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Journal articleShebanits O, Hadid L, Cao H, et al., 2021,
The conductive dusty ionosphere of Saturn
<jats:p>&lt;p&gt;Cassini&amp;#8217;s Grand Finale orbits brought us historical first in-situ measurements of Saturn&amp;#8217;s ionosphere, showing that it contains dusty plasma in the equatorial region. We present the Pedersen and Hall conductivities of the top ionosphere (10:50 &amp;#8211; 12:17 Saturn Local Time, 10N &amp;#8211; 20S planetocentric latitude), derived from particle and magnetometer data. We constrain the Pedersen conductivities to be at least 10&lt;sup&gt;-5&lt;/sup&gt; &amp;#8211; 10&lt;sup&gt;-4&lt;/sup&gt; S/m at ionospheric peak, a factor 10-100 higher than estimated previously by remote measurements, while the Hall conductivities are very close to 0 or in fact negative. We show that this is an effect of dusty plasma. Another effect is that ionospheric dynamo region thickness is increased to 300-800 km. Furthermore, our results suggest a temporal variation (decrease) of the plasma densities, mean ion masses and consequently the conductivities over the period of one month.&lt;/p&gt;</jats:p>
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Conference paperThomas C, Voulgarakis A, Lim G, et al., 2021,
An unsupervised learning approach to identifying blocking events: the case of European summer
<jats:p>&lt;p&gt;Atmospheric blocking events are mid-latitude weather patterns, which obstruct the usual path of the polar jet stream. Several blocking indices (BIs) have been developed to study blocking patterns and their associated trends, but these show significant seasonal and regional differences. Despite being central features of mid-latitude synoptic-scale weather, there is no well-defined historical dataset of blocking events. Here, we introduce a new blocking index using self-organizing maps (SOMs), an unsupervised machine learning approach, and compare its detection skill to some of the most widely applied BIs. To enable this intercomparison, we first create a new ground truth time series classification of European blocking based on expert judgement. We then demonstrate that our method (SOM-BI) has several key advantages over previous BIs because it exploits all the spatial information provided in the input data and avoids the need for arbitrary thresholds. Using ERA5 reanalysis data (1979-2019), we find that the SOM-BI identifies blocking events with a higher precision and recall than other BIs. We present a case study of the 2003 European heat wave and highlight that well-defined groups of SOM nodes can be an effective tool to reliably and accurately diagnose such weather events. This contrasts with the way SOMs are commonly used, where an individual SOM node can be wrongly assumed to represent a weather pattern. We also evaluate the SOM-BI performance on about 100 years of climate model data from a preindustrial simulation with the new UK Earth System Model (UK-ESM1). For the model data, all blocking detection methods have lower skill than for the ERA5 reanalysis, but SOM-BI performs significantly better than the conventional indices. This shows that our method can be effectively applied to climate models to develop our understanding of how climate change will affect regional blocking characteristics. Overall, our results demonstra
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Journal articleKieokaew R, Lavraud B, Ruffolo D, et al., 2021,
Solar Orbiter observations of magnetic Kelvin-Helmholtz waves in the solar wind
<jats:p>&lt;p&gt;The Kelvin-Helmholtz instability (KHI) is a nonlinear shear-driven instability that develops at the interfaces between shear flows in plasmas. KHI is ubiquitous in plasmas and has been observed in situ at planetary interfaces and at the boundaries of coronal mass ejections in remote-sensing observations. KHI is also expected to develop at flow shear interfaces in the solar wind, but while it was hypothesized to play an important role in the mixing of plasmas and exciting solar wind fluctuations, its direct observation in the solar wind was still lacking. We report first in-situ observations of ongoing KHI in the solar wind using Solar Orbiter during its cruise phase. The KHI is found in a shear layer in the slow solar wind near the Heliospheric Current Sheet. We find that the observed conditions satisfy the KHI onset criterion from linear theory and the steepening of the shear boundary layer is consistent with the development of KH vortices. We further investigate the solar wind source of this event to understand the conditions that support KH growth. In addition, we set up a local MHD simulation using the empirical values to reproduce the observed KHI.&amp;#160;This observed KHI in the solar wind provides robust evidence&amp;#160;that&amp;#160;shear instability develops in the solar wind, with obvious implications in the driving of solar wind fluctuations and turbulence. The reasons for the lack of previous such measurements are also discussed.&lt;/p&gt;</jats:p>
