Variations in the vertical profile of ozone at four high-latitude Arctic sites from 2005 to 2017 Atmospheric Chemistry and Physics

Understanding variations in atmospheric ozone in the Arctic is difficult because there are only a few long-term records of vertical ozone profiles in this region. We present 12 years of ozone profiles from February 2005 to February 2017 at four sites: Summit Station, Greenland; Ny-Ålesund, Svalbard, Norway; and Alert and Eureka, Nunavut, Canada. These profiles are created by combining ozonesonde measurements with ozone profile retrievals using data from the Microwave Limb Sounder (MLS). This combination creates a high-quality dataset with low uncertainty values by relying on in situ measurements of the maximum altitude of the ozonesondes (∼30 km) and satellite retrievals in the upper atmosphere (up to 60 km). For each station, the total column ozone (TCO) and the partial column ozone (PCO) in four atmospheric layers (troposphere to upper stratosphere) are analyzed. Overall, the seasonal cycles are similar at these sites. However, the TCO over Ny-Ålesund starts to decline 2 months later than at the other sites. In summer, the PCO in the upper stratosphere over Summit Station is slightly higher than at the other sites and exhibits a higher standard deviation. The decrease in PCO in the middle and upper stratosphere during fall is also lower over Summit Station. The maximum value of the lower- and middle-stratospheric PCO is reached earlier in the year over Eureka. Trend analysis over the 12-year period shows significant trends in most of the layers over Summit and Ny-Ålesund during summer and fall. To understand deseasonalized ozone variations, we identify the most important dynamical drivers of Arctic ozone at each level. These drivers are chosen based on mutual selected proxies at the four sites using stepwise multiple regression (SMR) analysis of various dynamical parameters with deseasonalized data. The final regression model is able to explain more than 80 % of the TCO and more than 70 % of the PCO in almost all of the layers. The regression model provides the greatest explanatory value in the middle stratosphere. The important proxies of the deseasonalized ozone time series at the four sites are tropopause pressure (TP) and equivalent latitude (EQL) at 370 K in the troposphere, the quasi-biennial oscillation (QBO) in the troposphere and lower stratosphere, the equivalent latitude at 550 K in the middle and upper stratosphere, and the eddy heat flux (EHF) and volume of polar stratospheric clouds throughout the stratosphere.

理解北极大气臭氧的变化颇具挑战，因为该区域现存的垂直臭氧廓线长期观测记录寥寥无几。本研究公开了2005年2月至2017年2月期间，4个观测站点的12年臭氧廓线数据，分别为格陵兰岛的萨米特站（Summit Station）、挪威斯瓦尔巴群岛的新奥尔松（Ny-Ålesund），以及加拿大努纳武特地区的奥尔德站（Alert）与尤里卡站（Eureka）。这些臭氧廓线由臭氧探空仪（ozonesonde）观测数据与基于微波临边探测仪（Microwave Limb Sounder, MLS）数据反演的臭氧廓线结合生成。该融合方案依托臭氧探空仪约30公里最大探测高度的原位观测数据，以及高层大气（最高可达60公里）的卫星反演数据，构建出低不确定性的高质量数据集。本研究针对每个站点，分析了对流层至平流层上层共四层大气中的总柱臭氧（total column ozone, TCO）与部分柱臭氧（partial column ozone, PCO）。整体而言，各站点的臭氧季节循环特征较为相似，但新奥尔松站的总柱臭氧浓度下降时间较其余站点晚2个月。夏季期间，萨米特站平流层上层的部分柱臭氧浓度略高于其余站点，且标准差更高。秋季时段，萨米特站平流层中上层的部分柱臭氧浓度降幅也相对更小。尤里卡站的平流层下层与中层部分柱臭氧浓度年最大值出现时间早于其他站点。对12年观测序列的趋势分析显示，夏季与秋季时段，萨米特站与新奥尔松站多数大气层的臭氧均存在显著变化趋势。为解析去季节化后的臭氧变化特征，本研究识别了各高度层北极臭氧的关键动力驱动因子。研究基于对去季节化数据开展的各类动力参数逐步多元回归（stepwise multiple regression, SMR）分析，在四个站点中筛选出共通的关键代理变量，进而确定上述驱动因子。最终构建的回归模型可解释几乎所有大气层中80%以上的总柱臭氧变化，以及70%以上的部分柱臭氧变化。该回归模型在平流层中层的解释能力最强。四个站点的去季节化臭氧时间序列的关键代理变量包括：对流层内370K等熵面的对流层顶气压（tropopause pressure, TP）与等效纬度（equivalent latitude, EQL）；对流层与平流层下层的准两年振荡（quasi-biennial oscillation, QBO）；平流层中上层550K等熵面的等效纬度；以及整个平流层内的涡动热通量（eddy heat flux, EHF）与极地平流层云体积。