Analysis of planetary boundary layer feedbacks on the multiple equilibria of the continental water cycle

Abstract

A simple soil-atmosphere interaction model is developed to study the bimodal distribution of soil moisture in regions where there is feedback between precipitation and soil moisture. Our study includes planetary boundary layer (PBL) feedback in the coupled analytical soil-atmosphere interaction model with a varying PBL height and entrainment from the free atmosphere. This study aims to reveal the dominant PBL feedbacks that impact the occurrence of soil moisture bimodality by comparing the evolution of prognostic variables for a detailed PBL scheme (with varying PBL height and entrainment of heat and moisture from the free atmosphere) with the simple PBL scheme (with fixed PBL height and no entrainment). This study has shown the existence of multiple equilibria in the continental water balance for both detailed PBL and simple PBL schemes when the model is integrated for different initial soil moisture up to equilibria. Although both with and without PBL feedback, the results are in qualitative agreement; the soil moisture initialization to realize multiple equilibria of a detailed PBL scheme is larger than the simple PBL scheme. Although the direct quantitative comparison with observation is clearly limited in the simple model, it also demonstrates how the non-linear dynamics of the coupled soil-atmosphere system may be expected to occur in observations.