【Intermittent】 , 【recurrent】 ,  【periodic】 ,  【alternate】  mean recurring or reappearing more or less regularly but in interrupted sequence.

Something is  【intermittent】 which from time to time is omitted or disappears but always returns.

Something is  【recurrent】  which returns or has the habit of returning after omission or disappearance. In contrast,  【intermittent】  stresses breaks in continuity and  【recurrent】 stresses repetition.

Something is  【periodic】 which is known to be 【recurrent】 at more or less fixed intervals over a long period of time and which, therefore, can be fairly accurately forecast.

Something is  【alternate】  which is both 【intermittent】 and 【recurrent】 , each in turn with something else. When applied to two contrasted or different things,  【alternate】 implies a succession of one after the other.

When applied to things of the same kind or description that follow each other in serial order,  【alternate】 means every other one.