Behavior of sink and source defects in a one-dimensional traveling finger pattern

We present the results of an experimental study of sink and source defects in a one-dimensional pattern of traveling fingers that form at a driven fluid-air interface. We find that sinks and sources behave differently: Sinks separate regions of differing wave number and move smoothly so as to keep the phase difference across the sink fixed. They are transient objects which are eventually destroyed at the boundaries of the experiment or by collision with a source. Sources, on the other hand, are long lived. They are symmetric and stationary on average, although individual sources move erratically and do not display the phase-matching behavior of the sinks.