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Solar wind quasi‐invariant as a new index of solar activity
Author(s) -
Osherovich Vladimir A.,
Fainberg J.,
Stone R. G.
Publication year - 1999
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/1999gl900583
Subject(s) - solar wind , sunspot , physics , solar maximum , sunspot number , solar minimum , correlation coefficient , solar cycle 22 , mach number , atmospheric sciences , meteorology , solar cycle , magnetic field , computational physics , mathematics , mechanics , statistics , quantum mechanics
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.