Differences in Ionospheric O+ and H+ Outflow During Storms With and Without Sawtooth Oscillations.

Autor: Nowrouzi, N., Kistler, L. M., Zhao, K., Lund, E. J., Mouikis, C., Payne, G., Klecker, B.
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Zdroj: Geophysical Research Letters; 8/16/2024, Vol. 51 Issue 15, p1-10, 10p
Abstrakt: Previous simulations have suggested that O+ outflow plays a role in driving the sawtooth oscillations. This study investigates the role of O+ by identifying the differences in ionospheric outflow between sawtooth and non‐sawtooth storms using 11 years of FAST/Time of flight Energy Angle Mass Spectrograph (TEAMS) ion composition data from 1996 through 2007 during storms driven by coronal mass ejections. We find that the storm's initial phase shows larger O+ outflow during non‐sawtooth storms, and the main and recovery phases revealed differences in the location of ionospheric outflow. On the pre‐midnight sector, a larger O+ outflow was observed during the main phase of sawtooth storms, while non‐sawtooth storms exhibited stronger O+ outflow during the recovery phase. On the dayside, the peak outflow shifts significantly toward dawn during sawtooth storms. This strong dawnside sector outflow during sawtooth storms warrants consideration. Plain Language Summary: A sawtooth event is a convection mode in Earth's magnetosphere, which transports solar wind plasma and energy into the inner magnetosphere and ionosphere. Despite three decades since their discovery, the mechanism behind sawtooth oscillations remains uncertain. One theory suggests that O+ outflow induces sawtooth oscillations through an internal feedback mechanism. In line with this theory, some simulations have generated sawtooth oscillations under steady geomagnetic conditions. Furthermore, previous observations indicate that some, but not all, geomagnetic storms exhibit sawtooth oscillations. This study utilizes data from the FAST/TEAMS instrument (1996–2007) and compares O+ outflow variations during geomagnetic storms with and without sawtooth oscillations. Findings indicate that during the storms' initial phase, sawtooth storms produce less O+ outflow than non‐sawtooth storms. Additionally, non‐sawtooth storms exhibit higher O+ outflow in the dayside during the main phase and in the pre‐midnight sector during the recovery phase, challenging the key role of O+ outflow in driving the feedback mechanism. However, observing large O+ outflow in the dawnside sector of sawtooth events suggests more investigation is needed. Key Points: The intensity and location of O+ outflow during storms are different in storms with and without sawtooth oscillationsThe peak dayside outflow is significantly shifted toward dawn during storms with sawtooth observationsThe nightside picture is mixed; the pre‐midnight O+ outflow is higher in the main phase but lower in the recovery phase of sawtooth storms [ABSTRACT FROM AUTHOR]
Databáze: Complementary Index
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