Publications
Results
- Showing results for:
- Reset all filters
Search results
-
Journal articleMcCoy DT, Hartmann DL, Zelinka MD, et al., 2015,
Mixed-phase cloud physics and Southern Ocean cloud feedback in climate models
, Journal of Geophysical Research: Atmospheres, Vol: 120, Pages: 9539-9554, ISSN: 2169-897XIncreasing optical depth poleward of 45° is a robust response to warming in global climate models. Much of this cloud optical depth increase has been hypothesized to be due to transitions from ice‐dominated to liquid‐dominated mixed‐phase cloud. In this study, the importance of liquid‐ice partitioning for the optical depth feedback is quantified for 19 Coupled Model Intercomparison Project Phase 5 models. All models show a monotonic partitioning of ice and liquid as a function of temperature, but the temperature at which ice and liquid are equally mixed (the glaciation temperature) varies by as much as 40 K across models. Models that have a higher glaciation temperature are found to have a smaller climatological liquid water path (LWP) and condensed water path and experience a larger increase in LWP as the climate warms. The ice‐liquid partitioning curve of each model may be used to calculate the response of LWP to warming. It is found that the repartitioning between ice and liquid in a warming climate contributes at least 20% to 80% of the increase in LWP as the climate warms, depending on model. Intermodel differences in the climatological partitioning between ice and liquid are estimated to contribute at least 20% to the intermodel spread in the high‐latitude LWP response in the mixed‐phase region poleward of 45°S. It is hypothesized that a more thorough evaluation and constraint of global climate model mixed‐phase cloud parameterizations and validation of the total condensate and ice‐liquid apportionment against observations will yield a substantial reduction in model uncertainty in the high‐latitude cloud response to warming.
-
Journal articleHunt GJ, Cowley SWH, Provan G, et al., 2015,
Field-aligned currents in Saturn's northern nightside magnetosphere: Evidence for interhemispheric current flow associated with planetary period oscillations
, Journal of Geophysical Research: Space Physics, Vol: 120, Pages: 7552-7584, ISSN: 2169-9402We investigate the magnetic perturbations associated with field-aligned currents observed on 34 Cassini passes over the premidnight northern auroral region during 2008. These are found to be significantly modulated not only by the northern planetary-period oscillation (PPO) system, similar to the southern currents by the southern PPO system found previously, but also by the southern PPO system as well, thus providing the first clear evidence of PPO-related interhemispheric current flow. The principal field-aligned currents of the two PPO systems are found to be co-located in northern ionospheric colatitude, together with the currents of the PPO-independent (subcorotation) system, located between the vicinity of the open-closed field boundary and field lines mapping to ~9 Saturn radius (Rs) in the equatorial plane. All three systems are of comparable magnitude, ~3 MA in each PPO half-cycle. Smaller PPO-related field-aligned currents of opposite polarity also flow in the interior region, mapping between ~6 and ~9 Rs in the equatorial plane, carrying a current of ~ ±2 MA per half-cycle, which significantly reduce the oscillation amplitudes in the interior region. Within this interior region the amplitudes of the northern and southern oscillations are found to fall continuously with distance along the field lines from the corresponding hemisphere, thus showing the presence of cross-field currents, with the southern oscillations being dominant in the south, and modestly lower in amplitude than the northern oscillations in the north. As in previous studies, no oscillations related to the opposite hemisphere are found on open field lines in either hemisphere.
-
Journal articleYang L, Wang L, Li G, et al., 2015,
THE ANGULAR DISTRIBUTION OF SOLAR WIND SUPERHALO ELECTRONS AT QUIET TIMES
, ASTROPHYSICAL JOURNAL LETTERS, Vol: 811, ISSN: 2041-8205- Author Web Link
- Cite
- Citations: 8
-
Journal articleSulaiman AH, Masters A, Dougherty MK, et al., 2015,
Quasiperpendicular high Mach number shocks
, Physical Review Letters, Vol: 115, ISSN: 1079-7114Shock waves exist throughout the Universe and are fundamental to understanding the nature of collisionless plasmas. Reformation is a process, driven by microphysics, which typically occurs at high Mach number supercritical shocks. While ongoing studies have investigated this process extensively both theoretically and via simulations, their observations remain few and far between. In this Letter we present a study of very high Mach number shocks in a parameter space that has been poorly explored and we identify reformation using in situ magnetic field observations from the Cassini spacecraft at 10 AU. This has given us an insight into quasiperpendicular shocks across 2 orders of magnitude in Alfvén Mach number (MA) which could potentially bridge the gap between modest terrestrial shocks and more exotic astrophysical shocks. For the first time, we show evidence for cyclic reformation controlled by specular ion reflection occurring at the predicted time scale of ∼0.3τc, where τc is the ion gyroperiod. In addition, we experimentally reveal the relationship between reformation and MA and focus on the magnetic structure of such shocks to further show that for the same MA, a reforming shock exhibits stronger magnetic field amplification than a shock that is not reforming.
