  The transfer of energy from large to small scales in solar wind turbulence is
an important ingredient of the longstanding question about the mechanism of the
interplanetary plasma heating. Previous studies have shown that
magnetohydrodynamic (MHD) turbulence is statistically compatible with the
observed solar wind heating as it expands in the heliosphere. However, in order
to understand which processes contribute to the plasma heating, it is necessary
to have a local description of the energy flux across scales. To this aim, it
is customary to use indicators such as the magnetic field partial variance of
increments (PVI), which is associated with the local, relative, scale-dependent
magnetic energy. A more complete evaluation of the energy transfer should also
include other terms, related to velocity and cross-helicity. This is achieved
here by introducing a proxy for the local, scale dependent turbulent energy
transfer rate epsilon_Dt(t), based on the third-order moment scaling law for
MHD turbulence. Data from Helios 2 are used to determine the statistical
properties of such a proxy in comparison with the magnetic and velocity fields
PVI, and the correlation with local solar wind heating is computed. PVI and
epsilon_Dt(t) are generally well correlated, however epsilon_Dt(t) is a very
sensitive proxy that can exhibit large amplitude values, both positive and
negative, even for low amplitude peaks in the PVI. Furthermore, epsilon_Dt(t)
is very well correlated with local increases of temperature when large
amplitude bursts of energy transfer are localized, thus suggesting an important
role played by this proxy in the study of plasma energy dissipation.