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Journal articleStawarz J, Matteini L, Parashar T, et al., 2021,
Comparative Analysis of the Various Generalized Ohm's Law Terms in Magnetosheath Turbulence as Observed by Magnetospheric Multiscale
<jats:p>&lt;p&gt;&lt;span&gt;Electric fields (&lt;strong&gt;E&lt;/strong&gt;) play a fundamental role in facilitating the exchange of energy between the electromagnetic fields and the changed particles within a plasma. &lt;/span&gt;Decomposing &lt;strong&gt;E&lt;/strong&gt; into the contributions from the different terms in generalized Ohm's law, therefore, provides key insight into both the nonlinear and dissipative dynamics across the full range of scales within a plasma. Using the unique, high&amp;#8208;resolution, multi&amp;#8208;spacecraft measurements of three intervals in Earth's magnetosheath from the Magnetospheric Multiscale mission, the influence of the magnetohydrodynamic, Hall, electron pressure, and electron inertia terms from Ohm's law, as well as the impact of a finite electron mass, on the turbulent electric field&lt;strong&gt; &lt;/strong&gt;spectrum are examined observationally for the first time. The magnetohydrodynamic, Hall, and electron pressure terms are the dominant contributions to &lt;strong&gt;E&lt;/strong&gt; over the accessible length scales, which extend to scales smaller than the electron gyroradius at the greatest extent, with the Hall and electron pressure terms dominating at sub&amp;#8208;ion scales. The strength of the non&amp;#8208;ideal electron pressure contribution is stronger than expected from linear kinetic Alfv&amp;#233;n waves and a partial anti&amp;#8208;alignment with the Hall electric field is present, linked to the relative importance of electron diamagnetic currents within the turbulence. The relative contributions of linear and nonlinear electric fields scale with the turbulent fluctuation amplitude, with nonlinear contributions playing the dominant role in shaping &lt;strong&am
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Conference paperVuorinen L, Vainio R, Hietala H, et al., 2021,
Jet-driven bow waves as electron accelerators in the magnetosheath: Monte Carlo simulations
<jats:p>&lt;p&gt;Magnetosheath jets are fast flows of plasma frequently observed downstream of the Earth's quasi-parallel shock. Previous observations have shown that these jets can exhibit supermagnetosonic speeds relative to the background flow and develop their own bow waves or shocks. Such jets have been observed to be able to accelerate ions and electrons. In our study, we model electron acceleration by jet-driven bow waves in the magnetosheath using test-particle Monte Carlo simulations that include magnetic mirroring and pitch-angle scattering of magnetic irregularities. We compare the simulation results to spacecraft observations of similar events to understand the acceleration mechanisms at play. Our preliminary results suggest that the energy increase of electrons can be explained by shock drift acceleration at the moving bow wave. Our simulations allow us to estimate the efficiency of acceleration as a function of different jet and magnetosheath parameters. The acceleration introduced by jet-driven bow waves amplifies shock acceleration downstream of the Earth&amp;#8217;s bow shock and may also be applicable to other shock environments.&lt;/p&gt;</jats:p>
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Journal articlePomoell J, Kilpua E, Price D, et al., 2021,
Modeling the magnetic structure of CMEs in the inner heliosphere based on data-driven time-dependent simulations of active region evolution
<jats:p>&lt;p&gt;Characterizing the detailed structure of the magnetic field in the active corona is of crucial importance for determining the chain of events from the formation to the destabilisation and subsequent eruption and propagation of coronal structures in the heliosphere. A comprehensive methodology to address these dynamic processes is needed in order to advance our capabilities to predict the properties of coronal mass ejections (CMEs) in interplanetary space and thereby for increasing the accuracy of space weather predictions. A promising toolset to provide the key missing information on the magnetic structure of CMEs are time-dependent data-driven simulations of active region magnetic fields. This methodology permits self-consistent modeling of the evolution of the coronal magnetic field from the emergence of flux to the birth of the eruption and beyond.&amp;#160;&lt;/p&gt;&lt;p&gt;In this presentation, we discuss our modeling efforts in which time-dependent data-driven coronal modeling together with heliospheric physics-based modeling are employed to study and characterize CMEs, in particular their magnetic structure, at various stages in their evolution from the Sun to Earth.&amp;#160;&lt;/p&gt;</jats:p>
