Some Aspects of Precipitation Relating to Topography

In this chapter, we briefly survey some of the ways in which complex terrain can influence precipitation. The survey is subdivided into four sections, the first three focusing on terrain influences extending upstream, downstream and at a distance from topography. Precipitation upstream of mountains can occur owing to blocking associated with topographically-induced convergence. Downstream influences include the creation and maintenance of quasistationary rainbands, which can result from orographically-generated lee waves. Storms or coherent circulations initiated as a result of topography can propagate away, bringing precipitation to locations far from their origin, an example being the vortices formed near the Tibetan Plateau. The final section considers examples of how terrain can influence precipitating systems formed elsewhere that encounter mountains as they move. Squall lines and cold fronts, for example, can both be dramatically affected by an encounter with complex terrain.