The influence of pickup protons, from interstellar neutral hydrogen, on the propagation of interplanetary shocks from the Halloween 2003 solar events to ACE and Ulysses: A 3-D MHD modeling study

Abstract

[1] We describe our 3-D, time-dependent, MHD solar wind model that we recently modified to include the physics of pickup protons from interstellar neutral hydrogen. The model has a time-dependent lower boundary condition, at 0.1 AU, that is driven by source surface map files through an empirical interface module. We describe the empirical interface and its parameter tuning to maximize model agreement with background (quiet) solar wind observations at ACE. We then give results of a simulation study of the famous Halloween 2003 series of solar events. We began with shock inputs from the Fearless Forecast real-time shock arrival prediction study, and then we iteratively adjusted input shock speeds to obtain agreement between observed and simulated shock arrival times at ACE. We then extended the model grid to 5.5 AU and compared those simulation results with Ulysses observations at 5.2 AU. Next we undertook the more difficult tuning of shock speeds and locations to get matching shock arrival times at both ACE and Ulysses. Then we ran this last case again with neutral hydrogen density set to zero, to identify the effect of pickup ions. We show that the speed of interplanetary shocks propagating from the Sun to Ulysses is reduced by the effects of pickup protons. We plan to make further improvements to the model as we continue our benchmarking process to 10 AU, comparing our results with Cassini observations, and eventually on to 100 AU, comparing our results with Voyager 1 and 2 observations.

MHD simulation of the inner‐heliospheric magnetic field

“…The respective set of equations was taken from Detman et al [2006Detman et al [ , 2011, who work on a very similar goal, i.e., space weather forecasting, for which they use input data similar to those used here. These kinds of interfaces are constantly augmented as testing goes on.…”

“…Correction for this with a respective scale factor has been applied here, so that R ' = 1.5R /(R gb /R ). This has been done in the recent update in Detman et al [2011] also, as R ' is now described (a) (b) Figure 3. Location of footpoints of open magnetic field lines in the photosphere (black/red crosses) for (a) minimum and (b) maximum conditions.…”

“…Although this is the key input to our code, it is however necessary to provide the code with initial conditions for all MHD variables. For this purpose the approach by Detman et al [2006Detman et al [ , 2011 is followed, which uses the empirical inverse relation between flux tube expansion factor and solar wind speed to determine the latter.…”

“…This approach allows for higher resolution than that of comparable observational data from synoptic magnetograms. The heliobase conditions for the other MHD quantities are obtained following the empirical approach by Detman et al [2006Detman et al [ , 2011, who employed the Wang-Sheeley-Arge approach.…”

Insights gained using HHMS-PI from the Sun to Voyager 2

“…IBEX integrated line of sight observations [4] revealed an Energetic Neutral Atom (ENA) ribbon in the LISM that also may be affected by the properties of the LISM, asymmetries, and the locations of the TS and the Heliopause (HP), as well as by heliospheric variability due to solar activity. [1] summarized the physics of HHMS-PI and detailed many of its simulation results for the Halloween 2003 solar events [5] at ACE and Ulysses. HHMS-PI [1] starts at the Sun, the origin of the SW and IMF, and is a 3D MHD time-dependent modeling system that also specifically includes the effects of pickup protons, and simulates both the slowly evolving background and disturbed SW and IMF throughout the 3D heliosphere.…”