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THEMIS observations of magnetic reconnection structures in the dayside geomagnetopause PRESENTER: Koji Kondoh ABSTRACT. We have studied asymmetric magnetic reconnection in the dayside geomagnetopause using magnetohydrodynamics simulations. We have indicated the new whole asymmetric magnetic reconnection structures (Nitta et al. 2016; Nitta and Kondoh 2019, 2021, 2022). One of them is the fast outflow structure. The fast reconnection jet is observed not only in the reconnection fan sandwiched by the slow shock pair, but also in the lower beta side plasmoid in the asymmetric case, while that is observed only in the reconnection fan in the symmetric reconnection. Usually we identify the magnetic reconnection event in the dayside magnetopause using the reconnection outflow speed from in-situ observation data. Our new findings in the previous studies about the asymmetric reconnection mean that we do not identify where we observe these reconnection events. In this study, we clarify the observation position in the asymmetric magnetic reconnection structure using THEMIS observations. |
GEOTAIL observations of magnetic reconnection environment around the dayside geomagnetopause PRESENTER: Koji Kondoh ABSTRACT. Magnetic reconnection in the dayside geomagnetopause occurs in the asymmetric current sheet system. We have indicated that these asymmetric reconnection are significantly different from the Petscheck type symmetric reconnection (Nitta et al. 2016; Nitta and Kondoh 2019, 2021, 2022). One of the new different characteristics is the formation of the forward fast shock. This fast shock are formed due to the different of the Alfvenic speeds in the both sides of the current sheet. The other one is the fast outflow structure. The fast reconnection jet is observed not only in the reconnection fan sandwiched by the slow shock pair, but also in the lower beta side plasmoid in the asymmetric case, while that is observed only in the reconnection fan in the symmetric reconnection. It is also indicated that these new features in the asymmetric reconnection are controlled by the physical conditions around the dayside magnetopause. GEOTAIL satellite had observed a lot of geomagnetopause crossings. In this paper, we show the physical conditions observed by GEOTAIL satellite around there. In particular, we focused on the ratio of the plasma density, temperature, and the magnetic field strength in the magnetosphere to those in the magnetosheath. |
Storm-time Very-Near-Earth Magnetotail Reconnection: A Statistical Perspective PRESENTER: Fekireselassie Beyene ABSTRACT. While a large body of work has studied the storm-time ring current energization, few studies have provided direct verification of the energy transport into the inner-magnetosphere that powers the ring current. Recent studies of very-near-Earth reconnection (VNERX, defined here as occurring at geocentric distance < 10 RE) during storms suggest that such reconnection may play a critical role in that regard. VNERX can host intense transient electric fields, on the order of 10s of kV/RE, allowing for significant acceleration and efficient transport of plasma sheet ions into the ring current. Here we address how common this process is. We use storm-time inner-magnetosphere and plasma sheet observations from three THEMIS satellites spanning 11 years of operation (2010-2021). Our analysis shows a VNERX occurrence rate of ~one event per thousand hours. This rate is less than previously published ion-diffusion-region occurrence rates seen in the near-Earth plasma sheet during non-storm times (likely substorms). Our results suggest that while VNERX events may play a significant role in the storm-time ring current’s initial buildup, that during the storm main phase, the enhanced convection powering the ring current during storm recovery is likely contributed by reconnection further down-tail than 10 RE. |
The self-similar reconnection model --a new MHD reconnection model for astrophysical applications-- PRESENTER: Shin-ya Nitta ABSTRACT. I present a new theoretical model of the magnetic reconnection (RX) designed for astrophysical applications; the self-similar RX model. The current sheet (CS) system which we frequently encounter in astrophysical problem is characterized by wide spatial scale much larger than the CS thickness. The outer circumstance does not influence the temporal evolution of the RX system for a long while. The RX system spontaneously expands along with the fast-mode rarefaction wave (FRW) emitted from the reconnection point. When the size of FRW dominates the CS thickness, the system no longer has proper spatial scale other than the propagating FRW scale. The RX system asymptotically tends to expand self-similarly (the self-similar phase). The self-similar RX model is an extension of the Petschek model that is characterized by the figure-X shaped slow shocks. Our new