A Specific Stratospheric Precursory Signal for the Extensive and Persistent Extreme Cold Events in China

On the basis of daily NCEP/NCAR data sets, this study investigates a stratospheric circulation precursor for the extensive and persistent extreme cold events (EPECEs) in China. Results show that 17 out of 52 EPECEs are characterized by a specific stratospheric circulation precursor. The precursor exhibits itself clearly in two aspects. (1) Strong positive geopotential height anomalies occur around the Barents Sea in the lower stratosphere (100 hPa) 10 days prior to the occurrence of the EPECE. (2) In relation to the eastward movement of the positive height anomalies, the zonal wind over the northwest of Lake Baikal is weakened significantly at 200 hPa about 5 days before the occurrence of an EPECE. According to these stratospheric precursor circulation features, two initial assessment conditions are proposed. To test prediction accuracy, the two assessment conditions are applied to the daily low-frequency data of all winter seasons (November to March) from 1949 to 2009. Results show that our two proposed assessment conditions, at least to some extent, can enable the prediction of the occurrence date of an EPECE. Regarding the physical mechanism of the influence of the stratospheric circulation precursor on the EPECE, potential vorticity (PV) inversion analysis shows that the mid and lower stratospheric PV anomalies around the Barents Sea can induce the geopotential height anomalies at the upper and midtroposphere. In particular, 25% of the real amplitude of the latter originates from the influence of former.