The unusually-heavy rains over Tamil Nadu and other parts of southern peninsula may have been caused by La Nina and the positive phase of southern oscillation (SO), global scale circulation features. La Nina, the opposite of El Nino, pertains to the anomalous decline in the temperature of the central tropical Pacific Ocean while the southern oscillation refers to the air pressure difference between Tahiti in the Pacific and Darwin in the northern Australia. (According to the website of the Climate Prediction Centre, National Weather Service of the National Oceanic and Atmospheric Administration of the United States Government, El Nino and La Ni