Comparison of the 3D MHD Solar Wind Model

Results with ACE Data

2007 SHINE Student DayWhistler, 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.

Illustration of MAS coronal model (left) and ENLIL heliospheric solar wind model (right)

Although shown above is an illustration of the MAS coronal input into ENLIL, the same concept can be applied for the WSA/ENLIL combination

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].

WSA/ENLIL and MAS/ENLIL are solar magnetogram-based

models 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.

Image credit: Mt. Wilson Solar Observatory

The time range chosen for this study: January 2003 to December 2005

(Carrington Rotations 1999 to 2038)

This period is an ideal time to make comparisons of the model data with spacecraft observations because it is a quiet solar cycle.

Time range of data set

CCMC User Interface

(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.

http://ccmc.gsfc.nasa.gov

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).

Comparison of different coronal models (left) and input solar magnetograms (right).

MAS Coronal Input

WSA Coronal Input

Mt. Wilson Solar Observatory (MWO)

Kitt Peak National Solar Observatory (NSO)

MAS-based values have less mid-range values (green) compared with WSA-based values.

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) .

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!