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 500 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.

The Effect of Qinghai-Tibet Plateau Forcing on the Meso-Scale Rain-bearing Circulation Systems over Eastern China during Presummer Rainy Season

“…An intensified LLJ, wind speed 15m s-1, is simulated around the south border of the QTP. This result is similar to that obtained in another numerical case study by Dell'Osso and Chen (1986). Also Bannon (1982) found that the slope of the Somali high land is essential in determining the strength of the cross-equatorial eastern Africa LLJ ; the steeper the slope, the stronger the LLJ.…”

“…The horizontal grid length is 1.875* longitude/latitude. This resolution may be too coarse for simulating meso-scale * disturbances, but is appropriate if our aim is to simulate the broad features of the circulation systems rather than its detail (Dell'Osso and Chen, 1986). The integration area is 0*N to 70*N and 40*E to 160*E. The boundary values are updated every time step (15 min) and obtained from a linear interpolation of the analyses taken at 12 h intervals.…”

Effect of the atmospheric heat source on the development and eastward movement of the Tibetan Plateau vortices

“…More cases for both types of vortices should be selected and numerical experiments should be performed in the future, to gain more credible conclusions on the evolution and movement mechanisms of the plateau vortices. In addition, because the topography can affect the dynamic and thermodynamic processes on the atmosphere over the Tibetan Plateau, and is an important factor affecting the evolution process of the vortices (Dell'Osso and Chen, 1986;Shen et al, 1986a;Wang, 1987), the influence of the topography on the evolution of the plateau vortices should also be investigated through numerical experiments in the future.…”

“…It is pointed out that the sensible heating exerts a major effect on the formation of the vortices, while the condensation latent heat release is most important during their development phase (Lhasa Group for Tibetan Plateau Meteorology Research, 1981;Dell'Osso and Chen, 1986;Shen et al, 1986aShen et al, , 1986bWang, 1987;Li and Zhao, 2002). Ding and Lu (1990) used a five-layer primitive equation model to simulate the eastward movement of a vortex over the Tibetan Plateau.…”

Impacts of Diabatic Heating on the Genesis and Development of an Inner Tibetan Plateau Vortex

“…The genesis and development of TPVs have been fundamentally attributed to the dynamic and thermodynamic effects of the TP (Luo, ; Wu & Chen, ; Zhang & Zhu, ). As for dynamic effects, the high terrain forces the lower tropospheric flow to split into two branches that join downstream in a region of convergence (Dell'Osso & Chen, ). As for thermodynamic effect, surface sensible heating plays an important role in the development of vortices over the TP in summer (Shen et al, ; Shen & Huang, ).…”