On a reported effect in ionospheric TEC around the time of the 6 April 2009 L'Aquila earthquake

Abstract. In a report published in Advances in Space Research, Nenovski et al. (2015) analyse ionospheric TEC (total electron content) data from GPS measurements around the time of the 6 April 2009 M_w 6. 1 L'Aquila (Italy) earthquake. According to the authors, TEC difference (DTEC) calculated from two GPS (Global Positioning System) receivers in central Italy shows a hump-like shape (an increase followed by a decrease) during the hours just before and shortly after the main shock. They maintain that the hump-like shape is anomalous and may be related to the earthquake. We show that the DTEC increase in the hours before the shock, as well as its subsequent slow decrease, does not have any characteristic that might support a possible relationship with the earthquake. We have also conducted our own independent analysis using the same GPS data analysed by Nenovski et al. (2015). We have found a diurnal variation in DTEC time series that shows hump-like shapes like that reported by Nenovski et al. (2015) throughout the investigated period. This demonstrates that the hump-like shape in DTEC close to the time of the 6 April earthquake is not anomalous and cannot be considered a possible earthquake-related effect.