A study of mid-latitude long-lasting positive storm effects in the American sector

Storm-generated disturbances can lead to profound modification of our planet's upper atmosphere, which appear as storm enhanced density (SED) or depletion of the plasma density distributions in the ionosphere. The characteristics and driving mechanisms of long-lasting SED (LLSED) events are largely still a subject of intense debate. In this study we examine the occurrence of mid-latitude LLSED events in the American sector during the period 2000-2018. Our analysis is based on GPS total electron content (TEC) data processed by the Millstone Hill Observatory team and made available via the NSF CEDAR Madrigal database. During the period of interest, about 665 geomagnetic storms with SYM-H index -40 nT were identified but only ~57 (< 8%) met the criterion for LLSED events. Results show that the occurrence of LLSED events and the corresponding amplitude of perturbations have a strong solar cycle and local time dependence. All LLSED events were associated with enhance AE index.