Assessing the impact of tropopause height on orographic precipitation using theory and numerical simulations

The impact of tropopause height on the dynamics of stable flow over mountains has been studied extensively for its contribution to downslope windstorms, but its impact on orographic precipitation has not been previously addressed. Here we use a combination of linear theory and numerical simulations to explore the sensitivity of orographic precipitation to variations in tropopause height. In idealized simulations of flow over both two-dimensional and three-dimensional ridges, the total amount of precipitation can vary by more than a factor of two in response to changes in tropopause height of one or two kilometers. We show that this result is related to changes primarily in the depth of windward ascent, but also in the location and strength of lee-side descent, with significant impacts on the distribution of precipitation across the range (i.e., the rain shadow effect). Using a modified version of Smith and Barstad's linear precipitation model, we demonstrate how such changes can impact the amount and distribution of precipitation in complex terrain like the Washington Cascades.