Diurnal variations in the middle atmosphere observed by UARS

This paper investigates diurnal variations in the dynamical and chemical st ructure of the middle atmosphere observed by UARS. Dynamical variations are of tidal nature and appear prominently in the temperature field near the e quator. The temperature field is smooth enough for higher harmonics of the diurnal cycle, which are unresolved by the UARS sampling, to be negligible. Diurnal variations in the temperature field can therefore be mapped synopt ically. Daily maps of the diurnal variation of temperature exhibit meridion al and vertical structure typical of the propagating solar diurnal tide. Th rough advective and photochemical effects, diurnal variations of temperatur e introduce diurnal variations of ozone in the middle and upper stratospher e, chemical variations which are mapped in similar fashion. Diurnal variati ons of other chemical species contain higher harmonics, which are undersamp led by UARS, preventing diurnal variations in those species from being mapp ed reliably. Instead, the average diurnal variation over a month or longer is composited from observations at individual local times. In the middle st ratosphere, diurnal variations of NOx are strongly influenced by the zonal mean distribution of NOx, which in turn is controlled by the mean meridiona l circulation. So too are diurnal variations of ClOx, but with sign opposit e to those of NOx, owing to the coupling of those families.