Climatology of Tibetan Plateau vortices derived from multiple reanalysis datasets

Abstract

The Tibetan Plateau vortex (TPV) is a mesoscale weather system active in the near-surface layer, which is one of the major systems for the generation of precipitation in the Tibetan Plateau (TP). However, no long-term observations of the TPVs are available due to the scarcity of observations in the TP. Thereby, long-term, high-accuracy reanalysis products are a reliable source for the analysis of characteristic TPV activities and possible mechanisms behind. In the present study, an objective analysis method is implemented to obtain a complete dataset of TPV based on several reanalysis products, including the ERA-Interim, ERA40, JRA55, NCEP CFSR, and NASA MERRA2. The TPVs are detected and tracked by the minima in geopotential height at 500 hPa. Results indicate that the TPVs derived from multiple reanalysis products have quite similar spatial patterns and temporal variability. The characteristic parameters of the TPVs derived from a given reanalysis data are related to the resolution of this reanalysis product. Higher-resolution reanalysis products can yield more low-pressure systems, which explains why the TPVs derived from high-resolution reanalysis datasets generally have longer lifetime, stronger and larger vortex scale than those from low-resolution reanalysis products, although the total number of TPVs are similar. The annual average number of TPVs generated in the TP is 63.5, and these TPVs largely originate in the mountainous area of the central western TP around (34° N, 78–95° E) and a belt zone (30° N, 80–84° E) in the southern TP, where the elevation is around 5500 m. The TPVs often dissipate in low valleys and the lee side of mountains. They mainly occur in the warm season during May–September, most active in the summer and least active in the winter. More TPVs form in the daytime than in the nighttime. Those TPVs that move out of the TP account for less than 10–14% of all TPVs, and they usually follow three moving paths: eastward (6.9–7.8%), northeastward (2.3–3.4%) and southward (2.3–3.5%).