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Journal articlewang S, Toumi R, 2019,
Impact of dry midlevel air on the tropical cyclone outer circulation
, Journal of the Atmospheric Sciences, Vol: 76, Pages: 1809-1826, ISSN: 0022-4928The impact of dry midlevel air on the outer circulation of tropical cyclones is investigated in idealized simulations with and without a moist envelope protecting the inner core. It is found that a dry midlevel layer away from the cyclone center can broaden the outer primary circulation and thus the overall destructive potential at both developing and mature stages. The midlevel outer drying enhances the horizontal gradient of latent heating in the rainbands and drives the expansion of the outer circulation. The moist convection at large radii is suppressed rapidly after the midlevel air is dried in the outer rainbands. An enhanced horizontal gradient of latent heating initiates a radial-vertical overturning circulation anomaly in the rainbands. This anomalous overturning circulation accelerates the radial inflow of the main secondary circulation, increases the angular momentum import, and thus increases the cyclone size. The dry air, mixed into the boundary layer from the midtroposphere, is “recharged” by high enthalpy fluxes due to the increased thermodynamical disequilibrium above the sea surface. This “recharge” process protects the eyewall convection from the environmental dry air ventilation. The proposed mechanism may explain the continuous expansion in the tropical cyclone outer circulation after maturity as found in observations.
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Journal articleLasslop G, Coppola A, Voulgarakis A, et al., 2019,
Influence of Fire on the Carbon Cycle and Climate
, CURRENT CLIMATE CHANGE REPORTS, Vol: 5, Pages: 112-123, ISSN: 2198-6061 -
Journal articleMatteini L, Stansby D, Horbury TS, et al., 2019,
The rotation angle distribution underlying magnetic field fluctuations in the 1/f range of solar wind turbulent spectra
, Il Nuovo Cimento C – Colloquia and Communications in Physics, Vol: 42, ISSN: 2037-4909We discuss properties of large amplitude magnetic field fluctuationsduring fast Alfv ́eenic solar wind streams, focussing on the statistics of the rotationangle between consecutive magnetic field vector measurements for different scalesin the plasma. Since in the fast solar wind fluctuations preserve the modulus ofthe magnetic field to a good approximation, the tip of the magnetic field vector isobserved to move on a sphere of approximately constant radius|B|.Wethencom-pare statistics of solar wind measurements with that of a simple model of a randomwalk bounded on a spherical surface. The analogy consists in the fact that in bothsystems the geometrical constraint imposes a limiting amplitude at large separa-tions and thus introduces a break scale in the power spectrum of the fluctuations,leading to a shallower slope for scales where the fluctuations amplitude becomesscale-independent. However, while in the case of the random walk the saturationof the fluctuations occurs when the pattern becomes uniform on the sphere (flatdistribution of the cosine of the rotation angle), transitioning then to a white noiseregime, in the solar wind magnetic field fluctuations saturate in amplitude maintain-ing a preferential direction. We suggest that this behaviour is due to the presence ofthe background interplanetary magnetic field, which keeps some long-range memoryin the system also when the fluctuations becomes independent of the scale. Thislong-range correlation is a necessary ingredient in order to produce the 1/fspectrumobserved at large scales in the solar wind.
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Journal articleJohnston C, Cargill P, antolin P, et al., 2019,
The effects of numerical resolution, heating timescales and background heating on thermal non-equilibrium in coronal loops
, Astronomy and Astrophysics, Vol: 625, ISSN: 0004-6361Thermal non-equilibrium (TNE) is believed to be a potentially important process in understanding some properties ofthe magnetically closed solar corona. Through one-dimensional hydrodynamic models, this paper addresses the importanceof the numerical spatial resolution, footpoint heating timescales and background heating on TNE. Inadequatetransition region (TR) resolution can lead to significant discrepancies in TNE cycle behaviour, with TNE being suppressedin under-resolved loops. A convergence on the periodicity and plasma properties associated with TNE requiredspatial resolutions of less than 2 km for a loop of length 180 Mm. These numerical problems can be resolved using anapproximate method that models the TR as a discontinuity using a jump condition, as proposed by Johnston et al.(2017a,b). The resolution requirements (and so computational cost) are greatly reduced while retaining good agreementwith fully resolved results. Using this approximate method we (i) identify different regimes for the response of coronalloops to time-dependent footpoint heating including one where TNE does not arise and (ii) demonstrate that TNE in aloop with footpoint heating is suppressed unless the background heating is sufficiently small. The implications for thegenerality of TNE are discussed.
