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Journal articleEllmeier M, Betzler A, Amtmann C, et al., 2024,
Lower magnetic field measurement limit of the coupled dark state magnetometer
, Measurement Science and Technology, Vol: 35, ISSN: 0957-0233The 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.
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Journal articleZeng Z, Yao Z, Liu J, et al., 2024,
Ultralow-frequency Waves in Jupiter’s Magnetopause Boundary Layer
, The Astrophysical Journal, Vol: 976, Pages: 92-92, ISSN: 0004-637X<jats:title>Abstract</jats:title> <jats:p>Ultralow-frequency (ULF) waves (∼tens of minutes period) are widely identified in the Jovian system and are believed to be associated with energy dissipation in the magnetosphere and ionosphere. Due to the magnetodisk oscillation related to planetary rotation, it is challenging to identify the periodicities inside the magnetosphere, although remote sensing observations of the polar emissions provide clear evidence of the tens of minutes pulsations. In this study, we take advantage of Juno’s in situ measurements in the magnetopause boundary layer for a long duration, i.e., >4 hr, to directly assess the tens of minutes periodicities of the boundary dynamics caused by the interactions between the internal plasma and external solar wind. Through periodogram analysis on the magnetic field and particle data, we find ULF waves with periodicities of ∼18 minutes, ∼40 minutes, and ∼70–80 minutes, which is generally consistent with pulsations in multiple remote sensing observations. A multiple-harmonic ULF phenomenon was also identified in the observations. The periodicities from in situ measurements provide crucial clues in understanding the origin of pulsating wave/auroral emissions in the Jovian system. The results could also further our understanding of energy transfer and release between the internal plasma of Jupiter and external solar wind.</jats:p>
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Journal articleBessho N, Chen L-J, Hesse M, et al., 2024,
Electron Acceleration in Magnetic Islands in Quasi-parallel Shocks
, The Astrophysical Journal, Vol: 975, Pages: 93-93, ISSN: 0004-637X<jats:title>Abstract</jats:title> <jats:p>We report new theories and simulations for electron acceleration in magnetic islands generated by magnetic reconnection in the shock turbulence in a quasi-parallel shock, using a 2 and 1/2 dimensional particle-in-cell simulation. When an island is moving, unmagnetized electrons are accelerated by the Hall electric field pointing toward the island center. In a stationary island, some electrons are energized by “island betatron acceleration” due to the induction electric field when the island core magnetic field changes with time. In the simulation, almost all of the high-energy electrons in the shock transition region that show a power-law distribution are accelerated in ion-skin-depth-scale magnetic flux ropes, and about half of them are accelerated by the Hall electric field and island betatron acceleration. These mechanisms can produce a power-law electron distribution, and also inject electrons into the diffusive shock acceleration. The mechanisms are applicable to quasi-parallel shocks with high Alfvén Mach numbers (<jats:italic>M</jats:italic> <jats:sub>A</jats:sub> > 10), including planetary bow shocks and shocks in astrophysical objects such as supernova remnants.</jats:p>
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Journal articleBlyth L, Graven H, Manning AJ, et al., 2024,
Radiocarbon as a tracer of the fossil fraction of regional carbon monoxide emissions
, Environmental Research Letters, Vol: 19Carbon 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 (14C) in CO could potentially be used to investigate the sources of CO on a regional scale because fossil sources lack 14C and reduce the 14C/C ratio (Δ14C) of atmospheric CO more than biogenic sources. We use regional Lagrangian model simulations to investigate the utility of Δ14CO 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 Δ14CO in atmospheric CO from cosmogenic production, both fossil and biogenic CO emissions cause large reductions in Δ14CO regionally, with larger reductions for fossil than biogenic CO per ppb added. There is a strong seasonal variation in Δ14CO in background air and in the sensitivity of Δ14CO 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 Δ14C 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 Δ14CO measurements could be an effective tool to understand regional CO sources and assess bottom-up emissions estimates.
