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Journal articleWarwick L, Murray J, Brindley H, 2024,
The Far-INfrarEd Spectrometer for Surface Emissivity (FINESSE) Part II: first measurements of the emissivity of water in the far-infrared
, Atmospheric Measurement Techniques, Vol: 17, Pages: 4777-4787, ISSN: 1867-1381In this paper we describe a method for retrieving surface emissivity across the wavenumber range 400–1600 cm-1 using novel radiance measurements from the Far INfrarEd Spectrometer for Surface Emissivity (FINESSE) instrument. FINESSE is described in detail in part I of this paper. We apply the method to two sets of measurements of distilled water. The first set of emissivity retrievals is of distilled water heated above ambient temperature to enhance the signal to noise ratio. The second set of emissivity retrievals is of ambient temperate water at a range of viewing angles. In both cases the observations agree well with calculations based on compiled refractive indices across the mid and far-infrared. It is found that the reduced contrast between the up and downwelling radiation in the ambient temperature case degrades the performance of the retrieval. Therefore a filter is developed to target regions of high contrast which improves the agreement between the ambient temperature emissivity retrieval and the predicted emissivity. These retrievals are, to the best of our knowledge, the first published 10 retrievals of the emissivity of water that extend into the far-infrared and demonstrate a method that can be used for the in-situ retrieval of the emissivity of other surfaces in the field.
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Journal articleGryspeerdt E, Stettler M, Teoh R, et al., 2024,
Operational differences lead to longer lifetimes of satellite detectable contrails from more fuel efficient aircraft
, Environmental Research Letters, Vol: 19, ISSN: 1748-9326Clouds produced by aircraft (known as contrails) contribute over half of the positive radiative forcing from aviation, but the size of this warming effect is highly uncertain. Their radiative effect is highly dependent on the microphysical properties and meteorological background state, varying strongly over the contrail lifecycle. In-situ observations have demonstrated an impact of aircraft and fuel type on contrail properties close to the aircraft, but there are few observational constraints at these longer timescales, despite these having a strong impact in high-resolution and global models. This work provides an observational quantification of these contrail controlling factors, matching air traffic data to satellite observations of contrails to isolate the role of the aircraft type in contrail properties and evolution. Investigating over 64 000 cases, a relationship between aircraft type and contrail formation is observed, with more efficient aircraft forming longer-lived satellite-detectable contrails more frequently, which could lead to a larger climate impact. This increase in contrail formation and lifetime is primarily driven by an increase in flight altitude. Business jets are also found to produce longer-lived satellite-detectable contrails despite their lower fuel flow, as they fly at higher altitudes. The increase in satellite-detected contrails behind more efficient aircraft suggests a trade-off between aircraft greenhouse gas emissions and the aviation climate impact through contrail production, due to differences in aircraft operation.
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Journal articleWilliams RG, Meijers AJS, Roussenov VM, et al., 2024,
Asymmetries in the Southern Ocean contribution to global heat and carbon uptake
, Nature Climate Change, Vol: 14, Pages: 823-831, ISSN: 1758-678XThe Southern Ocean provides dominant contributions to global ocean heat and carbon uptake, which is widely interpreted as resulting from its unique upwelling and circulation. Here we show a large asymmetry in these contributions, with the Southern Ocean accounting for 83 ± 33% of global heat uptake versus 43 ± 3% of global ocean carbon uptake over the historical period in state-of-the-art climate models. Using single radiative forcing experiments, we demonstrate that this historical asymmetry is due to suppressed heat uptake by northern oceans from enhanced aerosol forcing. In future projections, such as SSP2-4.5 where greenhouse gases increasingly dominate radiative forcing, the Southern Ocean contributions to global heat and carbon uptake become more comparable, 52 ± 5% and 47 ± 4%, respectively. Hence, the past is not a reliable indicator of the future, with the northern oceans becoming important for heat uptake while the Southern Ocean remains important for both heat and carbon uptake.
