GPS TEC observations of dynamics of the mid-latitude trough during substorms

In this study, we combine GPS vertical total electron content (VTEC) and other complementary instruments, such as the Poker Flat incoherent scatter radar and all-sky imagers, to investigate the dynamics of the mid-latitude trough during non-storm time substorms for solar minimum condition and focus on Alaska region. We find that the pole-ward wall of the mid-latitude trough shifts equatorward rapidly after substorm onset with a maximum speed reaching 4 degrees-5 degrees of geomagnetic latitude per hour. This equatorward motion results in narrowing and even disappearance of the mid-latitude trough and is due to enhanced energetic electron precipitation. The mid-latitude trough can reappear during the substorm recovery phase as auroral activity retreats pole-ward. This phenomenon has not been reported before probably because of limited field-of-view of previous instruments used in trough studies. Comparisons of the trough minimum location predicted by models that are based on global K-p and AE indices show good agreement before substorm activity reaches the peak and relatively poor agreement during the recovery phase. The observations suggest that a local index, such as the local AL index, may be a better index to use to parameterize the trough location at a given meridian than a global index. Citation: Zou, S., M. B. Moldwin, A. Coster, L.R. Lyons, and M. J. Nicolls (2011), GPS TEC observations of dynamics of the mid-latitude trough during substorms, Geophys. Res. Lett., 38, L14109, doi:10.1029/2011GL048178.