Global solar wind variations over the last four centuries

Area of Science:

• Space Physics
• Solar Physics
• Heliophysics

Background:

• The Maunder minimum (MM, 1650-1710) is a period of significantly reduced solar activity.
• Understanding grand solar minima is crucial for solar dynamo theory and predicting future solar activity.
• Reconstructing past heliospheric conditions is vital for interpreting climate and space weather data.

Purpose of the Study:

• To quantitatively estimate global solar wind variations over the last 400 years.
• To calibrate heliospheric reconstructions using a magnetohydrodynamic model and sunspot data.
• To understand the heliospheric conditions during the Maunder minimum and their impact on Earth.

Main Methods:

• Utilized nearly 30 years of output from a data-constrained magnetohydrodynamic model of the solar corona.
• Calibrated heliospheric reconstructions based on sunspot observations using empirical relations derived from the model.
• Estimated global solar wind variations, heliospheric magnetic field strength, and solar wind speed over the past 400 years.

Main Results:

• The Maunder minimum exhibited a factor 2 reduction in near-Earth heliospheric magnetic field strength and solar wind speed compared to the modern era.
• Solar wind Mach number increased up to a factor of 4 during the MM.
• The global heliosphere was smaller and more symmetric during the MM.

Conclusions:

• Reduced solar wind energy input during the MM led to a more Jupiter-like magnetosphere, explaining the scarcity of auroral reports.
• The altered heliospheric conditions during grand solar minima have significant implications for interpreting cosmogenic radionuclide data.
• Reconstructions suggest that total solar irradiance estimates during grand minima need careful consideration due to changes in heliospheric conditions.