Incoherent Scatter Radar Observations of Dynamic Ion Composition Changes at High Latitudes during Geomagnetic Storms

Two new methods are developed for estimating F region ion composition from field-aligned incoherent scatter rasar (IRS) measurements. These methods address incoherent scatter spectra temperature profiles-mass ambiguities by self-consistently modeling ion temperature profiles as a function of electric fields and plasma interactions with the neutral atmosphere. These two new methods improve on previous, similar work developed in Zettergren et al. by incorporating more accurate physical models and improving the estimation procedures. These techniques enable studies of ionospheric composition during highly disturbed conditions and are suitable for data collected with short integration times (2-10 minutes). The improved models incorporate The improved models incorporate the effects of variable scale height, altitude dependent neutral winds (taken from the horizontal wind model 2007), and Coulomb collisions, while the fitting schemes simultaneously determine both electric fields and features of composition. These new estimators are used to analyze Sondrestrom ISR datasets from 1998-2008 for quiet (Kp < 3) and storm (Kp > 3) times. Results are validated against previous observations of ionospheric compositions, in particular, showing consistency with quiet time crossover altitude (the altitude where n0+ = nN0+) diurnal trends, LT minimum and maximum, geomagnetic activity trends, and F region molecular ion increases due to frictional heating. Other results include rather large increases of F region molecular ion concentrations after sunrise during storms, a quantitative analysis of the crossover altitude dependence on effective electric field, and several observations of sudden composition variations in response to rapid Kp transitions. These methods are an improvement to existing approaches to fitting ISR data for ion composition, are applicable at high latitudes and during disturbed conditions, and illustrate several interesting features of how molecular ions respond to electric geomagnetic activity.