TY - JOUR

T1 - Impact of surface heterogeneity on energy imbalance

T2 - A study using LES

AU - Inagaki, Atsushi

AU - Letzel, Marcus Oliver

AU - Raasch, Siegfried

AU - Kanda, Manabu

N1 - Funding Information: This research was supported by CREST (Core Research for Evolution Science and Technol- ogy) of JST (Japan Science and Technology Corporation) and by the German National Academic Foundation, by the Deutsche For- schungsgemeinschaft Grant No. RA 617/6-1, and German BMBF Grants 07ATF37-UH and 01LD0103. All calculations were performed on the IBM Regatta P690 series of the Nord- deutscher Verbund fu ̈ r Hoch- und Ho ̈chs- tleistungsrechnen (HLRN) in Hannover and suggestions. Berlin, Germany (www.hlrn.de). We thank G. Steinfeld and J. Uhlenbrock (University of Fig. 8. Total domain average of vertical heat transport due to (a) TOS flux and (b) mesoscale heat flux with a horizontal mean wind. U g is the wind speed along the x direction (i.e., along the direc- tion of heterogeneity) and Vg is in the y direction. A. INAGAKI et al. 197February 2006 Hannover, Hannover, Germany) and R. Mor- iwaki (Tokyo Institute of Technology, Tokyo, Japan) for their useful comments and sugges-

PY - 2006/2

Y1 - 2006/2

N2 - Recent observational studies have described the non-closure of the energy balance when the eddy co-variance (EC) method is used for the measurements. We investigated this problem using a numerical simulation of a heterogeneous surface region. A typical daytime boundary layer was simulated, using the large eddy simulation (LES) method in which horizontal heterogeneity was imposed on the ground surface heating as a one-dimensional sinusoidal variation. This horizontal heterogeneity is expected to produce a mesoscale circulation. We decomposed the total vertical heat flux into the EC turbulent flux, the heat flux due to a mesoscale circulation (hereafter, mesoscale flux), and the "residual flux". The sum of the mesoscale flux, and residual flux accounts for the energy imbalance if we estimate the total flux only from the EC method. The numerical results demonstrated that larger amplitude of surface heating caused larger mesoscale flux, but smaller residual flux. As a result, the energy imbalance became minima at some weak amplitude of surface heating. The residual flux was caused by the turbulent organized structure (hereafter, TOS), which is a cluster of thermals moving, with a larger time scale than that of individual plumes. The larger surface heating amplitude weakened the TOS due to the following two mechanisms; (1) the TOS is organized in roll due to the strong horizontal pressure gradient, (2) the higher horizontal wind speed, parallel to the mesoscale circulation, advects the TOS faster then the ergodicity works better. The other cases with gepstrophic winds, resulted in the decrease of the energy imbalance with increasing wind velocity.

AB - Recent observational studies have described the non-closure of the energy balance when the eddy co-variance (EC) method is used for the measurements. We investigated this problem using a numerical simulation of a heterogeneous surface region. A typical daytime boundary layer was simulated, using the large eddy simulation (LES) method in which horizontal heterogeneity was imposed on the ground surface heating as a one-dimensional sinusoidal variation. This horizontal heterogeneity is expected to produce a mesoscale circulation. We decomposed the total vertical heat flux into the EC turbulent flux, the heat flux due to a mesoscale circulation (hereafter, mesoscale flux), and the "residual flux". The sum of the mesoscale flux, and residual flux accounts for the energy imbalance if we estimate the total flux only from the EC method. The numerical results demonstrated that larger amplitude of surface heating caused larger mesoscale flux, but smaller residual flux. As a result, the energy imbalance became minima at some weak amplitude of surface heating. The residual flux was caused by the turbulent organized structure (hereafter, TOS), which is a cluster of thermals moving, with a larger time scale than that of individual plumes. The larger surface heating amplitude weakened the TOS due to the following two mechanisms; (1) the TOS is organized in roll due to the strong horizontal pressure gradient, (2) the higher horizontal wind speed, parallel to the mesoscale circulation, advects the TOS faster then the ergodicity works better. The other cases with gepstrophic winds, resulted in the decrease of the energy imbalance with increasing wind velocity.

UR - http://www.scopus.com/inward/record.url?scp=33646396486&partnerID=8YFLogxK

U2 - 10.2151/jmsj.84.187

DO - 10.2151/jmsj.84.187

M3 - Article

AN - SCOPUS:33646396486

VL - 84

SP - 187

EP - 198

JO - Journal of the Meteorological Society of Japan

JF - Journal of the Meteorological Society of Japan

SN - 0026-1165

IS - 1

ER -