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Journal articleShebanits O, Wahlund J-E, Waite JH, et al., 2021,
Conductivities of Titan's dusty ionosphere
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Journal articleVuorinen L, Hietala H, Plaschke F, et al., 2021,
Magnetic field in magnetosheath jets: a statistical study of B-Z near the magnetopause
, Journal of Geophysical Research: Space Physics, Vol: 126, ISSN: 2169-9380Magnetosheath jets travel from the bow shock toward the magnetopause, and some of them eventually impact it. Jet impacts have recently been linked to triggering magnetopause reconnection in case studies by Hietala et al. (2018, https://doi.org/10.1002/2017gl076525) and Nykyri et al. (2019, https://doi.org/10.1029/2018ja026357). In this study, we focus on the enhancing or suppressing effect jets could have on reconnection by locally altering the magnetic shear via their own magnetic fields. Using observations from the years 2008–2011 made by the Time History of Events and Macroscale Interactions during Substorms spacecraft and solar wind OMNI data, we statistically study for the first time urn:x-wiley:21699380:media:jgra56695:jgra56695-math-0002 within jets in the Geocentric Solar Magnetospheric coordinates. We find that urn:x-wiley:21699380:media:jgra56695:jgra56695-math-0003 opposite to the prevailing interplanetary magnetic field (IMF) urn:x-wiley:21699380:media:jgra56695:jgra56695-math-0004 is roughly as common in jets as in the non-jet magnetosheath near the magnetopause, but these observations are distributed differently. 60–70% of jet intervals contain bursts of opposite polarity urn:x-wiley:21699380:media:jgra56695:jgra56695-math-0005 in comparison to around 40urn:x-wiley:21699380:media:jgra56695:jgra56695-math-0006 of similar non-jet intervals. The median duration of such a burst in jets is 10 s and strength is urn:x-wiley:21699380:media:jgra56695:jgra56695-math-0007nT. We also investigate the prevalence of the type of strong urn:x-wiley:21699380:media:jgra56695:jgra56695-math-0008nT pulses that Nykyri et al. (2019, https://doi.org/10.1029/2018ja026357) linked to a substorm onset. In our data set, such pulses were observed in around 13% of jets. Our statistical results indicate that jets may have the potential to affect local magnetopause reconnection via their magnetic fields. Future studies are needed to determine whether such effects can be ob
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Journal articlePalchetti L, Brindley H, Bantges R, et al., 2021,
Completing the Picture: The FORUM Mission: Unique Satellite Data to Fully Reveal How Earth Radiates Energy to Space
, Bulletin of the American Meteorological Society, Vol: 102, Pages: 851-855, ISSN: 0003-0007 -
Journal articleMozer FS, Bale SD, Bonnell JW, et al., 2021,
On the Origin of Switchbacks Observed in the Solar Wind
, ASTROPHYSICAL JOURNAL, Vol: 919, ISSN: 0004-637X- Author Web Link
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- Citations: 24
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Journal articleBurne S, Bertucci C, Mazelle C, et al., 2021,
The Structure of the Martian Quasi-Perpendicular Supercritical Shock as Seen by MAVEN
, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 126, ISSN: 2169-9380- Cite
- Citations: 11
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Journal articleLaMoury AT, Hietala H, Plaschke F, et al., 2021,
Solar wind control of magnetosheath jet formation and propagation to the magnetopause
, Journal of Geophysical Research: Space Physics, Vol: 126, Pages: 1-15, ISSN: 2169-9380Magnetosheath jets are localized high-dynamic pressure pulses originating at Earth's bow shock and propagating earthward through the magnetosheath. Jets can influence magnetospheric dynamics upon impacting the magnetopause; however, many jets dissipate before reaching it. In this study we present a database of 13,096 jets observed by the Time History of Events and Macroscale Interactions during Substorms spacecraft from 2008 to 2018, spanning a solar cycle. Each jet is associated with upstream solar wind conditions from OMNI. We statistically examine how solar wind conditions control the likelihood of jets forming at the shock, and the conditions favorable for jets to propagate through the magnetosheath and reach the magnetopause. We see that, for each solar wind quantity, these two effects are separate, but when combined, we find that jets are over 17 times more likely to reach and potentially impact the magnetopause when the interplanetary magnetic field (IMF) orientation is at a low cone angle, and approximately 8 times more likely during high speed solar wind. Low IMF magnitude, high Alfvén Mach number, and low density approximately double the number of jets at the magnetopause, while urn:x-wiley:21699380:media:jgra56749:jgra56749-math-0001 and dynamic pressure display no net effect. Due to the strong dependence on wind speed, we infer that jet impact rates may be solar cycle dependent as well as vary during solar wind transients. This is an important step towards forecasting the magnetospheric effects of magnetosheath jets, as it allows for predictions of jet impact rates based on measurements of the upstream solar wind.
