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  • Journal article
    Blyth L, Graven H, Manning AJ, Levy Pet al., 2024,

    Radiocarbon as a tracer of the fossil fraction of regional carbon monoxide emissions

    , Environmental Research Letters, Vol: 19, Pages: 114073-114073

    <jats:title>Abstract</jats:title> <jats:p>Carbon monoxide (CO) is an atmospheric pollutant with a positive net warming effect on the climate. The magnitude of CO sources and the fraction of fossil vs biogenic sources are still uncertain and vary across emissions inventories. Measurements of radiocarbon (<jats:sup>14</jats:sup>C) in CO could potentially be used to investigate the sources of CO on a regional scale because fossil sources lack <jats:sup>14</jats:sup>C and reduce the <jats:sup>14</jats:sup>C/C ratio (Δ<jats:sup>14</jats:sup>C) of atmospheric CO more than biogenic sources. We use regional Lagrangian model simulations to investigate the utility of Δ<jats:sup>14</jats:sup>CO measurements for estimating the fossil fraction of CO emissions and evaluating bottom-up emissions estimates (United Kingdom Greenhouse Gas, UKGHG, and TNO Copernicus Atmosphere Monitoring Service, TNO) in London, UK. Due to the high Δ<jats:sup>14</jats:sup>CO in atmospheric CO from cosmogenic production, both fossil and biogenic CO emissions cause large reductions in Δ<jats:sup>14</jats:sup>CO regionally, with larger reductions for fossil than biogenic CO per ppb added. There is a strong seasonal variation in Δ<jats:sup>14</jats:sup>CO in background air and in the sensitivity of Δ<jats:sup>14</jats:sup>CO to fossil and biogenic emissions of CO. In the UK, the CO emissions estimate from TNO has a higher fraction from fossil fuels than UKGHG (72% vs 67%). This results in larger simulated decreases in Δ<jats:sup>14</jats:sup>C per ppb CO for TNO emissions. The simulated differences between UKGHG and TNO are likely to be easily detectable by current measurement precision, suggesting that Δ<jats:sup>14</jats:sup>CO measurements could be an effective tool to understand regional CO so

  • Journal article
    Ellmeier M, Betzler A, Amtmann C, Pollinger A, Hagen C, Jernej I, Agú M, Magnes W, Windholz L, Dougherty M, Brown P, Lammegger Ret al., 2024,

    Lower magnetic field measurement limit of the coupled dark state magnetometer

    , Measurement Science and Technology, Vol: 35, ISSN: 0957-0233

    The Coupled Dark State Magnetometer (CDSM) is an optically pumped magnetometer. For the Jupiter Icy Moons Explorer mission, the CDSM and two fluxgate magnetometers are combined in the J-MAG instrument to measure the static and low frequency magnetic field in the Jupiter system. During certain calibration manoeuvres, the CDSM has to be able to measure magnetic field strengths down to 100 nT with an accuracy of 0.2 nT ( 1 σ ). At such low magnetic fields, the CDSM’s operational parameters must be carefully selected to obtain narrow resonance structures. Otherwise, the coupled dark state resonances, used for the magnetic field detection in different instrument modes, overlap and result in a systematic error. The overlap of the resonances and therefore the systematic error mainly depends on the resonance line width and the selected modulation frequencies for the detection of the resonances. We show that a line width of less than 200 Hz and selecting a modulation frequency of about the resonance line width are beneficial at magnetic field strengths B < 1.5 μ T. In this paper we demonstrate that with the found instrument settings the CDSM is able to measure magnetic field strengths below 100 nT with a systematic error less than 0.2 nT resulting from the overlap of the resonances.