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Journal articleDaei F, Pomoell J, Kilpua E, et al., 2021,
Modeling the formation and eruption of coronal structures by linking data-driven magnetofrictional and MHD simulations
<jats:p>&lt;p&gt;The time-dependent magnetofrictional model (TMFM) is a prevalent approach that has proven to be a very useful tool in the study of the formation of unstable structures in the solar corona. In particular, it is capable of incorporating observational data as initial and boundary conditions and requires shorter computational time compared to MHD simulations. To leverage the efficiency of data-driven TMFM and also to simulate eruptive events in the MHD framework, one can apply TMFM up to a certain time before the expected eruption(s) and then go on with simulation in the full or ideal MHD regime in order to more accurately capture the eruption process. However, due to the different evolution processes in these two models, using TMFM snapshots in an MHD simulation is non-trivial with several issues that need to be addressed, both physically and numerically.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;In this study, we showcase our progress in using magnetofrictional model results as input to dynamical MHD simulations. In particular, we discuss the incompatibility of the TMFM output to serve as the initial condition in MHD, and show our methods of mitigating this.&lt;/p&gt;&lt;p&gt;As our benchmark test-case, we study the evolution of NOAA active region 12673, which was previously studied using data-driven TMFM by Price et al. (2019).&lt;/p&gt;</jats:p>
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Journal articleWoolley T, Matteini L, Horbury TS, et al., 2021,
Characterisation and comparison of slow coronal hole wind intervals at 0.13au
<jats:p>&lt;p&gt;The slow solar wind is thought to consist of a component originating close to the Heliospheric Current Sheet (HCS) in the streamer belt and a component from over-expanded coronal hole boundaries. In order to understand the roles of these contributions with different origin, it is important to separate and characterise them. By exploiting the fact that Parker Solar Probe&amp;#8217;s fourth and fifth orbits were the same and the solar conditions were similar, we identify intervals of slow polar coronal hole wind sampled at approximately the same heliocentric distance and latitude. Here, solar wind properties are compared, highlighting typical conditions of the slow coronal hole wind closer to the Sun than ever before. We explore different properties of the plasma, including composition, spectra and microphysics, and discuss possible origins for the features that are observed.&lt;/p&gt;</jats:p>
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Journal articleGood S, Kilpua E, Ala-Lahti M, et al., 2021,
Cross helicity of magnetic clouds observed by Parker Solar Probe
<jats:p>&lt;p&gt;Magnetic clouds are large-scale transient structures in the solar wind with low plasma &lt;em&gt;&amp;#946;&lt;/em&gt;, low-amplitude magnetic field fluctuations, and twisted field lines with both ends often connected to the Sun. We analyse the normalised cross helicity, &lt;em&gt;&amp;#963;&lt;/em&gt;&lt;sub&gt;c&lt;/sub&gt;, and residual energy, &lt;em&gt;&amp;#963;&lt;/em&gt;&lt;sub&gt;r&lt;/sub&gt;, in magnetic clouds observed by Parker Solar Probe (PSP). In the November 2018 cloud observed at 0.25 au, a low value of &lt;em&gt;&amp;#963;&lt;/em&gt;&lt;sub&gt;c&lt;/sub&gt; was present in the cloud core, indicating that wave power parallel and anti-parallel to the mean field was approximately balanced, while the cloud&amp;#8217;s outer layers displayed larger amplitude Alfv&amp;#233;nic fluctuations with high &lt;em&gt;&amp;#963;&lt;/em&gt;&lt;sub&gt;c&lt;/sub&gt; values and &lt;em&gt;&amp;#963;&lt;/em&gt;&lt;sub&gt;r&lt;/sub&gt; ~ 0. These properties are compared and contrasted to those found in clouds observed by PSP at larger heliocentric distances. We suggest that low &lt;em&gt;&amp;#963;&lt;/em&gt;&lt;sub&gt;c&lt;/sub&gt; is likely a common feature of magnetic clouds given their typically closed field structure, in contrast to the generally higher &lt;em&gt;&amp;#963;&lt;/em&gt;&lt;sub&gt;c&lt;/sub&gt; found on the open field lines of the solar wind.&lt;/p&
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Journal articleMasters A, Dunn W, Stallard T, et al., 2021,
Low-altitude magnetic reconnection events as possible drivers of Jupiter&#8217;s polar auroras