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Journal articleMallet A, Squire J, Chandran BDG, et al., 2021,
Evolution of Large-amplitude Alfven Waves and Generation of Switchbacks in the Expanding Solar Wind
, ASTROPHYSICAL JOURNAL, Vol: 918, ISSN: 0004-637X- Author Web Link
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- Citations: 43
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Journal articleKellogg PJ, Bale SD, Goetz K, et al., 2021,
Toward a Physics Based Model of Hypervelocity Dust Impacts
, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 126, ISSN: 2169-9380- Cite
- Citations: 3
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Journal articleShuster JR, Gershman DJ, Dorelli JC, et al., 2021,
Structures in the terms of the Vlasov equation observed at Earth's magnetopause
, NATURE PHYSICS, Vol: 17, Pages: 1056-+, ISSN: 1745-2473- Cite
- Citations: 21
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Journal articleDesai RT, Freeman M, Eastwood J, et al., 2021,
Interplanetary shock-induced magnetopause motion: Comparison between theory and global magnetohydrodynamic simulations
, Geophysical Research Letters, Vol: 48, Pages: 1-11, ISSN: 0094-8276The magnetopause marks the outer edge of the Earth’s magnetosphere and a distinct boundary between solar wind and magnetospheric plasma populations. In this letter, we use global magneto-hydrodynamic simulations to examine the response of the terrestrial magnetopause to fast-forward interplanetary shocks of various strengths and compare to theoretical predictions. The theory and simulations indicate the magnetopause response can be characterised by three distinct phases; an initial acceleration as inertial forces are overcome, a rapid compressive phase comprising the majority of the distance travelled, and large-scale damped oscillations with amplitudes of the order of an Earth radius. The two approaches agree in predicting subsolar magnetopause oscillations with frequencies2–13 mHz but the simulations notably predict larger amplitudes and weaker damping rates. This phenomenon is of high relevance to space weather forecasting and provides a possible explanation for magnetopause oscillations observed following the large interplanetary shocks of August 1972 and March 1991.
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Journal articleTsui EYL, Toumi R, 2021,
Hurricanes as an enabler of Amazon fires
, Scientific Reports, Vol: 11, Pages: 1-8, ISSN: 2045-2322A teleconnection between North Atlantic tropical storms and Amazon fires is investigated as a possible case of compound remote extreme events. The seasonal cycles of the storms and fires are in phase with a maximum around September and have significant inter-annual correlation. Years of high Amazon fire activity are associated with atmospheric conditions over the Atlantic which favour tropical cyclones. We propose that anomalous precipitation and latent heating in the Caribbean, partly caused by tropical storms, leads to a thermal circulation response which creates anomalous subsidence and enhances surface solar heating over the Amazon. The Caribbean storms and precipitation anomalies could thus promote favourable atmospheric conditions for Amazon fire.