  • Journal article
    Ceppi P, Myers TA, Nowack P, Wall CJ, Zelinka MDet al., 2024,

    Implications of a Pervasive Climate Model Bias for Low‐Cloud Feedback

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

    <jats:title>Abstract</jats:title><jats:p>How low clouds respond to warming constitutes a key uncertainty for climate projections. Here we observationally constrain low‐cloud feedback through a controlling factor analysis based on ridge regression. We find a moderately positive global low‐cloud feedback (0.45 W , 90% range 0.18–0.72 W ), about twice the mean value (0.22 W ) of 16 models from the Coupled Model Intercomparison Project. We link this discrepancy to a pervasive model mean‐state bias: models underestimate the low‐cloud response to warming because (a) they systematically underestimate present‐day tropical marine low‐cloud amount, and (b) the low‐cloud sensitivity to warming is proportional to this present‐day low‐cloud amount. Our results hence highlight the importance of reducing model biases in both the mean state of clouds and their sensitivity to environmental factors for accurate climate change projections.</jats:p>

  • Journal article
    Waters C, Eastwood J, Fargette N, Newman D, Goldman Met al., 2024,

    Classifying magnetic reconnection regions using k-means clustering: applications to energy partition

    , JGR: Space Physics, Vol: 129, ISSN: 2169-9402

    Magnetic reconnection is a fundamental plasma process which facilitates the conversion of magnetic energy to particle energies. This local process both contributes to and is affected by a larger system, being dependent on plasma conditions and transporting energy around the system, such as Earth's magnetosphere. When studying the reconnection process with in situ spacecraft data, it can be difficult to determine where spacecraft are in relation to the reconnection structure. In this work, we use k-means clustering, an unsupervised machine learning technique, to identify regions in a 2.5-D PIC simulation of symmetric magnetic reconnection with conditions comparable to those observed in Earth’s magnetotail. This allows energy flux densities to be attributed to these regions. The ion enthalpy flux density is the most dominant form of energy flux density in the outflows, agreeing with previous studies. Poynting flux density may be dominant at some points in the outflows and is only half that of the Poynting flux density in the separatrices. The proportion of outflowing particle energy flux decreases as guide field increases. We find that k-means is beneficial for analysing data and comparing between simulations and in situ data. This demonstrates an approach which may be applied to large volumes of data to determine statistically different regions within phenomena in simulations and could be extended to in situ observations, applicable to future multi-point missions.

  • Journal article
    Auestad H, Spensberger C, Marcheggiani A, Ceppi P, Spengler T, Woollings Tet al., 2024,

    Spatio-temporal averaging of jets obscures the reinforcement of baroclinicity by latent heating

    , Weather and Climate Dynamics, Vol: 5, Pages: 1269-1286

    <jats:p>Abstract. Latent heating modifies the jet stream by modifying the vertical geostrophic wind shear, thereby altering the potential for baroclinic development. Hence, correctly representing diabatic effects is important for modelling the mid-latitude atmospheric circulation and variability. However, the direct effects of diabatic heating remain poorly understood. For example, there is no consensus on the effect of latent heating on the cross-jet temperature contrast. We show that this disagreement is attributable to the choice of spatio-temporal averaging. Jet representations relying on averaged wind tend to have the strongest latent heating on the cold flank of the jet, thus weakening the cross-jet temperature contrast. In contrast, jet representations reflecting the two-dimensional instantaneous wind field have the strongest latent heating on the warm flank of the jet. Furthermore, we show that latent heating primarily occurs on the warm flank of poleward directed instantaneous jets, which is the case for all storm tracks and seasons. </jats:p>

  • Journal article
    Cuesta ME, Cummings AT, Livadiotis G, McComas DJ, Cohen CMS, Khoo LY, Sharma T, Shen MM, Bandyopadhyay R, Rankin JS, Szalay JR, Farooki HA, Xu Z, Muro GD, Stevens ML, Bale SDet al., 2024,

    Observations of Kappa Distributions in Solar Energetic Protons and Derived Thermodynamic Properties