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Journal articleKaweeyanun N, Masters A, 2024,
Three-dimensional modelling of Ganymede’s Chapman–Ferraro magnetic field and its role in subsurface ocean induction
, Icarus, ISSN: 0019-1035In April 2023, the JUpiter ICy moon Explorer (JUICE) began its journey to orbit Jupiter’s largestand only magnetic moon, Ganymede. Part of the mission’s objectives aim to verify existence ofthe moon’s subsurface ocean and determine its structure through its induced response to externalexcitation by periodically varying magnetic field. Known contributions to the excitation are thosefrom Jupiter’s dipole (at synodic period) and quadrupole (at half-synodic period) variations,and Ganymede’s inclined eccentric orbit around Jupiter (at orbital period). We propose thatGanymede’s magnetopause, where the Chapman-Ferraro (C-F) magnetic field arises from localcurrents, also contributes to subsurface ocean induction. This article introduces the first three-dimensional model of the C-F field and its outputs at Ganymede’s subsurface ocean and largermagnetosphere. The field is shown to be non-uniform - strongest near upstream Ganymede’s subflow region and gradually weakening away from it. Magnetopause asymmetry due to the Jovianguide field results in largely synodic variation of the C-F field, with exceptions near Ganymede’sequator and subflow meridian where asymmetry effects are minimal and the variations are half-synodic. The C-F field amplitude is of general order 50 nT, which is significant relativeto excitation from the Jovian field. Comparisons to Galileo data and magnetohydrodynamicsimulation results suggest the model is useful, therefore the magnetopause effects must beconsidered in future induction modelling of Ganymede’s subsurface ocean ahead of the JUICEmission.
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Journal articleChakravorty S, Czaja A, Parfitt R, et al., 2024,
Tropospheric Response to Gulf Stream Intrinsic Variability: A Model Ensemble Approach
, Geophysical Research Letters, Vol: 51, ISSN: 0094-8276The Gulf Stream's (GS) impact on the marine boundary layer (MBL) is well established, yet the mechanisms and timescales through which it affects the upper-troposphere and contributes to precipitation are debatable. Using a high-resolution regional atmospheric model, we shed light on the impact of ocean intrinsic variability (OIV) along GS on midlatitude-atmosphere. Taking advantage of a 24-member ensemble of ocean model integrations, we devised a novel experimental setup where the same weather system feels different realizations of GS sea surface temperature (SST). We introduce the “Eddy Recharge-Frontal Lift” (ERFL) mechanism, highlighting the joint importance of synoptic variability and boundary layer processes. ERFL mechanism proposes that OIV recharges/discharges MBL with moisture and heat, while convergence associated with passing atmospheric-fronts uplifts these MBL-trapped anomalies to upper-troposphere and imprints on precipitation in surprisingly short periods (a month). The impact of OIV on precipitation depends on the background mean SST.
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Journal articleCeppi P, Myers TA, Nowack P, et al., 2024,
Implications of a Pervasive Climate Model Bias for Low-Cloud Feedback
, Geophysical Research Letters, Vol: 51, ISSN: 0094-8276How 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 (Formula presented.) (Formula presented.), 90% range 0.18–0.72 W (Formula presented.) (Formula presented.)), about twice the mean value (0.22 W (Formula presented.) (Formula presented.)) 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.
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Journal articleTannous SM, Bonnell JW, Pulupa M, et al., 2024,
Electron Temperatures in the Venusian Ionosphere From Parker Solar Probe Using Quasi-Thermal Noise Spectroscopy
, Geophysical Research Letters, Vol: 51, ISSN: 0094-8276Parker Solar Probe (PSP) uses Venus gravity assists (VGA) to achieve the closest orbits to the Sun by a spacecraft. During the third (VGA3) and fourth (VGA4) Venus gravity assists, the PSP entered the Venusian ionosphere. The core electrons could not be detected as they were below the SWEAP/SPAN electrostatic analyzer instrument energy threshold. However, there is another way to estimate the core temperature using quasi-thermal noise (QTN) data measured by the PSP/FIELDS Radio Frequency Spectrometer instrument. QTN spectroscopy offers an effective tool for measuring electron temperature and density when the electrons are too cold for other instruments to measure, as is the case with VGA3 and VGA4. Low-frequency plasma wave data from the closest approach during VGA3 and VGA4 was analyzed with the QTN spectroscopy technique to determine the density and first-ever in-situ thermal electron temperature of the Venusian ionosphere at solar minimum.