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Journal articleStier P, van den Heever SC, Christensen MW, et al., 2024,
Multifaceted aerosol effects on precipitation
, Nature Geoscience, Vol: 17, Pages: 719-732, ISSN: 1752-0894Aerosols have been proposed to influence precipitation rates and spatial patterns from scales of individual clouds to the globe. However, large uncertainty remains regarding the underlying mechanisms and importance of multiple effects across spatial and temporal scales. Here we review the evidence and scientific consensus behind these effects, categorized into radiative effects via modification of radiative fluxes and the energy balance, and microphysical effects via modification of cloud droplets and ice crystals. Broad consensus and strong theoretical evidence exist that aerosol radiative effects (aerosol–radiation interactions and aerosol–cloud interactions) act as drivers of precipitation changes because global mean precipitation is constrained by energetics and surface evaporation. Likewise, aerosol radiative effects cause well-documented shifts of large-scale precipitation patterns, such as the intertropical convergence zone. The extent of aerosol effects on precipitation at smaller scales is less clear. Although there is broad consensus and strong evidence that aerosol perturbations microphysically increase cloud droplet numbers and decrease droplet sizes, thereby slowing precipitation droplet formation, the overall aerosol effect on precipitation across scales remains highly uncertain. Global cloud-resolving models provide opportunities to investigate mechanisms that are currently not well represented in global climate models and to robustly connect local effects with larger scales. This will increase our confidence in predicted impacts of climate change.
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Journal articleJohnson D, Hood AW, Cargill PJ, et al., 2024,
The thermodynamic response of heating at coronal null points
, Monthly Notices of the Royal Astronomical Society, Vol: 532, Pages: 4261-4271, ISSN: 0035-8711Magnetic null points are an important aspect of the magnetic field structure of the solar corona and can be sites of enhanced dissipation. This paper uses analytical and numerical models to investigate the plasma structure around a heated null. It is shown that the temperature profile not only differs significantly from that in a uniform field, but also that the profile depends significantly on the spatial structure of the heating. Field lines close to the separatrices and the null point have higher temperatures than a uniform field for the same heating input. The dependence of the results near the null on both the ratio of perpendicular to parallel conduction, and numerical resolution is also explored. The comparison between analytic and numerical solutions also provides a useful benchmark to compare MHD codes with anisotropic thermal conduction.
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Journal articleTosi F, Roatsch T, Galli A, et al., 2024,
Characterization of the Surfaces and Near-Surface Atmospheres of Ganymede, Europa and Callisto by JUICE
, SPACE SCIENCE REVIEWS, Vol: 220, ISSN: 0038-6308 -
Journal articleMurray JE, Warwick L, Brindley H, et al., 2024,
The Far-INfrarEd Spectrometer for Surface Emissivity (FINESSE) – Part 1: instrument description and level 1 radiances
, Atmospheric Measurement Techniques, Vol: 17, Pages: 4757-4775, ISSN: 1867-1381The Far-INfrarEd Spectrometer for Surface Emissivity (FINESSE) instrument combines a commercial Bruker EM27 spectrometer with a front-end viewing and calibration rig developed at Imperial College London. FINESSE is specifically designed to enable accurate measurements of surface emissivity, covering the range 400–1600 cm−1, and, as part of this remit, can obtain views over the full 360° angular range.In this part, Part 1, we describe the system configuration, outlining the instrument spectral characteristics, our data acquisition methodology, and the calibration strategy. As part of the process, we evaluate the stability of the system, including the impact of knowledge of blackbody (BB) target emissivity and temperature. We also establish a numerical description of the instrument line shape (ILS), which shows strong frequency-dependent asymmetry. We demonstrate why it is important to account for these effects by assessing their impact on the overall uncertainty budget on the level 1 radiance products from FINESSE. Initial comparisons of observed spectra with simulations show encouraging performance given the uncertainty budget.
