Influence of off-Sun-Earth line distance on the accuracy of L1 solar
wind monitoring
Abstract
Upstream solar wind measurements from near the L1 Lagrangian point are
commonly used to investigate solar wind-magnetosphere coupling. The
off-Sun-Earth line distance of such solar wind monitors can be large, up
to 100 RE. We investigate how the correlation between measurements of
the interplanetary magnetic field and associated ionospheric responses
deteriorates as the off-Sun-Earth line distance increases. Specifically,
we use the magnitude and polarity of the dayside region 0 field-aligned
currents (R0 FACs) as a measure of IMF BY-associated magnetic tension
effects on newly-reconnected field lines, related to the
Svalgaard-Mansurov effect. The R0 FACs are derived from Advanced
Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE)
measurements by a principal component analysis, for the years 2010 to
2016. We perform cross-correlation analyses between time-series of IMF
BY, measured by the Wind spacecraft and propagated to the nose of the
bow shock by the OMNI technique, and these R0 FAC measurements.
Typically, in the summer hemisphere, cross-correlation coefficients
between 0.6 and 0.9 are found. However, there is a reduction of order
0.1 to 0.15 in correlation coefficient between periods when Wind is
close to (within 45 RE) and distant from (beyond 70 RE) the Sun-Earth
line. We find a time-lag of around 17 minutes between predictions of the
arrival of IMF features at the bow shock and their effect in the
ionosphere, irrespective of the location of Wind.