<jats:p>&lt;p&gt;Charged particles impacting Jupiter&amp;#8217;s atmosphere represent a major energy input, generating the most powerful auroral emissions in the Solar System. Most auroral features have now been explained as the result of impacting particles accelerated by quasi-static electric fields and/or wave-particle interactions in the surrounding space environment. However, the reason for Jupiter&amp;#8217;s bright and dynamic polar regions remains a long-standing mystery. Recent spacecraft observations above these regions of &amp;#8220;swirl&amp;#8221; auroras have shown that high-energy electrons are regularly beamed away from the planet, which is inconsistent with traditional auroral drivers. The unknown downward-electron-acceleration mechanism operating close to Jupiter represents a gap in our fundamental understanding of planetary auroras. Here we propose a possible explanation for both the swirl auroras and the upward electron beams. We show that the perturbations of Jupiter&amp;#8217;s strong magnetic field above the swirl regions that are driven by dynamics of the distant space environment can cause magnetic reconnection events at altitudes as low as ~0.2 Jupiter radii, rapidly releasing energy and potentially producing both the required downward and observed upward beams of electrons. Such an auroral driver has never before been postulated, resembling physics at work in the solar corona.&lt;/p&gt;</jats:p>
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Journal articleAsvestari E, Pomoell J, Kilpua E, et al., 2021,
Constraining the CME parameters of the spheromak flux rope implemented in EUHFORIA
<jats:p>&lt;p&gt;Coronal mass ejections (CMEs) are primary drivers of space weather phenomena. Modelling the evolution of the internal magnetic field configuration of CMEs as they propagate through the interplanetary space is an essential part of space weather forecasting. EUHFORIA (EUropean Heliospheric FORecasting Information Asset) is a data-driven, physics-based model, able to trace the evolution of CMEs and CME-driven shocks through realistic background solar wind conditions. It employs a spheromak-type magnetic flux rope that is initially force-free, providing it with the advantage of modelling CME as magnetised structures. For this work we assessed the spheromak CME model employed in EUHFORIA with a test CME case study. The selected CME eruption occurred on the 6th of January 2013 and was encountered by two spacecraft, Venus Express and STEREO--A, which were radially aligned at the time of the CME passage. Our focus was to constrain the input parameters, with particular interest in: (1) translating the angular widths of the graduated cylindrical shell (GCS) fitting to the spheromak radius, and (2) matching the observed magnetic field topology at the source region. We ran EUHFORIA with three different spheromak radii. The model predicts arrival times from half to a full day ahead of the one observed &lt;em&gt;in situ&lt;/em&gt;. We conclude that the choice of spheromak radius affected the modelled magnetic field profiles, their amplitude, arrival times, and sheath region length.&lt;/p&gt;</jats:p>
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Journal articleChen C, Chandran B, Woodham L, et al., 2021,
The Near-Sun Streamer Belt Solar Wind: Turbulence and Solar Wind Acceleration
<jats:p>&lt;p&gt;The fourth orbit of Parker Solar Probe (PSP) reached heliocentric distances down to 27.9 Rs, allowing solar wind turbulence and acceleration mechanisms to be studied in situ closer to the Sun than previously possible. The turbulence properties were found to be significantly different in the inbound and outbound portions of PSP's fourth solar encounter, likely due to the proximity to the heliospheric current sheet (HCS) in the outbound period. Near the HCS, in the streamer belt wind, the turbulence was found to have lower amplitudes, higher magnetic compressibility, a steeper magnetic field spectrum (with spectral index close to -5/3 rather than -3/2), a lower Alfvenicity, and a &quot;1/f&quot; break at much lower frequencies. These are also features of slow wind at 1 au, suggesting the near-Sun streamer belt wind to be the prototypical slow solar wind. The transition in properties occurs at a predicted angular distance of ~4 degrees from the HCS, suggesting ~8 degrees as the full-width of the streamer belt wind at these distances. While the majority of the Alfvenic turbulence energy fluxes measured by PSP are consistent with those required for reflection-driven turbulence models of solar wind acceleration, the fluxes in the streamer belt are significantly lower than the model predictions, suggesting that additional mechanisms are necessary to explain the acceleration of the streamer belt solar wind.&lt;/p&gt;</jats:p>
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Journal articleVoigt A, Albern N, Ceppi P, et al., 2021,
Clouds, radiation, and atmospheric circulation in the present-day climate and under climate change
