Abstract
Abstract. A multilinear parametric regression analysis was performed to assess the seasonal and interannual variations of stratospheric ozone profiles from the GROMOS (GROund-based Millimeter-wave Ozone Spectrometer) microwave radiometer at Bern, Switzerland (46.95° N, 7.44° E; 577 m). GROMOS takes part in the Network for the Detection of Atmospheric Composition Change (NDACC). The study covers the stratosphere from 50 to 0.5 hPa (from 21 to 53 km) and extends over the period from January 1997 to January 2015. The natural variability was fitted during the regression analysis through the annual and semi-annual oscillations (AO, SAO), the quasi-biennial oscillation (QBO), the El Niño–Southern Oscillation (ENSO) and the solar activity cycle. Seasonal ozone variations mainly appear as an annual cycle in the middle and upper stratosphere and a semi-annual cycle in the upper stratosphere. Regarding the interannual variations, they are primarily present in the lower and middle stratosphere. In the lower and middle stratosphere, ozone variations are controlled predominantly by transport processes, due to the long lifetime of ozone, whereas in the upper stratosphere its lifetime is relatively short and ozone is controlled mainly by photochemistry. The present study shows agreement in the observed naturally induced ozone signatures with other studies. Further, we present an overview of the possible causes of the effects observed in stratospheric ozone due to natural oscillations at a northern midlatitude station. For instance regarding the SAO, we find that polar winter stratopause warmings contribute to the strength of this oscillation since these temperature enhancements lead to a reduction in upper stratospheric ozone. We have detected a strong peak amplitude of about 5 % for the solar cycle in lower stratospheric ozone for our 1.5 cycles of solar activity. Though the 11-year ozone oscillation above Bern is in phase with the solar cycle, we suppose that the strong amplitude is partly due to meteorological disturbances and associated ozone anomalies in the Northern Hemisphere. Further, our observational study gave the result that ozone above Bern is anti-correlated with the ENSO phenomenon in the lower stratosphere and correlated in the middle stratosphere.
Highlights
There is a wealth of possible sources of natural variability in stratospheric ozone
On interannual timescales dynamical feedbacks in the Earth system lead to effects of originally tropical phenomena, such as quasi-biennial oscillation (QBO) and El Niño–Southern Oscillation (ENSO), on midlatitude wave structures and wave propagation
As a result of using them to fit the ozone monthly means during the regression analysis, we may use them to quantify the natural variability of ozone
Summary
There is a wealth of possible sources of natural variability in stratospheric ozone. The concentration of stratospheric ozone varies as a result of different factors, some interacting among themselves through their effects on chemistry and transport. Ball et al, 2016) in the response of ozone to a natural oscillation complicate the understanding of the cause of the observed effect. These modes of variability do not always play a role in isolation; there are numerous examples The understanding of ozone variability is very useful for the detection and attribution of long-term changes An analysis of this sort at a single station may offer valuable information, useful for the comprehension at regional levels and for the validation of model simulations.
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