-
Journal articlePilkington NM, Achilleos N, Arridge CS, et al., 2015,
Internally driven large-scale changes in the size of Saturn's magnetosphere
, Journal of Geophysical Research: Space Physics, Vol: 120, Pages: 7289-7306, ISSN: 2169-9402Saturn's magnetic field acts as an obstacle to solar wind flow, deflecting plasma around the planet and forming a cavity known as the magnetosphere. The magnetopause defines the boundary between the planetary and solar dominated regimes, and so is strongly influenced by the variable nature of pressure sources both outside and within. Following from Pilkington et al. (2014), crossings of the magnetopause are identified using 7 years of magnetic field and particle data from the Cassini spacecraft and providing unprecedented spatial coverage of the magnetopause boundary. These observations reveal a dynamical interaction where, in addition to the external influence of the solar wind dynamic pressure, internal drivers, and hot plasma dynamics in particular can take almost complete control of the system's dayside shape and size, essentially defying the solar wind conditions. The magnetopause can move by up to 10–15 planetary radii at constant solar wind dynamic pressure, corresponding to relatively “plasma-loaded” or “plasma-depleted” states, defined in terms of the internal suprathermal plasma pressure.
-
Journal articlePilkington NM, Achilleos N, Arridge CS, et al., 2015,
Asymmetries observed in Saturn's magnetopause geometry
, Geophysical Research Letters, Vol: 42, Pages: 6890-6898, ISSN: 1944-8007For over 10 years, the Cassini spacecraft has patrolled Saturn's magnetosphere and observed its magnetopause boundary over a wide range of prevailing solar wind and interior plasma conditions. We now have data that enable us to resolve a significant dawn-dusk asymmetry and find that the magnetosphere extends farther from the planet on the dawnside of the planet by 7 ± 1%. In addition, an opposing dawn-dusk asymmetry in the suprathermal plasma pressure adjacent to the magnetopause has been observed. This probably acts to reduce the size asymmetry and may explain the discrepancy between the degree of asymmetry found here and a similar asymmetry found by Kivelson and Jia (2014) using MHD simulations. Finally, these observations sample a wide range of season, allowing the “intrinsic” polar flattening (14 ± 1%) caused by the magnetodisc to be separated from the seasonally induced north-south asymmetry in the magnetopause shape found theoretically (5 ± 1% when the planet's magnetic dipole is tilted away from the Sun by 10–17°).
-
Journal articleBeth A, Garnier P, Toublanc D, et al., 2015,
Theory for planetary exospheres: II. Radiation pressure effect on exospheric density profiles
, Icarus, Vol: 266, Pages: 423-432, ISSN: 1090-2643The 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.
-
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,
Observing Magnetic Reconnection: The Influence of Jim Dungey
, Magnetospheric Plasma Physics: The Impact of Jim Dungey’s Research, Editors: Southwood, Cowley, Mitton, Publisher: Springer, Pages: 181-197, ISBN: 9783319183589This book makes good background reading for much of modern magnetospheric physics.
-
Journal articleYan GQ, Mozer FS, Phan T, et al., 2015,
Quasi-continuous reconnection accompanied by FTEs during IMF Bz≈0 nT observed by Double Star TC-1 at the dawnside magnetopause
, Advances in Space Research, Vol: 58, Pages: 208-217, ISSN: 0273-1177During 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.
-
Journal articleOsipov S, Stenchikov G, Brindley H, et al., 2015,
Diurnal cycle of the dust instantaneous direct radiative forcing over the Arabian Peninsula
, Atmospheric Chemistry and Physics, Vol: 15, Pages: 9537-9553, ISSN: 1680-7324In 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.
-
Journal articleChen CHK, Matteini L, Burgess D, et al., 2015,
Magnetic field rotations in the solar wind at kinetic scales
, Monthly Notices of the Royal Astronomical Society: Letters, Vol: 453, Pages: L64-L68, ISSN: 1745-3933The 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.
-
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.
-
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.
-
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.
-
Journal articleRichter I, Koenders C, Auster H-U, et al., 2015,
Observation of a new type of low frequency waves at comet 67P/Churyumov-Gerasimenko
, Annales Geophysicae, Vol: 33, Pages: 1031-1036, ISSN: 1432-0576We 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
-
Journal articleMatteini L, Schwartz SJ, Hellinger P, 2015,
Cometary ion instabilities in the solar wind
, Planetary and Space Science, ISSN: 1873-5088 -
Journal articleTam KV, Hood AW, Browning PK, et al., 2015,
Coronal heating in multiple magnetic threads
, Astronomy & Astrophysics, Vol: 580, ISSN: 1432-0746 -
Journal articleWang S, Toumi R, Czaja A, et al., 2015,
An analytic model of tropical cyclone wind profiles
, Quarterly Journal of the Royal Meteorological Society, Vol: 141, Pages: 3018-3029, ISSN: 1477-870XA 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.
