Time-of-day (UT)/time-of-year (F) plots of the modelled sensitivity of (top row) the northern-hemisphere an index, S_an; (middle row) the southern-hemisphere as index, S_as; and (bottom row) the global index am = (an + as)/2, S_am. The left hand plots are for relatively high geomagnetic activity (defined as am = 74 nT, the mean of the 60 ≤ am < 110 nT band) and the right hand plots are for relatively low geomagnetic activity (defined as am = 14 nT, the mean of the 10 ≤ am < 20 nT band). All plots are for the stations and longitudinal sector weighting functions used in 2014.