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Journal articleCobb A, Czaja A, 2019,
Mesoscale Signature of the North Atlantic Oscillation and Its Interaction With the Ocean
, GEOPHYSICAL RESEARCH LETTERS, Vol: 46, Pages: 5575-5581, ISSN: 0094-8276 -
Journal articleInai Y, Fujita R, Machida T, et al., 2019,
Seasonal characteristics of trace gas transport into the extratropical upper troposphere and lower stratosphere
, ATMOSPHERIC CHEMISTRY AND PHYSICS, Vol: 19, Pages: 7073-7103, ISSN: 1680-7316- Author Web Link
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- Citations: 4
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Journal articleBanks JR, Huenerbein A, Heinold B, et al., 2019,
The sensitivity of the colour of dust in MSG-SEVIRI Desert Dust infrared composite imagery to surface and atmospheric conditions
, Atmospheric Chemistry and Physics, Vol: 19, Pages: 6893-6911, ISSN: 1680-7316Infrared “Desert Dust” composite imagery taken by the Spinning Enhanced Visible and InfraRed Imager (SEVIRI), onboard the Meteosat Second Generation (MSG) series of satellites above the equatorial East Atlantic, has been widely used for more than a decade to identify and track the presence of dust storms from and over the Sahara Desert, the Middle East, and southern Africa. Dust is characterised by distinctive pink colours in the Desert Dust false-colour imagery; however, the precise colour is influenced by numerous environmental properties, such as the surface thermal emissivity and skin temperature, the atmospheric water vapour content, the quantity and height of dust in the atmosphere, and the infrared optical properties of the dust itself. For this paper, simulations of SEVIRI infrared measurements and imagery have been performed using a modelling system, which combines dust concentrations simulated by the aerosol transport model COSMO-MUSCAT (COSMO: COnsortium for Small-scale MOdelling; MUSCAT: MUltiScale Chemistry Aerosol Transport Model) with radiative transfer simulations from the RTTOV (Radiative Transfer for TOVS) model. Investigating the sensitivity of the synthetic infrared imagery to the environmental properties over a 6-month summertime period from 2011 to 2013, it is confirmed that water vapour is a major control on the apparent colour of dust, obscuring its presence when the moisture content is high. Of the three SEVIRI channels used in the imagery (8.7, 10.8, and 12.0 µm), the channel at 10.8 µm has the highest atmospheric transmittance and is therefore the most sensitive to the surface skin temperature. A direct consequence of this sensitivity is that the background desert surface exhibits a strong diurnal cycle in colour, with light blue colours possible during the day and purple hues prevalent at night. In dusty scenes, the clearest pink colours arise from high-altitude dust in dry atmospheres. Elevated dust
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Journal articleCui X, Newman S, Xu X, et al., 2019,
Atmospheric observation-based estimation of fossil fuel CO<sub>2</sub> emissions from regions of central and southern California
, SCIENCE OF THE TOTAL ENVIRONMENT, Vol: 664, Pages: 381-391, ISSN: 0048-9697- Author Web Link
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- Citations: 10
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Journal articlePhan TD, Eastwood JP, Shay MA, et al., 2019,
Publisher Correction: Electron magnetic reconnection without ion coupling in Earth's turbulent magnetosheath
, Nature, Vol: 569, Pages: E9-E9, ISSN: 0028-0836Change history: In this Letter, the y-axis values in Fig. 3f should go from 4 to -8 (rather than from 4 to -4), the y-axis values in Fig. 3h should appear next to the major tick marks (rather than the minor ticks), and in Fig. 1b, the arrows at the top and bottom of the electron-scale current sheet were going in the wrong direction; these errors have been corrected online.
