113
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Journal articleBale SD, Badman ST, Bonnell JW, et al., 2019,
Highly structured slow solar wind emerging from an equatorial coronal hole
, Nature, Vol: 576, Pages: 237-242, ISSN: 0028-0836During the solar minimum, when the Sun is at its least active, the solar wind1,2 is observed at high latitudes as a predominantly fast (more than 500 kilometres per second), highly Alfvénic rarefied stream of plasma originating from deep within coronal holes. Closer to the ecliptic plane, the solar wind is interspersed with a more variable slow wind3 of less than 500 kilometres per second. The precise origins of the slow wind streams are less certain4; theories and observations suggest that they may originate at the tips of helmet streamers5,6, from interchange reconnection near coronal hole boundaries7,8, or within coronal holes with highly diverging magnetic fields9,10. The heating mechanism required to drive the solar wind is also unresolved, although candidate mechanisms include Alfvén-wave turbulence11,12, heating by reconnection in nanoflares13, ion cyclotron wave heating14 and acceleration by thermal gradients1. At a distance of one astronomical unit, the wind is mixed and evolved, and therefore much of the diagnostic structure of these sources and processes has been lost. Here we present observations from the Parker Solar Probe15 at 36 to 54 solar radii that show evidence of slow Alfvénic solar wind emerging from a small equatorial coronal hole. The measured magnetic field exhibits patches of large, intermittent reversals that are associated with jets of plasma and enhanced Poynting flux and that are interspersed in a smoother and less turbulent flow with a near-radial magnetic field. Furthermore, plasma-wave measurements suggest the existence of electron and ion velocity-space micro-instabilities10,16 that are associated with plasma heating and thermalization processes. Our measurements suggest that there is an impulsive mechanism associated with solar-wind energization and that micro-instabilities play a part in heating, and we provide evidence that low-latitude coronal holes are a key source of the slow solar wind.
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Journal articleKasper JC, Bale SD, Belcher JW, et al., 2019,
Alfvenic velocity spikes and rotational flows in the near-Sun solar wind
, Nature, Vol: 576, Pages: 228-233, ISSN: 0028-0836The prediction of a supersonic solar wind1 was first confirmed by spacecraft near Earth2,3 and later by spacecraft at heliocentric distances as small as 62 solar radii4. These missions showed that plasma accelerates as it emerges from the corona, aided by unidentified processes that transport energy outwards from the Sun before depositing it in the wind. Alfvénic fluctuations are a promising candidate for such a process because they are seen in the corona and solar wind and contain considerable energy5,6,7. Magnetic tension forces the corona to co-rotate with the Sun, but any residual rotation far from the Sun reported until now has been much smaller than the amplitude of waves and deflections from interacting wind streams8. Here we report observations of solar-wind plasma at heliocentric distances of about 35 solar radii9,10,11, well within the distance at which stream interactions become important. We find that Alfvén waves organize into structured velocity spikes with duration of up to minutes, which are associated with propagating S-like bends in the magnetic-field lines. We detect an increasing rotational component to the flow velocity of the solar wind around the Sun, peaking at 35 to 50 kilometres per second—considerably above the amplitude of the waves. These flows exceed classical velocity predictions of a few kilometres per second, challenging models of circulation in the corona and calling into question our understanding of how stars lose angular momentum and spin down as they age12,13,14.
