04 Mar 2021

04 Mar 2021

Review status: this preprint is currently under review for the journal WCD.

Relative importance of tropopause structure and diabatic heating for baroclinic instability

Kristine Flacké Haualand and Thomas Spengler Kristine Flacké Haualand and Thomas Spengler
  • Geophysical Institute, University of Bergen, and Bjerknes Centre for Climate Research, Bergen, Norway

Abstract. Misrepresentations of wind shear and stratification around the tropopause in numerical weather prediction models can lead to errors in potential vorticity gradients with repercussions for Rossby wave propagation and baroclinic instability. Using a diabatic extension of the linear quasi-geostrophic Eady model featuring a tropopause, we investigate the influence of such discrepancies on baroclinic instability by varying tropopause sharpness and altitude as well as wind shear and stratification in the lower stratosphere, which can be associated with model or data assimilation errors or a downward extension of a weakened polar vortex. We find that baroclinic development is less sensitive to tropopause sharpness than to modifications in wind shear and stratification in the lower stratosphere, where the latter are associated with a net change in the vertical integral of the horizontal potential vorticity gradient across the tropopause. To further quantify the relevance of these sensitivities, we compare these findings to the impact of including mid-tropospheric latent heating. For representative modifications of wind shear, stratification, and latent heating intensity, the sensitivity of baroclinic instability to tropopause structure is significantly less than that to latent heating of different intensities. These findings indicate that tropopause sharpness is less important for baroclinic development than previously anticipated and that latent heating and the structure in the lower stratosphere play a more crucial role, with latent heating being the dominant factor.

Kristine Flacké Haualand and Thomas Spengler

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on wcd-2021-13', Anonymous Referee #1, 30 Mar 2021
    • AC1: 'Reply on RC1', Kristine Flacké Haualand, 01 Apr 2021
  • RC2: 'Comment on wcd-2021-13', Anonymous Referee #2, 17 Apr 2021

Kristine Flacké Haualand and Thomas Spengler

Model code and software

2D QG numerical model Kristine Flacké Haualand

Kristine Flacké Haualand and Thomas Spengler


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Short summary
Given the recent focus on the influence of upper tropospheric structure in wind and temperature on midlatitude weather, we use an idealised model to investigate how structural modifications impact cyclone development. We find that cyclone intensification is less sensitive to these modifications than to changes in the amount of cloud condensation, suggesting that an accurate representation of the upper-level troposphere is less important for midlatitude weather than previously anticipated.