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Journal articleChen L-J, Gershman D, Burkholder B, et al., 2024,
Earth's Alfvén Wings Driven by the April 2023 Coronal Mass Ejection
, GEOPHYSICAL RESEARCH LETTERS, Vol: 51, ISSN: 0094-8276 -
Journal articleWang S, Ren T, Yang P, et al., 2024,
Improved temperature-dependent ice refractive index compilation in the far-infrared spectrum
, Geophysical Research Letters, Vol: 51, ISSN: 0094-8276A new ice refractive index compilation is reported for a broad spectrum ranging from 0.0443 to 106 𝜇m, focusing on the pronounced temperature-dependence of ice optical properties in the far-infrared (far-IR) segment (15-100 µm). A sensitivity study assuming spherical particles shows that selecting ice refractive indices at 12 temperatures and 215 wavelengths in the far-IR region gives sufficient accuracy in interpolated refractive indices for developing a new ice crystal optical property database. Furthermore, we demonstrate the differences between the bulk single-scattering properties computed for hexagonal ice particles with this new compilation compared to a previous iteration at three far-IR wavelengths where substantial differences are noticed between the two ice refractive index compilations. We suggest that our new ice refractive index dataset will improve downstream light-scattering applications for upcoming far-IR satellite missions and allow robust modeling of outgoing longwave radiation (OLR) under ice cloud conditions.
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Journal articleSouthwood D, 2024,
Go/no-go for a Mars samples return
, SCIENCE, Vol: 385, Pages: 233-233, ISSN: 0036-8075 -
Journal articleGreene SM, Schachat SR, Arita-Merino N, et al., 2024,
Accessible interview practices for disabled scientists and engineers
, ISCIENCE, Vol: 27 -
Journal articleXu S, Mitchell DL, Whittlesey P, et al., 2024,
Closed magnetic topology in the Venusian magnetotail and ion escape at Venus
, NATURE COMMUNICATIONS, Vol: 15 -
Journal articleMathews JP, Czaja A, Vitart F, et al., 2024,
Gulf stream moisture fluxes impact atmospheric blocks throughout the Northern Hemisphere
, Geophysical Research Letters, Vol: 51, ISSN: 0094-8276In this study, we explore the impact of oceanic moisture fluxes on atmospheric blocks using the ECMWF IFS. Artificially suppressing surface latent heat flux over the Gulf Stream (GS) region reduces atmospheric blocking frequency across the Northern Hemisphere by up to 30%. Affected blocks show a shorter lifespan (−6%), smaller spatial extent (−10%), and reduced intensity (−0.4%), with an increased number of individual blocking anticyclones (+17%). These findings are robust across various blocking detection thresholds. Analysis reveals a qualitatively consistent response across all resolutions, with Tco639 (∼18 km) showing the largest statistically significant change across all blocking characteristics, although differences between resolutions are not statistically significant. Exploring the broader Rossby wave pattern, we observe that diminished moisture fluxes favor eastward propagation and higher zonal wavenumbers, while air-sea interactions promote stationary and westward-propagating waves with zonal wavenumber 3. This study underscores the critical role of the GS in modulating atmospheric blocking.
