El Niño is a weather pattern named after Our Saviour because it tends to impact South America most noticeably during Advent and Christmas.
La Nina and El Nino are two great natural Pacific currents whose effects are so huge they resonate round the world. El Nino warms the planet when it happens; La Nina cools it. 
Several aspects of the atmosphere's behavior are remarkable and entirely unique to the El Niño/Southern Oscillation (ENSO) phenomena. Some normally arid tropical habitats are transformed into virtual gardens during El Niño. Abundant and reliable rains in other tropical areas become sparse and intermittent during El Niño. Extreme climates have also been experienced in the higher latitudes during ENSO, though these are by no means unique to ENSO. One marvels that the atmosphere, especially thousands of kilometers remote from the equatorial Pacific, knows about the modest 1°° warming of those waters during El Niño! Yet, all regions of the globe are not equally affected, nor is ENSO's impact uniform throughout the year.