Seasonal forecast of French Mediterranean heavy precipitating events linked to weather regimes

Seasonal predictability of local precipitation is rather weak in the mid-latitudes. This is the case when assessing the skill of the seasonal forecast of Heavy Precipitating Event (HPE) extreme occurrence over the French Mediterranean coast during the fall season. Tropics to extra-tropics teleconnection patterns do appear when averaging analyzed fields over the years characterised by a frequency of HPE occurrence in the upper 17% of the distribution. A methodology taking weather regime occurrence into account as an intermediate step to forecast HPE extreme occurrence is presented. For the period 1960 to 2001 and four different sets of seasonal forecast, the Economical Value is doubled, compared to the score obtained with the simulated local precipitation data, when using a linear model (Linear Discriminant Analysis in this case) taking simulated 200 hPa velocity potential–stream function regime occurrences as predictors. Interestingly, larger scores are shown for this couple of fields over a large-scale domain including the tropics than for the 500 hPa geopotential height over an Euro–Atlantic domain, despite a tighter link of the latter field to the local precipitation

Intercomparison of methods of coupling between convection and large-scale circulation: 1. Comparison over uniform surface conditions

As part of an international intercomparison project, a set of single column models (SCMs) and cloud-resolving models (CRMs) are run under the weak temperature gradient (WTG) method and the damped gravity wave (DGW) method. For each model, the implementation of the WTG or DGW method involves a simulated column which is coupled to a reference state defined with profiles obtained from the same model in radiative-convective equilibrium. The simulated column has the same surface conditions as the reference state and is initialized with profiles from the reference state. We performed systematic comparison of the behavior of different models under a consistent implementation of the WTG method and the DGW method and systematic comparison of the WTG and DGW methods in models with different physics and numerics. CRMs and SCMs produce a variety of behaviors under both WTG and DGW methods. Some of the models reproduce the reference state while others sustain a large-scale circulation which results in either substantially lower or higher precipitation compared to the value of the reference state. CRMs show a fairly linear relationship between precipitation and circulation strength. SCMs display a wider range of behaviors than CRMs. Some SCMs under the WTG method produce zero precipitation. Within an individual SCM, a DGW simulation and a corresponding WTG simulation can produce different signed circulation. When initialized with a dry troposphere, DGW simulations always result in a precipitating equilibrium state. The greatest sensitivities to the initial moisture conditions occur for multiple stable equilibria in some WTG simulations, corresponding to either a dry equilibrium state when initialized as dry or a precipitating equilibrium state when initialized as moist. Multiple equilibria are seen in more WTG simulations for higher SST. In some models, the existence of multiple equilibria is sensitive to some parameters in the WTG calculations

Multi-model evaluation of the sensitivity of the global energy budget and hydrological cycle to resolution

This study undertakes a multi-model comparison with the aim to describe and quantify systematic changes of the global energy and water budgets when the horizontal resolution of atmospheric models is increased and to identify common factors of these changes among models. To do so, we analyse an ensemble of twelve atmosphere-only and six coupled GCMs, with different model formulations and with resolutions spanning those of state-of-the-art coupled GCMs, i.e. from resolutions coarser than 100 km to resolutions finer than 25 km. The main changes in the global energy budget with resolution are a systematic increase in outgoing longwave radiation and decrease in outgoing shortwave radiation due to changes in cloud properties, and a systematic increase in surface latent heat flux; when resolution is increased from 100 to 25 km, the magnitude of the change of those fluxes can be as large as 5 W m−2. Moreover, all but one atmosphere-only model simulate a decrease of the poleward energy transport at higher resolution, mainly explained by a reduction of the equator-to-pole tropospheric temperature gradient. Regarding hydrological processes, our results are the following: (1) there is an increase of global precipitation with increasing resolution in all models (up to 40 × 103 km3 year−1) but the partitioning between land and ocean varies among models; (2) the fraction of total precipitation that falls on land is on average 10% larger at higher resolution in grid point models, but it is smaller at higher resolution in spectral models; (3) grid points models simulate an increase of the fraction of land precipitation due to moisture convergence twice as large as in spectral models; (4) grid point models, which have a better resolved orography, show an increase of orographic precipitation of up to 13 × 103 km3 year−1 which explains most of the change in land precipitation; (5) at the regional scale, precipitation pattern and amplitude are improved with increased resolution due to a better simulated seasonal mean circulation. We discuss our results against several observational estimates of the Earth's energy budget and hydrological cycle and show that they support recent high estimates of global precipitation

