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Journal articleBeth A, Garnier P, Toublanc D, et al., 2015, , Icarus, Vol: 266, Pages: 423-432, ISSN: 1090-2643
The planetary exospheres are poorly known in their outer parts, since the neutral densities are low compared with the instruments detection capabilities. The exospheric models are thus often the main source of information at such high altitudes. We present a new way to take into account analytically the additional effect of the radiation pressure on planetary exospheres. In a series of papers, we present with an Hamiltonian approach the effect of the radiation pressure on dynamical trajectories, density profiles and escaping thermal flux. Our work is a generalization of the study by Bishop and Chamberlain (1989). In this second part of our work, we present here the density profiles of atomic Hydrogen in planetary exospheres subject to the radiation pressure. We first provide the altitude profiles of ballistic particles (the dominant exospheric population in most cases), which exhibit strong asymmetries that explain the known geotail phenomenon at Earth. The radiation pressure strongly enhances the densities compared with the pure gravity case (i.e. the Chamberlain profiles), in particular at noon and midnight. We finally show the existence of an exopause that appears naturally as the external limit for bounded particles, above which all particles are escaping.
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Book chapterHaigh JD, Matthes K, Hanslmeier A, 2015,
The Impact of Solar Variability on Climate.
, Earth’s climate response to a changing Sun, Editors: Lilensten, Dudok de Wit, Matthes, ISBN: 978-2-7598-1733-7 -
Book chapterEastwood J, 2015, , Magnetospheric Plasma Physics: The Impact of Jim Dungey’s Research, Editors: Southwood, Cowley, Mitton, Publisher: Springer, Pages: 181-197, ISBN: 9783319183589
This book makes good background reading for much of modern magnetospheric physics.
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Journal articleYan GQ, Mozer FS, Phan T, et al., 2015, , Advances in Space Research, Vol: 58, Pages: 208-217, ISSN: 0273-1177
During a one-hour interval of interplanetary magnetic field (IMF) Bz≈0 nT, the equatorialspacecraft Double Star TC-1 encountered the dawn flank magnetopause many times at the magnetic localtime (MLT) of about 08:00 and the latitude of about -27°. During each encounter, reconnection jets wereobserved with their velocities up to more than 500 km/s, significantly higher than the background flow inthe magnetosheath. The fast flows match the theoretical prediction of Alfvénic acceleration well. Themedium temperature and density of ions in the boundary layer indicate the open magnetic field topologyinside this layer. The mainly southward and tailward flows of the plasma jets alongside with the negativeslopes of the Walén test indicate that the spacecraft was located south of the reconnection site, consistentwith both anti-parallel and component reconnection models. The accelerated flows were observed lastingfor about one hour, with some modulations by the oscillations of the magnetopause, but no reversals inthe direction of Vz were found during the interval. The significantly enhanced flows in the boundary layercompared to the adjacent magnetosheath indicate that the reconnection was quasi-continuously active atthe magnetopause northward of the spacecraft under such IMF conditions. At the same time, the bipolarsignatures in BN with enhancements of the magnetic field indicate the occurrence of the Flux TransferEvents (FTEs). The observed reconnection was quasi-continuous, whereas the simultaneouslyaccompanied FTEs were time-dependent under the IMF Bz≈0 nT. For this event, however, it is notpossible to identify whether the reconnection was anti-parallel or component because the TC-1 was faraway from the reconnection site.
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Journal articleOsipov S, Stenchikov G, Brindley H, et al., 2015, , Atmospheric Chemistry and Physics, Vol: 15, Pages: 9537-9553, ISSN: 1680-7324
In this study we attempted to better quantify radiative effects of dust over the Arabian Peninsula and their dependence on input parameters. For this purpose we have developed a stand-alone column radiation transport model coupled with the Mie, T-matrix and geometric optics calculations and driven by reanalysis meteorological fields and atmospheric composition. Numerical experiments were carried out for a wide range of aerosol optical depths, including extreme values developed during the dust storm on 18–20 March 2012. Comprehensive ground-based observations and satellite retrievals were used to estimate aerosol optical properties, validate calculations and carry out radiation closure. The broadband surface albedo, fluxes at the bottom and top of the atmosphere as well as instantaneous dust radiative forcing were estimated both from the model and observations. Diurnal cycle of the shortwave instantaneous dust direct radiative forcing was studied for a range of aerosol and surface characteristics representative of the Arabian Peninsula. Mechanisms and parameters responsible for diurnal variability of the radiative forcing were evaluated. We found that intrinsic variability of the surface albedo and its dependence on atmospheric conditions, along with anisotropic aerosol scattering, are mostly responsible for diurnal effects.
