Modeling subauroral polarization streams during the 17 March 2013 storm

The subauroral polarization streams (SAPS) are one of the most important features in representing magnetosphere‐ionosphere coupling processes. In this study, we use a state‐of‐the‐art modeling framework that couples an inner magnetospheric ring current model RAM‐SCB with a global MHD model Block‐Adaptive Tree Solar‐wind Roe Upwind Scheme (BATS‐R‐US) and an ionospheric potential solver to study the SAPS that occurred during the 17 March 2013 storm event as well as to assess the modeling capability. Both ionospheric and magnetospheric signatures associated with SAPS are analyzed to understand the spatial and temporal evolution of the electrodynamics in the midlatitude regions. Results show that the model captures the SAPS at subauroral latitudes, where Region 2 field‐aligned currents (FACs) flow down to the ionosphere and the conductance is lower than in the higher‐latitude auroral zone. Comparisons to observations such as FACs observed by Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE), cross‐track ion drift from Defense Meteorological Satellite Program (DMSP), and in situ electric field observations from the Van Allen Probes indicate that the model generally reproduces the global dynamics of the Region 2 FACs, the position of SAPS along the DMSP, and the location of the SAPS electric field around L of 3.0 in the inner magnetosphere near the equator. The model also demonstrates double westward flow channels in the dusk sector (the higher‐latitude auroral convection and the subauroral SAPS) and captures the mechanism of the SAPS. However, the comparison with ion drifts along DMSP trajectories shows an underestimate of the magnitude of the SAPS and the sensitivity to the specific location and time. The comparison of the SAPS electric field with that measured from the Van Allen Probes shows that the simulated SAPS electric field penetrates deeper than in reality, implying that the shielding from the Region 2 FACs in the model is not well represented. Possible solutions in future studies to improve the modeling capability include implementing a self‐consistent ionospheric conductivity module from inner magnetosphere particle precipitation, coupling with the thermosphere‐ionosphere chemical processes, and connecting the ionosphere with the inner magnetosphere by the stronger Region 2 FACs calculated in the inner magnetosphere model.Key PointsSAPS simulation using BATS‐R‐US coupled with ring current model RAM‐SCBComparisons done with AMPERE, DMSP, and Van Allen Probes observationsCaptured the basic physics and mechanism of SAPSPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/111134/1/jgra51638.pd

Tilting Pad Journal Bearing Pivot Design For High Load Applications.

LecturePg. 33-48Reducing pivot stress, pivot wear and preventing pivot failure are major design challenges encountered by tilting pad bearing designers in the extremely high load regime where the bearing unit load may often range up to 500 psi. In an attempt to address these design challenges, simple equations are presented for the calculation of pivot stiffness and the resulting pivot contact stress for a nonaligning cylindrical pivot, a self-aligning spherical pivot and a self-aligning sphere-in-a-cylinder pivot. The effect of the pivot's flexibility on the bearing's stiffness and damping properties is also investigated. Comparisons are made between the three pivot designs. Utilizing the simple equations for pivot stress, a method to determine proper pivot sizing to prevent pivot failure due to high loads is outlined using a spherical pivot as a design example. A finite element stress analysis is also considered and the results compared to the simplified analysis

Van Allen Probes Observations of Second Harmonic Poloidal Standing Alfvén Waves

Long-lasting second-harmonic poloidal standing Alfvén waves (P2 waves) were observed by the twin Van Allen Probes (Radiation Belt Storm Probes, or RBSP) spacecraft in the noon sector of the plasmasphere, when the spacecraft were close to the magnetic equator and had a small azimuthal separation. Oscillations of proton fluxes at the wave frequency (∼10 mHz) were also observed in the energy (W) range 50–300 keV. Using the unique RBSP orbital configuration, we determined the phase delay of magnetic field perturbations between the spacecraft with a 2nπ ambiguity. We then used finite gyroradius effects seen in the proton flux oscillations to remove the ambiguity and found that the waves were propagating westward with an azimuthal wave number (m) of ∼−200. The phase of the proton flux oscillations relative to the radial component of the wave magnetic field progresses with W, crossing 0 (northward moving protons) or 180° (southward moving protons) at W ∼ 120 keV. This feature is explained by drift-bounce resonance (mωd ∼ ωb) of ∼120 keV protons with the waves, where ωd and ωb are the proton drift and bounce frequencies. At lower energies, the proton phase space density ( ) exhibits a bump-on-tail structure with occurring in the 1–10 keV energy range. This is unstable and can excite P2 waves through bounce resonance (ω ∼ ωb), where ω is the wave frequency

Statistical comparison of the temporal fluctuations of pulsating auroral luminosity and chorus wave intensity

第8回極域科学シンポジウム/個別セッション：[OS] 宙空圏12月5日（火）国立極地研究所 1階交流アトリウムThe Eighth Symposium on Polar Science/Ordinary sessions: [OS] Space and upper-atmosphere sciencesTue. 5 Dec./Entrance Hall (1st floor), National Institute of Polar Researc

