Publications
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Owens MJ, Riley P, Horbury TS, 2017, Probabilistic Solar Wind and Geomagnetic Forecasting Using an Analogue Ensemble or "Similar Day" Approach, Solar Physics, Vol: 292, ISSN: 0038-0938
Effective space-weather prediction and mitigation requires accurate forecastingof near-Earth solar-wind conditions. Numerical magnetohydrodynamic models of the solarwind, driven by remote solar observations, are gaining skill at forecasting the large-scalesolar-wind features that give rise to near-Earth variations over days and weeks. There remainsa need for accurate short-term (hours to days) solar-wind forecasts, however. In thisstudy we investigate the analogue ensemble (AnEn), or “similar day”, approach that wasdeveloped for atmospheric weather forecasting. The central premise of the AnEn is thatpast variations that are analogous or similar to current conditions can be used to provide agood estimate of future variations. By considering an ensemble of past analogues, the AnEnforecast is inherently probabilistic and provides a measure of the forecast uncertainty. Weshow that forecasts of solar-wind speed can be improved by considering both speed anddensity when determining past analogues, whereas forecasts of the out-of-ecliptic magneticfield [BN] are improved by also considering the in-ecliptic magnetic-field components. Ingeneral, the best forecasts are found by considering only the previous 6 – 12 hours of observations.Using these parameters, the AnEn provides a valuable probabilistic forecast forsolar-wind speed, density, and in-ecliptic magnetic field over lead times from a few hoursto around four days. For BN, which is central to space-weather disturbance, the AnEn onlyprovides a valuable forecast out to around six to seven hours. As the inherent predictabilityof this parameter is low, this is still likely a marked improvement over other forecast methods.We also investigate the use of the AnEn in forecasting geomagnetic indices Dst and Kp.The AnEn provides a valuable probabilistic forecast of both indices out to around four days.We outline a number of future improvements to AnEn forecasts of near-Earth solar-windand geomagnetic conditions.
Riley P, Ben-Nun M, Linker JA, et al., 2017, Forecasting the properties of the solar wind using simple pattern recognition, SPACE WEATHER-THE INTERNATIONAL JOURNAL OF RESEARCH AND APPLICATIONS, Vol: 15, Pages: 526-540, ISSN: 1542-7390
Stansby D, Horbury TS, Chen CHK, et al., 2016, Experimental determination of whistler wave dispersion relation in the solar wind, Astrophysical Journal Letters, Vol: 829, ISSN: 2041-8213
The origins and properties of large-amplitude whistler wavepackets in the solar wind are still unclear. In this Letter, we utilize single spacecraft electric and magnetic field waveform measurements from the ARTEMIS mission to calculate the plasma frame frequency and wavevector of individual wavepackets over multiple intervals. This allows direct comparison of experimental measurements with theoretical dispersion relations to identify the observed waves as whistler waves. The whistlers are right-hand circularly polarized, travel anti-sunward, and are aligned with the background magnetic field. Their dispersion is strongly affected by the local electron parallel beta in agreement with linear theory. The properties measured are consistent with the electron heat flux instability acting in the solar wind to generate these waves.
Mallet A, Schekochihin AA, Chandran BDG, et al., 2016, Measures of three-dimensional anisotropy and intermittency in strong Alfvénic turbulence, Monthly Notices of the Royal Astronomical Society, Vol: 459, Pages: 2130-2139, ISSN: 1365-2966
We measure the local anisotropy of numerically simulated strong Alfvénic turbulence with respect to two local, physically relevant directions: along the local mean magnetic field and along the local direction of one of the fluctuating Elsasser fields. We find significant scaling anisotropy with respect to both these directions: the fluctuations are ‘ribbon-like’ – statistically, they are elongated along both the mean magnetic field and the fluctuating field. The latter form of anisotropy is due to scale-dependent alignment of the fluctuating fields. The intermittent scalings of the nth-order conditional structure functions in the direction perpendicular to both the local mean field and the fluctuations agree well with the theory of Chandran, Schekochihin & Mallet, while the parallel scalings are consistent with those implied by the critical-balance conjecture. We quantify the relationship between the perpendicular scalings and those in the fluctuation and parallel directions, and find that the scaling exponent of the perpendicular anisotropy (i.e. of the aspect ratio of the Alfvénic structures in the plane perpendicular to the mean magnetic field) depends on the amplitude of the fluctuations. This is shown to be equivalent to the anticorrelation of fluctuation amplitude and alignment at each scale. The dependence of the anisotropy on amplitude is shown to be more significant for the anisotropy between the perpendicular and fluctuation-direction scales than it is between the perpendicular and parallel scales.
