Conjunction study of plasmapause location using ground‐based magnetometers, IMAGE‐EUV, and Kaguya‐TEX data

A statistical study comparing the plasmapause location determined using extreme ultraviolet (EUV) and cross‐phase measurements was performed over 50 days in May–July 2000 and 1 day in May 2008. In EUV images the plasmapause location was estimated using the sharp gradient in the brightness of 30.4 nm He + emission. We have taken EUV images obtained by the IMAGE and the Kaguya satellites, which were operated in a solar maximum and minimum periods, respectively. In the ground‐based cross‐phase measurement, the plasmapause was defined as a steep drop of mass density in its radial profile. Mass density was inferred from the eigenfrequency of field line resonances in the ULF band (∼1–1000 mHz), which was deduced from geomagnetic field data using cross‐phase analysis. The two measurements of the plasmapause have been compared in a same meridian at the same time and very good agreement was found in 18 of 19 events. Our result clearly indicates that the He + and mass density plasmapause are usually detected at the same place with the error range of ± 0.4 R E . In only one event, the He + and the mass density defined plasmapauses were not colocated. This event may be due to the difference of refilling time between He + and other dominant species.