Electric and magnetic radial diffusion coefficients using the Van Allen probes data

ULF waves are a common occurrence in the inner magnetosphere and they contribute to particle motion, significantly, at times. We used the magnetic and the electric field data from the Electric and Magnetic Field Instrument Suite and Integrated Sciences (EMFISIS) and the Electric Field and Waves instruments (EFW) on board the Van Allen Probes to estimate the ULF wave power in the compressional component of the magnetic field and the azimuthal component of the electric field, respectively. Using L∗, Kp, and magnetic local time (MLT) as parameters, we conclude that the noon sector contains higher ULF Pc-5 wave power compared with the other MLT sectors. The dawn, dusk, and midnight sectors have no statistically significant difference between them. The drift-averaged power spectral densities are used to derive the magnetic and the electric component of the radial diffusion coefficient. Both components exhibit little to no energy dependence, resulting in simple analytic models for both components. More importantly, the electric component is larger than the magnetic component by one to two orders of magnitude for almost all L∗ and Kp; thus, the electric field perturbations are more effective in driving radial diffusion of charged particles in the inner magnetosphere. We also present a comparison of the Van Allen Probes radial diffusion coefficients, including the error estimates, with some of the previous published results. This allows us to gauge the large amount of uncertainty present in such estimates

Pc5 wave power in the quiet‐time plasmasphere and trough: CRRES observations

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94876/1/grl26887.pd

Near-Earth injection of MeV electrons associated with intense dipolarization electric fields: Van Allen Probes observations.

Substorms generally inject tens to hundreds of keV electrons, but intense substorm electric fields have been shown to inject MeV electrons as well. An intriguing question is whether such MeVelectron injections can populate the outer radiation belt. Here we present observations of a substorm injection of MeV electrons into the inner magnetosphere. In the premidnight sector at L ∼ 5.5, Van Allen Probes (Radiation Belt Storm Probes)-A observed a large dipolarization electric field (50 mV/m) over ∼40 s and a dispersionless injection of electrons up to ∼3 MeV. Pitch angle observations indicated betatron acceleration of MeV electrons at the dipolarization front. Corresponding signals of MeV electron injection were observed at LANL-GEO, THEMIS-D, and GOES at geosynchronous altitude. Through a series of dipolarizations, the injections increased the MeV electron phase space density by 1 order of magnitude in less than 3 h in the outer radiation belt (L > 4.8). Our observations provide evidence that deep injections can supply significant MeV electrons

Nonlinear Drift Resonance Between Charged Particles and Ultralow Frequency Waves: Theory and Observations

In Earth’s inner magnetosphere, electromagnetic waves in the ultralow frequency (ULF) range play an important role in accelerating and diffusing charged particles via drift resonance. In conventional drift resonance theory, linearization is applied under the assumption of weak waveâ particle energy exchange so particle trajectories are unperturbed. For ULF waves with larger amplitudes and/or durations, however, the conventional theory becomes inaccurate since particle trajectories are strongly perturbed. Here we extend the drift resonance theory into a nonlinear regime, to formulate nonlinear trapping of particles in a waveâ carried potential well, and predict the corresponding observable signatures such as rolledâ up structures in particle energy spectrum. After considering how this manifests in particle data with finite energy resolution, we compare the predicted signatures with Van Allen Probes observations. Their good agreement provides the first observational evidence for the occurrence of nonlinear drift resonance, highlighting the importance of nonlinear effects in magnetospheric particle dynamics under ULF waves.Plain Language SummaryIn Earth’s Van Allen radiation belts, ultralow frequency (ULF) waves in the frequency range between 2 and 22 mHz play a crucial role in accelerating charged particles via a resonant process named drift resonance. When such a resonance occurs, a resonant particle observes a constant phase of the wave electric field, and it experiences a net energy excursion. In previous studies of drift resonance, a linearization approach is often applied with assumption of a weak waveâ particle energy exchange. In this study, we extend the linear theory into the nonlinear regime to formulate the particle behavior in the ULF wave field, and predict characteristic signatures of the nonlinear process observable from a virtual magnetospheric spacecraft. Such newly predicted signatures are found to agree with observations from the National Aeronautics and Space Administration’s Van Allen Probes, which provides the first identification of nonlinear drift resonance and highlights the importance of nonlinear effects in ULF waveâ particle interactions in the Van Allen radiation belts.Key PointsThe nonlinear theory of ULF waveâ particle drift resonance is developed to formulate the behavior of charged particles in ULF wave fieldSignatures of nonlinear drift resonance include rolledâ up structures and/or multiperiod oscillations in the particle energy spectrumIn situ observations of the newly predicted signatures validate the theory and provide a first identification of nonlinear drift resonancePeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/146432/1/grl57916_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/146432/2/grl57916.pd