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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, Vol: 455, Pages: L51-L51, ISSN: 1745-3933 -
Journal articleBrindley H, Osipov S, Bantges R, et al., 2015,
An assessment of the quality of aerosol retrievals over the Red Sea and evaluation of the climatological cloud-free dust direct radiative effect in the region
, Journal of Geophysical Research: Atmospheres, Vol: 120, Pages: 10862-10878, ISSN: 2169-897XGround-based and satellite observations are used in conjunction with the Rapid Radiative Transfer Model (RRTM) to assess climatological aerosol loading and the associated cloud-free aerosol direct radiative effect (DRE) over the Red Sea. Aerosol optical depth (AOD) retrievals from the Moderate Resolution Imaging Spectroradiometer and Spinning Enhanced Visible and InfraRed Imager (SEVIRI) instruments are first evaluated via comparison with ship-based observations. Correlations are typically better than 0.9 with very small root-mean-square and bias differences. Calculations of the DRE along the ship cruises using RRTM also show good agreement with colocated estimates from the Geostationary Earth Radiation Budget instrument if the aerosol asymmetry parameter is adjusted to account for the presence of large particles. A monthly climatology of AOD over the Red Sea is then created from 5 years of SEVIRI retrievals. This shows enhanced aerosol loading and a distinct north to south gradient across the basin in the summer relative to the winter months. The climatology is used with RRTM to estimate the DRE at the top and bottom of the atmosphere and the atmospheric absorption due to dust aerosol. These climatological estimates indicate that although longwave effects can reach tens of W m−2, shortwave cooling typically dominates the net radiative effect over the Sea, being particularly pronounced in the summer, reaching 60 W m−2 at the surface. The spatial gradient in summertime AOD is reflected in the radiative effect at the surface and in associated differential heating by aerosol within the atmosphere above the Sea. This asymmetric effect is expected to exert a significant influence on the regional atmospheric and oceanic circulation.
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Journal articlePalmroth M, Archer M, Vainio R, et al., 2015,
ULF foreshock under radial IMF: THEMIS observations and global kinetic simulation Vlasiator results compared
, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 120, Pages: 8782-8798, ISSN: 2169-9380 -
Journal articleVigren E, Galand M, Eriksson AI, et al., 2015,
ON THE ELECTRON-TO-NEUTRAL NUMBER DENSITY RATIO IN THE COMA OF COMET 67P/CHURYUMOV-GERASIMENKO: GUIDING EXPRESSION AND SOURCES FOR DEVIATIONS
, ASTROPHYSICAL JOURNAL, Vol: 812, ISSN: 0004-637X -
Journal articleParfitt R, Czaja A, 2015,
On the contribution of synoptic transients to the mean atmospheric state in the Gulf Stream region
, Quarterly Journal of the Royal Meteorological Society, Vol: 142, Pages: 1554-1561, ISSN: 1477-870XA new decomposition of the time mean sea level pressure, precipitation, meridional velocity (v) and pressure vertical velocity (ω) is applied to ERA-Interim reanalysis data over the North Atlantic ocean for the December-February 1979–2011 time period. The decomposition suggests that the atmosphere over the Gulf Stream is dominated by a continuous series of synoptic systems, or baroclinic waves, propagating across the region. The time mean value of precipitation, meridional velocity and ω (the latter being taken as a proxy for upward and downward motion) is accordingly set by the propagating waves. The result is particularly striking for ω (v) considering that ascent and descent (poleward and equatorward flow) could reasonably be expected to cancel out in such a series of waves.These results shed a new light on analyses of the storm track heat budget in which the residual between diabatic heating and “transient” eddy heat fluxes (singled out through band pass time filtering or spatial Fourier analysis) is interpreted as a Rossby wave source. This interpretation is questioned because, as a consequence of the filtering used, these studies prevent any direct contribution of the “transients” to the time mean ω or meridional velocity, attributing entirely both fields to the circulation associated with the thermally forced Rossby wave. The fact that “transients” directly contribute to the observed time mean ω over the Gulf Stream might also explain the discrepancy between the observed and predicted response of the vertical motion field to heating in midlatitudes.
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Journal articleFranci L, Landi S, Matteini L, et al., 2015,
High-resolution hybrid simulations of kinetic plasma turbulence at proton scales
, Astrophysical Journal, Vol: 812, ISSN: 1538-4357We investigate properties of plasma turbulence from magnetohydrodynamic (MHD) to sub-ion scales by means oftwo-dimensional, high-resolution hybrid particle-in-cell simulations. We impose an initial ambient magneticfield perpendicular to the simulation box, and we add a spectrum of large-scale magnetic and kineticfluctuations with energy equipartition and vanishing correlation. Once the turbulence is fully developed, weobserve an MHD inertial range, where the spectra of the perpendicular magnetic field and the perpendicular protonbulk velocity fluctuations exhibit power-law scaling with spectral indices of -5 3 and -3 2, respectively. Thisbehavior is extended over a full decade in wavevectors and is very stable in time. A transition is observed aroundproton scales. At sub-ion scales, both spectra steepen, with the former still following a power law with a spectralindex of ~-3. A-2.8 slope is observed in the density and parallel magnetic fluctuations, highlighting the presenceof compressive effects at kinetic scales. The spectrum of the perpendicular electric fluctuations follows that of theproton bulk velocity at MHD scales, and flattens at small scales. All these features, which we carefully testedagainst variations of many parameters, are in good agreement with solar wind observations. The turbulent cascadeleads to on overall proton energization with similar heating rates in the parallel and perpendicular directions. Whilethe parallel proton heating is found to be independent on the resistivity, the number of particles per cell, and theresolution employed, the perpendicular proton temperature strongly depends on these parameters.