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Journal articleRichardson TB, Forster PM, Smith CJ, et al., 2019,
Efficacy of climate forcings in PDRMIP models
, Journal of Geophysical Research: Atmospheres, Vol: 124, Pages: 12824-12844, ISSN: 2169-897XQuantifying the efficacy of different climate forcings is important for understanding the real‐world climate sensitivity. This study presents a systematic multimodel analysis of different climate driver efficacies using simulations from the Precipitation Driver and Response Model Intercomparison Project (PDRMIP). Efficacies calculated from instantaneous radiative forcing deviate considerably from unity across forcing agents and models. Effective radiative forcing (ERF) is a better predictor of global mean near‐surface air temperature (GSAT) change. Efficacies are closest to one when ERF is computed using fixed sea surface temperature experiments and adjusted for land surface temperature changes using radiative kernels. Multimodel mean efficacies based on ERF are close to one for global perturbations of methane, sulfate, black carbon, and insolation, but there is notable intermodel spread. We do not find robust evidence that the geographic location of sulfate aerosol affects its efficacy. GSAT is found to respond more slowly to aerosol forcing than CO2 in the early stages of simulations. Despite these differences, we find that there is no evidence for an efficacy effect on historical GSAT trend estimates based on simulations with an impulse response model, nor on the resulting estimates of climate sensitivity derived from the historical period. However, the considerable intermodel spread in the computed efficacies means that we cannot rule out an efficacy‐induced bias of ±0.4 K in equilibrium climate sensitivity to CO2 doubling when estimated using the historical GSAT trend.
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Journal articleVerscharen D, Chandran BDG, Jeong S-Y, et al., 2019,
Self-induced Scattering of Strahl Electrons in the Solar Wind
, ASTROPHYSICAL JOURNAL, Vol: 886, ISSN: 0004-637X- Author Web Link
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- Citations: 63
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Conference paperWeiss Z, Pickering JC, Hoffmann V, 2019,
Sixty years of spectroscopic research: a tribute to Professor Edward B. M. Steers
, 16th Czech-Slovak Spectroscopic Conference (CSSC), Publisher: SPRINGER INTERNATIONAL PUBLISHING AG, Pages: 2891-2896, ISSN: 2585-7290 -
Journal articleScannell C, Booth BBB, Dunstone NJ, et al., 2019,
The influence of remote aerosol forcing from industrialized economies on the future evolution of East and West African rainfall
, Journal of Climate, Vol: 32, Pages: 8335-8354, ISSN: 0894-8755Past changes in global industrial aerosol emissions have played a significant role in historical shifts in African rainfall, and yet assessment of the impact on African rainfall of near-term (10–40 yr) potential aerosol emission pathways remains largely unexplored. While existing literature links future aerosol declines to a northward shift of Sahel rainfall, existing climate projections rely on RCP scenarios that do not explore the range of air quality drivers. Here we present projections from two emission scenarios that better envelop the range of potential aerosol emissions. More aggressive emission cuts result in northward shifts of the tropical rainbands whose signal can emerge from expected internal variability on short, 10–20-yr time horizons. We also show for the first time that this northward shift also impacts East Africa, with evidence of delays to both onset and withdrawal of the short rains. However, comparisons of rainfall impacts across models suggest that only certain aspects of both the West and East African model responses may be robust, given model uncertainties. This work motivates the need for wider exploration of air quality scenarios in the climate science community to assess the robustness of these projected changes and to provide evidence to underpin climate adaptation in Africa. In particular, revised estimates of emission impacts of legislated measures every 5–10 years would have a value in providing near-term climate adaptation information for African stakeholders.
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Journal articleWellbrock A, Coates AJ, Jones GH, et al., 2019,
Heavy negative ion growth in Titan's polar winter
, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 490, Pages: 2254-2261, ISSN: 0035-8711 -
Journal articleCzaja A, Frankignoul C, Minobe S, et al., 2019,
Simulating the midlatitude atmospheric circulation: What might we gain from high-resolution modeling of air-sea interactions?
, Current Climate Change Reports, Vol: 5, Pages: 390-406, ISSN: 2198-6061Purpose of ReviewTo provide a snapshot of the current research on the oceanic forcing of the atmospheric circulation in midlatitudes and a concise update on previous review papers.Recent FindingsAtmospheric models used for seasonal and longer timescales predictions are starting to resolve motions so far only studied in conjunction with weather forecasts. These phenomena have horizontal scales of ~ 10–100 km which coincide with energetic scales in the ocean circulation. Evidence has been presented that, as a result of this matching of scale, oceanic forcing of the atmosphere was enhanced in models with 10–100 km grid size, especially at upper tropospheric levels. The robustness of these results and their underlying mechanisms are however unclear.SummaryDespite indications that higher resolution atmospheric models respond more strongly to sea surface temperature anomalies, their responses are still generally weaker than those estimated empirically from observations. Coarse atmospheric models (grid size greater than 100 km) will miss important signals arising from future changes in ocean circulation unless new parameterizations are developed.
