Temporal variations of the frequency shifts in μHz averaged over the modes l = 0,1, and 2, ⟨ Δν_{n,l = 0, 1, 2} ⟩, and calculated for four different frequency ranges (black dots). From left to right, the frequency ranges are the following: a) 1800 μHz ≤ ν< 3790 μHz; b) 1800 μHz ≤ ν< 2450 μHz; c) 2450 μHz ≤ ν< 3110 μHz; and d) 3110 μHz ≤ ν< 3790 μHz. The 10.7 cm radio flux, F_10.7, averaged over the same 365-day timespan and scaled to match the rising phase and maximum of Cycle 23 is shown as a proxy of the solar surface activity (solid line).