Insights into Solar Wind Flow Speeds from the Coronal Radio occultation Experiment: Findings from the Indian Mars Orbiter Mission

TL;DR

This study uses data from the Indian Mars Orbiter Mission to analyze solar wind speeds near the Sun during a quiet solar cycle phase, introducing a simplified method to estimate velocities from radio signal data.

Contribution

It presents a new simplified equation to directly relate Doppler spectral width to solar wind velocity from radio occultation data.

Findings

Solar wind speeds ranged from 100 to 150 km/s.

Electron densities were around 10^10 m^(-3).

Results align with models but are at the lower edge due to weak solar activity.

Abstract

Using data collected by the Indian Mars Orbiter Mission in October 2021, we investigated coronal regions of the Sun by analyzing the Doppler spectral width of radio signals to estimate solar wind velocity. A simplified equation is introduced to directly relate these two parameters. The study focuses on observations conducted from October 2 to October 14, 2021, a relatively quiet phase of solar cycle 25. The analysis targeted the coronal region within heliocentric distances of 5-8 RSun, near the ecliptic plane. In this region, solar wind velocities ranged from 100 to 150 kms^-1, while electron densities were on the order of 10^10 m^(-3). We also compared our results with electron density observations and models derived from previous studies. Though the decrease in the electron densities with respect to increasing helio-centric distance matches quite well with the theoretical models, MOM estimates fall at the lower edge of the distribution. This difference may be attributed to the prolonged weak solar activity during the MOM observations, in contrast to prior studies conducted during periods of comparatively higher solar activity in earlier solar cycles.