69 research outputs found
Signatures of magnetic reconnection at boundaries of interplanetary small-scale magnetic flux ropes
The interaction between interplanetary small-scale magnetic flux ropes and
the magnetic field in the ambient solar wind is an important topic to
understand- ing the evolution of magnetic structures in the heliosphere.
Through a survey of 125 previously reported small flux ropes from 1995 to 2005,
we find that 44 of them reveal clear signatures of Alfvenic fluctuations, and
thus classify them into Alfven wave trains rather than flux ropes. Signatures
of magnetic reconnection, generally including a plasma jet of ~30 km/s within a
magnetic field rotational region, are clearly present at boundaries of about
42% of the flux ropes and 14% of the wave trains. The reconnection exhausts are
often observed to show a local increase in the proton temperature, density and
plasma beta. About 66% of the reconnection events at flux rope boundaries are
associated with a magnetic field shear angle larger than 90 deg and 73% of them
reveal a decrease by 20% or more in the magnetic field magnitude, suggesting a
dominance of anti-parallel reconnec- tion at flux rope boundaries. The
occurrence rate of magnetic reconnection at flux rope boundaries through the
year of 1995 to 2005 is also investigated and we find that it is relatively low
around solar maximum and much higher when ap- proaching solar minima. The
average magnetic field depression and shear angle for reconnection events at
flux rope boundaries also reveal a similar trend from 1995 to 2005. Our results
demonstrate for the first time that boundaries of a substantial fraction of
small-scale flux ropes have properties similar to those of magnetic clouds, in
the sense that both of them exhibit signatures of magnetic reconnection. The
observed reconnection signatures could be related either to the formation of
small flux ropes, or to the interaction between flux ropes and the
interplanetary magnetic fields.Comment: 10 figures, accepted by Ap
Longâlasting goodshielding at the equatorial ionosphere
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95323/1/jgra20828.pd
Observations of rapidly growing whistler waves in front of space plasma shock
Whistler mode wave is a fundamental perturbation of electromagnetic fields and plasmas in various environments including planetary space, laboratory and astrophysics. The origin and evolution of the waves are a long-standing question due to the limited instrumental capability in resolving highly variable plasma and electromagnetic fields. Here, we analyse data with the high time resolution from the multi-scale magnetospheric spacecraft in the weak magnetic environment (i.e., foreshock) enabling a relatively long gyro-period of whistler mode wave. Moreover, we develop a novel approach to separate the three-dimensional fluctuating electron velocity distributions from their background, and have successfully captured the coherent resonance between electrons and electromagnetic fields at high frequency, providing the resultant growth rate of unstable whistler waves. Regarding the energy origin for the waves, the ion distributions are found to also play crucial roles in determining the eigenmode disturbances of fields and electrons. The quantification of wave growth rate can significantly advance the understandings of the wave evolution and the energy conversion with particles
Episodic Occurrence of FieldâAligned Energetic Ions on the Dayside
The tens of kiloelectron volt ions observed in the ring current region at L ~ 3â7 generally have pancake pitch angle distributions, that is, peaked at 90°. However, in this study, by using the Van Allen Probe observations on the dayside, unexpectedly, we have found that about 5% time, protons with energies of ~30 to 50 keV show two distinct populations, having an additional fieldâaligned population overlapping with the original pancake population. The newly appearing fieldâaligned populations have higher occurrence rates at ~12â16 magnetic local time during geomagnetically active times. In particular, we have studied eight such events in detail and found that the source regions are located around 12 to 18 magnetic local time which coincides with our statistical result. Based on the ionospheric and geosynchronous observations, it is suggested that these energetic ions with fieldâaligned pitch angle distributions probably are accelerated near postnoon in association with ionospheric disturbances that are triggered by tail injections.Plain Language SummaryProtons of different sources have different pitch angle distributions (PADs). For example, warm plasma cloak protons, which come directly from the ionosphere, have fieldâaligned PADs, while ring current protons that generally originate from tail plasma sheet have pancakeâshaped PADs. In this study, unexpectedly, we have found that about 5% of the time on the dayside, protons of ring current energies show two distinct populations according to their PADs: higher fluxes of fieldâaligned populations overlapping with the original pancake populations. The newly appeared fieldâaligned populations have higher occurrence rates at ~12â16 magnetic local time during geomagnetically active times. In order to find the mechanism that generates