New subauroral K-derived sector indices are proposed. They are based on the K local geomagnetic activity indices from the planetary am network stations, and their derivation scheme draws directly from that of am indices. Four Magnetic Local Time (MLT) sectors are considered, leading to four different K-derived MLT sector indices: the aσDawn (03–09 MLT), aσNoon (09–15 MLT), aσDusk (15–21 MLT), and aσMidnight (21–03 MLT) indices. They cover more than four solar cycles and, thus, allow robust statistical analysis. Statistical studies of the whole aσ data series and case studies for two geomagnetic storms are presented. These analyses clearly show that the four aσ have specific behaviors and that it is possible to get insight into both the statistical properties of the physical processes responsible for the observed geomagnetic activity and contribution to the dynamics of a given storm.