What are they? ENSO is the weather cycle that includes La Niña's and El Niño's. It is a scientific term that describes the fluctuations in temperature between the ocean and atmosphere in the central equatorial Pacific. El Niño and La Niña are defined as large scale ocean-atmosphere climate interaction and are opposite from one another. How do they form? They occur from deviations from normal surface temperature and they have large effects on global processes. How do they impact the world, United States, and Indiana? Even though they are very far south, ithey still effect the whole world. Weather patterns of high and low pressure get messed up because of them and dramatic weather changes occur especially in the regions of northwest South America, and Australia, New Zealand, and Indonesia. When El Niño occurs the are of Peru and Ecuador receive plentiful rain and warm ocean temperature which is opposite of what they would normally get. On the other hand, Australia, Indonesia, and New Zealand will receive little to no rain due to the high pressure that has formed in the absence of warm water. La Niña is the opposite of El Niño so the conditions will switch for those places. What instruments do scientists use to study them? Weather satellites, weather balloons, and hygrometer are examples of instruments that study El Niño, La Niña, and ENSO. When was the last time Indiana was affected by El Niño, La Niña, or ENSO? The last time Indiana was affected by one of these was the El Niño las spring. Farther north in the Pacific, waters were warmer than average. This created additional effects upon the weather pattern in the winter since the warmer waters persisted through the winter. In the spring it brought warm and dry temperatures.