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Journal articleChen CHK, Matteini L, Burgess D, et al., 2015, , Monthly Notices of the Royal Astronomical Society: Letters, Vol: 453, Pages: L64-L68, ISSN: 1745-3933
The solar wind magnetic field contains rotations at a broad range of scales, which have been extensively studied in the magnetohydrodynamics range. Here, we present an extension of this analysis to the range between ion and electron kinetic scales. The distribution of rotation angles was found to be approximately lognormal, shifting to smaller angles at smaller scales almost self-similarly, but with small, statistically significant changes of shape. The fraction of energy in fluctuations with angles larger than α was found to drop approximately exponentially with α, with e-folding angle 9.8° at ion scales and 0.66° at electron scales, showing that large angles (α > 30°) do not contain a significant amount of energy at kinetic scales. Implications for kinetic turbulence theory and the dissipation of solar wind turbulence are discussed.
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Book chapterSouthwood DJ, 2015,
Introduction: Jim Dungey and Magnetospheric Plasma Physics
, Magnetospheric Plasma Physics: The Impact of Jim Dungey’s Research, Editors: Southwood, Cowley, Mitton, Publisher: Springer, ISBN: 9783319183596This book makes good background reading for much of modern magnetospheric physics.
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BookSouthwood D, FRS SWHC, Mitton S, 2015,
Magnetospheric Plasma Physics: The Impact of Jim Dungey’s Research
, Publisher: Springer, ISBN: 9783319183596This book makes good background reading for much of modern magnetospheric physics.
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Book chapterSouthwood DJ, 2015,
From the Carrington Storm to the Dungey Magnetosphere
, Magnetospheric Plasma Physics: The Impact of Jim Dungey’s Research, Editors: Southwood, Cowley, Mitton, Publisher: Springer, Pages: 253-271, ISBN: 9783319183596This book makes good background reading for much of modern magnetospheric physics.
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Journal articleRichter I, Koenders C, Auster H-U, et al., 2015, , Annales Geophysicae, Vol: 33, Pages: 1031-1036, ISSN: 1432-0576
We report on magnetic field measurements madein the innermost coma of 67P/Churyumov-Gerasimenkoin its low activity state. Quasi-coherent, large-amplitude(δB/B ∼ 1), compressional magnetic field oscillations at5 ∼ 40 mHz dominate the immediate plasma environmentof the nucleus. This differs from previously studied cometinteractionregions where waves at the cometary ion gyrofrequenciesare the main feature. Thus classical pick-up iondriven instabilities are unable to explain the observations. We10 propose a cross-field current instability associated with newborncometary ion currents as a possible source mechanism
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Journal articleMatteini L, Schwartz SJ, Hellinger P, 2015, , Planetary and Space Science, ISSN: 1873-5088
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Journal articleTam KV, Hood AW, Browning PK, et al., 2015, , Astronomy & Astrophysics, Vol: 580, ISSN: 1432-0746
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Journal articleWang S, Toumi R, Czaja A, et al., 2015, , Quarterly Journal of the Royal Meteorological Society, Vol: 141, Pages: 3018-3029, ISSN: 1477-870X
A physically based analytic model (λ model) is presented to describe the wind profile of tropical cyclones in terms of the pressure deficit and a single shape parameter (λ). To test the λ model, an idealized full-physics numerical model is employed to provide wind-profile samples and also to show the influence of environmental temperature and the properties of initial vortices on tropical cyclone size. It is found that the λ model provides an accurate fit of the azimuthal wind profile at the top of the boundary layer. In the simulations, tropical cyclone size is sensitive to sea-surface temperature, upper tropospheric temperature and initial vortex structure. The numerical model confirms the assumed Gaussian distribution with width λ of the moist entropy in the boundary layer. A linear relationship between model cyclone size and inline image is found, in agreement with the λ model. The λ model predicts a weak relationship between tropical cyclone size and intensity, as is observed. In addition, the λ model suggests that change in tropical cyclone size should be closely related to angular momentum transport near the boundary layer, as has been found in observations. The good agreement of the λ model with the numerical model shows that the λ model could be a reasonable alternative for characterizing the wind structure of tropical cyclones with only one scaling parameter.
