Abstract. Chlorine dioxide (OClO) is a by-product of the ozone depleting halogen chemistry in the stratosphere. Although being rapidly photolysed at low solar zenith angles (SZAs) it plays an important role as an indicator of the chlorine activation in polar regions during polar winter and spring at twilight conditions because of the nearly linear dependence of its formation to chlorine oxide (ClO). Here we compare slant column densities (SCDs) of chlorine dioxide (OClO) retrieved by means of differential optical absorption spectroscopy (DOAS) from spectra measured by the TROPOspheric Monitoring Instrument (TROPOMI) with meteorological data for both Antarctic and Arctic regions for the first three winters in each of the hemispheres (November 2017–October 2020). TROPOMI, a UV-VIS-NIR-SWIR instrument on board of the Sentinel-5P satellite monitors the Earth’s atmosphere in a near polar orbit at an unprecedented spatial resolution and signal to noise ratio and provides daily global coverage at the equator and thus even more frequent observations at polar regions. The observed OClO SCDs are generally well correlated with the meteorological conditions in the polar winter stratosphere: e.g. the chlorine activation signal appears as a sharp gradient in the time series of the OClO SCDs once the temperature drops to values well below the Nitric Acid Trihydrate (NAT) existence temperature T_NAT. Also a relation of enhanced OClO values at lee sides of mountains can be observed at the beginning of the winters indicating a possible effect of occurring lee waves on chlorine activation. The dataset is also compared with CALIPSO Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) polar stratospheric cloud (PSC) observations. In general, OClO SCDs coincide well with CALIOP measurements for which PSCs are detected. Very high OClO levels are observed for the northern hemispheric winter 2019/2020 with an extraordinarly long period with a stable polar vortex being even close to the values found for Southern Hemispheric winters. Also the extraordinary winter in 2019 in the Southern Hemisphere with a minor sudden stratospheric warming at the beginning of September was observed. In this winter similar OClO values were measured in comparison to the previous (usual) winter till that event but with a 1–2 week earlier OClO deactivation.

中文翻译：

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TROPOMI 观测到的 OClO：与气象参数和 PSC 观测的比较

摘要。二氧化氯 (OClO) 是平流层中消耗臭氧层的卤素化学反应的副产品。尽管在低太阳天顶角 (SZAs) 下快速​​光解，但由于其形成与氧化氯 (ClO) 几乎线性相关，因此在极地冬季和春季在黄昏条件下作为极地地区氯活化的指标起着重要作用. 在这里，我们将通过差分光学吸收光谱 (DOAS) 从对流层监测仪器 (TROPOMI) 测量的光谱中获取的二氧化氯 (OClO) 的斜柱密度 (SCD) 与前三个南极和北极地区的气象数据进行比较每个半球的冬天（2017 年 11 月至 2020 年 10 月）。特罗波米，Sentinel-5P 卫星上的 UV-VIS-NIR-SWIR 仪器以前所未有的空间分辨率和信噪比监测近极轨道上的地球大气，并提供赤道的每日全球覆盖范围，从而提供更频繁的观测在极地地区。观察到的 OClO SCD 通常与极地冬季平流层的气象条件密切相关：例如，一旦温度下降到远低于三水合硝酸 (NAT )存在温度T_{网络地址转换}. 在冬季开始时还可以观察到山背风侧 OClO 值增强的关系，这表明发生的背风波可能对氯活化产生影响。该数据集还与具有正交极化 (CALIOP) 极地平流层云 (PSC) 观测的 CALIPSO 云-气溶胶激光雷达进行了比较。通常，OClO SCD 与检测到 PSC 的 CALIOP 测量值吻合。在 2019/2020 年北半球冬季观察到非常高的 OClO 水平，其周期非常长，稳定的极地涡旋甚至接近南半球冬季的值。还观察到南半球 2019 年非同寻常的冬季，9 月初平流层出现轻微突然变暖。