Relating the Solar Wind Turbulence Spectral Break in the Dissipation Range with Upstream Spectral Bump at Planetary Bow Shocks

At scales much larger than the ion inertial scale and the gyro-radius of thermal protons, Magnetohydrodynamics (MHD) theory is well equipped to describe the nature of solar wind turbulence. The turbulent spectrum itself is defined by a power law manifesting the energy cascading process. A break in the turbulence spectrum develops at smaller scales, signaling the onset of energy dissipation. The exact mechanism for the spectral break is still a matter of debate. In this work, we use the 20 Hz \textit{MESSENGER} magnetic field data during four planetary flybys at different heliocentric distances to examine the nature of the spectral break in solar wind turbulence. By carefully selecting the spacecraft trajectory, we relate the spectral break in the quiet solar wind with a well-known upstream wave phenomenon at planetary bow shocks which is the characteristic spectral bump at frequencies $\sim 1$ Hz. We identify both spectral breaks and spectral bumps in the turbulence spectrum during four planetary flybys and examine the radial dependence of the ratio of these two frequencies. We argue that the spectral break likely occurs at the cyclotron resonance scale more than the inertial length scale.