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Journal articleBowen TA, Zhivun E, Wickenbrock A, et al., 2019,
A network of magnetometers for multi-scale urban science and informatics
, GEOSCIENTIFIC INSTRUMENTATION METHODS AND DATA SYSTEMS, Vol: 8, Pages: 129-138, ISSN: 2193-0856- Author Web Link
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- Citations: 5
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Journal articleBarnes D, Davies JA, Harrison RA, et al., 2019,
CMEs in the heliosphere: II. A statistical analysis of the kinematic properties derived from single-spacecraft geometrical modelling techniques applied to CMEs detected in the heliosphere from 2007 to 2017 by STEREO/HI-1
, Solar Physics, Vol: 294, ISSN: 0038-0938Recent observations with the Heliospheric Imagers (HIs) onboard the twin NASA Solar Terrestrial Relations Observatory (STEREO) spacecraft have provided unprecedented observations of a large number of coronal mass ejections (CMEs) in the inner heliosphere. In this article we discuss the generation of the HIGeoCAT CME catalogue and perform a statistical analysis of its events. The catalogue was generated as part of the EU FP7 HELCATS (Heliospheric Cataloguing, Analysis and Techniques Service) project ( www.helcats-fp7.eu/ ). It is created by generating time/elongation maps for CMEs using observations from the inner (HI-1) and outer (HI-2) cameras along a position angle close to the CME apex. Next, we apply single-spacecraft geometric-fitting techniques to determine the kinematic properties of these CMEs, including their speeds, propagation directions, and launch times. The catalogue contains a total of 1455 events (801 from STEREO-A and 654 from STEREO-B) from April 2007 to the end of August 2017. We perform a statistical analysis of the properties of CMEs in HIGeoCAT and compare the results with those from the Large Angle Spectrometric Coronagraph (LASCO) CDAW catalogues (Yashiro et al.J. Geophys. Res. Space Phys.109, A07105, 2004) and the COR-2 catalogue of Vourlidas et al. (Astrophys. J.838, 141, 2004) during the same period. We find that the distributions of both speeds and latitudes for the HIGeoCAT CMEs correlate with the sunspot number over the solar cycle. We also find that the HI-derived CME speed distributions are generally consistent with coronagraph catalogues over the solar cycle, albeit with greater absolute speeds due to the differing methods with which each is derived.
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Journal articleTang T, Shindell D, Faluvegi G, et al., 2019,
Comparison of effective radiative forcing calculations using multiple methods, drivers, and models
, Journal of Geophysical Research: Atmospheres, Vol: 124, Pages: 4382-4394, ISSN: 2169-897XAmerican Geophysical Union. All Rights Reserved. We compare six methods of estimating effective radiative forcing (ERF) using a set of atmosphere-ocean general circulation models. This is the first multiforcing agent, multimodel evaluation of ERF values calculated using different methods. We demonstrate that previously reported apparent consistency between the ERF values derived from fixed sea surface temperature simulations and linear regression holds for most climate forcings, excluding black carbon (BC). When land adjustment is accounted for, however, the fixed sea surface temperature ERF values are generally 10–30% larger than ERFs derived using linear regression across all forcing agents, with a much larger (~70–100%) discrepancy for BC. Except for BC, this difference can be largely reduced by either using radiative kernel techniques or by exponential regression. Responses of clouds and their effects on shortwave radiation show the strongest variability in all experiments, limiting the application of regression-based ERF in small forcing simulations.
