Figure 12From: Global and frequent appearance of small spatial scale field-aligned currents possibly driven by the lower atmospheric phenomena as observed by the CHAMP satellite in middle and low latitudesOccurrence frequency. (a) The occurrence frequency on the nightside in spring (upper left), summer (upper right), fall (lower left), and winter (lower right) from 2001 to 2003. (b) The occurrence frequency on the nightside in spring (upper left), summer (upper right), fall (lower left), and winter (lower right) from 2007 to 2010.Back to article page