Observations of solar irradiance variability

Area of Science:

• Solar physics
• Astronomy
• Space science

Background:

• Total solar irradiance (TSI) is a fundamental parameter for Earth's climate.
• Variability in TSI can impact climate and space weather.
• Previous measurements had limitations in precision and temporal resolution.

Purpose of the Study:

• To present high-precision measurements of TSI from the Solar Maximum Mission (SMM).
• To analyze the variability of TSI during the initial 153 days of observation.
• To investigate the relationship between TSI fluctuations and solar activity.

Main Methods:

• Utilized the Active Cavity Radiometer Irradiance Monitor (ACRIM) on the SMM satellite.
• Collected high-precision TSI data with uncertainties as small as 0.001%.
• Analyzed orbit-to-orbit variations and spectral characteristics of irradiance fluctuations.

Main Results:

• Observed significant variability in TSI over 153 days, with amplitudes around +/- 0.05% of the mean (1368.31 W/m²).
• Identified irradiance fluctuations consistent with band-limited noise, with a high-frequency cutoff near 0.15 day⁻¹.
• Found two major irradiance decreases (up to 0.2%, lasting ~1 week) strongly correlated with sunspot group development.

Conclusions:

• TSI exhibits notable variability on short timescales.
• Solar active regions, particularly sunspots, play a significant role in TSI fluctuations.
• The observed variability suggests substantial energy storage within the solar convection zone in active regions.