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Toulouse, France

Météo-France is the French national meteorological service. The organisation was established by decree in June 1993 and is a department of the Ministry of Transportation. It is headquartered in Paris but many domestic operations have been decentralised to Toulouse. Its budget of around €300 million is funded by state grants, aeronautic royalties and sale of commercial services.Météo-France has a particularly strong international presence, and is the French representative at the World Meteorological Organization. The organisation is a leading member of EUMETSAT, responsible for the procurement of Meteosat weather satellites. It is also member of the Institut au service du spatial, de ses applications et technologies.In addition to its operations in metropolitan France, the agency provides forecasts and warnings for the French overseas départements and collectivités. It has four sub-divisions based in Martinique , New Caledonia, French Polynesia and Réunion. Some of these sub-divisions have particularly important international responsibilities: For example the French Guiana office based at Cayenne-Rochambeau airport maintains facilities at the ESA/CNES Centre Spatial Guyanais spaceport in Kourou which assists with launch campaigns of the Ariane rocket. The Réunion sub-division is the official World Meteorological Organisation designated Regional Specialized Meteorological Centre for the provision of forecasts and warnings of tropical cyclones in the south-west Indian Ocean. The French Polynesia sub-division, whilst not the official RSMC for tropical cyclones in the South Pacific, has been mandated by the WMO to issue forecasts and warnings of tropical cyclones for the neighbouring British Pitcairn Islands. Wikipedia.

Benard P.,Meteo - France
Quarterly Journal of the Royal Meteorological Society | Year: 2015

The spherical geopotential approximation (SGA) used in most meteorological global models assumes a spherical shape for the Earth and its geopotential field, together with a horizontally uniform gravity field (for physical consistency). This approximation has largely been used from the outset and is still used in operational meteorological forecast systems. However, the magnitude of the errors linked to this approximation is debated, especially for long integrations. Consistent mathematical models of the atmosphere in the ellipsoidal geopotential approximation (EGA) have recently been developed, thus allowing a clean assessment of the errors linked to using the SGA. Two types of error may be anticipated: those arising due to geometrical distortions and those arising due to the spatial differences in the magnitude of the gravity field. The shallow-water system, which is the minimal framework in which both types of errors are likely to manifest themselves, is used in this study. The link between the 'pure forecast errors' examined here and the 'numerical weather prediction (NWP) errors' that would arise in a concrete NWP application (with a data assimilation system) is discussed, in relation to the experimental protocol chosen here. Medium-range forecast errors for idealized fully deterministic flows are first considered in a phenomenological way (phase errors, distortions, etc.) and then some widely documented real cases are examined. © 2014 Royal Meteorological Society. Source

Land surface hydrology (LSH) is a potential source of long-range atmospheric predictability that has received less attention than sea surface temperature (SST). In this study, we carry out ensemble atmospheric simulations driven by observed or climatological SST in which the LSH is either interactive or nudged towards a global monthly re-analysis. The main objective is to evaluate the impact of soil moisture or snow mass anomalies on seasonal climate variability and predictability over the 1986-1995 period. We first analyse the annual cycle of zonal mean potential (perfect model approach) and effective (simulated vs. observed climate) predictability in order to identify the seasons and latitudes where land surface initialization is potentially relevant. Results highlight the influence of soil moisture boundary conditions in the summer mid-latitudes and the role of snow boundary conditions in the northern high latitudes. Then, we focus on the Eurasian continent and we contrast seasons with opposite land surface anomalies. In addition to the nudged experiments, we conduct ensembles of seasonal hindcasts in which the relaxation is switched off at the end of spring or winter in order to evaluate the impact of soil moisture or snow mass initialization. LSH appears as an effective source of surface air temperature and precipitation predictability over Eurasia (as well as North America), at least as important as SST in spring and summer. Cloud feedbacks and large-scale dynamics contribute to amplify the regional temperature response, which is however, mainly found at the lowest model levels and only represents a small fraction of the observed variability in the upper troposphere. © Springer-Verlag 2009. Source

