Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
Within the framework of the international field campaign COPS (Convective and Orographically induced Precipitation Study), a large suite of state-of-the-art meteorological instrumentation was operated, partially combined for the first time. This includes networks of in situ and remote-sensing systems such as the Global Positioning System as well as a synergy of multi-wavelength passive and active remote-sensing instruments such as advanced radar and lidar systems. The COPS field phase was performed from 01 June to 31 August 2007 in a low-mountain area in southwestern Germany/eastern France covering the Vosges mountains, the Rhine valley and the Black Forest mountains. The collected dataset covers the entire evolution of convective precipitation events in complex terrain from their initiation, to their development and mature phase until their decay. Eighteen Intensive Observations Periods with 37 operation days and eight additional Special Observations Periods were performed, providing a comprehensive dataset covering different forcing conditions. In this article, an overview of the COPS scientific strategy, the field phase, and its first accomplishments is given. Highlights of the campaign are illustrated with several measurement examples. It is demonstrated that COPS research provides new insight into key processes leading to convection initiation and to the modification of precipitation by orography, in the improvement of quantitative precipitation forecasting by the assimilation of new observations, and in the performance of ensembles of convection-permitting models in complex terrain.
ISSN: 0035-9009

hal-00565513
https://hal.archives-ouvertes.fr/hal-00565513
DOI : 10.1002/qj.752

Éditeur(s) : HAL CCSD
Résumé : International audience
The Cenozoic weathering of peninsular India has been advocated as a major driver of globalcooling, however, its timing remains virtually unconstrained such that proposed links betweentropical weathering of the Deccan Traps, regional monsoonal intensity and global climate remainsspeculative. To solve this conundrum we present here a revised weathering chronologybased on the identification of lateritic paleosurfaces and their dating using 40Ar/39Ar on supergeneK-rich manganese oxides. We focus on the Indian western passive margin where theWestern Ghats Escarpment (WGE) – a ~1000 m high topographic barrier resulting from thecontinental break up of Greater India – exposes exceptionally preserved weathering profilesfrom the western coastal lowlands to the eastern highland plateaus above the WGE. Four mainlateritic paleosurfaces have been identified: Three in the highland; a high landsurface (Al-Femostly bauxite) at elevation 1200-1000 m asl, an intermediate landsurface covered by a Feduricrustat 1000-900 m asl and a lower pediment landsurface at 850-600 m asl; and one inthe coastal lowland underneath a pediment landsurface at 150-50 m asl. The 40Ar/39Ar agesdocument three major weathering periods over the Cenozoic. The oldest weathering period(W1) is recorded between 53 Ma to 45 Ma both in the highland and the lowland. This correlatesto the Global Eocene climatic Optimum, and allows defining a bauxitic paleolandsurface acrossthe escarpment. Intense bauxitic weathering between ~ 45 and 47 Ma in the lowland indicatethat the WGE was stabilized before ~ 47 Ma on its margin and also implies low denudation rateat the foot of the WGE (<5 m Ma-1) since that time. The second weathering period between37 Ma to 19 Ma (W2) occurred in two distinctive stages (W2a and W2b). From 37 to 26 (W2a),weathering is only recorded in the highland and affect intermediate surfaces. The intensityof chemical weathering decreased sensibly between 32 and 29 Ma – potentially linked to theEarly Oligocene cooling – and resulted in the formation of the lower pediment surface. From~26 Ma to 19 Ma (W2b), only the western coastal lowland weathered while the highland surfacesare mostly dissected. This change and the highland/lowland weathering mitigation after~26 Ma documents a change in climatic patterns over peninsular India that signs the onset ofmodern-like monsoon regime. These results are being interpolated to the Deccan Traps basaltsto quantify their weathering and ultimately estimate of the contribution to CO2 fluxes of thesethree weathering periods and their potential link to Asian Monsoons and global cooling.
Source to Sink: a long term perspective of sediment budgets and sources characterization, Abstracts
Rennes, France

insu-01406455
https://hal-insu.archives-ouvertes.fr/insu-01406455