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  • Journal article
    Greaves JS, Richards AMS, Bains W, Rimmer PB, Sagawa H, Clements DL, Seager S, Petkowski JJ, Sousa-Silva C, Ranjan S, Drabek-Maunder E, Fraser HJ, Cartwright A, Mueller-Wodarg I, Zhan Z, Friberg P, Coulson I, Lee E, Hoge Jet al., 2021,

    Phosphine gas in the cloud deck of Venus (vol 5, pg 655, 2021)

    , Nature Astronomy, Vol: 5, Pages: 726-728, ISSN: 2397-3366
  • Journal article
    Chen Y-J, Hwang Y-T, Ceppi P, 2021,

    The impacts of cloud-radiative changes on poleward atmospheric and oceanic energy transport in a warmer climate

    , Journal of Climate, Vol: 34, Pages: 7857-7874, ISSN: 0894-8755

    Based on theory and climate model experiments, previous studies suggest most of the uncertainties in projected future changes in meridional energy transport and zonal mean surface temperature can be attributed to cloud feedback. To investigate how radiative and dynamical adjustments modify the influence of cloud-radiative changes on energy transport, this study applies a cloud-locking technique in a fully-coupled climate model, CESM. Under global warming, the impacts of cloud-radiative changes on the meridional energy transport are asymmetric in the two hemispheres. In the Northern Hemisphere, the cloud-radiative changes have little impact on energy transport, because 89% of the cloud-induced heating is balanced locally by increasing outgoing longwave radiation. In the Southern Hemisphere, on the other hand, cloud-induced dynamical changes in the atmosphere and the ocean cause enhanced poleward energy transport, accounting for most of the increase in energy transport under warming. Our experiments highlight that the local longwave radiation adjustment induced by temperature variation can partially offset the impacts of cloud-radiative changes on energy transport, making the estimated impacts smaller than those obtained from directly integrating cloud-radiative changes in previous studies. It is also demonstrated that the cloud-radiative impacts on temperature and energy transport can be significantly modulated by the oceanic circulation, suggesting the necessity of considering atmospheric-oceanic coupling when estimating the impacts of cloud-radiative changes on the climate system.
  • Journal article
    Chen L, Ma B, Wu D, Zhao G, Tang J, Bale SDet al., 2021,

    An Interplanetary Type IIIb Radio Burst Observed by Parker Solar Probe and Its Emission Mechanism

    , ASTROPHYSICAL JOURNAL LETTERS, Vol: 915, ISSN: 2041-8205
  • Journal article
    Gristey JJ, Su W, Loeb NG, Vonder Haar TH, Tornow F, Schmidt KS, Hakuba MZ, Pilewskie P, Russell JEet al., 2021,

    Shortwave radiance to irradiance conversion for earth radiation budget satellite observations: a review

    , Remote Sensing, Vol: 13, ISSN: 2072-4292

    Observing the Earth radiation budget (ERB) from satellites is crucial for monitoring and understanding Earth’s climate. One of the major challenges for ERB observations, particularly for reflected shortwave radiation, is the conversion of the measured radiance to the more energetically relevant quantity of radiative flux, or irradiance. This conversion depends on the solar-viewing geometry and the scene composition associated with each instantaneous observation. We first outline the theoretical basis for algorithms to convert shortwave radiance to irradiance, most commonly known as empirical angular distribution models (ADMs). We then review the progression from early ERB satellite observations that applied relatively simple ADMs, to current ERB satellite observations that apply highly sophisticated ADMs. A notable development is the dramatic increase in the number of scene types, made possible by both the extended observational record and the enhanced scene information now available from collocated imager information. Compared with their predecessors, current shortwave ADMs result in a more consistent average albedo as a function of viewing zenith angle and lead to more accurate instantaneous and mean regional irradiance estimates. One implication of the increased complexity is that the algorithms may not be directly applicable to observations with insufficient accompanying imager information, or for existing or new satellite instruments where detailed scene information is not available. Recent advances that complement and build on the base of current approaches, including machine learning applications and semi-physical calculations, are highlighted.
  • Journal article
    Wang R, Vasko IY, Mozer FS, Bale SD, Kuzichev IV, Artemyev AV, Steinvall K, Ergun R, Giles B, Khotyaintsev Y, Lindqvist P-A, Russell CT, Strangeway Ret al., 2021,

