Preprints
https://doi.org/10.5194/acp-2017-230
https://doi.org/10.5194/acp-2017-230
23 May 2017
 | 23 May 2017
Status: this preprint was under review for the journal ACP but the revision was not accepted.

Statistics of vertical velocities in supercooled cloud layers over Leipzig and Praia measured with Doppler lidar

Johannes Bühl, Patric Seifert, Ronny Engelmann, Julia Fruntke, and Albert Ansmann

Abstract. This study presents statistics of vertical air velocity at the bases of supercooled shallow cloud layers separately for mixed-phase and liquid-only clouds. For the first time, this statistics is compared for clouds observed over a sub-tropical site at Cape Verde (14.9° N, 26° W) and a mid-latitudinal site at Leipzig, Germany (51.3° N, 12.4° E). Phase properties and spatio-temporal extent of the cloud layers were obtained from combined observations with Doppler lidar, Raman polarization lidar, and cloud radar. The statistical properties of the vertical-velocity distributions in both mixed-phase and pure-liquid cloud layers are found to be similar at both measurement sites. Standard deviation of the vertical velocities at both sites was found to be 0.4 m s−1 and was also the same in pure-liquid and mixed-phase layers. Skewness groups around −0.4 for both sites, pointing to radiative cooling as the driver for the cloud turbulence. Occasionally, positive skewness in some cloud layers indicated external drivers, e.g., gravity waves, for the turbulence. From the observed similarity in the vertical-velocity statistics derived at the base of supercooled liquid cloud layers at Praia and Leipzig it can be concluded that other factors besides cloud dynamics are responsible for the differences in ice formation efficiency reported previously for both sites.

Johannes Bühl, Patric Seifert, Ronny Engelmann, Julia Fruntke, and Albert Ansmann
 
Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version Supplement - Supplement
Johannes Bühl, Patric Seifert, Ronny Engelmann, Julia Fruntke, and Albert Ansmann
Johannes Bühl, Patric Seifert, Ronny Engelmann, Julia Fruntke, and Albert Ansmann

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Short summary
Vertical air motion is a key driver of physical processes in clouds. The stability of clouds and the process of ice formation have been shown to depend critically on vertical air motions. However, observations of vertical air motions and ice formation in clouds are rare. This motivated us in the Up- and downdraft in Drop and Ice Nucleation Experiment (UDINE) to deliver a comprehensive statistics, connecting remote-sensing observations of vertical motions and ice formation.
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