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Journal articleLaker R, Horbury TS, Bale SD, et al., 2021,
Multi-spacecraft study of the solar wind at solar minimum: Dependence on latitude and transient outflows
, Astronomy and Astrophysics: a European journal, Vol: 652, Pages: 1-10, ISSN: 0004-6361Context. The recent launches of Parker Solar Probe, Solar Orbiter (SO), and BepiColombo, along with several older spacecraft, have provided the opportunity to study the solar wind at multiple latitudes and distances from the Sun simultaneously.Aims. We take advantage of this unique spacecraft constellation, along with low solar activity across two solar rotations between May and July 2020, to investigate how the solar wind structure, including the heliospheric current sheet (HCS), varies with latitude.Methods. We visualise the sector structure of the inner heliosphere by ballistically mapping the polarity and solar wind speed from several spacecraft onto the Sun’s source surface. We then assess the HCS morphology and orientation with the in situ data and compare this with a predicted HCS shape.Results. We resolve ripples in the HCS on scales of a few degrees in longitude and latitude, finding that the local orientations of sector boundaries were broadly consistent with the shape of the HCS but were steepened with respect to a modelled HCS at the Sun. We investigate how several CIRs varied with latitude, finding evidence for the compression region affecting slow solar wind outside the latitude extent of the faster stream. We also identified several transient structures associated with HCS crossings and speculate that one such transient may have disrupted the local HCS orientation up to five days after its passage.Conclusions. We have shown that the solar wind structure varies significantly with latitude, with this constellation providing context for solar wind measurements that would not be possible with a single spacecraft. These measurements provide an accurate representation of the solar wind within ±10° latitude, which could be used as a more rigorous constraint on solar wind models and space weather predictions. In the future, this range of latitudes will increase as SO’s orbit becomes more inclined.
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Journal articleSorland SL, Brogli R, Pothapakula PK, et al., 2021,
COSMO-CLM regional climate simulations in the Coordinated Regional Climate Downscaling Experiment (CORDEX) framework: a review
, GEOSCIENTIFIC MODEL DEVELOPMENT, Vol: 14, Pages: 5125-5154, ISSN: 1991-959X -
Journal articleKaweeyanun N, Masters A, Jia X, 2021,
Analytical assessment of Kelvin-Helmholtz instability growth at Ganymede's upstream magnetopause
, Journal of Geophysical Research: Space Physics, Vol: 126, Pages: 1-14, ISSN: 2169-9380Ganymede is the only Solar System moon that generates a permanent magnetic field. Dynamics within the Ganymedean magnetosphere is thought to be driven by energy-transfer interactions on its upstream magnetopause. Previously in Kaweeyanun et al. (2020), https://doi.org/10.1029/2019GL086228 we created a steady-state analytical model of Ganymede's magnetopause and predicted global-scale magnetic reconnection to occur frequently throughout the surface. This paper subsequently provides the first assessment of Kelvin-Helmholtz (K-H) instability growth on the magnetopause. Using the same analytical model, we find that linear K-H waves are expected on both Ganymedean magnetopause flanks. Once formed, the waves propagate downstream at roughly half the speed of the external Jovian plasma flow. The Ganymedean K-H instability growth is asymmetric between magnetopause flanks due to the finite Larmor radius effect arising from large gyroradii of Jovian plasma ions. A small but notable enhancement is expected on the sub-Jovian flank according to the physical understanding of bulk plasma and local ion flows alongside comparisons to the well-observed magnetopause of Mercury. Further evaluation shows that nonlinear K-H vortices should be strongly suppressed by concurring global-scale magnetic reconnection at Ganymede. Reconnection is therefore the dominant cross-magnetopause energy-transfer mechanism and driver of global-scale plasma convection within Ganymede's magnetosphere.
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Journal articleReid J, Cargill PJ, Johnston CD, et al., 2021,
Linking computational models to follow the evolution of heated coronal plasma
, Monthly Notices of the Royal Astronomical Society, Vol: 505, Pages: 4141-4150, ISSN: 0035-8711A ‘proof of principle’ is presented, whereby the Ohmic and viscous heating determined by a three-dimensional (3D) MHD model of a coronal avalanche are used as the coronal heating input for a series of field-aligned, one-dimensional (1D) hydrodynamic models. Three-dimensional coronal MHD models require large computational resources. For current numerical parameters, it is difficult to model both the magnetic field evolution and the energy transport along field lines for coronal temperatures much hotter than 1MK, because of severe constraints on the time step from parallel thermal conduction. Using the 3D MHD heating derived from a simulation and evaluated on a single field line, the 1D models give coronal temperatures of 1MK and densities 1014--1015m−3 for a coronal loop length of 80Mm. While the temperatures and densities vary smoothly along the field lines, the heating function leads to strong asymmetries in the plasma flows. The magnitudes of the velocities in the 1D model are comparable with those seen in 3D reconnection jets in our earlier work. Advantages and drawbacks of this approach for coronal modelling are discussed.