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Journal articleAuestad H, Spensberger C, Marcheggiani A, et al., 2024,
Spatio-temporal averaging of jets obscures the reinforcement of baroclinicity by latent heating
, Weather and Climate Dynamics, Vol: 5, Pages: 1269-1286Latent 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.
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Journal articleMozer FS, Agapitov O, Bale SD, et al., 2024,
Origin of the type III radiation observed near the Sun
, Astronomy and Astrophysics, Vol: 690, ISSN: 0004-6361Aims. We investigate processes associated with the generation of type III radiation using Parker Solar Probe measurements. Methods. We measured the amplitudes and phase velocities of electric and magnetic fields and their associated plasma density fluctuations. Results. 1. There are slow electrostatic waves near the Langmuir frequency and at as many as six harmonics, the number of which increases with the amplitude of the Langmuir wave. Their electrostatic nature is shown by measurements of the plasma density fluctuations. From these density fluctuations and the electric field magnitude, the k-value of the Langmuir wave is estimated to be 0.14 and kλd = 0.4. Even with the large uncertainty in this quantity (more than a factor of two), the phase velocity of the Langmuir wave was < 10 000 km/s. 2. The electromagnetic wave near the Langmuir frequency has a phase velocity lower than 50 000 km/s. 3. We cannot determine whether there are electromagnetic waves at the harmonics of the Langmuir frequency. If they existed, their magnetic field components would be below the noise level of the measurement. 4. The rapid (less than one millisecond) amplitude variations typical of the Langmuir wave and its harmonics are artifacts resulting from the addition of two waves, one of which has small frequency variations that arise because the wave travels through density irregularities. None of these results are expected in or consistent with the conventional model of the three-wave interaction of two counter-streaming Langmuir waves that coalesce to produce the type III wave. They are consistent with a new model in which electrostatic antenna waves are produced at the harmonics by radiation of the Langmuir wave, after which at least the first harmonic wave evolved through density irregularities such that its wave number decreased and it became the type III radiation.
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Journal articleRivera YJ, Badman ST, Stevens ML, et al., 2024,
Mixed Source Region Signatures inside Magnetic Switchback Patches Inferred by Heavy Ion Diagnostics
, Astrophysical Journal, Vol: 974, ISSN: 0004-637XSince Parker Solar Probe’s (Parker’s) first perihelion pass at the Sun, large-amplitude Alfvén waves grouped in patches have been observed near the Sun throughout the mission. Several formation processes for these magnetic switchback patches have been suggested with no definitive consensus. To provide insight into their formation, we examine the heavy ion properties of several adjacent magnetic switchback patches around Parker’s 11th perihelion pass, capitalizing on a spacecraft lineup with Solar Orbiter where each samples the same solar wind streams over a large range of longitudes. Heavy ion properties (Fe/O, C6+/C5+, O7+/O6+) related to the wind’s coronal origin, measured with Solar Orbiter, can be linked to switchback patch structures identified near the Sun with Parker. We find that switchback patches do not contain distinctive ion and elemental compositional signatures different from the surrounding nonswitchback solar wind. Both the patches and ambient wind exhibit a range of fast and slow wind qualities, indicating coronal sources with open and closed field lines in close proximity. These observations and modeling indicate switchback patches form in coronal hole boundary wind and with a range of source region magnetic and thermal properties. Furthermore, the heavy ion signatures suggest interchange reconnection and/or shear-driven processes may play a role in their creation.
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Journal articleTippett A, Gryspeerdt E, Manshausen P, et al.,
Weak liquid water path response in ship tracks
, Atmospheric Chemistry and Physics, ISSN: 1680-7316 -
Journal articleCuesta ME, Cummings AT, Livadiotis G, et al., 2024,
Observations of Kappa Distributions in Solar Energetic Protons and Derived Thermodynamic Properties
, Astrophysical Journal, Vol: 973, ISSN: 0004-637XIn 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.
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Journal articleQuaas J, Andrews T, Bellouin N, et al., 2024,
Adjustments to climate perturbations—mechanisms, implications, observational constraints
, AGU Advances, Vol: 5, ISSN: 2576-604XSince 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, https://doi.org/10.1175/bams-d-13-00167.1), 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.
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Journal articleFargette N, Eastwood JP, Waters CL, et 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: 2169-9380The 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.
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Journal articleMurray-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: 1680-7316Clouds 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.
