Analysis of isentropic potential vorticities for the relationship between stratospheric polar vortex and the cooling process in China

Abstract:

We analyze the relationships between stratospheric polar vortex anomalies and cooling events in eastern China using isentropic reanalysis data from the European Center for Medium-Range Weather Forecasts. Daily mean data from 2000 to 2011 are used to explore the effective stratospheric signals. First, diagnoses of the 2009/2010 winter show that after the stratospheric sudden warming (SSW) of the Atlantic-East Asian (AEA) pattern, the stratospheric high isentropic potential vorticity(IPV) center derived from the split polar vortex will move to the northeast of the Eurasian continent. The air mass, accompanied by some southward and eastward movements and characterized by high IPV values, will be stretched vertically, leading to apparent reinforcements of the positive vorticity and the development of a cold vortex system in the troposphere. The northerly wind on the western side of the cold vortex can transport cold air southward and downward, resulting in this distinct cooling process in eastern China. Secondly, the Empirical Orthogonal Function analyses of IPV anomalies on the 430 K isentropic surface during 2000–2011 winters indicate that the IPV distribution and time series of the first mode are able to represent the polar vortex variation features, which significantly influence cold-air activity in eastern China, especially in the AEA-type SSW winter. When the time series increases significantly, the polar vortex will be split and the high-IPV center will move to the northeast of the Eurasian continent with downward and southward developments, inducing obvious cooling in eastern China. Moreover, all the four times SSW events of AEA pattern from 2000 to 2011 are reflected in the first time series, and after the strong polar vortex disturbances, cooling processes of different intensities are observed in eastern China. The cooling can sustain at least one week. For this reason the first time series can be used as an available index of polar vortex oscillation and has the power to predict cold-air activity in winter.