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Advances in Science and Research The open-access proceedings of the European Meteorological Society (EMS)

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Adv. Sci. Res., 14, 157-162, 2017
https://doi.org/10.5194/asr-14-157-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
 
13 Jun 2017
GPS – Zenith Total Delay assimilation in different resolution simulations of a heavy precipitation event over southern France
Alberto Caldas-Álvarez1, Samiro Khodayar1, and Olivier Bock2 1Institute of Meteorology and Climate Research (IMK-TRO), Karlsruhe Institute of Technology (KIT), Karlsruhe, 76344, Germany
2IGN LAREG, Univ Paris Diderot, Sorbonne Paris Cité, 5 rue Thomas Mann, 75205 Paris CEDEX 13, France
Abstract. The aim of this study is to investigate the different pathways of the interaction between an improved atmospheric moisture distribution by Data Assimilation (DA) of Global Positioning System Zenith Total Delays (GPS-ZTD) on the simulation of a selected Heavy Precipitation Event (HPE) across different model horizontal resolutions (7 km, 2.8 km and 500 m). The initiation and evolution of deep moist convection and heavy precipitation taking place on the 24 September 2012, which had a dedicated Intensive Observation Period (IOP6) during the Hydrological cycle in the Mediterranean eXperiment (HyMeX) Special Observation period 1, are analysed. The results show an improvement in the representation of the Integrated Water Vapour (IWV) spatial distribution and temporal evolution when the data assimilation is applied as well as through the refinement of the model grids. However, important discrepancies between the simulated and the observed vertical profiles of humidity still remain after the DA, thus affecting the representation of convection and heavy precipitation. For the presented case study, the model simulations exhibited a wet bias. The assimilation entailed a drying of the low to middle troposphere over the study region during the 6 h prior to the storm initiation for every horizontal resolution. This reduced the instability present at the moment of storm initiation, weakening in return the intensity of convection and the number of cells triggered. The improvement observed in the atmospheric moisture content and distribution was not followed by an improved precipitation representation closer to observations. This highlights the relevance of correctly distributing the assimilated IWV in the vertical direction in the models.

Citation: Caldas-Álvarez, A., Khodayar, S., and Bock, O.: GPS – Zenith Total Delay assimilation in different resolution simulations of a heavy precipitation event over southern France, Adv. Sci. Res., 14, 157-162, https://doi.org/10.5194/asr-14-157-2017, 2017.
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The representation of the atmospheric moisture distribution in weather and climate prediction models has been identified as a source of error in the representation of heavy precipitation events. This research work shows the relevance of overcoming deficiencies in the representation of the moisture content in the vertical direction, even after assimilating humidity data for a case study characteristic of the western Mediterranean by early autumn.
The representation of the atmospheric moisture distribution in weather and climate prediction...
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