The Development of a Space Climatology: 1. Solar Wind Magnetosphere Coupling as a Function of Timescale and the Effect of Data Gaps

Lockwood, Mike, Bentley, Sarah, Owens, Mathew J., Barnard, Luke A., Scott, Chris J., Watt, Clare and Allanson, Oliver (2019) The Development of a Space Climatology: 1. Solar Wind Magnetosphere Coupling as a Function of Timescale and the Effect of Data Gaps. Space Weather, 17 (1). pp. 133-156. ISSN 1542-7390

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Abstract

Different terrestrial space weather indicators (such as geomagnetic indices, transpolar voltage, and ring current particle content) depend on different ?coupling functions? (combinations of near-Earth solar wind parameters) and previous studies also reported a dependence on the averaging timescale, $tau. We study the relationships of the am and SME geomagnetic indices to the power input into the magnetosphere P$alpha, estimated using the optimum coupling exponent $alpha for a range of $tau between 1 min and 1 year. The effect of missing data is investigated by introducing synthetic gaps into near-continuous data and the best method for dealing with them when deriving the coupling function, is formally defined. Using P$alpha, we show that gaps in data recorded before 1995 have introduced considerable errors into coupling functions. From the near-continuous solar wind data for 1996-2016, we find $alpha = 0.44 plus/minus 0.02 and no significant evidence that $alpha depends on $tau, yielding P$alpha = B 0.88 Vsw 1.90 (mswNsw) 0.23 sin4($theta/2), where B is the Interplanetary Magnetic Field (IMF), Nsw the solar wind number density, msw its mean ion mass, Vsw its velocity and $theta is the IMF clock angle in the Geocentric Solar Magnetospheric reference frame. Values of P$alpha that are accurate to within plus/minus 5996-2016 have an availability of 83.8% and the correlation between P$alpha and am for these data is shown to be 0.990 (between 0.972 and 0.997 at the 2$sigma uncertainty level), 0.897 plus/minus 0.004, and 0.790 plus/minus 0.03, for $tau of 1 year, 1 day and 3 hours, respectively, and that between Palpha and SME at $tau of 1 min. is 0.7046 plus/minus 0.0004.

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