Identification of the Coronal Sources of the Fast Solar Wind

Area of Science:

• Solar physics
• Plasma astrophysics
• Space weather

Background:

• Coronal holes are regions of open magnetic field lines in the Sun's outer atmosphere.
• The fast solar wind originates from these regions, but the precise acceleration mechanisms are not fully understood.
• Polar coronal holes are key sites for solar wind outflow.

Purpose of the Study:

• To identify the specific regions within a polar coronal hole responsible for fast solar wind acceleration.
• To quantify the expansion rates of the solar corona in different regions of the polar hole.
• To investigate the relationship between coronal expansion and solar wind velocity.

Main Methods:

• Spectroscopic analysis of ultraviolet coronal emission using the Ultraviolet Coronagraph Spectrometer (UVCS) on the Solar and Heliospheric Observatory (SOHO) spacecraft.
• Measurement of Doppler dimming of Oxygen VI (O VI) spectral lines (1032, 1037 Å).
• Inference of ion velocity distributions from spectral line profiles.

Main Results:

• Interplume lanes and background coronal hole regions are identified as preferential channels for fast solar wind acceleration.
• Coronal expansion rates in interplume lanes reach 105–150 km/s at 1.7 solar radii.
• Outflow velocities in plumes are significantly lower, ranging from 0–65 km/s.

Conclusions:

• The study confirms that interplume lanes are critical for fast solar wind acceleration.
• The observed expansion rates provide direct evidence for efficient energy transfer and acceleration in these specific regions.
• Understanding these processes is crucial for modeling solar wind dynamics and space weather prediction.