Publications

Journal article

Archer M, Shi X, Walach M-T, Hartinger M, Gillies DM, Di Matteo S, Staples F, Nykyri Ket al., 2024,

Crucial future observations and directions for unveiling magnetopause dynamics and their geospace impacts

, Frontiers in Astronomy and Space Sciences, Vol: 11, ISSN: 2296-987X

The dynamics of Earth's magnetopause, driven by several different external/internal physical processes, plays a major role in the geospace energy budget. Given magnetopause motion couples across many space plasma regions, numerous forms of observations may provide valuable information in understanding these dynamics and their impacts. \textit{In-situ} multi-point spacecraft measurements measure the local plasma environment, dynamics and processes; with upcoming swarms providing the possibility of improved spatiotemporal reconstruction of dynamical phenomena, and multi-mission conjunctions advancing understanding of the mesoscale'' coupling across the geospace system of systems''. Soft X-ray imaging of the magnetopause should enable boundary motion to be directly remote sensed for the first time. Indirect remote sensing capabilities might be enabled through the field-aligned currents associated with disturbances to the magnetopause; by harnessing data from satellite mega-constellations in low-Earth orbit, and taking advantage of upgraded auroral imaging and ionospheric radar technology. Finally, increased numbers of closely-spaced ground magnetometers in both hemispheres may help discriminate between high-latitude processes in what has previously been a zone of confusion''. Bringing together these multiple modes of observations for studying magnetopause dynamics is crucial. These may also be aided by advanced data processing techniques, such as physics-based inversions and machine learning methods, along with comparisons to increasingly sophisticated geospace assimilative models and simulations.

Journal article

Trotta D, Dimmock AP, Blanco-Cano X, Forsyth RJ, Hietala H, Fargette N, Larosa A, Lugaz N, Palmerio E, Good SW, Soljento JE, Kilpua EKJ, Yordanova E, Pezzi O, Nicolaou G, Horbury TS, Vainio R, Dresing N, Owen CJ, Wimmer-Schweingruber RFet al., 2024,

Observation of a Fully-formed Forward–Reverse Shock Pair due to the Interaction between Two Coronal Mass Ejections at 0.5 au

, The Astrophysical Journal Letters, Vol: 971, Pages: L35-L35, ISSN: 2041-8205

<jats:title>Abstract</jats:title> <jats:p>We report direct observations of a fast magnetosonic forward–reverse shock pair observed by Solar Orbiter on 2022 March 8 at the short heliocentric distance of 0.5 au. The structure, sharing some features with fully-formed stream interaction regions, is due to the interaction between two successive coronal mass ejections (CMEs), never previously observed to give rise to a forward–reverse shock pair. The scenario is supported by remote observations from extreme ultraviolet cameras and coronagraphs, where two candidate eruptions compatible with the in situ signatures have been found. In the interaction region, we find enhanced energetic particle activity, strong nonradial flow deflections, and evidence of magnetic reconnection. At 1 au, well radially aligned Wind observations reveal a complex event, with characteristic observational signatures of both stream interaction region and CME–CME interaction, thus demonstrating the importance of investigating the complex dynamics governing solar eruptive phenomena.</jats:p>

Journal article

Phan TD, Drake JF, Larson D, Oieroset M, Eriksson S, Yin Z, Lavraud B, Swisdak M, Bale SD, Livi R, Romeo O, Whittlesey P, Halekas J, Rahmati A, Pulupa M, Szabo A, Koval A, Moncuquet M, Kasper J, Stevens M, Desai M, Raouafi Net al., 2024,

Multiple Subscale Magnetic Reconnection Embedded inside a Heliospheric Current Sheet Reconnection Exhaust: Evidence for Flux Rope Merging

, Astrophysical Journal Letters, Vol: 971, ISSN: 2041-8205

We report observations of multiple subscale reconnecting current sheets embedded inside a large-scale heliospheric current sheet (HCS) reconnection exhaust. The discovery was made possible by the unusual skimming trajectory of Parker Solar Probe through a sunward-directed HCS exhaust, sampling structures convecting with the exhaust outflows for more than 3 hr during Encounter 14, at a radial distance of ∼17 solar radii. A large number of subscale current sheets (SCSs) were detected inside the HCS exhaust. Remarkably, five SCSs showed direct evidence for reconnection, displaying near-Alfvénic outflow jets and bifurcated current sheets. The reconnecting SCSs all had small magnetic shears (27°-81°), i.e., strong guide fields. The thickness of the subscale reconnecting current sheets ranged from ∼60 km to ∼5000 km (∼20-2000 ion inertial lengths). The SCS exhausts were directed predominantly in the normal or out-of-plane direction of the HCS, i.e., nearly orthogonal to the HCS exhaust direction. The presence of multiple low-magnetic-shear reconnecting current sheets inside a large-scale exhaust could be associated with coalescence of multiple large flux ropes inside the HCS exhaust. The orientation of some SCS exhausts was partly in the ecliptic plane of the HCS, which may indicate that the coalescence process is highly three-dimensional. Since the coalescence process is likely short-lived, the detection of five such events inside a single HCS crossing could imply the common occurrence of flux rope coalescence in large-scale HCS reconnection exhausts.