-
Journal articleChen CHK, Matteini L, Burgess D, et al., 2015,
Erratum: Magnetic field rotations in the solar wind at kinetic scales (Monthly Notices of the Royal Astronomical Society: Letters DOI: 10.1093/mnrasl/slv107)
, Monthly Notices of the Royal Astronomical Society: Letters, Vol: 455, ISSN: 1745-3925This 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.
-
Journal articleGraven HD, 2015,
Impact of fossil fuel emissions on atmospheric radiocarbon and various applications of radiocarbon over this century
, Proceedings of the National Academy of Sciences of the United States of America, Vol: 112, Pages: 9542-9545, ISSN: 1091-6490Radiocarbon 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.
-
Journal articleWeiss Z, Steers EBM, Pickering JC, 2015,
Transition rates and transition rate diagrams in atomic emission spectroscopy: A review
, SPECTROCHIMICA ACTA PART B-ATOMIC SPECTROSCOPY, Vol: 110, Pages: 79-90, ISSN: 0584-8547- Author Web Link
- Cite
- Citations: 18
-
Journal articleAuster H-U, Apathy I, Berghofer G, et al., 2015,
The nonmagnetic nucleus of comet 67P/Churyumov-Gerasimenko
, Science, Vol: 349, ISSN: 0036-8075<jats:p> 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 magnetic field measurements during the descent and subsequent multiple touchdown of the Rosetta lander Philae on the comet 67P/Churyumov-Gerasimenko (67P), we show that no global magnetic field was detected within the limitations of analysis. The Rosetta Magnetometer and Plasma Monitor (ROMAP) suite of sensors measured an upper magnetic field magnitude of less than 2 nanotesla at the cometary surface at multiple locations, with the upper specific magnetic moment being <3.1 × 10 <jats:sup>−5</jats:sup> ampere–square meters per kilogram for meter-size homogeneous magnetized boulders. The maximum dipole moment of 67P is 1.6 × 10 <jats:sup>8</jats:sup> ampere–square meters. We conclude that on the meter scale, magnetic alignment in the preplanetary nebula is of minor importance. </jats:p>
-
Journal articleRyder CL, McQuaid JB, Flamant C, et al., 2015,
Advances in understanding mineral dust and boundary layer processes over the Sahara from Fennec aircraft observations
, Atmospheric Chemistry and Physics, Vol: 15, Pages: 8479-8520, ISSN: 1680-7324The 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
-
Journal articleYates JN, Southwood DJ, Dougherty MK, 2015,
Reply to the comment by Cowley et al. on “Magneticphase structure of Saturn’s 10.7h oscillations”
, Journal of Geophysical Research: Space Physics, Vol: 120, Pages: 5691-5693, ISSN: 2169-9402 -
Journal articleVoulgarakis A, Marlier ME, Faluvegi G, et al., 2015,
Interannual variability of tropospheric trace gases and aerosols: The role of biomass burning emissions
, Journal of Geophysical Research: Atmospheres, Vol: 120, Pages: 7157-7173, ISSN: 2169-897XFires 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
-
Journal articleMarsham JH, Parker DJ, Todd MC, et al., 2015,
The contrasting roles of water and dust in controlling daily variations in radiative heating of the summertime Saharan Heat Low
, Atmospheric Chemistry and Physics Discussions, Vol: 15, Pages: 19447-19476, ISSN: 1680-7367The 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
-
Journal articleBalikhin MA, Shprits YY, Walker SN, et al., 2015,
Observations of discrete harmonics emerging from equatorial noise
, Nature Communications, Vol: 6, ISSN: 2041-1723A 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.
-
Journal articleGryspeerdt E, Stier P, White BA, et al., 2015,
Wet scavenging limits the detection of aerosol effects on precipitation
, Atmospheric Chemistry and Physics, Vol: 15, Pages: 7557-7570, ISSN: 1680-7324 -
Journal articleGood SW, Forsyth RJ, Raines JM, et al., 2015,
Radial Evolution of a Magnetic Cloud: MESSENGER, STEREO, and Venus Express Observations
, Astrophysical Journal, Vol: 807, Pages: 177-189, ISSN: 1538-4357The 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.
This data is extracted from the Web of Science and reproduced under a licence from Thomson Reuters. You may not copy or re-distribute this data in whole or in part without the written consent of the Science business of Thomson Reuters.