Quantifies the time it takes for soil moisture to lose information of its initial state, meaning the time it takes for the lagged autocorrelation of soil moisture to fall below its e-folding time. This method can be calculated from most in-situ and remotely sensed observations to be compared against model data in an effort to show regions where models might be incorrectly retaining or losing soil moisture information. May also shed light on potential soil moisture retention biases related to various land cover type.
Prototype Subroutine Call
*** Note: Memory is defined as time when the lagged autocorrelation falls below the e-folding time. The day at which this occurs is smemory so the unit of time depends on the timestep used for the lagged correlation. For example if daily soil moisture data are used, then the smemory would be returned as the day when the lagged autocorrelation is less than 1/e.
How to Calculate
Thomas L. Delworth and Syukuro Manabe, 1988: The Influence of Potential Evaporation on the Variabilities of Simulated Soil Wetness and Climate. J. Climate, 1, 523–547.  Detailed Evaluation
Thomas Delworth and Syukuro Manabe, 1989: The Influence of Soil Wetness on Near-Surface Atmospheric Variability. J. Climate, 2, 1447–1462.