Marine Heat Waves Dominate Australia/South America Climate Pattern

Fig. 1-2: The daily global SSTA analysis and identification of marine heat waves in the southern hemisphere and the correlating upper-level pattern at 500 MB.

Discussion: Getting the most (research) attention regarding a new phenomenon referred to as marine heat waves (MHW) is typically the Northeast Pacific MHW and more recently in research published in Journal of Climate, the East Asia/West Pacific MHW. However, the southern hemisphere has certainly acquired large areas of surface/subsurface water much warmer than normal and well-correlated to upper atmosphere pressure patterns somewhat stagnant in character leading to long lasting climate regimes featuring both very wet and dry-to-drought regimes.

While the tendency (and meteorological interest) of influence on the upper air pattern by these large oceanic “warm blobs” is usually increased subtropical high-pressure strength, the (sometimes) overlooked residual effect is the atmospheric compensation that takes place by producing nearby potent semi-permanent trough areas.

One classic example is the persistent stormy trough across Australia enhanced by the wet climate influence of negative Indian Ocean dipole (-IOD) and the cold ENSO regime. The wet and cool climate-producing trough is atmospheric compensation for the upstream titanic upper-level ridge pattern across the New Zealand MHW which has recently expanded to northeast of Australia.

A titanic upper-level ridge rests over the Argentina MHW extending to Argentina and responsible for drought. However, just north of the amplified ridge, a wet upper trough has affected Brazil climate.

The latest 15-day percent of normal rainfall outlooks shift the wet pattern northward in Australia while much of Brazil rains wet but Northern Argentina stays dry (Fig. 3-4).

Fig. 3-4: The 15-day percent of normal precipitation forecast for Australia and South America.