Observation of low-level wind reversals in the Gulf of Lion area and their impact on the water vapour variability

Abstract : Water vapour measurements from a ground-based Raman lidar and an airborne differential absorption lidar, complemented by high resolution numerical simulations from two mesoscale models (AROME-WMED and Meso-NH), are considered to investigate three transition events from Mistral/Tramontane to southerly marine flow taking place in the Montpellier region (Southern France) in the time frame September-October 2012, during the Hydrological Cycle in the Mediterranean Experiment Special Observation Period 1. Low-level wind reversals associated with these transitions are found to have a strong impact on water vapour transport, leading to a large variability of the water vapour vertical and horizontal distributions. Water vapour mixing ratio within the boundary layer is found to vary from typical values in the range 4–8 g kg−1 during the northerly Mistral/Tramontane flows to values in the range 8–15 g kg−1 during the southerly marine flows. The increase/decrease in water vapour mixing ratio within the boundary layer may be abrupt and marked during these transition periods, with values increasing-decreasing by a factor of 2 to 4 within 1 hour. The high spatial and temporal resolutions of the lidar data allow monitoring the time evolution of the water vapour field during these transitions from predominantly northerly Mistral/Tramontane flow to a predominantly southerly flow, permitting to identify the quite sharp separation between these flows, which is also satisfactorily well captured by the mesoscale models. Water vapour measurements from the ground-based lidar are complemented by particle backscatter measurements from the same system, which allow also revealing the significant variability in the aerosol and cloud fields associated with these transition events.
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Submitted on : Wednesday, February 17, 2016 - 4:28:15 PM
Last modification on : Tuesday, August 6, 2019 - 3:26:01 PM

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Paolo Di Girolamo, Cyrille Flamant, Marco Cacciani, Evelyne Richard, Véronique Ducrocq, et al.. Observation of low-level wind reversals in the Gulf of Lion area and their impact on the water vapour variability. Quarterly Journal of the Royal Meteorological Society, Wiley, 2016, 142 (S1), pp.153-172. ⟨10.1002/qj.2767⟩. ⟨insu-01275554⟩

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