Response of the Intermediate Layers at Brazilian low latitude to geomagnetic activity during the solar minimum of 2009

In this study, we investigate the dependence of the intermediate layers (ILs) altitudes/vertical velocities on the geomagnetic activity during the rather extended duration solar minimum of 2009. Based on an empirical climatological model developed from Digisonde data over the Brazilian low latitude station Cachoeira Paulista (22.42° S; 45° W, I: −34.4°), the virtual height (h'IL) and the top frequency (ftIL) of the ILs were analyzed as a function of the different levels of Kp index. Our results show that even a small variation in the geomagnetic activity during low solar activity can affect the ILs altitudes over Cachoeira Paulista. A downward movement of the ILs probably due to an overshielding electric field was observed during the early morning. Besides that, during daytime, the smooth rise of the ILs can be related to the regular undisturbed day-to-day F-region zonal electric field of the ionosphere.