Relation between the mean value of AATR of sub-auroral receivers (top panel) and the SBAS availability during a nominal hour (2 h, second panel) and during two storm hours (16 h, third and 23 h, bottom panel) within DoY 76 of 2015 (March 17). The colour bar depicts the percentage of epochs where the Protection Levels are under the Alarm Limits of 40 m (horizontal) and 50 m (vertical) simultaneously. Each pixel represents a square of 1 degree of resolution, without applying any interpolation.