Distinct Eurasian climate anomalies associated with strong and weak MJO events

Abstract

AbstractThe MJO‐related tropical Indian Ocean outgoing longwave radiation anomalies display a bimodal distribution, indicating two types of MJO events. The present study distinguishes 14 strong and 16 weak MJO events during the 37 winters from 1979 to 2016 and compares the circulation and climate over the mid‐latitude Eurasia between strong and weak MJO events. Cold anomalies appear over Siberia and East Asia during strong MJO events when the MJO‐related convection is located over the tropical Indian Ocean, whereas the temperature anomalies are weak over Eurasia during weak MJO events. The cold anomalies over Eurasia in strong MJO events are associated with the development of surface anticyclonic anomalies and the accompanying northerly wind anomalies. On one hand, the enhancement of surface anticyclonic anomalies can be attributed to the poleward Rossby wave packets triggered by the MJO convection over the tropical Indian Ocean. On the other hand, the strong convective heating over the tropical Indian Ocean can induce anomalous meridional overturning circulation between the tropics and mid‐latitudes. The anomalous divergent winds associated with the convective heating can reach western Siberia and the descending branch of the vertical cell contributes to the enhancement of surface anticyclonic anomalies and northerly wind anomalies, leading to cold anomalies over Siberia and East Asia. In weak MJO events, the poleward Rossby waves are weak and anomalous meridional overturning is of limited meridional extent. As a result, the MJO‐related wind anomalies are weak and the associated temperature anomalies are small over large areas of Eurasia.