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Journal articleChen CHK, Matteini L, Burgess D, et al., 2015, , Monthly Notices of the Royal Astronomical Society Letters, Vol: 455, ISSN: 1745-3925
This is an erratum to the paper entitled 'Magnetic field rotations in the solar wind at kinetic scales", published in MNRAS, 2015, 453, L64. Fig. 1 appeared without the key. The correct image is given below.
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Journal articleGraven HD, 2015, , Proceedings of the National Academy of Sciences of the United States of America, Vol: 112, Pages: 9542-9545, ISSN: 1091-6490
Radiocarbon analyses are commonly used in a broad range of fields, including earth science, archaeology, forgery detection, isotope forensics, and physiology. Many applications are sensitive to the radiocarbon ((14)C) content of atmospheric CO2, which has varied since 1890 as a result of nuclear weapons testing, fossil fuel emissions, and CO2 cycling between atmospheric, oceanic, and terrestrial carbon reservoirs. Over this century, the ratio (14)C/C in atmospheric CO2 (Δ(14)CO2) will be determined by the amount of fossil fuel combustion, which decreases Δ(14)CO2 because fossil fuels have lost all (14)C from radioactive decay. Simulations of Δ(14)CO2 using the emission scenarios from the Intergovernmental Panel on Climate Change Fifth Assessment Report, the Representative Concentration Pathways, indicate that ambitious emission reductions could sustain Δ(14)CO2 near the preindustrial level of 0‰ through 2100, whereas "business-as-usual" emissions will reduce Δ(14)CO2 to -250‰, equivalent to the depletion expected from over 2,000 y of radioactive decay. Given current emissions trends, fossil fuel emission-driven artificial "aging" of the atmosphere is likely to occur much faster and with a larger magnitude than previously expected. This finding has strong and as yet unrecognized implications for many applications of radiocarbon in various fields, and it implies that radiocarbon dating may no longer provide definitive ages for samples up to 2,000 y old.
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Journal articleWeiss Z, Steers EBM, Pickering JC, 2015, , SPECTROCHIMICA ACTA PART B-ATOMIC SPECTROSCOPY, Vol: 110, Pages: 79-90, ISSN: 0584-8547
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- Citations: 23
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Journal articleCarr CM, Auster H-U, Apathy I, et al., 2015, , Science, Vol: 349, ISSN: 0036-8075
Knowledge of the magnetization of planetary bodies constrains their origin and evolution,as well as the conditions in the solar nebular at that time. On the basis of magneticfield measurements during the descent and subsequent multiple touchdown of the Rosettalander Philae on the comet 67P/Churyumov-Gerasimenko (67P), we show that no globalmagnetic field was detected within the limitations of analysis. The Rosetta Magnetometerand Plasma Monitor (ROMAP) suite of sensors measured an upper magnetic fieldmagnitude of less than 2 nanotesla at the cometary surface at multiple locations, withthe upper specific magnetic moment being <3.1 × 10−5 ampere–square meters perkilogram for meter-size homogeneous magnetized boulders. The maximum dipole momentof 67P is 1.6 × 108 ampere–square meters. We conclude that on the meter scale,magnetic alignment in the preplanetary nebula is of minor importance.
