Dynamic Pressure Enhancements Research Articles

Joint observations of the large-scale ULF wave activity from space to ground associated with the solar wind dynamic pressure enhancement

Joint observations of the large-scale ULF wave activity from space to ground associated with the solar wind dynamic pressure enhancement

Candidates for downstream jets at interplanetary shocks

Abstract Localised dynamic pressure enhancements arising from kinetic processes are frequently observed downstream of the Earth’s bow shock. These structures, called jets, modify their plasma surroundings and participate in particle energisation. Here, we report the first observations of jet-like structures at a non-planetary shock environment: downstream of interplanetary shocks. We introduce an analysis approach suitable for such conditions and apply it to Wind spacecraft data. We present one event with a Mach number similar to the Earth’s bow shock as a benchmark, as well as two low Mach number, low beta shocks: a parameter range that is difficult to access at planets. The jet-like structures we find are tens of ion inertial lengths in size, and some are observed further away from the shock than in a limited magnetosheath. We find that their properties are similar to those of magnetosheath jets: in the frame of the shock these structures are fast, cold, and most have no strong magnetic field variations. All three interplanetary shocks feature foreshock activity, but no strongly compressive waves. We discuss the implications these findings have for the proposed jet formation mechanisms.

Solar wind dynamic pressure enhancements in upstream region near Mars

While it has been recognized that solar wind dynamic pressure (Pdy) enhancements have dramatic impacts on the Martian system, their characteristics have not been systematically analyzed due to the lack of upstream plasma observations. Simultaneous measurements of plasma and magnetic field made by MAVEN provide such an opportunity. In this paper, we analyze the distribution of solar wind dynamic pressure and the association of Pdy enhancements with various solar wind structures using MAVEN data from 2014 December 6 to 2021 August 14, covering the declining phase of solar cycle 24 to the ascending phase of solar cycle 25. The results suggest that Pdy above 2 nPa (4 nPa) occurs about 5.82% (0.59%) of the time. Stream interaction region (SIR) encounters, together with heliosphere plasma sheet (HPS) within SIR encounters, are responsible for 36.6% and 31.4% of the dynamic pressure enhancement events with Pdy> 2 nPa and with durations > 10 min, respectively. It is also found that HPSs tend to occur in the leading portion of SIRs, causing an additional deceleration of the slow stream and an additional enhanced local compression in the interaction region. As a result, the Pdy and the magnetic field strength reveal a faster and greater increase and recovery during the SIR with HPS events than they do during the SIR without HPS events. In addition, we compare these results with similar analyses based on the measurements from the Wind spacecraft at 1 AU.

Prompt Appearance of Large‐Amplitude EMIC Waves Induced by Solar Wind Dynamic Pressure Enhancement and the Subsequent Relativistic Electron Precipitation

AbstractElectromagnetic ion cyclotron (EMIC) waves play an important role in relativistic electron dynamics. In this study, we find a large‐amplitude EMIC wave event induced by the prompt enhancement of solar wind dynamic pressure on 6 November 2015. These large‐amplitude EMIC waves are simultaneously observed by multiple satellites over 13 hr in magnetic local time (MLT) with a peak amplitude of ∼4 nT. Satellites at different locations observed different bands of EMIC waves, implying the importance of background plasma density in EMIC wave generation. Electron pitch angle distributions show obvious responses to EMIC wave activities. During EMIC wave appearance, the fluxes of relativistic electrons with pitch angles around 90° increase, while the fluxes of field‐aligned relativistic electrons decrease, showing distinct “bite‐out” signatures, indicating pitch angle scattering by EMIC waves, and the scattering efficiency depends on the amplitude and polarization of EMIC waves. Combined with phase space density profiles of electrons that are nearly constant at energies below the minimum resonant energy of electrons (Emin) but show dropout at energies above the Emin after EMIC wave activities, we conclude that large‐amplitude EMIC waves can cause rapid electron loss down to several hundred keV. In addition, simultaneous observations of hundreds of keV electron precipitation and tens of keV proton precipitation by Polar Operational Environmental Satellites near the region where EMIC waves are observed, provide direct evidence of relativistic electron precipitation caused by the large‐amplitude EMIC waves, ultimately driven by solar wind structures.