, Wiley Interdisciplinary Reviews: WIREs Climate Change, Vol: 12, Pages: 1-22, ISSN: 1757-7780By interacting with radiation, clouds modulate the flow of energy through the Earth system, the circulation of the atmosphere, and regional climate. We review the impact of cloud‐radiation interactions for the atmospheric circulation in the present‐day climate, its internal variability and its response to climate change. After summarizing cloud‐controlling factors and cloud‐radiative effects, we clarify the scope and limits of the Clouds On‐Off Klimate Model Intercomparison Experiment (COOKIE) and cloud‐locking modeling methods. COOKIE showed that the presence of cloud‐radiative effects shapes the circulation in the present‐day climate in many important ways, including the width of the tropical rain belts and the position of the extratropical storm tracks. Cloud locking, in contrast, identified how clouds affect internal variability and the circulation response to global warming. This includes strong, but model‐dependent, shortwave and longwave cloud impacts on the El‐Nino Southern Oscillation, and the finding that most of the poleward circulation expansion in response to global warming can be attributed to radiative changes in clouds. We highlight the circulation impact of shortwave changes from low‐level clouds and longwave changes from rising high‐level clouds, and the contribution of these cloud changes to model differences in the circulation response to global warming. The review in particular draws attention to the role of cloud‐radiative heating within the atmosphere. We close by raising some open questions which, among others, concern the need for studying the cloud impact on regional scales and opportunities created by the next generation of global storm‐resolving models.
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Journal articleKlein KG, Verniero JL, Alterman B, et al., 2021,
Inferred Linear Stability of Parker Solar Probe Observations Using One- and Two-component Proton Distributions
, ASTROPHYSICAL JOURNAL, Vol: 909, ISSN: 0004-637X- Author Web Link
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- Citations: 19
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Journal articleWang L, Zong Q, Shi Q, et al., 2021,
Solar Energetic Electrons Entering the Earth's Cusp/Lobe
, ASTROPHYSICAL JOURNAL, Vol: 910, ISSN: 0004-637X -
Journal articleHe J, Cui B, Yang L, et al., 2021,
The Encounter of the Parker Solar Probe and a Comet-like Object Near the Sun: Model Predictions and Measurements
, ASTROPHYSICAL JOURNAL, Vol: 910, ISSN: 0004-637X- Author Web Link
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- Citations: 2
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Journal articleHuang SY, Sahraoui F, Andres N, et al., 2021,
The Ion Transition Range of Solar Wind Turbulence in the Inner Heliosphere: Parker Solar Probe Observations
, ASTROPHYSICAL JOURNAL LETTERS, Vol: 909, ISSN: 2041-8205- Author Web Link
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- Citations: 17
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Journal articleXu S, Schwartz SJ, Mitchell DL, et al., 2021,
Cross-Shock Electrostatic Potentials at Mars Inferred From MAVEN Measurements
, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 126, ISSN: 2169-9380- Author Web Link
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- Citations: 5
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Journal articleProvan G, Bradley TJ, Bunce EJ, et al., 2021,
Saturn's Nightside Ring Current During Cassini's Grand Finale
, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 126, ISSN: 2169-9380- Author Web Link
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- Citations: 3
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Journal articleSchwartz SJ, Kucharek H, Farrugia CJ, et al., 2021,
Energy Conversion Within Current Sheets in the Earth's Quasi-Parallel Magnetosheath
, GEOPHYSICAL RESEARCH LETTERS, Vol: 48, ISSN: 0094-8276- Author Web Link
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- Citations: 8
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Journal articleHeyns MJ, Lotz SI, Gaunt CT, 2021,
Geomagnetic Pulsations Driving Geomagnetically Induced Currents