Bale SD, Goetz K, Harvey PR, et al., 2016, The FIELDS Instrument Suite for Solar Probe Plus, Space Science Reviews, Vol: 204, Pages: 49-82, ISSN: 0038-6308
NASA’s Solar Probe Plus (SPP) mission will make the first in situ measurementsof the solar corona and the birthplace of the solar wind. The FIELDS instrument suiteon SPP will make direct measurements of electric and magnetic fields, the properties ofin situ plasma waves, electron density and temperature profiles, and interplanetary radioemissions, amongst other things. Here, we describe the scientific objectives targeted by theSPP/FIELDS instrument, the instrument design itself, and the instrument concept of operationsand planned data products.
Chen 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
Chen 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: 1745-3933
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.
Chen 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: 1745-3925
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.
Horbury TS, Archer MO, Brown P, et al., 2015, The MAGIC of CINEMA: First in-flight science results from a miniaturised anisotropic magnetoresistive magnetometer, Annales Geophysicae, Vol: 33, Pages: 725-735, ISSN: 1432-0576
We present the first in-flight results from a novel miniaturised anisotropic magnetoresistive space magnetometer, MAGIC (MAGnetometer from Imperial College), aboard the first CINEMA (CubeSat for Ions, Neutrals, Electrons and MAgnetic fields) spacecraft in low Earth orbit. An attitude-independent calibration technique is detailed using the International Geomagnetic Reference Field (IGRF), which is temperature dependent in the case of the outboard sensor. We show that the sensors accurately measure the expected absolute field to within 2% in attitude mode and 1% in science mode. Using a simple method we are able to estimate the spacecraft's attitude using the magnetometer only, thus characterising CINEMA's spin, precession and nutation. Finally, we show that the outboard sensor is capable of detecting transient physical signals with amplitudes of ~ 20–60 nT. These include field-aligned currents at the auroral oval, qualitatively similar to previous observations, which agree in location with measurements from the DMSP (Defense Meteorological Satellite Program) and POES (Polar-orbiting Operational Environmental Satellites) spacecraft. Thus, we demonstrate and discuss the potential science capabilities of the MAGIC instrument onboard a CubeSat platform.
Matteini L, Horbury TS, Pantellini F, et al., 2015, Ion kinetic energy conservation and magnetic field strength constancy in multi-fluid solar wind alfvénic turbulence, Astrophysical Journal, Vol: 802, ISSN: 1538-4357
We investigate the properties of plasma fluid motion in the large-amplitude, low-frequency fluctuations of highlyAlfvénic fast solar wind. We show that protons locally conserve total kinetic energy when observed from aneffective frame of reference comoving with the fluctuations. For typical properties of the fast wind, this frame canbe reasonably identified by alpha particles which, due to their drift with respect to protons at about the Alfvénspeed along the magnetic field, do not partake in the fluid low-frequency fluctuations. Using their velocity totransform the proton velocity into the frame of Alfvénic turbulence, we demonstrate that the resulting plasmamotion is characterized by a constant absolute value of the velocity, zero electric fields, and aligned velocity andmagnetic field vectors as expected for unidirectional Alfvénic fluctuations in equilibrium. We propose that thisconstraint, via the correlation between velocity and magnetic field in Alfvénic turbulence, is the origin of theobserved constancy of the magnetic field; while the constant velocity corresponding to constant energy can only beobserved in the frame of the fluctuations, the corresponding constant total magnetic field, invariant for Galileantransformations, remains the observational signature in the spacecraft frame of the constant total energy in theAlfvén turbulence frame
Brown P, Whiteside BJ, Beek TJ, et al., 2014, Space magnetometer based on an anisotropic magnetoresistive hybrid sensor, Review of Scientific Instruments, Vol: 85, ISSN: 1089-7623
Archer MO, Turner DL, Eastwood JP, et al., 2014, Global impacts of a Foreshock Bubble: Magnetosheath, magnetopause and ground-based observations, Planetary and Space Science, Vol: 106, Pages: 56-66, ISSN: 1873-5088
