noun, plural: diurnal rhythms
A biological rhythm that primarily express a periodicity during daylight hours
Biological rhythms pertain to the synchronized cyclic pattern demonstrated by an organism as its response to a particular stimulus. Biological clock that synchronizes with biological rhythm may be endogenous or exogenous. An endogenous type is one in which the internal biological clock is the one that controls it. An exogenous type is one that which involves an external cue (i.e. zeitgeber). There are the different types of biological rhythms: circadian rhythms, diurnal rhythm, ultradian rhythms, and infradian rhythms.1
A diurnal rhythm is a biological rhythm that is synchronized with the day/night cycle. It may or may not be a circadian rhythm. A biological rhythm is considered a circadian if these three criteria are met: (1) an endogenous free-running (approximately) 24-hour period, (2) a rhythm that is entrainable, i.e. capable of phase reset by environmental cues and synchronization to the 24-h day, and (3) exhibiting temperature compensation.2
An example of a diurnal rhythm is the release of microfilariae of loa loa into the peripheral blood predominantly at daytime.
1 Hedge, A. (2013). Biological Rhythms. Retrieved from ://ergo.human.cornell.edu/studentdownloads/dea3250pdfs/biorhythms.pdf
2 Johnson, C. (2004). Chronobiology: Biological Timekeeping. Sunderland, Massachusetts, USA: Sinauer Associates, Inc. pp. 67–105.