Publications

Journal article

Kilpua E, Good S, Dresing N, Vainio R, Davies E, Forsyth R, Lavraud B, Heyner D, Horbury T, Angeli V, O'Brien H, Evans V, Wimmer B, Rodriguez-Pacheco J, Gomez-Herrero R, Ho Get al., 2021,

The sheath region of April 2020 magnetic cloud and the associated energetic ions&#160;

<jats:p>&lt;p&gt;Acceleration of energetic particles is a fundamental and ubiquitous mechanism in space and astrophysical plasmas. One of the open questions is the role of the sheath region behind the shock in the acceleration process. We analyze observations by Solar Orbiter, BepiColombo and the L1 spacecraft to explore the structure of a coronal mass ejection (CME)-driven sheath and its relation to enhancements of energetic ions that occurred on April 19-20, 2020. Our detailed analysis of the magnetic field, plasma and particle observations show that the enhancements were related to the Heliospheric Current Sheet crossings related to the reconnecting current sheets in the vicinity of the shock and a mini flux rope that was compressed at the leading edge of the CME ejecta. This study highlights the importance of smaller-scale sheath structures for the energization process. These structures likely formed already closer to the Sun and were swept and compressed from the upstream wind past the shock into the sheath. The upcoming observations by the recent missions (Solar Orbiter, Parker Solar Probe and BepiColombo) provide an excellent opportunity to explore further their role. &amp;#160;&lt;/p&gt;</jats:p>

Journal article

Asvestari E, Pomoell J, Kilpua E, Good S, Chatzistergos T, Temmer M, Palmerio E, Poedts S, Magdalenic Jet 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>

Journal article

Chen C, Chandran B, Woodham L, Jones S, Perez J, Bourouaine S, Bowen T, Klein K, Moncuquet M, Kasper J, Bale Set 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>

Journal article

Voigt A, Albern N, Ceppi P, Grise K, Li Y, Medeiros Bet 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: 1757-7780

By 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.

Journal article

He J, Cui B, Yang L, Hou C, Zhang L, Ip W-H, Jia Y-D, Dong C, Duan D, Zong Q, Bale SD, Pulupa M, Bonnell JW, Dudok De Wit T, Goetz K, Harvey PR, MacDowall RJ, Malaspina DMet 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

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Citations: 2

Journal article

Wang L, Zong Q, Shi Q, Wimmer-Schweingruber RF, Bale SDet al., 2021,

Solar Energetic Electrons Entering the Earth's Cusp/Lobe

, ASTROPHYSICAL JOURNAL, Vol: 910, ISSN: 0004-637X

Journal article

Klein KG, Verniero JL, Alterman B, Bale S, Case A, Kasper JC, Korreck K, Larson D, Lichko E, Livi R, McManus M, Martinovic M, Rahmati A, Stevens M, Whittlesey Pet al., 2021,

Inferred Linear Stability of Parker Solar Probe Observations Using One- and Two-component Proton Distributions

, ASTROPHYSICAL JOURNAL, Vol: 909, ISSN: 0004-637X

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Citations: 19

Journal article

Huang SY, Sahraoui F, Andres N, Hadid LZ, Yuan ZG, He JS, Zhao JS, Galtier S, Zhang J, Deng XH, Jiang K, Yu L, Xu SB, Xiong QY, Wei YY, Dudok de Wit T, Bale SD, Kasper JCet 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

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Citations: 17

Journal article

Xu S, Schwartz SJ, Mitchell DL, Horaites K, Andersson L, Halekas J, Mazelle C, Gruesbeck JRet al., 2021,

Cross-Shock Electrostatic Potentials at Mars Inferred From MAVEN Measurements

, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 126, ISSN: 2169-9380

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Citations: 5

Journal article

Provan G, Bradley TJ, Bunce EJ, Cowley SWH, Cao H, Dougherty M, Hunt GJ, Roussos E, Staniland NR, Tao Cet al., 2021,

