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Theoretical and Applied Climatology

, Volume 105, Issue 1–2, pp 217–228 | Cite as

The study of near-ground free convection conditions at Nam Co station on the Tibetan Plateau

  • Degang Zhou
  • Rafael Eigenmann
  • Wolfgang Babel
  • Thomas Foken
  • Yaoming Ma
Original Paper

Abstract

This study investigates the near-ground free convection conditions (FCCs) based on eddy covariance (EC) measurements at Nam Co station near the Nam Co Lake on the Tibetan Plateau (TP). The spatial and temporal structure of EC measurements at this station is evaluated by using the comprehensive software package TK2 together with a footprint model. The obtained high-quality turbulent flux data are used to study the occurrence of FCCs, which can be detected with the EC system by calculating the stability parameter. Two types of generation of FCCs can be identified. (1) During the wind direction change of a diurnal thermally forced land-lake circulation system in the morning, strongly reduced wind speeds and simultaneously high buoyancy fluxes lead to a period of dominance of buoyancy over shear, and hence, to the occurrence of FCCs. (2) On days with the appearance of clouds, the land-lake circulation is weakened or reversed, dependent on the temperature gradients between the land and the Nam Co Lake. During the period of adaptation of the land-lake breeze to the alternating situation of heating differences, wind speeds decrease and buoyancy again dominates over shear near the ground. These are the situations where FCCs are also detected during the entire day at Nam Co station. The investigation of FCCs regarding the whole measurement period shows that FCCs can be mainly attributed to case (1) during the non-monsoon period, while FCCs are generated by both mechanisms (1 and 2) during the monsoon season. An impact of the FCCs on the near-ground profiles of air temperature and humidity is demonstrated. The FCCs are assumed to play an important role for the land surface-atmosphere exchange processes and the atmospheric boundary layer (ABL) conditions on the TP by providing an effective transport mechanism of near-ground air mass characteristics into upper parts of the ABL.

Keywords

Tibetan Plateau Atmospheric Boundary Layer Eddy Covariance Horizontal Wind Speed Surface Skin Temperature 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Notes

Acknowledgements

This paper was realized under the auspices of the National Natural Science Foundation of China (40825015), the Chinese National Key Program for Developing Basic Sciences (2010CB951701), and EU-FP7 CEOP-AEGIS(212921). The authors wish to acknowledge the support and data provision by the participants of Nam Co Monitoring and Research Station for Multisphere Interactions. The visit of the first author at Bayreuth was funded by the German Science Foundation (DFG) within the Priority Program SPP 1372 and the Chinese Academy of Science. The contribution of the University of Bayreuth to this study was funded within the DFG projects FO 226/18-1 and FO 226/19-1.

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Copyright information

© Springer-Verlag 2010

Authors and Affiliations

  • Degang Zhou
    • 1
  • Rafael Eigenmann
    • 2
  • Wolfgang Babel
    • 2
  • Thomas Foken
    • 2
  • Yaoming Ma
    • 3
  1. 1.Centre for Monsoon System Research, Institute of Atmospheric PhysicsChinese Academy of SciencesBeijingChina
  2. 2.Department of MicrometeorologyUniversity of BayreuthBayreuthGermany
  3. 3.Institute of Tibetan Plateau ResearchChinese Academy of SciencesBeijingChina

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