Abstract
Abstract. For the first time three different methods have been used to calculate the global merging rate during the same substorm growth phase. The ionospheric plasma drift was monitored by six of the Northern Hemisphere SuperDARN radars, allowing the convection pattern to be studied over 12 h of magnetic local time. The radars observed reconnection signatures on the dayside simultaneously with substorm signatures on the nightside. The three methods to calculate the global merging rate are: (i) the equatorward expansion of radar backscatter on the nightside, which provides an estimate of the rate of polar cap expansion, while upstream WIND measurements gave an estimate of the reconnection electric fields; (ii) the derivation of the dayside boundary normal plasma flow velocity and an estimate of the extent of the ionospheric merging gap, from radar observation of dayside reconnection; (iii) utilizing the map-potential technique to map the high-latitude plasma flow and cross polar cap potential (Ruohoniemi and Baker, 1998), allowing the global dayside merging rate to be calculated. The three methods support an extensive magnetopause X-line length of between 30 ± 12RE and 35 ± 15 RE (assuming a single X-line and constant merging rate). Such close agreement between the different methods of calculation are unexpected, especially as the length of the magnetopause X-line is not well known.Key words. Magnetospheric physics (magnetopause, cusp and boundary layers; magnetosphere – ionosphere interactions; solar-wind magnetosphere interactions)
Highlights
Dungey (1961) stated that during periods of southward interplanetary magnetic field (IMF), reconnection on the dayside would lead to the creation of open magnetic flux in the Earth’s polar caps (PC)
A 75±5 min lag-time between when the IMF is observed by the satellite and when it impinges on the subsolar magnetopause has been calculated using the method outlined by Lester et al (1993); this time has been added onto the time scale of the plot
We calculated the flow across the dayside merging gap during the substorm growth phase, concentrating on the interval 04:35 to 05:50 UT, as this was the time interval we studied in detail on the nightside
Summary
The two-cell convection pattern observed in the high-latitude ionosphere was initially explained by Dungey’s (1961) reconnection cycle. Dungey (1961) stated that during periods of southward interplanetary magnetic field (IMF), reconnection on the dayside would lead to the creation of open magnetic flux in the Earth’s polar caps (PC). Provan et al (1998) have previously used data from the Hankasalmi radar to perform a detailed study of the dynamics and extent of pulsed anti-sunward moving transient features, detected poleward of a convection reversal boundary (CRB) at high-latitudes in the CUTLASS field-of-view (f-o-v.). These pulsed ionospheric flows (PIFs) had an average recurrence rate of 7 to 8 min, which is close to the average recurrence rate of FTEs, as first reported by Rijnbeek et al (1984). All calculations assume a uniform merging rate and a single X-line
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