    , Astrophysical Journal, Vol: 973, ISSN: 0004-637X

    In this paper, we model the high-energy tail of observed solar energetic proton energy distributions with a kappa distribution function. We employ a technique for deriving the thermodynamic parameters of solar energetic proton populations measured by the Parker Solar Probe Integrated Science Investigation of the Sun EPI-Hi high-energy telescope, over energies from 10 to 60 MeV. With this technique, we explore, for the first time, the characteristic thermodynamic properties of the solar energetic protons associated with an interplanetary coronal mass ejection (ICME) and its driven shock. We find that: (1) the spectral index or, equivalently, the thermodynamic parameter kappa of solar energetic protons (κ EP) gradually increases, starting from the pre-ICME region (upstream of the CME-driven shock), reaching a maximum in the CME ejecta (κ EP ≈ 3.5), followed by a gradual decrease throughout the trailing portion of the CME; (2) the solar energetic proton temperature and density (T EP and n EP) appear anticorrelated, a behavior consistent with subisothermal polytropic processes; and (3) values of T EP and κ EP appear to be positively correlated, indicating an increasing entropy with time. Therefore, these proton populations are characterized by a complex and evolving thermodynamic behavior, consisting of multiple subisothermal polytropic processes, and a large-scale trend of increasing temperature, kappa, and entropy. This study and its companion study by Livadiotis et al. open up a new set of procedures for investigating the thermodynamic behavior of energetic particles and their shared thermal properties.

  • Journal article
    Fargette N, Eastwood JP, Waters CL, Øieroset M, Phan TD, Newman DL, Stawarz JE, Goldman MV, Lapenta Get al., 2024,

    Statistical study of energy transport and conversion in electron diffusion regions at earth's dayside magnetopause

    , Journal of Geophysical Research: Space Physics, Vol: 129, ISSN: 2169-9380

    The electron diffusion region (EDR) is a key region for magnetic reconnection, but the typical energy transport and conversion in EDRs is still not well understood. In this work, we perform a statistical study of 80 previously published near X-line events identified at the dayside magnetopause in Magnetospheric Multiscale data. We find 44 events that clearly present all commonly accepted EDR signatures and use this database to investigate energy flux partition and energy conversion. We find that energy partition is changed inside EDRs, with a 71%–29% allocation of particle energy flux density between electrons and ions respectively. The electron enthalpy flux density is found to dominate locally at all EDRs and is predominantly oriented in the out-of-plane direction, perpendicular to the reconnecting magnetic field. We also examine the transition from electron- to ion-dominated energy flux partition further from the EDR, finding this typically occurs at scales of the order of the ion inertial length, larger than the typical EDR size. We then investigate energy conversion and transport and highlight complex processes, with potential non-steady-state energy accumulation and release near the EDR. We discuss the implications of our results for reconnection energy conversion, and for magnetopause dynamics in general.

  • Journal article
    Quaas J, Andrews T, Bellouin N, Block K, Boucher O, Ceppi P, Dagan G, Doktorowski S, Eichholz HM, Forster P, Goren T, Gryspeerdt E, Hodnebrog Ø, Jia H, Kramer R, Lange C, Maycock AC, Mülmenstädt J, Myhre G, OConnor FM, Pincus R, Samset BH, Senf F, Shine KP, Smith C, Stjern CW, Takemura T, Toll V, Wall CJet al., 2024,

    Adjustments to Climate Perturbations—Mechanisms, Implications, Observational Constraints

