  Recently, an observational paper presented spatially resolved observations of
a wind outflow in CSWA13, a gravitationally lensed Star-Forming galaxy at z =
1.87. The gravitational lensing allowed for a substantially improved spatial
and kinematic resolution of the wind and of the nebular gas. In this paper we
take advantage of the resolved data to test for the existence of turbulence and
to study its nature. We derive the spatial structure functions of the residual
nebular and wind velocities along the major axis of the galaxy. The structure
functions, of both velocity fields, reveal a supersonic compressible large
scale turbulence. The turbulent timescale corresponding to the largest scale is
about 200 Myr, an order of magnitude larger than the estimated age of the wind
and of the young stars. This implies that the turbulence in the ism formed well
before the wind and the young stars. Given the large spatial scale of the
turbulence, it is plausible that the source of the turbulence is a large scale
one e.g. a merger or tidal event that triggered the formation of molecular
clouds, in the cores of which the young stars formed. A steepening of the
structure functions on the smaller scales provides an estimate of the effective
depth along the line of sight of the turbulent layer. The latter turns out to
be about 2kpc. S
