Pergamon Phys. Chem Xurth (B), Vol. 25,No. 2, pp. 135-139,200O 0 2000 Elsevier Science Ltd All rights reserved 1464-l 909/00/$ - see front matter PII: S1464-1909(99)00124-O Calculation of Near-Surface Layer Turbulent Transport and Analysis of Surface Thermal Equilibrium Features in Nagqu of Tibet Zhiqui Gao’, Jiemin Wang’, Yaomin Ma’, Joon Kim’, Taejin Choi’, Heechoon Lee*, Jun Asanuma3, Zhongbo Su4 ‘Lanzhou Institute of Plateau Atmospheric Physics, Academia Sinica, Gansu, Lanzhou 730000, China. ‘Department of Atmospheric Science, Yonsei University, Korea 3Department of Civil and Environmental Engineeering, Nagaoka University, Japan. 4Wageningen UR, ALTERRA Green World Research, P.O. Box 47,670O AA Wageningen, The Netherlands. Received 23 April 1999; revised 23 September 1999; accepted 24 September 1999 Abstract. This study investigates aerodynamic roughness zO, drag coefficient C, , momentum flux 2 , sensible heat flux H and latent heat flux LE in terms of the extended gradient method, followed by dealing with net radiation R and coefficient of soil thermal exchange G with the daily variation by dint of the thermal balance technique and Fourier law. The data used in this analysis are those of the Nagqu near-surface layer flux observations obtained during GAME/Tibet (GEWEX Asian Monsoon Experiments/Tibet) in the period June 1 to July 20, 1998. 0 2000 Elsevier Science Ltd. All rights reserved 1 Introduction As the most prominent and complicated terrain on the globe, the Tibetan plateau, with an elevation of more than 4000 m on average above mean sea level (msl) makes up approximately one fourth of the land area of China Long-term operation and research have shown that the giant prominence exerts thermal effects on the atmosphere, thus greatly influencing circulations over China, Asia and even the globe. Its land surface processes, especially momentum transport, energy exchange and water cycle, has been one of the topics of great importance in Tibetan plateau meteorology. Yeh et al. (1979) performed a study of long-term averaged turbulent heat with the mean drag coefficient CD of 8.0 X 10.’ based on the dataset of the target region. Chen et al. (1984) formulated an empirical expression of CD with the aid of the technique for decadal total of sensible/latent heat measured over the plateau for May - August, 1979, indicating that CD ranges over 3 - 5 X 10.’ for most of the highland. Ma (1990) indicated that the CD is not a constant but a function of wind, which contains the integrated effects of atmospheric stability and wind gradient in her study on summer turbulent transport features in the east Tibetan near-surface layer through the total transfer coefficient and relations among relevant factors. The present study investigated aerodynamic roughness zO, drag coefficient c, , momentum flux 2 , sensible heat flux H and latent heat flux LE in terms of the extended gradient method for the GAME/ Tibet Nagqu near-surface layer flux observations made in the Correspondence to: Dr. Z. Su, Wageningen UR, ALTERRA Green World Research, P.O. Box 47, 6700 AA Wageningen, the Netherlands, E-Mail: su@sc.dlo.nl 135 period June 1 to July 20, 1998, followed by dealing with net radiation R and coefficient of soil thermal exchange G with the daily variation by dint of the thermal balance technique and Fourier law, arriving at realistic results and proving the usefulness of the schemes. 2 Experimental Site and Observations The team consisting of scientists from Japan, South Korea and China made a large-scale meteorological observation experiment (GAME/Tibet) in of the plateau in April to September, 1998 for a range of measurements by means of advanced instruments. Used in this work were the profile data measured for June 1 to July 20 at the flux observing site ( 31°22.164N, 91’54.165E) in the suburb of Nagqu city, which was located 4496 m above msl in the central highland. There were no plants higher than 10 cm and small stones were scattered over ground with grass 2-4 cm tall distributed unevenly over the meadow, and the terrain was open and covered with sandy loam. The location made the observing site well-representative on a regional basis. 2 km to the east were continuous mountains with the mean height around 4650 m above msl and little or no vegetation covered; 3 km to the south there stretched the Qinghai-Tibet highway where few cars passed over; 6-7 km to the southwest were mountains with permanently snow-covered tops, looking magnificent; to the west the ground is quite level and open; 2 km to the northwest and north, mountains are connected with those to the east. The used meteorological facilities, including the 3D supersonic anemograph, were offered by Yonsei University of Korea and made measurement of the direction/speed of winds at 3.5 m, 2.2 m, 1.3 m and 0.7 m level; temperature, humidity and vapor pressure at 3.5 m and 1.3 m level; the temperature and thermal flux of soil, 0.015 m and 0.04 m deep; up- and downward long- and shortwave radiation, and 3D turbulent data in the near-surface layer. The sampling interval was 30 min. 3 Gradient Method-Calculated Turbulent Transport Coefficient and FIux The vertical distribution of the means in the near-surface layer takes an approximate logarithmic profile so that the gradients