The sawtooth mode of convection of Earth's magnetosphere is a 2- to 4-hour planetary-scale oscillation powered by the solar wind-magnetosphere-ionosphere (SW-M-I) interaction. Using global simulations of geospace, we have shown that ionospheric O(+) outflows can generate sawtooth oscillations. As the outflowing ions fill the inner magnetosphere, their pressure distends the nightside magnetic field. When the outflow fluence exceeds a threshold, magnetic field tension cannot confine the accumulating fluid; an O(+)-rich plasmoid is ejected, and the field dipolarizes. Below the threshold, the magnetosphere undergoes quasi-steady convection. Repetition and the sawtooth period are controlled by the strength of the SW-M-I interaction, which regulates the outflow fluence.

[1] It is widely accepted that the ionosphere is an important source of ions in the magnetosphere and until recently this population has largely been neglected from many global simulations. In this study, a causally regulated cusp O + outflow is added to the multifluid version of the Lyon-Fedder-Mobarry (LFM) global simulation. The cusp outflow algorithm uses empirical relationships to regulate the outflow flux with further conditioning to isolate the outflow spatially to a dynamic cusp. The impact cusp O + outflow has on the magnetosphere-ionosphere (MI) system is investigated for a moderate storm on 31 August 2005. It is found the MI system response depends upon the specification of the outflow velocity and temperature. More energetic outflow tends to flow downtail whilst colder, slower outflow fills the inner magnetosphere. High O + densities in the inner magnetosphere can increase the strength of the ring current, reducing Dst and inflating the magnetosphere. This effect is mostly found for the less energetic outflow specification. O + outflow is found to reduce the access of solar wind ions to the inner magnetosphere, which, through the MI coupling in LFM reduces the precipitating electron power, conductance and field-aligned currents. The effect outflow has on the cross polar cap potential (CPCP) depends upon two competing factors. The reduction in Region I currents when outflow is present appears to increase the CPCP whilst the inflation of the magnetosphere due to an enhanced ring current decreases the CPCP.

General methods for improving the specification of electron precipitation in global simulations are described and implemented in the Lyon-Fedder-Mobarry (LFM) global simulation model, and the quality of its predictions for precipitation is assessed. LFM's existing diffuse and monoenergetic electron precipitation models are improved, and new models are developed for lower energy, broadband, and direct-entry cusp precipitation. The LFM simulation results for combined diffuse plus monoenergetic electron precipitation exhibit a quadratic increase in the hemispheric precipitation power as the intensity of solar wind driving increases, in contrast with the prediction from the OVATION Prime (OP) 2010 empirical precipitation model which increases linearly with driving intensity. Broadband precipitation power increases approximately linearly with driving intensity in both models. Comparisons of LFM and OP predictions with estimates of precipitating power derived from inversions of Polar satellite UVI images during a double substorm event (28-29 March 1998) show that the LFM peak precipitating power is > 4× larger when using the improved precipitation model and most closely tracks the larger of three different inversion estimates. The OP prediction most closely tracks the double peaks in the intermediate inversion estimate, but it overestimates the precipitating power between the two substorms by a factor >2 relative to all other estimates. LFMs polar pattern of precipitating energy flux tracks that of OP for broadband precipitation exhibits good correlation with duskside region 1 currents for monoenergetic energy flux that OP misses and fails to produce sufficient diffuse precipitation power in the prenoon quadrant that is present in OP. The prenoon deficiency is most likely due to the absence of drift kinetic physics in the LFM simulation.

Observed distributions of high-speed plasma flows at distances of 10 to 30 Earth radii (R(E)) in Earth's magnetotail neutral sheet are highly skewed toward the premidnight sector. The flows are a product of the magnetic reconnection process that converts magnetic energy stored in the magnetotail into plasma kinetic and thermal energy. We show, using global numerical simulations, that the electrodynamic interaction between Earth's magnetosphere and ionosphere produces an asymmetry consistent with observed distributions in nightside reconnection and plasmasheet flows and in accompanying ionospheric convection. The primary causal agent is the meridional gradient in the ionospheric Hall conductance which, through the Cowling effect, regulates the distribution of electrical currents flowing within and between the ionosphere and magnetotail.

[1] The mechanisms by which ionospheric O + stretches the plasma sheet causing variations in polar cap flux during magnetospheric sawtooth substorms are investigated using the multi-fluid Lyon-Fedder-Mobarry simulation code. O + outflow is induced in the simulation by Alfvénic Poynting flux flowing to low altitude during the sawtooth expansion and growth phases. The O + fluid populates the plasma sheet and causes it to stretch tailward in response to the increased mass density. The ionospheric outflow thus functions as a feedback loop in the magnetosphere-ionosphere system wherein O + ions released during the expansion phase alter the magnetospheric configuration and enable the development of the next substorm. We also find that the nightside reconnection rate is strongly dependent on the position of the tail merging line. As the x-line moves tailward, the inflow speed and magnetic field strength are reduced, creating an imbalance between dayside and nightside merging. This imbalance is responsible for the buildup and release of open magnetic flux in the magnetosphere during the sawtooth cycle.