model also includes figure-X shaped MHD shocks: Combination of the slow shock, intermediate shock, or rotational discontinuity followed by slow-mode expansion. These shocks work as the main energy convertor, and extend self-similarly. Thus, the magnetic energy conversion power increases in proportion both to the time from the onset of the RX and the reconnection rate. We clarified the properties of the spatial structure of the self-similar RX system (Nitta+2001, 2002, Nitta 2007, Nitta+2016, Nitta and Kondoh 2019, 2021, 2022). In addition, we systematically investigated the dependence of the reconnection rate on the plasma-beta (Nitta 2004, 2006), magnetic Reynolds number (Nitta2007), asymmetry of the thermodynamic quantities with regard to the CS (Nitta+2016, Nitta and Kondoh 2019, 2022), magnetic shear (Nitta and Kondoh 2021, 2022) in our series of papers. The self-similar RX model is categorized as the fast RX regime in the maximum case, however its reconnection rate significantly decreases to almost like the slow RX regime depending on parameters. We summarize these properties in my talk. |
Direct observations of energy transfer from resonant electrons to whistler-mode waves in magnetosheath of Earth PRESENTER: Naritoshi Kitamura ABSTRACT. Electromagnetic whistler-mode waves in space plasmas play critical roles in collisionless energy transfer between the electrons and the electromagnetic field. Although resonant interactions have been considered as the likely generation process of the waves, observational identification has been extremely difficult due to the short time scale of resonant electron dynamics. Here we show strong nongyrotropy, which rotate with the wave, of cyclotron resonant electrons as direct evidence for the locally ongoing secular energy transfer from the resonant electrons to the whistler-mode waves using ultra-high temporal resolution data obtained by NASA’s Magnetospheric Multiscale (MMS) mission in the magnetosheath. The nongyrotropic electrons carry a resonant current, which is the energy source of the wave as predicted by the nonlinear wave growth theory. This result proves the nonlinear wave growth theory, and furthermore demonstrates that the degree of nongyrotropy, which cannot be predicted even by that nonlinear theory, can be studied by observations. |
Nonlinear wave damping of chorus emission at 0.5 electron gyrofrequency gap due to Landau resonance PRESENTER: Yikai Hsieh ABSTRACT. Whistler mode chorus emissions are usually observed in the Earth’s inner magnetosphere with a gap around 0.5 electron gyrofrequency (fce) in dynamic spectra. Chorus emissions initially generate at the equator with broadband frequency and then damp at 0.5 fce during propagation toward higher latitudes. Electrons nonlinearly trapped by Landau resonance gain energies from waves. The Landau resonance velocity becomes very close to the group velocity of nearly parallel whistler mode waves at frequencies around 0.5 fce, resulting in a long interaction time and possible wave damping. Evidence of the mechanism has been observed by the Geotail satellite [1]. In this study, we reproduced the formation of the gap of an obliquely propagating chorus emission in test-particle simulation and self-consistent two-dimensional general curvilinear particle-in-cell (2D gcPIC) simulation. Analyzing the simulation results, we confirm that Landau resonance contributes to wave damping, which transfers energies from the wave to electrons. We further found that the energy exchanges occur on the perpendicular component of the wave electric field and perpendicular electron velocities rather than the parallel components [2]. [1] Yagitani, S., T. Habagishi, and Y. Omura (2014), Geotail observation of upper band and lower band chorus elements in the outer magnetosphere, J. Geophys. Res. Space Physics, 119, https://10.1002/2013JA019678. [2] Hsieh, Y.-K., & Omura, Y. (2018). Nonlinear damping of oblique whistler mode waves via Landau resonance. Journal of Geophysical Research: Space Physics, 123. https://doi.org/10.1029/2018JA025848 |
Non-extensive Tsallis entropy analysis on long-term variation of Joule heating at high latitudes PRESENTER: Sumesh Gopinath ABSTRACT. A notable quantity of the solar wind energy crossing the magnetopause reaches the high-latitude thermosphere-ionosphere system, the consequences of which are remarkable as well as global in nature. Non-extensive Tsallis entropy, a generalization of Shannon entropy, provides a promising tool for studying various features of nonextensive dynamical systems. It can give information regarding the intrinsic fluctuations in such a system by characterizing the degree of nonextensivity. We report in this paper for the first time the calculation of the Tsallis entropy of Joule heating in high latitude upper atmosphere and discuss its yearly relationship with the solar wind forcing during solar maxima and minima periods. We have used theoretical models to calculate the Poynting flux flowing onto the Earth’s ionosphere and associated Joule heating due to the solar wind-magnetosphere-ionosphere dynamo. The investigation reveals that the Tsallis entropy values clearly reflect the complexity variations during solar maxima and minima periods of solar cycle 23 and solar cycle 24. |
