From boreal spring to summer Tropical Atlantic inter-annual variability

 

The tropical Atlantic variability is thought to be controlled by two air-sea independent couple modes, denoted as Meridional (MM) and Equatorial Mode (EM). The MM and EM pattern peak in boreal spring and summer respectively, and exhibit pronounced environmental and socioeconomic impacts on the tropical countries. FESTIVAL MSCA-IF-H2020 project (grant agreement 797236) has investigated the connection between the traditional MM and EM, the air-sea mechanisms and oceanic wave activity involved and its multidecadal modulation. The main conclusions achieved during the development of FESTIVAL project are:

1. Evolving modes, from winter to summer, emerge in the tropical Atlantic basin during the 20th century.

2. These evolving patterns resemble different (same-phase and opposite-phase) connections between the traditional MM and EM.

3. Evolving modes interact between each other at inter-decadal time scales along the historical record, associated with natural variability low-frequency variability patterns.

4. The North Tropical Atlantic SSTs act as a precursor of equatorial Atlantic variability during the whole 20th century, providing significant predictive skill up to 6 months in advance.

5. Oceanic Rossby waves, boundary-reflected into equatorial Kelvin waves, are the essential mechanism underlying the evolving modes and thus the MM-EM connection.

6. The effectiveness of the oceanic waves in generating equatorial SST variability during summer months is modulated by the local wind forcing.

7. The emergence of evolving modes causes a pronounced impact over the precipitation regime over Africa and South-America that substantially changes from winter to summer seasons.

FESTIVAL results provide, for the first time, an integrated view of the boreal spring and summer interannual variability. The predictor role of North Tropical Atlantic SSTs to develop equatorial Atlantic variability is quite valuable to improve the current seasonal forecast systems. Furthermore, the seasonal varying rainfall patterns induced by the evolving modes over African and South-American countries significantly influence the agricultural practices, which allows the local governments and insurance companies to adapt specific strategies to guarantee a sustained development.

For more information, please contact: mmartin(at)icm.csic.es; mmartindelrey(at)fis.ucm.es.

Acknowledgments: This research has been funding by the MSCA-IF-H2020-EU FESTIVAL project, (grant agreement number 797236).