A Study of Persistence in the Land–Atmosphere System Using a General Circulation Model and Observations

Abstract

Persistence in the land?atmosphere system simulated with the National Center for Atmosphere Research Community Climate Model Version 2 (CCM2) coupled with the Biosphere?Atmosphere Transfer Scheme (BATS) is examined. BATS simulates various vegetation and soil types and explicitly predicts soil temperature. Thus, it is well equipped to study persistence in different climatic regions, and to compare the relative importance of soil hydrological and thermal processes. An evaluation of a 10-yr simulation produced with CCM2?BATS indicates that this coupled model is able to reproduce the observed spatial patterns of soil moisture and soil temperature in China. Also, the magnitude of these two soil variables in the simulation are, in general, close to observations. The major exception is soil temperature during wintertime. Analysis of this simulation indicates a significant persistence in soil moisture and soil temperature. The timescales of the persistence are of the order of months to seasons. In comparison with soil temperature, soil moisture has a much stronger persistence, as indicated by larger autocorrelations and longer timescales. Persistence of the simulated soil moisture depends on latitude and regional climatology. This regional dependence is also found in the observations. This study emphasizes that persistence of soil moisture is determined mainly by actual evaporation, and its impact on atmospheric persistence is determined mainly by the nature of internal moisture exchanges in the land?atmosphere system.