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Journal article

Vinogradov A, Alexandrova O, Demoulin P, Artemyev A, Maksimovic M, Mangeney A, Vasiliev A, Petrukovich AA, Bale Set al., 2024,

Embedded Coherent Structures from Magnetohydrodynamics to Sub-ion Scales in Turbulent Solar Wind at 0.17 au

, Astrophysical Journal, Vol: 971, ISSN: 0004-637X

We study intermittent coherent structures in solar wind turbulence from MHD to kinetic plasma scales using Parker Solar Probe data during its first perihelion (at 0.17 au) in the highly Alfvenic slow solar wind. We detect coherent structures using Morlet wavelets. For the first time, we apply a multiscale analysis in physical space. At MHD scales within the inertial range, times scales τ ∈ (1, 102) s, we find (i) current sheets including switchback boundaries and (ii) Alfven vortices. Within these events are embedded structures at smaller scales: typically Alfven vortices at ion scales, τ ∈ (0.08, 1) s, and compressible vortices at sub-ion scales, τ ∈ 8(10−3, 10−2) s. The number of coherent structures grows toward smaller scales: we observe ∼200 events during a 5 hr time interval at MHD scales, ∼103 at ion scales, and ∼104 at sub-ion scales. In general, there are multiple structures of ion and sub-ion scales embedded within one MHD structure. There are also examples of ion and sub-ion scale structures outside MHD structures. To quantify the relative importance of different types of structures, we do a statistical comparison of the observed structures with the expectations of models of the current sheets and vortices. The results show the dominance of Alfven vortices at all scales in contrast to the widespread view of the dominance of current sheets. This means that Alfven vortices are important building blocks of Alfvenic solar wind turbulence.

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Journal article

Shi C, Zhao J, Liu S, Xiao F, Wu Y, Bowen TA, Livi R, Bale SDet al., 2024,

Coexistence of Antisunward and Sunward Ion Cyclotron Waves in the Near-Sun Solar Wind: Excitation by the Proton Cyclotron Instability

, Astrophysical Journal Letters, Vol: 971, ISSN: 2041-8205

Based on observations from the Parker Solar Probe in the near-Sun solar wind, this study identifies an ion-scale wave event characterized by two distinct frequency bands. The lower-band waves exhibit right-hand polarization, while the upper-band waves have left-hand polarization. Alongside these waves, there are clear indications of the existence of both proton core and beam components, with the perpendicular temperature being higher than the parallel temperature in the measured proton velocity distribution functions (VDFs). Utilizing the plasma parameters derived from typical proton VDFs, instability analyses are conducted to investigate the mode nature of the observed waves and their excitation mechanism. The lower-band waves are identified as sunward ion cyclotron waves (ICWs), generated through the proton beam cyclotron instability; the upper-band waves are recognized as antisunward ICWs, induced by the proton core cyclotron instability. This study provides the first direct observational evidence confirming the presence of counterpropagating ICWs and proton cyclotron instability in the solar wind.

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Journal article

Warwick L, Murray J, Brindley H, 2024,

The Far-INfrarEd Spectrometer for Surface Emissivity (FINESSE) Part II: first measurements of the emissivity of water in the far-infrared

, Atmospheric Measurement Techniques, Vol: 17, Pages: 4777-4787, ISSN: 1867-1381

In this paper we describe a method for retrieving surface emissivity across the wavenumber range 400–1600 cm-1 using novel radiance measurements from the Far INfrarEd Spectrometer for Surface Emissivity (FINESSE) instrument. FINESSE is described in detail in part I of this paper. We apply the method to two sets of measurements of distilled water. The first set of emissivity retrievals is of distilled water heated above ambient temperature to enhance the signal to noise ratio. The second set of emissivity retrievals is of ambient temperate water at a range of viewing angles. In both cases the observations agree well with calculations based on compiled refractive indices across the mid and far-infrared. It is found that the reduced contrast between the up and downwelling radiation in the ambient temperature case degrades the performance of the retrieval. Therefore a filter is developed to target regions of high contrast which improves the agreement between the ambient temperature emissivity retrieval and the predicted emissivity. These retrievals are, to the best of our knowledge, the first published 10 retrievals of the emissivity of water that extend into the far-infrared and demonstrate a method that can be used for the in-situ retrieval of the emissivity of other surfaces in the field.

