Abstract
Land–atmosphere energy and moisture exchange can strongly influence local and regional climates. However, high uncertainty exists in the representation of land–atmosphere interactions in numerical models. Parameterization of surface exchange processes is greatly affected by parameter Czil, which, however, is typically defined as a domain-wide constant value. In this study, we examine the sensitivity of regional climate simulations over China to different surface exchange strengths via three Czil schemes (default (without Czil), constant (Czil = 0.1), and dynamic canopy-height-dependent Czil-h schemes) within a 13-km-resolution Weather Research and Forecasting model coupled with the Noah land surface model with multiparameterization options (WRF/Noah-MP). Our results demonstrate that compared to the other two schemes, the Czil-h scheme substantially reduces land–atmosphere coupling strength overestimation, and comparison to Chinese terrestrial ecosystem flux research network (ChinaFLUX) observations reveals the capability of the Czil-h scheme to better match observed surface energy and water variations. The results of the application of the various Czil schemes in four typical climate zones in China demonstrate that the Czil-h simulations achieve the closest agreement with field observations. The Czil-h scheme can narrow the positive discrepancies in the simulated precipitation and surface fluxes and the negative biases of the land surface temperature in Northeast China, North China, eastern Northwest China, and Southwest China. In particular, the above remarkable improvements produced by the Czil-h scheme primarily occur in areas covered with short vegetation. Additionally, the precipitation simulated with the Czil-h scheme exhibits more intricate and uncertain changes compared with surface flux simulations due to the nonlocal impacts of the surface exchange strength resulting from atmospheric fluidity. Overall, our findings highlight the applicability of the dynamic Czil scheme as a better physical alternative to the current treatment of surface exchange processes in atmosphere coupling models.
Highlights
Land–surface processes, through controlling energy, momentum, and mass transportation to lower atmosphere and affecting local planetary boundary layer profiles and differential surface heating (Betts et al 1996; Los et al 2006), may play a significant role in cloud formation and precipitation generation (Findell and Eltahir2003; Trier et al 2004)
Ruiz-Barradas and Nigam (2005) demonstrated that excessively land–atmosphere coupling in numerical models produces too much latent heat flux (LH), resulting in potentially incorrect feedback between soil moisture and precipitation
The simulated Ta can capture the observed large-scale pattern, colder simulations occur in southwest and warmer values are in northwest China
Summary
Land–surface processes, through controlling energy, momentum, and mass transportation to lower atmosphere and affecting local planetary boundary layer profiles and differential surface heating (Betts et al 1996; Los et al 2006), may play a significant role in cloud formation and precipitation generation (Findell and Eltahir2003; Trier et al 2004). Previous studies of the midwestern U.S drought in 1988 and flood in 1993, suggested that the soil moisture condition helps to sustain the extreme circumstances throughout the summer (Atlas et al 1993; Trenberth and Guillemot 1996). These studies underline that land–atmosphere interactions may hold the key for the improvements of weather forecast and climate prediction. The coupling issue regarding the exchange efficiencies of energy and moisture between land surface and atmosphere, quantified as a parameter
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