Uncertainties in the heliosheath ion temperatures

TL;DR

This paper proposes a method to convert Maxwellian temperature estimates from Voyager data into $ppa$ distribution-based temperatures, explaining the observed discrepancies in heliosheath ion temperatures.

Contribution

It introduces a simple formula to estimate $ppa$ temperatures from Maxwellian data, enhancing the interpretation of Voyager plasma observations.

Findings

$ppa$ temperatures can be derived from Maxwellian estimates using the proposed formula.

Truncated $ppa$ distributions yield pressures similar to Maxwellians at lower truncation velocities.

Application to Voyager-2 data demonstrates the method's effectiveness in explaining temperature discrepancies.

Abstract

The Voyager plasma observations show that the physics of the heliosheath is rather complex, and especially that the temperature derived from observation differs from expectations. To explain this fact the temperature in the heliosheath should be based on $\kappa$ distributions instead of Maxwellians because the former allows for much higher temperature. Here we show an easy way to calculate the $\kappa$ temperatures when those estimated from the data are given as Maxwellian temperatures. We use the moments of the Maxwellian and $\kappa$ distributions to estimate the $\kappa$ temperature. Moreover, we show that the pressure (temperature) given by a truncated $\kappa$ distribution is similar to that given by a Maxwellian and only starts to increase for higher truncation velocities. We deduce a simple formula to convert the Maxwellian to $\kappa$ pressure or temperature. We apply this result to the Voyager-2 observations in the heliosheath.