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Conference paperNowack P, Ong QYE, Braesicke P, et al., 2019,
Machine learning parameterizations for ozone: climate model transferability
, https://sites.google.com/view/climateinformatics2019/proceedings, 9th International Workshop on Climate Informatics, Publisher: UCAR, Pages: 263-268Many climate modeling studies have demon-strated the importance of two-way interactions betweenozone and atmospheric dynamics. However, atmosphericchemistry models needed for calculating changes in ozoneare computationally expensive. Nowack et al. [1] high-lighted the potential of machine learning-based ozoneparameterizations in constant climate forcing simulations,with ozone being predicted as a function of the atmo-spheric temperature state. Here we investigate the roleof additional time-lagged temperature information underpreindustrial forcing conditions. In particular, we testif the use of Long Short-Term Memory (LSTM) neuralnetworks can significantly improve the predictive skill ofthe parameterization. We then introduce a novel workflowto transfer the regression model to the new UK EarthSystem Model (UKESM). For this, we show for the firsttime how machine learning parameterizations could betransferred between climate models, a pivotal step tomaking any such parameterization widely applicable inclimate science. Our results imply that ozone parame-terizations could have much-extended scope as they arenot bound to individual climate models but, once trained,could be used in a number of different models. We hope tostimulate similar transferability tests regarding machinelearning parameterizations developed for other Earthsystem model components such as ocean eddy modeling,convection, clouds, or carbon cycle schemes.
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Journal articleErgun RE, Hoilijoki S, Ahmadi N, et al., 2019,
Magnetic Reconnection in Three Dimensions: Observations of Electromagnetic Drift Waves in the Adjacent Current Sheet
, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 124, Pages: 10104-10118, ISSN: 2169-9380- Author Web Link
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- Citations: 7
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Journal articleErgun RE, Hoilijoki S, Ahmadi N, et al., 2019,
Magnetic Reconnection in Three Dimensions: Modeling and Analysis of Electromagnetic Drift Waves in the Adjacent Current Sheet
, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 124, Pages: 10085-10103, ISSN: 2169-9380- Author Web Link
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- Citations: 21
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Journal articleSparks N, Hon KK, Chan PW, et al., 2019,
Aircraft observations of tropical cyclone boundary layer turbulence over the South China Sea
, Journal of the Atmospheric Sciences, Vol: 76, Pages: 3773-3783, ISSN: 0022-4928There have been no high-frequency aircraft observations of tropical cyclone (TC) eyewall boundary layer turbulence since two flights into Atlantic hurricanes in the 1980s. We present an analysis of the first TC boundary layer flight observations in the South China Sea by the Hong Kong Observatory comprising four eyewall penetrations. We derive the vertical flux of momentum and vertical momentum diffusivity from observed turbulence parameters. We observe negative (upward) vertical fluxes of tangential momentum near the eyewall consistent with a jet below the flight level near the radius of maximum wind. Our observations of vertical momentum diffusivity support a superlinear relationship between diffusivity and wind speed at the high wind speeds in the inner-core of TCs (power-law exponent of 1.73 ± 0.20) while the few existing boundary layer hurricane observations in the North Atlantic suggest a more linear relationship.
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Journal articleHoilijoki S, Ergun RE, Schwartz SJ, et al., 2019,
Electron-Scale Magnetic Structure Observed Adjacent to an Electron Diffusion Region at the Dayside Magnetopause
, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 124, Pages: 10153-10169, ISSN: 2169-9380- Author Web Link
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- Citations: 4
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