A re-examination is made of the two-dimensional interaction of a plane, tim
e-harmonic sound wave with a rectilinear vortex of small core diameter at l
ow Mach number. Sakov [1] and Ford and Smith [2] have independently resolve
d the "infinite forward scatter" paradox encountered in earlier application
s of the Born approximation to this problem. The first order scattered fiel
d (Born approximation) has nulls in the forward and back scattering directi
ons, but the interaction of the wave with non-acoustically compact componen
ts of the vortex velocity field causes wavefront distortion, and the phase
of the incident wave to undergo a significant variation across a parabolic
domain whose axis extends along the direction of forward scatter from the v
ortex core. The transmitted wave crests of the incident wave become concave
and convex, respectively, on opposite sides of the axis of the parabola, a
nd focusing and defocusing of wave energy produces corresponding increases
and decreases in wave amplitude. Wave front curvature decreases with increa
sing distance from the vortex core, with the result that the wave amplitude
and phase are asymptotically equal to the respective values they would hav
e attained in the absence of the vortex. The transverse acoustic dipole gen
erated by translational motion of the vortex at the incident wave acoustic
particle velocity, and the interaction of the incident wave with acoustical
ly compact components of the vortex velocity field, are responsible for a s
ystem of cylindrically spreading, scattered waves outside the parabolic dom
ain. (C) 1999 Academic Press.