Preprints
https://doi.org/10.5194/acp-2020-1057
https://doi.org/10.5194/acp-2020-1057

  19 Oct 2020

19 Oct 2020

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

Lidar observations of Cirrus clouds at Palau island (7°33′ N, 134°48′ E)

Francesco Cairo1, Mauro De Muro1,a, Marcel Snels1, Luca Di Liberto1, Silvia Bucci2, Bernard Legras2, Ajil Kottayil3, Andrea Scoccione1,b, and Stefano Ghisu4 Francesco Cairo et al.
  • 1Institute of Atmospheric and Climate Sciences, National Research Council of Italy (CNR), I-00133, Roma, Italy
  • 2Laboratoire de Météorologie Dynamique (LMD), UMR CNRS 8539, CNRS, IPSL, ENS-PSL, École Polytechnique, Sorbonne Université, Paris, France
  • 3Advanced Centre for Atmospheric Radar Research, Cochin University of Science and Technology, Cochin, India
  • 4Università degli Studi di Roma "Tor Vergata", Dipartimento di Fisica, Roma, Italy
  • anow at: AIT Thales Alenia Space, Roma, Italy
  • bnow at: Centro Operativo per la Meteorologia, Aeronautica Militare, Pomezia, Italy

Abstract. A polarization diversity elastic backscatter lidar has been deployed in the equatorial island of Palau in February and March 2016, in the framework of the EU Stratoclim project. The system operated unattended in the Atmospheric Observatory of Palau Island from 15 February to 25 March 2016, during nighttime. Each lidar profile extends from the ground to 30 km height. Here the dataset is presented and discussed in terms of the temperature structure of the UTLS, obtained from co-located radiosondings. During the campaign, several high altitude clouds were observed, peaking approximately 3 km below the Cold Point Tropopause (CPT) located above 17 km. Their occurrence was associated with cold anomalies in the Upper Troposphere (UT). Conversely, when warm UT anomalies occurred, the presence of cirrus was restricted to a 5 km thick layer centered 5 km below the CPT. Thin and subvisible cirrus were frequently detected close to the CPT. The particle depolarization ratios of these cirrus was generally lower than the values detected in the UT clouds. CPT cirrus occurrence showed a correlation with cold anomalies likely triggered by stratospheric wave activity penetrating the UT. The back trajectories study revealed a thermal and convective history compatible with the convective outflow formation for most of the cirrus clouds, suggesting that the majority of air masses related to the clouds had encountered convection in the past and had reached the minimum temperature during its transport in less than 48 hours before the observation. A subset of SVC, with low depolarization and high lidar ratio and with no sign of significative recent uplifting, may be originated in situ.

Francesco Cairo et al.

 
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Francesco Cairo et al.

Francesco Cairo et al.

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Short summary
A lidar was in Palau Island in February–March 2016. Clouds were observed, peaking at 3 km below the high Cold Point Tropopause (CPT). Their occurrence was linked with cold anomalies, while in warm cases, cirrus were restricted to 5 km below the CPT. Thin subvisible cirrus near the CPT had distinctive characteristics. They were linked to wave induced cold anomalies. Back trajectories are mostly compatible with convective outflow, while some distinctive SVC may be originated in situ.
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