Assessing the Impact of Clouds on UV-visible Total Column Ozone Measurements in the High Arctic

• Main Authors: Zhao, Xiaoyi, Bognar, Kristof, Fioletov, Vitali, Pazmino, Andrea, Goutail, Florence, Millán, Luis, Manney, Gloria, Adams, Cristen, Strong, Kimberly
• Other Authors: Department of Physics Toronto, University of Toronto, Environment and Climate Change Canada, STRATO - LATMOS, Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS), Sorbonne Université (SU)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS), Jet Propulsion Laboratory (JPL), NASA-California Institute of Technology (CALTECH), NorthWest Research Associates (NWRA), Department of Physics Socorro, New Mexico Institute of Mining and Technology New Mexico Tech (NMT), Environmental Monitoring and Science Division of Alberta (EMSD), Alberta Government
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2018
• Subjects: [PHYS.PHYS.PHYS-AO-PH]Physics [physics]/Physics [physics]/Atmospheric and Oceanic Physics [physics.ao-ph]; Arctic; Canada; Eureka
• Online Access: https://hal-insu.archives-ouvertes.fr/insu-01877039; https://hal-insu.archives-ouvertes.fr/insu-01877039/document; https://hal-insu.archives-ouvertes.fr/insu-01877039/file/amt-2018-261.pdf; https://doi.org/10.5194/amt-2018-261

International audience Zenith-Sky scattered light Differential Optical Absorption Spectroscopy (ZS-DOAS) has been used widely to retrieve total column ozone (TCO). ZS-DOAS measurements have the advantage of being less sensitive to clouds than direct-sun measurements. However, the presence of clouds still affects the quality of ZS-DOAS TCO. Clouds are thought to be the largest contributor to random uncertainty in ZS-DOAS TCO, but their impact on data quality still needs to be quantified. This study has two goals: (1) to study whether clouds have a significant impact on ZS-DOAS TCO, and (2) to develop a cloud-screening algorithm to improve ZS-DOAS measurements in the Arctic under cloudy conditions. To quantify the impact of weather, eight years of measured and modelled TCO have been used, along with information about weather conditions at Eureka, Canada (80.05°N, 86.41°W). Relative to direct-sun TCO measurements by Brewer spectrophotometers and modelled TCO, a positive bias is found in ZS-DOAS TCO measured in cloudy weather, and a negative bias is found for clear conditions, with differences of up to 5% between clear and cloudy conditions. A cloud-screening algorithm is developed for high-latitudes using the colour index calculated from ZS-DOAS spectra. The quality of ZS-DOAS TCO datasets is assessed using a statistical uncertainty estimation model, which suggests a 3–4% random uncertainty. The new cloud-screening algorithm reduces the random uncertainty by 0.6%. If all measurements collected during cloudy conditions, as identified using the weather station observations, are removed, the random uncertainty is reduced by 1.3%. This work demonstrates that clouds are a significant contributor to uncertainty in ZS-DOAS TCO and proposes a method that can be used to screen clouds in high-latitude spectra.