Global Pc5 caused by a <i>DP</i> 2–type ionospheric current system

<jats:p>A global Pc5 geomagnetic pulsation (period of ∼6 min) was observed coherently from the auroral to equatorial latitudes in the local time sector of 0700–2100 LT during 1834–1900 UT on 21 April 1993. The Pc5 at the dayside dip equator (Sao Luiz, Brazil, and Ancon, Peru) was characterized by an equatorial enhancement with an enhancement ratio of ∼4. In the afternoon sector (1200–1600 magnetic local time) the Pc5 at the auroral latitude was coherent with that at the dip equator within a time resolution of 3 s. The Pc5 amplitudes decreased sharply away from the auroral zone but were enhanced in the dayside dip equator, in a manner that resembled the latitudinal profile of a <jats:italic>DP</jats:italic> 2 magnetic fluctuation (period of ∼40 min) studied by <jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#jgra16453-bib-0012"><jats:italic>Kikuchi et al.</jats:italic> [1996]</jats:ext-link> except for the enhanced amplitude in the auroral zone. In the dayside auroral oval the Pc5 fluctuations in the magnetic <jats:italic>X</jats:italic>/<jats:italic>H</jats:italic> component were reversed in phase between the morning and afternoon sectors. Additionally, the magnetic <jats:italic>Y</jats:italic>/<jats:italic>D</jats:italic> component fluctuations around noon were correlated with the dayside equatorial Pc5. At most dayside middle‐/low‐latitude stations the Pc5 fluctuations in the <jats:italic>H</jats:italic> component, which are regarded as evidence for magnetospheric compressions, were strong. However, near the dawn terminator the <jats:italic>D</jats:italic> component was dominant rather than the <jats:italic>H</jats:italic> component, suggesting the influences of ionospheric currents originating in the polar region. There was no significant azimuthal phase propagation away from noon for the auroral to equatorial Pc5 signals. The global observational results suggest that the dawn‐dusk electric field in the polar ionosphere accompanying a pair of field‐aligned currents extends instantaneously to the equatorial ionosphere and completes a <jats:italic>DP</jats:italic> 2–type ionospheric current system responsible for the global coherent Pc5.</jats:p>