Daily ozone cycle in the stratosphere: global, regional and seasonal behaviour modelled with the Whole Atmosphere Community Climate Model

Abstract

The Whole Atmosphere Community Climate Model (WACCM) is utilised to study the daily ozone cycle and underlying photochemical and dynamical processes. The analysis is focused on the daily ozone cycle in the middle stratosphere at 5 hPa where satellite-based trend estimates of stratospheric ozone are most biased by diurnal sampling effects and drifting satellite orbits. The simulated ozone cycle shows a minimum after sunrise and a maximum in the late afternoon. Further, a seasonal variation of the daily ozone cycle in the stratosphere was found. Depending on season and latitude, the peak-to-valley difference of the daily ozone cycle varies mostly between 3 and 5 % (0.4 ppmv) with respect to the midnight ozone volume mixing ratio. The maximal variation of 15 % (0.8 ppmv) is found at the polar circle in summer. The global pattern of the strength of the daily ozone cycle is mainly governed by the solar zenith angle and the sunshine duration. In addition, we find synoptic-scale variations in the strength of the daily ozone cycle. These variations are often anti-correlated to regional temperature anomalies and are due to the temperature dependence of the rate coefficients k 2 and k 3 of the Chapman cycle reactions. Further, the NO x catalytic cycle counteracts the accumulation of ozone during daytime and leads to an anti-correlation between anomalies in NO x and the strength of the daily ozone cycle. Similarly, ozone recombines with atomic oxygen which leads to an anti-correlation between anomalies in ozone abundance and the strength of the daily ozone cycle. At higher latitudes, an increase of the westerly (easterly) wind cause a decrease (increase) in the sunshine duration of an air parcel leading to a weaker (stronger) daily ozone cycle.

Sunset–sunrise difference in solar occultation ozone measurements (SAGE II, HALOE, and ACE–FTS) and its relationship to tidal vertical winds

“…Schanz et al, 2014). The relationship between the SSD and vertical tidal winds will be further demonstrated in the next section, where we will examine the seasonal variations of the SSD.…”

“…At 32 km, ozone levels show a significant diurnal variation during the daytime due to photochemistry but they are almost zero at SR and SS, resulting in almost zero SSD. Chapman mechanism and NOx chemistry are related to the photochemical variations (Pallister and Tuck, 1983;Schanz et al, 2014). At 42 km, ozone levels show a diurnal variation caused by both vertical transport and photochemistry.…”

A climatology of the diurnal variations in stratospheric and mesospheric ozone over Bern, Switzerland

“…In the daytime stratosphere, the catalytic NO cycle counteracts the ozone production by the Chapman cycle (Schanz et al, 2014). In the daytime mesosphere, catalytic ozone depletion by odd hydrogen has to be considered in addition to the Chapman cycle.…”

“…It is beyond the scope of the present observational study to give a tutorial on the physics and chemistry of the diurnal variation in stratospheric ozone. For a tutorial, the reader is referred to a numerical simulation study of Schanz et al (2014), who described the global, regional and seasonal behaviour of the diurnal ozone variation in the middle stratosphere.…”

“…After sunset the atomic oxygen in the mesosphere rapidly recombines with molecular oxygen under formation of ozone. For further explanation of the physics and chemistry of the diurnal ozone variation, the reader is referred to Haefele et al (2008) and Schanz et al (2014).…”