Modeling the Effects of Solar Wind Structure on Nanodust Dynamics in the Inner Heliosphere

Abstract:

Over the past decade, nanometer sized dust grains (“nanodust”) have become an intense area of research due to their detection in various spacecraft radio wave antenna datasets as transient voltage “spikes” or anomalous waveform spectra. Nanodust grains are presumed to originate in the inner heliosphere (i.e., <1 AU) due to either the collisional evolution of the interplanetary meteoroid complex or the impulsive disruption of cometary and/or asteroidal bodies. Upon creation, nanodust grains couple strongly to the interplanetary plasma and magnetic field environment due to their relatively high charge-to-mass ratio. Thus, the morphology and variability of the interplanetary plasma and field environment play a significant role in determining the dynamics and evolution of nanodust grains. Despite this, we still do not understand the highly variable temporal and spatial observations of nanodust at 1 AU and the implications of these observations for the production and distribution of nanodust in the inner heliosphere.

To further explore the dynamics and distribution of nanodust grains in the inner heliosphere, we have used a combination of the WSA-Enlil model, which is a coupled solar corona-solar wind 3D MHD model driven by solar photospheric magnetic field observations, and a nanodust dynamics and charging model. With WSA-Enlil, we have modeled the interplanetary plasma and field environment between 0.1 au and 1.0 au for eight Carrington rotation (CR) periods that overlap with the prime STEREO mission. For each CR, we have used the WSA-Enlil simulation results to model the behavior of grains between 1 nm and 30 nm, calculating the density, flux, velocity distributions, and impact charge distributions. We will describe the inputs and assumptions to both the WSA-Enlil and nanodust models and describe the results for the nanodust distribution. In particular, we will show how the solar wind and IMF structure is imprinted onto the nanodust grain distributions as a function of the heliospheric current sheet structure, nanodust grain size, and position in the inner heliosphere. Finally, we compare the modeled nanodust fluxes with impact rates determined from STEREO A and B WAVES instrument and discuss implications for the formation mechanism(s) of nanodust grains in the inner heliosphere.