    Electrostatic Solitary Waves in the Earth's Bow Shock: Nature, Properties, Lifetimes, and Origin

    , JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 126, ISSN: 2169-9380
  • Journal article
    Farrell WM, Rasca AP, MacDowall RJ, Gruesbeck JR, Bale SD, Kasper JCet al., 2021,

    Switchback Boundary Dissipation and Relative Age

    , ASTROPHYSICAL JOURNAL, Vol: 915, ISSN: 0004-637X
  • Journal article
    Halekas JS, Bercic L, Whittlesey P, Larson DE, Livi R, Berthomier M, Kasper JC, Case AW, Stevens ML, Bale SD, MacDowall RJ, Pulupa MPet al., 2021,

    The Sunward Electron Deficit: A Telltale Sign of the Sun's Electric Potential

    , ASTROPHYSICAL JOURNAL, Vol: 916, ISSN: 0004-637X
  • Journal article
    Madanian H, Schwartz SJ, Fuselier SA, Burgess D, Turner DL, Chen L-J, Desai MI, Starkey MJet al., 2021,

    Direct Evidence for Magnetic Reflection of Heavy Ions from High Mach Number Collisionless Shocks

    , ASTROPHYSICAL JOURNAL LETTERS, Vol: 915, ISSN: 2041-8205
  • Journal article
    Yao Z, Dunn WR, Woodfield EE, Clark G, Mauk BH, Ebert RW, Grodent D, Bonfond B, Pan D, Rae IJ, Ni B, Guo R, Branduardi-Raymont G, Wibisono AD, Rodriguez P, Kotsiaros S, Ness J-U, Allegrini F, Kurth WS, Gladstone GR, Kraft R, Sulaiman AH, Manners H, Desai RT, Bolton SJet al., 2021,

    Revealing the source of Jupiter's x-ray auroral flares

    , SCIENCE ADVANCES, Vol: 7, ISSN: 2375-2548
    • Cite
    • Citations: 14
  • Journal article
    Duan D, He J, Bowen TA, Woodham LD, Wang T, Chen CHK, Mallet A, Bale SDet al., 2021,

    Anisotropy of solar wind turbulence in the inner heliosphere at kinetic scales: PSP observations

    , Letters of the Astrophysical Journal, Vol: 915, Pages: 1-7, ISSN: 2041-8205

    The anisotropy of solar wind turbulence is a critical issue in understanding the physics of energy transfer between scales and energy conversion between fields and particles in the heliosphere. Using the measurement of Parker Solar Probe (PSP), we present an observation of the anisotropy at kinetic scales in the slow, Alfvénic, solar wind in the inner heliosphere. The magnetic compressibility behaves as expected for kinetic Alfvénic turbulence below the ion scale. A steepened transition range is found between the inertial and kinetic ranges in all directions with respect to the local background magnetic field direction. The anisotropy of k⊥ ≫ k∥ is found evident in both transition and kinetic ranges, with the power anisotropy P⊥/P∥ > 10 in the kinetic range leading over that in the transition range and being stronger than that at 1 au. The spectral index varies from αt∥ = −5.7 ± 1.0 to αt⊥ = −3.7 ± 0.3 in the transition range and αk∥ = −3.12 ± 0.22 to αk⊥ = −2.57 ± 0.09 in the kinetic range. The corresponding wavevector anisotropy has the scaling of ${k}_{\parallel }\sim {k}_{\perp }^{0.71\pm 0.17}$ in the transition range, and changes to ${k}_{\parallel }\sim {k}_{\perp }^{0.38\pm 0.09}$ in the kinetic range, consistent with the kinetic Alfvénic turbulence at sub-ion scales.
  • Journal article
    Kuhn-Régnier A, Voulgarakis A, Nowack P, Forkel M, Prentice IC, Harrison SPet al., 2021,

    Quantifying the Importance of antecedent fuel-related vegetationproperties for burnt area using random forests

