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An improved algorithm was developed to estimate the polar rain electron path length from the magnetotail X-line to the polar ionosphere using the information of polar rain electron energy-latitude dispersion. Recent particle tracing simulations using APLOPM model (Applied Physics Laboratory – Open-field line particle Precipitation Model) ( Wing et al., 2001 ; Wing and Zhang, 2015 ) indicate that an existing or traditional method underestimates the path length by at least 33%. A new method for estimating electron path length that introduces a new parameter (energy parameter) is proposed. The improved algorithm has been validated using the APLOPM simulation data. By applying the new algorithm to two real events measured by DMSP satellites, we found the polar rain electron path lengths of 67 and 114 R E , (X-lines estimated at X =−54 and −91 R E ), respectively (assuming the distance from the X-line to the Earth is 80% of the electron path length). The associated IMF B z were 1 and –11 nT, respectively for the two events. This is consistent with the expected stretched magnetotail configuration under a strongly southward IMF. The results are also consistent with statistical results of the X-line locations from Geotail measurements. [ABSTRACT FROM AUTHOR]

Consecutive bursts of low-latitude Pi2 pulsations are examined with magnetic field data obtained by the Sino Magnetic Array at Low Latitudes (SMALL) in 1999. To ascertain the relationship with the substorm onset, 33 events consisting of two consecutive Pi2 bursts are selected from the observations at the Wuhan and Beijing stations, with reference to H-component magnetic bays in high-latitude magnetograms. The dominant frequencies of these consecutive Pi2 bursts are mostly in the range 10–20 mHz. The frequencies of the two Pi2 bursts are less correlated with each other at the lower latitude station, Wuhan, than at Beijing. The dominant frequency increases as the Kp index increases. Observations with ACE and Wind satellite show that the first Pi2 burst occurs significantly after the southward turning of the interplanetary magnetic field (IMF) and the second Pi2 often occurs shortly after a northward turning of the IMF. Thus, the first Pi2 burst is not a signature of the beginning of the flux transfer to the tail but perhaps signals the initial onset of reconnection in the tail. The interplanetary data can be used to estimate the amount of reconnected magnetic flux transported to the tail. The delay time of two consecutive bursts of low-latitude Pi2 is correlated with this estimated flux pileup. If the second burst of Pi2 signals the onset of reconnection of the open field lines in the tail lobes, then this observation implies that the rate of reconnection of the closed field lines in the plasma sheet is more rapid the greater is the rate of reconnection at the nose. Thus, we would expect plasmoids to be created more quickly for strong southward IMF than for weakly southward IMF. [Copyright &y& Elsevier]

A review of the impact of the cold-ion and cold-electron populations in the Earth's magnetosphere is presented. The cold populations are defined by total energy less than approximately 100 eV, i.e. in the energy range which is strongly affected by spacecraft charging and that often dominates the total plasma density. We also include the warm plasma cloak in the review, since it overlaps partially with the cold energy range and is a population that is still not well understood. The known impacts of cold ions and cold electrons that are discussed are: the source of hot magnetospheric plasma, solar-wind/magnetosphere coupling, magnetotail reconnection and substorms, Kelvin–Helmholtz instabilities on the magnetopause, chorus, hiss, electromagnetic-ion-cyclotron and ultra-low-frequency wave–particle interactions, aurora structuring and spacecraft charging. Other possible impacts are associated with refilling on open-drift trajectories, the remnant layer and plasmapause disruption. A discussion of the difficulty of cold-plasma measurements and the need for new measurement techniques that measure the full cold-ion and cold-electron distribution functions is also presented. There remain a lot of unknowns about the cold-ion and cold-electron populations, associated with their origin, properties, drivers and impacts. These populations will need to be fully understood before the magnetosphere–ionosphere system can be fully understood. • The cold-particle populations play a critical role in the Earth's magnetosphere. • This paper reviews their known and probable impacts in magnetospheric physics. • The need for new cold-plasma measurement techniques is also discussed. • The lack of understanding of the cold populations hinders magnetospheric research. [ABSTRACT FROM AUTHOR]