Journal article

Murray JE, Warwick L, Brindley H, Last A, Quigley P, Rochester A, Dewar A, Cummins Det al., 2024,

The Far-INfrarEd Spectrometer for Surface Emissivity (FINESSE) – Part 1: instrument description and level 1 radiances

, Atmospheric Measurement Techniques, Vol: 17, Pages: 4757-4775, ISSN: 1867-1381

The Far-INfrarEd Spectrometer for Surface Emissivity (FINESSE) instrument combines a commercial Bruker EM27 spectrometer with a front-end viewing and calibration rig developed at Imperial College London. FINESSE is specifically designed to enable accurate measurements of surface emissivity, covering the range 400–1600 cm−1, and, as part of this remit, can obtain views over the full 360° angular range.In this part, Part 1, we describe the system configuration, outlining the instrument spectral characteristics, our data acquisition methodology, and the calibration strategy. As part of the process, we evaluate the stability of the system, including the impact of knowledge of blackbody (BB) target emissivity and temperature. We also establish a numerical description of the instrument line shape (ILS), which shows strong frequency-dependent asymmetry. We demonstrate why it is important to account for these effects by assessing their impact on the overall uncertainty budget on the level 1 radiance products from FINESSE. Initial comparisons of observed spectra with simulations show encouraging performance given the uncertainty budget.

Journal article

Johnson D, Hood AW, Cargill PJ, Reid J, Johnston CDet al., 2024,

The thermodynamic response of heating at coronal null points

, Monthly Notices of the Royal Astronomical Society, Vol: 532, Pages: 4261-4271, ISSN: 0035-8711

Magnetic null points are an important aspect of the magnetic field structure of the solar corona and can be sites of enhanced dissipation. This paper uses analytical and numerical models to investigate the plasma structure around a heated null. It is shown that the temperature profile not only differs significantly from that in a uniform field, but also that the profile depends significantly on the spatial structure of the heating. Field lines close to the separatrices and the null point have higher temperatures than a uniform field for the same heating input. The dependence of the results near the null on both the ratio of perpendicular to parallel conduction, and numerical resolution is also explored. The comparison between analytic and numerical solutions also provides a useful benchmark to compare MHD codes with anisotropic thermal conduction.

Journal article

Gryspeerdt E, Stettler M, Teoh R, Burkhardt U, Delovski T, Driver O, Painemal Det al., 2024,

Operational differences lead to longer lifetimes of satellite detectable contrails from more fuel efficient aircraft

, Environmental Research Letters, Vol: 19, ISSN: 1748-9326

Clouds produced by aircraft (known as contrails) contribute over half of the positive radiative forcing from aviation, but the size of this warming effect is highly uncertain. Their radiative effect is highly dependent on the microphysical properties and meteorological background state, varying strongly over the contrail lifecycle. In-situ observations have demonstrated an impact of aircraft and fuel type on contrail properties close to the aircraft, but there are few observational constraints at these longer timescales, despite these having a strong impact in high-resolution and global models. This work provides an observational quantification of these contrail controlling factors, matching air traffic data to satellite observations of contrails to isolate the role of the aircraft type in contrail properties and evolution. Investigating over 64 000 cases, a relationship between aircraft type and contrail formation is observed, with more efficient aircraft forming longer-lived satellite-detectable contrails more frequently, which could lead to a larger climate impact. This increase in contrail formation and lifetime is primarily driven by an increase in flight altitude. Business jets are also found to produce longer-lived satellite-detectable contrails despite their lower fuel flow, as they fly at higher altitudes. The increase in satellite-detected contrails behind more efficient aircraft suggests a trade-off between aircraft greenhouse gas emissions and the aviation climate impact through contrail production, due to differences in aircraft operation.

Journal article

Williams RG, Meijers AJS, Roussenov VM, Katavouta A, Ceppi P, Rosser JP, Salvi Pet al., 2024,

Asymmetries in the Southern Ocean contribution to global heat and carbon uptake

, Nature Climate Change, Vol: 14, Pages: 823-831, ISSN: 1758-678X

The Southern Ocean provides dominant contributions to global ocean heat and carbon uptake, which is widely interpreted as resulting from its unique upwelling and circulation. Here we show a large asymmetry in these contributions, with the Southern Ocean accounting for 83 ± 33% of global heat uptake versus 43 ± 3% of global ocean carbon uptake over the historical period in state-of-the-art climate models. Using single radiative forcing experiments, we demonstrate that this historical asymmetry is due to suppressed heat uptake by northern oceans from enhanced aerosol forcing. In future projections, such as SSP2-4.5 where greenhouse gases increasingly dominate radiative forcing, the Southern Ocean contributions to global heat and carbon uptake become more comparable, 52 ± 5% and 47 ± 4%, respectively. Hence, the past is not a reliable indicator of the future, with the northern oceans becoming important for heat uptake while the Southern Ocean remains important for both heat and carbon uptake.