    , AGU Advances, Vol: 5, ISSN: 2576-604X

    <jats:title>Abstract</jats:title><jats:p>Since the 5th Assessment Report of the Intergovernmental Panel on Climate Change (AR5) an extended concept of the energetic analysis of climate change including forcings, feedbacks and adjustment processes has become widely adopted. Adjustments are defined as processes that occur in response to the introduction of a climate forcing agent, but that are independent of global‐mean surface temperature changes. Most considered are the adjustments that impact the Earth energy budget and strengthen or weaken the instantaneous radiative forcing due to the forcing agent. Some adjustment mechanisms also impact other aspects of climate not related to the Earth radiation budget. Since AR5 and a following description by Sherwood et al. (2015, <jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://doi.org/10.1175/bams-d-13-00167.1">https://doi.org/10.1175/bams‐d‐13‐00167.1</jats:ext-link>), much research on adjustments has been performed and is reviewed here. We classify the adjustment mechanisms into six main categories, and discuss methods of quantifying these adjustments in terms of their potentials, shortcomings and practicality. We furthermore describe aspects of adjustments that act beyond the energetic framework, and we propose new ideas to observe adjustments or to make use of observations to constrain their representation in models. Altogether, the problem of adjustments is now on a robust scientific footing, and better quantification and observational constraint is possible. This allows for improvements in understanding and quantifying climate change.</jats:p>

  • Journal article
    Murray-Watson R, Gryspeerdt E, 2024,

    Air mass history linked to the development of Arctic mixed-phase clouds

    , Atmospheric Chemistry and Physics, Vol: 24, Pages: 11115-11132, ISSN: 1680-7316

    Clouds formed during marine cold-air outbreaks (MCAOs) exhibit a distinct transition from stratocumulus decks near the ice edge to broken cumuliform fields further downwind. The mechanisms associated with ice formation are believed to be crucial in driving this transition, yet the factors influencing such formation remain unclear. Through Lagrangian trajectories collocated with satellite data, this study investigates the development of mixed-phase clouds using these outbreaks. Cloud formed in MCAOs are characterized by a swift shift from liquid to ice-containing states, contrasting with non-MCAO clouds also moving off the ice edge. These mixed-phase clouds are predominantly observed at temperatures below −20 °C near the ice edge. However, further into the outbreak, they become dominant at temperatures as high as −13 °C. This shift is consistent with the influence of biological ice-nucleating particles (INPs), which become more prevalent as the air mass ages over the ocean. The evolution of these clouds is closely linked to the history of the air mass, especially the length of time it spends over snow- and ice-covered surfaces – terrains may that be deficient in INPs. This connection also accounts for the observed seasonal variations in the development of Arctic clouds, both within and outside of MCAO events. The findings highlight the importance of understanding both local marine aerosol sources near the ice edge and the overarching INP distribution in the Arctic for modelling of cloud phase in the region.

  • Journal article
    Masters A,

    Solar wind power likely governs Uranus’ thermosphere temperature

    , Geophysical Research Letters, ISSN: 0094-8276
  • Journal article
    Trencham NE, Czaja A, Haigh JD, 2024,

    The Impact of Oceanic Feedbacks on Stratosphere-Troposphere Coupling in an Idealized Model

    , Journal of Geophysical Research: Atmospheres, Vol: 129, ISSN: 2169-897X

    Stratospheric temperature perturbations (STPs) caused by for example, variations in stratospheric ozone, are an important driver of changes in tropospheric dynamics, particularly pertinent to the long-term climatic evolution of the Southern Hemisphere. However, the impact of ocean feedbacks on this interaction has not been fully examined. To study it, positive STPs were applied in three otherwise identical, idealized model configurations –atmosphere-only (A), atmosphere + slab-ocean (AS), and fully-coupled atmosphere-ocean (AO)–and the resulting atmospheric changes compared. In the AO model, changes in the tropics (extratropics) experienced a poleward-expansion (shift) and positive (negative) feedback after ∼100–200 years, whilst the AS model showed atmospheric and sea surface temperature changes that did not resemble those seen in the AO model. In the AO model, changes in tropical ocean heat content were responsible for the atmospheric changes, attributable to changes in the Ekman transport. These results indicate that full atmosphere-ocean coupling should be accounted for when studying the long-term (100+ years) tropospheric response to STPs in the Southern Hemisphere. Validation with higher-resolution and more realistic models is necessary.

