One year of ASPEX-SWIS operation: characteristic features, observations and science potential

Abstract

The Aditya-L1 mission, India’s first dedicated solar observatory at the first Lagrange point of the Sun-Earth system, carries the Solar Wind Ion Spectrometer (SWIS) as part of the Aditya Solar Wind Particle Experiment (ASPEX) payload suite. Even before settling down at the Halo orbit, AL1-ASPEX-SWIS has been delivering nearly continuous in situ measurements of solar wind ion spectra. Moments of the velocity distribution function (VDFs) have been calculated to derive the solar wind bulk parameters like density, bulk speed, temperature etc. Through this work, we evaluate the performance of AL1-ASPEX-SWIS through comparisons with contemporaneous measurements from the Wind and DSCOVR spacecrafts. A detailed case study of the 07 August 2024 interplanetary coronal mass ejection (ICME) is presented where sharp transitions in bulk speed, thermal speed, and number density were well-aligned with independent observations, confirming the instrument’s capability in capturing dynamic solar wind features. Spectral analysis of kinetic fluctuations revealed a well-defined inertial range with a spectral slope consistent with magnetohydrodynamic (MHD) turbulence. Additionally, a 17-month statistical comparison (January 2024–May 2025) shows strong agreement in bulk velocity ( with Wind), with expected variability in thermal speed and density due to inter-instrument differences. These results confirm the scientific utility of AL1-ASPEX-SWIS in monitoring both transient events and long-term solar wind conditions.