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Journal articleRyder CL, McQuaid JB, Flamant C, et al., 2015, , Atmospheric Chemistry and Physics, Vol: 15, Pages: 8479-8520, ISSN: 1680-7324
The Fennec climate programme aims to improve understanding of the Saharan climate system through a synergy of observations and modelling. We present a description of the Fennec airborne observations during 2011 and 2012 over the remote Sahara (Mauritania and Mali) and the advances in the understanding of mineral dust and boundary layer processes they have provided. Aircraft instrumentation aboard the UK FAAM BAe146 and French SAFIRE (Service des Avions Français Instrumentés pour la Recherche en Environnement) Falcon 20 is described, with specific focus on instrumentation specially developed for and relevant to Saharan meteorology and dust. Flight locations, aims and associated meteorology are described. Examples and applications of aircraft measurements from the Fennec flights are presented, highlighting new scientific results delivered using a synergy of different instruments and aircraft. These include (1) the first airborne measurement of dust particles sizes of up to 300 microns and associated dust fluxes in the Saharan atmospheric boundary layer (SABL), (2) dust uplift from the breakdown of the nocturnal low-level jet before becoming visible in SEVIRI (Spinning Enhanced Visible Infra-Red Imager) satellite imagery, (3) vertical profiles of the unique vertical structure of turbulent fluxes in the SABL, (4) in situ observations of processes in SABL clouds showing dust acting as cloud condensation nuclei (CCN) and ice nuclei (IN) at −15 °C, (5) dual-aircraft observations of the SABL dynamics, thermodynamics and composition in the Saharan heat low region (SHL), (6) airborne observations of a dust storm associated with a cold pool (haboob) issued from deep convection over the Atlas Mountains, (7) the first airborne chemical composition measurements of dust in the SHL region with differing composition, sources (determined using Lagrangian backward trajectory calculations) and absorption properties between 2011 and 2012, (8) coincident ozone and
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Journal articleYates JN, Southwood DJ, Dougherty MK, 2015, , Journal of Geophysical Research: Space Physics, Vol: 120, Pages: 5691-5693, ISSN: 2169-9402
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Journal articleVoulgarakis A, Marlier ME, Faluvegi G, et al., 2015, , Journal of Geophysical Research: Atmospheres, Vol: 120, Pages: 7157-7173, ISSN: 2169-897X
Fires are responsible for a range of gaseous and aerosol emissions. However, their influence onthe interannual variability of atmospheric trace gases and aerosols has not been systematically investigatedfrom a global perspective. We examine biomass burning emissions as a driver of interannual variability oflarge-scale abundances of short-lived constituents such as carbon monoxide (CO), hydroxyl radicals (OH),ozone, and aerosols using the Goddard Institute for Space Studies ModelE composition-climate model and arange of observations, with an emphasis on satellite information. Our model captures the observed variabilityof the constituents examined in most cases, but with substantial underestimates in boreal regions. Thestrongest interannual variability on a global scale is found for carbon monoxide (~10% for its global annualburden), while the lowest is found for tropospheric ozone (~1% for its global annual burden). Regionally,aerosol optical depth shows the largest variability which exceeds 50%. Areas of strong variability of bothaerosols and CO include the tropical land regions (especially Equatorial Asia and South America) and northernhigh latitudes, while even regions in the northern midlatitudes experience substantial interannual variability ofaerosols. Ozone variability peaks over equatorial Asia in boreal autumn, partly due to varying biomass burningemissions, and over the western and central Pacific in the rest of the year, mainly due to meteorologicalfluctuations. We find that biomass burning emissions are almost entirely responsible for global CO interannualvariability, and similarly important for OH variability. The same is true for global and regional aerosol variability,especially when not taking into account dust and sea-salt particles. We show that important implications canarise from such interannual influences for regional climate and air quality
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Journal articleMarsham JH, Parker DJ, Todd MC, et al., 2015, , Atmospheric Chemistry and Physics Discussions, Vol: 15, Pages: 19447-19476, ISSN: 1680-7367
