ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-12-6863-2012 Meteorological conditions in the central Arctic summer during the Arctic Summer Cloud Ocean Study (ASCOS) Tjernström M. 1 2 Birch C. E. 3 Brooks I. M. 3 Shupe M. D. 4 5 Persson P. O. G. 4 5 Sedlar J. 6 Mauritsen T. 7 Leck C. 1 2 Paatero J. 8 Szczodrak M. 9 Wheeler C. R. 4 Department of Meteorology, Stockholm University, Stockholm, Sweden Bert Bolin Center for Climate Research, Stockholm University, Sweden Institute for Climate & Atmospheric Science, School of Earth and Environment, University of Leeds, Leeds, UK Cooperative Institute for Research in the Environmental Sciences (CIRES), University of Colorado, Boulder, CO, USA National Atmospheric and Oceanic Administration, Physical Sciences Division, Boulder, Colorado, USA Swedish Meteorological and Hydrological Institute, Norrköping, Sweden Max Planck Institute for Meteorology, Hamburg, Germany Finnish Meteorological Institute, Helsinki, Finland Rosensthiel School of Marine and Atmospheric Sciences, University of Miami, Miami, USA 01 08 2012 12 15 6863 6889 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/12/6863/2012/acp-12-6863-2012.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/12/6863/2012/acp-12-6863-2012.pdf

Understanding the rapidly changing climate in the Arctic is limited by a lack of understanding of underlying strong feedback mechanisms that are specific to the Arctic. Progress in this field can only be obtained by process-level observations; this is the motivation for intensive ice-breaker-based campaigns such as the Arctic Summer Cloud-Ocean Study (ASCOS), described here. However, detailed field observations also have to be put in the context of the larger-scale meteorology, and short field campaigns have to be analysed within the context of the underlying climate state and temporal anomalies from this. <br><br> To aid in the analysis of other parameters or processes observed during this campaign, this paper provides an overview of the synoptic-scale meteorology and its climatic anomaly during the ASCOS field deployment. It also provides a statistical analysis of key features during the campaign, such as key meteorological variables, the vertical structure of the lower troposphere and clouds, and energy fluxes at the surface. In order to assess the representativity of the ASCOS results, we also compare these features to similar observations obtained during three earlier summer experiments in the Arctic Ocean: the AOE-96, SHEBA and AOE-2001 expeditions. <br><br> We find that these expeditions share many key features of the summertime lower troposphere. Taking ASCOS and the previous expeditions together, a common picture emerges with a large amount of low-level cloud in a well-mixed shallow boundary layer, capped by a weak to moderately strong inversion where moisture, and sometimes also cloud top, penetrate into the lower parts of the inversion. Much of the boundary-layer mixing is due to cloud-top cooling and subsequent buoyant overturning of the cloud. The cloud layer may, or may not, be connected with surface processes depending on the depths of the cloud and surface-based boundary layers and on the relative strengths of surface-shear and cloud-generated turbulence. The latter also implies a connection between the cloud layer and the free troposphere through entrainment at cloud top.

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