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Journal articleMatteini L, Hellinger P, Schwartz SJ, et al., 2015,
FIRE HOSE INSTABILITY DRIVEN BY ALPHA PARTICLE TEMPERATURE ANISOTROPY
, Astrophysical Journal, Vol: 812, ISSN: 1538-4357We investigate properties of a solar wind-like plasma, including a secondary alpha particle population exhibiting aparallel temperature anisotropy with respect to the background magnetic field, using linear and quasi-linearpredictions and by means of one-dimensional hybrid simulations. We show that anisotropic alpha particles candrive a parallel fire hose instability analogous to that generated by protons, but that, remarkably, can also betriggered when the parallel plasma beta of alpha particles is below unity. The wave activity generated by the alphaanisotropy affects the evolution of the more abundant protons, leading to their anisotropic heating. When both ionspecies have sufficient parallel anisotropies, both of them can drive the instability, and we observe the generationof two distinct peaks in the spectra of the fluctuations, with longer wavelengths associated to alphas and shorterones to protons. If a non-zero relative drift is present, the unstable modes propagate preferentially in the directionof the drift associated with the unstable species. The generated waves scatter particles and reduce their temperatureanisotropy to a marginally stable state, and, moreover, they significantly reduce the relative drift between the twoion populations. The coexistence of modes excited by both species leads to saturation of the plasma in distinctregions of the beta/anisotropy parameter space for protons and alpha particles, in good agreement with in situ solarwind observations. Our results confirm that fire hose instabilities are likely at work in the solar wind and limit theanisotropy of different ion species in the plasma.
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Journal articleSouthwood D, 2015,
James Wynne Dungey 1923-2015 OBITUARY
, Astronomy & Geophysics, Vol: 56, Pages: 8-8, ISSN: 1468-4004 -
Journal articleBeskin VS, Balogh A, Falanga M, et al., 2015,
Magnetic Fields at Largest Universal Strengths: Overview
, SPACE SCIENCE REVIEWS, Vol: 191, Pages: 1-12, ISSN: 0038-6308- Author Web Link
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- Citations: 6
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Journal articleHellinger P, Matteini L, Landi S, et al., 2015,
Plasma turbulence and kinetic instabilities at ion scales in the expanding solar wind
, Astrophysical Journal Letters, Vol: 811, ISSN: 2041-8213The relationship between a decaying strong turbulence and kinetic instabilities in a slowly expanding plasma isinvestigated using two-dimensional (2D) hybrid expanding box simulations. We impose an initial ambientmagnetic field perpendicular to the simulation box, and we start with a spectrum of large-scale, linearly polarized,random-phase Alfvénic fluctuations that have energy equipartition between kinetic and magnetic fluctuations andvanishing correlation between the two fields. A turbulent cascade rapidly develops; magnetic field fluctuationsexhibit a power-law spectrum at large scales and a steeper spectrum at ion scales. The turbulent cascade leads to anoverall anisotropic proton heating, protons are heated in the perpendicular direction, and, initially, also in theparallel direction. The imposed expansion leads to generation of a large parallel proton temperature anisotropywhich is at later stages partly reduced by turbulence. The turbulent heating is not sufficient to overcome theexpansion-driven perpendicular cooling and the system eventually drives the oblique firehose instability in a formof localized nonlinear wave packets which efficiently reduce the parallel temperature anisotropy. This workdemonstrates that kinetic instabilities may coexist with strong plasma turbulence even in a constrained 2D regime.
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Journal articleHietala H, Drake JF, Phan TD, et al., 2015,
Ion temperature anisotropy across a magnetotail reconnection jet
, Geophysical Research Letters, Vol: 42, Pages: 7239-7247, ISSN: 1944-8007A significant fraction of the energy released by magnetotail reconnection appears to go into ion heating, but this heating is generally anisotropic. We examine ARTEMIS dual-spacecraft observations of a long-duration magnetotail exhaust generated by anti-parallel reconnection in conjunction with Particle-In-Cell simulations, showing spatial variations in the anisotropy across the outflow far (> 100di) downstream of the X-line. A consistent pattern is found in both the spacecraft data and the simulations: Whilst the total temperature across the exhaust is rather constant, near the boundaries Ti,|| dominates. The plasma is well-above the firehose threshold within patchy spatial regions at |BX| ∈ [0.1, 0.5]B0, suggesting that the drive for the instability is strong and the instability is too weak to relax the anisotropy. At the mid-plane (|BX|0.1 B0), Ti,⊥ > Ti,|| and ions undergo Speiser-like motion despite the large distance from the X-line.
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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.
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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.
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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
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- Citations: 8
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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.
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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.
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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°).
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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.
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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,
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.
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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.
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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.
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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.
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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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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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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
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Journal articleTam KV, Hood AW, Browning PK, et al., 2015,
Coronal heating in multiple magnetic threads
, Astronomy & Astrophysics, Vol: 580, ISSN: 1432-0746 -
Journal articleMatteini L, Schwartz SJ, Hellinger P, 2015,
Cometary ion instabilities in the solar wind
, Planetary and Space Science, ISSN: 1873-5088 -
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.
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