  • Journal article
    Grimmich N, Plaschke F, Grison B, Prencipe F, Escoubet CP, Archer MO, Constantinescu OD, Haaland S, Nakamura R, Sibeck DG, Darrouzet F, Hayosh M, Maggiolo Ret al., 2024,

    The Cluster spacecrafts' view of the motion of the high-latitude magnetopause

    , Annales Geophysicae: atmospheres, hydrospheres and space sciences, Vol: 42, Pages: 371-394, ISSN: 0992-7689

    The magnetopause is the boundary between the interplanetary magnetic field and the terrestrial magnetic field. It is influenced by different solar-wind conditions, which lead to a change in the shape and location of the magnetopause. The interaction between the solar wind and the magnetosphere can be studied from in situ spacecraft observations. Many studies focus on the equatorial plane as this is where recent spacecraft constellations such as THEMIS or MMS operate. However, to fully capture the interaction, it is important to study the high-latitude regions as well. Since the Cluster spacecraft operate in a highly elliptical polar orbit, the spacecraft often pass through the magnetopause at high latitudes. This allows us to collect a dataset of high-latitude magnetopause crossings and to study magnetopause motion in this region, as well as deviations from established magnetopause models. We use multi-spacecraft analysis tools to investigate the direction of the magnetopause motion in the high latitudes and to compare the occurrence of crossings at different locations with the result in the equatorial plane. We find that the high-latitude magnetopause motion is generally consistent with previously reported values and seems to be more often associated with a closed magnetopause boundary. We show that, on average, the magnetopause moves faster inwards than outwards. Furthermore, the occurrence of magnetopause positions beyond those predicted by the Shue et al. (1998) model at high latitudes is found to be caused by the solar-wind parameters that are similar to those in the equatorial plane. Finally, we highlight the importance of the dipole tilt angle at high latitudes. Our results may be useful for the interpretation of plasma measurements from the upcoming SMILE mission (Branduardi-Raymont et al., 2018) as this spacecraft will also fly frequently through the high-latitude magnetopause.

  • Journal article
    Bowen TA, Vasko IY, Bale SD, Chandran BDG, Chasapis A, Dudok de Wit T, Mallet A, McManus M, Meyrand R, Pulupa M, Squire Jet al., 2024,

    Extended Cyclotron Resonant Heating of the Turbulent Solar Wind

    , Astrophysical Journal Letters, Vol: 972, ISSN: 2041-8205

    Circularly polarized, nearly parallel propagating waves are prevalent in the solar wind at ion-kinetic scales. At these scales, the spectrum of turbulent fluctuations in the solar wind steepens, often called the transition range, before flattening at sub-ion scales. Circularly polarized waves have been proposed as a mechanism to couple electromagnetic fluctuations to ion gyromotion, enabling ion-scale dissipation that results in observed ion-scale steepening. Here we study Parker Solar Probe observations of an extended stream of fast solar wind ranging from ∼15 to 55 R ⊙. We demonstrate that, throughout the stream, transition range steepening at ion scales is associated with the presence of significant left-handed ion-kinetic-scale waves, which are thought to be ion cyclotron waves. We implement quasilinear theory to compute the rate at which ions are heated via cyclotron resonance with the observed circularly polarized waves given the empirically measured proton velocity distribution functions. We apply the Von Kármán decay law to estimate the turbulent decay of the large-scale fluctuations, which is equal to the turbulent energy cascade rate. We find that the ion cyclotron heating rates are correlated with, and amount to a significant fraction of, the turbulent energy cascade rate, implying that cyclotron heating is an important dissipation mechanism in the solar wind.