The summertime Sahara Heat Low (SHL) is a key component of the West African Monsoon (WAM) system. Considerable uncertainty remains over the relative roles of water vapour and dust aerosols in controlling the radiation budget over the Sahara and therefore our ability to explain variability and trends in the SHL, and in turn, the WAM. Here, new observations from the Fennec field campaign during June 2011 and June 2012, together with satellite retrievals from GERB, are used to quantify how total column water vapour (TCWV) and dust aerosols (from aerosol optical depth, AOD) control day-to-day variations in energy balance in both observations and ECWMF reanalyses (ERA-I). The data show that the earth-atmosphere system is radiatively heated in June 2011 and 2012. It is TCWV that largely determines variations in daily mean TOA net flux and the net heating of the earth-atmosphere system. In contrast, dust provides the primary control on surface heating, but the decreased surface heating from dust is largely compensated by increased atmospheric heating, and so dust control on net TOA radiation is weak. Dust and TCWV are both important for direct atmospheric heating. ERA-I captures the control of TOA net flux by TCWV, with a positive correlation (r = 0.6) between observed and modelled TOA net radiation, despite the use of a monthly dust climatology in ERA-I that cannot capture the daily variations in dustiness. Variations in surface net radiation, and so the vertical profile of radiative heating, are not captured in ERA-I, since it does not capture variations in dust. Results show that ventilation of the SHL by cool moist air leads to a radiative warming, stabilising the SHL with respect to such perturbations. It is known that models struggle to capture the advective moistening of the SHL, especially that associated with mesoscale convective systems. Our results show that the typical model errors in Saharan water vapour will lead to substantial errors in the modelled TOA ener
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Journal articleBalikhin MA, Shprits YY, Walker SN, et al., 2015, , Nature Communications, Vol: 6, ISSN: 2041-1723
A number of modes of oscillations of particles and fields can exist in space plasmas. Since the early 1970s, space missions have observed noise-like plasma waves near the geomagnetic equator known as 'equatorial noise'. Several theories were suggested, but clear observational evidence supported by realistic modelling has not been provided. Here we report on observations by the Cluster mission that clearly show the highly structured and periodic pattern of these waves. Very narrow-banded emissions at frequencies corresponding to exact multiples of the proton gyrofrequency (frequency of gyration around the field line) from the 17th up to the 30th harmonic are observed, indicating that these waves are generated by the proton distributions. Simultaneously with these coherent periodic structures in waves, the Cluster spacecraft observes 'ring' distributions of protons in velocity space that provide the free energy for the waves. Calculated wave growth based on ion distributions shows a very similar pattern to the observations.
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Journal articleGryspeerdt E, Stier P, White BA, et al., 2015, , Atmospheric Chemistry and Physics, Vol: 15, Pages: 7557-7570, ISSN: 1680-7324
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Journal articleGood SW, Forsyth RJ, Raines JM, et al., 2015, , Astrophysical Journal, Vol: 807, Pages: 177-189, ISSN: 1538-4357
The Solar Orbiter and Solar Probe Plus missions will provide observations of magnetic clouds closer to the Sunthan ever before, and it will be good preparation for these missions to make full use of the most recent in situ datasets from the inner heliosphere—namely, those provided by MErcury Surface, Space ENvironment, GEochemistry,and Ranging (MESSENGER) and Venus Express—for magnetic cloud studies. We present observations of thesame magnetic cloud made by MESSENGER at Mercury and later by Solar TErrestrial RElations Observatory-B(STEREO-B), while the spacecraft were radially aligned in 2011 November. Few such radial observations ofmagnetic clouds have been previously reported. Estimates of the solar wind speed at MESSENGER are alsopresented, calculated through the application of a previously established technique. The cloudʼs flux rope has beenanalyzed using force-free fitting; the rope diameter increased from 0.18 to 0.41 AU (corresponding to an rH0.94dependence on heliocentric distance, rH), and the axial magnetic field strength dropped from 46.0 to 8.7 nT (an -rH1.84 dependence) between the spacecraft, clear indications of an expanding structure. The axial magnetic flux was∼0.50 nT AU2 at both spacecraft, suggesting that the rope underwent no significant erosion through magneticreconnection between MESSENGER and STEREO-B. Further, we estimate the change in the cloudʼs angular widthby assuming helicity conservation. It has also been found that the rope axis rotated by 30° between the spacecraftto lie close to the solar equatorial plane at STEREO-B. Such a rotation, if it is a common feature of coronal massejection propagation, would have important implications for space weather forecasting.
