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Table 2 Categories of mid-latitude irregularities with respect to the Equatorward Precipitation Boundary (EPB)

From: Review of the accomplishments of mid-latitude Super Dual Auroral Radar Network (SuperDARN) HF radars

  Location in relation to the EPB Occurrence/properties
Auroral irregularities Poleward of the EPB Observed at nearer ranges during storms, high-speed flow (~ 100s m s−1)
SAPS irregularities On the equatorward side of the EPB and usually extending only a few degrees in latitude Occurrence increases with disturbance level; westward, high-speed flow (~ 100s m s−1) in the pre-midnight sector
Sub-auroral irregularities Extending equatorward of the EPB indefinitely Nightside, low-speed flow (~10s m s−1), predominantly westward
Temperate mid-latitude irregularities Equatorward of the EPB by more than 10° Strong association with MSTIDs