Journal article

Stier P, van den Heever SC, Christensen MW, Gryspeerdt E, Dagan G, Saleeby SM, Bollasina M, Donner L, Emanuel K, Ekman AML, Feingold G, Field P, Forster P, Haywood J, Kahn R, Koren I, Kummerow C, LEcuyer T, Lohmann U, Ming Y, Myhre G, Quaas J, Rosenfeld D, Samset B, Seifert A, Stephens G, Tao W-Ket al., 2024,

Multifaceted aerosol effects on precipitation

, Nature Geoscience, Vol: 17, Pages: 719-732, ISSN: 1752-0894

Aerosols have been proposed to influence precipitation rates and spatial patterns from scales of individual clouds to the globe. However, large uncertainty remains regarding the underlying mechanisms and importance of multiple effects across spatial and temporal scales. Here we review the evidence and scientific consensus behind these effects, categorized into radiative effects via modification of radiative fluxes and the energy balance, and microphysical effects via modification of cloud droplets and ice crystals. Broad consensus and strong theoretical evidence exist that aerosol radiative effects (aerosol–radiation interactions and aerosol–cloud interactions) act as drivers of precipitation changes because global mean precipitation is constrained by energetics and surface evaporation. Likewise, aerosol radiative effects cause well-documented shifts of large-scale precipitation patterns, such as the intertropical convergence zone. The extent of aerosol effects on precipitation at smaller scales is less clear. Although there is broad consensus and strong evidence that aerosol perturbations microphysically increase cloud droplet numbers and decrease droplet sizes, thereby slowing precipitation droplet formation, the overall aerosol effect on precipitation across scales remains highly uncertain. Global cloud-resolving models provide opportunities to investigate mechanisms that are currently not well represented in global climate models and to robustly connect local effects with larger scales. This will increase our confidence in predicted impacts of climate change.

Journal article

Wang S, Ren T, Yang P, Saito M, Brindley HEet al., 2024,

Improved temperature-dependent ice refractive index compilation in the far-infrared spectrum

, Geophysical Research Letters, Vol: 51, ISSN: 0094-8276

A new ice refractive index compilation is reported for a broad spectrum ranging from 0.0443 to 106 𝜇m, focusing on the pronounced temperature-dependence of ice optical properties in the far-infrared (far-IR) segment (15-100 µm). A sensitivity study assuming spherical particles shows that selecting ice refractive indices at 12 temperatures and 215 wavelengths in the far-IR region gives sufficient accuracy in interpolated refractive indices for developing a new ice crystal optical property database. Furthermore, we demonstrate the differences between the bulk single-scattering properties computed for hexagonal ice particles with this new compilation compared to a previous iteration at three far-IR wavelengths where substantial differences are noticed between the two ice refractive index compilations. We suggest that our new ice refractive index dataset will improve downstream light-scattering applications for upcoming far-IR satellite missions and allow robust modeling of outgoing longwave radiation (OLR) under ice cloud conditions.

Journal article

Chen LJ, Gershman D, Burkholder B, Chen Y, Sarantos M, Jian L, Drake J, Dong C, Gurram H, Shuster J, Graham DB, Le Contel O, Schwartz SJ, Fuselier S, Madanian H, Pollock C, Liang H, Argall M, Denton RE, Rice R, Beedle J, Genestreti K, Ardakani A, Stanier A, Le A, Ng J, Bessho N, Pandya M, Wilder F, Gabrielse C, Cohen I, Wei H, Russell CT, Ergun R, Torbert R, Burch Jet al., 2024,

Earth's Alfvén Wings Driven by the April 2023 Coronal Mass Ejection

, Geophysical Research Letters, Vol: 51, ISSN: 0094-8276

We report a rare regime of Earth's magnetosphere interaction with sub-Alfvénic solar wind in which the windsock-like magnetosphere transforms into one with Alfvén wings. In the magnetic cloud of a Coronal Mass Ejection (CME) on 24 April 2023, NASA's Magnetospheric Multiscale mission distinguishes the following features: (a) unshocked and accelerated low-beta CME plasma coming directly against Earth's dayside magnetosphere; (b) dynamical wing filaments representing new channels of magnetic connection between the magnetosphere and foot points of the Sun's erupted flux rope; (c) cold CME ions observed with energized counter-streaming electrons, evidence of CME plasma captured due to by reconnection between magnetic-cloud and Alfvén-wing field lines. The reported measurements advance our knowledge of CME interaction with planetary magnetospheres, and open new opportunities to understand how sub-Alfvénic plasma flows impact astrophysical bodies such as Mercury, moons of Jupiter, and exoplanets close to their host stars.

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Citations: 1

Journal article

Greene SM, Schachat SR, Arita-Merino N, Cao XE, Gurnani H, Heyns M, Cagigas ML, Maikawa CL, Needham EJ, Perets EA, Phillips E, Waddle AW, Wilkinson CE, Zhou KC, Zlotnick HMet al., 2024,

Accessible interview practices for disabled scientists and engineers.

, iScience, Vol: 27

Increasing representation of people with disabilities in science and engineering will require systemic changes to the culture around support and accommodations. Equitable interview practices can help foster such changes. We, an interdisciplinary group of disabled and nondisabled early-career scientists who care deeply about making science more accessible to all, present a framework of suggestions based on Universal Design principles for improving the accessibility and equitability of interviews for people with disabilities and other underrepresented groups. We discuss potential challenges that may arise when implementing these suggestions and provide questions to guide discussions about addressing them.

Journal article

Xu S, Mitchell DL, Whittlesey P, Rahmati A, Livi R, Larson D, Luhmann JG, Halekas JS, Hara T, McFadden JP, Pulupa M, Bale SD, Curry SM, Persson Met al., 2024,

Closed magnetic topology in the Venusian magnetotail and ion escape at Venus.

