Assessment of Roughness Length Schemes Implemented within the Noah Land Surface Model for High-Altitude Regions

Abstract

Current land surface models still have difficulties with producing reliable surface heat fluxes and skin temperature (T sfc ) estimates for high-altitude regions, which may be addressed via adequate parameterization of the roughness lengths for momentum (z 0m ) and heat (z 0h ) transfer. In this study, the performance of various z 0h and z 0m schemes developed for the Noah land surface model is assessed for a high-altitude site (3430 m) on the northeastern part of the Tibetan Plateau. Based on the in situ surface heat fluxes and profile measurements of wind and temperature, monthly variations of z 0m and diurnal variations of z 0h are derived through application of the Monin-Obukhov similarity theory. These derived values together with the measured heat fluxes are utilized to assess the performance of those z 0m and z 0h schemes for different seasons. The analyses show that the z 0m dynamics are related to vegetation dynamics and soil water freeze-thaw state, which are reproduced satisfactorily with current z 0m schemes. Further, it is demonstrated that the heat flux simulations are very sensitive to the diurnal variations of z 0h . The newly developed z 0h schemes all capture, at least over the sparse vegetated surfaces during the winter season, the observed diurnal variability much better than the original one. It should, however, be noted that for the dense vegetated surfaces during the spring and monsoon seasons, not all newly developed schemes perform consistently better than the original one. With the most promising schemes, the Noah simulated sensible heat flux, latent heat flux, T sfc , and soil temperature improved for the monsoon season by about 29%, 79%, 75%, and 81%, respectively. In addition, the impact of T sfc calculation and energy balance closure associated with measurement uncertainties on the above findings are discussed, and the selection of the appropriate z 0h scheme for applications is addressed.

The interactions between soil–biosphere–atmosphere (ISBA) land surface model multi-energy balance (MEB) option in SURFEXv8 – Part 2: Introduction of a litter formulation and model evaluation for local-scale forest sites

“…The Bowen ratio closure method is often adopted to correct the non-closure. It takes on the assumption that the Bowen ratio (ratio of the sensible to the latent heat fluxes) is well estimated by the eddy covariance system, so that the turbulent fluxes can be adjusted while conserving the Bowen ratio to ensure closure (Blyth et al, 2010;Zheng et al, 2014;Er-Raki et al, 2008). The adjusted sensible and latent heat fluxes can be computed as…”

Determination of the Optimal Mounting Depth for Calculating Effective Soil Temperature at L-Band: Maqu Case

“…In 2008, a soil moisture monitoring network was set up at Maqu [28,29]. Maqu is located in the source region of the Yellow River and the east margin of the Tibetan Plateau.…”

“…To avoid introducing the additional complexity of frozen soil, the calculation in Section 3.2 is based only on the time series where ST > 0. Additionally, to obtain T e f f time series via the Wilheit's scheme, the Noah Land surface model [28] was adopted to generate ST/SM profiles with 37 layers (0 to 500 cm) between 12 and 28 June 2010.…”

Effects of climate variability and human activity on terrestrial water storage changes at basin scale: a case study of the Yangtze river basin

“…In this study, we extend on the previous study of Zheng et al (2014) by assessing parameterizations of roughness lengths for Tsfc and heat fluxes estimation at a regional scale for the Tibetan Plateau. Furthermore, we explore their effects on the simulations of water fluxes and states.…”

“…This kind of revision was performed by Zheng et al (2014), in which they used field measurements to revise the values of z0m for Z95, C09 and Z12 for a Tibetan site in different seasons. Zheng et al (2014) showed that revising the values for z0m and z0h dramatically improves the performance of the Noah LSM on the simulations of Tsfc and surface heat fluxes at a point scale, and suggested using the C09 with the newly revised z0m for actual application, due to its consistent performance in different seasons.…”