The ozone controlled by stratosphere–troposphere exchange in the upper troposphere and lower stratosphere plays an important role in the radiation balance and global climate change. Cut-off lows, which occurs frequently in summer over Northeast China, are an important phenomenon that could induce stratosphere–troposphere exchange and affect the vertical structure of ozone. 

The Key Laboratory of Middle Atmosphere and Global Environment Observation, Institute of Atmospheric Physics, Chinese Academy of Sciences, conducted a field campaign in which data on the vertical distribution of ozone over Changchun (43.53°N, 125.13°E), China, were gathered in the summers of 2010–13, using ozonesondes developed at the institute (Fig. 1). The measurements lasted about one month, around June, in each year. Several cut-off lows were detected during the observation period. Based on the dataset, the effects of cut-off-lows on the ozone concentration could be investigated statistically. 

Fig. 1. A balloon equipped with an ozonesonde and radiosonde was launched in Changchun at around 1400 LST every day in the summers of 2010–13. (Photo credit: Zhixuan Bai) 

During the cut-off low events, an increase in the ozone concentration and a lower height of the tropopause were observed (Fig. 2). Statistical analysis showed that the ozone concentrations of the in-cut-off-low profiles were significantly higher than those of other profiles in the upper troposphere–lower stratosphere region. The cut-off lows induced an increase in the upper troposphere–lower stratosphere column ozone by 32% on average. Meanwhile, they depressed the lapse-rate tropopause/dynamical tropopause height by 1.4/1.7 km. Furthermore, a positive correlation between cut-off low strength and lower stratosphere column ozone was found. 

Fig. 2. Time–height cross sections of ozone at Changchun in (a) 2010, (b) 2011 and (c) 2012. 

This research was pre-published in Advances in Atmospheric Sciences.

References 

Song, Y., D. Lü, Q. Li, J. Bian, X. Wu, and D. Li, 2016: The impact of cut-off lows on ozone in the upper troposphere and lower stratosphere over Changchun from ozonesonde observations. Adv. Atmos. Sci., In Press.