Formation of a kind of heavy‐precipitation‐producing mesoscale vortex around the Sichuan Basin: An along‐track vorticity budget analysis. (3rd January 2020)

• Record Type: Journal Article
• Authors: Feng, Shuang‐Lei; Jin, Shuang‐Long; Fu, Shen‐Ming; Sun, Jian‐Hua; Zhang, Yuan‐Chun
• Is Part Of: Atmospheric science letters. Volume 21:Number 1(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-01-03
• Subjects: Atmospheric physics -- Periodicals; 551
• DOI: 10.1002/asl2.949
• Languages: English
• ISSNs: 1530-261X

Abstract

Abstract: This study investigates the formation of a type of mesoscale vortex around the Sichuan Basin (i.e., the southwest vortex [SWV]) that usually induces heavy precipitation, based on a semi‐idealized simulation of eight similar SWV‐formation events. After producing a reasonable SWV that shares salient features with the events used in composite, a trajectory analysis is conducted and an along‐track vorticity budget is constructed. The results show that approximately 64.7% of the air particles related to SWV formation originate from four source regions outside the vortex. The largest contribution of cyclonic vorticity associated with the SWV formation (approximately 67.7%) comes from the lower levels southwest of the vortex and is due mainly to tilting. The second‐largest contribution (approximately 19.4%) is made by air particles that originate from the upper levels south of the SWV and is also due mainly to tilting. By contrast, for the other two sources (the upper levels west and southwest of the vortex), the convergence‐related horizontal shrinking generally dominates their cyclonic‐vorticity production. Overall, along the tracks of the air particles, vertical motions and water‐vapor phase transitions affect the vorticity variation significantly via modulating divergence‐related vorticity production/dissipation (i.e., the stretching effect), and this is vital for the SWV formation. Abstract : Based on a semi‐idealized simulation of eight similar southwest vortex (SWV) formation events under the influences of the eastward‐propagating convective systems that originate over the Tibetan Plateau, a semi‐idealized SWV is produced. This vortex shows the salient common features of the eight events and is therefore used as a representative for this type of event. The origins of the air particles that form the SWV are tracked and analyzed as the above shows. The results show that approximately 64.7% of the air particles related to SWV formation originate from four source regions outside the vortex. The largest contribution of cyclonic vorticity associated with the SWV formation (approximately 67.7%) comes from the lower levels southwest of the vortex and is due mainly to tilting. The second‐largest contribution (approximately 19.4%) is made by air particles that originate from the upper levels south of the SWV and is also due mainly to tilting. By contrast, for the other two sources (the upper levels west and southwest of the vortex), the convergence‐related horizontal shrinking generally dominates their cyclonic‐vorticity production.