    , Biogeosciences, Vol: 8, ISSN: 1726-4170

    The seasonal and longer-term dynamics of fuel accumulation affect fire seasonality and the occurrence of extreme wildfires. Failure to account for their influence mayhelp to explain why state-of-the-art fire models do not simulate the length and timing of the fire season or interannual variability in burnt area well. We investigated the impact of accounting for different timescales of fuel production and accumulation on burnt area using a suite of random forest regression models that included the immediateimpact of climate, vegetation, and human influences in agiven month and tested the impact of various combinationsof antecedent conditions in four productivity-related vegetation indices and in antecedent moisture conditions. Analyses were conducted for the period from 2010 to 2015 inclusive. Inclusion of antecedent vegetation conditions representing fuel build-up led to an improvement of the global,climatological out-of-sample R2from 0.579 to 0.701, but theinclusion of antecedent vegetation conditions on timescales≥ 1 year had no impact on simulated burnt area. Currentmoisture levels were the dominant influence on fuel drying. Additionally, antecedent moisture levels were importantfor fuel build-up. The models also enabled the visualisationof interactions between variables, such as the importanceof antecedent productivity coupled with instantaneous drying. The length of the period which needs to be consideredvaries across biomes; fuel-limited regions are sensitive to antecedent conditions that determine fuel build-up over longertime periods (∼ 4 months), while moisture-limited regionsare more sensitive to current conditions that regulate fuel drying.
  • Journal article
    Kuhn- Regnier A, Voulgarakis A, Nowack P, Forkel M, Prentice IC, Harrison Set al., 2021,

    The importance of antecedent vegetation and drought conditions as global drivers of burnt areas

    , Biogeosciences, Vol: 18, Pages: 3861-3879, ISSN: 1726-4170

    The seasonal and longer-term dynamics of fuel accumulation affect fire seasonality and the occurrence of extreme wildfires. Failure to account for their influence may help to explain why state-of-the-art fire models do not simulate the length and timing of the fire season or interannual variability in burnt area well. We investigated the impact of accounting for different timescales of fuel production and accumulation on burnt area using a suite of random forest regression models that included the immediate impact of climate, vegetation, and human influences in a given month and tested the impact of various combinations of antecedent conditions in four productivity-related vegetation indices and in antecedent moisture conditions. Analyses were conducted for the period from 2010 to 2015 inclusive. Inclusion of antecedent vegetation conditions representing fuel build-up led to an improvement of the global, climatological out-of-sample R2 from 0.579 to 0.701, but the inclusion of antecedent vegetation conditions on timescales ≥ 1 year had no impact on simulated burnt area. Current moisture levels were the dominant influence on fuel drying. Additionally, antecedent moisture levels were important for fuel build-up. The models also enabled the visualisation of interactions between variables, such as the importance of antecedent productivity coupled with instantaneous drying. The length of the period which needs to be considered varies across biomes; fuel-limited regions are sensitive to antecedent conditions that determine fuel build-up over longer time periods (∼ 4 months), while moisture-limited regions are more sensitive to current conditions that regulate fuel drying.
  • Journal article
    Hall RJ, Mitchell DM, Seviour WJM, Wright CJet al., 2021,

    Persistent Model Biases in the CMIP6 Representation of Stratospheric Polar Vortex Variability

    , JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, Vol: 126, ISSN: 2169-897X
    • Cite
    • Citations: 27
  • Journal article
    Malaspina DM, Wilson LB, Ergun RE, Bale SD, Bonnell JW, Goodrich K, Goetz K, Harvey PR, MacDowall RJ, Pulupa M, Halekas J, Case A, Kasper JC, Larson D, Stevens M, Whittlesey Pet al., 2021,

    Electron Bernstein waves and narrowband plasma waves near the electron cyclotron frequency in the near-Sun solar wind

    , ASTRONOMY & ASTROPHYSICS, Vol: 650, ISSN: 0004-6361
    • Cite
    • Citations: 13
  • Journal article
    Joyce CJ, McComas DJ, Schwadron NA, Christian ER, Wiedenbeck ME, McNutt RL, Cohen CMS, Leske RA, Mewaldt RA, Stone EC, Labrador AW, Davis AJ, Cummings AC, Mitchell DG, Hill ME, Roelof EC, Allen RC, Szalay JR, Rankin JS, Desai M, Giacalone J, Matthaeus WH, Bale SD, Kasper JCet al., 2021,