Waves in Magnetosheath Jets—Classification and the Search for Generation Mechanisms Using MMS Burst Mode Data

AbstractMagnetosheath jets are localized dynamic pressure enhancements in the magnetosheath. We make use of the high time resolution burst mode data of the Magnetospheric Multiscale mission for an analysis of waves in plasmas associated with three magnetosheath jets. We find both electromagnetic and electrostatic waves over the frequency range from 0 to 4 kHz that can be probed by the instruments on board the MMS spacecraft. At high frequencies we find electrostatic solitary waves, electron acoustic waves, and whistler waves. Electron acoustic waves and whistler waves show the typical properties expected from theory assuming approximations of a homogeneous plasma and linearity. In addition, 0.2 Hz waves in the magnetic field, 1 Hz electromagnetic waves, and lower hybrid waves are observed. For these waves the approximation of a homogeneous plasma does not hold anymore and the observed waves show properties from several different basic wave modes. In addition, we investigate how the various types of waves are generated. We show evidence that, the 1 Hz waves are connected to gradients in the density and magnetic field. The whistler waves are generated by a butterfly‐shaped pitch‐angle distribution and the electron acoustic waves by a cold electron population. The lower hybrid waves are probably generated by currents at the boundary of the jets. As for the other waves we can only speculate about the generation mechanism due to limitations of the instruments. Studying waves in jets will help to address the microphysics in jets which can help to understand the evolution of jets better.

Simulation of Dawn‐To‐Dusk Electric Field in the Jovian Inner Magnetosphere via Region 2‐Like Field‐Aligned Current

AbstractThe presence of the dawn‐to‐dusk electric field of about 4 mV/m in the Jovian inner magnetosphere and its response to the enhancement of the solar wind dynamic pressure are still a mystery of the rotation‐dominated Jovian magnetosphere. Previous studies have suggested that magnetosphere‐ionosphere (M‐I) coupling via Region 2‐like (R2‐like) field‐aligned current (FAC) could be the origin of the Jovian dawn‐to‐dusk electric field. This study investigates whether the dawn‐to‐dusk electric field is formed from this scenario by using a Jovian ionosphere model and a two‐dimensional ionospheric potential solver. Our results show that the dawn‐dusk asymmetry in the ionospheric potential form even at middle latitudes and that the dawn‐to‐dusk electric field is induced in the inner magnetosphere if the electric potential is mapped to the magnetospheric equatorial plane. Around the Io orbit, the calculated electric field strength for the ionosphere without meteoroid influx is too large, 200 mV/m at dawn and 88 mV/m at dusk. One of the solutions is to consider long‐lived meteoric ions in the Jovian ionosphere, which reduce the electric field strength to 15 mV/m at dawn and 12 mV/m at dusk. The model also shows that the electric field strength increases with the intensity of R2‐like FAC, consistent with its response to the solar wind dynamic pressure observed by the Hisaki satellite.

Magnetosheath Jet Formation Influenced by Parameters in Solar Wind Structures.

Magnetosheath jets are dynamic pressure enhancements observed in the terrestrial magnetosheath. Their generation mechanisms are currently debated but the majority of jets can be linked to foreshock processes. Recent results showed that jets are less numerous when coronal mass ejections (CMEs) cross the magnetosheath and more numerous when stream interaction regions (SIRs) cross it. Here, we show for the first time how the pronounced substructures of CMEs and SIRs are related to jet production. We distinguish between compression and magnetic ejecta (ME) regions for the CME as well as compression region associated with the stream interface and high-speed streams (HSSs) for the SIR. Based on THEMIS and OMNI data covering 2008-2021, we show the 2D probability distribution of jet occurrence using the cone angle and Alfvén Mach number. We compare this distribution with the values within each solar wind (SW) structure. We find that both high cone angles and low Alfvén Mach numbers within CME-MEs are unfavorable for jet production as they may inhibit a well-defined foreshock region. 1D histograms of all parameters show, which SW parameters govern jet occurrence in each SW structure. In terms of the considered parameters the most favorable conditions for jet generation are found for HSSs due to their associated low cone angles, low densities, and low magnetic field strengths.