Using multipoint observations we show, for the first time, that Foreshock Bubbles (FBs) have a global impact on Earth׳s magnetosphere. We show that an FB, a transient kinetic phenomenon due to the interaction of backstreaming suprathermal ions with a discontinuity, modifies the total pressure upstream of the bow shock showing a decrease within the FB׳s core and sheath regions. Magnetosheath plasma is accelerated towards the intersection of the FB׳s current sheet with the bow shock resulting in fast, sunward, flows as well as outward motion of the magnetopause. Ground-based magnetometers also show signatures of this magnetopause motion simultaneously across at least 7 h of magnetic local time, corresponding to a distance of 21.5RE transverse to the Sun–Earth line along the magnetopause. These observed global impacts of the FB are in agreement with previous simulations and in stark contrast to the known localised, smaller scale effects of Hot Flow Anomalies (HFAs).
Archer MO, Turner DL, Eastwood JP, et al., 2014, The role of pressure gradients in driving sunward magnetosheath flows and magnetopause motion, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 119, Pages: 8117-8125, ISSN: 2169-9380
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- Citations: 39
Owens MJ, Horbury TS, Wicks RT, et al., 2014, Ensemble downscaling in coupled solar wind-magnetosphere modeling for space weather forecasting, Space Weather, Vol: 12, Pages: 395-405, ISSN: 1539-4956
Advanced forecasting of space weather requires simulation of the whole Sun-to-Earth system, which necessitates driving magnetospheric models with the outputs from solar wind models. This presents a fundamental difficulty, as the magnetosphere is sensitive to both large-scale solar wind structures, which can be captured by solar wind models, and small-scale solar wind “noise,” which is far below typical solar wind model resolution and results primarily from stochastic processes. Following similar approaches in terrestrial climate modeling, we propose statistical “downscaling” of solar wind model results prior to their use as input to a magnetospheric model. As magnetospheric response can be highly nonlinear, this is preferable to downscaling the results of magnetospheric modeling. To demonstrate the benefit of this approach, we first approximate solar wind model output by smoothing solar wind observations with an 8 h filter, then add small-scale structure back in through the addition of random noise with the observed spectral characteristics. Here we use a very simple parameterization of noise based upon the observed probability distribution functions of solar wind parameters, but more sophisticated methods will be developed in the future. An ensemble of results from the simple downscaling scheme are tested using a model-independent method and shown to add value to the magnetospheric forecast, both improving the best estimate and quantifying the uncertainty. We suggest a number of features desirable in an operational solar wind downscaling scheme.
Wicks RT, Roberts DA, Mallet A, et al., 2014, CORRELATIONS AT LARGE SCALES AND THE ONSET OF TURBULENCE IN THE FAST SOLAR WIND (vol 778, pg 177, 2013), ASTROPHYSICAL JOURNAL, Vol: 782, ISSN: 0004-637X
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- Citations: 1
Matteini L, Horbury TS, Neugebauer M, et al., 2014, Dependence of solar wind speed on the local magnetic field orientation: Role of Alfvenic fluctuations, Geophysical Research Letters, Vol: 41, Pages: 259-265, ISSN: 0094-8276
We report an analysis of correlations between magnetic field and velocity fluctuations in the fast solar wind beyond 1 AU at high latitudes. We have found that on scales shorter than the microstream structures, there exists a well‐defined dependence of the flow speed on the angle between the magnetic field vector and the radial direction. Solar wind is found to be slightly faster when the measured magnetic field vector is transverse to the velocity, while it is always slower when the magnetic field is parallel, or antiparallel, to the radial direction. We show that this correlation is a direct consequence of the high Alfvénicity of fast wind fluctuations and that it can be reasonably described by a simple model taking into account the main properties of the low‐frequency antisunward Alfvén fluctuations as observed in the solar wind plasma. We also discuss how switchbacks, short periods of magnetic field reversals, naturally fit in this new observed correlation.
