= Bruno Bavassano
{c}
<Bruno Bavassano> is a <solar wind> researcher whose publications connect spacecraft observations with the statistical behavior of <magnetohydrodynamic turbulence>. A 2003 study with <Roberto Bruno>, <Vincenzo Carbone> and <Luca Sorriso-Valvo> compared <velocity> and <magnetic field> fluctuations between $0.3$ and $1$ astronomical unit from the Sun. It separated fast from slow <solar wind>, and changes in field magnitude from changes in field direction.<Radial evolution of solar wind intermittency in the inner heliosphere by Roberto Bruno and others>[byline and abstract, observing intervals and comparisons]{ref}
The diagnostic was scale-dependent <kurtosis>. For a fluctuation $X$ with mean zero, $K=\mathbb E[X^4]/\mathbb E[X^2]^2$ weights rare large events strongly. A <Gaussian distribution> has $K=3$; a rising value as the separation shrinks indicates that small-scale changes are becoming more unevenly distributed. The study found stronger <intermittency (turbulence)> in compressive magnetic fluctuations than in the corresponding velocity fluctuations, and a radial increase in fast-wind <intermittency (turbulence)>.<Radial evolution of solar wind intermittency in the inner heliosphere by Roberto Bruno and others>[abstract, flatness and radial evolution]{ref}
For intuition, replacing one ordinary increment by an increment ten times larger multiplies its contribution to the <fourth moment> by $10^4$, rather than $10^2$ for its squared contribution. This is why a sparse set of sharp changes can matter even when most samples look modest.
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