Numerical experiments on the genesis of vortices over the Qinghai-Tibet plateau

Abstract

The formation of a vortex and shear line over the Qinghai-Tibet Plateau (QTP) was investigated with numerical experiments using the ECMWF grid point model. The case chosen occurred between 24 and 26 July, 1982, when the south-west monsoon invaded the QTP and a vortex developed.The correct simulation of the vortex in the model shows that it is possible to predict the atmospheric circulation over the QTP and the consequent weather over China. When the simulation was rerun with a dry model (i.e., without the release of latent heat), it was found that only a weak vortex formed. This shows that the release of latent heat is an extremely important factor in the development of the vortex over the QTP, and confirms earlier diagnostic and synoptic studies.The surface sensible heat fluxes, large near the northern and southern flanks of the QTP, appear to have a damping effect on the formation of the vortex; i.e., the vortex was greatly intensified in their absence. It was also found that the intensity of the vortex was dependent upon the height of the QTP: when the mountain height was reduced, the westerly trough invaded the QTP and no vortex formed at 5 0 0 mb; when it was increased, the south-west monsoon travelled along the southern boundary of the QTP and intensified the low-level jet south of the vortex area.The results of a 48-h integration with a fine-mesh model (resolution 0.5" of latitude and longitude) showed an improvement in forecasting the location of the vortex with respect to the coarse-mesh model (1.875" of latitude and longitude). However, when compared with the coarse-mesh analysis, the intensity of the vortex was overpredicted. This may be due to mesoscale orographic forcing and exaggerated latent heating.

Clustering of Tibetan Plateau Vortices by 10–30-Day Intraseasonal Oscillation*

“…These mesoscale convective systems are called Tibetan Plateau vortices (Gao et al 1981;Tao and Ding 1981), whose geneses and development are largely influenced by the unique thermo-dynamical and dynamical environments of the plateau, such as topography, latent heat release, low-level convergence, surface sensible heating, etc. (e.g., Dell'Osso and Chen 1986;Gao 2000;Li et al 2002;Shen et al 1986;Shi et al 2008;Sugimoto and Ueno 2010;Wang 1987). The TP vortices usually form in the western and central plateau and propagate eastward with a life span of several hours to 3 days.…”

Characteristics of Summer Convective Systems Initiated over the Tibetan Plateau. Part I: Origin, Track, Development, and Precipitation

“…Various methods have been utilized in the processes, such as boundary layer observational analysis (Yanai and Li 1994;Gao et al 2002), objective analyses of synoptic weather and general atmospheric circulation (Ye 1981;Yanai et al 1992), statistical study of synoptic weather systems (Tao and Ding 1981;Leber et al 1995), analysis of satellite measurements (Jin 1997;Ueno 1998), diagnostic studies of meteorological variables and atmospheric energy (Dell'Osso and Chen 1986;Reiter 1987), numerical simulations (Shen et al 1986b), fluid dynamic experiments (Boyer and Chen 1987), and theoretic studies of dynamics (Xie 1981;Leroux 1993). The ultimate goal of these investigations is to describe the processes of thermodynamics and dynamics of the Tibetan Plateau, and to understand their impact on global climate change.…”

Subtropical Westerly Jet Influence on Occurrence of Western Disturbances and Tibetan Plateau Vortices

“…The structure of WDs has been explored in detail in both case studies (e.g., Dimri, 2004;Ramanathan & Saha, 1972) and composite studies (Hunt et al, 2017); and while the quantity of analogous research on TPVs is markedly less in the English literature, there have been several case studies (Dell'Osso & Chen, 1986;Wang, 1987) as well as a composite study (Feng et al, 2017). These studies indicate that despite substantial interpopulation variance, there are strong similarities between TPVs and WDs, for example, a warm-over-cold thermal structure, a quadrupolar signature in divergence, and a tropospheric vorticity column indicative of baroclinic growth.…”