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Journal articleHellinger P, Papini E, Verdini A, et al., 2021,
Spectral Transfer and Karman-Howarth-Monin Equations for Compressible Hall Magnetohydrodynamics
, ASTROPHYSICAL JOURNAL, Vol: 917, ISSN: 0004-637X- Cite
- Citations: 11
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Journal articleStansby D, Green LM, van Driel-Gesztelyi L, et al., 2021,
Active Region Contributions to the Solar Wind over Multiple Solar Cycles
, SOLAR PHYSICS, Vol: 296, ISSN: 0038-0938- Cite
- Citations: 8
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Journal articleMasters A, Dunn W, Stallard T, et al., 2021,
Magnetic reconnection near the planet as a possible driver of Jupiter's mysterious polar auroras
, Journal of Geophysical Research: Space Physics, Vol: 126, Pages: 1-10, ISSN: 2169-9380Auroral emissions have been extensively observed at the Earth, Jupiter, and Saturn. These planets all have appreciable atmospheres and strong magnetic fields, and their auroras predominantly originate from a region encircling each magnetic pole. However, Jupiter’s auroras poleward of these “main” emissions are brighter and more dynamic, and the drivers responsible for much of these mysterious polar auroras have eluded identification to date. We propose that part of the solution may stem from Jupiter’s stronger magnetic field. We model large-scale Alfvénic perturbations propagating through the polar magnetosphere toward Jupiter, showing that the resulting <0.1° deflections of the magnetic field closest to the planet could trigger magnetic reconnection as near as ∼0.2 Jupiter radii above the cloud tops. At Earth and Saturn this physics should be negligible, but reconnection electric field strengths above Jupiter’s poles can approach ∼1 V m−1, typical of the solar corona. We suggest this near-planet reconnection could generate beams of high-energy electrons capable of explaining some of Jupiter’s polar auroras.
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Journal articleRasca AP, Farrell WM, MacDowall RJ, et al., 2021,
Near-Sun Switchback Boundaries: Dissipation with Solar Distance
, ASTROPHYSICAL JOURNAL, Vol: 916, ISSN: 0004-637X- Author Web Link
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- Citations: 6
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Journal articleBrooks DH, Harra L, Bale SD, et al., 2021,
The Formation and Lifetime of Outflows in a Solar Active Region
, ASTROPHYSICAL JOURNAL, Vol: 917, ISSN: 0004-637X- Cite
- Citations: 9
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Journal articleZank GP, Zhao L-L, Adhikari L, et al., 2021,
Turbulence transport in the solar corona: Theory, modeling, and Parker Solar Probe
, PHYSICS OF PLASMAS, Vol: 28, ISSN: 1070-664X- Author Web Link
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- Citations: 74
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Journal articleLiu YY, Fu HS, Cao JB, et al., 2021,
Characteristics of Interplanetary Discontinuities in the Inner Heliosphere Revealed by Parker Solar Probe
, ASTROPHYSICAL JOURNAL, Vol: 916, ISSN: 0004-637X- Author Web Link
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- Citations: 20
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Journal articleNew AL, Smeed DA, Czaja A, et al., 2021,
Labrador Slope Water connects the subarctic with the Gulf Stream
, ENVIRONMENTAL RESEARCH LETTERS, Vol: 16, ISSN: 1748-9326- Cite
- Citations: 13
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Journal articleChoi TH, Brindley H, Ekins-Daukes N, et al., 2021,
Developing automated methods to estimate spectrally resolved direct normal irradiance for solar energy applications
, Renewable Energy, Vol: 173, Pages: 1070-1086, ISSN: 0960-1481We describe four schemes designed to estimate spectrally resolved direct normal irradiance (DNI) formulti-junction concentrator photovoltaic systems applications. The schemes have increasing levels ofcomplexity in terms of aerosol and circumsolar irradiance (CSI) treatment, ranging from a climatologicalaerosol classification with no account of CSI, to an approach which includes explicit aerosol typing andtype dependent CSI contribution. When tested against ground-based broadband and spectral measurements at five sites spanning a range of aerosol conditions, the most sophisticated scheme yields anaverage bias of þ 0:068%, well within photometer calibration uncertainties. The average