Ionospheric flow fluctuations at mid-latitudes during storms as seen by SuperDARN-Van Allen Probes-Arase conjunctions PRESENTER: T. Hori ABSTRACT. The recent Super Dual Auroral Radar Network (SuperDARN) observations show that ionospheric flow fluctuations of the mHz or lower frequency range appear even in the subauroral to mid-latitude region during magnetic storm times. An interesting feature of the flow fluctuations is that they appear to propagate azimuthally either westward or eastward, and occasionally bifurcate toward the both directions. Taking a closer look with high spatial resolution measurements provided by the radars reveals that those flow fluctuations consist of meso-scale patchy structures of ionospheric convection with a significant latitudinal flow component and a longitudinal scale of ~1h MLT. The azimuthal propagation properties strongly suggest that westward-drifting ions and eastward-drifting electrons of tens of keV in the inner magnetosphere can be the moving sources responsible for excitation of MHD waves seen by the radars at the ionospheric footprint. However, only few observations in the magnetosphere have been reported on the source of the waves at the subauroral to mid-latitudes. Recent observations in the inner magnetosphere by the Arase satellite and the Van Allen Probes have provided a good opportunity to examine their magnetospheric counterpart in further detail. On the basis of in-situ measurement of ring current particles and the magnetic field in the inner magnetosphere, we discuss the generation mechanism of the observed flux tube fluctuations in terms of resonant or non-resonant processes. |
Energetic electron injection leading to the formation of zebra pattern in the Earth’s inner magnetosphere PRESENTER: Megha Pandya ABSTRACT. The interaction between the solar wind and the Earth’s magnetic field induces catastrophic effects within the Earth's magnetosphere-ionosphere system. Under active geomagnetic conditions, the geomagnetic tail often releases the stored energy that bring particles into the near-Earth environment. Under the influence of magnetospheric electric and magnetic fields, these energetic particles undergo a variety of motions and give rise to multiple features. One such interesting feature is electron zebra stripes, which manifest as bands in the energy versus L-value spectrogram. During an intense geomagnetic storm of September 2017, the RBSPICE instrument on board Van Allen Probe-A recorded the distortion and reformation of the electron zebra stripes. We conduct an advection simulation under the time-dependent electric and magnetic fields acquired from the MHD simulation to reproduce the observed electron zebra stripe structures. Our study provides a detailed understanding of the magnetospheric condition that is responsible for the generation of electron zebra stripes. We find that the day-night asymmetry of the azimuthal component the electric fields, which are driven by the Region-1 field-aligned currents (FACs), play a crucial role in the formation of intense electron flux peaks and valleys in the zebra stripes. On the nightside, the dawn-to-dusk electric field gives rise to the transport of electrons from the geomagnetic tail to the Earth’s inner radiation belt. The peak-forming electrons of the zebra stripes come primarily from the nightside. Thus, the electron zebra stripes are the consequence of the enhancements of the Region-1 FACs that are driven by the solar wind-magnetosphere coupling. Thus, the zebra stripes are the manifestation of the solar wind-inner magnetosphere coupling via the ionosphere associated with earthward transport of electrons from the geomagnetic tail region. |
Estimating the spacecraft potential of Comet Interceptor – simulation results and implications for plasma measurements PRESENTER: Sofia Bergman ABSTRACT. In 2019, Comet Interceptor was selected by ESA as a new F-class mission. This mission will visit a dynamically new comet that is yet-to-be-discovered. For the first time, multipoint measurements will be made in the cometary environment using three spacecraft: spacecraft A (ESA), probe B1 (JAXA) and probe B2 (ESA). All spacecraft will carry plasma instruments, allowing, for the first time, a three-dimensional study of the cometary plasma environment. The plasma measurements are, however, expected to be affected by the spacecraft potential. A spacecraft interacts with the surrounding environment which results in an accumulation of charge on the spacecraft surface. This process is problematic for low-energy plasma measurements. The charged particles are