First direct observations of interplanetary shock impact angle effects on actual geomagnetically induced currents: The case of the Finnish natural gas pipeline system

TL;DR

This study investigates how the impact angle of interplanetary shocks influences geomagnetically induced currents in the Finnish gas pipeline system, revealing that nearly frontal shocks cause immediate GIC peaks, while inclined shocks lead to delayed, more intense GICs.

Contribution

It is the first to analyze the effect of shock impact angle on GICs using real pipeline data, distinguishing immediate and delayed GIC responses to different shock geometries.

Findings

Nearly frontal shocks cause immediate GIC peaks in the post-noon/dusk sector.

Inclined shocks are associated with delayed, more intense GIC peaks around midnight.

GIC peaks are linked to magnetospheric processes like ring current intensification and particle injections.

Abstract

The impact of interplanetary (IP) shocks on the Earth's magnetosphere can greatly disturb the geomagnetic field and electric currents in the magnetosphere-ionosphere system. At high latitudes, the current systems most affected by the shocks are the auroral electrojet currents. These currents then generate ground geomagnetically induced currents (GICs) that couple with and are highly detrimental to ground artificial conductors including power transmission lines, oil/gas pipelines, railways, and submarine cables. Recent research has shown that the shock impact angle, the angle the shock normal vector performs with the Sun-Earth line, plays a major role in controlling the subsequent geomagnetic activity. More specifically, due to more symmetric magnetospheric compressions, nearly frontal shocks are usually more geoeffective than highly inclined shocks. In this study, we utilize a subset (332 events) of a shock list with more than 600 events to investigate, for the first time, shock impact angle effects on the subsequent GICs right after shock impact (compression effects) and several minutes after shock impact (substorm-like effects). We use GIC recordings from the Finnish natural gas pipeline performed near the M\"ants\"al\"a compression station in southern Finland. We find that GIC peaks (> 5 A) occurring after shock impacts are mostly caused by nearly frontal shocks and occur in the post-noon/dusk magnetic local time sector. These GIC peaks are presumably triggered by partial ring current intensifications in the dusk sector. On the other hand, more intense GIC peaks (> 20 A) generally occur several minutes after shock impacts and are located around the magnetic midnight terminator. These GIC peaks are most likely caused by intense energetic particle injections from the magnetotail which frequently occur during substorms.