page_title: Alpine planetary boundary layer
section_title: Mountain-Plain winds
hierarchical_section_title: Alpine planetary boundary layer / Wind systems / Mountain-Plain winds
caption_attribution_description: English: Daytime mountain-plain wind system
context_page_description: The alpine planetary boundary layer is the planetary boundary layer associated with mountainous regions. Due to its high spatial and temporal variability, its behavior is more complex than over a flat terrain. The fast changing local wind system directly linked to topography and the variable land cover that goes from snow to vegetation have a significant effect on the growth of the PBL and make it much harder to predict.
  Understanding the processes inducing changes in the mountain PBL have critical applications for predicting air pollution transport, fire weather and local intense thunderstorm events. While some processes, such as mountain waves, have been well studied in the mountain PBL due to their importance for aviation, most of the behaviors of the alpine PBL are relatively unknown.
context_section_description: The Mountain-Plain winds system is the largest scale phenomenon going across the mountain range. 
  During daytime, incoming solar radiation heats up the mountain top faster than the plain, creating a mean low pressure zone at the top. Winds then blow towards the mountain on all sides, flow up the slope and converge at the top. A return flow occurs aloft and comes back down into the plains.  The exact opposite happens during nighttime, when the top cools down faster than the plain, which creates a mean high pressure zone leading to winds coming from the mountain top down to the plain. This represents the idealized situation since many complications can arise from cross currents, forced or pressure driven channeling or even  cold fronts approaching the mountain barrier.
caption: Daytime mountain-plain wind system