SH11A-2185: Modeling the Solar Wind - Local Interstellar Medium Interaction Using the MHD-IPS TomographyTae K. Kim1 (tae.kim@uah.edu), Keiji Hayashi2, Munetoshi Tokumaru3, Nikolai V. Pogorelov1, Sergey N. Borovikov1

1Department of Physics / Center for Space Plasma and Aeronomic Research, The University of Alabama in Huntsville, 2W. W. Hansen Experimental Physics Lab., Stanford University, 3Solar-Terrestrial Environment Laboratory, Nagoya University

● AbstractAs the Voyager spacecraft cruise toward the heliopause to eventually become the first man-made objects ever to permanently leave the heliosphere and the influence of the solar wind (SW), they continue to return enlightening measurements from the heliosheath that immensely help us, and often challenge us, in our modeling efforts. Modeling the SW outflow to the heliospheric boundary with the local interstellar medium (LISM) requires computational resources capable of handling the complex physical processes taking place in the partially ionized plasma in the heliosheath and a set of time-dependent boundary conditions that closely replicate the cyclical and day-to-day variations in the SW parameters. We rely on the interplanetary scintillation (IPS) observations from the Solar-Terrestrial Environment Laboratory (Nagoya University, Japan) to construct such boundary conditions for Multi-Scale Fluid-Kinetic Simulations Suite (MS-FLUKSS), which is a set of numerical codes consisting of several modules suitable for simulating the interactions between ions and neutral atoms that characterize the region of our interest. However, since IPS observations contain a line-of-sight integration effect, they must be deconvolved through a tomographic procedure to provide a more accurate, three-dimensional map of the SW parameters. In this case, we use the MHD-IPS tomography with the improved, Ulysses-based, correlations of temperature and density with speed to generate the boundary conditions at 5 AU for an extended period of time, which we feed into MS-FLUKSS to model the SW-LISM interaction. To conclude, we compare the results with Voyager measurements in the inner heliosheath.

2. STEL IPS Observations

5. Time-dependent 3D MHD-Kinetic Simulation Results (Part 2)

6. Summary and Discussions4. Time-dependent 3D MHD-Kinetic Simulation Results (Part 1)

1. Introduction

● References

● Acknowledgments

1. B. V. Jackson, P. L. Hick, M. Kojima, and A. Yokobe, J. Geophys. Res. 103, A6, 12049-12067 (1998). 2. M. Kojima, M. Tokumaru, H. Watanabe, A. Yokobe, K. Asai, B. V. Jackson, and P. L. Hick, J. Geophys. Res. 103, A2, 1981-1989 (1998). 3. K. Asai, M. Kojima, M. Tokumaru, A. Yokobe, B. V. Jackson, P. L. Hick, and P. K. Manoharan, J. Geophys. Res. 103, A2, 1991-2001 (1998).4. K. Hayashi, M. Kojima, M. Tokumaru, and K. Fujiki, J. Geophys. Res. 108, A3, 1102 (2003).5. T. K. Kim, N. V. Pogorelov, S. N. Borovikov, and K. Hayashi, Numerical Modeling of Space Plasma Flows (ASTRONUM 2011), 459, 209 (2012).

This research was supported by the Alabama EPSCoR Graduate Research Scholars Program, NASA grants NNX09AW44G, NNX10AE46G, NNX09AP74A, and NNX12AB30G, and also by an allocation of advanced computing resources provided by NSF. The computations were performed on Kraken Cray XT5 at the National Institute for Computational Sciences (http://www.nics.tennessee.edu). The Voyager 1 and Voyager 2 data are courtesy of R. A. Decker and J. D. Richardson, respectively. T. K. Kim would also like to acknowledge the NSF EAPSI fellowship and the JSPS fellowship for supporting his visit to STEL (Nagoya University, Japan) for 10 weeks in the summer of 2012.

3. Boundary Conditions

Figure 4. MHD-IPS tomography results at 5 AU

Figure 7. Number density (top, in cm-3) and radial velocity (bottom, in km/s) extracted along the Voyager 1 trajectory

Figure 6. Proton number density (left column, in cm-3) and radial velocity (right column, in km/s) shown in the meridional plane at three different times

Figure 9. Proton number density (left column, in cm-3) and radial velocity (right column, in km/s) shown in the meridional plane at three different times

Figure 3. Baseline geometry of the IPS stations near Nagoya, Japan [Source: STEL]

Figure 2. Interplanetary scintillation [Source: STEL]

Figure 1. The heliosphere and the Voyager spacecraft trajectories [Source: NASA]

Figure 5. SW dynamic pressure measured by spacecraft (top) and reproduced by the MHD-IPS tomography (bottom). Ulysses data have been scaled to 1AU.