Effects of Force in the Martian Plasma Environment With Solar Wind Dynamic Pressure Enhancement

AbstractDisturbed solar wind dynamic pressure is one of the important external drivers which could cause significant impacts on Martian plasma environment. In this study, a 3D multifluid multispecies numerical model is established to simulate the interaction between solar wind and Mars. Functions of electromagnetic forces applied on different ion species were analyzed. We found that the total electromagnetic force peaks near bow shock (BS) and magnetic pileup boundary (MPB) with clear asymmetry features, acting to decelerate solar wind plasma across boundary layers, and compresses heavy ions toward the planet inside the MPB. For solar wind protons, electron pressure gradient force dominates near BS and Hall electric field force dominates near MPB, controlling the location of plasma boundary. Furthermore, the morphology of motional electric field force shows clear north‐south asymmetry, leading to the formation of asymmetric structures and plasma flow in Martian space environment. The response of BS, MPB to a solar wind dynamic pressure enhancement event, as well as the effects of electromagnetic forces in this process are also investigated. After the arrival of solar wind pulse, the magnitudes of electromagnetic forces increased simultaneously to balance the enhanced solar wind dynamic pressure, while the peaks of forces moved inward with BS and MPB. The magnitudes and peaks of ion velocity in subsolar region show similar variations as well, with the greater enhancement of forces leading to the greater increase of ion velocities, indicating that the changes of forces influence boundary layers through the variation of plasma speed.

Time‐Varying Magnetopause Reconnection During Sudden Commencement: Global MHD Simulations

AbstractIn response to a solar wind dynamic pressure enhancement, the compression of the magnetosphere generates strong ionospheric signatures and a sharp variation in the ground magnetic field, termed sudden commencement (SC). While such compressions have also been associated with a contraction of the ionospheric polar cap due to the triggering of reconnection in the magnetotail, the effect of any changes in dayside reconnection is less clear and is a key component in fully understanding the system response. In this study, we explore the time‐dependent nature of dayside coupling during SC by performing global simulations using the Gorgon magnetohydrodynamic code and impact the magnetosphere with a series of interplanetary shocks with different parameters. We identify the location and evolution of the reconnection region in each case as the shock propagates through the magnetosphere, finding strong enhancement in the dayside reconnection rate and prompt expansion of the dayside polar cap prior to the eventual triggering of tail reconnection. This effect pervades for a variety of interplanetary magnetic field orientations, and the reconnection rate is most enhanced for events with higher dynamic pressure. We explain this by repeating the simulations with a large explicit resistivity, showing that compression of the magnetosheath plasma near the propagating shock front allows for reconnection of much greater intensity and at different locations on the dayside magnetopause than during typical solar wind conditions. The results indicate that the dynamic behavior of dayside coupling may render steady models of reconnection inaccurate during the onset of a severe space weather event.

Distribution of O<sup>+</sup> and ${\text{O}}_{\text{2}}^{\text{+}}$ fluxes and their escape rates in the near-Mars magnetotail: A survey of MAVEN observations

Tailward ion outflows in the Martian-induced magnetotail are known to be one of the major channels for Martian atmospheric escape. On the basis of nearly 6.5 years of observations from the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission, we investigate the statistical distribution of tailward and Marsward fluxes of heavy ions (i.e., O⁺ and <inline-formula><tex-math id="Z-20220914082156">\begin{document}${\rm{O}}_2^+ $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="RA335-duhengle-F_Z-20220914082156.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="RA335-duhengle-F_Z-20220914082156.png"/></alternatives></inline-formula>) in the near-Mars magnetotail and explore their characteristic responses to the corotating interaction region (CIR), solar wind dynamic pressure, and local magnetic field intensity. Our results show that the tailward fluxes of oxygen ions and molecular oxygen ions in the magnetotail are significantly greater than their Marsward fluxes and that the tailward flux of molecular oxygen ions is generally larger than that of oxygen ions. Furthermore, the tailward ion flux distribution exhibits dependence on the CIR, solar wind dynamic pressure, and local magnetic field strength in a manner stronger than the Marsward ion flux distribution. According to the distribution of tailward ion fluxes, we calculate the corresponding escape rates of heavy ions and show that when the CIR occurs, the total escape rates of oxygen ions and molecular oxygen ions increase by a factor of ~2 and ~1.2, respectively. We also find that the escape rates of heavy ions increase with the enhancement of solar wind dynamic pressure, whereas the overall effect of the local magnetic field is relatively weak. Our study has important implications for improved understanding of the underlying mechanisms responsible for the Martian atmospheric escape and the evolution of the Martian atmospheric climate.

