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The role of ocean variability for droughts and wet periods in South America
1  University of New South Wales, Climate Change Research Centre, Sydney, Australia


Interannual precipitation over South America is largely modulated by the large-scale modes of variability in the surrounding oceans. In particular, the El Niño – Southern Oscillation (ENSO) affects South American rainfall generating a dipole pattern of precipitation over the northern and southeastern regions. In this study the role of the oceans for South American rainfall variability is investigated using the National Centre for Atmospheric Research (NCAR) Community Earth System Model (CESM). Multi-century simulations are performed to estimate rainfall mean and variability in South America in a fully coupled climate system and in the absence of ocean variability. Results show that interannual and decadal rainfall variability over South America is primarily associated with sea surface temperature anomalies in the Indo-Pacific region and variations in the extent of the Pacific warm pool. In the absence of ocean variability, droughts tend to last longer, particularly over the northeastern region. Thus, ENSO acts as a restoring mechanism for rainfall deficits and surplus over the continent. Interestingly, ENSO events are not only crucial for modulating rainfall variability, but also for determining mean precipitation over South America.


Keywords: South America, precipitation, El Niño-Southern Oscillation, drought
Comments on this paper
Anita Drumond
about the experiment ATM
Dear authors,

Firstly, thank you very much for your participation in this conference.

Please, could you clarify some questions concerning the experiment ATM?
- I found the acronym AGCM reading the document. Does it refer to the ATM, right?
- Does the seasonal cycle of SST and sea--ice consider the monthly climatological values around the world? Or is the monthly climatology applied only over the pacific ocean, and the remaining oceans consider the SST varying along the years?

- In case of forcing with the climatological seasonal cyle of SST around the world, have you tried to relate the results for Northeastern with any Atlantic variability mode? For example the Inter-Hemispheric Atlantic gradient?

Congratulations for this very interesting contribution!

kind regards,

Andrea Taschetto
Hello Anita,

- Yes, that is correct. AGCM = ATM.
- Yes, that is correct again: monthly climatology of SST and sea-ice over the global oceans was used to force the ATM experiment.
- Not yet. The purpose of the study is to assess the effect of ocean variability (not restricted to the Pacific) for South American rainfall. As such, the experimental design was planned not to restrict variability from a single ocean basin. Indeed, the difference between ATM and CPLD can be associated with variability in the Atlantic, Pacific and Indian Oceans. Another interesting way to interpret the differences between ATM and CPLD it is to associate with the internal atmosphere-land variability only. ENSO is used in the study as it has significant impacts over South America and it is well represented in the model. We will definitely be looking at other climate modes that impact SA rainfall, thanks for your suggestion.