The Variation of the Solar Wind Correlation Scale and Taylor Scale Upstream of Mars Observed by MAVEN

Abstract

The correlation scale and Taylor scale, which characterize the turbulence and dissipation levels, of the solar wind upstream of Mars are determined using the Mars atmosphere and volatile evolution magnetic field data from 2015 to 2020, which covers half of a solar cycle from the solar maximum to the solar minimum. Our analysis suggests that the correlation scale varies between 10 and 20 hr and the Taylor scale between 0.3 and 1 s. Applying the frozen-in flow approximation, we convert the two temporal scales to the two spatial scales, which are about (1.5–3.0) × 107 km and 150–500 km, respectively. We further compare the correlation scale and Taylor scale to the sunspot number (SSN) to study the impacts of solar activity. The highest correlation coefficient between the correlation scale and the SSN is 0.78, where the two data sets are shifted by 16 months with the correlation scale behind the SSN. For the Taylor scale, the highest correlation coefficient is 0.52 with the time lag of 17 months. We also analyze the effective magnetic Reynolds number that is the square of the ratio of the two scales. It is more than 3 × 109, suggesting the good assumption of the frozen-in flow. However, its correlation with the SSN is weak.