Including ionospheric outflow leads to sawteeth oscillations

The magnetosphere is created by the interaction between the solar wind and the Earth’s magnetic field. On the dayside of the Earth pressure from the solar wind compresses the Earth’s dipole magnetic field and on the night side this interaction stretches it out forming a region of space commonly referred to as the magnetotail. Depending on the direction of the magnetic field in the solar wind, mass, momentum and energy can be transferred into the magnetosphere. The magnetic field lines that form the magnetosphere pass through the upper levels of the Earth’s atmosphere known as the ionosphere. HAO scientists Michael Wiltberger and Binzheng Zhang working with colleagues at SRI International and Dartmouth College have worked to model the outflow of mass from the ionosphere into the magnetosphere by including the Ionosphere Polar Wind Model (IPWM) to the Coupled Magnetosphere-Ionosphere-Thermosphere (CMIT) framework. Accurate modeling of the fundamental mode of the magnetosphere-ionosphere system is essential in the creation of tools for predicting space weather, especially those aspects that can affect the operations of satellites.

Movie caption: Scientific visualization illustrating sawteeth oscillations within the magnetosphere-ionosphere system. The saw blade pattern shown in the open magnetic flux on the pattern leads to the name of this process as sawteeth oscilations.

Earlier research with the CMIT framework indicated a connection between ionospheric outflow and periodic responses in the magnetosphere-ionosphere system. Scientists refer to this behavior as sawteeth oscillations because of sawtooth like pattern seen in the parameters such as the amount of open flux plotted in the bottom panel of the scientific visualization. The coupled system is periodically loading and unloading magnetic flux from the magnetosphere. The panel on the right-hand side of the visualization shows dynamics in the magnetotail. The pink line shows the region of close magnetic flux within the magnetosphere. Throughout the time series you see it growing in size followed by region breaking off and being released down the tail. The releasing of flux down the tail corresponds to the peaks of the sawteeth seen in the bottom trace. The two panels on the left show how this process setups a feedback loop with a release of flux triggering an injection of new material from the ionosphere which prevents the system from reaching equilibrium and resulting in a new tooth in the saw. Simulations that do not include the outflow only have one tooth and do not demonstrate the sawteeth behavior. Work is now underway to verify this model prediction with comparison to observations.

This work was supported by NSF grant AGS-1555801 and base funds.