Time series of the LoS Doppler velocity at the four locations marked in Fig. 1, and the resulting modes decomposed via EMD. The colors of the curves correspond to the same colors of the four locations marked in Fig. 1. For each location, the top panel shows the original time series, and the subsequent four panels show the EMD modes from c₁ to c₄. Time 0 denotes the start of the observation corresponding to 19:05:09 UT. The gray area at around 50 minutes represents the observing time gap. The negative value in velocity represents the upward motion (i.e., blueshift). Note that the y axes are scaled differently in each panel.