Preprints
https://doi.org/10.5194/gmd-2020-384
https://doi.org/10.5194/gmd-2020-384

Submitted as: development and technical paper 05 Jan 2021

Submitted as: development and technical paper | 05 Jan 2021

Review status: a revised version of this preprint is currently under review for the journal GMD.

Vertical grid refinement for stratocumulus clouds in the radiation scheme of a global climate model

Paolo Pelucchi1,a, David Neubauer1, and Ulrike Lohmann1 Paolo Pelucchi et al.
  • 1Institute of Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland
  • anow at: Universitat de València, Valencia, Spain

Abstract. In this study, we implement a vertical grid refinement scheme in the radiation routine of the global aerosol-climate model ECHAM-HAM, aiming to improve the representation of stratocumulus clouds and address the underestimation of their cloud cover. The scheme is based on a reconstruction of the temperature inversion as a physical constraint for the cloud top. On the refined grid, the boundary layer and the free troposphere are separated and the cloud's layer is made thinner. The cloud cover is re-calculated either by conserving the cloud volume (SC-VOLUME) or by using the Sundqvist cloud cover routine on the new grid representation (SC-SUND). In global climate simulations, we find that the SC-VOLUME approach is inadequate, as in most cases there is a mismatch between the layer of the inversion and of the stratocumulus cloud, which prevents its application and is itself likely caused by too-low vertical resolution. With the SC-SUND approach, the possibility for new clouds to be formed on the refined grid results in a large increase in mean total cloud cover in stratocumulus regions. In both cases, however, the changes exerted in the radiation routine are too weak to produce a significant improvement of the simulated stratocumulus cloud cover. The grid refinement scheme could be used more effectively for this purpose if implemented directly in the model's cloud microphysics and cloud cover routines.

Paolo Pelucchi et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on gmd-2020-384', Anonymous Referee #1, 24 Jan 2021
  • RC2: 'Comment on gmd-2020-384', Anonymous Referee #2, 12 Feb 2021
  • CEC3: 'Comment on gmd-2020-384', Astrid Kerkweg, 26 Feb 2021
  • AC1: 'Author response to all reviewer comments', Paolo Pelucchi, 10 Apr 2021

Paolo Pelucchi et al.

Data sets

Data for the publication "Vertical grid refinement for stratocumulus clouds in the radiation scheme of a global climate model" Paolo Pelucchi, David Neubauer, and Ulrike Lohmann https://doi.org/10.5281/zenodo.4268194

Model code and software

Scripts for the publication "Vertical grid refinement for stratocumulus clouds in the radiation scheme of a global climate model" Paolo Pelucchi, David Neubauer, and Ulrike Lohmann https://doi.org/10.5281/zenodo.4268168

Paolo Pelucchi et al.

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Short summary
Stratocumulus are thin clouds whose cloud cover is underestimated in climate models partly due to too-low vertical resolution. We develop a scheme that locally refines the vertical grid based on a physical constraint for the cloud top. Global simulations reveal that the scheme, implemented only in the radiation routine, can increase stratocumulus cloud cover. However, this effect is not propagated to the simulated cloud cover. The scheme could be more effective if implemented in other routines.