Vimeux, F; Maignan, F; Reutenauer, C; Pouyaud, B (2011). Evaluation of cloudiness over Monte San Valentin, Northern Patagonia Icefield, from 2000 to 2008 using MODIS satellite images: implications for paleoclimate investigations from ice cores. JOURNAL OF GLACIOLOGY, 57(202), 221-230.
An unexpectedly low annual net accumulation (20 cm w.e. a(-1)) has been inferred from analyses of a firn core extracted from Glaciar Monte San Valentin, Northern Patagonia Icefield (46 degrees 35'S, 73 degrees 19'W; 3747 m a.s.l.). We test a hypothesis linking the low accumulation to a frequent lack of cloud cover over the mountain range at this altitude. The cloudiness over Monte San Valentin and surrounding regions is examined using similar to 3000 daily MODIS satellite images from 2000 to 2008. The visual evaluation of the synoptic situation leads to the definition of a daily cloudiness index (El) for the San Valentin summit and for the regions to the southwest (SW) and northeast (NE). We check its robustness by applying different tests and comparisons. Three levels are assigned for the El: 'clear' (El = 0), 'cloudy' (El = 1) and 'mixed' (El = 0.5). The results show that the SV cloud cover is similar to the regional cloudiness for more than half the year (54%) and that the case in which the San Valentin summit is clear while both SW and NE regions are cloudy is exceptional (2%). As clouds are necessary to provide precipitation, we show that the low annual net accumulation cannot be explained by an uncommon low cloudiness. This result implies that net accumulation inferred from ice cores in this Andean region must be cautiously interpreted. We also point out that the Andes at this latitude acts as an orographic barrier but without a total blocking of air masses.