Saturn's Nightside Ring Current During Cassini's Grand Finale

, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 126, ISSN: 2169-9380

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Citations: 3

Journal article

Schwartz SJ, Kucharek H, Farrugia CJ, Trattner K, Gingell I, Ergun RE, Strangeway R, Gershman Det al., 2021,

Energy Conversion Within Current Sheets in the Earth's Quasi-Parallel Magnetosheath

, GEOPHYSICAL RESEARCH LETTERS, Vol: 48, ISSN: 0094-8276

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Citations: 8

Journal article

Heyns 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>

Journal article

Archer 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: 2569-7110

Impact 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.

Journal article

Hall RJ, Mitchell DM, Seviour WJM, Wright CJet al., 2021,

Tracking the Stratosphere-to-Surface Impact of Sudden Stratospheric Warmings

, JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, Vol: 126, ISSN: 2169-897X

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Citations: 19

Journal article

Allen RC, Ho GC, Mason GM, Li G, Jian LK, Vines SK, Schwadron NA, Joyce CJ, Bale SD, Bonnell JW, Case AW, Christian ER, Cohen CMS, Desai M, Filwett R, Goetz K, Harvey PR, Hill ME, Kasper JC, Korreck KE, Lario D, Larson D, Livi R, MacDowall RJ, Malaspina DM, McComas DJ, McNutt R, Mitchell DG, Paulson KW, Pulupa M, Raouafi N, Stevens ML, Whittlesey PL, Wiedenbeck Met 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

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Citations: 14

Journal article

Archer M, DeWitt J, Davenport C, Keenan O, Coghill L, Christodoulou A, Durbin S, Campbell H, Hou Let 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: 2399-8121

A 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.

Journal article

Liou K, Paranicas C, Vines S, Kollmann P, Allen R, Clark G, Mitchell D, Jackman C, Masters A, Achilleos N, Roussos E, Krupp Net al., 2021,

Dawn-dusk asymmetry in energetic (>20 keV) particles adjacent to Saturn's magnetopause

, Journal of Geophysical Research: Space Physics, Vol: 126, ISSN: 2169-9380

Energetic 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.

Journal article

Kilpua EKJ, Good SW, Ala-Lahti M, Osmane A, Fontaine D, Hadid L, Janvier M, Yordanova Eet 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

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Citations: 15

Journal article

Zappa 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 article

Southwood DJ, Cao H, Shebanits O, Elsden T, Hunt GJ, Dougherty MKet al., 2021,

Discovery of Alfven waves planetward of Saturn's rings

, Journal of Geophysical Research: Space Physics, Vol: 126, Pages: 1-18, ISSN: 2169-9380

Between 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.

Journal article

Sparks 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: 1530-261X

To 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.

Journal article

Chandler MO, Schwartz SJ, Avanov LA, Coffey VN, Giles BL, Moore TE, Pollock CJ, Burch JL, Russell CT, Torbert RBet al., 2021,

Observations of Mirror Mode Structures in the Dawn-Side Magnetosphere

, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 126, ISSN: 2169-9380

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Citations: 2

Journal article

Lai T-K, Hendricks EA, Menelaou K, Yau MKet al., 2021,

Roles of Barotropic Instability across the Moat in Inner Eyewall Decay and Outer Eyewall Intensification: Three-Dimensional Numerical Experiments

, JOURNAL OF THE ATMOSPHERIC SCIENCES, Vol: 78, Pages: 473-496, ISSN: 0022-4928

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Journal article

Jannet G, de Wit TD, Krasnoselskikh V, Kretzschmar M, Fergeau P, Bergerard-Timofeeva M, Agrapart C, Brochot J-Y, Chalumeau G, Martin P, Revillet C, Bale SD, Maksimovic M, Bowen TA, Brysbaert C, Goetz K, Guilhem E, Harvey PR, Leray V, Lorfevre Eet al., 2021,