spread of erroris 2:5%. These statistics are markedly better than the climatological approach, which carries an averagebias of 1:76% and a spread of 4%. They also improve on an intermediate approach which uses Angstrom€exponents to estimate the spectral variation in aerosol optical depth across the solar energy relevantwavelength domain. This approach results in systematic under and over-estimations of DNI at short andlong wavelengths respectively. Incorporating spectral CSI particularly benefits sites which experience asignificant amount of coarse aerosol. All approaches we describe use freely available reanalyses andsoftware tools, and can be easily applied to alternative aerosol measurements, including those fromsatellite.
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Journal articleSchwartz SJ, Ergun R, Kucharek H, et al., 2021,
Evaluating the deHoffmann-Teller Cross-Shock Potential at Real Collisionless Shocks
, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 126, ISSN: 2169-9380- Author Web Link
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- Citations: 4
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Journal articleCeppi P, Nowack P, 2021,
Observational evidence that cloud feedback amplifies global warming
, Proceedings of the National Academy of Sciences, Vol: 118, ISSN: 0027-8424Global warming drives changes in Earth’s cloud cover, which, in turn, may amplify or dampen climate change. This “cloud feedback” is the single most important cause of uncertainty in Equilibrium Climate Sensitivity (ECS)—the equilibrium global warming following a doubling of atmospheric carbon dioxide. Using data from Earth observations and climate model simulations, we here develop a statistical learning analysis of how clouds respond to changes in the environment. We show that global cloud feedback is dominated by the sensitivity of clouds to surface temperature and tropospheric stability. Considering changes in just these two factors, we are able to constrain global cloud feedback to 0.43 ± 0.35 W⋅m<jats:sup>−2</jats:sup>⋅K<jats:sup>−1</jats:sup> (90% confidence), implying a robustly amplifying effect of clouds on global warming and only a 0.5% chance of ECS below 2 K. We thus anticipate that our approach will enable tighter constraints on climate change projections, including its manifold socioeconomic and ecological impacts.
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Journal articleThomas C, Voulgarakis A, Lim G, et al., 2021,
An unsupervised learning approach to identifying blocking events:the case of European summer
, Weather and Climate Dynamics, Vol: 2, ISSN: 2698-4016Atmospheric blocking events are mid-latitudeweather patterns, which obstruct the usual path of the polar jet streams. They are often associated with heat wavesin summer and cold snaps in winter. Despite being centralfeatures of mid-latitude synoptic-scale weather, there is nowell-defined historical dataset of blocking events. Variousblocking indices (BIs) have thus been suggested for automatically identifying blocking events in observational and inclimate model data. However, BIs show significant regionaland seasonal differences so that several indices are typicallyapplied in combination to ensure scientific robustness. Here,we introduce a new BI using self-organizing maps (SOMs),an unsupervised machine learning approach, and compare itsdetection skill to some of the most widely applied BIs. Toenable this intercomparison, we first create a new groundtruth time series classification of European blocking basedon expert judgement. We then demonstrate that our method(SOM-BI) has several key advantages over previous BIs because it exploits all of the spatial information provided in theinput data and reduces the dependence on arbitrary thresholds. Using ERA5 reanalysis data (1979–2019), we find thatthe SOM-BI identifies blocking events with a higher precision and recall than other BIs. In particular, SOM-BI alreadyperforms well using only around 20 years of training data sothat observational records are long enough to train our newmethod. We present case studies of the 2003 and 2019 European heat waves and highlight that well-defined groups ofSOM nodes can be an effective tool to diagnose such weatherevents, although the domain-based approach can still lead toerrors in the identification of certain events in a fashion similar to the other BIs. We further test the red blocking detectionskill of SOM-BI depending on the meteorological variableused to study blocking, including geopotential height, sealevel pressure and four variables related to potential vorticity,and t
