Energy transfer in the Solar Wind: The interplay between turbulence and kinetic instabilities.

Precisely how and where energy transfer between scales in the Solar Wind takes place remains an open question. We use the occurrence of conditions predicted by linear theory to promote the growth of kinetic instabilities, to infer how turbulence drives temperature anisotropies. We analyse Solar Orbiter data by applying the measure of local energy transfer (LET) derived from the Politano and Pouquet exact law to identify the relative distributions of energy transfer processes in the solar wind. We quantify these processes with the application of a radial rate of strain computed from single spacecraft data, a measure that we define as an approximation of the strain rate in fully three-dimensional turbulence. We find good agreement with the theoretical prediction that velocity shear is responsible for driving temperature anisotropies. We conclude that the turbulent velocity field plays a key role in the creation of unstable conditions in the Solar Wind.