Routine determination of the plasmapause based on COSMIC GPS total electron content observations of the midlatitude trough

Observations from the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) GPS precise orbit determination (POD) antennae are used to create a database of vertical total electron content (VTEC) measurements between roughly 800 and 20,200 km. Owing to the correlation between the midlatitude trough and the plasmapause, the COSMIC GPS VTEC observations are used to determine the plasmapause location throughout 2008. The COSMIC observations of the plasmapause during 2008 are used to illustrate the variations with local time and geomagnetic activity as well as to reveal periodic behavior of the plasmapause. The plasmapause variation with geomagnetic activity obtained by the COSMIC observations is found to be consistent with previous results based on different observation methods. The similarity to prior results demonstrates the effectiveness of using the COSMIC POD observations for determining the plasmapause. The COSMIC observations further reveal that the plasmapause exhibits significant variability and is, on average, primarily invariant in local time. The plasmapause is also found to oscillate at periods of 9 and 13.5 days during 2008 in connection with recurrent geomagnetic activity due to high-speed solar wind streams. This is the first time that multiday oscillations have been observed in the plasmapause. The presence of a periodic modulation of the plasmapause further demonstrates the importance of periodic high-speed streams in the Earth's upper atmosphere and inner magnetosphere during the current solar minimum.