  The time dependence of the survival probability, S(t), is determined for
diffusing particles in two dimensions which are also driven by a random
unidirectional zero-mean velocity field, v_x(y). For a semi-infinite system
with unbounded y and x>0, and with particle absorption at x=0, a qualitative
argument is presented which indicates that S(t)~t^{-1/4}. This prediction is
supported by numerical simulations. A heuristic argument is also given which
suggests that the longitudinal probability distribution of the surviving
particles has the scaling form P(x,t)~ t^{-1}u^{1/3}g(u). Here the scaling
variable u is proportional to x/t^{3/4}, so that the overall time dependence of
P(x,t) is proportional to t^{-5/4}, and the scaling function g(u) has the
limiting dependences g(u) approaching a constant as u--->0 and
g(u)~exp(-u^{4/3}) as u--->infinity. This argument also suggests an effective
continuum equation of motion for the infinite system which reproduces the
correct asymptotic longitudinal probability distribution.
