predict Cevennes episodes by studying water vapor in the Mediterranean


Innovative convention, this Tuesday at La Grande-Motte. Météo-France, Sète and the University of Montpellier are carrying out a research project: measuring and studying the water vapor of the troposphere by equipping cruise ships to refine the weather forecasts for Cévennes episodes.

The Cévennes or Mediterranean episodes often have dramatic and even fatal consequences in Languedoc-Roussillon. The Gard was again the victim of disastrous floods not two weeks ago.

Predicting these phenomena is inherently very delicate since they generate very localized thunderstorm sequences. Today Météo-France predicts the Cevennes episodes, but is still struggling to determine their amplitude and the precise areas of their potential impact. Weather phenomena that originate in the Mediterranean because it is the wind and cloudy clusters coming from the open sea which then cause damage inland when this warm front turns into stormy formations in contact with colder air masses from the Gard or Hérault hinterland.

The Mediterranean, swell and sea breeze in Port-la-Nouvelle before the last Cévennes episode.

© Sylvie BONNET

It is in this context of “danger” coming from the sea that the agreement signed on Tuesday at La Grande-Motte may prove to be of great use in the long term, when it has passed the experimental phase.

Equip cruise ships with GNSS stations

The port of Sète is associated with the convention because it is the main anchor point for cruise ships in Occitania. These ships will be equipped with a very advanced positioning system (in English G.N.S.S, pour Global Navigation Satellite System, is a set of satellites which provide very precise geographic coordinates of the boat’s position).
The information collected on the quantity of water vapor present in the Mediterranean at the heart of the birth of the Cevennes episodes, in the troposphere, this layer of the terrestrial atmosphere between the surface of the globe and the stratosphere, will then be transferred in almost time. real to partners by means of a nanosatellite.

The triple CubeSat of the University Space Center of Montpellier

This is the nanosatellite designed and produced by the Montpellier University Space Center which will be responsible, in partnership with Météo-France, to collect meteorological data on the quantity of water present in the lower layers of the atmosphere in a short time. to improve the models for predicting Cevennes episodes.

Students from the Montpellier University Space Center have already developed several nanosatellites including Robusta 1B, which has circled the Earth more than 18,000 times.  ARCHIVES

Students from the Montpellier University Space Center have already developed several nanosatellites including Robusta 1B which has circled the Earth more than 18,000 times. ARCHIVES

© csum

This nanosatellite, on which some 300 students have been working for 7 years, was co-financed by the Van Allen Foundation and the CNRS as part of the Janus project.

A national project

A modeling system that remains to be built, in partnership with Meteo France and theNational Geographic Institute. And the project will benefit from another expertise: that of the engineers of Brest, theENSTA Brittany, at the cutting edge of maritime research, being associated with experience.
The interest of such an approach is indisputable. And validated at the highest level since the Minister of the Sea, Annick Girardin is participating in the signing of this agreement alongside the other players in the project:
– Jean-Claude Gayssot, President of the Van Allen Foundation (which supports the Montpellier University Space Center), former Minister
– Philippe Augé, President of the University of Montpellier
– Marc Pontaud, Director of Higher Education and Research at Météo-France
– Pierre Laulier, South-East Territorial Director of IGN
– Bruno Gruselle, Director of ENSTA Bretagne
– Olivier Carmes, General Manager of the Port of Sète Sud de France

Long-term experimentation

Before Météo-France can use this data, IGN and ENSTA Bretagne will have to validate their processing methods. At this stage, it is a question of carrying out a technological demonstration, to validate the methods of treatment and to quantify the contribution of the system. If this contribution is demonstrated, an operational system could materialize.
The signing of the convention on Tuesday morning took place at La Grande-Motte as part of the Salon du littoral.

Commercial ships and planes already partners of Météo-France

Weather forecasts already benefit from information relayed by real stations on board merchant ships. In the Mediterranean, ferries to Corsica have been equipped since 2015.

Weather sensors are usually installed in the "nose" planes, here an A 320.

Weather sensors are generally installed in the “nose” of planes, here an A 320.


As for airplanes, they are also valuable relays for observing the sky from above since they have been equipped with sensors since the 2000s. Thanks to the European AMDAR system, in cruising flight at 10 kilometers altitude, each equipped plane sends a measurement every 2 to 3 minutes to Météofrance. This makes more than 40,000 observations every day over France. A system slowed down this spring by confinement and planes pinned to the ground.

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