STEL IPS Stations1. Toyokawa (2008~current)

- length (N-S): 106 m- width (E-W): 41 m- collecting area: 3382 m2

2. Kiso (1993~current) - length (E-W): 75 m - width (N-S): 27 m- collecting area: ~2000 m2

3. Fuji (1983~current) - length (E-W): 100 m - width (N-S): 20 m- collecting area: ~2000 m2

4. Sugadaira (1983~current) - Almost same as Fuji

Interplanetary Scintillation (IPS)➔fluctuation in observed intensity of a distant, compact radio source due to electron density irregularities in the SW

Solar-Terrestrial Environment Laboratory (STEL)location: Nagoya University in Nagoya, Japan (~35oN)operating frequency: 327 MHz, multi-site (4 stations)number of sources observed: <100 daily

STEL IPS Datadaily measurements of the scintillation indexSW speed estimated from multi-site observationsoccasional data outages due to heavy snowfall, power failure, system upgrades, routine maintenance, etc.various tomography methods developed by STEL and/or external collaborators to deconvolve the line-of-sight integration effect in the IPS data [1, 2, 3, 4]

LISM parameters Part 1 Part 2|B| (µG) 3 3Proton density (cm-3) 0.06 0.06Neutral H density (cm-3) 0.15 0.15Temperature (K) 6527 6527Flow speed (km/s) 26.4 22.0

Table 1. Outer boundary conditions in the LISM

SW parameters (time-varying)➢ MHD-IPS tomography data

Heliocentric distance: 5 AUResolution

-spatial: 5.625o x 5.625o

-temporal: 1 dayUse of empirical correlations (Ulysses-based) to calculate SW number density and temperature from SW speedSee [4] for details.

➢ Availability: 2001 ~ current➢ Examples shown in Figure 4.

LISM parameters➢ See Table 1 for details.

Figure 8. Number density (top, in cm-3) and radial velocity (bottom, in km/s) extracted along the Voyager 2 trajectory

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Figure 10. Number density (top, in cm-3) and radial velocity (bottom, in km/s) extracted along the Voyager 1 trajectory

Figure 11. Number density (top, in cm-3) and radial velocity (bottom, in km/s) extracted along the Voyager 2 trajectory

The Solar Wind (SW)- a stream of charged particles originating from the Sun- the medium in which the solar magnetic field and energy propagate outward- primary driver of space weather

The Heliosphere- a “bubble-like” structure formed by the pressure balance between the SW and the local interstellar medium (LISM)- size and shape largely affected by fluctuations in the SW parameters

Termination Shock (TS) Crossing of Voyager 1 and 2- Voyager 1: 94 AU (December 2004)- Voyager 2: 83.6 AU (August 2007)

●It is important to use realistic time-varying inner boundary conditions in modeling the SW-LISM interactions.●Previously, we obtained our boundary conditions via the MHD-IPS tomography in which the SW number density and temperature were estimated using correlations derived from the Helios spacecraft measurements, but the simulation results suggested that the boundary conditions must be improved to more realistically reproduce the variation in the SW dynamic pressure [5].●We again obtain our boundary conditions using the MHD-IPS tomography; however, we use the Ulysses-based correlations this time to estimate the SW number density and temperature.●Since the MHD-IPS tomography results contain only the steady, persistent background component of the global SW (with the high speed, non-ambient component associated with transient structures such as fast coronal mass ejections discarded), the LISM flow speed must be scaled down appropriately to reproduce the TS at the observed distances in 2004 and 2007.●Our next step would be to find a way to include the non-ambient component of the SW in the MHD-IPS tomography to further improve our boundary conditions; we may then test various LISM parameters to fit Voyager observations.

Note that to compensate for the smaller-than-observed dynamic pressure in the inner boundary conditions between 2001 and 2006, we have scaled the LISM flow speed down by ~20%. The simulated TS crossings of Voyager 1 and 2 are now much closer to the observed TS crossings.

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