Precipitation processes at windward and leeward sides of the mountains have been object of study for many decades. Instead, inner mountain valleys, where usually most mountain population lives, have received considerably less attention. This article examines precipitation processes during a winter field campaign in an inner valley of the Pyrenees (NE Spain) using, among other instruments, a K-band vertically pointing Doppler radar (Micro Rain Radar) and a laser-based optical disdrometer (Parsivel). A decoupling is found between the stalled air of the valley and the air of the free atmosphere above the mountain crest level, evidenced by an increase of turbulence and spectral width of precipitation particles. Wind shear layer may promote riming and aggregation of the ice and snow particles. Two main rainfall regimes are found during the campaign: (1) stratiform rainfall mostly produced by water vapour deposition processes, although sometimes riming and aggregation become important, and (2) weak convection with slight dominance of collision-coalescence processes. Precipitation characteristics at the bottom of the valley show typical continental features such as low Liquid Water Content, despite the valley is only about 100 km from the sea. This study demonstrates that inner valley may present distinct precipitation features with respect to windward and leeward precipitation.

几十年来，山区迎风侧和背风侧的降水过程一直是研究的对象。相反，通常大多数山区人口居住的内山谷受到的关注要少得多。本文使用 K 波段垂直指向多普勒雷达（微雨雷达）和基于激光的光学偏差计（Parsivel）等仪器，研究了比利牛斯山脉内谷（西班牙东北部）冬季野外活动期间的降水过程. 在山谷的停滞空气与山峰水平以上的自由大气空气之间发现了解耦，这可以通过降水粒子的湍流和光谱宽度的增加来证明。风切变层可能会促进冰雪颗粒的形成和聚集。活动期间发现了两种主要的降雨情况：(1) 层状降雨主要由水汽沉积过程产生，尽管有时边缘和聚集变得重要，和 (2) 弱对流，碰撞合并过程略占优势。谷底的降水特征显示出典型的大陆特征，如低液态水含量，尽管谷地距大海仅约 100 公里。该研究表明，在迎风和背风降水方面，内谷可能呈现出明显的降水特征。谷底的降水特征显示出典型的大陆特征，如低液态水含量，尽管谷地距大海仅约 100 公里。该研究表明，在迎风和背风降水方面，内谷可能呈现出明显的降水特征。谷底的降水特征显示出典型的大陆特征，如低液态水含量，尽管谷地距大海仅约 100 公里。该研究表明，在迎风和背风降水方面，内谷可能呈现出明显的降水特征。