, Space Weather, Vol: 19, ISSN: 1542-7390<jats:title>Abstract</jats:title><jats:p>Geomagnetically induced currents (GICs) are driven by the geoelectric field induced by fluctuations of Earth's magnetic field. Drivers of intense GICs are often associated with large impulsive events such as coronal mass ejections. To a lesser extent fluctuations from regular oscillations of the geomagnetic field, or geomagnetic pulsations, have also been identified as possible drivers of GICs. In this work we show that these low‐frequency pulsations are directly observed in measured GIC data from power networks. Due to the low‐pass nature of GICs, Pc5 and lower‐frequency pulsations drive significant GICs for an extended duration even at midlatitudes. Longer‐period Ps6‐type disturbances apparently not typical of midlatitudes are seen with GIC amplitudes comparable to the peak GIC at storm sudden commencement. The quasi‐ac (alternating current) nature of the sustained pulsation driving affects the power system response and cannot be properly modeled using only direct current (dc) models. A further consideration is that the often used <jats:styled-content><jats:italic>d</jats:italic><jats:italic>B</jats:italic>/<jats:italic>d</jats:italic><jats:italic>t</jats:italic></jats:styled-content> GIC proxy is biased to the sampling rate of the geomagnetic field measurements used. The <jats:styled-content><jats:italic>d</jats:italic><jats:italic>B</jats:italic>/<jats:italic>d</jats:italic><jats:italic>t</jats:italic></jats:styled-content> metric does not adequately characterize GIC activity at frequencies in the low ultralow‐frequency (ULF) range, and a frequency‐weighted proxy akin to geoelectric field should be used instead.</jats:p>
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Journal articleArcher MO, Day N, Barnes S, 2021,
Demonstrating change from a drop-in space soundscape exhibit by using graffiti walls both before and after
, Geoscience Communication, Vol: 4, Pages: 57-67, ISSN: 2569-7110Impact evaluation in public engagement necessarily requires measuring change. However, this is extremely challenging for drop-in activities due to their very nature. We present a novel method of impact evaluation which integrates graffiti walls into the experience both before and after the main drop-in activity. The activity in question was a soundscape exhibit, where young families experienced the usually inaudible sounds of near-Earth space in an immersive and accessible way. We apply two analysis techniques to the captured before and after data – quantitative linguistics and thematic analysis. These analyses reveal significant changes in participants' responses after the activity compared to before, namely an increased diversity in language used to describe space and altered conceptions of what space is like. The results demonstrate that the soundscape was surprisingly effective at innately communicating key aspects of the underlying science simply through the act of listening. The impacts also highlight the power of sonification in stimulating public engagement, which, through reflection, can lead to altered associations, perceptions, and understanding. Therefore, we show that this novel approach to drop-in activity evaluation, using graffiti walls both before and after the activity and applying rigorous analysis to this data, has the power to capture change and, thus, have a short-term impact. We suggest that commonly used evaluation tools suitable for drop-in activities, such as graffiti walls, should be integrated both before and after the main activity in general, rather than only using them afterwards as is typically the case.
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Journal articleHall RJ, Mitchell DM, Seviour WJM, et al., 2021,
Tracking the Stratosphere-to-Surface Impact of Sudden Stratospheric Warmings
, JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, Vol: 126, ISSN: 2169-897X- Author Web Link
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- Citations: 19
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Journal articleArcher M, DeWitt J, Davenport C, et al., 2021,
Going beyond the one-off: How can STEM engagement programmes with young people have real lasting impact?
, Research for All, Vol: 5, Pages: 67-85, ISSN: 2399-8121A major focus in the STEM public engagement sector concerns engaging withyoung people, typically through schools. The aims of these interventions areoften to positively affect students' aspirations towards continuing STEMeducation and ultimately into STEM-related careers. Most schools engagementactivities take the form of short one-off interventions that, while able toachieve positive outcomes, are limited in the extent to which they can havelasting impacts on aspirations. In this paper we discuss various differentemerging programmes of repeated interventions with young people, assessing whatimpacts can realistically be expected. Short series of interventions appearalso to suffer some limitations in the types of impacts achievable. However,deeper programmes that interact with both young people and those that influencethem over significant periods of time (months to years) seem to be moreeffective in influencing aspirations. We discuss how developing a Theory ofChange and considering young people's wider learning ecologies are required inenabling lasting impacts in a range of areas. Finally, we raise severalsector-wide challenges to implementing and evaluating these emergingapproaches.