attracted to, or repelled from, the charged spacecraft surface, resulting in an energy shift and a distortion of the effective field of view of the instrument. To maximize the science return from the plasma instruments on Comet Interceptor, the measurements need to be optimized taking the spacecraft potential into account. In this study, we use the Spacecraft Plasma Interaction Software (SPIS) to make Particle-In-Cell (PIC) simulations of the expected spacecraft potential of probe B1 of Comet Interceptor. We study the spacecraft potential both in the solar wind and in different regions of the cometary plasma environment during the cometary flyby. This is done for different activity levels of the target comet and at different flyby velocities. The final step of the study is to use particle tracing to study the expected influence of the spacecraft potential on ion measurements to be made by the Cometary Ion Mass Spectrometer (CIMS) on probe B1. |
Simulation of ENA Imaging measurement on Chang’E-7 relay Satellite and expectation of scientific results PRESENTER: Li Lu ABSTRACT. Chang 'E-7 relay satellite (CE-7) is a lunar orbiting satellite, ENA imager aboard CE-7 can realize ENA imaging telemetry of different regions of the Earth's magnetosphere with the moon's revolution. Based on the clean particle radiation environment near lunar orbit and the balance of ENA telemetry fluxes near lunar orbit caused by differences in ENA emission diffusion modes in different regions of the magnetosphere, the ENA Imager aboard CE-7 provides us with an excellent opportunity to monitor the causal sequence of geomagnetic activity. Using the 20°×20° field of view, the 0.5°×0.5° angle resolution, and the ~0.17 cm2sr geometric factor, a two-dimensional ENA imager is being designed. The magnetospheric ring current simulation at a 4-20 keV energy channel for a medium geomagnetic storm (KP=5) shows that:(1) at ~60 earth radii (RE), the imager can collect 104 ENA events within 3 min to meet the statistical requirements of 2D coded imaging data inversion, so as to meet requirements of the analysis of the sub-storm ring current evolution process of magnetic storms above medium; (2) The pitch angle of ions in the magnetopause and magnetotail plasma sheet region is ~ 90°, and the ENA emission is only diffused in the equatorial plane. Therefore, its decay rate is relatively slow, and it will reach a balance with the ENA emission flux generated by the ring current at ~ 60RE lunar orbit. High spatial-temporal resolution ENA imaging monitoring of these two important regions will provide the measurement basis for the solar wind energy input process and generation mechanism; (3) the average sampling interval of ENA particle events is about 16 ms at the moon’s orbit; the spectral time difference for the set energy range is on the order of minutes, which can provide location information to track the trigger of geomagnetic storm particle events. |
Venus Dynamics Tracer (VdT), a mission dedicated for in-situ measurements of the Venus atmosphere PRESENTER: Moa Persson ABSTRACT. Recent Venus missions (Venus Express and Akatsuki) provided a large-scale view of Venus atmosphere and discovered new phenomena, such as high-altitude extension of the mountain wave to the cloud layer and a dawn-dusk asymmetry in the ionospheric motion. The superrotation of the cloud layer is assumed to be driven by the thermal tide but its relation to any meridional convection or waves is still unknown. The key to understand all these phenomena is to determine the multi-step re-distribution of the absorbed solar radiation to other forms of energy: (1) internal energy; including temperature, latent heat, and chemical energy (2) kinetic energy both in large scale flows/waves and in minor deviations of convection motions, (3) electric energy including ionization. To understand how the motion of Venus atmosphere is driven by the energy originating from the absorption of solar radiation, we proposed Venus Dynamics Tracer (VdT), a mission for in-situ measurements, as a response to the ESA call for new M-class missions. Specific targets were two major energy absorption regions: the cloud layer and the ionized upper atmosphere. The scientific goals were to investigate (a) the roles of the vertical and meridional circulation in maintaining major atmospheric dynamics near the cloud layer where visible light is absorbed and drives the vertical motions of the air, and to understand (b) the global dynamics of ions and neutrals in the upper atmosphere where EUV is absorbed both by neutrals and ions and where energy and momentum are transferred between them. For the first target, multiple-balloons are deployed for in situ observations with supporting camera/s on an orbiter giving global context. For the second target, the motions of ions and neutrals are directly measured. This presentation discusses required measurements to answer the scientific goals. |