South America Pattern Change

Fig. 1-3: The summer 2021-22 prevailing upper air pattern across South America reverses in late summer due to a change in the Madden Julian oscillation.

South America discussion: The convective phase of the Madden Julian oscillation (MJO) has shifted from the tropical Pacific Ocean for much of summer 2021-22 to the East Indian Ocean during February and recently intensified. The influence on tropical vertical motion has changed from convection to subsidence across Brazil which reverses the historic heavy rainfall of summer 2021-22 to a much drier pattern to finish meteorological summer. The dry weather inducing upper-level high-pressure ridge over Southeast Brazil in the 15-day outlook is compensated for by a wet trough angled over Argentina where a rainy pattern change emerges.