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Journal articleYang L, Wang L, Li G, et al., 2019,
Electron Acceleration by ICME-driven Shocks at 1 au
, ASTROPHYSICAL JOURNAL, Vol: 875, ISSN: 0004-637X- Author Web Link
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- Citations: 16
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Journal articleGryspeerdt E, Goren T, Sourdeval O, et al., 2019,
Constraining the aerosol influence on cloud liquid water path
, Atmospheric Chemistry and Physics, Vol: 19, Pages: 5331-5347, ISSN: 1680-7316The impact of aerosols on cloud properties is one of the largest uncertainties in the anthropogenic radiative forcing of the climate. Significant progress has been made in constraining this forcing using observations, but uncertainty remains, particularly in the magnitude of cloud rapid adjustments to aerosol perturbations. Cloud liquid water path (LWP) is the leading control on liquid-cloud albedo, making it important to observationally constrain the aerosol impact on LWP.Previous modelling and observational studies have shown that multiple processes play a role in determining the LWP response to aerosol perturbations, but that the aerosol effect can be difficult to isolate. Following previous studies using mediating variables, this work investigates use of the relationship between cloud droplet number concentration (Nd) and LWP for constraining the role of aerosols. Using joint-probability histograms to account for the non-linear relationship, this work finds a relationship that is broadly consistent with previous studies. There is significant geographical variation in the relationship, partly due to role of meteorological factors (particularly relative humidity). The Nd–LWP relationship is negative in the majority of regions, suggesting that aerosol-induced LWP reductions could offset a significant fraction of the instantaneous radiative forcing from aerosol–cloud interactions (RFaci).However, variations in the Nd–LWP relationship in response to volcanic and shipping aerosol perturbations indicate that the Nd–LWP relationship overestimates the causal Nd impact on LWP due to the role of confounding factors. The weaker LWP reduction implied by these “natural experiments” means that this work provides an upper bound to the radiative forcing from aerosol-induced changes in the LWP.
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Journal articleMisios S, Gray LJ, Knudsen MF, et al., 2019,
Slowdown of the Walker circulation at solar cycle maximum
, Proceedings of the National Academy of Sciences of USA, Vol: 116, Pages: 7186-7191, ISSN: 0027-8424The Pacific Walker Circulation (PWC) fluctuates on interannual and multidecadal timescales under the influence of internal variability and external forcings. Here, we provide observational evidence that the 11-y solar cycle (SC) affects the PWC on decadal timescales. We observe a robust reduction of east-west sea-level pressure gradients over the Indo-Pacific Ocean during solar maxima and the following 1-2 y. This reduction is associated with westerly wind anomalies at the surface and throughout the equatorial troposphere in the western/central Pacific paired with an eastward shift of convective precipitation that brings more rainfall to the central Pacific. We show that this is initiated by a thermodynamical response of the global hydrological cycle to surface warming, further amplified by atmosphere-ocean coupling, leading to larger positive ocean temperature anomalies in the equatorial Pacific than expected from simple radiative forcing considerations. The observed solar modulation of the PWC is supported by a set of coupled ocean-atmosphere climate model simulations forced only by SC irradiance variations. We highlight the importance of a muted hydrology mechanism that acts to weaken the PWC. Demonstration of this mechanism acting on the 11-y SC timescale adds confidence in model predictions that the same mechanism also weakens the PWC under increasing greenhouse gas forcing.
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Journal articleHesse M, Norgren C, Tenfjord P, et al., 2019,
Erratum: "On the role of separatrix instabilities in heating the reconnection outflow region" [Phys. Plasmas 25, 122902 (2018)]
, Physics of Plasmas, Vol: 26, ISSN: 1070-664XIn a recent paper1 about electron heating at the reconnection separatrix, two figures depicting the contributions to the electron energy balance and the contribution to the total, quasi-viscous heating are incorrectly displayed. The correct figures are as follows: [Table Presented].
