Date of Award

Winter 2022

Project Type

Dissertation

Program or Major

Physics

Degree Name

Doctor of Philosophy

First Advisor

Lynn L. M. K Kistler

Second Advisor

Kai K. G Germaschewski

Third Advisor

Marc M. L Lessard

Abstract

A geomagnetic storm begins when solar wind carrying southward IMF Bz impinges upon the Earth’s magnetosphere. There are two major structures that can cause a geomagnetic storm: streaminteraction regions (SIRs) and coronal mass ejections (CMEs). The two types of structures differ in the strength of the magnetic field and the time length of southward Bz, and so the effects on the magnetosphere are different. One result of the energy input from the solar wind is ionospheric outflow. Because of solar wind-magnetosphere-ionosphere coupling, ionospheric ions can become a significant source for the magnetosphere during geomagnetic storms. In this thesis, I performed a superposed epoch analysis to study the variation of ionospheric O+ and H+ outflow, measured by the FAST(TEAMS) data, as a function of geomagnetic storm phases. To do that, the SIR and CME magnetic storms of solar cycle 23rd, with Dstminimum < -50nT, and the storm phases have been identified. I observed that the O+ and H+ outflows increased with storm intensity. For CME storms, the O+ and H+ outflows increased in the dayside and nightside of the initial phase, reaching a maximum in the main phase and decreasing in the recovery phase. For SIR storms, there was no increase of O+ and H+ outflow in the initial phase, but the outflow in the main and recovery phases were about the same as for CMEs. In addition, I investigated the effect of solar EUV flux, including changes with solar cycle (F10.7), and seasonal effects on storm time O+ and H+ outflow flux. Our results showed that in the dayside, O+ outflow during storm phases was enhanced in solar maximum compared to the solar minimum, while H+ showed no change xx between solar maximum and minimum. For the nightside, the enhancement during solar maximum was for O+ and during solar minimum was for H+. Then I limited the data to solar minimum years and CME moderate storms to study the seasonal effect on storm time ionospheric outflow. The results showed more dayside O+ outflow in summer and more nightside H+ outflow in winter. However, nightside O+ outflow and dayside H+ outflows were independent of seasonal effects. Sawtooth events, one of the magnetospheric convection modes, often occur during geomagnetic storms. Since O+ density and pressure in the plasma sheet increase during storms, ionospheric O+ outflow has been suggested as a sawtooth events driver. Although simulations have generated sawtooth oscillations after embedding ionospheric O+ outflow in the models, there has been a lack of comprehensive observational study on ionospheric O+ outflow during storms with and without sawtooth events to see the differences between them. In my second study, I used FAST (TEAMS) data during geomagnetic CME and SIR storms from solar cycle 23 to study the storm time ionospheric O+ outflow and to investigate the outflow differences between storms with and without sawtooth events. I performed a superposed epoch analysis to study ionospheric O+ outflow as a function of magnetic local time and storm phases. I found a difference in the total auroral O+ outflow fluence. Our observations from the main phase of CME storms showed that: the O+ outflow fluence in the night side of sawtooth storms was close to 2 times higher than during non-sawtooth storms, while in the dayside sector, the non-sawtooth storms produce 3.7 times more O+ outflow fluence than sawtooth storms. We also found a peak in the O+ outflow in the dawnside sector of sawtooth events, while the outflow was peaked in the dayside sector of non-sawtooth storms. The observed differences in outflow flux were relatively minor, so it seems unlikely that they caused the difference between sawtooth and non-sawtooth storms. It is possible that the different location of the outflow during sawtooth events brought O+ to a region in the plasma sheet where it has a bigger effect. It is also possible that the key factor that determines whether a sawtooth event occurs is not related to O+ outflow.

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