11 Mar 2020

11 Mar 2020

Review status: this preprint is currently under review for the journal HESS.

Changes in the simulation of instability indices over the Iberian Peninsula due to the use of 3DVAR data assimilation

Santos J. González-Rojí1,2, Sheila Carreno-Madinabeitia3,4, Jon Sáenz4,5, and Gabriel Ibarra-Berastegi6,5 Santos J. González-Rojí et al.
  • 1Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland
  • 2Climate and Environmental Physics, University of Bern, Bern, Switzerland
  • 3TECNALIA, Basque Research and Technology Alliance (BRTA), Parque Tecnológico de Álava, Vitoria-Gasteiz, Spain
  • 4Department of Applied Physics II, University of the Basque Country (UPV/EHU), Leioa, Spain
  • 5Plentzia Itsas Estazioa, PIE, University of the Basque Country (UPV/EHU), Plentzia, Spain
  • 6Department of NE and Fluid Mechanics, University of the Basque Country (UPV/EHU), Bilbao Engineering School, Bilbao, Spain

Abstract. The ability of two downscaling experiments to correctly simulate the instability conditions that can trigger thunderstorms over the Iberian Peninsula is compared in this paper. To do so, three instability indices are evaluated: TT index, CAPE and CIN. The WRF model is used for the simulations. The N experiment is driven by ERA-Interim’s initial and boundary conditions; The D experiment has the same configuration as N, but the 3DVAR data assimilation step is additionally run at 00, 06, 12 and 18 UTC. Eight radiosondes are available over the IP, and the values for these indices calculated from the University of Wyoming were chosen as reference in the validation of both simulations. Additionally, measured variables at different pressure levels from the radiosondes provided byWyoming were used to calculate the three instability indices by our own methodology using the R package aiRthermo. According to the validation, the correlation, SD and RMSE obtained by the experiment D for all the indices in most of the stations are better than those for N. The different methodologies produce small discrepancies between the values for TT, but these are larger for CAPE and CIN due to the dependency of these indices on the initial conditions assumed for the calculation of an air parcel’s vertical evolution. Similar results arise from the seasonal analysis concerning both WRF experiments: N tends to overestimate or underestimate (depending on the index) the variability of the reference values, but D is able to capture it in most of the seasons. The heterogeneity of the indices is highlighted in the mean maps over the Iberian Peninsula. According to those from D, the ingredients for the development of convective precipitation during winter are found along the entire Atlantic coast, but in summer they are located particularly in the Mediterranean coast. The chances of developing thunderstorms in those areas at 12 UTC is much higher than at 00 UTC; The convective inhibition is more extended towards inland at 00 UTC in those areas, which prevents storms from developing. However, high values are observed near Murcia also at 12 UTC.

Santos J. González-Rojí et al.

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Santos J. González-Rojí et al.

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Santos J. González-Rojí et al.


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Short summary
The simulation of precipitation extreme events is a well-known problem in modeling. That is why the atmospheric conditions favorable for its development as simulated by two WRF experiments are evaluated in this paper. The experiment including 3DVAR data assimilation outperforms the one without at simulating CAPE, CIN and TT indices over the Iberian Peninsula. The ingredients for convective precipitation in winter are found in the Atlantic coast, but in summer they are in the Mediterranean coast.