Structures of Different Tibetan Plateau Vortex Types

A Tibetan Plateau vortex (TPV) is defined as a shallow cyclonic meso-α-scale low-pressure system that originates over the main body of the Tibetan Plateau in the warm season and presents most notably at 500 hPa. It is the main precipitation-inducing weather system over the plateau in the warm season.

Knowledge of the TPV structure is of considerable importance for understanding the generation and development mechanisms of this mesoscale system. However, our understanding of vortex structures and our ability to classify them on a physical basis is limited due to insufficient observations. The high-resolution NCEP Climate Forecast System Reanalysis (CFSR) dataset is used in the present paper to investigate the general structural features of various types of mature TPV through classification and composite structure analysis. Results indicate that the dynamic and thermodynamic structures show regional and seasonal dependency, as well as being influenced by attributes of translation, associated precipitation, and the South Asian high (SAH).

The common precipitating TPV (type I), frequently occurring in the west–east-oriented zonal region between 33° and 36°N, is a notably low-level baroclinic and asymmetric system. It resides within a large-scale confluent zone and preferentially travels eastwards, potentially moving out of the plateau. The heavy rain vortex (type II) corresponds to a deep vortex circulation occurring in midsummer. The low-level baroclinic sub-category (type IIa) is associated with a low-level jet and mainly originates in the area (32°–35°N, 86°–94°E), preferentially moving east of 90°E and even away from the plateau; meanwhile, the nearly upright sub-category (type IIb), which has a cold center at low levels and a warm center at mid-upper levels, is a quasi-stationary and quasi-symmetric system favorably occurring west of 92°E. A western-pattern SAH exists in the upper troposphere for these two sub-categories. The springtime dry vortex in the western plateau (type III) is warm and shallow (~100 hPa deep), and zonal circulation dominates the large-scale environmental flows in the middle and upper troposphere. The precipitating vortex in the southern plateau occurring during July–August (type IV) is not affected by northerly flow at low levels. It is vertically aligned and controlled by a banded SAH.