February 23rd, 2018, 1:00 pm - 2:00 pm
November 9th, 1:00 pm - 2:00 pm
Understanding ion spectral dynamics near the inner edge of the plasma sheet
Cristian Ferradas, New Mexico Consortium
The inner magnetosphere is a highly dynamic space environment in which particles strongly interact with the magnetic and electric fields. During the last few decades, several missions have recorded the presence of dynamic spectral features of energetic ions in in situ measurements, which represent the observational signatures of ion transport, acceleration, and loss in the inner magnetosphere. These ion spectral features constitute the inner extent of access of the plasma sheet to the low L values and play an important role in the dynamics of the inner magnetosphere. In this talk, I will present results of the species dependence and preferred conditions for the formation of one type of ion spectral feature, the so-called nose structure. This work combines data analysis of ion flux measurements and numerical modeling of the observed spectral features. The spatial distribution, and dependence on energy, geomagnetic activity, and ion species (H+, He+, and O+) are established through large-scale statistical studies of ion nose structures using measurements from the Cluster and Van Allen Probes missions. To gain physical insight into the main observational results, these are interpreted employing numerical modeling of ion drift under a steady-state convection model with losses due to charge exchange. Moreover, the characteristics of ion noses during geomagnetic storms are addressed in a case study of the geomagnetic storm of 2 October 2013. Van Allen Probes observations over the storm and simulations using a time-dependent convection model reveal that the characteristics of the ion structures are determined by the intensity of the convection electric field. Furthermore, the cause for the observation of multiple-nose structures is investigated. A detailed examination of the drift trajectories of ions composing multiple noses shows their exact formation mechanism, i.e., multiple noses are formed by ions with resonant energies and whose trajectories (1) encircle the Earth different number of times or (2) encircle the Earth equal number of times but with different drift time, before being detected by the spacecraft. Additionally, a consideration of the conditions necessary for the formation of multiple noses shows that they are intrinsically associated to the time variability of the convection electric field, and that the IMF clock angle can play a dominant role in their formation.