.[1] Modeling the densification of polar firn is essential to estimate variations of close-off characteristics (density, close-off depth, delta age) in relation with past climate parameters (temperature and accumulation rates). Furthermore, the air composition in the firn is modified by gravitational and thermal fractionation, and stable isotope measurements of permanent gases like nitrogen or argon can provide information on the amplitude of these fractionations. In this work, we propose a new model coupling firn densification and heat diffusion. In addition to the determination of the firn thickness and gas-ice age differences, the model allows a reconstruction of the time evolution of the temperature for different sites in Antarctica (Vostok) and Greenland (GISP2) and therefore the evolution of gravitational and thermal isotopic fractionations in firn. Under present-day conditions, the modeled profiles are in good agreement with the available temperature measurements in firn. For sites with low accumulation rates such as Vostok, the results show the existence of temperature gradients in the firn column even when no rapid climatic changes occur. The comparison of the modeled d15 N results to measurements allows to better constrain the d 18 O-temperature relationship, used to infer the surface temperature history, and for GISP2, the model validates the long-term borehole-based temperature.INDEX TERMS: 1827 Hydrology: Glaciology (1863); 1863 Hydrology: Snow and ice (1827); 3344 Meteorology and Atmospheric Dynamics: Paleoclimatology; KEYWORDS: firn densification, temperature reconstruction, gas fractionation Citation: Goujon, C., J.-M. Barnola, and C. Ritz, Modeling the densification of polar firn including heat diffusion: Application to close-off characteristics and gas isotopic fractionation for Antarctica and Greenland sites,

Recent studies have pointed out the importance of the basal friction on the dynamics of granular flows. We present experimental results on the influence of the roughness of the inclined plane on the dynamics of a monodisperse dry granular flow. We found experimentally that it exists a maximum of the friction for a given relative roughness. This maximum is shown to be independent of the angle of the slope. This behavior is observed for four planes with different bump sizes (given by the size of the beads glued on the plane) from 200 µm to 2 mm. The relative roughness corresponding to the maximum of the friction can be predicted with a geometrical model of stability of one single bead on the plane. The main parameters are the size of the bumps and the size of the flowing beads. In order to obtain a higher precision, the model also takes into account of the spacing between the bumps of the rough plane. Experimental results and model are in good agreement for all the planes we studied. Other parameters, like the sphericity of the beads, or irregularities in the thickness of the layer of glued particles, are shown to be of influence on the friction.