||The potential vorticity (PV) on each isentropic surface and potential temperature at the lower boundary play important roles in dynamic process of midlatitude synoptic-scale systems. But single isobaric surface or isentropic surface can not represent both PV and potential temperature at the same time. We need understand the dynamic process by combining variant isobaric or isentropic surfaces when exploring the synoptic-scale system. In this paper, we use 310K isentropic surface as the interface to simplify the atmosphere into a two layer system. The main purpose is to explore whether the layered potential vorticity (LPV) can represent the characteristic and dynamic process of midlatitude synoptic-scale system more clearly and concisely than isentropic potential vorticity (IPV).|
This study is divided into two parts. The first part is, by comparing LPV of lower troposphere with satellite image, 1000 hPa geopotential height, and TRMM rainfall data, during January 2001, to examine whether LPV can show appropriately the characteristics of intensity, position, growth, movement and precipitation of midlatitude synoptic-scale system. The results clearly shows lower troposphere is consistent with satellite image, 1000 hPa geopotential height, and precipitation. The maximum of PV is well-matched with the extratropical cyclone center, low pressure trough, front and rain belt. Similarly, low PV has salient relation with high pressure ridge. The second part is by computing local meridional PV gradients of upper and lower troposphere to get stability, then comparing the pressure of weather systems in stable and unstable status to explore the connection between the local baroclinic instability and the growth of synoptic-scale system. From Monte Carlo test, local baroclinic instability has highly relationship with the intensity of synoptic-scale system. In other words, the system intensity in unstable status is stronger then stable status.
In summary, this study indeed shows LPV can represent the characteristics and dynamic process of midlatitude synoptic-scale system more clearly and concisely than IPV. Besides, we also discover that LPV consistent with perturbation in tropical area pretty well. Thus, LPV is a very good tool in studying the dynamic process of system.
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