AE Index

In the ionospheric regions of the active auroras, the electrical conductivity of both the Northern and Southern Hemispheres is greatly enhanced by the bombardment of particles associated with the storm process. The strong night-side, field-aligned (Figure 4.11), and auroral electrojet currents (Figure 4.12) flowing there change the horizontal field (often by 100 to 1000 gammas or more) at the nearby ground locations. For each Universal Time hour, a special global auroral electrojet index (AE) of the magnetic storm strength is calculated from the maximum range (amplitude between the most positive and most negative) of values obtained in an overplot of the horizontal variation component values from a collection (typically 5 to 12) of observatories in the northern high-latitude auroral-zone circle (Figure 4.17).

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