First six a _i splitting coefficients of the low-frequency p-modes with 1 ⩽ l ⩽ 35 measured in 3960 days of GONG data. The a-coefficients are represented as a function of the mode frequency ν (left column) and ν/ L, with (right column). The different colors and symbols correspond to selected ranges of radial orders n: green triangles, modes with n = 1,  2; purple stars, n = 3,  4; blue upside-down triangles, n = 5,  6; orange squares, n = 7,  8; and black dots, n ⩾ 9.