ISSN 1006-9895

CN 11-1768/O4

Physically Consistent Atmospheric Variational Objective Analysis and Applications over Tibetan Plateau (II): Cloud-precipitation, heat and moisture structures in the Naqu region

1.Sun Yat-sen University;2.National Meteorological Information Center;3.State Key Laboratory of Severe Weather,Chinese Academy of Meteorological Sciences;4.Guangdong Province Key Laboratory for Climate Change and Natural Disaster Studies,School of Atmospheric Sciences,Sun Yat-sen University,Southern Marine Science and Engineering Guangdong Laboratory Zhuhai

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    This study sets up a long-term (2013-2017) dynamically and thermodynamically consistent atmospheric dataset over the Tibetan Plateau-Naqu analysis region. This dataset is derived by the constrained variational objective analysis with ground-based, sounding, and satellite measurements as well as ERA-Interim reanalysis data. Using averaged results from this five-year dataset, the annual evolutions of the atmospheric basic environments, cloud-precipitation, and large-scale dynamic and thermal structures in the Naqu analysis region are analyzed. The results show that: 1) the seasonal variation of wind speed above 350 hPa is significant, with a maximum (> 50 m/s) from November to February in the next year, and the vertical variation of wind speed is the weakest while that of temperature is the strongest from July to August. The high humidity area is located at 350 - 550hPa in summer and autumn but at 300 - 400 hPa in winter and spring. 2) The precipitation in the analysis region is rich from June to early July. In spring, autumn, and winter, the layer of 300 - 400hPa (as the junction of atmospheric ascending and descending motion) is the cloud concentration area. But in summer, the enhanced atmospheric ascending convection and water vapor lead to an increase of total and high clouds whereas a decrease of medium and low clouds. 3) The surface latent heat flux and the total air-column latent heat are the strongest whereas the air-column net radiative cooling is the weakest in summer. The strong surface sensible heating in the plateau leads to the horizontal warm advection below 500hPa, while the strong westerly and radiative cooling cause the cold advection above 500hPa. In addition, the analysis region is characterized by dry advection in the whole year, however, there is a weak moist advection in summer. 4) The apparent heat source Q1 has obvious vertical stratification characteristics, that is, showing diabatic cooling below 500 hPa and diabatic heating in 300 - 500 hPa and 100 - 150 hPa in the whole year; while the layer of 150~300 hPa has diabatic cooling in the dry seasons (winter and spring) and diabatic heating in the wet seasons (from the end of spring to autumn). In summer, the entire air column is almost dominated by diabatic heating because of the enhanced ascending motion, net latent heating, the transport of sensible heat by rising turbulence, and the existence of high clouds.

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  • Received:May 08,2021
  • Revised:October 11,2021
  • Adopted:October 18,2021
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