Abstract
We compare electromagnetic ion cyclotron (EMIC) waves observed by the electric field instrument on Polar to simultaneous Pc1 pulsations detected at the subauroral Sodankylä station. We studied 44 passes where Polar was within ±1.5 hours in magnetic local time (MLT) from Sodankylä during a Pc1 pulsation event. In 70% of these passes a matching EMIC wave was observed in space. This shows that ground Pc1s indeed originate at high altitudes in the magnetosphere and have their source field line within a rather limited (±1–1.5 hours) MLT range. It also limits horizontal ducting of waves in the longitude direction to less than ∼1000–1500 km, and it gives a lower limit of ∼3 hours on the MLT extent of a typical EMIC wave band in space. Out of 69 EMIC events, 75% were observed at Sodankylä. This restricts the scale of ionospheric modification on the amplitude and frequency of waves. In several passes, two or three EMIC waves corresponding to different frequency branches were observed simultaneously. We discuss the location, frequency, amplitude, and ground visibility of the EMIC waves of these three branches separately. The results emphasize the high‐latitude dayside as a source of EMIC waves observed on the ground.
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