Whiteside BJ, Brown P, Beek TJ, et al., 2014, TID Response of a Hybrid AMR Vector Magnetometer, IEEE Radiation Effects Data Workshop (REDW) is part of the Nuclear and Space Radiation Effect Conference (NSREC), Publisher: IEEE
Alexandrova O, Chen CHK, Sorriso-Valvo L, et al., 2014, Solar Wind Turbulence and the Role of Ion Instabilities, MICROPHYSICS OF COSMIC PLASMAS, Editors: Balogh, Bykov, Cargill, Dendy, DeWit, Raymond, Publisher: SPRINGER, Pages: 25-63, ISBN: 978-1-4899-7412-9
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- Citations: 4
Wicks RT, Roberts DA, Mallet A, et al., 2013, Correlations at Large Scales and the Onset of Turbulence in the Fast Solar Wind, The Astrophysical Journal, Vol: 778, Pages: 177-177, ISSN: 0004-637X
We show that the scaling of structure functions of magnetic and velocity fields in a mostly highly Alfvénic fast solar wind stream depends strongly on the joint distribution of the dimensionless measures of cross helicity and residual energy. Already at very low frequencies, fluctuations that are both more balanced (cross helicity ~0) and equipartitioned (residual energy ~0) have steep structure functions reminiscent of "turbulent" scalings usually associated with the inertial range. Fluctuations that are magnetically dominated (residual energy ~−1), and so have closely anti-aligned Elsasser-field vectors, or are imbalanced (cross helicity ~1), and so have closely aligned magnetic and velocity vectors, have wide "1/f" ranges typical of fast solar wind. We conclude that the strength of nonlinear interactions of individual fluctuations within a stream, diagnosed by the degree of correlation in direction and magnitude of magnetic and velocity fluctuations, determines the extent of the 1/f region observed, and thus the onset scale for the turbulent cascade.
Alexandrova O, Chen CHK, Sorriso-Valvo L, et al., 2013, Solar Wind Turbulence and the Role of Ion Instabilities, Space Science Reviews, Vol: 178, Pages: 101-139, ISSN: 0038-6308
Wicks RT, Mallet A, Horbury TS, et al., 2013, Alignment and Scaling of Large-Scale Fluctuations in the Solar Wind, Physical Review Letters, Vol: 110, Pages: 025003-025003, ISSN: 0031-9007
Seo Y, Chae KS, Mochizuki B, et al., 2013, Instrument interface module between the on-board-computer and payloads in cinema CUBESAT as developed with FPGA, Pages: 4275-4281, ISSN: 0074-1795
TRiplet Ionospheric Observatory-Cubesat for Ion, Neutral, Electron and MAgnetic fields (TRIO-CINEMA) is a space science mission consisting of three identical 3U CubeSats to provide stereo Energetic Neutral Atom (ENA) imaging of the ring current, multi-point in-situ measurement of supra thermal electrons and ions, and measurement of magnetic fields in Low Earth Orbit (LEO). Each spacecraft is equipped with a Supra Thermal Electrons, Ions, Neutrals (STEIN) instrument and a MAGnetometer from Imperial College (MAGIC) instrument in order to measure the plasma particles with diverse species and energies and magnetic fields. STEIN is able to distinguish electrons, ions, and neutrals by applying electric field in the entrance aperture. MAGIC is a dual 3-axis magnetoresistive sensor intended for attitude control and scientific measurement. The standard spacecraft CubeSat employed for the TRIO- CINEMA mission often utilizes Commercial-Off-The Shelf (COTS) electronics to build bus avionics that provides power and communications, whereas payloads are usually built in accordance with specific requirements that are often more demanding in terms of generation, transmission