The variable source of the plasma sheet during a geomagnetic storm

Area of Science:

• Space Physics
• Magnetospheric Physics
• Plasma Physics

Background:

• The magnetotail plasma sheet is supplied by both solar wind and ionospheric sources.
• Understanding these sources is crucial as plasma sheet properties influence the ring current, a key driver of geomagnetic storms.
• How these contributions vary during geomagnetic storms remains an open question.

Purpose of the Study:

• To investigate the changing sources of the magnetotail plasma sheet during geomagnetic storms.
• To determine how solar wind and ionospheric contributions evolve as a storm progresses.
• To link plasma sheet source variations to geomagnetic storm dynamics.

Main Methods:

• Utilizing solar wind composition as a tracer to identify plasma sources.
• Analyzing changes in plasma composition within the magnetotail plasma sheet.
• Correlating plasma source variations with the development phases of geomagnetic storms.

Main Results:

• The plasma sheet source transitions from predominantly solar wind to predominantly ionospheric during storm development.
• Initially, ionospheric plasma is dominated by singly ionized hydrogen (H+) from polar wind.
• Later, ionospheric plasma shifts to singly ionized oxygen (O+) from auroral outflows.

Conclusions:

• The composition of the magnetotail plasma sheet significantly changes during geomagnetic storms.
• The transition from H+ to O+ dominance indicates a shift in ionospheric outflow sources.
• These dynamic source changes directly impact the evolution and severity of geomagnetic storms.