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Journal articleAllen RC, Ho GC, Mason GM, et al., 2021,
Radial Evolution of a CIR: Observations From a Nearly Radially Aligned Event Between Parker Solar Probe and STEREO-A
, GEOPHYSICAL RESEARCH LETTERS, Vol: 48, ISSN: 0094-8276- Author Web Link
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- Citations: 14
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Journal articleLiou K, Paranicas C, Vines S, et al., 2021,
Dawn-dusk asymmetry in energetic (>20 keV) particles adjacent to Saturn's magnetopause
, Journal of Geophysical Research: Space Physics, Vol: 126, ISSN: 2169-9380Energetic particles (>∼25 keV) have been observed routinely in the terrestrial magnetosheath, but have not been well studied at the magnetosheaths of the outer planets. Here we analyze energetic electrons and ions (mostly protons) in the vicinity (±1 RS) of Saturn's magnetopause, using particle data acquired with the low‐energy magnetosphere measurements system, one of the three sensors of the magnetosphere imaging instrument on board the Cassini spacecraft, during a period of ∼14 years (2004–2017). It is found that energetic particles, especially ions, are also common in Saturn's magnetosheath. A clear inward (toward Saturn) gradient in the electron differential flux is identified, suggestive of magnetospheric sources. Such an inward gradient does not appear in some of the ion channels. We conclude that Saturn's magnetopause acts as a porous barrier for energetic electrons and, to a lesser extent, for energetic ions. A dawn‐dusk asymmetry in the gradient of particle flux across the magnetopause is also identified, with a gradual decrease at the dawn and a sharp decrease at the dusk magnetopause. It is also found that magnetic reconnection enhanced flux levels just outside of the magnetopause, with evidence suggesting that these particles are from magnetospheric sources. These findings strongly suggest that Saturn's magnetosphere is most likely the main source of energetic particles in Saturn's magnetosheath and magnetosphere leakage is an important process responsible for the presence of the energetic particles in Saturn's magnetosheath.
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Journal articleKilpua EKJ, Good SW, Ala-Lahti M, et al., 2021,
Statistical Analysis of Magnetic Field Fluctuations in Coronal Mass Ejection-Driven Sheath Regions
, FRONTIERS IN ASTRONOMY AND SPACE SCIENCES, Vol: 7, ISSN: 2296-987X- Author Web Link
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- Citations: 15
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Journal articleZappa G, Ceppi P, Shepherd TG, 2021,
Eurasian cooling in response to Arctic sea-ice loss is not proved by maximum covariance analysis
, Nature Climate Change, Vol: 11, Pages: 106-108, ISSN: 1758-678X -
Journal articleSparks N, Toumi R, 2021,
On the seasonal and sub-seasonal factors influencing East China tropical cyclone landfall
, Atmospheric Science Letters, Vol: 22, Pages: 1-8, ISSN: 1530-261XTo date it has proved difficult to make seasonal forecasts of tropical cyclones, particularly for landfall and in East China specifically. This study examines sources of predictability for the number of landfalling typhoons in East China on seasonal (June–October) and sub‐seasonal time scales. East China landfall count is shown to be independent of basin‐scale properties of TC tracks, such the genesis location, duration, basin track direction and length, and basin total count. Large‐scale environmental climate indices which are potential basin scale drivers are also shown to be largely uncorrelated with landfall prior to and throughout the season. The most important factor is the steering in the final stages to landfall. The seasonal landfall is strongly anti‐correlated with the more local zonal mid‐tropospheric wind field over the East China sea (r = −.61, p < .001). It is proposed that geopotential height anomalies over Korea/Japan cause anomalous easterly winds in the East China Sea and enhance landfall rates by steering typhoons onto the coast. Early, peak, and late sub‐seasonal landfall counts are shown to be independent of each other yet share this predictor. This local feature may be dynamically predictable allowing a potential hybrid dynamical‐statistical seasonal forecast of landfall.
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Journal articleSouthwood DJ, Cao H, Shebanits O, et al., 2021,
Discovery of Alfven waves planetward of Saturn's rings
, Journal of Geophysical Research: Space Physics, Vol: 126, Pages: 1-18, ISSN: 2169-9380Between April and September 2017 in the final stages of the Cassini Saturn Orbiter mission the spacecraft executed 22 orbits passing planetward of the innermost ring, the D-ring. During all periapsis passes oscillations were detected in the azimuthal magnetic field components on typical time scales of a few minutes. We argue that these time-varying magnetic signals detected on the spacecraft are also primarily time-varying in the plasma frame. Furthermore, we show that nearly all signals exhibit a spatial feature, namely a magnetic node near the effective field line equator. We propose that the oscillations are associated with Alfvén waves excited in local field line resonances, most likely driven from global sources.
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