A Novel Determination of the Foreshock ULF Boundary: Statistical Approach

Area of Science:

• Space Physics
• Plasma Physics
• Astrophysics

Background:

• Foreshock waves are crucial for understanding space plasma dynamics.
• Interplanetary Magnetic Field (IMF) orientation influences foreshock wave characteristics.
• Previous studies have indicated a dependence of wave activity on solar wind conditions.

Purpose of the Study:

• To systematically investigate the spatial extent and location of Ultra-low Frequency (ULF) foreshock waves.
• To statistically analyze wave activity in relation to solar wind parameters and IMF orientation.
• To define and utilize a foreshock coordinate system for improved characterization.

Main Methods:

• Statistical analysis of THEMIS mission data.
• Quantification of wave activity using standard deviations of IMF magnitude and components.
• Application of a foreshock coordinate system based on bow shock normal and upstream magnetic field vectors.
• Analysis of wave activity as a function of solar wind bulk speed and Mach number.

Main Results:

• The Ultra-low Frequency (ULF) foreshock boundary is well-defined in the applied coordinate system.
• The foreshock boundary shifts outward with increasing solar wind bulk speed and Mach number.
• Increasing solar wind bulk speed enhances wave activity near the bow shock, while increasing Mach number intensifies it at the foreshock boundary.

Conclusions:

• The spatial extent of foreshock waves is strongly dependent on IMF orientation and solar wind conditions.
• The foreshock coordinate system provides a robust framework for studying wave phenomena.
• Solar wind bulk speed and Mach number have distinct effects on ULF wave activity within the foreshock region.