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The relationship between a decaying strong turbulence and kineticinstabilities in a slowly expanding plasma is investigated usingtwo-dimensional (2-D) hybrid expanding box simulations. We impose an initialambient magnetic field perpendicular to the simulation box, and we start with aspectrum of large-scale, linearly-polarized, random-phase Alfv\'enicfluctuations which have energy equipartition between kinetic and magneticfluctuations and vanishing correlation between the two fields. A turbulentcascade rapidly develops, magnetic field fluctuations exhibit a Kolmogorov-likepower-law spectrum at large scales and a steeper spectrum at ion scales. Theturbulent cascade leads to an overall anisotropic proton heating, protons areheated in the perpendicular direction, and, initially, also in the paralleldirection. The imposed expansion leads to generation of a large parallel protontemperature anisotropy which is at later stages partly reduced by turbulence.The turbulent heating is not sufficient to overcome the expansion-drivenperpendicular cooling and the system eventually drives the oblique firehoseinstability in a form of localized nonlinear wave packets which efficientlyreduce the parallel temperature anisotropy. This work demonstrates that kineticinstabilities may coexist with strong plasma turbulence even in a constrained2-D regime.

Plasma turbulence and kinetic instabilities at ion scales in the expanding solar wind