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Journal articleKajdic P, Preisser L, Blanco-Cano X, et al., 2019,
First Observations of Irregular Surface of Interplanetary Shocks at Ion Scales by <i>Cluster</i>
, ASTROPHYSICAL JOURNAL LETTERS, Vol: 874, ISSN: 2041-8205- Author Web Link
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- Citations: 26
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Journal articleLai T-K, Menelaou K, Yau MK, 2019,
Barotropic Instability across the Moat and Inner Eyewall Dissipation: A Numerical Study of Hurricane Wilma (2005)
, JOURNAL OF THE ATMOSPHERIC SCIENCES, Vol: 76, Pages: 989-1013, ISSN: 0022-4928 -
Book chapterGryspeerdt E, 2019,
Ruskin and Meteorology
, Ruskin, Turner and the Storm Cloud, Editors: Cooper, Johns, Publisher: Paul Holberton Publishing, ISBN: 978-1-911300-60-1 -
Journal articleMüller-Wodarg ICF, Koskinen TT, Moore L, et al., 2019,
Atmospheric waves and their possible effect on the thermal structure of Saturn's thermosphere
, Geophysical Research Letters, Vol: 46, Pages: 2372-2380, ISSN: 0094-8276Atmospheric waves have been discovered for the first time in Saturn's neutral upper atmosphere (thermosphere). Waves may be generated from instabilities, convective storms or other atmospheric phenomena. The inferred wave amplitudes change little with height within the sampled region, raising the possibility of the waves being damped, which in turn may enhance the eddy friction within the thermosphere. Using our Saturn Thermosphere Ionosphere General Circulation Model, we explore the parameter space of how an enhanced Rayleigh drag in different latitude regimes would affect the global circulation pattern within the thermosphere and, in turn, its global thermal structure. We find that Rayleigh drag of sufficient magnitude at midlatitudes may reduce the otherwise dominant Coriolis forces and enhance equatorward winds to transport energy from poles toward the equator, raising the temperatures there to observed values. Without this Rayleigh drag, energy supplied into the polar upper atmosphere by magnetosphere‐atmosphere coupling processes remains trapped at high latitudes and causes low‐latitude thermosphere temperatures to remain well below the observed levels. Our simulations thus suggest that giant planet upper atmosphere global circulation models need to include additional Rayleigh drag in order to capture the effects of physical processes otherwise not resolved by the codes.
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Journal articleHanson ELM, Agapitov OV, Mozer FS, et al., 2019,
Cross-Shock Potential in Rippled Versus Planar Quasi-Perpendicular Shocks Observed by MMS
, GEOPHYSICAL RESEARCH LETTERS, Vol: 46, Pages: 2381-2389, ISSN: 0094-8276- Author Web Link
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- Citations: 23
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Journal articleFox S, Mendrok J, Eriksson P, et al., 2019,
Airborne validation of radiative transfer modelling of ice clouds at millimetre and sub-millimetre wavelengths
, ATMOSPHERIC MEASUREMENT TECHNIQUES, Vol: 12, Pages: 1599-1617, ISSN: 1867-1381 -
Journal articleBrophy K, Graven H, Manning AJ, et al., 2019,
Characterizing uncertainties in atmospheric inversions of fossil fuel CO2 emissions in California
, Atmospheric Chemistry and Physics, Vol: 19, Pages: 2991-3006, ISSN: 1680-7316Atmospheric inverse modelling has become an increasingly useful tool for evaluating emissions of greenhouse gases including methane, nitrous oxide, and synthetic gases such as hydrofluorocarbons (HFCs). Atmospheric inversions for emissions of CO2 from fossil fuel combustion (ffCO2) are currently being developed. The aim of this paper is to investigate potential errors and uncertainties related to the spatial and temporal prior representation of emissions and modelled atmospheric transport for the inversion of ffCO2 emissions in the US state of California. We perform simulation experiments based on a network of ground-based observations of CO2 concentration and radiocarbon in CO2 (a tracer of ffCO2), combining prior (bottom-up) emission models and transport models currently used in many atmospheric studies. The potential effect of errors in the spatial and temporal distribution of prior emission estimates is investigated in experiments by using perturbed versions of the emission estimates used to create the pseudo-data. The potential effect of transport error was investigated by using three different atmospheric transport models for the prior and pseudo-data simulations. We