Structure of a shear-line polar low

Research output: Contribution to journalArticle

Open Access permissions





Organisational units


During March 2013 a series of polar lows originated in a high-vorticity (>10−3 s−1) shear zone that was associated with a prolonged marine cold-air outbreak over the Norwegian Sea. A detailed analysis of one shear-line polar low at the leading edge of the outbreak is presented using comprehensive observations from a well-instrumented aircraft, dropsondes, scatterometer and CloudSat data; and numerical modelling output from a convection-resolving configuration of the Met Office Unified Model. The maximum low-level wind gradient across the shear line was 25 m s−1 over 50 km. High windsto the north and west were within the cold-air mass and were associated with large surface turbulent heat fluxes and convective clouds. Low wind speed to the south and east of the shear line were associated with low heat fluxes and a clear ‘eye’ in the polarlow. Shear-line meso-γ-scale instabilities merging into the polar low appeared important to its structure and development. The model captured the shear line and the polar low structure very well — in particular the strength of the horizontal shear and the mesoscale thermodynamic fields.The spatialstructure of convective cloud bands around the polar low wassimulated reasonably well, but the modelsignificantly underestimated the liquid water content and height of the cloud layers compared to the observations. Shear-line polar lows are relatively common, however this case is arguably the first to be examined with a wide range of in-situ and remote observations allied with numerical model output.


Original languageEnglish
Pages (from-to)12–26
JournalQuarterly Journal of the Royal Meteorological Society
Issue number702
Early online date28 Aug 2016
Publication statusPublished - Jan 2017


    Research areas

  • polar low, shear line, Norwegian Sea, aircraft observations, CloudSat, Met Office Unified Model

Bibliographic note

© 2016 The Authors. Quarterly Journal of the Royal Meteorological Society published by John Wiley & Sons Ltd on behalf of the Royal Meteorological Society. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

View graph of relations

ID: 90761311

Related by author
  1. The Iceland Greenland Seas Project

    Research output: Contribution to journalArticle

  2. Atmospheric sensitivity to marginal-ice-zone drag: local and global responses

    Research output: Contribution to journalArticle

  3. Modification of Polar Low Development by Orography and Sea Ice

    Research output: Contribution to journalArticle