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1. Introduction
Precipitation is a critical component of the global water and energy cycle and is one of the most societally relevant aspects of the weather and climate system. The coupling and feedback between soil moisture and precipitation have been studied extensively in the last several decades (Budyko 1974; Charney et al. 1977; Shukla and Mintz 1982; Brubaker et al. 1993; Eltahir and Bras 1994).
The direct impact of soil moisture on precipitation is based on its control on evapotranspiration, that is, a direct moisture supply to precipitation and associated water recycling (Brubaker et al. 1993; Eltahir and Bras 1994; Joussaume et al. 1984; Koster et al. 1986; Dirmeyer and Brubaker 1999; Brubaker et al. 2001; Bosilovich and Schubert 2002; Bosilovich and Chern 2006). However, soil moisture can also affect many other physical processes, such as the surface albedo, vegetation, and partition of surface water and heat fluxes. These can further affect planetary boundary development and moist convection (Betts and Ball 1998; Eltahir 1998; Notaro et al. 2006; Seneviratne and Stöckli 2008; Taylor and Lebel 1998; Dirmeyer et al. 2006; Koster et al. 2004; Meng et al. 2011; Pielke et al. 1999; Santanello et al. 2011; Weaver et al. 2002; Zaitchik et al. 2007). For example, Betts and Ball (1998) proposed a positive feedback mechanism through soil moisture impacting the partition of latent and sensible heat flux into the boundary layer. Under this hypothesis, drier soil moisture reduces latent heat flux but increases sensible heat flux, resulting in higher Bowen ratio and lower moist static energy (MSE), higher boundary layer height, and lifting condensation level (LCL) that tends to inhibit the shallow convection. A similar hypothesis is proposed by Eltahir (1998) through modulation of surface net radiation flux.
In addition to the local effect, the large-scale and nonlocal effect of soil moisture has been found through the impact of large-scale circulation patterns and advection of moisture from one region to another (Shukla and Mintz 1982; Meehl 1994; Douville 2002; Rowell and Blondin 1990; Beljaars et al. 1996; Zhu et al. 2009), but the scale and mechanism for these impacts are still not well understood (Cook et al. 2006; Conil et al. 2007).
As discussed above, the soil moisture-precipitation interaction involves many complicated physical processes. The...