    Time evolution of stream interaction region energetic particle spectra in the inner heliosphere

    , ASTRONOMY & ASTROPHYSICS, Vol: 650, ISSN: 0004-6361
  • Journal article
    Froment C, Krasnoselskikh V, de Wit TD, Agapitov O, Fargette N, Lavraud B, Larosa A, Kretzschmar M, Jagarlamudi VK, Velli M, Malaspina D, Whittlesey PL, Bale SD, Case AW, Goetz K, Kasper JC, Korreck KE, Larson DE, MacDowall RJ, Mozer FS, Pulupa M, Revillet C, Stevens MLet al., 2021,

    Direct evidence for magnetic reconnection at the boundaries of magnetic switchbacks with Parker Solar Probe

    , ASTRONOMY & ASTROPHYSICS, Vol: 650, ISSN: 0004-6361
  • Journal article
    Jagarlamudi VK, de Wit TD, Froment C, Krasnoselskikh V, Larosa A, Bercic L, Agapitov O, Halekas JS, Kretzschmar M, Malaspina D, Moncuquet M, Bale SD, Case AW, Kasper JC, Korreck KE, Larson DE, Pulupa M, Stevens ML, Whittlesey Pet al., 2021,

    Whistler wave occurrence and the interaction with strahl electrons during the first encounter of Parker Solar Probe

    , ASTRONOMY & ASTROPHYSICS, Vol: 650, ISSN: 0004-6361
  • Journal article
    Shi C, Velli M, Panasenco O, Tenerani A, Reville V, Bale SD, Kasper J, Korreck K, Bonnell JW, de Wit TD, Malaspina DM, Goetz K, Harvey PR, MacDowall RJ, Pulupa M, Case AW, Larson D, Verniero JL, Livi R, Stevens M, Whittlesey P, Maksimovic M, Moncuquet Met al., 2021,

    Alfvenic versus non-Alfvenic turbulence in the inner heliosphere as observed by Parker Solar Probe

    , ASTRONOMY & ASTROPHYSICS, Vol: 650, ISSN: 0004-6361
    • Cite
    • Citations: 42
  • Journal article
    Halekas JS, Whittlesey PL, Larson DE, McGinnis D, Bale SD, Berthomier M, Case AW, Chandran BDG, Kasper JC, Klein KG, Korreck KE, Livi R, MacDowall RJ, Maksimovic M, Malaspina DM, Matteini L, Pulupa MP, Stevens MLet al., 2021,

    Electron heat flux in the near-Sun environment

    , ASTRONOMY & ASTROPHYSICS, Vol: 650, ISSN: 0004-6361
  • Journal article
    Allen RC, Ho GC, Jian LK, Vines SK, Bale SD, Case AW, Hill ME, Joyce CJ, Kasper JC, Korreck KE, Malaspina DM, McComas DJ, McNutt R, Mostl C, Odstrcil D, Raouafi N, Schwadron NA, Stevens MLet al., 2021,

    A living catalog of stream interaction regions in the Parker Solar Probe era

    , ASTRONOMY & ASTROPHYSICS, Vol: 650, ISSN: 0004-6361
  • Journal article
    Drake JF, Agapitov O, Swisdak M, Badman ST, Bale SD, Horbury TS, Kasper JC, MacDowall RJ, Mozer FS, Phan TD, Pulupa M, Szabo A, Velli Met al., 2021,

    Are switchbacks signatures of magnetic flux ropes generated by interchange reconnection in the corona?

