We propose a three-year research program to investigate the formation mechanisms, properties, and global impacts of foreshock bubbles (FBS). Our electromagnetic hybrid (kinetic ions, fluid…

This is a $432,236 research grant awarded by the National Aeronautics and Space Administration (NASA) Shared Services Center to Solana Scientific, Inc., a small disadvantaged business, to investigate the formation, properties, and global impacts of foreshock bubbles. The three-year research program will focus on determining the solar wind conditions that lead to foreshock bubble formation, understanding the particle acceleration mechanisms within them, and examining how the shape and magnetospheric impacts of foreshock bubbles vary with the orientation of the interplanetary magnetic field. This research builds on Solana Scientific's prior work in predicting and observing the existence of foreshock bubbles and their effects on the magnetosphere and ionosphere. The grant does not have a set-aside designation.

We propose a three-year research program to investigate the formation mechanisms, properties, and global impacts of foreshock bubbles (FBS). Our electromagnetic hybrid (kinetic ions, fluid electrons) simulations were the first to predict the existence of FBS. They showed that the interaction of solar wind rotational discontinuities (RDS) with backstreaming ions in the foreshock results in the formation of FBS with dimensions comparable to the width of the foreshock (~10 RE). The same simulations predict that the solar wind convects FBS into the BOW shock, initiating changes that extend from the magnetosheath to magnetosphere and down to the ionosphere. Since then, multipoint observations have confirmed the existence of FBS and their global effects in the solar wind, magnetosheath, inner magnetosphere, and in the ionosphere. Observations demonstrate that not only RDS but also solar wind tangential discontinuities (TDS) can create FBS. Spacecraft observations have also established that FBS have far greater effects upon the magnetosphere and ionosphere than any other feature generated by kinetic processes within the foreshock. Both simulations and observations indicate that foreshock bubbles are highly efficient particle accelerators. Upon encountering the BOW shock, the high fluxes of energetic ions within their core regions are injected into the magnetosheath and possibly into the magnetosphere. Although we know that FBS form when solar wind RDS and TDS interact with the backstreaming ions in the foreshock, we do not know the conditions determining which RDS or TDS form foreshock bubbles. The objectives of the proposed study are to (1) determine which solar wind discontinuities can form foreshock bubbles; (2) determine the physical processes responsible for the highly efficient particle acceleration within FBS; (3) determine the properties of FBS in the magnetosheath and their impacts upon the magnetosphere as a function of solar wind conditions, especially the (cone) angle between the interplanetary magnetic field (IMF) and solar wind velocity. During the first year of this investigation, we will conduct a series of hybrid simulations to address how RDS and TDS form foreshock bubbles for different solar wind conditions. We will compare simulation predictions to FB observations to establish that the two are in agreement. In this regard, we note that spacecraft observations have already established the need for modeling and theoretical efforts to address how TDS in addition to RDS can be responsible for the formation of FBS given the absence of a magnetic field component normal to TDS. During the second year, we will use hybrid simulations to determine the nature of particle acceleration mechanisms within FBS, such as 1ST and 2ND order fermi processes. We will also compare the predicted fluxes, energies and velocity distribution functions of the energetic ions with spacecraft observations. During the third year, we will examine how the shape and impacts of FBS with the magnetosphere change with the IMF cone angle. For example, we expect FBS to form upstream of the dayside magnetopause for small IMF cone angles, but upstream of the flank or high latitude BOW shock for large IMF cone angles. The former events would impact the subsolar magnetopause, whereas the latter would strike the magnetotail or high latitude magnetopause. The proposing team consists of DRS. N. Omidi (PI), d. Sibeck (CO-i) and a postdoc at gsfc. The proposing team has played a key role in predicting and the spacecraft discovery of foreshock bubbles, and has the ideal expertise and tools to achieve the objectives of this study.