these fieldâaligned energetic proton populations, we have studied eight such events in detail by using the lowâaltitude DMSP, POES satellites, and the NOAAâLANL satellite at the geosynchronous orbit. The results imply that these energetic ions with fieldâaligned PADs probably are accelerated by ionospheric disturbances that are triggered by tail injections. These results provide evidence of another possibly important source of the ring current ions.Key PointsWe have found that about 5% of the time on the dayside, protons with energies of ~30 to 50 keV have strong fieldâaligned PADsThe fieldâaligned PADs have higher occurrence rates at ~12â16 MLT during geomagnetically active timesThese energetic fieldâaligned ions possibly are accelerated by ionospheric disturbances triggered by tail injectionsPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/153687/1/grl60102_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/153687/2/grl60102.pd
Predictability of variable solar-terrestrial coupling
In October 2017, the Scientific Committee on Solar-Terrestrial Physics (SCOSTEP) Bureau established a committee for the design of SCOSTEP's Next Scientific Programme (NSP). The NSP committee members and authors of this paper decided from the very beginning of their deliberations that the predictability of the Sun-Earth System from a few hours to centuries is a timely scientific topic, combining the interests of different topical communities in a relevant way. Accordingly, the NSP was christened PRESTO - PREdictability of the variable Solar-Terrestrial cOupling. This paper presents a detailed account of PRESTO; we show the key milestones of the PRESTO roadmap for the next 5 years, review the current state of the art and discuss future studies required for the most effective development of solar-terrestrial physics.Peer reviewe
Predictability of variable solar-terrestrial coupling
In October 2017, the Scientific Committee on Solar-Terrestrial Physics (SCOSTEP) Bureau established a committee for the design of SCOSTEP's Next Scientific Programme (NSP). The NSP committee members and authors of this paper decided from the very beginning of their deliberations that the predictability of the Sun-Earth System from a few hours to centuries is a timely scientific topic, combining the interests of different topical communities in a relevant way. Accordingly, the NSP was christened PRESTO -PREdictability of the variable Solar-Terrestrial cOupling. This paper presents a detailed account of PRESTO; we show the key milestones of the PRESTO roadmap for the next 5 years, review the current state of the art and discuss future studies required for the most effective development of solar-terrestrial physics.Fil: Daglis, Ioannis A.. Hellenic Space Center; Grecia. Universidad Nacional y Kapodistriaca de Atenas; GreciaFil: Chang, Loren C.. National Central University; ChinaFil: Dasso, Sergio Ricardo. Consejo Nacional de InvestigaciĂłnes CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Ciudad Universitaria. Instituto de AstronomĂa y FĂsica del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de AstronomĂa y FĂsica del Espacio; ArgentinaFil: Gopalswamy, Nat. NASA Goddard Space Flight Center; Estados UnidosFil: Khabarova, Olga V.. Russian Academy Of Sciences; RusiaFil: Kilpua, Emilia. University of Helsinki; FinlandiaFil: Lopez, Ramon. University of Texas; Estados UnidosFil: Marsh, Daniel. National Center for Atmospheric Research; Estados Unidos. University of Leeds; Reino UnidoFil: Matthes, Katja. Geomar-Helmholtz Centre for Ocean Research Kiel; Alemania. Christian Albrechts Universitat Zu Kiel; AlemaniaFil: Nandy, Dibyendu. Indian Institute Of Science Education And Research Kolkata; IndiaFil: SeppĂ€lĂ€, Annika. University of Otago; Nueva ZelandaFil: Shiokawa, Kazuo. Nagoya University; JapĂłnFil: ThiĂ©blemont, RĂ©mi. UniversitĂ© Pierre et Marie Curie; FranciaFil: Zong, Qiugang. Peking University; Chin
Evidence for lunar tide effects in Earthâs plasmasphere
Tides are universal and affect spatially distributed systems, ranging from planetary to galactic scales. In the EarthâMoon system, effects caused by lunar tides were reported in the Earthâs crust, oceans, neutral gas-dominated atmosphere (including the ionosphere) and near-ground geomagnetic field. However, whether a lunar tide effect exists in the plasma-dominated regions has not been explored yet. Here we show evidence of a lunar tide-induced signal in the plasmasphere, the inner region of the magnetosphere, which is filled with cold plasma. We obtain these results by analysing variations in the plasmasphereâs boundary location over the past four decades from multisatellite observations. The signal possesses distinct diurnal (and monthly) periodicities, which are different from the semidiurnal (and semimonthly) variations dominant in the previously observed lunar tide effects in other regions. These results demonstrate the importance of lunar tidal effects in plasma-dominated regions, influencing understanding of the coupling between the Moon, atmosphere and magnetosphere system through gravity and electromagnetic forces. Furthermore, these findings may have implications for tidal interactions in other two-body celestial systems
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