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Solar wind quasi‐invariant as a new index of solar activity

1999; American Geophysical Union; Volume: 26; Issue: 16 Linguagem: Inglês

10.1029/1999gl900583

1944-8007

V. A. Osherovich, J. Fainberg, R. G. Stone,

Global Energy and Sustainability Research

Solar wind parameters, such as magnetic field strength B, plasma density ρ and bulk speed υ correlate with solar cycle measured by sunspot numbers SSN . Using hourly data in the solar wind near the Earth, we show that the energy density ratio QI = ( B ²/8π)/( ρυ ²/2) has a correlation coefficient ( cc ) with SSN which is appreciably higher than for each of B , ρ and υ taken separately. The proposed quasi‐invariant is related to magnetic Mach number M A ( QI = M A −2 ). The yearly median QI for the last 28 years holds a linear relation with SSN with high cc = 0.98, which makes it the best index of solar activity derived from solar wind parameters so far.