  We measure the local harmonic generation from an YBa_2Cu_3O_(7-d)(YBCO)
bi-crystal grain boundary to examine the local Josephson nonlinearities.
Spatially resolved images of second and third harmonic signals generated by the
grain boundary are shown. The harmonic generation and the vortex dynamics along
the grain boundary are modeled with the Extended Resistively Shunted Josephson
(ERSJ) array model, which shows reasonable agreement with the experimental
data. The model also gives qualitative insight into the vortex dynamics induced
in the junction by the probing current distribution. A characteristic
nonlinearity scaling current density JNL ~ 1.5 x 10^5 A/cm^2 for the Josephson
nonlinearity is also extracted.
