Vertical profile of the radial velocity for the case p = −2. In both panels, the solid line is identical to that plotted on the right panel of Fig. 3 (time average over  [400,600]  and radial average over  [3,6] ). The left panel investigates the sensitivity of the result on the time average while keeping the same radial range: the time average is taken over  [400,500]  (dotted line) and  [500,600]  (dashed line). The right panel shows data obtained with the same time average,  [400,600] , but different radial range, namely R ∈  [2,4.5]  (dotted line) and R ∈  [4.5,7]  (dashed line).