Comparison of the 3D MHD Solar Wind Model Results with ACE Data 2007 SHINE Student Day Whistler, B. C., Canada C. O. Lee*, J. G. Luhmann, D. Odstrcil, P. MacNeice, I. de Pater, P. Riley, and C. N. Arge

INTRODUCTION We generate results from inner heliospheric model ENLIL together with the Wang-Sheeley-Arge (WSA/ENLIL) and MHD-Around-a-Sphere (MAS/ENLIL) coronal magnetic field models. The 3-D WSA/ENLIL and MAS/ENLIL models are available at CCMC for simulating the ambient solar wind (out to 10 AU!). We show our 1 AU results of the comparison with ACE plasma observations. Such tests validate the models for use at quiet times, as well as establishing their usefulness for describing the ambient conditions prior to disturbances. Agreement of the model with observations could suggest that a viable option is available both to predict such enhancements from co-rotating stream interaction regions, as well as to provide an approximation to solar wind conditions when Cassini is inside Saturn's magnetosphere

Illustration of MAS coronal model (left) and ENLIL heliospheric solar wind model (right) Illustration of the coupled MAS (MHD around a sphere) [cf. Linker et al., J. Geophys. Res., 104, 9809, 1999] coronal model and the ENLIL solar wind model [cf. Odstrcil and Pizzo, J. Geophys. Res., 104, 483, 1999]. X Assumptions of model: polytropic X Coronal part can be an MAS MHD model or semi-empircal model, both of which uses magnetograms as innermost BCs Although shown above is an illustration of the MAS coronal input into ENLIL, the same concept can be applied for the WSA/ENLIL combination

WSA/ENLIL and MAS/ENLIL are solar magnetogram-based models Image credit: Mt. Wilson Solar Observatory Magnetograms are maps of line-of-sight component of magnetic flux at the photosphere. Regions of strong positive (blue) and strong negative (red) magnetic flux are shown. Input magnetograms to the solar corona models at CCMC either comes from the Mt. Wilson Solar Observatory (MWO) or the National Solar Observatory (NSO) at Kitt Peak Arizona. The fields are measured by detecting the Zeeman shift between right-hand and left-hand circularly polarized light in a magnetically sensitive absorption line (e.g. 5250 Angstroms, neutral iron Fe I).

The time range chosen for this study: January 2003 to December 2005 (Carrington Rotations 1999 to 2038) Time range of data set - Explain time range chose - Sun Solar Cycle (Sun Spot Number plot) - Ideal time to make comparison because it’s quiet solar cycle From Ron: Definitely mention which part of the solar cycle I am looking at and maybe mention why I am looking at this right now (Cassini driven). Mention in my paper that I will do the study for other parts of the same solar cycle using ACE if post-launch in 1997. He warned me that the analysis that I make from the existing data sets would only be applicable to that part of the solar cycle, which is why it important for me to mention to the audience which part of the solar cycle my research is focusing on. He said that I will find that when we are on the part of the cycle that is going from min to max, the solar wind will look quite different from the solar wind coming off from max to min. So I need to take care of the statements that I make about the solar wind and be very specific about the solar cycle that I look at! This period is an ideal time to make comparisons of the model data with spacecraft observations because it is a quiet solar cycle.

CCMC User Interface http://ccmc.gsfc.nasa.gov (top) User can select preferences in the run request interface: - desired Carrington Rotation (solar rotation of 27.3 days as observed from Earth) - input solar coronal model (MAS or WSA) - solar magnetograms from NSO or MWO - maximum radial distance of run (2 AU or 10 AU) (bottom) User can produce various output data in different formats such as color contour plots, 1D line plots, surface plots, etc., and can select the plotting parameters, such as plot variables (up to 3), plot axes range, etc.

Illustration from model results of how solar wind dynamic pressure evolves for one Carrington Rotation (top) An example of CCMC-generated output of a 2-D color contour plot for the variation in pressure with radial distance. (bottom) An example of a time series for dynamic pressure generated by the authors from the CCMC-generated ASCII text data output file.

Adopted plot style for displaying solar wind parameters Shown are time series of dynamic pressure (left) modeled at 1 AU for Carrington Rotation (CR) 2017 and 2018. The time series can be stacked against each other, where the magnitude of the dynamic pressure is now represented in color (above); highs = red, lows = blue. A time series organized by CR can be displayed in this fashion, forming a color contour plot of CR vs. day of CR (day 1, day 2, . . . day 27). +

Kitt Peak National Solar Comparison of different coronal models (left) and input solar magnetograms (right). Mt. Wilson Solar Observatory (MWO) MAS Coronal Input MAS-based values have less mid-range values (green) compared with WSA-based values. Kitt Peak National Solar Observatory (NSO) WSA Coronal Input There are small differences between MWO- and NSO-based values

Comparison of MAS/Enlil and WSA/Enlil with ACE Density at 1 AU For CRs 1999-2020 where the stream interaction regions are a 2-sector structure, there are 2 corresponding high-density ridges (reds). For CRs 2020 to 2038, there are 4 high-density ridges corresponding with a 4-sector structure. The model (right) compares fairly well with ACE (above). Although the model values are much higher than the observations, it should be noted that there are data dropouts in ACE densities whenever the values are very high.

Comparison of MAS/Enlil and WSA/Enlil with ACE Velocity at 1 AU In the modeled velocity (right), it can be seen that the pattern of high velocity values (orange-red) match fairly well with those from the ACE observations (above). Noticeable in the model velocity plots are the high values – they are not as high (orange) as those from the ACE observations (more red) . Ron also mentioned that some of the velocity data is off (sometimes the values goes to 250 km/sec, which is wrong). This is a somewhat systematic error that may or may not be documented in the publications. He said the way to check for whether the velocity values are trustworthy or not is to look at the SIS data, where there are measurements of 2 energy levels. He said to look at the higher energy channel data and look at whether there are values (differential flux) that hits the 50 mark. If so, then take a look at the velocities to see if they go to 250 km/sec. If so, don't trust that velocity value. Ron said the person to talk to this about if I have any questions is someone named Ruth over at LANL. (Keep in mind that the velocity values can go to 250 km/sec in reality but as far as whether the solar wind instrument measured the values correctly, that is another story.)

Comparison of MAS/Enlil and WSA/Enlil with ACE Dynamic Pressure at 1 AU Compared to ACE observations (above), the MAS/Enlil result (bottom right) seem to compare better overall than those from WSA/Enlil (top right). High pressure ridges (reds) are more accurately derived by MAS/Enlil than WSA/Enlil in terms of structure and magnitude of the values.

CONCLUDING REMARKS The model results at 1 AU correlate fairly well with ACE spacecraft observations for density, velocity, and dynamic pressure. We are in the process of comparing results for magnetic field polarities – ACE magnetic field data in GSE coordinates needs to be transformed to the coordinate system of the ENLIL model (HEEQ, sun-centered). This model runs routinely at CCMC. Note that the models do not yet include CMEs but future plans include adding such transient structures. Future work includes comparing results with the STEREO observations. In addition, we will also test the models for their performance in simulating the solar wind at other radial distances other than 1 AU.

Thank you!