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Journal articleWaters C, Eastwood J, Fargette N, et al., 2024,
Classifying magnetic reconnection regions using k-means clustering: applications to energy partition
, JGR: Space Physics, Vol: 129, ISSN: 2169-9402Magnetic 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.
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Journal articleMasters A,
Solar wind power likely governs Uranus’ thermosphere temperature
, Geophysical Research Letters, ISSN: 0094-8276 -
Journal articleTrencham 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: 2169-897XStratospheric 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.
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Journal articleGrimmich N, Plaschke F, Grison B, et 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: 0992-7689The 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.
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Journal articlePal S, Luiz LF, Weiss AJ, et al., 2024,
Automatic Detection of Large-scale Flux Ropes and Their Geoeffectiveness with a Machine-learning Approach
, Astrophysical Journal, Vol: 972, ISSN: 0004-637XDetecting 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.
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Journal articleDavies EE, Rüdisser HT, Amerstorfer UV, et al., 2024,
Flux Rope Modeling of the 2022 September 5 Coronal Mass Ejection Observed by Parker Solar Probe and Solar Orbiter from 0.07 to 0.69 au
, Astrophysical Journal, Vol: 973, ISSN: 0004-637XAs both Parker Solar Probe (PSP) and Solar Orbiter (SolO) reach heliocentric distances closer to the Sun, they present an exciting opportunity to study the structure of coronal mass ejections (CMEs) in the inner heliosphere. We present an analysis of the global flux rope structure of the 2022 September 5 CME event that impacted PSP at a heliocentric distance of only 0.07 au and SolO at 0.69 au. We compare in situ measurements at PSP and SolO to determine global and local expansion measures, finding a good agreement between magnetic field relationships with heliocentric distance, but significant differences with respect to flux rope size. We use PSP/Wide-Field Imager for Solar Probe images as input to the ELlipse Evolution model based on Heliospheric Imager data (or ELEvoHI), providing a direct link between remote and in situ observations; we find a large discrepancy between the resulting modeled arrival times, suggesting that the underlying model assumptions may not be suitable when using data obtained close to the Sun, where the drag regime is markedly different in comparison to larger heliocentric distances. Finally, we fit the SolO's magnetometer and PSP's FIELDS data independently with the 3D Coronal ROpe Ejection (or 3DCORE) model, and find that many parameters are consistent between spacecraft. However, challenges are apparent when reconstructing a global 3D structure that aligns with arrival times at PSP and SolO, likely due to the large radial and longitudinal separations between spacecraft. From our model results, it is clear the solar wind background speed and drag regime strongly affect the modeled expansion and propagation of CMEs and need to be taken into consideration.
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Journal articleErvin T, Bale SD, Badman ST, et al., 2024,
Near Subsonic Solar Wind Outflow from an Active Region
, Astrophysical Journal, Vol: 972, ISSN: 0004-637XDuring 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.
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Journal articleHuang Z, Shi C, Velli M, et al., 2024,
Solar Wind Structures from the Gaussianity of Magnetic Magnitude
, Astrophysical Journal Letters, Vol: 973, ISSN: 2041-8205The 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.
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Journal articleBowen TA, Vasko IY, Bale SD, et al., 2024,
Extended Cyclotron Resonant Heating of the Turbulent Solar Wind
, Astrophysical Journal Letters, Vol: 972, ISSN: 2041-8205Circularly 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.
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Journal articleRussell J, Bantges R, Brindley H, et 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: 1866-3508A 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
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Journal articleRivera YJ, Badman ST, Stevens ML, et al., 2024,
In situ observations of large-amplitude Alfvén waves heating and accelerating the solar wind.
, Science, Vol: 385, Pages: 962-966After 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.
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Journal articleKelly H, Archer M, Ma X, et al., 2024,
Identification of Kelvin-Helmholtz generated vortices in magnetised fluids
, Frontiers in Astronomy and Space Sciences, Vol: 11, ISSN: 2296-987XThe 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.
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Journal articleWarwick 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>
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Journal articleGettelman A, Christensen MW, Diamond MS, et al., 2024,
Has reducing ship emissions brought forward global warming?
, Geophysical Research Letters, Vol: 51, ISSN: 0094-8276Ships 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.
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