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Conference paperBeth A, Galand M, Modolo R, et al., 2024,
Impact of ion-neutral chemistry on Ganymede's ionosphere
<jats:p>The Galileo spacecraft flew by Ganymede, down to 0.1 RG from the surface for the closest, six times giving us insight into its plasma environment. Its ionosphere, made of ions born from the ionisation of neutrals present in Ganymede's exosphere, represents the bulk of the plasma near the moon around closest approach. As it has been revealed by Galileo and Juno, near closest approach the ion population is dominated by low-energy ions from the water ion group (O+, HO+, H2O+) and O2+. As we showed in [1] by means of a test particle model, the ion composition during most flybys was a priori dominated by H2+and O2+. However, during Juno's flyby of Ganymede, plasma data revealed the additional presence of H3+ that may only stem from ion neutral reactions between H2 and H2+.&#160;&#160;We have updated our test particle model to account for these ion-neutral collisions of which &#160;H2 + H2+. We show how it modifies the ion composition compared with [1] and assess the role of these collisions in the production of new ion species within Ganymede's exo-ionosphere. This will help to interpret plasma observations made by Juno and in the future by JUICE around Ganymede.&#160;[1] Beth et al., EGU24, https://doi.org/10.5194/egusphere-egu24-11772, 2024</jats:p>
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Conference paperLewis Z, Stephenson P, Kallio E, et al., 2024,
Evolution of the ion dynamics at comet 67P during the escort phase
<jats:p>Comet 67P/Churyumov-Gerasimenko was escorted by the Rosetta spacecraft through a 2 year section of its 6 year orbit around the Sun. This enabled the observation of a large variation in comet outgassing and the resulting evolution of the plasma environment. The diamagnetic cavity, a region of negligible magnetic field arising from the interaction of the unmagnetised cometary plasma with the solar wind, began to be detected sporadically by the Rosetta Plasma Consortium/ Magnetometer (RPC/MAG) in April 2015 at a heliocentric distance of 1.8 au [1]. The last detections were in February 2016 at 2.4 au. Within this cavity, the flow of cometary ions has been shown to be largely radial [2]; the ions are accelerated above the neutral gas speed by an ambipolar electric field, but many newborn ions still undergo multiple ion-neutral chemical reactions before escaping [3,4]. Outside the diamagnetic cavity boundary, which is itself highly variable, the ion flow is considerably more complex, and the ambipolar electric field plays a more minor role compared to the convective electric field of the solar wind [2]. &#160;At large heliocentric distances (>2.5 au), the total plasma density observed from RPC plasma sensors is well explained by a simple flux conservation model that assumes the ions travel radially away from the nucleus at speed close to that of neutrals [5,6]. However, closer to perihelion and once the diamagnetic cavity has formed, such an approach does not hold [7]. We aim to better understand this transition, the driver of ions' acceleration, and the role that the diamagnetic cavity plays.In this study, we explore the varying ion dynamics both in the presence (e.g. during high outgassing activity) and absence (low outgassing activity) of a diamagnetic cavity. Electric and magnetic fields from hybrid simulations of the cometary environment are used to drive a 3D test particle model of the cometary ions for a range of comet activity levels.
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Journal articleErvin T, Bale SD, Badman ST, et al., 2024,
Compositional Metrics of Fast and Slow Alfvénic Solar Wind Emerging from Coronal Holes and Their Boundaries
, ASTROPHYSICAL JOURNAL, Vol: 969, ISSN: 0004-637X -
Journal articleSchwadron NA, Bale SD, Bonnell J, et al., 2024,
Parker Solar Probe Observations of Energetic Particles in the Flank of a Coronal Mass Ejection Close to the Sun
, ASTROPHYSICAL JOURNAL, Vol: 970, ISSN: 0004-637X -
Journal articleWilson Kemsley S, Ceppi P, Andersen H, et al., 2024,
A systematic evaluation of high-cloud controlling factors
, Atmospheric Chemistry and Physics, Vol: 24, Pages: 8295-8316, ISSN: 1680-7316Clouds strongly modulate the top-of-the-atmosphere energy budget and are a major source of uncertainty in climate projections. “Cloud controlling factor” (CCF) analysis derives relationships between large-scale meteorological drivers and cloud radiative anomalies, which can be used to constrain cloud feedback. However, the choice of meteorological CCFs is crucial for a meaningful constraint. While there is rich literature investigating ideal CCF setups for low-level clouds, there is a lack of analogous research explicitly targeting high clouds. Here, we use ridge regression to systematically evaluate the addition of five candidate CCFs to previously established core CCFs within large spatial domains to predict longwave high-cloud radiative anomalies: upper-tropospheric static stability (SUT), sub-cloud moist static energy, convective available potential energy, convective inhibition, and upper-tropospheric wind shear (ΔU300). We identify an optimal configuration for predicting high-cloud radiative anomalies that includes SUT and ΔU300 and show that spatial domain size is more important than the selection of CCFs for predictive skill. We also find an important discrepancy between the optimal domain sizes required for predicting locally and globally aggregated radiative anomalies. Finally, we scientifically interpret the ridge regression coefficients, where we show that SUT captures physical drivers of known high-cloud feedbacks and deduce that the inclusion of SUT into observational constraint frameworks may reduce uncertainty associated with changes in anvil cloud amount as a function of climate change. Therefore, we highlight SUT as an important CCF for high clouds and longwave cloud feedback.
