Precipitation Analysis over the French Alps Using a Variational Approach and Study of Potential Added Value of Ground-Based Radar Observations

Abstract

A one-dimensional variational data assimilation (1DVar) method to retrieve profiles of precipitation in mountainous terrain is described. The method combines observations from the French Alpine region rain gauges and precipitation estimates from weather radars with background information from short-range numerical weather prediction forecasts in an optimal way. The performance of this technique is evaluated using measurements of precipitation and of snow depth during two years (2012/13 and 2013/14). It is shown that the 1DVar model allows an effective assimilation of measurements of different types, including rain gauge and radar-derived precipitation. The use of radar-derived precipitation rates over mountains to force the numerical snowpack model Crocus significantly reduces the bias and standard deviation with respect to independent snow depth observations. The improvement is particularly significant for large rainfall or snowfall events, which are decisive for avalanche hazard forecasting. The use of radar-derived precipitation rates at an hourly time step improves the time series of precipitation analyses and has a positive impact on simulated snow depths.

Snowpack modelling in the Pyrenees driven by kilometric-resolution meteorological forecasts

“…To deal with that, the use of complementary observations in complex terrain is necessary, with a particular emphasis on precipitation. For instance, Birman et al (2016) recently developed a new precipitation analysis system, combining a priori information from AROME with ground-based and radar observations. Satellite cloud masks could also be used to improve incoming radiations (e.g.…”

10th European Conference on Radar in Meteorology and Hydrology (ERAD 2018) : 1-6 July 2018, Ede-Wageningen, The Netherlands

“…(Durand, 1993), (Durand, 2009), (Barry, 2012, and the impact of relief on precipitation has been studied in two thesis in the region between de cities of Lyon and Grenoble, using data from a one-dimensional dense rain gauges network (a transect) through the BasDauphiné, Chartreuse and Belledonne massifs (Desurosne, 1994). Climatological vertical profiles of precipitation have been defined for each massif in the French Alps an Pyrenees, and are used in the SAFRAN Analysis system, initially designed to provide atmospheric forcing data in mountainous areas for snow models and avalanche hazard forecasting (Durand, 1993), (Birman, 2017). …”

Glacier-wide summer surface mass-balance calculation: hydrological balance applied to the Argentière and Mer de Glace drainage basins (Mont Blanc)

“…Given that the SAFRAN reanalysis only partially represents the spatial variability of the meteorological conditions within a massif (Durand and others, 2009; Vionnet and others, 2016; Birman and others, 2017), we propose a correction of the SAFRAN precipitation values based on the comparison with the pwSMB measurements (Gerbaux and others, 2005; Dumont and others, 2012; Réveillet and others, 2017). Glacier winter surface mass-balance observations have often been used to either replace precipitation measurements or to validate precipitation estimates at high altitudes (Bucher and others, 2004; Carturan and others, 2012).…”