AROME: an overview

AROME is a small scale numerical prediction model, operational at Meteo-France since December 2008. It was designed to improve short range forecasts of severe events such as intense Mediterranean precipitations (Cévenole events), severe storms, fog, urban heat during heat waves.

Computational domain of Arome 1,3km
AROME was developed in close collaboration with national and international institutes so as to benefit from the latest research in atmospheric modelling. The physical parametrizations of the model come mostly from the research Méso-NH model whereas the dynamic core is the Non-Hydrostratic ALADIN one.
The size of the mesh, many time smaller than previous model, is 1.3km against 5km for ARPEGE over France.
The model is initialized from data assimilation derived from the ARPEGE-IFS variational assimilation system and adapted to the AROME finer resolution. Besides available data from ARPEGE, AROME is supplied, for instance, by precise data from the ARAMIS radar network (doppler wind and precipitation), assimilated on an hourly basis.

Evolution of monthly cumulated observations number per observation type in Arome
Operational use
Five daily forecasts are made with AROME, thus helping to better predict meteorological events of the day and of the morrow (48h forecast range).
AROME has proved to be particularly useful during the intense precipitation events which occured during the autumn season over the Western Mediterranean region.

Maps of 3 h cumulated precipitations (mm) between 18:00 and 21:00 UTC over the southeast of France, for the case of 3 October 2015. (a) AROME-France forecast starting at 03:00 UTC, (b) Antilope 3 h precipitation analysis

From the onset, AROME showed it improved forecasts against the coupling model (that give information at the boundaries) ALADIN (a LAM version of ARPEGE over Europe).
During Spring 2010, the vertical resolution of the second version AROME increased and became better than that of ALADIN in the lower levels (less than 3000m above ground). New data were added in the initialization process, especially on radar de tected precipitations by the ARAMIS network. From this version of the model onwards, the increase of the horizontal resolution of ARPEGE over Europe made it possible to coupled AROME and ARPEGE.
The third version of AROME characterized by a 76% increase of the geographic horizontal resolution and a free from ARPEGE surface field initialization was made possible by the gain in computation power which occurred at the beginning of 2010.
Our computation power increased anew and has permit to further increase the AROME horizontal resolution to 1.3km and a 1.5 times finer vertical resolution.
A dedicated version to nowcasting (at a few hours range) is operational. An AROME ensemble prediction system (either to estimate the uncertainty of a prediction or to give a probability warning whenever a hazard level is reached) has been complemented the deterministic version of AROME since 2016.
Model versions of AROME dedicated to overseas territories are also used operationally.
With added information on the boundary, AROME gains from systematic improvements of its coupling model ARPEGE. Specific modifications are also implemented in AROME to solve some of its weak points which have been identified either by forecasters or by the computation of objective scores.
 Looking abroad
Within Europe, the fine scale model AROME is used by some fifteen countries already with some more expected to do so shortly. At the same time, it is more and more used as a research model too.
On the long term
Model use on nowcasting on rapidly developing events (at few hours range), on ensemble prediction (either to estimate the uncertainty of a prediction or to give a probability warning whenever a hazard level is reached) and also as a research model will carry on.
Experiments at finer scales, typically down to the size of a town, a mountain or an airport are ongoing with hectometric horizontal resolution (typically 500m).
Improvements in physical parameterization of the model, its dynamics, and its initialization are regularly implemented to improve the quality of forecasts in new versions of the model.
Vidéo sur AROME en flash

The genesis of the AROME model