  • Journal article
    Ervin T, Bale SD, Badman ST, Bowen TA, Riley P, Paulson K, Rivera YJ, Romeo O, Sioulas N, Larson D, Verniero JL, Dewey RM, Huang Jet al., 2024,

    Near Subsonic Solar Wind Outflow from an Active Region

    , Astrophysical Journal, Vol: 972, ISSN: 0004-637X

    During Parker Solar Probe (Parker) Encounter 15 (E15), we observe an 18 hr period of near-subsonic (M S ∼ 1) and sub-Alfvénic (SA), M A ⋘ 1, slow-speed solar wind from 22 to 15.6 R ⊙. As the most extreme SA interval measured to date and skirting the solar wind sonic point, it is the deepest Parker has probed into the formation and acceleration region of the solar wind in the corona. The stream is also measured by Wind and the Magnetosonic Multiscale mission near 1 au at times consistent with ballistic propagation of this slow stream. We investigate the stream source, properties, and potential coronal heating consequences via combining these observations with coronal modeling and turbulence analysis. Through source mapping, in situ evidence, and multipoint arrival time considerations of a candidate coronal mass ejection, we determine the stream is a steady (nontransient), long-lived, and approximately Parker spiral aligned and arises from overexpanded field lines mapping back to an active region. Turbulence analysis of the Elsässer variables shows the inertial range scaling of the z + mode (f ∼ −3/2) to be dominated by the slab component. We discuss the spectral flattening and difficulties associated with measuring the z − spectra, cautioning against making definitive conclusions from the z − mode. Despite being more extreme than prior SA intervals, its turbulent nature does not appear to be qualitatively different from previously observed streams. We conclude that this extreme low-dynamic-pressure solar wind interval (which has the potential for extreme space-weather conditions) is a large, steady structure spanning at least to 1 au.

  • Journal article
    Huang Z, Shi C, Velli M, Sioulas N, Panasenco O, Bowen T, Matteini L, Xia M, Shi X, Huang S, Huang J, Casillas Let al., 2024,

    Solar Wind Structures from the Gaussianity of Magnetic Magnitude

    , Astrophysical Journal Letters, Vol: 973, ISSN: 2041-8205

    The heliosphere is permeated with highly structured solar wind originating from the Sun. One of the primary science objectives of Parker Solar Probe (PSP) is to determine the structures and dynamics of the plasma and magnetic fields at the sources of the solar wind. However, establishing the connection between in situ measurements and structures and dynamics in the solar atmosphere is challenging: most of the magnetic footpoint mapping techniques have significant uncertainties in the source localization of a plasma parcel observed in situ, and the PSP plasma measurements suffer from a limited field of view. Therefore, it lacks a universal tool to self-contextualize the in situ measurements. Here we develop a novel time series visualization method named Gaussianity Scalogram. Utilizing this method, by analyzing the magnetic magnitude data from both PSP and Ulysses, we successfully identify in situ structures that are possible remnants of solar atmospheric and magnetic structures spanning more than 7 orders of magnitude, from years to seconds, including polar and midlatitude coronal holes, as well as structures compatible with supergranulation, “jetlets” and “picoflares.” Furthermore, computer simulations of Alfvénic turbulence successfully reproduce the Gaussianization of magnetic magnitude, supporting the observed distribution. Building upon these discoveries, the Gaussianity Scalogram can help future studies to reveal the fractal-like fine structures in the solar wind time series from both PSP and a decades-old data archive.

  • Journal article
    Pal S, Luiz LF, Weiss AJ, Narock T, Narock A, Nieves-Chinchilla T, Jian LK, Good SWet al., 2024,

    Automatic Detection of Large-scale Flux Ropes and Their Geoeffectiveness with a Machine-learning Approach

