The natural oscillations in stratospheric ozone observed by the GROMOS microwave radiometer at the NDACC station Bern

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 semiannual 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.

The Role of Quasi-Stationary Waves in Annual Cycle in Mid-Latitude Stratospheric and Mesospheric Ozone in 2011-2020

“…Extended summer maximum with barely perceptible SAO is seen in the middle stratosphere at 10 hPa (32 km; Fig. 6f and 6o), in consistency with the stratospheric ozone profiles from the GROMOS (GROund-based Millimeter-wave Ozone Spectrometer) microwave radiometer at Bern, Switzerland (47N, 8E) described in [55].…”

“…Accordingly, prevailing photochemical production of ozone at 30-40 km [23,58] is replaced by catalytic ozone destruction, which peaks in the northern midlatitude upper stratosphere (40-50 km) during the summer months [59]. The summer ozone minimum in the upper stratosphere-stratopause region is explained by the temperature-dependent photochemistry, with the anti-correlation of ozone and temperature and higher ozone depletion of in warmer air conditions in summer [55].…”

“…These annual changes are commonly referred to as the annual oscillation (AO) and the semi-annual oscillation (SAO) (e.g. [54][55][56]. Note that we describe these annual changes by isolating and comparing altitude changes in peak or specific ozone VMR levels (curves in Fig.…”

Investigation of Arctic middle-atmospheric dynamics using 3 years of H<sub>2</sub>O and O<sub>3</sub> measurements from microwave radiometers at Ny-Ålesund

“…Nevertheless periodicities are found in the ozone time series. They might result from temperature variabilities because of temperature dependent photochemistry (Moreira et al, 2016;Flury et al, 2009;Pendlebury et al, 2008). In the SD-WACCM datasets we see a positive correlation of ozone and temperature around 10 hPa in summer, however in the MLS temperature data of Ny-Ålesund no signature of a Q16DW was found.…”

Interannual Variation of Upper Stratospheric Ozone in the Northern Midlatitudes in Early Winter Caused by Planetary Waves

“…In contrast to many other observation methods, observations by millimeter-wave radiometer (MWR) make it possible to obtain ozone mixing ratios with high temporal resolution (~1 hr) over a wide altitude range from the stratosphere to the lower mesosphere (e.g., Moreira et al, 2016;Parrish et al, 2014;Schranz et al, 2018;Solomonov et al, 2012). The largest positive ozone trend after 2000 was observed around 1 hPa in the Northern midlatitude, owing mainly to a decline in the atmospheric abundance of chlorine (WMO, 2018); however, factors that cause interannual ozone variations at that pressure level have been examined to a lesser degree.…”