Fig. 2
![Fig. 2](http://media.springernature.com/full/springer-static/image/art%3A10.1186%2Fs40645-021-00424-9/MediaObjects/40645_2021_424_Fig2_HTML.png)
Time series of O3 concentrations for the 0–1 km layer measured by ozonesondes launched at Tsukuba (Tateno), Japan (blue). The ozonesonde was launched around 14:30 LT once per week. The linear trend is shown by the blue line. Mean O3 concentrations for 13:00–15:00 LT retrieved from MAX-DOAS observations at Chiba and Tsukuba are shown daily in red and black, respectively. For clarity, MAX-DOAS data are shown only for the days when ozonesonde data were available. Error bars represent standard deviations within 13:00–15:00 LT (plus spatial variabilities in four different azimuth directions for Chiba)