    , Astronomy and Astrophysics: a European journal, Vol: 650, Pages: 1-8, ISSN: 0004-6361

    The structure of magnetic flux ropes injected into the solar wind duringreconnection in the coronal atmosphere is explored with particle-in-cellsimulations and compared with {\it in situ} measurements of magnetic"switchbacks" from the Parker Solar Probe. We suggest that multi-x-linereconnection between open and closed flux in the corona will inject flux ropesinto the solar wind and that these flux ropes can convect outward over longdistances before disintegrating. Simulations that explore the magneticstructure of flux ropes in the solar wind reproduce key features of the"switchback" observations: a rapid rotation of the radial magnetic field intothe transverse direction (a consequence of reconnection with a strong guidefield); and the potential to reverse the radial field component. The potentialimplication of the injection of large numbers of flux ropes in the coronalatmosphere for understanding the generation of the solar wind is discussed.
  • Journal article
    Woodham L, Horbury T, Matteini L, Woolley T, Laker R, Bale S, Nicolaou G, Stawarz J, Stansby D, Hietala H, Larson D, Livi R, Verniero J, McManus M, Kasper J, Korreck K, Raouafi N, Moncuquet M, Pulupa Met al., 2021,

    Enhanced proton parallel temperature inside patches of switchbacks in the inner heliosphere

    , Astronomy and Astrophysics: a European journal, Vol: 650, Pages: 1-7, ISSN: 0004-6361

    Context. Switchbacks are discrete angular deflections in the solar wind magnetic field that have been observed throughout the helio-sphere. Recent observations by Parker Solar Probe(PSP) have revealed the presence of patches of switchbacks on the scale of hours to days, separated by ‘quieter’ radial fields. Aims. We aim to further diagnose the origin of these patches using measurements of proton temperature anisotropy that can illuminate possible links to formation processes in the solar corona. Methods. We fit 3D bi-Maxwellian functions to the core of proton velocity distributions measured by the SPAN-Ai instrument onboard PSP to obtain the proton parallel, Tp,‖, and perpendicular, Tp,⊥, temperature. Results. We show that the presence of patches is highlighted by a transverse deflection in the flow and magnetic field away from the radial direction. These deflections are correlated with enhancements in Tp,‖, while Tp,⊥remains relatively constant. Patches sometimes exhibit small proton and electron density enhancements. Conclusions. We interpret that patches are not simply a group of switchbacks, but rather switchbacks are embedded within a larger-scale structure identified by enhanced Tp,‖that is distinct from the surrounding solar wind. We suggest that these observations are consistent with formation by reconnection-associated mechanisms in the corona.
  • Journal article
    Laker R, Horbury TS, Bale SD, Matteini L, Woolley T, Woodham LD, Badman ST, Pulupa M, Kasper JC, Stevens M, Case AW, Korreck KEet al., 2021,

    Statistical analysis of orientation, shape, and size of solar wind switchbacks

    , Astronomy & Astrophysics, Vol: 650, Pages: 1-7, ISSN: 0004-6361

    One of the main discoveries from the first two orbits of Parker Solar Probe(PSP) was the presence of magnetic switchbacks, whose deflections dominated themagnetic field measurements. Determining their shape and size could provideevidence of their origin, which is still unclear. Previous work with a singlesolar wind stream has indicated that these are long, thin structures althoughthe direction of their major axis could not be determined. We investigate ifthis long, thin nature extends to other solar wind streams, while determiningthe direction along which the switchbacks within a stream were aligned. We tryto understand how the size and orientation of the switchbacks, along with theflow velocity and spacecraft trajectory, combine to produce the observedstructure durations for past and future orbits. We searched for the alignmentdirection that produced a combination of a spacecraft cutting direction andswitchback duration that was most consistent with long, thin structures. Theexpected form of a long, thin structure was fitted to the results of the bestalignment direction, which determined the width and aspect ratio of theswitchbacks for that stream. The switchbacks had a mean width of $50,000 \,\rm{km}$, with an aspect ratio of the order of $10$. We find that switchbacksare not aligned along the background flow direction, but instead aligned alongthe local Parker spiral, perhaps suggesting that they propagate along themagnetic field. Since the observed switchback duration depends on how thespacecraft cuts through the structure, the duration alone cannot be used todetermine the size or influence of an individual event. For future PSP orbits,a larger spacecraft transverse component combined with more radially alignedswitchbacks will lead to long duration switchbacks becoming less common.
  • Journal article
    Stansby D, Bercic L, Matteini L, Owen CJ, French RJ, Baker D, Badman STet al., 2021,

