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The Parkes telescope has been monitoring 286 radio pulsars
approximately monthly since 2007. The wide Dispersion Measure
range of the pulsar sample and the uniformity of the observing
procedure make the data-set extremely valuable for studies of flux
density variability and the interstellar medium. In the plot above,
Kumamoto et al. show
the modulation index (a measure of how variable the pulsar is, defined
as the standard deviation of the measured flux densities divided
by the mean flux density) as a function of DM, and compare them with
theoretical predictions -- see
the preprint for more
details. Despite a large scatter, the modulation index is inversely
correlated with DM, and can be generally described by a power-law with
an index of -0.7 covering DMs from 10 to 1000 cm^{-3} pc. These studies
also show that local structures and non-Kolmogorov density
fluctuations are likely playing important roles in the observed flux
density variation of many of these pulsars.
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