, Nat Commun, Vol: 15

Venus, lacking an intrinsic global dipole magnetic field, serves as a textbook example of an induced magnetosphere, formed by interplanetary magnetic fields (IMF) enveloping the planet. Yet, various aspects of its magnetospheric dynamics and planetary ion outflows are complex and not well understood. Here we analyze plasma and magnetic field data acquired during the fourth Venus flyby of the Parker Solar Probe (PSP) mission and show evidence for closed topology in the nightside and downstream portion of the Venus magnetosphere (i.e., the magnetotail). The formation of the closed topology involves magnetic reconnection-a process rarely observed at non-magnetized planets. In addition, our study provides an evidence linking the cold Venusian ion flow in the magnetotail directly to magnetic connectivity to the ionosphere, akin to observations at Mars. These findings not only help the understanding of the complex ion flow patterns at Venus but also suggest that magnetic topology is one piece of key information for resolving ion escape mechanisms and thus the atmospheric evolution across various planetary environments and exoplanets.

Journal article

Mathews JP, Czaja A, Vitart F, Roberts Cet al., 2024,

Gulf Stream Moisture Fluxes Impact Atmospheric Blocks Throughout the Northern Hemisphere

, Geophysical Research Letters, Vol: 51, ISSN: 0094-8276

In this study, we explore the impact of oceanic moisture fluxes on atmospheric blocks using the ECMWF IFS. Artificially suppressing surface latent heat flux over the Gulf Stream (GS) region reduces atmospheric blocking frequency across the Northern Hemisphere by up to 30%. Affected blocks show a shorter lifespan (−6%), smaller spatial extent (−10%), and reduced intensity (−0.4%), with an increased number of individual blocking anticyclones (+17%). These findings are robust across various blocking detection thresholds. Analysis reveals a qualitatively consistent response across all resolutions, with Tco639 (∼18 km) showing the largest statistically significant change across all blocking characteristics, although differences between resolutions are not statistically significant. Exploring the broader Rossby wave pattern, we observe that diminished moisture fluxes favor eastward propagation and higher zonal wavenumbers, while air-sea interactions promote stationary and westward-propagating waves with zonal wavenumber 3. This study underscores the critical role of the GS in modulating atmospheric blocking.

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Citations: 1

Conference paper

Lewis Z, Stephenson P, Kallio E, Galand M, Beth Aet al., 2024,

Evolution of the ion dynamics at comet 67P during the escort phase

<jats:p>Comet 67P/Churyumov-Gerasimenko was escorted by the Rosetta spacecraft through a 2 year section of its 6 year orbit around the Sun. This enabled the observation of a large variation in comet outgassing and the resulting evolution of the plasma environment. The diamagnetic cavity, a region of negligible magnetic field arising from the interaction of the unmagnetised cometary plasma with the solar wind, began to be detected sporadically by the Rosetta Plasma Consortium/ Magnetometer (RPC/MAG) in April 2015 at a heliocentric distance of 1.8 au [1]. The last detections were in February 2016 at 2.4 au. Within this cavity, the flow of cometary ions has been shown to be largely radial [2]; the ions are accelerated above the neutral gas speed by an ambipolar electric field, but many newborn ions still undergo multiple ion-neutral chemical reactions before escaping [3,4]. Outside the diamagnetic cavity boundary, which is itself highly variable, the ion flow is considerably more complex, and the ambipolar electric field plays a more minor role compared to the convective electric field of the solar wind [2]. &#160;At large heliocentric distances (>2.5 au), the total plasma density observed from RPC plasma sensors is well explained by a simple flux conservation model that assumes the ions travel radially away from the nucleus at speed close to that of neutrals [5,6]. However, closer to perihelion and once the diamagnetic cavity has formed, such an approach does not hold [7]. We aim to better understand this transition, the driver of ions' acceleration, and the role that the diamagnetic cavity plays.In this study, we explore the varying ion dynamics both in the presence (e.g. during high outgassing activity) and absence (low outgassing activity) of a diamagnetic cavity. Electric and magnetic fields from hybrid simulations of the cometary environment are used to drive a 3D test particle model of the cometary ions for a range of comet activity levels.

Conference paper

Beth A, Galand M, Modolo R, Leblanc F, Jia Xet al., 2024,

Impact of ion-neutral chemistry on Ganymede's ionosphere

<jats:p>The Galileo spacecraft flew by Ganymede, down to 0.1 RG from the surface for the closest, six times giving us insight into its plasma environment. Its ionosphere, made of ions born from the ionisation of neutrals present in Ganymede's exosphere, represents the bulk of the plasma near the moon around closest approach. As it has been revealed by Galileo and Juno, near closest approach the ion population is dominated by low-energy ions from the water ion group (O+, HO+, H2O+) and O2+. As we showed in [1] by means of a test particle model, the ion composition during most flybys was a priori dominated by H2+and O2+. However, during Juno's flyby of Ganymede, plasma data revealed the additional presence of H3+ that may only stem from ion neutral reactions between H2 and H2+.&#160;&#160;We have updated our test particle model to account for these ion-neutral collisions of which &#160;H2 + H2+. We show how it modifies the ion composition compared with [1] and assess the role of these collisions in the production of new ion species within Ganymede's exo-ionosphere. This will help to interpret plasma observations made by Juno and in the future by JUICE around Ganymede.&#160;[1] Beth et al., EGU24, https://doi.org/10.5194/egusphere-egu24-11772, 2024</jats:p>