    Sensitivity of solar wind mass flux to coronal temperature

    , ASTRONOMY & ASTROPHYSICS, Vol: 650, ISSN: 0004-6361
  • Journal article
    Bandyopadhyay R, Matthaeus WH, McComas DJ, Joyce CJ, Szalay JR, Christian ER, Giacalone J, Schwadron NA, Mitchell DG, Hill ME, McNutt RL, Desai M, Bale SD, Bonnell JW, de Wit TD, Goetz K, Harvey PR, MacDowall RJ, Malaspina DM, Pulupa M, Kasper JC, Stevens Met al., 2021,

    Energetic particle behavior in near-Sun magnetic field switchbacks from PSP

    , ASTRONOMY & ASTROPHYSICS, Vol: 650, ISSN: 0004-6361
    • Cite
    • Citations: 16
  • Journal article
    Badman ST, Bale SD, Rouillard AP, Bowen TA, Bonnell JW, Goetz K, Harvey PR, MacDowall RJ, Malaspina DM, Pulupa Met al., 2021,

    Measurement of the open magnetic flux in the inner heliosphere down to 0.13 AU

    , ASTRONOMY & ASTROPHYSICS, Vol: 650, ISSN: 0004-6361
  • Journal article
    Zhao L-L, Zank GP, Hu Q, Telloni D, Chen Y, Adhikari L, Nakanotani M, Kasper JC, Huang J, Bale SD, Korreck KE, Case AW, Stevens M, Bonnell JW, de Wit TD, Goetz K, Harvey PR, MacDowall RJ, Malaspina DM, Pulupa M, Larson DE, Livi R, Whittlesey P, Klein KG, Raouafi NEet al., 2021,

    Detection of small magnetic flux ropes from the third and fourth Parker Solar Probe encounters

    , ASTRONOMY & ASTROPHYSICS, Vol: 650, ISSN: 0004-6361
  • Journal article
    Quaas J, Gryspeerdt E, Vautard R, Boucher Oet al., 2021,

    Climate impact of aircraft-induced cirrus assessed from satellite observations before and during COVID-19

    , Environmental Research Letters, Vol: 16, Pages: 1-6, ISSN: 1748-9326

    Aircraft produce condensation trails, which are thought to increase high-level cloudiness under certain conditions. Howeverthe magnitude of such an effect and whether this contributes substantially to the radiative forcing due to the aviation sectorremain uncertain. The very substantial, near-global reduction in air traffic in response to the COVID-19 outbreak offers anunprecedented opportunity to identify the anthropogenic contribution to the observed cirrus coverage and thickness. Here weshow, using an analysis of satellite observations for the period March-May 2020, that in the 20% of the Northern Hemispheremid-latitudes with the largest air traffic reduction, cirrus fraction was reduced by ~9 ± 1.5% on average, and cirrus emissivitywas reduced by ~2 ±5% relative to what they should have been with normal air traffic. The changes are corroborated by aconsistent estimate based on linear trends over the period 2011 – 2019. The change in cirrus translates to a global radiativeforcing of 61 ±39 mWm-2. This estimate is somewhat smaller than previous assessments.
  • Journal article
    Larosa A, Krasnoselskikh V, de Wit TD, Agapitov O, Froment C, Jagarlamudi VK, Velli M, Bale SD, Case AW, Goetz K, Harvey P, Kasper JC, Korreck KE, Larson DE, MacDowall RJ, Malaspina D, Pulupa M, Revillet C, Stevens MLet al., 2021,

    Switchbacks: statistical properties and deviations from Alfvenicity

    , ASTRONOMY & ASTROPHYSICS, Vol: 650, ISSN: 0004-6361
  • Journal article
    Liu M, Issautier K, Meyer-Vernet N, Moncuquet M, Maksimovic M, Halekas JS, Huang J, Griton L, Bale S, Bonnell JW, Case AW, Goetz K, Harvey PR, Kasper JC, MacDowall RJ, Malaspina DM, Pulupa M, Stevens MLet al., 2021,

    Solar wind energy flux observations in the inner heliosphere: first results from Parker Solar Probe

    , ASTRONOMY & ASTROPHYSICS, Vol: 650, ISSN: 0004-6361

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