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© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 10 Jul 2018

Research article | 10 Jul 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Impact of humidity biases on light precipitation occurrence: observations versus simulations

Sophie Bastin1, Philippe Drobinski2, Marjolaine Chiriaco1, Olivier Bock3, Romain Roehrig4, Clemente Gallardo5, Dario Conte6, Marta Dominguez-Alonso5, Laurent Li2, Piero Lionello6,7, and Ana C. Parracho1,3 Sophie Bastin et al.
  • 1LATMOS/IPSL, UVSQ Université Paris-Saclay, UPMC Univ. Paris 06, CNRS, Guyancourt, France
  • 2LMD/IPSL, UPMC Univ. Paris 06, Ecole Polytechnique, ENS, CNRS, Palaiseau, France
  • 3IGN LAREG, Université Paris Diderot, Sorbonne Paris Cité, Paris, 75013, France
  • 4CNRM/Meteo-France, Toulouse, France
  • 5UCLM, Instituto de Ciencias Ambiantales, Toledo, Spain
  • 6CMCC, Euro Mediterranean Center on Climage Change, 73100 Lecce, Italy
  • 7DiSTeBA, University of Salento, 73100 Lecce, Italy

Abstract. This work uses a network of GPS stations over Europe from which a homogenised integrated water vapor (IWV) dataset has been retrieved, completed with colocated temperature and precipitation measurements over specific stations to i) estimate the biases of six regional climate models over Europe in terms of humidity; ii) understand their origins; iii) and finally assess the impact of these biases on the frequency of occurrence of precipitation. The evaluated simulations have been performed in the framework of HYMEX/Med-CORDEX programs and cover the Mediterranean area and part of Europe at horizontal resolutions of 50 to 12km.

The analysis shows that models tend to overestimate the low values of IWV and the use of the nudging technique reduces the differences between GPS and simulated IWV. Results suggest that physics of models mostly explain the mean biases, while dynamics affects the variability. The land surface/atmosphere exchanges affect the estimation of IWV over most part of Europe, especially in summer. The limitations of the models to represent these processes explain part of their baises in IWV. However, models correctly simulate the dependance between IWV and temperature, and specifically the deviation that this relationship experiences regarding the Clausius-Clapeyron law after a critical value of temperature (Tbreak). The high spatial variability of Tbreak indicates that it has a strong dependence on local processes which drive the local humidity sources. This explains why the maximum values of IWV are not necessarely observed over warmer area, that are often dry area.

Finally, it is shown over SIRTA observatory (near Paris) that the frequency of occurrence of light precipitation is strongly conditioned by the biases in IWV and by the precision of the models to reproduce the distribution of IWV as a function of the temperature. The results of the models indicate that a similar dependence occurs in other areas of Europe, especially where precipitation has a predominantly convective character. According to the observations, for each range of temperature, there is a critical value of IWV from which precipitation picks up. The critical values and the probability to exceed them are simulated with a bias that depends on the model. Those models which present too often light precipitation generally show lower critical values and higher probability to exceed them.

Sophie Bastin et al.
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Status: final response (author comments only)
Status: final response (author comments only)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Sophie Bastin et al.
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