Interference of the running waves on LB 1 at Hα − 0.4 Å. From top to bottom, the images in turn are the filtered components of v > 14 km s⁻¹, P = 4.2–5.7 and 4 < v < 14 km s⁻¹, and the Doppler velocity. The FOV is ﹩5\buildrel{\prime\prime}\over{.} 2\times 6\buildrel{\prime\prime}\over{.} 7﹩ shown in panel (b) of Figure 4. The solid circles highlight the wavefronts in the 4 < v < 14 km s⁻¹ images, of which the red denotes WF2 shown in Figure 4(b). Otherwise, the white/light-blue color denotes the preceding/following waves.