  In the absence of a magnetic field, scattered wavefunction inside a circular
p-n junction in graphene exhibits an interference pattern with high intensity
maximum located around the caustics. We investigate the wavefunctions in the
presence of a uniform magnetic field outside the circular region to show how
the loci of the high intensity region changes by forming Landau level structure
outside the circular region and a central high intensity region inside the
circular p-n junction due to the strong reflection of massless Dirac fermions
by the outside magnetic field. We conclude by suggesting experimental ways to
detect such change of pattern due to the effect of the magnetic field.
