Both positive and negative AO can lead to cold anomalies over eastern China

Highlights: Cold anomalies over eastern China can occur following both positive and negative Arctic Oscillation (AO) phases. The positive and negative AO-induced atmospheric wave train takes a different path. The resultant cold anomalies have different extent and location in positive and negative AO phases.

Summary: The occurrence of cold events over East Asia is related to the Arctic Oscillation (AO). Most previous studies on the relationship between the AO and temperature anomalies over East Asia are based on monthly mean AO index. The time lag between the AO and temperature anomalies cannot be well described based on monthly mean AO analysis. It is more proper to use daily AO index and temperature anomalies to obtain their time lag relationship and to identify the preferred time of the occurrence of cold temperature anomalies in relation to the evolution of the AO life cycle.

In a recent study published in Journal of Geophysical Research-Atmospheres, Dr. SONG Lei and Prof. WU Renguang found that cold temperature anomalies occur over eastern China following both positive and negative AO phases with nearly the same probability. They identified prominent differences in surface temperature and tropospheric circulation anomalies between the two types of years. During the years when negative AO leads cold anomalies (Figure 1a), the AO-related pressure anomalies extend to Eurasia, inducing an enhanced Siberian high with a large spatial coverage in the mid- and high-latitudes; the midtropospheric wave train along the polar front jet takes an eastward path and induces the deepening of the East Asian trough; the resultant cold surface temperature anomalies affect a large region over East Asia. During the years when positive AO leads cold anomalies (Figure 1b), the AO-related pressure anomalies extend to North America and the high pressure anomalies over East Asia are located at the mid-latitudes with a relatively small spatial coverage; the midtropospheric wave train along the polar front jet takes a southward path over Asia, inducing the development of a trough over subtropical Asia with a supplementary contribution from a subtropical wave train; the resultant cold surface temperature anomalies influence inland East Asia with a relatively small extent.

Figure 1. Schematic diagrams showing the main features of the cold anomalies related to (a) negative and (b) positive AO phases. The red contour denotes the region of surface high pressure anomaly, the blue contour denotes the region of the cold anomaly, the black contour refers to the 500-hPa geopotential height at 5,300 gpm, the light blue and red shadings denote negative and positive geopotential height anomalies at 500-hPa.

Citation:
Song, L., and R. Wu, 2018: Comparison of intraseasonal East Asian winter cold temperature anomalies in positive and negative phases of the Arctic Oscillation. Journal of Geophysical Research: Atmospheres, 123(16), 8518-8537, doi:10.1029/2018JD028343.

Web: https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018JD028343

Contact: WU Renguang, renguang@mail.iap.ac.cn