Journal article

Lester JG, Graven HD, Khatiwala S, McNichol APet al., 2024,

Changes in Oceanic Radiocarbon and CFCs Since the 1990s

, Journal of Geophysical Research: Oceans, Vol: 129, ISSN: 2169-9275

Anthropogenic perturbations from fossil fuel burning, nuclear bomb testing, and chlorofluorocarbon (CFC) use have created useful transient tracers of ocean circulation. The atmospheric 14C/C ratio (∆14C) peaked in the early 1960s and has decreased now to pre-industrial levels, while atmospheric CFC-11 and CFC-12 concentrations peaked in the early 1990s and early 2000s, respectively, and have now decreased by 10%–20%. We present the first analysis of a decade of new observations (2007 to 2018–2019) and give a comprehensive overview of the changes in ocean ∆14C and CFC concentration since the WOCE surveys in the 1990s. Surface ocean ∆14C decreased at a nearly constant rate from the 1990–2010s (20‰/decade). In most of the surface ocean ∆14C is higher than in atmospheric CO2 while in the interior ocean, only a few places are found to have increases in ∆14C, indicating that globally, oceanic bomb 14C uptake has stopped and reversed. Decreases in surface ocean CFC-11 started between the 1990 and 2000s, and CFC-12 between the 2000–2010s. Strong coherence in model biases of decadal changes in all tracers in the Southern Ocean suggest ventilation of Antarctic Intermediate Water was enhanced from the 1990 to the 2000s, whereas ventilation of Subantarctic Mode Water was enhanced from the 2000 to the 2010s. The decrease in surface tracers globally between the 2000 and 2010s is consistently stronger in observations than in models, indicating a reduction in vertical transport and mixing due to stratification.

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Journal article

Ervin T, Bale SD, Badman ST, Rivera YJ, Romeo O, Huang J, Riley P, Bowen TA, Lepri ST, Dewey RMet al., 2024,

Compositional Metrics of Fast and Slow Alfvénic Solar Wind Emerging from Coronal Holes and Their Boundaries

, Astrophysical Journal, Vol: 969, ISSN: 0004-637X

We seek to understand the composition and variability of fast solar wind (FSW) and slow Alfvénic solar wind emerging from coronal holes (CHs). We leverage an opportune conjunction between Solar Orbiter and Parker Solar Probe (PSP) during PSP Encounter 11 to include compositional diagnostics from the Solar Orbiter Heavy Ion Sensor as these variations provide crucial insights into the origin and nature of the solar wind. We use potential field source surface and magnetohydrodynamic models to connect the observed plasma at PSP and Solar Orbiter to its origin footpoint in the photosphere and compare these results with the in situ measurements. A very clear signature of a heliospheric current sheet crossing as evidenced by enhancements in low first ionization potential (FIP) elements, ion charge state ratios, proton density, low Alfvénicity, and polarity estimates validates the combination of modeling, data, and mapping. We identify two FSW streams emerging from small equatorial CHs with low ion charge state ratios, low FIP bias, high Alfvénicity, and low footpoint brightness, yet anomalously low alpha particle abundance for both streams. We identify high-Alfvénicity slow solar wind emerging from the overexpanded boundary of a CH having intermediate alpha abundance, high Alfvénicity, and dips in ion charge state ratios corresponding to CH boundaries. Through this comprehensive analysis, we highlight the power of multi-instrument conjunction studies in assessing the sources of the solar wind.

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Citations: 2

Journal article

Schwadron NA, Bale SD, Bonnell J, Case A, Shen M, Christian ER, Cohen CMS, Davis AJ, Desai MI, Goetz K, Giacalone J, Hill ME, Kasper JC, Korreck K, Larson D, Livi R, Lim T, Leske RA, Malandraki O, Malaspina D, Matthaeus WH, McComas DJ, McNutt RL, Mewaldt RA, Mitchell DG, Niehof JT, Pulupa M, Pecora F, Rankin JS, Smith C, Stone EC, Szalay JR, Vourlidas A, Wiedenbeck ME, Whittlesey Pet al., 2024,

Parker Solar Probe Observations of Energetic Particles in the Flank of a Coronal Mass Ejection Close to the Sun