Avant-Propos

Guérémy Pierre. Avant-Propos. In: Méditerranée, troisième série, tome 51, 1-2-1984. Actes du colloque «Effets des séismes sur les reliefs de forte énergie». pp. 1-2

L'Atlas de Sardaigne - R. Pracchi et A. Terrosu Asole, Cagliari, La Zattera éd., 1971

Guérémy Pierre. L'Atlas de Sardaigne - R. Pracchi et A. Terrosu Asole, Cagliari, La Zattera éd., 1971. In: Espace géographique, tome 1, n°4, 1972. p. 250

Réponse aux commentaires de Bernard Dumas sur « Réflexions sur l’apport de la géomorphologie à la mise en évidence des variations du niveau de la mer au cours de l’Holocène en Calabre méridionale »

Ma réponse aux « commentaires » de mon collègue et ami Bernard Dumas, à mon article récent, portant sur l’Holocène de Calabre méridionale, peut être simple et courte. Il s’agit de la définition géomorphologique des limites inférieures et supérieures de chaque unité géomorphostratigraphique marine (UGM) distincte, à mettre en rapport avec une oscillation du niveau des mers. Notre désaccord porte sur l’interprétation de trois coupes du littoral de Scilla, dont des figures ont été publiées par F..

Instabilité climatique, variations du niveau de la mer et géomorphologie au cours du dernier interglaciaire et de la dernière glaciation : état de la question / Climatic instability, sea-level changes and geomorphology during the last interglacial and the last glacial periods: a review

Abstract Millennial-scale climatic oscillations (frequency # 1,5 ka) occurring during the last glacial and interglacial periods have been detected from high-resolution records in ice cores and marine or continental sediments. These results are compared with those which aim to identify sea-level changes during the same period. Better than the eustatic curves deduced from marine oxygen isotope records, the geo- morphological study of raised marine terraces, in highly uplifted areas, gives evidence that the periodicity (up to 2,8 ka) of sea-level changes is approximately in phase with climatic variations since 128 ka.Résumé Divers enregistrements extraits des archives glaciaires et de sédiments marins ou continentaux témoignent d'une instabilité climatique de fréquence millénnale (# 1,5 ka) durant la dernière glaciation et le dernier interglaciaire. Ces résultats sont confrontés aux recherches visant à établir les variations eustatiques durant la même période. Mieux que les courbes eustatiques tirées de la composition isotopique de l'oxygène de l'eau de mer, l'étude géomorphologique des terrasses marines étagées, dans les régions fortement soulevées, prouve que la périodicité des variations du niveau des océans (jusqu'à 2,8 ka), est proche de celle des changements climatiques, depuis 128 ka.Guérémy Pierre. Instabilité climatique, variations du niveau de la mer et géomorphologie au cours du dernier interglaciaire et de la dernière glaciation : état de la question / Climatic instability, sea-level changes and geomorphology during the last interglacial and the last glacial periods: a review. In: Géomorphologie : relief, processus, environnement, Avril-juin, vol. 9, n°2. pp. 63-82

Principes de cartographie des risques inhérents à la dynamique des versants

The mapping of natural hasards which are connected with the processes of slope movement rests on a number of principles, which are briefly reviewerd here. The detection of hazards presupposes, as a preliminary, a survey of all the signs and factors of instability, are they connected with topography, vegetation, hydrology, geology or with man. The zonation implies the determination of area, type and degree of hazard.La cartographie des risques liés aux processus de façonnement des versants, mouvements de terrain et érosion hydrique, repose sur un certain nombre de principes, qui sont brièvement rappelés ici. La détection des risques suppose un inventaire préalable des indices et des facteurs d'instabilité, qu'ils soient d'ordre topographique, phytogéographique, hydrologique, géologique ou anthropique. La représentation de risques doit prendre en compte leur localisation prévisible, leur nature et leur gradation.Guérémy Pierre. Principes de cartographie des risques inhérents à la dynamique des versants. In: Travaux de l'Institut Géographique de Reims, n°69-72, 1987. Géomorphologie et risques naturels, sous la direction de Pierre Gueremy et Alain Marre. pp. 5-41

Recherches morphologiques sur le versant oriental du massif de la Sila (Calabre)

Guérémy Pierre. Recherches morphologiques sur le versant oriental du massif de la Sila (Calabre). In: Bulletin de l'Association de géographes français, N°311-312, 40e année, Janvier-février 1963. pp. 29-40