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  • Conference paper
    Thomas C, Voulgarakis A, Lim G, Haigh J, Nowack Pet al., 2021,

    An unsupervised learning approach to identifying blocking events: the case of European summer

    <jats:p>&amp;lt;p&amp;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
  • 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>&amp;lt;p&amp;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 &amp;quot;1/f&amp;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.&amp;lt;/p&amp;gt;</jats:p>
  • Journal article
    Schwartz SJ, Ergun RE, Harald K, Wilson LB, Chen L-J, Goodrich KA, Turner DL, Gingell I, Madanian H, Gershman DJ, Strangeway RJet al., 2021,

    Evaluating the de Hoffmann-Teller cross-shock potential at real collisionless shocks
  • 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
    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
  • Journal article
    Morimoto S, Goto D, Murayama S, Fujita R, Tohjima Y, Ishidoya S, Machida T, Inai Y, Patra PK, Maksyutov S, Ito A, Aoki Set al., 2021,

    Spatio-temporal variations of the atmospheric greenhouse gases and their sources and sinks in the Arctic region

    , POLAR SCIENCE, Vol: 27, ISSN: 1873-9652
  • 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
  • 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
  • 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
    • Cite
    • Citations: 44
  • 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
    • Cite
    • Citations: 32
  • 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
  • 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
    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>
  • 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
    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
    • Cite
    • Citations: 14
  • 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
    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
    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
    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
    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
    • Cite
    • Citations: 28
  • 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
  • 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
  • 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
  • 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
    • Cite
    • Citations: 17
  • 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
  • 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
  • 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.
  • 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
    Bowen TA, Bale SD, Bandyopadhyay R, Bonnell JW, Case A, Chasapis A, Chen CHK, Curry S, de Wit TD, Goetz K, Goodrich K, Gruesbeck J, Halekas J, Harvey PR, Howes GG, Kasper JC, Korreck K, Larson D, Livi R, MacDowall RJ, Malaspina DM, Mallet A, McManus MD, Page B, Pulupa M, Raouafi N, Stevens ML, Whittlesey Pet al., 2021,

    Kinetic-Scale Turbulence in the Venusian Magnetosheath

    , GEOPHYSICAL RESEARCH LETTERS, Vol: 48, ISSN: 0094-8276
    • Cite
    • Citations: 13

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