Variability of OH(3-1) emission altitude from 2003 to 2011: Long-term stability and universality of the emission rate-altitude relationship

Vertical volume emission rate profiles of the OH(3-1) Meinel emission near the mesopause are retrieved from nighttime limb-emission observations with the SCIAMACHY (Scanning Imaging Absorption spectroMeter for Atmospheric CHartographY) instrument on the Envisat satellite. Mean emission altitudes are determined by weighting altitude with the vertical OH(3-1) volume emission rate profile. Analysis of the SCIAMACHY data set from January 2003 to December 2011 shows a clear semi-annual variation of the mean emission altitudes at low latitudes - where SCIAMACHY performs measurements throughout the year - with an amplitude of 0.5-1.0 km. Confirming earlier studies, we find a near constant, or universal, scaling of mean OH emission altitude and vertically integrated emission rate, which can be employed by ground-based observers to infer indirect information on OH emission altitude and its variability, if measurements of OH emission rates are performed. For this purpose we provide climatological fit parameters for the altitude/emission rate relationship. No obvious long-term trends or 11-year solar cycle signatures are present in the OH emission altitude time series, partly contradicting earlier studies. The long-term stability in OH emission altitude at the local time of the SCIAMACHY nighttime observations (10 p.m.) strengthens the use of ground-based OH rotational temperature measurements to study middle atmospheric climate change.