Evidence of Alfvén Waves Generated by Mode Coupling in the Magnetotail Lobe

AbstractMode coupling is an important mechanism to excite Alfvén waves and has been extensively investigated based on numerical simulations. However, no direct observational evidence has been found regarding to this mechanism in the magnetotail lobe. Here, we report an in‐situ observation that an Alfvén wave with a period of several minutes is clearly relevant to a fast mode wave in the magnetotail lobe based on observations of the Cluster spacecraft. These waves occur at the region where the Alfvén speed has a gradient during an enhancement of the solar wind dynamic pressure. This suggests that the Alfvén wave is generated by the mode conversion at the region where the Alfvén speed has a gradient, and the fast mode wave might be driven by the solar wind. Our observations provide an important insight into the wave generation and energy conversion in the magnetosphere.

Relative Contribution of ULF Waves and Whistler‐Mode Chorus to the Radiation Belt Variation During the May 2017 Storm

AbstractWe investigate the time and location where ULF waves and whistler‐mode chorus contributed to the net flux enhancement of relativistic electrons during the magnetic storm of May 2017. During the early recovery phase, both ULF and chorus waves contribute to the enhancement of relativistic electron fluxes, but ULF waves play roles of the inward diffusion. During the late recovery phase, both Van Allen Probe‐B and Arase show that whistler‐mode chorus contributes to the flux enhancement confined in the L‐value. The CRCM coupled with BATS‐R‐US simulation qualitatively reproduces the global evolution of ULF waves. Although the electron flux is underestimated by the simulation, this study reveals a large anisotropy of hot electrons in the region where whistler‐mode chorus waves were actually observed by satellites. In addition, the estimated magnetic field curvature on the dayside is small during the recovery phase. Furthermore, we investigate the control of wave evolution. Both observations and the simulation suggest that the observed ULF waves in the frequency range of ∼2–5 mHz are excited by the enhancement of the solar wind dynamic pressure. Observations also indicate that whistler‐mode chorus on the nightside is predominantly excited by hot electrons with temperature anisotropy, whereas the dayside chorus is enhanced by the change of the magnetic field line configuration. The estimated spatial distributions of electron anisotropy and magnetic field curvature provide an explanation for the presence of enhanced whistler‐mode chorus in the dusk sector, which is far from the usual location of wave generation.

Conceptual Design and Multi-Disciplinary Computational Investigations of Multirotor Unmanned Aerial Vehicle for Environmental Applications

This study focuses on establishing a conceptual design for a multirotor unmanned aerial vehicle (UAV). The objectives of this octocopter are to reduce the number of flight cancelations and car accidents owing to low-visibility issues and to improve abnormal environmental conditions due to the presence of smoke. The proposed octocopter contains a convergent–divergent [CD] duct-based storage tank, which provides a platform to store saltwater and allows it to fly in foggy zones. Fine saltwater is sprayed from the octocopter and dispersed into the low clouds, thereby altering the vapor’s microphysical processes to break it up and improve visibility. The nature of the seawater and its enhanced fluid properties, due to the involvement of octocopter, creates the fluid flow mixing between atmospheric fluids and spraying particles, which increases the settling of foggy and smokey content groundward. For deployment, the conceptual design of the octocopter was initially constructed through analytical approaches. Additionally, three unique historical relationships were created. The standard engineering approaches involved in this work were stability analysis through MATLAB and fluid-property analysis through computational fluid dynamics (CFD) cum multiple reference frame (MRF) tools. The systematic model of this octocopter was developed by CATIA, and thereafter CFD and fluid–structure-interaction (FSI) analyses were computed, in ANSYS Workbench, on the octocopter for various environmental conditions. The aerodynamic forces on the drone, the enhancement of dynamic pressure by the presence of high amounts of rotors and nozzle sprayer, suitable material to resist aerodynamic loadings, and tests on the efficiency of the controller and its electronic components were investigated in detail. Finally, the proposed octocopter-based dynamic system was conceptually constructed.

