  The ratio of the rms electron density fluctuations to the background density
in the solar wind (density modulation index, $\epsilon_{N} \equiv \Delta{N}/N$)
is of vital importance in understanding several problems in heliospheric
physics related to solar wind turbulence. In this paper, we have investigated
the behavior of $\epsilon_{N}$ in the inner-heliosphere from 0.26 to 0.82 AU.
The density fluctuations $\Delta{N}$ have been deduced using extensive
ground-based observations of interplanetary scintillation (IPS) at 327 MHz,
which probe spatial scales of a few hundred km. The background densities ($N$)
have been derived using near-Earth observations from the Advanced Composition
Explorer ($\it{ACE}$). Our analysis reveals that $0.001 \lesssim \epsilon_{N}
\lesssim 0.02$ and does not vary appreciably with heliocentric distance. We
also find that $\epsilon_{N}$ declines by 8% from 1998 to 2008. We discuss the
impact of these findings on problems ranging from our understanding of Forbush
decreases to the behavior of the solar wind dynamic pressure over the recent
peculiar solar minimum at the end of cycle 23..

Solar and Stellar Astrophysics;Space Physics