A new model of the location of the plasmapause: CRRES results

Abstract

[1] A new empirical model of the plasmapause location has been developed using density data from the plasma wave receiver onboard the CRRES spacecraft for nearly 1000 orbits. The ''plasmapause'' is identified here as the innermost sharp gradient in density (change of a factor of 5 in <0.5 L). Such a sharp gradient was observed on 73% of the CRRES inbound and outbound orbits that returned data. The plasmapause location is expressed as a linear function of Kp (previous 12 hour maximum) and local time. The model gives the linear best fit location of the plasmapause as well as the standard deviations of the model parameters. We found a slight noon-midnight asymmetry with the plasmapause located on average an L shell farther from the Earth at midnight than in the noon sector. This is in the opposite sense to the noon-midnight asymmetry found previously. Significant variability (with standard deviations up to +/À 1 L shell) in the plasmapause location is seen and suggests that though the mean plasmapause is roughly circular, the instantaneous plasmapause has significant time variable localized structure at all local times but most especially in the duskside sector.

The relationship between plasmapause, solar wind and geomagnetic activity between 2007 and 2011

“…The scatter around the fit of the plasmapause is larger for lowest values of L PP indicators as noted also by Moldwin et al (2002). This is the most prominent in Sector2.…”

“…The maximum (in an absolute sense) value of the L PP indicators that precedes the plasmapause crossing is generally higher for smaller L PP than for larger L PP . However, our analyses show that the value at the highest-correlation time lag is more appropriate for describing the plasmapause responses to any disturbances rather than the maximum values in the prevailing interval before the L PP , as commonly used in other studies (e.g., Moldwin et al, 2002;O'Brien and Moldwin, 2003, and references therein). Thus, the obtained results (fit parameters) cannot be directly compared, but general findings confirm those of previous research (Carpenter and Anderson, 1992;Moldwin et al, 2002;O'Brien and Moldwin, 2003;Heilig and Lühr, 2013).…”

“…The often cited model of Carpenter and Anderson (1992) gives the L PP as a function of the maximum of the geomagnetic Kp index observed in the previous 24 h. Moldwin et al (2002) expressed the L PP as a function of the maximum Kp index in the previous 12 h. O'Brien and Moldwin (2003) extended that investigation by using Kp, Dst and AE geomagnetic indices taking the hours relative to the plasmapause crossing: 36 for Kp, 24 for Dst and 36 for AE. The new feature in their model is the L PP magnetic local time (MLT) dependence.…”

“…Empirical L PP has been estimated by examining groundbased whistler observations, in situ satellite density measurements (e.g., ISEE, CRRES), field-aligned current signature observations (CHAMP) and geomagnetic indices (Chappell et al, 1970b;Horwitz et al, 1986;Carpenter and Anderson, 1992;Gallagher et al, 2000;Moldwin et al, 2002;O'Brien and Moldwin, 2003;Heilig and Lühr, 2013).…”

Concerning long-term geomagnetic variations and space climatology

“…The figure also indicates the variability of the current plasmapause position as observed by, for example, Laakso and Jarva (2001) and Moldwin et al (2002). We conclude that relative variations introduced by secular changes in the dipole moment are much larger than changes introduced by magnetospheric activity.…”