Impact of Mesoscale Motions on Monin-Obukhov Similarity and Surface Energy Balance over a Homogeneous Surface

Yang Guo,Hongchao Zuo

doi:10.1155/2017/6425695

Abstract

Mesoscale motions are an important factor influencing the applicability of Monin-Obukhov similar theory (MOST) and the surface energy balance. The heterogeneous surface and the vegetation-covered surface also increase the complexity of these two problems. In order to understand the effect of mesoscale motions on turbulent fluxes more clearly, this study analyzes the impact of mesoscale motions on MOST and surface energy balance using the multiresolution decomposition method and the observational data over a homogeneous bare soil surface. Two conclusions are obtained: (1) When mesoscale motions are excluded, the scatter of similarity relations is evidently reduced; the observed values of the dimensionless velocity gradient and dimensionless temperature gradient in stable conditions become less than the values estimated using the universal functions, and the flux-variance relationship for temperature clearly deviates from the −1/3 power law. (2) When mesoscale motions are excluded, the number of energy balance closure outliers at night is dramatically reduced, and the energy balance ratio (EBR) is increased. However, when turbulent mixing is weak, even if mesoscale motions are excluded, the EBR is still relatively low, which is possibly due to the fact that the energy is mainly transported by mesoscale motions instead of turbulence.

Highlights

Turbulence is an important atmospheric movement in the boundary layer, and the exchange of energy and matter between surface and atmosphere is mainly conducted by turbulent transport
There is a large scatter in the relationship between φm and ζ before mesoscale motions are removed (Figure 3(a)), and the scatter is even larger in stable conditions
After mesoscale motions are thoroughly excluded by the EMT 3 method (Figure 3(c)), the relationship between φm and ζ is further improved, but the observed values of φm become smaller than the values estimated using the five universal functions in stable conditions

Summary

Introduction

Turbulence is an important atmospheric movement in the boundary layer, and the exchange of energy and matter between surface and atmosphere is mainly conducted by turbulent transport. With the advance of observational research, the energy balance closure problem [6,7,8,9], noticed in the 1980s, further complicated the application of MOST. Foken [2] pointed out that if the energy balance closure problem is caused by underestimation of the turbulent fluxes, the accuracy of the universal functions of MOST will be affected. The applicability of MOST and the surface energy balance closure have become two significant problems restricting the development of boundary layer and land-surface process.

Methods

Results

Conclusion