Solar Cycle Dependence of Mass Density and Ion Composition at Geosynchronous Orbit

Richard E. Denton, Dartmouth

Kazue Takahashi, APL

Michelle Thomsen, LANL

Solar Cycle DependenceMPA ion densityMass density

f10.7 f10.7

Same But Just on Dayside

MPA, total, low energy, and high energy – Still Dayside

Conclusions

• At geosynchronous orbit, the mass density peaks at solar maximum while ion density peaks at solar minimum, the opposite of the expected trend for electron density

• This implies a much higher concentration of O+ at solar maximum.

• VERY preliminary and not quite right: MPA underestimates ion density by a factor of 4 for O+. Assuming a H+/O+ plasma, we can use the average values at solar max and solar min to find nO+/ne = 0.42 and average ion mass M = 7 at solar max, and nO+/ne = 0.08 and M = 2.2 at solar min.