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 Valentín, Northern Patagonia Icefield (46° 5'S, 73°19'W; 3747 ma.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 Valentín and surrounding regions is examined using ~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 (EI) for the San Valentín 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 EI: 'clear' (EI = 0), 'cloudy' (EI = 1) and 'mixed' (EI =
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 Valentín 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.
The Journal of Glaciology is published six times per year. It accepts submissions from any discipline related to the study of snow and ice. All articles are peer reviewed. The Journal is included in the ISI Science Citation Index.