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Journal articleThomas C, Voulgarakis A, Lim G, et al., 2021,
An unsupervised learning approach to identifying blocking events: the case of European summer
, Weather and Climate Dynamics, Vol: 2, Pages: 581-608, ISSN: 2698-4016Atmospheric blocking events are mid-latitude weather patterns, which obstruct the usual path of the polar jet streams. They are often associated with heat waves in summer and cold snaps in winter. Despite being central features of mid-latitude synoptic-scale weather, there is no well-defined historical dataset of blocking events. Various blocking indices (BIs) have thus been suggested for automatically identifying blocking events in observational and in climate model data. However, BIs show significant regional and seasonal differences so that several indices are typically applied in combination to ensure scientific robustness. Here, we introduce a new BI using self-organizing maps (SOMs), an unsupervised machine learning approach, and compare its detection skill to some of the most widely applied BIs. To enable this intercomparison, we first create a new ground truth time series classification of European blocking based on expert judgement. We then demonstrate that our method (SOM-BI) has several key advantages over previous BIs because it exploits all of the spatial information provided in the input data and reduces the dependence on arbitrary thresholds. Using ERA5 reanalysis data (1979–2019), we find that the SOM-BI identifies blocking events with a higher precision and recall than other BIs. In particular, SOM-BI already performs well using only around 20 years of training data so that observational records are long enough to train our new method. We present case studies of the 2003 and 2019 European heat waves and highlight that well-defined groups of SOM nodes can be an effective tool to diagnose such weather events, although the domain-based approach can still lead to errors in the identification of certain events in a fashion similar to the other BIs. We further test the red blocking detection skill of SOM-BI depending on the meteorological variable used to study blocking, including geopotential height, sea level pressure and four variables related to
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Journal articleZazzeri G, Xu X, Graven H, 2021,
Efficient sampling of atmospheric methane for radiocarbon analysis and quantification of fossil methane.
, Environmental Science and Technology (Washington), Vol: 55, Pages: 8535-8541, ISSN: 0013-936XRadiocarbon (14C) measurements offer a unique investigative tool to study methane emissions by identifying fossil-fuel methane in air. Fossil-fuel methane is devoid of 14C and, when emitted to the atmosphere, causes a strong decrease in the ratio of radiocarbon to total carbon in methane (Δ14CH4). By observing the changes in Δ14CH4, the fossil fraction of methane emissions can be quantified. Presently, there are very few published Δ14CH4 measurements, mainly because it is challenging to collect and process the large volumes of air needed for radiocarbon measurements. We present a new sampling system that collects enough methane carbon for high precision Δ14CH4 measurements without having to transport large volumes of air. The system catalytically combusts CH4 into CO2 and adsorbs the combustion-derived CO2 onto a molecular sieve trap, after first removing CO2, CO, and H2O. Tests using reference air show a Δ14CH4 measurement repeatability of 5.4‰, similar or better than the precision in the most recent reported measurements. We use the system to produce the first Δ14CH4 measurements in central London and show that day-to-day differences in Δ14CH4 in these samples can be attributed to fossil methane input. The new system could be deployed in a range of settings to investigate CH4 sources.
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Journal articleJoyce CJ, McComas DJ, Schwadron NA, et al., 2021,
Energetic particle evolution during coronal mass ejection passage from 0.3 to 1 AU
, ASTRONOMY & ASTROPHYSICS, Vol: 651, ISSN: 0004-6361- Author Web Link
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- Citations: 11
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