Based on the four-times-daily ERA-Interim data with the resolution of 0.75°×0.75°,the structure and evolution characteristics of a transverse shear line(TSL)over the Qinghai-Tibet Plateau in April 2017 ...Based on the four-times-daily ERA-Interim data with the resolution of 0.75°×0.75°,the structure and evolution characteristics of a transverse shear line(TSL)over the Qinghai-Tibet Plateau in April 2017 were analyzed,and the influence mechanism of the frontogenesis and frontolysis caused by the upper-level jet on its evolution was also investigated.The results show that the TSL was mainly located near the axis of the positive vorticity zone,which was a low-value area of the wind speed.It was a shallow baroclinic system with weak ascending motion.In the vertical direction,the TSL extended to the lowest height at 00:00 and the highest at 18:00.In the horizontal direction,the length of the TSL in the east-west direction was relatively shorter during 00:00-06:00 and relatively longer during 12:00-18:00.Besides,the position of the TSL was slightly northward at 06:00 and slightly southward at 18:00.The moving direction of the TSL was generally consistent with that of the upper-level jet.In addition,the vertical stretching height of the TSL and the near-surface wind speed were positively correlated with the intensity of the upper-level jet.The calculation by frontogenesis function indicates that the frontogenesis(frontolysis)was conducive to the formation(weakening)and strengthening(dissipation)of the TSL.The horizontal deformation-induced and diabatic heating-induced frontogenesis were favorable for the formation of the TSL,while the middle-level horizontal convergence-induced and diabatic heating-induced frontogenesis were beneficial to its maintenance.Besides,the moving direction and baroclinicity of the TSL over the Qinghai-Tibet Plateau were determined by the horizontal deformation-induced frontogenesis.In the frontogenesis function,the terms of horizontal deformation and horizontal convergence together determined the position of the TSL,and the diabatic heating term was conducive to the upward extension of the TSL.展开更多
Geostrophic adjustment and frontogenesis are examined by means of the 2-D ARPS model. The simulation shows that.without the large-scale forcing,both the frontogenesis and frontolysis are observed during the geostrophi...Geostrophic adjustment and frontogenesis are examined by means of the 2-D ARPS model. The simulation shows that.without the large-scale forcing,both the frontogenesis and frontolysis are observed during the geostrophic adjustment process and the intensity of the front oscillates in the case of no discontinuity.The convergence (divergence) induced by the secondary circulation is the most important factor for frontogenesis (frontolysis) at the top and bottom boundaries.The amplitude and period of oscillation are dependent on the initial atmospheric stratification and the Coriolis frequency,and they are related to the inertio-gravity wave.展开更多
基金Supported by Project of Qinghai Science and Technology Department (2020-ZJ-739)Project of Key Laboratory for Disaster Prevention and Mitigation of Qinghai Province (QFZ-2021-Z04)Key Project of Qinghai Provincial Meteorological Bureau (QXZ2020-03)
文摘Based on the four-times-daily ERA-Interim data with the resolution of 0.75°×0.75°,the structure and evolution characteristics of a transverse shear line(TSL)over the Qinghai-Tibet Plateau in April 2017 were analyzed,and the influence mechanism of the frontogenesis and frontolysis caused by the upper-level jet on its evolution was also investigated.The results show that the TSL was mainly located near the axis of the positive vorticity zone,which was a low-value area of the wind speed.It was a shallow baroclinic system with weak ascending motion.In the vertical direction,the TSL extended to the lowest height at 00:00 and the highest at 18:00.In the horizontal direction,the length of the TSL in the east-west direction was relatively shorter during 00:00-06:00 and relatively longer during 12:00-18:00.Besides,the position of the TSL was slightly northward at 06:00 and slightly southward at 18:00.The moving direction of the TSL was generally consistent with that of the upper-level jet.In addition,the vertical stretching height of the TSL and the near-surface wind speed were positively correlated with the intensity of the upper-level jet.The calculation by frontogenesis function indicates that the frontogenesis(frontolysis)was conducive to the formation(weakening)and strengthening(dissipation)of the TSL.The horizontal deformation-induced and diabatic heating-induced frontogenesis were favorable for the formation of the TSL,while the middle-level horizontal convergence-induced and diabatic heating-induced frontogenesis were beneficial to its maintenance.Besides,the moving direction and baroclinicity of the TSL over the Qinghai-Tibet Plateau were determined by the horizontal deformation-induced frontogenesis.In the frontogenesis function,the terms of horizontal deformation and horizontal convergence together determined the position of the TSL,and the diabatic heating term was conducive to the upward extension of the TSL.
基金This research was supported by the National Natural Science Foundation of China under Grants:49675259 and 49735180The National Key Basic Research Development Program:CHERES
文摘Geostrophic adjustment and frontogenesis are examined by means of the 2-D ARPS model. The simulation shows that.without the large-scale forcing,both the frontogenesis and frontolysis are observed during the geostrophic adjustment process and the intensity of the front oscillates in the case of no discontinuity.The convergence (divergence) induced by the secondary circulation is the most important factor for frontogenesis (frontolysis) at the top and bottom boundaries.The amplitude and period of oscillation are dependent on the initial atmospheric stratification and the Coriolis frequency,and they are related to the inertio-gravity wave.
