The unusual summer of 1994 in East Asia: IOD teleconnections

TLDR

The 1994 East Asian summer was unusually hot and dry, driven by anomalous cyclonic and anticyclonic circulations that weakened the monsoon, with lower potential vorticity accumulation linked to Mediterranean/Sahara wave activity and Rossby wave patterns affecting regional circulation. The monsoon‑desert mechanism links a Rossby wave source to Indian Ocean Dipole–induced diabatic heating around the Bay of Bengal. Observational data show that the Indian Ocean Dipole is at least one possible cause of the abnormal East Asian summer climate.

Abstract

An extremely hot and dry summer of 1994 was reported in East Asian countries. Using observational data, we have demonstrated that the Indian Ocean Dipole (IOD) is at least one possible cause of the abnormal East Asian summer climate. An anomalous cyclonic circulation over the western Pacific and the southern China weakened the monsoonal northward flow in the lower troposphere. An anomalous anticyclonic circulation with the equivalent barotropic structure around Japan, Korea and the northeastern part of China caused the hot and dry summer of 1994. This accumulation of the lower potential vorticity in the Far East is related to the wave activity from the Mediterranean/Sahara region. The monsoon‐desert mechanism connects a Rossby wave source with the IOD‐induced diabatic heating around the Bay of Bengal. Another Rossby wave‐train pattern was generated in the upper troposphere and propagates northeastward from the southern China. Both the Rossby wave patterns influenced the circulation changes over East Asia.