, Astrophysical Journal, Vol: 970, ISSN: 0004-637X

We present an event observed by Parker Solar Probe (PSP) at ∼0.2 au on 2022 March 2 in which imaging and in situ measurements coincide. During this event, PSP passed through structures on the flank of a streamer blowout coronal mass ejection (CME) including an isolated flux tube in front of the CME, a turbulent sheath, and the CME itself. Imaging observations and in situ helicity and principal variance signatures consistently show the presence of flux ropes internal to the CME. In both the sheath and the CME interval, the distributions are more isotropic, the spectra are softer, and the abundance ratios of Fe/O and He/H are lower than those in the isolated flux tube, and yet elevated relative to typical plasma and solar energetic particle abundances. These signatures in the sheath and the CME indicate that both flare populations and those from the plasma are accelerated to form the observed energetic particle enhancements. In contrast, the isolated flux tube shows large streaming, hard spectra, and large Fe/O and He/H ratios, indicating flare sources. Energetic particle fluxes are most enhanced within the CME interval from suprathermal through energetic particle energies (∼keV to >10 MeV), indicating particle acceleration, as well as confinement local to the closed magnetic structure. The flux-rope morphology of the CME helps to enable local modulation and trapping of energetic particles, in particular along helicity channels and other plasma boundaries. Thus, the CME acts to build up energetic particle populations, allowing them to be fed into subsequent higher-energy particle acceleration throughout the inner heliosphere where a compression or shock forms on the CME front.

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Journal article

Wilson Kemsley S, Ceppi P, Andersen H, Cermak J, Stier P, Nowack Pet al., 2024,

A systematic evaluation of high-cloud controlling factors

, Atmospheric Chemistry and Physics, Vol: 24, Pages: 8295-8316, ISSN: 1680-7316

Clouds strongly modulate the top-of-the-atmosphere energy budget and are a major source of uncertainty in climate projections. “Cloud controlling factor” (CCF) analysis derives relationships between large-scale meteorological drivers and cloud radiative anomalies, which can be used to constrain cloud feedback. However, the choice of meteorological CCFs is crucial for a meaningful constraint. While there is rich literature investigating ideal CCF setups for low-level clouds, there is a lack of analogous research explicitly targeting high clouds. Here, we use ridge regression to systematically evaluate the addition of five candidate CCFs to previously established core CCFs within large spatial domains to predict longwave high-cloud radiative anomalies: upper-tropospheric static stability (SUT), sub-cloud moist static energy, convective available potential energy, convective inhibition, and upper-tropospheric wind shear (ΔU300). We identify an optimal configuration for predicting high-cloud radiative anomalies that includes SUT and ΔU300 and show that spatial domain size is more important than the selection of CCFs for predictive skill. We also find an important discrepancy between the optimal domain sizes required for predicting locally and globally aggregated radiative anomalies. Finally, we scientifically interpret the ridge regression coefficients, where we show that SUT captures physical drivers of known high-cloud feedbacks and deduce that the inclusion of SUT into observational constraint frameworks may reduce uncertainty associated with changes in anvil cloud amount as a function of climate change. Therefore, we highlight SUT as an important CCF for high clouds and longwave cloud feedback.

Journal article

Acevski M, Masters A, ZomerdijkRussell S, 2024,

Asymmetry in Uranus' high energy proton radiation belt

, Geophysical Research Letters, Vol: 51, ISSN: 0094-8276

Uranus is one of the least explored planets in our solar system, it exhibits a unique magnetic field structure which was observed by NASA's Voyager 2 mission nearly 50 years ago. Notably, Uranus displays extreme magnetic field asymmetry, a feature exclusive to the icy giants. We use the Boris algorithm to investigate how high energy protons behave within this unusual magnetic field, which is motivated by Voyager 2's observation of lower-than-expected high energy proton radiation belt intensities at Uranus. When considering full drift motions of high energy protons around Uranus, the azimuthal drift velocity can vary by as much as 15% around the planet. This results in areas around Uranus where particles will be more depleted (faster drift) and other regions where there is a surplus of particles (slower drift). This could provide a partial explanation for the “weak” proton radiation belts observed by Voyager 2.

Journal article

Kasoar M, Perkins O, Millington JDA, Mistry J, Smith Cet al., 2024,

Model fires, not ignitions: capturing the human dimension of global fire regimes

, Cell Reports Sustainability, Vol: 1, ISSN: 2949-7906

Fire regimes are intrinsically shaped by humans, but current global fire models do not reflect the diverse objectives humans have for managing fire. With new data sources and collaboration across disciplines, an improved understanding of human influences on fire regimes is increasingly possible and essential to represent.

