Browsing by Author "Chen, L.-J."

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    High‐Frequency Wave Generation in Magnetotail Reconnection: Linear Dispersion Analysis
    (Wiley, 2019) Burch, J.L.; Dokgo, K.; Hwang, K.J.; Torbert, R.B.; Graham, D.B.; Webster, J.M.; Ergun, R.E.; Giles, B.L.; Allen, R.C.; Chen, L.-J.; Wang, S.; Genestreti, K.J.; Russell, C.T.; Strangeway, R.J.; Contel, O. Le
    Plasma and wave measurements from the NASA Magnetospheric Multiscale mission are presented for magnetotail reconnection events on 3 July and 11 July 2017. Linear dispersion analyses were performed using distribution functions comprising up to six drifting bi‐Maxwellian distributions. In both events electron crescent‐shaped distributions are shown to be responsible for upper hybrid waves near the X‐line. In an adjacent location within the 3 July event a monodirectional field‐aligned electron beam drove parallel‐propagating beam‐mode waves. In the 11 July event an electron distribution consisting of a drifting core and two crescents was shown to generate upper‐hybrid and beam‐mode waves at three different frequencies, explaining the observed broadband waves. Multiple harmonics of the upper hybrid waves were observed but cannot be explained by the linear dispersion analysis since they result from nonlinear beam interactions.
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    Magnetospheric Multiscale Dayside Reconnection Electron Diffusion Region Events
    (Wiley, 2018) Webster, J.M.; Burch, J.L.; Reiff, P.H.; Daou, A.G.; Genestreti, K.J.; Graham, D.B.; Torbert, R.B.; Ergun, R.E.; Sazykin, S.Y.; Marshall, A.; Allen, R.C.; Chen, L.-J.; Wang, S.; Phan, T.D.; Giles, B.L.; Moore, T.E.; Fuselier, S.A.; Cozzani, G.; Russell, C.T.; Eriksson, S.; Rager, A.C.; Broll, J.M.; Goodrich, K.; Wilder, F.
    We use high‐resolution data from dayside passes of the Magnetospheric Multiscale (MMS) mission to create for the first time a comprehensive listing of encounters with the electron diffusion region (EDR), as evidenced by electron agyrotropy, ion jet reversals, and j • E′ > 0. We present an overview of these 32 EDR or near‐EDR events, which demonstrate a wide variety of observed plasma behavior inside and surrounding the reconnection site. We analyze in detail three of the 21 new EDR encounters, which occurred within a 1‐min‐long interval on 23 November 2016. The three events, which resulted from a relatively low and oscillating magnetopause velocity, exhibited large electric fields (up to ~100 mV/m), crescent‐shaped electron velocity phase space densities, large currents (≥2 μA/m2), and Ohmic heating of the plasma (~10 nW/m3). We include an Ohm's law analysis, in which we show that the divergence of the electron pressure term usually dominates the nonideal terms and is much more turbulent on the magnetosphere versus the magnetosheath side of the EDR.
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    Temporal, Spatial, and Velocity-Space Variations of Electron Phase Space Density Measurements at the Magnetopause
    (Wiley, 2023) Shuster, J. R.; Gershman, D. J.; Giles, B. L.; Bessho, N.; Sharma, A. S.; Dorelli, J. C.; Uritsky, V.; Schwartz, S. J.; Cassak, P. A.; Denton, R. E.; Chen, L.-J.; Gurram, H.; Ng, J.; Burch, J.; Webster, J.; Torbert, R.; Paterson, W. R.; Schiff, C.; Viñas, A. F.; Avanov, L. A.; Stawarz, J.; Li, T. C.; Liu, Y.-H.; Argall, M. R.; Afshari, A.; Payne, D. S.; Farrugia, C. J.; Verniero, J.; Wilder, F.; Genestreti, K.; da Silva, D. E.
    Temporal, spatial, and velocity-space variations of electron phase space density are measured observationally and compared for the first time using the four magnetospheric multiscale (MMS) spacecraft at Earth's magnetopause. Equipped with these unprecedented spatiotemporal measurements offered by the MMS tetrahedron, we compute each term of the electron Vlasov equation that governs the evolution of collisionless plasmas found throughout the universe. We demonstrate how to use single spacecraft measurements to improve the resolution of the electron pressure gradient that supports nonideal parallel electric fields, and we develop a model to intuit the types of kinetic velocity-space signatures that are observed in the Vlasov equation terms. Furthermore, we discuss how the gradient in velocity-space sheds light on plasma energy conversion mechanisms and wave-particle interactions that occur in fundamental physical processes such as magnetic reconnection and turbulence.