and storage of the data and power consumption. Therefore, designing and developing the interface to be compatible between mission payloads and the CubeSat avionics built with COTS will be required for many CubeSat missions. In this presentation, we describe the instrument interface module between the On-Board-Computer (OBC) and the mission payloads for TRIO-CINEMA spacecraft. The module is developed to provide required communication and power interfaces. In the instrument interface module, a Field Programmable Gate Array (FPGA) is employed to support computing power of the OBC and communication interfaces. It is exclusively operated as data buffer and framer for generated data from mission payloads and their subsequent transmission through S-band to the ground station. The interface module provides various elect
Archer MO, Horbury TS, 2013, Magnetosheath dynamic pressure enhancements: Occurrence and typical properties, Ann. Geophys., Vol: 31, Pages: 319-331
Archer MO, Horbury TS, Eastwood JP, et al., 2013, Magnetospheric response to magnetosheath pressure pulses: A low pass filter effect, Journal of Geophysical Research, Vol: 118, Pages: 5454-5466
Abstract. We present observations from the magnetopause to the ground during periods of large amplitude, transient dynamic pressure pulses in the magnetosheath. While individual magnetosheath pulses are sharp and impulsive, the magnetospheric response is much smoother with frequencies in the Pc5-6 range being excited in the compressional and poloidal components of the magnetic field. We show that the magnetopause acts like a low pass filter, suppressing timescales shorter than a few minutes. Further filtering appears to occur locally within the magnetosphere, which may be due to the unusual field line resonance frequency profile on this day. Ground magnetometer and radar data along with equivalent ionospheric currents show signatures of travelling convection vortices, similar to the response from pressure variations of solar wind origin. However, the signatures are associated with groups of magnetosheath pulses rather than individual ones due to the impulsive nature of the pressure variations. Thus the scale-dependent magnetospheric response to these transient pressure variations, results in coherent signatures on longer timescales than any individual pulse.
Archer MO, Hartinger MD, Horbury TS, 2013, Magnetospheric “magic” frequencies as magnetopause surface eigenmodes, Geophysical Research Letters, Vol: 40, Pages: 5003-5008
Abstract. The persistent so-called “magic” magnetospheric frequencies are thought to be either directly driven by monochromatic solar wind pressure fluctuations or resonantly excited global (cavity/waveguide) or magnetopause surface eigenmodes. We distinguish between these cases by statistically investigating, using simultaneous observations, the magnetospheric response to jets in the subsolar magnetosheath. The broadband jets do not exhibit discrete frequencies, but do drive waves at the discrete “magic” frequencies, with both direct and resonant driving. We show that the expected fundamental frequencies of magnetopause surface eigenmodes have two preferential values over a wide range of upstream conditions, corresponding to fast and slow solar wind, and that their harmonics are in good agreement with the “magic” frequencies. We also show that the waves are largely inconsistent with global modes outside the plasmasphere. Thus we conclude that these “magic” frequencies are most likely due to magnetopause surface eigenmodes.
