A vertical transport window of water vapor in the troposphere over the Tibetan Plateau with implication for global change

Abstract. By using the multi-source data of meteorology over recent decades, this study discovered a summertime “hollow wet pool” in the troposphere with a center of high water vapor over Asian water tower (AWT) on the Tibetan Plateau (TP), where is featured by a vertical transport “window” in the troposphere. The water vapor transport in the upper troposphere extends from the vertical transport window over the TP with the significant connections among the Arctic, Antarctic and TP regions, highlighting an effect of TP’s vertical transport window of tropospheric vapor in the “hollow wet pool” on global change. The vertical transport window was built by the AWT’s thermal forcing in associated with the dynamic effect of the TP’s “hollow heat island”. Our study improve the understanding on the vapor transport over the TP with an important implication to global change.


. The ratio of strong convective clouds to total 48 clouds over the Tibetan Plateau (TP) is about 5 times to the global ratio, and the frequent 49 occurrences of strong convective clouds could be largely attributed to the TP's large 50 topography (Luo et al.,2011;Su et al.,2006). The water vapor in the tropical upper 51 troposphere is mainly originated from the tropical lower troposphere through convective 52 transport and evaporation of convectively transported or in situ produced cloud ices (Tian 53 et al.,2004;James, et al.,2008). Water vapor was first lifted by convection over the Bay 54 of Bengal and the South China Sea and then transported upwards the tropical tropopause 55 layer via the monsoon anticyclonic circulations towards Northwest India (Yanai, et al., 56 https://doi.org/10.5194/acp-2021-697 Preprint. Discussion started: 25 August 2021 c Author(s) 2021. CC BY 4.0 License. 1973;Chen, et al., 2012). TP is a moisture sink in summer, having a net moisture 57 convergence of 4 mm/day, where the convergence was enhanced from 1979 to 2018 58 (Feng and Zhou, 2012;Xu, et al., 2020). In general, Asian monsoon circulation provides 59 an effective pathway for regional water vapor transport to the TP (Wang, et al.,2017). An 60 important role of the anticyclone over the TP is verified in the exchange of water vapor 61 between the troposphere and stratosphere (Garny, et al., 2016;Fu, et al., 2006) . Many 62 studies have been focused on the transport of water vapor into upper troposphere and 63 lower stratosphere from the tropical oceans to the TP (Chen, et al., 2012;Wang, et 64 al.,2017;Xie, et al.,2018;Randel, et al.,2013) . However, not enough attention has been 65 paid to the vertical transport of water vapor in the troposphere over the TP. The following questions are also of great concern in the TP' vertical transport of 68 water vapor study with implication for global change, for example, what is the forcing 69 mechanism forming the vertical transport window of water vapor in the tropophere on the 70 TP? How is the AWT's special column constructor built for the vertical transport of 71 water vapor in the TP' troposphere? From the perspective of global atmospheric energy 72 and water vapor exchanges, this study characterizes a window of water vapor vertical 73 transport within the troposphere over the TP and the implication for global change.

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The daily meteorological data of cloud amount are provided by the meteorological 77 observatories in the TP in the period of 1979 to 2016. The AIRS remote sensing products 78 of water vapor and the ECMWF-interim data of meteorology are used in this study. 80 In this study, the inverse algorithm is used to calculate the apparent heat source Q1, 81 and the formula is as follows ( Su et al.,2006) : (1) 83 where T is air temperature; ω is the vertical velocity at the p coordinate, P0 = 1000 hPa;

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; V is the horizontal wind vector; θ is the potential temperature. 85 Vertical integration of Q1 is expressed as: 86 (2) 87 where ps is the surface air pressure, pt is the top air pressure, here taken as 100hpa.
88 89 In order to analyze the relationship between water vapor source tracing and its 90 channels in the atmospheric water cycle over the TP, the correlation vector calculation 91 was used to calculate the temporal and spatial variations of the water vapor transport 92 channel. The expression is:

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Through the correlation analysis of the whole layer of apparent heat source Q1 over 154 the plateau region, the three-dimensional structure of vorticity and divergence, it can be 155 found that the apparent heat source Q1 in TP are an important forcing factor (Figure 4). 156 The results show that the air heat island over the AWT is located at 300-500 hPa (