Bursty magnetic reconnection at the Earth's magnetopause triggered by high-speed jets

The impact of high-speed jets—dynamic pressure enhancements in the magnetosheath—on the Earth's magnetopause has been observed to trigger local magnetic reconnection. We perform a three-dimensional hybrid simulation to study the magnetosheath and magnetopause under turbulent conditions using a quasi-radial southward interplanetary magnetic field (IMF). In contrast to quasi-steady reconnection with a strong southward IMF, we show that after the impact of a jet on the magnetopause, the magnetopause moves inward, the current sheet is compressed and intensified and signatures of local magnetic reconnection are observed, showing similarities to spacecraft measurements.

ULF‐Modulation of Whistler‐Mode Waves in the Inner Magnetosphere During Solar Wind Compression

AbstractThe solar wind plays important roles in terrestrial magnetosphere dynamics, including the particle population and plasma wave generation. Here, we report an interesting event that ultralow frequency (ULF) waves are enhanced right after solar wind compression and the compressional mode ULF wave subsequently modulates both the intensity and energy flux direction of whistler‐mode waves. Quasi‐periodic whistler‐mode wave packets are observed around = 5.6 at noon sector by Van Allen Probes. Growth rate calculation demonstrates that the compressional mode ULF wave can modulate the whistler‐mode wave intensity by modulating the energetic electron anisotropy. Moreover, the direction of wave energy flux is observed to alternate between northward and southward at equator, which is probably because the intense ULF waves periodically alter the relative direction of the wave source region with respect to the spacecraft. The current results provide a chain of observational evidences to illustrate how the generation and propagation of whistler‐mode waves in the inner magnetosphere are affected by ULF waves during the solar wind dynamic pressure enhancement.

Automated Technique for the Detection of Step‐Like Solar Wind Dynamic Pressure Changes: Application to the Response of the Transpolar Potential to Solar Wind Dynamic Pressure Fronts

AbstractThe input from the solar wind (SW) and the accompanying Interplanetary Magnetic Field (IMF) is the defining feature of the solar wind‐magnetosphere interactions. One of the most important SW drivers is the solar wind dynamic pressure, and most significantly its sharp changes known as pressure fronts. Sudden enhancements in solar wind dynamic pressure, , have been shown to lead to intensification of the auroral electrojets (and Region 1 field‐aligned currents), increase in auroral emissions, and significant enhancement in ionospheric convection and the transpolar potential. Case studies of the interaction between pressure fronts and the terrestrial space environment shed great light on their importance to the structure and dynamics of the system. However, thorough understanding of the interaction requires fully statistical investigations. These statistical studies require a large number of suitable pressure front events. In the past these have been obtained through laborious manual inspection of solar wind data. We present an automated procedure that identifies sudden step enhancements in that satisfy a desired set of limiting step‐like characteristics, such as magnitude of the change, sign of the change (positive/negative), and rate of change. The procedure yields a list of suitable events, along with their step features within minutes. The technique is tested for missed events and false positives by direct comparison to manual inspection of the data. Its utility is illustrated by application to the statistical effect of pressure fronts to the transpolar potential as measured by the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) technique.

3D Space‐Time Adaptive Hybrid Simulations of Magnetosheath High‐Speed Jets

AbstractWe study the generation and evolution of spatially localized dynamic plasma pressure enhancements in the magnetosheath (high‐speed jets) by carrying out three‐dimensional hybrid simulations of the Earth's dayside magnetosphere with a novel, space‐time adaptive code, HYPERS. High‐speed jets are shown to occur downstream of quasi‐parallel bow shocks under southward and northward quasi‐radial interplanetary magnetic field conditions. The physical properties and three‐dimensional morphology of simulation jets are found to be consistent with general statistical knowledge acquired from the satellite observations. We discuss a “magnetokinetic” mechanism for jet origin whereby the compression of solar wind plasma and its penetration into the magnetosheath is tied to the turbulence‐driven magnetic field perturbations. We compare three‐dimensional jets to dynamic pressure structures observed in two‐dimensional hybrid simulations and demonstrate the impact of large jets on the magnetopause and the cusp.

Soft X-ray and ENA Imaging of the Earth's Dayside Magnetosphere.

