Barium cloud striations revisited

Rocket‐based barium cloud striation observations from the 1970s are revisited based on a better knowledge of naturally occurring irregularities and on a previously unpublished analysis. A sharp drop in the spectral density of the plasma density fluctuation power is found near 25 m wavelength. This mimics equatorial spread F (ESF) spectra reported in the 1990s. Structure balance arguments show that the effective perpendicular ambipolar diffusion coefficient is 25 times the classical value, in good agreement with the natural case. We speculate that three‐wave coupling occurs to small scales where damped modes provide this anomalous diffusion effect, which is one‐tenth the value of the Bohm diffusion.