find that the magnitude of biases in posterior total state emissions arising from errors in the spatial and temporal distribution in prior emissions in these experiments are 1 %–15 % of posterior total state emissions and are generally smaller than the 2σ uncertainty in posterior emissions. Transport error in these experiments introduces biases of −10 % to +6 % into posterior total state emissions. Our results indicate that uncertainties in posterior total state ffCO2 estimates arising from the choice of prior emissions or atmospheric transport model are on the order of 15 % or less for the ground-based network in California we consider. We highlight the need for temporal variations to be included in prior emissions and for continuing efforts to
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Journal articleStansby D, Horbury TS, Wallace S, et al., 2019,
Predicting Large-scale Coronal Structure for Parker Solar Probe Using Open Source Software
, Research Notes of the AAS, Vol: 3, Pages: 57-57 -
Journal articlePerrone D, Stansby D, Horbury T, et al., 2019,
Radial evolution of the solar wind in pure high-speed streams: HELIOS revised observations
, Monthly Notices of the Royal Astronomical Society, Vol: 483, Pages: 3730-3737, ISSN: 0035-8711Spacecraft observations have shown that the proton temperature in the solar wind falls off with radial distance more slowly than expected for an adiabatic prediction. Usually, previous studies have been focused on the evolution of the solar-wind plasma by using the bulk speed as an order parameter to discriminate different regimes. In contrast, here, we study the radial evolution of pure and homogeneous fast streams (i.e. well-defined streams of coronal-hole plasma that maintain their identity during several solar rotations) by means of re-processed particle data, from the HELIOS satellites between 0.3 and 1 au. We have identified 16 intervals of unperturbed high-speed coronal-hole plasma, from three different sources and measured at different radial distances. The observations show that, for all three streams, (i) the proton density decreases as expected for a radially expanding plasma, unlike previous analysis that found a slower decrease; (ii) the magnetic field deviates from the Parker prediction, with the radial component decreasing more slowly and the tangential more quickly than expected; (iii) the double-adiabatic invariants are violated and an increase of entropy is observed; (iv) the collisional frequency is not constant, but decreases as the plasma travels away from the Sun. This work provides an insight into the heating problem in pure fast solar wind, fitting in the context of the next solar missions, and, especially for Parker Solar Probe, it enables us to predict the high-speed solar-wind environment much closer to the Sun.
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Journal articleDAmicis R, Matteini L, Bruno R, 2019,
On slow solar wind with high Alfvénicity: from composition and microphysics to spectral properties
, Monthly Notices of the Royal Astronomical Society, Vol: 483, Pages: 4665-4677, ISSN: 0035-8711Alfvénic fluctuations are very common features in the solar wind and are found especially within the main portion of fast-wind streams while the slow wind usually is less Alfvénic and more variable. In general, the fast and slow winds show many differences, which span from the large-scale structure to small-scale phenomena, including also a different turbulent behaviour. Recent studies, however, have shown that even the slow wind can sometimes be highly Alfvénic, with fluctuations as large as those of the fast wind. This study is devoted to presenting many facets of this Alfvénic slow solar wind, including for example the study of the source regions and their connection to coronal structures, large-scale properties, and microscale phenomena and also impact on the spectral features. This study will be conducted performing a comparative analysis with the typical slow wind and with the fast wind. It has been found that the fast wind and the Alfvénic slow wind share common characteristics, probably attributable to their similar solar origin, that is coronal-hole solar wind. Given these similarities, it is suggested that in the Alfvénic slow wind a major role is played by the superradial expansion responsible for the lower velocity. Relevant implications of these new findings for the upcoming Solar Orbiter and Solar Probe Plus missions, and more in general for turbulence measurements close to the Sun, will be discussed.
