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Hot and cold ion outflow: Observations and implications for numerical models
Author(s) -
Nilsson H.,
Barghouthi I. A.,
Slapak R.,
Eriksson A. I.,
André M.
Publication year - 2013
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1029/2012ja017975
Subject(s) - outflow , ion , polar , polar wind , physics , effects of high altitude on humans , altitude (triangle) , atomic physics , geophysics , computational physics , plasma , magnetosphere , magnetopause , meteorology , geometry , nuclear physics , mathematics , quantum mechanics , astronomy
Cluster observations of oxygen ion outflow and low‐frequency waves at high altitude above the polar cap and cold ion outflow in the lobes are used to determine ion heating rates and low‐altitude boundary conditions suitable for use in numerical models of ion outflow. Using our results, it is possible to simultaneously reproduce observations of high‐energy O + ions in the high‐altitude cusp and mantle and cold H + ions in the magnetotail lobes. To put the Cluster data in a broader context, we first compare the average observed oxygen temperatures and parallel velocities in the high‐altitude polar cap with the idealized cases of auroral (cusp) and polar wind (polar cap) ion outflow obtained from a model based on other data sets. A cyclotron resonance model using average observed electric field spectral densities as input fairly well reproduces the observed velocities and perpendicular temperatures of both hot O + and cold H + , if we allow the fraction of the observed waves, which is efficient in heating the ions to increase with altitude and decrease toward the nightside. Suitable values for this fraction are discussed based on the results of the cyclotron resonance model. Low‐altitude boundary conditions, ion heating rates, and centrifugal acceleration are presented in a format suitable as input for models aiming to reproduce the observations.