AUTHOR=Lazar Marian , López R.A. , Shaaban Shaaban Mohammed , Poedts Stefaan , Yoon Peter Haesung , Fichtner Horst TITLE=Temperature Anisotropy Instabilities Stimulated by the Solar Wind Suprathermal Populations JOURNAL=Frontiers in Astronomy and Space Sciences VOLUME=8 YEAR=2022 URL=https://www.frontiersin.org/journals/astronomy-and-space-sciences/articles/10.3389/fspas.2021.777559 DOI=10.3389/fspas.2021.777559 ISSN=2296-987X ABSTRACT=

This review paper compiles recent results obtained by the present group of authors describing the effects of suprathermal populations present in space plasmas (up to a few keVs) on temperature anisotropy instabilities. Of particular interest are the electromagnetic cyclotron and firehose excitations, which play a major role in limiting temperature anisotropy, resulting, for instance, from the adiabatic expansion of the solar wind. Relying on a rigorous modeling and interpretation of the observed velocity distributions, both theoretical models and numerical simulations indicate a systematic stimulation of these excitations in the presence of suprathermal populations of electrons or protons. Moreover, the enhanced fluctuations react back on particles, and determine a faster and deeper relaxation of their anisotropy. The present comparative analysis suggests that previous studies, considering only quasi-thermal low-energy populations, may have significantly underestimated these excitations and their implications in various applications in space plasmas.