A hidden component of magnetic storms makes Earth's mantle transition zone look drier than it is

Seokhoon Oh 

Electromagnetic sounding provides a primary geophysical constraint on water in
Earth's mantle transition zone, yet conductivity models disagree by up to an
order of magnitude. We identify a source-side systematic invisible to internal
consistency checks: omitting the degree-3 zonal (P₃⁰) storm-field component
biases transition-zone conductivity by 0.1–0.35 decades, a tenth to a quarter
of that spread. The bias scales with network sparsity. The carrier is not
power but phase: a storm-band component nearly anti-phase to the ring current.
Injection reproduces the bias quantitatively; independent storm catalogs and
null, shuffled-geometry, and network controls exclude artifacts. It maps to
factors of 1.5–3.8 in water, 80–275 K, and 30% of the 660-km contrast. At the highest laboratory dry floors it becomes a dry/wet
misclassification. Source co-estimation removes it.