Modeling Ionospheric Outflow and its Consequences
Nithin Sivadas, 08 February 2021
Plasma in the magnetosphere originates from the solar wind and the ionosphere. In a previous seminar, Prof. Charles Rick Chappell discussed how the ionosphere might influence the magnetosphere, especially the magnetospheric storms. In this seminar, Dr. Alex Glocer discusses in more detail one of the processes by which the ionosphere does this - the ionospheric outflow. He uses two simulation-based case studies to show that ionospheric outflow has a system-wide impact and is a significant source of hot and cold magnetospheric plasma in at least some magnetospheric storms.
In the first study, Dr. Glocer’s team solves plasma transport along multiple convecting magnetic field lines using the Polar Wind Outflow Model (PWOM) for dayside field lines in a steady-state that enters the cusp region. By changing the solar EUV and precipitation influx and varying the strength of wave power along the field lines, they reaffirmed that ion outflow scales as a power-law with input energy beyond a minimum threshold, with the outflow saturating at an upper limit. The polar winds determine the lower limit of the outflow for both H+ and O+, and the rate of ion production in the ionosphere constrains the upper limit.
For the second study, Dr. Glocer asks the question: What is the impact of ionospheric outflow on near-Earth space? To address this, his team simulated a magnetospheric storm using the Space Weather Modeling Framework that couples several models together: the global magnetospheric model BATS-R-US, the ring current model CIMI, the ionosphere electrodynamics model RIM, and PWOM. The results show that for the specific storm the team modeled, the ionosphere is the source of a substantial number of magnetospheric protons in the later phase of the storm. They also noted that cold outflowing ions could turn into a hot magnetospheric plasma that populates the warm plasma cloak around the plasma sheet and the ring currents. And any seasonal hemispheric asymmetry could result in an asymmetric composition of the outflow between the hemispheres and, as a consequence, different ion compositions on either side of the magnetotail reconnection region. Further simulations with and without a plasmasphere coupled to the model demonstrated the inhibiting effect of the plasmasphere on the dayside reconnection, outflow, and ring current pressure. This effect results from the enhanced density diminishing the reconnection at those portions of the magnetopause which the plasmaspheric plume reaches during the storm.
Finally, Dr. Glocer discusses two new methods that he is incorporating into his simulations. Since PWOM solves multiple field lines convecting around the polar cap, coarse resolution can be inadequate in resolving mesoscale outflow structures. And a high resolution might still result in under-resolved regions where field lines are concentrated. To tackle the above challenge, Dr. Glocer’s team plans to remap each model solution to a uniform Lagrangian grid. Initial results demonstrate that the remapping avoids artifacts and provides uniformly distributed points, saving computation time. Secondly, the CIMI model of the plasmasphere only provides total flux tube content without density or temperature variation along the field line. Dr. Glocer has been working with Joe Huba and others to couple the existing model with a better physics-based plasmasphere model: SAMI-3, which allows the definition of field-aligned density structure instead of merely the total flux tube content. Initial results promise an improved simulation with a more realistic plasmasphere.
You can find a recording of Dr. Glocer’s seminar on our YouTube Channel.