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Journal articleCampagnola S, Boutonnet A, Martens W, et al., 2015, , IEEE Aerospace and Electronic Systems Magazine, Vol: 30, Pages: 6-17, ISSN: 0885-8985
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Journal articleMessori G, Czaja A, 2015, , QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Vol: 141, Pages: 2376-2389, ISSN: 0035-9009
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- Citations: 9
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Journal articleLavvas P, Yelle RV, Heays AN, et al., 2015, , Icarus, Vol: 260, Pages: 29-59, ISSN: 1090-2643
We present a detailed model for the vibrational population of all non pre-dissociating excited electronic states of N2, as well as for the ground and ionic states, in Titan’s atmosphere. Our model includes the detailed energy deposition calculations presented in the past (Lavvas, P. et al. [2011]. Icarus 213(1), 233–251) as well as the more recent developments in the high resolution N2 photo-absorption cross sections that allow us to calculate photo-excitation rates for different vibrational levels of singlet nitrogen states, and provide information for their pre-dissociation yields. In addition, we consider the effect of collisions and chemical reactions in the population of the different states. Our results demonstrate that above 600 km altitude, collisional processes are efficient only for a small sub-set of the excited states limited to the A and W(ν = 0) triplet states, and to a smaller degree to the a′ singlet state. In addition, we find that a significant population of vibrationally excited ground state N2 survives in Titan’s upper atmosphere. Our calculations demonstrate that this hot N2 population can improve the agreement between models and observations for the emission of the View the MathML source state that is significantly affected by resonant scattering. Moreover we discuss the potential implications of the vibrationally excited population on the ionospheric densities.
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Journal articleSagnieres LBM, Galand MIF, Cui J, et al., 2015, , Journal of Geophysical Research: Space Physics, Vol: 120, Pages: 5899-5921, ISSN: 2169-9402
Titan has the most chemically complex ionosphere of the Solar System. The main sources of ions on the dayside are ionization by EUV solar radiation and on the nightside include ionization by precipitated electrons from Saturn's magnetosphere and transport of ions from the dayside, but many questions remain open. How well do models predict local ionization rates? How strongly do the ionization processes drive the ionospheric densities locally? To address these questions, we have carried out an analysis of ion densities from the Ion and Neutral Mass Spectrometer (INMS) from 16 close flybys of Titan's upper atmosphere. Using a simple chemical model applied to the INMS dataset, we have calculated the ion production rates and local ionization frequencies associated with primary ions inline image and inline image. We find that on the dayside the solar energy deposition model overestimates the INMS-derived inline image production rates by a factor of 2. On the nightside, however, the model driven by suprathermal electron intensities from the Cassini Plasma Spectrometer (CAPS) Electron Spectrometer (ELS) sometimes agrees, other times underestimates the INMS-derived inline image production rates by a factor of up to 2-3. We find that below 1200 km, all ion number densities correlate with the local ionization frequency, although the correlation is significantly stronger for short-lived ions than long-lived ions. Furthermore, we find that for a given N2 local ionization frequency inline image has higher densities on the day-side than on the nightside. We explain that this is due to inline image being more efficiently ionized by solar photons than by magnetospheric electrons for a given amount of N2 ionization.
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BookHaigh JD, Cargill P, 2015,
The Sun's Influence on Climate
, ISBN: 9780691153841"--Peter Pilewskie, University of Colorado Boulder "This succinct volume will be invaluable to scientists and general readers who want to learn more about the Sun and its effects on our climate system.
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Journal articleHoraites K, Boldyrev S, Krasheninnikov SI, et al., 2015, , PHYSICAL REVIEW LETTERS, Vol: 114, ISSN: 0031-9007
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- Citations: 17
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