# Effect of Mesoscale Land Use Change on Characteristics of Convective Boundary Layer: Semi-Idealized Large Eddy Simulations over Northwest China

• Corresponding author: Shuwen ZHANG, zhangsw@lzu.edu.cn
• Funds:

Supported by the National Key Research and Development Program of China (2017YFC1502101), National Natural Science Foundation of China (41575098), and Specialized Research Fund for the Doctoral Program of Higher Education (20120211110019)

• doi: 10.1007/s13351-018-7185-8
• Although large-scale topography and land use have been properly considered in weather and climate models, the effect of mesoscale and microscale heterogeneous land use on convective boundary layer (CBL) has not been fully understood yet. In this study, the influence of semi-idealized strip-like patches of oases and deserts, which resemble irrigated land use in Northwest China, on the CBL characteristics, is investigated based on the Weather Research and Forecasting (WRF)-large eddy simulation (LES) driven by observed land surface data. The influences of soil water content in oases on aloft CBL flow structure, stability, turbulent kinetic energy (TKE), and vertical fluxes are carefully examined through a group of sensitivity experiments. The results show that secondary circulation (SC)/turbulent organized structures (TOS) is the strongest/weakest when soil water content in oases is close to saturation (e.g., when the oases are irrigated). With the decrease of soil water content in oases (i.e., after irrigation), SC (TOS) becomes weak (strong) in the lower and middle CBL, the flux induced by SC and TOS becomes small (large), which has a dramatic impact on point measurement of eddy covariance (EC) fluxes. The flux induced by SC and TOS has little influence on EC sensible heat flux, but great influence on EC latent heat flux. Under this circumstance, the area averaged heat flux cannot be represented by point measurement of flux by the EC method, especially just after irrigation in oases. Comparison of imbalance ratio (i.e., contribution of SC and TOS to the total flux) reveals that increased soil moisture in oases leads to a larger imbalance ratio as well as enhanced surface heterogeneity. Moreover, we found that the soil layer configuration at different depths has a negligible impact on the CBL flux properties.
• Fig. 1.  Schematic diagram showing the coupling of the LES model to the LSM.

Fig. 2.  Temporal evolutions of soil water content at four different depths (0.04, 0.10, 0.40, and 0.80 m) from 1 to 25 August (irrigation was carried out on 29 July) at observation sites of (a) Daman and (b) Shenshawo.

Fig. 3.  Snap shots of (a) vertical velocity and (b) water vapor mixing ratio, averaged along the y-axis of the study domain, after 3.5-h integration for D03-10S.

Fig. 4.  Temporal averages of vertical velocity ($\overline w$) for (a) D03-10S and (b) D23-10S, and TOS ($[\overline w ] - {[\overline w ]_{\rm p}}$) for (e) D03-10S and (f) D23-10S. The SC (${[\overline w ]_{\rm p}}$) averaged along the y-axis of the domain for (c) D03-10S and (d) D23-10S. Values in all panels are at the height of 100 m, and the contours range from 0.1 to 0.6 m s–1 at an interval of 0.1 m s–1 in (a, b, e, f).

Fig. 5.  (a) Standard deviation of temporal average of vertical velocity, (b) temporal average of velocity in the x-direction, and (c) Ri at the height of 100 m (dot-dashed line is background atmosphere Ri).

Fig. 6.  Comparison of normalized total flux, EC, SC, and TOS for (a) sensible heat and (b) latent heat fluxes for case D03-10S.

Fig. 7.  Comparison of vertical profiles of (a) normalized vertical advection sensible heat flux ($[\overline w \overline \theta ]$), (b) SC sensible heat flux ($[{[\overline w ]_{\rm p}}{[\overline \theta ]_{\rm p}}]$), and (c) TOS sensible heat flux ($[\overline w _{\rm p}'\overline \theta _{\rm p}']$), for cases D03-10S and D23-10S.

Fig. 8.  As in Fig. 7, but for latent heat flux.

Fig. 9.  Vertical variations of horizontal domain average of the imbalance ratios for (a) sensible heat flux, (b) SC sensible heat flux, and (c) TOS sensible heat flux.

Fig. 10.  As in Fig. 9, but for latent heat flux.

Fig. 11.  Comparison of the simulated (a) soil temperature and (b) soil water content over oases for D03-10S (dashed line) and D03-10SA (solid line) with the observations (dots) at depth of 0.1 m.

Fig. 12.  Normalized vertical profiles of (a) total heat flux and (b) total latent heat flux from D03-10S and D03-10SA.

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###### 通讯作者: 陈斌, bchen63@163.com
• 1.

沈阳化工大学材料科学与工程学院 沈阳 110142

## Effect of Mesoscale Land Use Change on Characteristics of Convective Boundary Layer: Semi-Idealized Large Eddy Simulations over Northwest China

###### Corresponding author: Shuwen ZHANG, zhangsw@lzu.edu.cn;
• 1. School of Atmospheric Sciences, Chengdu University of Information Technology, Chengdu 610225
• 2. Key Laboratory for Semi-Arid Climate Change of the Ministry of Education, College of Atmospheric Sciences, Lanzhou University, Lanzhou 730000
• 3. Shenyang Central Meteorological Observatory, Shenyang 110016
• 4. Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou 730000
Funds: Supported by the National Key Research and Development Program of China (2017YFC1502101), National Natural Science Foundation of China (41575098), and Specialized Research Fund for the Doctoral Program of Higher Education (20120211110019)

Abstract: Although large-scale topography and land use have been properly considered in weather and climate models, the effect of mesoscale and microscale heterogeneous land use on convective boundary layer (CBL) has not been fully understood yet. In this study, the influence of semi-idealized strip-like patches of oases and deserts, which resemble irrigated land use in Northwest China, on the CBL characteristics, is investigated based on the Weather Research and Forecasting (WRF)-large eddy simulation (LES) driven by observed land surface data. The influences of soil water content in oases on aloft CBL flow structure, stability, turbulent kinetic energy (TKE), and vertical fluxes are carefully examined through a group of sensitivity experiments. The results show that secondary circulation (SC)/turbulent organized structures (TOS) is the strongest/weakest when soil water content in oases is close to saturation (e.g., when the oases are irrigated). With the decrease of soil water content in oases (i.e., after irrigation), SC (TOS) becomes weak (strong) in the lower and middle CBL, the flux induced by SC and TOS becomes small (large), which has a dramatic impact on point measurement of eddy covariance (EC) fluxes. The flux induced by SC and TOS has little influence on EC sensible heat flux, but great influence on EC latent heat flux. Under this circumstance, the area averaged heat flux cannot be represented by point measurement of flux by the EC method, especially just after irrigation in oases. Comparison of imbalance ratio (i.e., contribution of SC and TOS to the total flux) reveals that increased soil moisture in oases leads to a larger imbalance ratio as well as enhanced surface heterogeneity. Moreover, we found that the soil layer configuration at different depths has a negligible impact on the CBL flux properties.

Reference (36)

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