A Study of Persistence in the Land–Atmosphere System with a Fourth-Order Analytical Model

Abstract

In a companion paper, Y. Liu and R. Avissar analyzed the features of persistence in the land?atmosphere system simulated with the National Center for Atmospheric Research Community Climate Model Version 2 coupled with the Biosphere?Atmosphere Transfer Scheme (CCM2?BATS). To interpret the results obtained in that study, a fourth-order land?atmosphere analytical model is developed and used to investigate the timescales of disturbances in the land?atmosphere system, and the major parameters and processes affecting them. This analytical model has four damping timescales, namely seasonal, monthly, weekly, and daily. It is found that the seasonal scale is caused by self-feedback of soil moisture, and its length increases significantly due to the interactions between soil moisture and the other system variables. A sensitivity analysis performed with the Fourier amplitude sensitivity test indicates that the seasonal timescale is mostly affected by the physical parameters related to hydrological processes (namely, evaporation, runoff, and soil moisture diffusion), while the thermal characteristics of the land?atmosphere system mostly affect the monthly timescale. Thus, the results of this analytical study indicate that the persistence obtained in the CCM2?BATS simulation is an inherent property of the land?atmosphere system. They also emphasize the importance of soil moisture disturbances on persistence in the climatic system.