Abstract
Over complex terrain, convection and thermally-driven circulations simultaneously occur under fair weather conditions during the day. To investigate these processes on the basis of observations, simultaneous measurements on different scales are necessary. Comprehensive measurements with the mobile observation platform KITcube were performed on the mountainous island of Corsica during the HYdrological cycle in Mediterranean EXperiment (HyMeX) field campaign in late summer and autumn 2012. Using a case study, the benefit of integrated measurement systems and coordinated scan strategies was demonstrated, and experimental evidence of, and new insights into, convective and advective transport processes in a valley were obtained. Convection, thermally-driven circulations and topographic and advective venting led to the diurnal cycle of temperature, humidity and wind over complex terrain in the mountain atmospheric boundary layer (mountain ABL), which was deeper than an ABL over homogeneous terrain under equal surface forcing. Due to the combined transport processes on different scales, the mountain ABL in a valley also extended beyond the convection layer, which was characterized by surface-based, buoyancy-driven turbulent mixing. Strong subsidence, with a vertical velocity of about 1 m s\(^{-1}\), was present within the mountain ABL for several hours around noon and suppressed the convection-layer growth. Above the layer with subsidence, elevated vertical motions, consisting of alternating updrafts and downdrafts, occurred. Once the convection layer grew to the bottom of the layer with elevated vertical motions, surface-based convective cells occasionally coupled to the elevated updrafts, as a result of which the convection layer rapidly deepened.
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Acknowledgments
This work is a contribution to the HyMeX programme. We would like to thank Veronique Ducrocq from METEO-FRANCE and Evelyne Richard and Dominique Lambert from the University of Toulouse/CNRS for their support in performing the measurements of KITcube on the island of Corsica during HyMeX. We also acknowledge the help of Antoine Pieri from the fire brigade at Corte/University of Corsica and Olivier Pailly from INRA in San Giuliano and thank them for hosting us during the nearly 3-month campaign. We are also grateful to Jan Handwerker, Martin Kohler and Andreas Wieser and the whole IMK team for their efforts in deploying KITcube. We would also like to thank Markus Ramatschi from GFZ Potsdam for installing the GPS stations. We further thank Rolf Hankers and the aircraft team from the University of Braunschweig for performing the aircraft measurements. The authors acknowledge METEO-FRANCE for supplying the data and the HyMeX database teams (ESPRI/IPSL and SEDOO/Observatoire Midi–Pyrénées) for their help in accessing the data.
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Adler, B., Kalthoff, N. Multi-scale Transport Processes Observed in the Boundary Layer over a Mountainous Island. Boundary-Layer Meteorol 153, 515–537 (2014). https://doi.org/10.1007/s10546-014-9957-8
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DOI: https://doi.org/10.1007/s10546-014-9957-8