Evidence for superadiabatic heating and cooling of Alfvénic solar wind

Abstract

ABSTRACT Alfvénic fluctuations are widespread and crucial in various physical processes of space & astrophysical plasma. However, their role in heating and work done remains unexplored. Here, we have used Wind spacecraft’s data situated at 1 au distance to examine 12 distinct Alfvénic regions using polytropic analysis. The study finds an average polytropic index value α = 2.64, which is consistent with a superadiabatic behaviour for plasma particles with three effective degrees of freedom (f = 3). Moreover, this study examines several scenarios for plasma particles with different degrees of freedom. We noted that the investigated Alfvénic region could be adiabatic only for plasma particles with f = 1.26 degrees of freedom. In addition to this, for α = 2.64, the ratio of work done to the total heat supply within the system is $\frac{\delta w}{\delta q} = -0.68$, indicating that 68 per cent of the total supplied heat is utilized to accomplish work by the system on the surrounding (expansion phenomena), and the remaining is used to increase the internal energy of the system. As a result, we hypothesized that the Alfvénic plasma region is cooling more than the adiabatic expectation, resulting in supercooling phenomena. Thus, we propose that the discovered possible superadiabatic process would be critical in understanding the energy transfer from the Alfvénic zone to the surrounding plasma.