Stratospheric OClO observed with ground-based DOAS over Kiruna in the Arctic winters 1996/1997 – 2019/2020

<p>Recent research on stratospheric ozone indicates signs of ozone recovery, but on the other hand, ozone recovery is also expected to be delayed by many aspects (e.g climate change). Therefore, it is important to monitor continuously stratospheric trace gases to predict the future evolution of the Arctic ozone and other trace gases which are involved in the ozone depletion chemistry. OClO is well known as an indicator of the stratospheric chlorine activation and can be measured using remote sensing techniques.</p><p>In this study, we present long-term measurements of OClO slant column densities at Kiruna, Sweden (67.84°N, 20.41°E) which were obtained from the ground-based zenith sky DOAS instruments since 1997. The measurement site is located north of the polar circle in which the variability of the OClO abundance depends on the state of stratospheric chlorine activation but also whether the polar vortex is located above the measurement site.</p><p>The aim of this study is to give an overview of the measured stratospheric OClO abundance for 19 years, and to investigate the dominant parameters affecting ozone and OClO during periods of stratospheric chlorine activation. One particular focus is on the parameters which trigger the activation and de-activation at the beginning and the end of the polar winter.</p><p>To do so, we compare the general dependencies of OClO on other trace gases and meteorological conditions.</p>

Revisiting the factors that drive interannual variability in stratospheric entry water vapour

<p>Understanding the sinks, sources and transport processes of stratospheric trace gases can improve our prediction of mid to long term climate change. In this study we consider the processes that lead to variability in stratospheric water vapor. We perform a Multiple Linear Regression(MLR) on the SWOOSH combined anomaly filled water vapor product with ENSO, QBO, BDC, mid-tropospheric temperature, and CH4 as predictors, in an attempt to find the factors that most succinctly explain observed water vapor variability. We also consider the fraction of entry water vapor variability that can be accounted for by variations of the cold point temperature as an upper bound on how much water vapor variability is predictable from large scale processes. Several periods in which the MLR fails to account for interannual variability are treated as case studies in order to better understand variability in entry water not governed by these large scale processes.</p>

Ground-Based DOAS Measurements of Stratospheric Trace Gases at Two Antarctic Stations during the 2002 Ozone Hole Period

Compared to recent years, the development of the Antarctic ozone hole in 2002 showed very unusual dynamical features. The midwinter polar vortex was one of the smallest observed during the past decade. Driven by planetary waves, the vortex showed a strong asymmetry in early spring. A large air mass separated in late September, leaving what was previously a small vortex even smaller. Furthermore, stratospheric temperatures exceeded the polar stratospheric cloud (PSC) threshold earlier than in previous years, leading to a decrease in halogen activation by heterogeneous surface reactions. Ground-based observation of stratospheric trace gases in austral spring of 2001 and 2002 using passive Differential Optical Absorption Spectroscopy (DOAS) observations of zenith-scattered sunlight in the UV and visible wavelength region (320–650 nm) are presented. Using DOAS measurements of ozone, NO2, BrO, and OClO at two different Antarctic sites, Neumayer Station (70°S, 8°W) and Arrival Heights (78°S, 167°E), the chemical composition of the stratosphere is investigated under the unusual conditions of the 2002 ozone hole period and compared to the more typical observations of the previous year (2001).