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Journal articleLester JG, Graven HD, Khatiwala S, et al., 2024,
Changes in Oceanic Radiocarbon and CFCs Since the 1990s
, JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS, Vol: 129, ISSN: 2169-9275 -
Journal articleMathews J, Czaja A, 2024,
Oceanic maintenance of atmospheric blocking in wintertime in the North Atlantic
, Climate Dynamics, Vol: 62, ISSN: 0930-7575The connection between atmospheric blocking over the North Atlantic and the diabatic influence of the Gulf Stream is investigated using potential vorticity and moist potential vorticity diagnostics in the ERA5 reanalysis data set during wintertime (1979 - 2020). In line with previous research, the reliance atmospheric blocking has on turbulent heat fluxes over the Gulf Stream and its extension, for induction and maintenance, is shown to be significant. The air-sea heat flux generates negative potential vorticity air masses in the atmospheric boundary layer. These air masses subsequently contribute to the block’s negative potential vorticity anomaly at upper levels through ascending motion in the warm conveyor belt. It is shown that the block’s size and frequency partially depends on oceanic preconditioning via anomalous oceanic heat transport and heat content, prior to the blocking event, both of which allow for stronger turbulent heat fluxes. It is further hypothesized that the block feeds back positively on itself through the advection of cold dry air over the Gulf Stream, sustaining this air-sea interaction. This in turn decreases ocean heat content, eventually halting this air-sea interaction and severing the atmospheric block from its maintenance pathway.
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Journal articleAcevski M, Masters A, ZomerdijkRussell S, 2024,
Asymmetry in Uranus' high energy proton radiation belt
, Geophysical Research Letters, Vol: 51, ISSN: 0094-8276Uranus is one of the least explored planets in our solar system, it exhibits a unique magnetic field structure which was observed by NASA's Voyager 2 mission nearly 50 years ago. Notably, Uranus displays extreme magnetic field asymmetry, a feature exclusive to the icy giants. We use the Boris algorithm to investigate how high energy protons behave within this unusual magnetic field, which is motivated by Voyager 2's observation of lower-than-expected high energy proton radiation belt intensities at Uranus. When considering full drift motions of high energy protons around Uranus, the azimuthal drift velocity can vary by as much as 15% around the planet. This results in areas around Uranus where particles will be more depleted (faster drift) and other regions where there is a surplus of particles (slower drift). This could provide a partial explanation for the “weak” proton radiation belts observed by Voyager 2.
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Journal articleKasoar M, Perkins O, Millington JDA, et al., 2024,
Model fires, not ignitions: capturing the human dimension of global fire regimes
, Cell Reports Sustainability, Vol: 1, ISSN: 2949-7906Fire regimes are intrinsically shaped by humans, but current global fire models do not reflect the diverse objectives humans have for managing fire. With new data sources and collaboration across disciplines, an improved understanding of human influences on fire regimes is increasingly possible and essential to represent.
