Comparison of Heliospheric Magnetic Flux from

Observations and the SAIC MHD Model

S. T. Lepri, The University of MichiganS. K. Antiochos, Naval Research Laboratory

5/2/07

Quasi-Steady Heliospheric Magnetic Flux -- Method 1

• First apply a two-sigma filter to the data (+/-14.24 nT AU2)

• Require a steady period to last at least 2.5 days when data varies by less than 10% from the mean value of the flux in that 2.5+ day interval.

• Find that flux – Varies by factor of ≤ 2

w/o transients– Flux is lowest at solar

minimum, highest near maximum

Quasi-Steady Heliospheric Magnetic Flux -- Method 2

• |BrR2| from OMNI data (red) has been digitally filtered using low pass filter suppressing frequencies < 1.5 months, eliminating ICMEs, interaction regions.

• The MAS MHD model (green) exhibits lower flux at solar maximum

• The MHD model tends to agree much better with the observations in solar minimum years.

• The SS model (calculated by SAIC) tends to overestimate the magnetic flux near solar minimum and does not consistently agree with observations at other times of the solar cycle.

• Aside from a few spikes in the flux at solar maximum, the SS model shows enhanced flux at solar minimum. The SS model is most successful in matching the observed flux near 1980.

Quasi-Steady Heliospheric Magnetic Flux -- Method 2

• |BrR2| from OMNI data (red) has smoothed using a running 27 day running average.

• The 27-day averaged flux is larger than the filtered data, suggesting: – The filter is effective at eliminating transient fluctuations that mask the

long term evolution of the field– 27-day averages of unsigned flux enhance the effects of CMEs and

interaction regions, resulting in a falsely enhanced flux• The SS model agrees best with the 27-day averaged flux,

especially during solar maximum– indicates that the flux derived from the SS model is sensitive to the

presence of active regions, which correlate with magnetic field compressions from ICMEs observed in-situ.

• The MHD and SS models differ significantly. The MHD model is less sensitive to the dipole strength than the SS model.

Variation of the Heliospheric Flux: CME Effects

Topic 2