Sporadically and infrequently:
— He was arrogant and occasionally callous.
— Open areas are only occasionally interrupted by clumps of trees.

synonyms: at times, from time to time, now and again, now and then, on occasion, once in a while.

Roget 136: often, oft; ofttimes^†, oftentimes; frequently; repeatedly etc. 104; unseldom^†, not unfrequently^†; in quick succession, in rapid succession; many a time and oft; daily, hourly &c.; every day, every hour, every moment &c., perpetually, continually, constantly, incessantly, without ceasing, at all times, daily and hourly, night and day, day and night, day after day, morning noon and night, ever anon, invariably (habit) 613.    most often; commonly etc. (habitually) 613.    sometimes, occasionally, at times, now and then, from time to time, there being times when, toties quoties [Lat.], often enough, when the mood strikes, again and again.    ... show more