Measurement of Magnetic Field Fluctuations in the Parker Solar Probe and Solar Orbiter Missions

, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 126, ISSN: 2169-9380

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Citations: 16

Journal article

Agiwal O, Cao H, Cowley SWH, Dougherty MK, Hunt GJ, Muller-Wodarg I, Achilleos Net al., 2021,

Constraining the Temporal Variability of Neutral Winds in Saturn's Low-Latitude Ionosphere Using Magnetic Field Measurements

, JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS, Vol: 126, ISSN: 2169-9097

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Citations: 5

Journal article

Madanian H, Desai M, Schwartz SJ, Wilson LB, Fuselier SA, Burch JL, Le Contel O, Turner DL, Ogasawara K, Brosius AL, Russell CT, Ergun RE, Ahmadi N, Gershman DJ, Lindqvist P-Aet al., 2021,

The Dynamics of a High Mach Number Quasi-perpendicular Shock: MMS Observations

, ASTROPHYSICAL JOURNAL, Vol: 908, ISSN: 0004-637X

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Citations: 19

Journal article

Liggins FS, Pickering JC, Nave G, Kramida A, Gamrath S, Quinet Pet al., 2021,

New Ritz Wavelengths and Transition Probabilities of Parity-forbidden [Mn II] Lines of Astrophysical Interest

, ASTROPHYSICAL JOURNAL, Vol: 907, ISSN: 0004-637X

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Citations: 2

Journal article

Shi C, Zhao J, Huang J, Wang T, Wu D, Chen Y, Hu Q, Kasper JC, Bale SDet al., 2021,

Parker Solar Probe Observations of Alfvenic Waves and Ion-cyclotron Waves in a Small-scale Flux Rope

, ASTROPHYSICAL JOURNAL LETTERS, Vol: 908, ISSN: 2041-8205

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Citations: 7

Journal article

Choi KTH, Brindley H, 2021,

COVID-19 lockdown air quality change implications for solar energy generation over China

, Environmental Research Letters, Vol: 16, Pages: 1-10, ISSN: 1748-9326

We exploit changes in air quality seen during the COVID-19 lockdown over China to show how a cleaner atmosphere has notable co-benefits for solar concentrator photovoltaic energy generation. We use satellite observations and analyses of the atmospheric state to simulate surface broadband and spectrally resolved direct normal irradiance (DNI). Over Wuhan, the first city placed under lockdown, we show how the atmospheric changes not only lead to a 19.8% increase in broadband DNI but also induce a significant blue-shift in the DNI spectrum. Feeding these changes into a solar cell simulator results in a 29.7% increase in the power output for a typical triple-junction photovoltaic cell, with around one-third of the increase arising from enhanced cell efficiency due to improved spectral matching. Our estimates imply that these increases in power and cell efficiency would have been realised over many parts of China during the lockdown period. This study thus demonstrates how a cleaner atmosphere may enable more efficient large scale solar energy generation. We conclude by setting our results in the context of future climate change mitigation and air pollution policies.

Journal article

Toumi R, Wang S, 2021,

Recent migration of tropical cyclones toward coasts

, Science, Vol: 371, Pages: 514-517, ISSN: 0036-8075

Poleward migrations of tropical cyclones have been observed globally, but their impact on coastal areas remains unclear. We investigated the change in global tropical cyclone activity in coastal regions over the period 1982–2018. We found that the distance of tropical cyclone maximum intensity to land has decreased by about 30 kilometers per decade, and that the annual frequency of global tropical cyclones increases with proximity to land by about two additional cyclones per decade. Trend analysis reveals a robust migration of tropical cyclone activity toward coasts, concurrent with poleward migration of cyclone locations as well as a statistically significant westward shift. This zonal shift of tropical cyclone tracks may be mainly driven by global zonal changes in environmental steering flow.

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