    , Astrophysical Journal, Vol: 972, ISSN: 0004-637X

    Detecting large-scale flux ropes (FRs) embedded in interplanetary coronal mass ejections (ICMEs) and assessing their geoeffectiveness are essential, since they can drive severe space weather. At 1 au, these FRs have an average duration of 1 day. Their most common magnetic features are large, smoothly rotating magnetic fields. Their manual detection has become a relatively common practice over decades, although visual detection can be time-consuming and subject to observer bias. Our study proposes a pipeline that utilizes two supervised binary classification machine-learning models trained with solar wind magnetic properties to automatically detect large-scale FRs and additionally determine their geoeffectiveness. The first model is used to generate a list of autodetected FRs. Using the properties of the southward magnetic field, the second model determines the geoeffectiveness of FRs. Our method identifies 88.6% and 80% of large-scale ICMEs (duration ≥ 1 day) observed at 1 au by the Wind and the Solar TErrestrial RElations Observatory missions, respectively. While testing with continuous solar wind data obtained from Wind, our pipeline detected 56 of the 64 large-scale ICMEs during the 2008-2014 period (recall = 0.875), but also many false positives (precision = 0.56), as we do not take into account any additional solar wind properties other than the magnetic properties. We find an accuracy of 0.88 when estimating the geoeffectiveness of the autodetected FRs using our method. Thus, in space-weather nowcasting and forecasting at L1 or any planetary missions, our pipeline can be utilized to offer a first-order detection of large-scale FRs and their geoeffectiveness.

  • Journal article
    Russell J, Bantges R, Brindley H, Bodas-Salcedo Aet al., 2024,

    The GERB Obs4MIPs: a dataset for evaluating diurnal and monthly variation in top of atmosphere radiative fluxes in climate models

    , Earth System Science Data, Vol: 16, Pages: 4243-4266, ISSN: 1866-3508

    A newly available radiative flux dataset specifically designed to enable the evaluation of the diurnal cycle in top-of-atmosphere (TOA) fluxes as captured by climate and Earth system models is presented. Observations over the period 2007–2012 made by the Geostationary Earth Radiation Budget (GERB) instrument are used to derive monthly hourly mean outgoing longwave radiation (OLR) and reflected shortwave (RSW) fluxes on a regular 1° latitude–longitude grid covering approximately 60° N–60° S and 60° E–60° W. The impact of missing data is evaluated in detail, and a data-filling solution is implemented using estimates of broadband fluxes from the Spinning Enhanced Visible and Infrared Imager flying on the same Meteosat platform, scaled to the GERB observations. This relatively simple approach is shown to deliver an approximate improvement by a factor of 10 in both the bias caused by missing data and the associated variability in the error. To demonstrate the utility of this V1.1 filled GERB Observations for Climate Model Intercomparison Projects (Obs4MIPs) dataset, comparisons are made to radiative fluxes from two climate configurations of the Hadley Centre's Global Environmental Model: HadGEM3-GC3.1 and HadGEM3-GC5.0. Focusing on marine stratocumulus and deep convective cloud regimes, diurnally resolved comparisons between the models and observations highlight discrepancies between the model configurations in terms of their ability to capture the diurnal amplitude and the phase in TOA fluxes, details that cannot be diagnosed by comparisons at lower temporal resolutions. For these cloud regimes the GC5.0 configuration shows improved fidelity to the observations relative to GC3.1, although notable differences remain. The V1.1 filled GERB Obs4MIPs monthly hourly TOA fluxes are available from the Centre for Environmental Data Analysis, with the OLR fluxes accessible at https://doi.org/10.5285/90148d9b1

  • Journal article
    Rivera YJ, Badman ST, Stevens ML, Verniero JL, Stawarz JE, Shi C, Raines JM, Paulson KW, Owen CJ, Niembro T, Louarn P, Livi SA, Lepri ST, Kasper JC, Horbury TS, Halekas JS, Dewey RM, De Marco R, Bale SDet al., 2024,

    In situ observations of large-amplitude Alfvén waves heating and accelerating the solar wind.

    , Science, Vol: 385, Pages: 962-966

    After leaving the Sun's corona, the solar wind continues to accelerate and cools, but more slowly than expected for a freely expanding adiabatic gas. Alfvén waves are perturbations of the interplanetary magnetic field that transport energy. We use in situ measurements from the Parker Solar Probe and Solar Orbiter spacecraft to investigate a stream of solar wind as it traverses the inner heliosphere. The observations show heating and acceleration of the plasma between the outer edge of the corona and near the orbit of Venus, along with the presence of large-amplitude Alfvén waves. We calculate that the damping and mechanical work performed by the Alfvén waves are sufficient to power the heating and acceleration of the fast solar wind in the inner heliosphere.

