SAFRAN (Système d’analyse fournissant des renseignements atmosphériques à la neige) is a mesoscale atmospheric analysis system for surface variables.It produces an analysis at the hourly time step using ground data observations. Originally intended for mountainous areas, it was later extended to cover France. The detailed description can be found in Durand et al. (1993, 2009).

SAFRAN uses an optimal interpolation method to analyze most of the parameters. One of the main features of SAFRAN is that the analyses are performed over climatically homogeneous zones, which are areas of irregular shape covering a surface usually smaller than 1000 km² and where the horizontal climatic gradients (especially for precipitation) are weak. SAFRAN estimates one value of each parameter for each zone at several altitude levels. Within the zone, analyzed parameters depend only on elevation and aspect. Zones are not isolated: observations from the neighbouring zones are used if necessary. In SAFRAN, both observations from meteorological stations and surface analyzes from numerical weather prediction systems are used. The observations are those collected by Météo-France (French national weather service, www.meteofrance.com). The analyzes are those from the ECMWF (www.ecmwf.int).

Data description

 Source :

• Météo-France : http://www.cnrm.meteo.fr/spip.php?article424 and https://donneespubliques.meteofrance.fr/?fond=produit&id_produit=122&id_rubrique=40

 Manipulation

• Optimal interpolation of observations from meteorological stations and numerical analyzes from numerical weather prediction systems.

Availability

• See conditions at https://donneespubliques.meteofrance.fr/?fond=produit&id_produit=122&id_rubrique=40

 Spatial and temporal coverage

• France metropolitan area ;
• Spatial resolution of 8 km ;
• From 1958 to present ;
• Hourly time step.

 Evaluation

Evaluation methodolology (reference, quantities that are compared)

• Comparison against independent observations from meteorological stations ;
• Comparison against other methods at a longer time step :
• For more details see : Quintana-Segui et al. (2008) and Vidal et al. (2010).

 Results of the evaluation

• Temperature and relative humidity were well reproduced, presenting no bias.
• Wind speed was also well reproduced; however, its bias was −0.3 m s^–1. The interpolation from the 6-h time step of the analysis to the 1-h time step was one of the sources of error.
• The precipitation analysis was robust and not biased; its root-mean-square error was 2.4 mm day⁻¹. This error was mainly due to the spatial heterogeneity of the precipitation within the geographical zones of analysis (1000 km²).
• The analysis of incoming solar radiation presented some biases, especially in coastal areas.

 Recommendation

 Strengths and weakness

• Strengths
  • Temporal coverage up to 1958 with constant method
  • Spatial coverage
  • Combine observations and numerical weather prediction systems
  • Takes into account orography
  • Run operationally every day
  • Quality of the temperature, moisture, wind and precipitation estimates at the daily time step
  • Weaknesses
    • Biases for solar radiation
    • Precipitation estimates at hourly time step

 Limit of validity

• Data are representative of areas of 8 km x 8 km and for that reason can present differences with local meteorological stations at a very specific location.

 References

Y. Durand, E. Brun, L. Mérindol, G. Guyomarc’h, B. Lesaffre, E. Martin, A meteorological estimation of relevant parameters for snow models, Ann. Glaciol. 18 (1993) 65–71.

Y. Durand, G. Giraud, M. Laternser, P. Etchevers, L. Mérindol, B. Lesaffre, Reanalysis of 47 Years of Climate in the French Alps (1958–2005): Climatology and Trends for Snow Cover, J. Appl. Meteorol. Climatol. 48 (2009) 2487–2512.

P. Quintana-Seguí, P. Le Moigne, Y. Durand, E. Martin, F. Habets, M. Baillon, et al., Analysis of Near-Surface Atmospheric Variables: Validation of the SAFRAN Analysis over France, J. Appl. Meteorol. Climatol. 47 (2008) 92–107.

J.-P. Vidal, E. Martin, L. Franchistéguy, M. Baillon, J.-M. Soubeyroux, A 50-year high-resolution atmospheric reanalysis over France with the Safran system, Int. J. Climatol. 30 (2010) 1627–1644.