The Effects of Solar Cycle Variability on Nanodust Dynamics in the Inner Heliosphere: Predictions for Future STEREO A/WAVES Measurements

Abstract

AbstractThe collisional grinding of interplanetary meteoroids should continually produce grains over a wide range of sizes, including down to the nanometer‐size regime. Once generated, nanodust grains are subject to interplanetary electromagnetic forces from the solar wind due to their relatively large charge‐to‐mass ratios, resulting in complex and highly time‐dependent dynamics. Here, we use the coupled Wang‐Sheeley‐Arge solar corona and Enlil solar wind models together with a nanodust charging and dynamics model to explore the behavior and variability of nanodust dynamics in the inner heliosphere (<1 au) both within and across multiple solar cycles. In particular, we quantify the relative accessibility of these grains to 1 au across solar cycles 23 and 24, including focusing and defocusing heliospheric conditions. Finally, we qualitatively compare our model results with STEREO A (STA)/WAVES observations and identify correlations between the STA/WAVES single‐hit rate and the relative flux of >10 nm grains. Using solar cycle 23 as a proxy for the behavior of solar cycle 25, since both solar cycles share the same defocusing‐to‐focusing transition, we predict the relative flux of nanodust grains in the future and identify times at which nanodust impacts may reappear in the STA/WAVES data set. Continued analysis of future STA/WAVES observations will provide an important test of this prediction, either bolstering or weakening the interpretation of electromagnetically accelerated nanodust grains as the source of single‐hit events in the STA/WAVES Time Domain Sampler data set.