  • Journal article
    Kelly H, Archer M, Ma X, Nykyri K, Eastwood J, Southwood Det al., 2024,

    Identification of Kelvin-Helmholtz generated vortices in magnetised fluids

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

    The Kelvin-Helmholtz Instability (KHI), arising from velocity shear across the magnetopause, plays a significant role in the viscous-like transfer of mass, momentum, and energy from the shocked solar wind into the magnetosphere. While the KHI leads to growth of surface waves and vortices, suitable detection methods for these applicable to magnetohydrodynamics (MHD) are currently lacking. A novel method is derived based on the well-established λ-family of hydrodynamic vortex identification techniques, which define a vortex as a local minimum in an adapted pressure field. The J × B Lorentz force is incorporated into this method by using an effective total pressure in MHD, including both magnetic pressure and a pressure-like part of the magnetic tension derived from a Helmholtz decomposition. The λMHD method is shown to comprise of four physical effects: vortical momentum, density gradients, fluid compressibility, and the rotational part of the magnetic tension. A local three-dimensional MHD simulation representative of near-flank magnetopause conditions (plasma β’s 0.5–5 and convective Mach numbers Mf ∼ 0.4) under northward interplanetary magnetic field (IMF) is used to validate λMHD. Analysis shows it correlates well with hydrodynamic vortex definitions, though the level of correlation decreases with vortex evolution. Overall, vortical momentum dominates λMHD at all times. During the linear growth phase, density gradients act to oppose vortex formation. By the highly nonlinear stage, the formation of small-scale structures leads to a rising importance of the magnetic tension. Compressibility was found to be insignificant throughout. Finally, a demonstration of this method adapted to tetrahedral spacecraft observations is performed.

  • Journal article
    Warwick L, Murray JE, Brindley H, 2024,

    The Far-INfrarEd Spectrometer for Surface Emissivity (FINESSE) – Part 2: First measurements of the emissivity of water in the far-infrared

    , Atmospheric Measurement Techniques, Vol: 17, Pages: 4777-4787

    <jats:p>Abstract. In this paper, we describe a method for retrieving the surface emissivity of specular surfaces across the wavenumber range of 400–1600 cm−1 using novel radiance measurements of the Far-INfrarEd Spectrometer for Surface Emissivity (FINESSE) instrument. FINESSE is described in detail in Part 1 (Murray et al., 2024) 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 simultaneous retrievals of the surface temperature and emissivity of water that extend into the far-infrared and demonstrate a method that can be used and further developed for the in situ retrieval of the emissivity of other surfaces in the field. </jats:p>

  • Journal article
    Gettelman A, Christensen MW, Diamond MS, Gryspeerdt E, Manshausen P, Stier P, WatsonParris D, Yang M, Yoshioka M, Yuan Tet al., 2024,

    Has reducing ship emissions brought forward global warming?

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

    Ships brighten low marine clouds from emissions of sulfur and aerosols, resulting in visible “ship tracks”. In 2020, new shipping regulations mandated an ∼80% reduction in the allowed fuel sulfur content. Recent observations indicate that visible ship tracks have decreased. Model simulations indicate that since 2020 shipping regulations have induced a net radiative forcing of +0.12 Wm−2. Analysis of recent temperature anomalies indicates Northern Hemisphere surface temperature anomalies in 2022–2023 are correlated with observed cloud radiative forcing and the cloud radiative forcing is spatially correlated with the simulated radiative forcing from the 2020 shipping emission changes. Shipping emissions changes could be accelerating global warming. To better constrain these estimates, better access to ship position data and understanding of ship aerosol emissions are needed. Understanding the risks and benefits of emissions reductions and the difficultly in robust attribution highlights the large uncertainty in attributing proposed deliberate climate intervention.

  • 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

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

    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.

  • 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.

  • 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.

  • 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.

  • 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.

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