Riviere G.,Meteo - France
Journal of the Atmospheric Sciences | Year: 2011

The role played by enhanced upper-tropospheric baroclinicity in the poleward shift of the jet streams in global warming scenarios is investigated. Major differences between the twentieth- and twenty-first-century simulations are first detailed using two coupled climate model outputs. There is a poleward shift of the eddydriven jets, an increase in intensity and poleward shift of the storm tracks, a strengthening of the uppertropospheric baroclinicity, and an increase in the eddy length scale. These properties are more obvious in the Southern Hemisphere. A strengthening of the poleward eddy momentum fluxes and a relative decrease in frequency of cyclonic wave breaking compared to anticyclonic wave breaking events is also observed. Then, baroclinic instability in the three-level quasigeostrophic model is studied analytically and offers a simple explanation for the increased eddy spatial scale. It is shown that if the potential vorticity gradient changes its sign below the midlevel (i.e., if the critical level is located in the lower troposphere as in the real atmosphere), long and short wavelengths become respectively more and less unstable when the uppertropospheric baroclinicity is increased. Finally, a simple dry atmospheric general circulation model (GCM) is used to confirm the key role played by the upper-level baroclinicity by employing a normal-mode approach and long-term simulations forced by a temperature relaxation. The eddy length scale is shown to largely determine the nature of the breaking: long (short) wavelengths break more anticyclonically (cyclonically). When the upper-tropospheric baroclinicity is reinforced, long wavelengths become more unstable, break more strongly anticyclonically, and push the jet more poleward. Short wavelengths being less unstable, they are less efficient in pushing the jet equatorward. This provides an interpretation for the increased poleward eddy momentum fluxes and thus the poleward shift of the eddy-driven jets. © 2011 American Meteorological Society. Source

Marquet P.,Meteo - France
Quarterly Journal of the Royal Meteorological Society | Year: 2014

A new potential vorticity is derived by using a specific entropy formulation expressed in terms of a moist-air entropy potential temperature. The new formulation is compared with Ertel's version and with others based on virtual and equivalent potential temperatures. The new potential vorticity is subject to conservative properties ensured by the Second Law applied to the moist-air material derivatives. It is shown that the upper tropospheric and stratospheric (dry) structures are nearly the same as those obtained with Ertel's component. Moreover, new structures are observed in the low troposphere, with negative values associated with moist frontal regions. The negative values are observed in the frontal regions where slantwise convection instabilities may take place, but they are smaller than those observed with the equivalent potential vorticity. The main purpose of the article is to diagnose the behaviour of the new potential vorticity from numerical output generated by the ARPEGE NWP model, with the help of isobaric charts and vertical cross-sections. Two inversion methods are suggested. The first method could be based on the invertibility principle verified by the virtual potential vorticity, with a possibility to control and modify separately potential vorticity components in the (dry) upper and (moist) lower atmospheric levels. The other method may consist of an inversion process directly applied to the new moist-air entropy potential vorticity, because the negative values and the solenoidal term are smaller than those observed with equivalent potential vorticity, as shown by numerical evaluations. © 2013 Royal Meteorological Society. Source

Mahfouf J.-F.,Meteo - France
Quarterly Journal of the Royal Meteorological Society | Year: 2010

A simplified Extended Kalman Filter is developed for the assimilation of satellite derived surface soil moisture from the Advanced Scatterometer (ASCAT) instrument (on board the polar-orbiting satellite METOP) in a limited-area NWP model where soil water vertical transfers are described by a force-restore method. An analytic formulation of the land surface scheme Jacobians is derived to simplify the coupling between land surface and atmospheric data assimilation systems. Various steps necessary before the assimilation of ASCAT products are defined: projection of satellite data on the model grid, screening based on various criteria, bias correction using a CDF matching technique, and specification of model and observation errors. Three-dimensional variational data assimilation experiments are then performed during a four-week period in May 2009 over western Europe. A control assimilation is also run where the soil moisture evolves freely. Forecasts from these analyses show that the assimilation of ASCAT data slightly reduces the daytime low-level relative humidity positive bias of the control run. Forecast skill scores with respect to other variables are rather neutral. A comparison of the control run with the operational system where soil moisture is corrected from short-range forecast errors of screen-level observations show similar improvements but are more pronounced. These differences come from the fact that the number of screen-level observations from the surface network over Europe is significantly larger than those provided by a polar-orbiting satellite. These results are consistent with those obtained at ECMWF using soil moisture products derived from other satellite instruments (X-band radiometer TMI and C-band scatterometer ERS). Several avenues for improving this preliminary methodology are proposed. © 2010 Royal Meteorological Society. Source

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