Characterisation and surface radiative impact of Arctic low clouds from the IAOOS field experiment

• Main Authors: J. Maillard, F. Ravetta, J.-C. Raut, V. Mariage, J. Pelon
• Format: Article
• Language: English
• Published: Copernicus Publications 2021-03-01
• Series: Atmospheric Chemistry and Physics
• Online Access: https://acp.copernicus.org/articles/21/4079/2021/acp-21-4079-2021.pdf
• ISSN: 1680-7316; 1680-7324

<p>The Ice, Atmosphere, Arctic Ocean Observing System (IAOOS) field experiment took place from 2014 to 2019. Over this period, more than <span class="inline-formula">20</span> instrumented buoys were deployed at the North Pole. Once locked into the ice, the buoys drifted for periods of a month to more than a year. Some of these buoys were equipped with <span class="inline-formula">808</span> nm wavelength lidars which acquired a total of <span class="inline-formula">1777</span> profiles over the course of the campaign. This IAOOS lidar dataset is exploited to establish a novel statistic of cloud cover and of the geometrical and optical characteristics of the lowest cloud layer. The average cloud frequency from April to December over the course of the campaign was <span class="inline-formula">75</span> %. Cloud occurrence frequencies were above <span class="inline-formula">85</span> % from May to October. Single layers are thickest in October/November and thinnest in the summer. Meanwhile, their optical depth is maximum in October. On the whole, the cloud base height is very low, with the great majority of first layer bases beneath <span class="inline-formula">120</span> m. In April and October, surface temperatures are markedly warmer when the IAOOS profile contains at least one low cloud than when it does not. This temperature difference is statistically insignificant in the summer months. Indeed, summer clouds have a shortwave cooling effect which can reach <span class="inline-formula">−60</span> <span class="inline-formula">W m⁻²</span> and balance out their longwave warming effect.</p>