ISSN 1006-9895

CN 11-1768/O4

Potential vorticity source, potential vorticity circulationand their weather and climatic significance
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State Key Laboratory of Numerical Modelling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG), Institute of Atmospheric Physics, Chinese Academy of Sciences

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    Abstract:

    Based on a brief review of the research progress of surface potential vorticity, this paper introduces the calculation of potential vorticity and its generation under complex terrain, and the research progress on the source of potential vorticity and potential vorticity circulation in recent years, focusing on the particularity of the surface potential vorticity on the Tibetan Plateau and its important influence on weather and climate. It is clarified that for adiabatic and frictionless atmospheric motion, the structural recombination of the potential vorticity itself (potential vortex reconstruction) can cause the development of vertical vorticity, which can excite the formation of plateau vortex in summer and make the eastern part of the plateau an important source of surface vorticity in winter. Based on the derived equation for the vertical motion associated with isentropic displacement () and including diabatic heating, it is further demonstrated that the eastward propagation of the positive vorticity created on the Tibetan Plateau along the westerly wind will cause the development in the downstream area of cyclonic vorticity, southerly wind, and upward motion in the lower troposphere, resulting in the increase of potential vorticity advection with altitude, which stimulates the development of extreme weather and climate events. It was pointed out that the diurnal variations of surface heating and latent heat release at the cloud bottom over the Tibetan Plateau significantly affect the diurnal variation of the potential vorticity near the surface, resulting in the development of the low-vortex and precipitation system over the Tibetan Plateau from late afternoon to night. It is proved that compared with the traditional surface sensible heating index, the surface potential vorticity index of the Tibetan Plateau can better characterize the seasonal changes of local precipitation, and is more closely related to the Asian summer monsoon precipitation. The concept of potential vortex circulation (PVC) is also briefly introduced. It is pointed out that since the change of convergence of PVC across the close boundary of an area is directly related to the change of potential vorticity of the area, in order to maintain the relative stability of the total potential vorticity in the northern hemisphere, the change of PVC on the trans-equatorial plane and the change of surface PVC must complement each other, so the change of the potential vortex circulation on the trans-equatorial plane can be considered a window for monitoring near-surface climate change. The near-equatorial air-sea interaction can directly cause the change of vertical shear of the zonal wind on the vertical plane across the equator, stimulate the trans-equatorial PVC anomaly, and thus affect the climate change near the surface of the northern hemisphere through the change of PVC in the atmosphere and the regulation of the Tibetan Plateau. The analysis shows that PVC analysis opens up a new way for establishing the link between tropical and extra-tropical atmospheric circulation changes, and has broad application prospects.

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History
  • Received:June 05,2023
  • Revised:June 05,2023
  • Adopted:December 06,2023
  • Online: December 07,2023
  • Published: