Phase shift between the velocities at the bottom and top of the photosphere φ(V,V) as a function of the phase shift between the velocity and temperature at the upper photosphere φ(T,V) for the plage area (upper row) and for the quiet area (bottom row). The yellow and red colours denote a greater density of points in the distribution. Negative velocity–velocity shifts, φ(V,V), mean upward waves.