Articles | Volume 12, issue 15
Atmos. Chem. Phys., 12, 6863–6889, 2012

Special issue: Arctic Summer Cloud Ocean Study (ASCOS) (ACP/AMT/OS inter-journal...

Atmos. Chem. Phys., 12, 6863–6889, 2012

Research article 01 Aug 2012

Research article | 01 Aug 2012

Meteorological conditions in the central Arctic summer during the Arctic Summer Cloud Ocean Study (ASCOS)

M. Tjernström1,2, C. E. Birch3, I. M. Brooks3, M. D. Shupe4,5, P. O. G. Persson4,5, J. Sedlar6, T. Mauritsen7, C. Leck1,2, J. Paatero8, M. Szczodrak9, and C. R. Wheeler4 M. Tjernström et al.
  • 1Department of Meteorology, Stockholm University, Stockholm, Sweden
  • 2Bert Bolin Center for Climate Research, Stockholm University, Sweden
  • 3Institute for Climate & Atmospheric Science, School of Earth and Environment, University of Leeds, Leeds, UK
  • 4Cooperative Institute for Research in the Environmental Sciences (CIRES), University of Colorado, Boulder, CO, USA
  • 5National Atmospheric and Oceanic Administration, Physical Sciences Division, Boulder, Colorado, USA
  • 6Swedish Meteorological and Hydrological Institute, Norrköping, Sweden
  • 7Max Planck Institute for Meteorology, Hamburg, Germany
  • 8Finnish Meteorological Institute, Helsinki, Finland
  • 9Rosensthiel School of Marine and Atmospheric Sciences, University of Miami, Miami, USA

Abstract. 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.

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.

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.

Final-revised paper