Forman MA, Wicks RT, Horbury TS, et al., 2013, Scaling Anisotropy of the Power in Parallel and Perpendicular Components of the Solar Wind Magnetic Field, 13th International Solar Wind Conference (Solar Wind), Publisher: AMER INST PHYSICS, Pages: 167-170, ISSN: 0094-243X
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Wicks RT, Matteini L, Horbury TS, et al., 2013, Temperature anisotropy instabilities; combining plasma and magnetic field data at different distances from the Sun., 13th International Solar Wind Conference (Solar Wind), Publisher: AMER INST PHYSICS, Pages: 303-306, ISSN: 0094-243X
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Yoon S, Kim V, Yun J, et al., 2012, Operations for two spacecraft of triple-cubesat mission trio-cinema with a single rf chain, Pages: 4240-4245, ISSN: 0074-1795
TRiplet Ionospheric Observatory - Cubesat for Ion, Neutral, Electron and MAgnetic fields (TRIO-CINEMA) mission consists of three identical 3U cubesats for scientific observation. The TRIO-CINEMA mission will provide high sensitivity mapping and high cadence measurements of ring current Energetic Neutral Atom (ENA) in the range of 4 - 200 keV with 1 keV FWHM energy resolution in Low Earth Orbit (LEO). Each spacecraft is equipped with a Supra Thermal Electrons, Ions, Neutrals (STEIN) instrument and a MAGnetometer Imperial College (MAGIC) instrument. STEIN instrument is improved from those in SupraThermal Electron (STE) instrument flown on NASA's Solar TERrestrial Relations Observatory (STEREO) spacecraft and is capable of identifying electrons, positive ions and neutrals through the application of an electric field in the entrance aperture. MAGIC is dual 3-axis magnetoresistive sensor for attitude control and scientific measurement. First spacecraft of TRIO-CINEMA is developed and will be operated by Space Science Laboratory of University of California, Berkeley (UCB). Another two spacecraft are developed by Kyung Hee University (KHU) in Republic of Korea. TRIO-CINEMA is expected to provide stereo imaging of ENAs and multi-point measurements of ions, electrons and Earth magnetic fields. It is also expected that the TRIO-CINEMA measurements will complement the measurements with NASA's Radiation Belt Storm Probes (RBSP) mission by stereo imaging of the ring current through ENA measurements at low altitudes. TRIO-CINEMA data will be transmitted at 1 Mbps via S-band, whereas a UHF receiver is used for uplink communication. UCB will operate the mission via Mission Operations Center (MOC) and Berkeley Ground Station (BGS) of Space Science Laboratory (SSL). KHU has constructed a new ground station with one UHF RF system for uplink. The two KHU's spacecraft will be initially contiguous with each other deployed from the same launcher. Because the ground S-band antenna can prov
Chen CHK, Mallet A, Schekochihin AA, et al., 2012, Three-Dimensional Structure of Solar Wind Turbulence, The Astrophysical Journal, Vol: 758, Pages: 120-120
We present a measurement of the scale-dependent, three-dimensional structureof the magnetic field fluctuations in inertial range solar wind turbulence withrespect to a local, physically motivated coordinate system. The Alfvenicfluctuations are three-dimensionally anisotropic, with the sense of thisanisotropy varying from large to small scales. At the outer scale, the magneticfield correlations are longest in the local fluctuation direction, consistentwith Alfven waves. At the proton gyroscale, they are longest along the localmean field direction and shortest in the direction perpendicular to the localmean field and the local field fluctuation. The compressive fluctuations arehighly elongated along the local mean field direction, although axiallysymmetric perpendicular to it. Their large anisotropy may explain why they arenot heavily damped in the solar wind.
Archer MO, Horbury TS, Eastwood JP, 2012, Magnetosheath pressure pulses: Generation downstream of the bow shock from solar wind discontinuities, Journal of Geophyical Research, Vol: 117, ISSN: 0148-0227
We present multipoint Time History of Events and Macroscale Interactions duringSubstorms (THEMIS) observations of transient dynamic pressure pulses in themagnetosheath 3–10 times the background in amplitude, due to enhancements in both theion density and velocity. Their spatial dimensions are of the order of 1 RE parallel tothe flow and 0.2–0.5 RE perpendicular to it, inferred from the difference in theamplitudes observed by the different spacecraft. For the first time, simultaneousobservations of the solar wind and foreshock are also shown, proving no similar dynamicpressure enhancements exist upstream of the bow shock and that the majority of pulsesare downstream of the quasi-parallel shock. By considering previously suggestedmechanisms for their generation, we show that the pressure pulses cannot be caused byreconnection, hot flow anomalies, or short, large-amplitude magnetic structures andthat at least some of the pressure pulses appear to be consistent with previoussimulations of solar wind discontinuities interacting with the bow shock. Thesesimulations predict large-amplitude pulses when the local geometry of the shock changesfrom quasi-perpendicular to quasi-parallel, while the opposite case should also producenotable pulses but typically of lower amplitude. Therefore, in a given region of themagnetosheath, some of the discontinuities in the solar wind should generate pressurepulses, whereas others are expected not to. There is also evidence that the pulses canimpinge upon the magnetopause, causing its motion.
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