The Development of a Space Climatology: 1. Solar Wind Magnetosphere Coupling as a Function of Timescale and the Effect of Data Gaps. Issue 1 (30th January 2019)

• Record Type: Journal Article
• Authors: Lockwood, Mike; Bentley, Sarah N.; Owens, Mathew J.; Barnard, Luke A.; Scott, Chris J.; Watt, Clare E.; Allanson, Oliver
• Is Part Of: Space weather. Volume 17:Issue 1(2019)
• Page Start: 133
• Page End: 156
• Publication Date: 2019-01-30
• Subjects: space climate -- solar wind power -- solar wind coupling -- geomagnetic activity; Space environment -- Periodicals; 551.509992
• DOI: 10.1029/2018SW001856
• Languages: English
• ISSNs: 1542-7390

Abstract

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, τ . We study the relationships of the am and SME geomagnetic indices to the power input into the magnetosphere P α, estimated using the optimum coupling exponent α, for a range of τ 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 α, 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 that α = 0.44 ± 0.02 and no significant evidence that α depends on τ, yielding P α ∝ B 0.88 V sw 1.90 ( m sw N sw ) 0.23 sin 4 ( θ /2), where B is the interplanetary magnetic field, N sw the solar wind number density, m sw its mean ion mass, V sw its velocity, and θ the interplanetary magnetic field clock angle in the geocentric solar magnetospheric reference frame. Values of P α that are accurate to within ±5% for 1996–2016 have an availability of 83.8%, and the correlation between P α and am for these data is shown to be 0.990 (between 0.972 and 0.997 at the 2 σ uncertainty level), 0.897 ± 0.004, and 0.790 ± 0.03, for τ of 1 year, 1 day, and 3 hr, respectively, and that between P α and SME at τ of 1 min is 0.7046 ± 0.0004. Plain Language Summary: This is the first step of three toward constructing a climatology describing the statistics of how space weather has varied over the past 400 years. This climatology will be valuable in the design of systems vulnerable to space weather. To do this, we here investigate how best to quantify the power extracted from the solar wind by the magnetosphere. We need to do this over a range of timescales from the annual averages used to describe long‐term changes ( space climate ) down to fluctuations over minutes and hours, which drive space weather events. Key Points: Gaps in interplanetary data from minutes to years generate significant errors in empirically derived solar wind coupling functions All coupling functions derived using data from before 1995 need to be critically reevaluated and checked for overfitting The optimum coupling function quantifying power input to the magnetosphere has no detectable variation with averaging timescale