Journal article

Mülmenstädt J, Gryspeerdt E, Dipu S, Quaas J, Ackerman AS, Fridlind AM, Tornow F, Bauer SE, Gettelman A, Ming Y, Zheng Y, Ma P-L, Wang H, Zhang K, Christensen MW, Varble AC, Leung LR, Liu X, Neubauer D, Partridge DG, Stier P, Takemura Tet al., 2024,

General circulation models simulate negative liquid water path–droplet number correlations, but anthropogenic aerosols still increase simulated liquid water path

, Atmospheric Chemistry and Physics, Vol: 24, Pages: 7331-7345, ISSN: 1680-7316

General circulation models' (GCMs) estimates of the liquid water path adjustment to anthropogenic aerosol emissions differ in sign from other lines of evidence. This reduces confidence in estimates of the effective radiative forcing of the climate by aerosol–cloud interactions (ERFaci). The discrepancy is thought to stem in part from GCMs' inability to represent the turbulence–microphysics interactions in cloud-top entrainment, a mechanism that leads to a reduction in liquid water in response to an anthropogenic increase in aerosols. In the real atmosphere, enhanced cloud-top entrainment is thought to be the dominant adjustment mechanism for liquid water path, weakening the overall ERFaci. We show that the latest generation of GCMs includes models that produce a negative correlation between the present-day cloud droplet number and liquid water path, a key piece of observational evidence supporting liquid water path reduction by anthropogenic aerosols and one that earlier-generation GCMs could not reproduce. However, even in GCMs with this negative correlation, the increase in anthropogenic aerosols from preindustrial to present-day values still leads to an increase in the simulated liquid water path due to the parameterized precipitation suppression mechanism. This adds to the evidence that correlations in the present-day climate are not necessarily causal. We investigate sources of confounding to explain the noncausal correlation between liquid water path and droplet number. These results are a reminder that assessments of climate parameters based on multiple lines of evidence must carefully consider the complementary strengths of different lines when the lines disagree.

Journal article

Graven HD, Warren H, Gibbs HK, Khatiwala S, Koven C, Lester J, Levin I, Spawn-Lee SA, Wieder Wet al., 2024,

Bomb radiocarbon evidence for strong global carbon uptake and turnover in terrestrial vegetation

, Science, Vol: 384, Pages: 1335-1339, ISSN: 0036-8075

Vegetation and soils are taking up approximately 30% of anthropogenic carbon dioxide emissions because of small imbalances in large gross carbon exchanges from productivity and turnover that are poorly constrained. We combined a new budget of radiocarbon produced by nuclear bomb testing in the 1960s with model simulations to evaluate carbon cycling in terrestrial vegetation. We found that most state-of-the-art vegetation models used in the Coupled Model Intercomparison Project underestimated the radiocarbon accumulation in vegetation biomass. Our findings, combined with constraints on vegetation carbon stocks and productivity trends, imply that net primary productivity is likely at least 80 petagrams of carbon per year presently, compared with the 43 to 76 petagrams per year predicted by current models. Storage of anthropogenic carbon in terrestrial vegetation is likely more short-lived and vulnerable than previously predicted.

Journal article

Amtmann C, Pollinger A, Ellmeier M, Dougherty M, Brown P, Lammegger R, Betzler A, Agú M, Hagen C, Jernej I, Wilfinger J, Baughen R, Strickland A, Magnes Wet al., 2024,

Accuracy of the scalar magnetometer aboard ESA's JUICE mission

, Geoscientific Instrumentation, Methods and Data Systems, Vol: 13, Pages: 177-191, ISSN: 2193-0856

This paper discusses the accuracy of the scalar Coupled Dark State Magnetometer on board the Jupiter Icy Moons Explorer (JUICE) mission of the European Space Agency (ESA). The scalar magnetometer, referred to as MAGSCA, is part of the J-MAG instrument. MAGSCA is an optical omnidirectional scalar magnetometer based on coherent population trapping, a quantum interference effect, within the hyperfine manifold of the 87Rb D1 line. The measurement principle is only based on natural constants; therefore, it is in principle drift-free, and no calibration is required. However, the technical realisation can influence the measurement accuracy. The most dominating effects are heading characteristics, which are deviations of the magnetic field strength measurements from the ambient magnetic field strength. These deviations are a function of the angle between the sensor axis and the magnetic field vector and are an intrinsic physical property of the measurement principle of the magnetometer. The verification of the accuracy of the instrument is required to ensure its compliance with the performance requirement of 0.2 nT (1σ) with a data rate of 1 Hz. The verification is carried out with four dedicated sensor orientations in a Merritt coil system, which is located in the geomagnetic Conrad Observatory (COBS). The coil system is used to compensate the Earth's magnetic field and to apply appropriate test fields to the sensor. This paper presents a novel method to separate the heading characteristics of the instrument from residual (offset) fields within the coil system by fitting a mathematical model to the measured data and by the successful verification of the MAGSCA performance requirement.

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Journal article

Agiwal O, Cao H, Hsu H-W, Moore L, Sulaiman AH, O'Donoghue J, Dougherty MKet al., 2024,

Current Events at Saturn: Ring-Planet Electromagnetic Coupling

, PLANETARY SCIENCE JOURNAL, Vol: 5

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Journal article

Hou C, Rouillard AP, He J, Gannouni B, Reville V, Louarn P, Fedorov A, Prech L, Owen CJ, Verscharen D, D'Amicis R, Sorriso-Valvo L, Fargette N, Coburn J, Genot V, Raines JM, Bruno R, Livi S, Lavraud B, Andre N, Fruit G, Kieokaew R, Plotnikov I, Penou E, Barthe A, Kataria D, Berthomier M, Allegrini F, Fortunato V, Mele G, Horbury Tet al., 2024,