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Journal articleMülmenstädt J, Gryspeerdt E, Dipu S, et al., 2024,
General circulation models simulate negative liquid water path–droplet number correlations, but anthropogenic aerosols still increase simulated liquid water path
, Atmospheric Chemistry and Physics, Vol: 24, Pages: 7331-7345, ISSN: 1680-7316General circulation models' (GCMs) estimates of the liquid water path adjustment to anthropogenic aerosol emissions differ in sign from other lines of evidence. This reduces confidence in estimates of the effective radiative forcing of the climate by aerosol–cloud interactions (ERFaci). The discrepancy is thought to stem in part from GCMs' inability to represent the turbulence–microphysics interactions in cloud-top entrainment, a mechanism that leads to a reduction in liquid water in response to an anthropogenic increase in aerosols. In the real atmosphere, enhanced cloud-top entrainment is thought to be the dominant adjustment mechanism for liquid water path, weakening the overall ERFaci. We show that the latest generation of GCMs includes models that produce a negative correlation between the present-day cloud droplet number and liquid water path, a key piece of observational evidence supporting liquid water path reduction by anthropogenic aerosols and one that earlier-generation GCMs could not reproduce. However, even in GCMs with this negative correlation, the increase in anthropogenic aerosols from preindustrial to present-day values still leads to an increase in the simulated liquid water path due to the parameterized precipitation suppression mechanism. This adds to the evidence that correlations in the present-day climate are not necessarily causal. We investigate sources of confounding to explain the noncausal correlation between liquid water path and droplet number. These results are a reminder that assessments of climate parameters based on multiple lines of evidence must carefully consider the complementary strengths of different lines when the lines disagree.
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Journal articleGraven HD, Warren H, Gibbs HK, et al., 2024,
Bomb radiocarbon evidence for strong global carbon uptake and turnover in terrestrial vegetation
, Science, Vol: 384, Pages: 1335-1339, ISSN: 0036-8075Vegetation and soils are taking up approximately 30% of anthropogenic carbon dioxide emissions because of small imbalances in large gross carbon exchanges from productivity and turnover that are poorly constrained. We combined a new budget of radiocarbon produced by nuclear bomb testing in the 1960s with model simulations to evaluate carbon cycling in terrestrial vegetation. We found that most state-of-the-art vegetation models used in the Coupled Model Intercomparison Project underestimated the radiocarbon accumulation in vegetation biomass. Our findings, combined with constraints on vegetation carbon stocks and productivity trends, imply that net primary productivity is likely at least 80 petagrams of carbon per year presently, compared with the 43 to 76 petagrams per year predicted by current models. Storage of anthropogenic carbon in terrestrial vegetation is likely more short-lived and vulnerable than previously predicted.
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Journal articleAmtmann C, Pollinger A, Ellmeier M, et al., 2024,
Accuracy of the scalar magnetometer aboard ESA's JUICE mission
, GEOSCIENTIFIC INSTRUMENTATION METHODS AND DATA SYSTEMS, Vol: 13, Pages: 177-191, ISSN: 2193-0856 -
Journal articleHou C, Rouillard AP, He J, et al., 2024,
Connecting Solar Wind Velocity Spikes Measured by Solar Orbiter and Coronal Brightenings Observed by SDO
, ASTROPHYSICAL JOURNAL LETTERS, Vol: 968, ISSN: 2041-8205 -
Journal articleKrupar V, Kruparova O, Szabo A, et al., 2024,
Radial Variations in Solar Type III Radio Bursts
, ASTROPHYSICAL JOURNAL LETTERS, Vol: 967, ISSN: 2041-8205 -
Journal articleVasko IY, Mozer FS, Bowen T, et al., 2024,
Resonance of Low-frequency Electromagnetic and Ion-sound Modes in the Solar Wind
, ASTROPHYSICAL JOURNAL LETTERS, Vol: 967, ISSN: 2041-8205 -
Journal articleJebaraj IC, Agapitov O, Krasnoselskikh V, et al., 2024,
Acceleration of Electrons and Ions by an "Almost" Astrophysical Shock in the Heliosphere
, ASTROPHYSICAL JOURNAL LETTERS, Vol: 968, ISSN: 2041-8205 -
Journal articleAgiwal O, Cao H, Hsu H-W, et al., 2024,
Current Events at Saturn: Ring-Planet Electromagnetic Coupling
, PLANETARY SCIENCE JOURNAL, Vol: 5
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