The LEXI and SMILE missions will provide soft X‐ray images of the Earth's magnetosheath and cusps after their anticipated launch in 2023 and 2024, respectively. The IBEX mission showed the potential of an Energetic Neutral Atom (ENA) instrument to image dayside magnetosheath and cusps, albeit over the long hours required to raster an image with a single pixel imager. Thus, it is timely to discuss the two imaging techniques and relevant science topics. We simulate soft X‐ray and low‐ENA images that might be observed by a virtual spacecraft during two interesting solar wind scenarios: a southward turning of the interplanetary magnetic field and a sudden enhancement of the solar wind dynamic pressure. We employ the OpenGGCM global magnetohydrodynamics model and a simple exospheric neutral density model for these calculations. Both the magnetosheath and the cusps generate strong soft X‐rays and ENA signals that can be used to extract the locations and motions of the bow shock and magnetopause. Magnetopause erosion corresponds closely to the enhancement of dayside reconnection rate obtained from the OpenGGCM model, indicating that images can be used to understand global‐scale magnetopause reconnection. When dayside imagers are installed with high‐ENA inner‐magnetosphere and FUV/UV aurora imagers, we can trace the solar wind energy flow from the bow shock to the magnetosphere and then to the ionosphere in a self‐standing manner without relying upon other observatories. Soft X‐ray and/or ENA imagers can also unveil the dayside exosphere density structure and its response to space weather.

Classifying Magnetosheath Jets Using MMS: Statistical Properties

AbstractUsing Magnetospheric Multiscale (MMS) data, we find, classify, and analyze transient dynamic pressure enhancements in the magnetosheath (jets) from May 2015 to May 2019. A classification algorithm is presented, using in situ MMS data to classify jets ( ) into different categories according to their associated angle between interplanetary magnetic field (IMF) and the bow shock normal vector (θBn). Jets appearing for θBn &lt; 45 are referred to as quasi‐parallel, while jets appearing for θBn &gt; 45 as quasi‐perpendicular jets. Furthermore, we define those jets that occur at the boundaries between quasi‐parallel and quasi‐perpendicular magnetosheath as boundary jets. Finally, encapsulated jets are jet‐like structures with similar characteristics to quasi‐parallel jets while the surrounding plasma is of quasi‐perpendicular nature. We present the first statistical results of such a classification and provide comparative statistics for each class. Furthermore, we investigate correlations between jet quantities. Quasi‐parallel jets have the highest dynamic pressure while occurring more often than quasi‐perpendicular jets. The infrequent quasi‐perpendicular jets have a much smaller duration, velocity, and density and are therefore relatively weaker. We conclude that quasi‐parallel and boundary jets have similar properties and are unlikely to originate from different generation mechanisms. Regarding the encapsulated jets, we suggest that they are a special subset of quasi‐parallel jets originating from the flanks of the bow shock, for large IMF cone angles although a relation to flux transfer events (FTEs) and magnetospheric plasma is also possible. Our results support existing generation theories, such as the bow shock ripple and SLAMS‐associated mechanisms while indicating that other factors may contribute as well.

Magnetosheath Microstructure: Mirror Mode Waves and Jets during Southward IP Magnetic Field

AbstractIn the Earth's magnetosheath plasma waves, nonlinear structures associated with characteristic ion populations can occur. Understanding the interaction of the solar wind with the magnetosphere requires a deeper knowledge of the underlying magnetosheath kinetic microstructure. We study a 45 min interval when the MMS spacecraft observed a southward magnetic field (Bz &lt; 0 nT) in the dayside magnetosheath. Using magnetic field and plasma data, we analyze three transient dynamic pressure enhancements identified as magnetosheath jets. The characteristics of these jets are different, suggesting different origins. While two of them, called J1 and J2, exhibit large increment in velocity and almost no density increment, the third jet (J3) shows large density enhancements with almost no velocity increment. The duration of J3 is ∼7 times longer than those of J1 and J2. J3 occurs at the region where the negative Bz becomes positive. Ion distributions inside the jets are different. J1 and J2 show a secondary field‐aligned beam, which is not present in J3, suggesting that magnetic reconnection at the magnetopause is responsible for their formation. Distributions inside J3 are more isotropic. B field and plasma signatures inside J3 correspond to the crossing of a sector boundary, similar to the heliospheric plasma sheet, suggesting that J3 forms by the evolution and interaction of a solar wind structure with the bow shock and magnetosheath. Fluctuations inside J3 have larger transverse components, although they propagate at large angles to B. In contrast, waves in regions between the jets are compressive and are identified as mirror mode waves.