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Journal articleStansby D, Perrone D, Matteini L, et al., 2019,
Alpha particle thermodynamics in the inner heliosphere fast solar wind
, Astronomy and Astrophysics, Vol: 623, ISSN: 0004-6361Context. Plasma processes occurring in the corona and solar wind can be probed by studying the thermodynamic properties ofdifferent ion species. However, most in-situ observations of positive ions in the solar wind are taken at 1 AU, where information ontheir solar source properties may have been irreversibly erased.Aims. In this study we aimed to use the properties of alpha particles at heliocentric distances between 0.3 and 1 AU to study plasmaprocesses occurring at the points of observation, and to infer processes occurring inside 0.3 AU by comparing our results to previousremote sensing observations of the plasma closer to the Sun.Methods. We reprocessed the original Helios positive ion distribution functions, isolated the alpha particle population, and computedthe alpha particle number density, velocity, and magnetic field perpendicular and parallel temperatures. We then investigated the radialvariation of alpha particle temperatures in fast solar wind observed between 0.3 and 1 AU.Results. Between 0.3 and 1 AU alpha particles are heated in the magnetic field perpendicular direction, and cooled in the magneticfield parallel direction. Alpha particle evolution is bounded by the alpha firehose instability threshold, which provides one possiblemechanism to explain the observed parallel cooling and perpendicular heating. Closer to the Sun our observations suggest that thealpha particles undergo heating in the perpendicular direction, whilst the large magnetic field parallel temperatures observed at 0.3 AUmay be due to the combined effect of double adiabatic expansion and alpha particle deceleration inside 0.3 AU.
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Journal articleGoodrich KA, Ergun R, Schwartz SJ, et al., 2019,
Impulsively Reflected Ions: A Plausible Mechanism for Ion Acoustic Wave Growth in Collisionless Shocks
, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 124, Pages: 1855-1865, ISSN: 2169-9380- Author Web Link
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- Citations: 15
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Journal articleKilpua EKJ, Turner DL, Jaynes AN, et al., 2019,
Outer Van Allen Radiation Belt Response to Interacting Interplanetary Coronal Mass Ejectionsy
, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 124, Pages: 1927-1947, ISSN: 2169-9380 -
Journal articleGraven H, Hocking T, Zazzeri G, 2019,
Detection of fossil and biogenic methane at regional scales using atmospheric radiocarbon
, Earth's Future, Vol: 7, Pages: 283-299, ISSN: 2328-4277Regional emissions of methane and their attribution to a variety of sources presently have large uncertainties. Measurements of radiocarbon (14C) in methane (CH4) may provide a method for identifying regional CH4 emissions from fossil versus biogenic sources because adding 14C‐free fossil carbon reduces the 14C/C ratio (Δ14CH4) in atmospheric CH4 much more than biogenic carbon does. We describe an approach for estimating fossil and biogenic CH4 at regional scales using atmospheric Δ14CH4 observations. As a case study to demonstrate expected Δ14CH4 and Δ14CH4‐CH4 relationships, we simulate and compare Δ14CH4 at a network of sites in California using two gridded CH4 emissions estimates (Emissions Database for Global Atmospheric Research, EDGAR, and Gridded Environmental Protection Agency, GEPA) and the CarbonTracker‐Lagrange model for 2014, and for 2030 under business‐as‐usual and mitigation scenarios. The fossil fraction of CH4 (F) is closely linked with the simulated Δ14CH4‐CH4 slope and differences of 2–21% in median F are found for EDGAR versus GEPA in 2014, and 7–10% for business‐as‐usual and mitigation scenarios in 2030. Differences of 10% in F for >200 ppb of added CH4 produce differences of >10‰ in Δ14CH4, which are likely detectable from regular observations. Nuclear power plant 14CH4 emissions generally have small simulated median influences on Δ14CH4 (0–7‰), but under certain atmospheric conditions they can be much stronger (>30‰) suggesting they must be considered in applications of Δ14CH4 in California. This study suggests that atmospheric Δ14CH4 measurements could provide powerful constraints on regional CH4 emissions, complementary to other monitoring techniques.
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